JP6455793B2 - Power converter and power conditioner using the same - Google Patents

Description

  The present invention relates to a power conversion device and a power conditioner using the same.

  In recent years, with the spread of residential solar power generation devices, fuel cells, power storage devices, and the like, various circuits have been proposed and provided as power conversion devices that convert the output of these DC power sources into AC. For example, Patent Documents 1 and 2 disclose a power converter that generates an AC output converted from a DC voltage source into a plurality of voltage levels (“Multi-level power converter” in Patent Document 1 and “Converter Circuit” in Patent Document 2) Is disclosed.

  According to the description of Patent Document 1, the power conversion device is a 5-level inverter that outputs a 5-level voltage, and includes two DC capacitors, two flying capacitors, and 10 switching elements. ing. In this power converter, in the state where the DC voltage E is applied to the series circuit of two DC capacitors, the voltage of each DC capacitor becomes E / 2 and the voltage of each flying capacitor becomes E / 4. By controlling the switching element, a five-level voltage is output.

  By the way, in the power converters described in Patent Documents 1 and 2 described above, as described above, when outputting a voltage of five levels (five steps), the current input from the DC voltage source is equal to ten switching elements. Of these, 6 elements pass through. Therefore, in this power conversion device, the sum of conduction loss (loss) of the switching elements is relatively large, and further improvement in power conversion efficiency is desired.

JP 2014-64431 A (paragraphs [0002] to [0006], FIGS. 16 and 17) Japanese Patent No. 4369425

  This invention is made | formed in view of the said reason, and it aims at providing the power converter device which can aim at the further improvement of power conversion efficiency, and a power conditioner using the same.

  A power conversion device according to an aspect of the present invention includes a first conversion circuit and a second conversion circuit, and includes a first bidirectional switch, a second bidirectional switch, and first to fourth protection diodes. It has more. The first conversion circuit and the second conversion circuit are electrically in parallel between a first input point on the high potential side of the DC power supply and a second input point on the low potential side of the DC power supply. It is connected. The first conversion circuit includes first to fourth switching elements and a first capacitor. The first to fourth switching elements include a first switching element, a second switching element, and a third switching element from the first input point side between the first input point and the second input point. In this order, the fourth switching elements are electrically connected in series. The first capacitor is electrically connected in parallel with a series circuit of the second switching element and the third switching element. The first conversion circuit uses a connection point between the second switching element and the third switching element as a first output point. The second conversion circuit includes fifth to eighth switching elements and a second capacitor. The fifth to eighth switching elements include a fifth switching element, a sixth switching element, and a seventh switching element from the first input point side between the first input point and the second input point. In this order, the eighth switching elements are electrically connected in series. The second capacitor is electrically connected in parallel with a series circuit of the sixth switching element and the seventh switching element. The second conversion circuit uses a connection point between the sixth switching element and the seventh switching element as a second output point. The first bidirectional switch is a connection point between a first connection point, which is a connection point between the first switching element and the second switching element, and a connection point between the seventh switching element and the eighth switching element. The second connection point is electrically connected. The second bidirectional switch is a connection point of a third connection point that is a connection point of the third switching element and the fourth switching element, and a connection point of the fifth switching element and the sixth switching element. It is electrically connected to the fourth connection point. The first protection diode is electrically connected in parallel with a series circuit of the first switching element and the second switching element between the first input point and the first output point, A current flowing from the first output point to the first input point is passed. The second protection diode is electrically connected in parallel with a series circuit of the third switching element and the fourth switching element between the second input point and the first output point, A current flowing from the second input point to the first output point is passed. The third protection diode is electrically connected in parallel with a series circuit of the fifth switching element and the sixth switching element between the first input point and the second output point, A current flowing from the second output point to the first input point is passed. The fourth protection diode is electrically connected in parallel with a series circuit of the seventh switching element and the eighth switching element between the second input point and the second output point. A current flowing from the second input point to the second output point is passed. The power converter is configured to generate an output voltage between the first output point and the second output point.

  The power conditioner which concerns on 1 aspect of this invention is equipped with said power converter device and the disconnector electrically connected between the said 1st output point and the said 2nd output point, and a system | strain power supply.

FIG. 1 is a circuit diagram illustrating a configuration of a power conversion device according to an embodiment. FIG. 2A is an explanatory diagram of a first mode of the power conversion device according to the embodiment, and FIG. 2B is an explanatory diagram of a second mode of the power conversion device according to the embodiment. FIG. 3A is an explanatory diagram of a third mode of the power conversion device according to the embodiment, and FIG. 3B is an explanatory diagram of a fourth mode of the power conversion device according to the embodiment. 4A is an explanatory diagram of a fifth mode of the power conversion device according to the embodiment, and FIG. 4B is an explanatory diagram of a sixth mode of the power conversion device according to the embodiment. FIG. 5A is an explanatory diagram of a seventh mode of the power conversion device according to the embodiment, and FIG. 5B is an explanatory diagram of an eighth mode of the power conversion device according to the embodiment. FIG. 6 is a waveform diagram of an output voltage of the power conversion device according to the embodiment. FIG. 7 is a schematic diagram illustrating a configuration of a power conditioner according to the embodiment. FIG. 8 is a waveform diagram showing the relationship between the output voltage and the output current of the power converter according to the embodiment. 9A is an explanatory diagram of a dead time between the first and second modes of the power conversion device according to the embodiment, and FIG. 9B is an explanatory diagram of a dead time between the first and third modes of the power conversion device according to the embodiment. is there. 10A is an explanatory diagram of a dead time between the second and fourth modes of the power conversion device according to the embodiment, and FIG. 10B is an explanatory diagram of a dead time between the third and fourth modes of the power conversion device according to the embodiment. is there. FIG. 11A is an explanatory diagram of a dead time between the first and third modes of the power converter of the comparative example, and FIG. 11B is an explanatory diagram of a third mode of the power converter of the comparative example. 12A is an explanatory diagram of a dead time between the first and second modes of the power conversion device according to the embodiment, and FIG. 12B is an explanatory diagram of a dead time between the first and third modes of the power conversion device according to the embodiment. is there. FIG. 13A is an explanatory diagram of a dead time between the second and fourth modes of the power conversion device according to the embodiment, and FIG. 13B is an explanatory diagram of a dead time between the third and fourth modes of the power conversion device according to the embodiment. is there.

  The following embodiments relate to a power converter and a power conditioner using the power converter, and more particularly to a power converter that converts power from a DC power source and a power conditioner using the power converter.

(1) Outline As shown in FIG. 1, the power conversion device 1 according to the present embodiment includes a first conversion circuit 11 and a second conversion circuit 12, and includes a first bidirectional switch 13 and a second bidirectional circuit. And a switch 14. The power conversion device 1 further includes first to fourth protection diodes D101 to D104.

  The first conversion circuit 11 and the second conversion circuit 12 are electrically connected between a first input point 101 on the high potential side of the DC power supply 100 and a second input point 102 on the low potential side of the DC power supply 100. Connected in parallel.

  The first conversion circuit 11 includes first to fourth switching elements Q1 to Q4 and a first capacitor C1. Here, the first conversion circuit 11 sets a connection point between the second switching element Q <b> 2 and the third switching element Q <b> 3 as the first output point 103.

  The first to fourth switching elements Q1 to Q4 are electrically connected in series between the first input point 101 and the second input point 102. The first to fourth switching elements Q1 to Q4 are in the order of the first switching element Q1, the second switching element Q2, the third switching element Q3, and the fourth switching element Q4 from the first input point 101 side. Connected in series. The first capacitor C1 is electrically connected in parallel with the series circuit of the second switching element Q2 and the third switching element Q3.

  The second conversion circuit 12 includes fifth to eighth switching elements Q5 to Q8 and a second capacitor C2. Here, the second conversion circuit 12 sets a connection point between the sixth switching element Q6 and the seventh switching element Q7 as the second output point 104.

  The fifth to eighth switching elements Q5 to Q8 are electrically connected in series between the first input point 101 and the second input point 102. The fifth to eighth switching elements Q5 to Q8 are in the order of the fifth switching element Q5, the sixth switching element Q6, the seventh switching element Q7, and the eighth switching element Q8 from the first input point 101 side. Connected in series. The second capacitor C2 is electrically connected in parallel with the series circuit of the sixth switching element Q6 and the seventh switching element Q7.

  The first bidirectional switch 13 is a connection point between a first connection point 201 that is a connection point between the first switching element Q1 and the second switching element Q2, and a connection point between the seventh switching element Q7 and the eighth switching element Q8. It is electrically connected to a certain second connection point 202.

  The second bidirectional switch 14 is a connection point between the third switching element Q3 and the fourth switching element Q4, the third connection point 203 and the fifth switching element Q5 and the sixth switching element Q6. It is electrically connected to a certain fourth connection point 204.

  The first protection diode D101 is electrically connected in parallel with the series circuit of the first switching element Q1 and the second switching element Q2 between the first input point 101 and the first output point 103. . The first protection diode D101 allows a current flowing from the first output point 103 to the first input point 101 to pass therethrough.

  The second protection diode D102 is electrically connected in parallel with the series circuit of the third switching element Q3 and the fourth switching element Q4 between the second input point 102 and the first output point 103. . The second protection diode D102 allows a current flowing from the second input point 102 to the first output point 103 to pass therethrough.

  The third protection diode D103 is electrically connected in parallel with the series circuit of the fifth switching element Q5 and the sixth switching element Q6 between the first input point 101 and the second output point 104. . The third protection diode D103 allows a current flowing from the second output point 104 to the first input point 101 to pass therethrough.

  The fourth protection diode D104 is electrically connected in parallel with the series circuit of the seventh switching element Q7 and the eighth switching element Q8 between the second input point 102 and the second output point 104. . The fourth protection diode D104 allows a current flowing from the second input point 102 to the second output point 104 to pass therethrough.

  The power conversion device 1 is configured to generate an output voltage between the first output point 103 and the second output point 104.

(2) Details Hereinafter, the power conversion device 1 according to the present embodiment and the power conditioner 20 (see FIG. 7) using the power conversion device 1 will be described in detail. However, the configuration described below is only an example of the present invention, and the present invention is not limited to the following embodiment, and the technical idea according to the present invention is not deviated from this embodiment. Various changes can be made in accordance with the design or the like as long as they are not.

  In the present embodiment, the case where the power conditioner 20 is a residential power conditioner that is used by being electrically connected to a photovoltaic power generation device serving as the DC power source 100 is exemplified. However, the use of the power conditioner 20 is illustrated. It is not intended to limit. The power conditioner 20 may be used by being electrically connected to a DC power source 100 other than a solar power generation device, such as a household fuel cell or a power storage device. For example, the power conditioner 20 may be used in a non-residential such as a store, a factory, or an office. Furthermore, the power converter 1 is not intended to limit the application to the power conditioner 20, and the power converter 1 may be used other than the power conditioner 20.

(2.1) Configuration of Power Converter The power converter 1 of the present embodiment is electrically connected to a DC power source 100 as shown in FIG. Here, the power converter 1 is connected to the DC power source 100 via a connection box.

  The power conversion device 1 of this embodiment includes a conversion circuit 10 and a control unit 6. Further, the power conversion device 1 further includes a filter circuit 5.

  The conversion circuit 10 includes a first conversion circuit 11, a second conversion circuit 12, a first bidirectional switch 13, a second bidirectional switch 14, and first to fourth protection diodes D101 to D104.

  The first input point 101 and the second input point 102 correspond to a pair of input terminals in the power conversion device 1. A DC power source 100 is electrically connected between the pair of input terminals (the first input point 101 and the second input point 102).

  The first output point 103 of the first conversion circuit 11 and the second output point 104 of the second conversion circuit 12 are electrically connected to the third output point 105 and the fourth output point 106 through the filter circuit 5, respectively. Has been. In the present embodiment, the third output point 105 and the fourth output point 106 correspond to a pair of output terminals in the power conversion device 1.

  In the present embodiment, the output voltage of the power conversion device 1 is an AC voltage, and the third output point 105 and the fourth output point 106 are electrically connected to the system power supply (commercial power system) 7. Furthermore, a load 8 that operates by receiving supply of AC power is electrically connected to the third output point 105 and the fourth output point 106.

  Specifically, the pair of output terminals of the power conversion device 1 is connected to the load 8 and the system power supply 7 by being electrically connected to an interconnection breaker provided in the distribution board. That is, the power conversion device 1 converts the DC power input from the DC power source 100 into AC power, and the AC power is transferred from the pair of output terminals (the third output point 105 and the fourth output point 106) to the load 8 and the system. Output to power supply 7. In FIG. 1, the system power supply 7 is a single-phase three-wire system having a U-phase and a W-phase.

  Next, the structure of each part of the power converter device 1 will be described in detail.

  The power conversion apparatus 1 uses the input terminal on the high potential (positive electrode) side of the DC power supply 100 among the pair of input terminals connected to the DC power supply 100 as the first input point 101, and the low potential (negative electrode) of the DC power supply 100. The input terminal on the side is the second input point 102. Therefore, a DC voltage output from the DC power supply 100 is applied as an input voltage between the first input point 101 and the second input point 102.

  Here, it is assumed that the input terminal (second input point 102) on the low potential side of the DC power supply 100 is the circuit ground of the power converter 1, and the potential thereof is 0 [V]. Then, using the output voltage E [V] of the DC power supply 100, the potential of the first input point 101 is represented by E [V].

  As described above, the first conversion circuit 11 includes the first to fourth switching elements Q1 to Q4 connected in series between the first input point 101 and the second input point 102, and the first capacitor C1. doing. For each of the first to fourth switching elements Q1 to Q4, a depletion type n-channel MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) is used here as an example.

  The drain of the first switching element Q1 is electrically connected to the first input point 101. The drain of the second switching element Q2 is electrically connected to the source of the first switching element Q1. The drain of the third switching element Q3 is electrically connected to the source of the second switching element Q2. The drain of the fourth switching element Q4 is electrically connected to the source of the third switching element Q3. Further, the source of the fourth switching element Q 4 is electrically connected to the second input point 102.

  Here, the connection point between the source of the second switching element Q 2 and the drain of the third switching element Q 3 corresponds to the first output point 103. Further, the connection point between the source of the first switching element Q1 and the drain of the second switching element Q2 corresponds to the first connection point 201, and the source of the third switching element Q3 and the drain of the fourth switching element Q4. The connection point to corresponds to the third connection point 203.

  One end of the first capacitor C1 is electrically connected to the drain (first connection point 201) of the second switching element Q2, and the other end is electrically connected to the source (third connection point 203) of the third switching element Q3. Connected. In other words, the first capacitor C1 has one end electrically connected to the first input point 101 via the first switching element Q1 and the other end connected to the second input point 102 via the fourth switching element Q4. Electrically connected.

  As described above, the second conversion circuit 12 includes the fifth to eighth switching elements Q5 to Q8 connected in series between the first input point 101 and the second input point 102, and the second capacitor C2. doing. Here, the second conversion circuit 12 has basically the same configuration as the first conversion circuit 11, and the fifth to eighth switching elements Q5 to Q8 are replaced with the first to fourth switching elements Q1 to Q4, respectively. The second capacitor C2 corresponds to the first capacitor C1. As each of the fifth to eighth switching elements Q5 to Q8, a depletion type n-channel MOSFET is used similarly to each of the first to fourth switching elements Q1 to Q4.

  That is, the drain of the fifth switching element Q5 is electrically connected to the first input point 101. The drain of the sixth switching element Q6 is electrically connected to the source of the fifth switching element Q5. The drain of the seventh switching element Q7 is electrically connected to the source of the sixth switching element Q6. The drain of the eighth switching element Q8 is electrically connected to the source of the seventh switching element Q7. Further, the source of the eighth switching element Q8 is electrically connected to the second input point 102.

  Here, the connection point between the source of the sixth switching element Q 6 and the drain of the seventh switching element Q 7 corresponds to the second output point 104. Further, the connection point between the source of the fifth switching element Q5 and the drain of the sixth switching element Q6 corresponds to the fourth connection point 204, and the source of the seventh switching element Q7 and the drain of the eighth switching element Q8. The connection point is equivalent to the second connection point 202.

  The second capacitor C2 has one end electrically connected to the drain (fourth connection point 204) of the sixth switching element Q6 and the other end electrically connected to the source (second connection point 202) of the seventh switching element Q7. Connected. In other words, the second capacitor C2 has one end electrically connected to the first input point 101 via the fifth switching element Q5 and the other end connected to the second input point 102 via the eighth switching element Q8. Electrically connected.

  The circuit constant (capacitance) of the second capacitor C2 is equal to the circuit constant (capacitance) of the first capacitor C1.

  In FIG. 1, the first to eighth switching elements Q1 to Q8 are connected to the first to eighth diodes D1 to D8 in a one-to-one manner and in antiparallel. These first to eighth diodes D1 to D8 are parasitic diodes of the first to eighth switching elements Q1 to Q8, respectively. That is, the parasitic diode of the first switching element Q1 constitutes the first diode D1, and similarly, the parasitic diodes of the second, third,... Switching elements Q2, Q3,. D3... For example, the first diode D1 is connected in such a direction that the drain side of the first switching element Q1 is a cathode and the source side is an anode.

  The first conversion circuit 11 and the second conversion circuit 12 configured as described above are electrically connected in parallel between the first input point 101 and the second input point 102. That is, the first conversion circuit 11 and the second conversion circuit 12 are connected in parallel between both ends of the DC power supply 100.

  The first bidirectional switch 13 is electrically connected between the first connection point 201 and the second connection point 202. That is, the first connection point 201 of the first conversion circuit 11 is electrically connected to the second connection point 202 of the second conversion circuit 12 via the first bidirectional switch 13. Here, the first bidirectional switch 13 includes a ninth switching element Q9 and a tenth switching element Q10 electrically connected in series between the first connection point 201 and the second connection point 202. have. The ninth switching element Q9 and the tenth switching element Q10 are connected in the order of the ninth switching element Q9 and the tenth switching element Q10 from the first connection point 201 side.

  More specifically, a depletion type n-channel MOSFET is used for each of the ninth and tenth switching elements Q9 and Q10, similarly to each of the first to eighth switching elements Q1 to Q8. The source of the ninth switching element Q9 is connected to the first connection point 201, and the drain of the ninth switching element Q9 is connected to the drain of the tenth switching element Q10. The source of the tenth switching element Q <b> 10 is connected to the second connection point 202. In short, the ninth switching element Q9 and the tenth switching element Q10 are connected in anti-series between the first connection point 201 and the second connection point 202 so that the drains are connected to each other. .

  The second bidirectional switch 14 is electrically connected between the third connection point 203 and the fourth connection point 204. That is, the third connection point 203 of the first conversion circuit 11 is electrically connected to the fourth connection point 204 of the second conversion circuit 12 via the second bidirectional switch 14. Here, the second bidirectional switch 14 includes the twelfth switching element Q12 and the eleventh switching element Q11 electrically connected in series between the third connection point 203 and the fourth connection point 204. have. The eleventh switching element Q11 and the twelfth switching element Q12 are connected in order of the twelfth switching element Q12 and the eleventh switching element Q11 from the third connection point 203 side.

  More specifically, a depletion type n-channel MOSFET is used for each of the eleventh and twelfth switching elements Q11 and Q12, similarly to each of the first to eighth switching elements Q1 to Q8. The source of the eleventh switching element Q11 is connected to the fourth connection point 204, and the drain of the eleventh switching element Q11 is connected to the drain of the twelfth switching element Q12. The source of the twelfth switching element Q12 is connected to the third connection point 203. In short, the eleventh switching element Q11 and the twelfth switching element Q12 are connected in anti-series between the third connection point 203 and the fourth connection point 204 so that the drains are connected to each other. .

  The ninth to twelfth diodes D9 to D12 are connected in antiparallel to the ninth to twelfth switching elements Q9 to Q12, respectively. The ninth to twelfth diodes D9 to D12 are parasitic diodes of the ninth to twelfth switching elements Q9 to Q12, respectively. That is, the parasitic diode of the ninth switching element Q9 forms a ninth diode D9, and similarly, the parasitic diodes of the tenth, eleventh and twelfth switching elements Q10, Q11 and Q12 are the tenth, eleventh and twelfth parasitic diodes, respectively. Diodes D10, D11, and D12 are configured. For example, the ninth diode D9 is connected in such a direction that the drain side of the ninth switching element Q9 is a cathode and the source side is an anode.

  In the present embodiment, the first bidirectional switch 13 is configured to be able to switch between operation states including an all-off state and an all-on state. The all-off state of the first bidirectional switch 13 is a state in which a bidirectional current is interrupted between the first connection point 201 and the second connection point 202. The all-on state of the first bidirectional switch 13 is a state in which bidirectional current passes between the first connection point 201 and the second connection point 202. Similarly, the second bidirectional switch 14 is configured to be able to switch the operation state including the all-off state and the all-on state. The all-off state of the second bidirectional switch 14 is a state in which bidirectional current is interrupted between the third connection point 203 and the fourth connection point 204. The all-on state of the second bidirectional switch 14 is a state in which bidirectional current passes between the third connection point 203 and the fourth connection point 204.

  In the present embodiment, the operating state of the first bidirectional switch 13 blocks the current flowing from the second connection point 202 to the first connection point 201, and from the first connection point 201 to the second connection point 202. It further includes a half-on state for passing a flowing current. The operating state of the second bidirectional switch 14 is a half-on state that interrupts the current flowing from the third connection point 203 to the fourth connection point 204 and passes the current flowing from the fourth connection point 204 to the third connection point 203. It further includes a state.

  Therefore, in the power conversion device 1 of the present embodiment, bidirectional current can pass between the first connection point 201 and the second connection point 202 by setting the first bidirectional switch 13 to the all-on state. Can create a unique state. Moreover, the power converter device 1 of this embodiment can pass a bidirectional | two-way electric current between the 3rd connection point 203 and the 4th connection point 204 by making the 2nd bidirectional switch 14 all the ON states. Can create a unique state.

  That is, the first bidirectional switch 13 is turned off when the ninth and tenth switching elements Q9 and Q10 are both off, and the ninth and tenth switching elements Q9 and Q10 are both on. All are turned on. Further, in the first bidirectional switch 13, when the tenth switching element Q10 is on and the ninth switching element Q9 is off, the direction of the current is limited to one direction by the ninth diode D9. Semi-on state.

  Further, the second bidirectional switch 14 is fully turned off when the eleventh and twelfth switching elements Q11 and Q12 are both off, and the eleventh and twelfth switching elements Q11 and Q12 are both on. All are turned on. Furthermore, in the second bidirectional switch 14, when the twelfth switching element Q12 is on and the eleventh switching element Q11 is off, the direction of the current is limited to one direction by the eleventh diode D11. Semi-on state.

  As described above, the bidirectional switch in the present embodiment (each of the first bidirectional switch 13 and the second bidirectional switch 14) has three operation states consisting of a full-off state, a full-on state, and a half-on state. Can be switched.

  In other words, the first bidirectional switch 13 is electrically connected between the positive terminal of the first capacitor C1 and the negative terminal of the second capacitor C2. The second bidirectional switch 14 is electrically connected between the negative terminal of the first capacitor C1 and the positive terminal of the second capacitor C2. In other words, the first capacitor C1 of the first conversion circuit 11 and the second capacitor C2 of the second conversion circuit 12 are connected in a crossed manner via the first bidirectional switch 13 and the second bidirectional switch 14. Has been.

  The first protection diode D101 and the second protection diode D102 are electrically connected in parallel with the first conversion circuit 11 between the first input point 101 and the second input point 102. The first protection diode D101 and the second protection diode D102 are connected in order of the first protection diode D101 and the second protection diode D102 from the first input point 101 side. The cathode of the first protection diode D101 is connected to the first input point 101, and the anode of the first protection diode D101 is connected to the cathode of the second protection diode D102. The anode of the second protection diode D102 is connected to the second input point 102. A connection point between the first protection diode D101 and the second protection diode D102 is connected to the first output point 103.

  In short, the first protection diode D101 is electrically connected to the series circuit of the first switching element Q1 and the second switching element Q2 so as to pass a current flowing from the first output point 103 to the first input point 101. Connected in parallel. The second protection diode D102 is electrically in parallel with the series circuit of the third switching element Q3 and the fourth switching element Q4 so as to pass the current flowing from the second input point 102 to the first output point 103. It is connected.

  The third protection diode D103 and the fourth protection diode D104 are electrically connected in parallel with the second conversion circuit 12 between the first input point 101 and the second input point 102. The third protection diode D103 and the fourth protection diode D104 are connected in order of the third protection diode D103 and the fourth protection diode D104 from the first input point 101 side. The cathode of the third protection diode D103 is connected to the first input point 101, and the anode of the third protection diode D103 is connected to the cathode of the fourth protection diode D104. The anode of the fourth protection diode D104 is connected to the second input point. A connection point between the third protection diode D 103 and the fourth protection diode D 104 is connected to the second output point 104.

  In short, the third protection diode D103 is electrically connected to the series circuit of the fifth switching element Q5 and the sixth switching element Q6 so as to pass the current flowing from the second output point 104 to the first input point 101. Connected in parallel. The fourth protection diode D104 is electrically in parallel with the series circuit of the seventh switching element Q7 and the eighth switching element Q8 so as to pass the current flowing from the second input point 102 to the second output point 104. It is connected.

  Each of the first to fourth protection diodes D101 to D104 is a fast recovery diode (FRD). The fast recovery diode is a diode having a recovery characteristic (reverse recovery characteristic) superior to a general rectifying diode. The recovery characteristic here is a characteristic of the diode when the bias applied to the diode is changed from the forward bias to the reverse bias, and the reverse recovery current (Irr), the reverse recovery time (trr), or the reverse recovery charge. (Qrr) or the like. The reverse recovery current is a current that flows through the diode in the reverse direction (from the cathode to the anode) when the bias changes from the forward bias to the reverse bias. The reverse recovery time is the time required for the diode to turn off when the bias changes from the forward bias to the reverse bias, that is, the time required for the current flowing through the diode (reverse current) to reach a predetermined value. . The reverse recovery charge is a time integral value of the reverse recovery current. The smaller the (or shorter) reverse recovery current, reverse recovery time, and reverse recovery charge, the better the recovery characteristics.

  By the way, in the conversion circuit 10 having the above configuration, each of the first, fourth, fifth, and eighth switching elements Q1, Q4, Q5, and Q8 is required to have a particularly high breakdown voltage and a low on-resistance. Therefore, in this embodiment, a trench gate type MOSFET is used for each of the first, fourth, fifth, and eighth switching elements Q1, Q4, Q5, and Q8. In this type of MOSFET, the recovery characteristic of the parasitic diode is worse than that of a general MOSFET. That is, the recovery characteristics of the first, fourth, fifth, and eighth diodes D1, D4, D5, and D8 are relatively poor.

  In the present embodiment, each of the first to fourth protection diodes D101 to D104 has a better recovery characteristic than at least each of the first, fourth, fifth, and eighth diodes D1, D4, D5, and D8. For example, regarding the recovery time, each of the first to fourth protection diodes D101 to D104 is about 1/10 to 1 / 100th of each of the first, fourth, fifth, and eighth diodes D1, D4, D5, and D8. It is. Furthermore, in the present embodiment, each of the first to fourth protection diodes D101 to D104 has better recovery characteristics than each of the second, third, sixth, and seventh diodes D2, D3, D6, and D7.

  The gates of the first to eighth switching elements Q1 to Q8 and the ninth to twelfth switching elements Q9 to Q12 are electrically connected to the control unit 6. The control unit 6 can individually switch on / off the first to fourth switching elements Q <b> 1 to Q <b> 4 and thereby controls the first conversion circuit 11. The control unit 6 can individually switch on / off the fifth to eighth switching elements Q5 to Q8, and thereby controls the second conversion circuit 12. The controller 6 can individually switch on / off the ninth and tenth switching elements Q9 and Q10, and thereby controls the first bidirectional switch 13. The controller 6 can individually switch on / off the eleventh and twelfth switching elements Q11 and Q12, and thereby controls the second bidirectional switch 14.

  The control unit 6 may be provided for each of the first conversion circuit 11, the second conversion circuit 12, the first bidirectional switch 13, and the second bidirectional switch 14.

  In the present embodiment, the control unit 6 includes a drive circuit 61 that supplies drive signals to the first to twelfth switching elements Q1 to Q12, a microcomputer 62 that supplies signals to the drive circuit 61, and a detection circuit 63. Have.

  The drive circuit 61 is configured to drive (control) each element by giving a drive signal to each control terminal (gate) of each of the first to twelfth switching elements Q1 to Q12. The microcomputer 62 is configured to control the drive circuit 61 by giving a PWM (Pulse Width Modulation) signal to the drive circuit 61. That is, the control unit 6 individually controls the first to twelfth switching elements Q1 to Q12 by a drive signal generated by the drive circuit 61 in response to an instruction from the microcomputer 62.

  The detection circuit 63 is configured to detect the magnitude of the voltage across the first capacitor C1 and the voltage across the second capacitor C2. The operation of the control unit 6 using the detection result of the detection circuit 63 will be described later.

  Here, it is preferable that the drive circuit 61 also has a function as a short-circuit prevention circuit that prevents two or more switching elements from being simultaneously turned on to prevent a short-circuit current from flowing. That is, when switching elements of a specific combination are simultaneously turned on, for example, the first input point 101 and the second input point 102 may be short-circuited, and the current from the DC power supply 100 may flow as a short-circuit current to the switching element. There is. Therefore, it is preferable that the drive circuit 61 is configured such that such specific combination of switching elements does not turn on at the same time. For example, the drive circuit 61 is specified by forcibly dropping the drive signal to the L level (Low Level) when the drive signals input to the gates of the switching elements of the specific combination simultaneously become the H level (High Level). The switching elements of the combination are configured so as not to be turned on simultaneously.

  As shown in FIG. 1, the filter circuit 5 has a pair of inductors L1 and L2 and a third capacitor C3. One inductor L <b> 1 is electrically connected between the first output point 103 and the third output point 105. The other inductor L 2 is electrically connected between the second output point 104 and the fourth output point 106. However, if the inductors L1 and L2 are electrically connected between at least one of the first output point 103 and the second output point 104 and the output terminal (the third output point 105 and the fourth output point 106). Any one of the inductors L1 and L2 may be omitted. That is, the inductor L1 is only electrically connected between the first output point 103 and the third output point 105, or the inductor L2 is electrically connected between the second output point 104 and the fourth output point 106. It may be only connected to.

  The third capacitor C <b> 3 is electrically connected between the third output point 105 and the fourth output point 106. In other words, the filter circuit 5 is a series circuit of an inductor L1, a third capacitor C3, and an inductor L2, which are electrically connected between the first output point 103 and the second output point 104.

(2.2) Basic Operation of Power Converter The basic operation of the power converter 1 having the above-described configuration will be briefly described with reference to FIGS. 2A, 2B, 3A, 3B, 4A, 4B, 5A, and 5B. In the figure, a thick line arrow represents a current path, and a switching element with a dotted circle represents an on-state element.

  Here, the basic operation of the power conversion device 1 is the operation of the power conversion device 1 after the start-up period has elapsed. The starting period here is a period from when the supply of power from the DC power supply 100 is started until both the first capacitor C1 and the second capacitor C2 are charged to the reference voltage. That is, the operation of the power conversion device 1 from a state where both the first capacitor C1 and the second capacitor C2 are charged to the reference voltage is defined as a basic operation of the power conversion device 1.

  The reference voltage for the first capacitor C <b> 1 is a voltage that is ¼ of the applied voltage applied from the DC power source 100 between the first input point 101 and the second input point 102. Similarly, the reference voltage for the second capacitor C <b> 2 is a voltage that is ¼ of the applied voltage applied between the first input point 101 and the second input point 102 from the DC power supply 100.

  In the following, it is assumed that the output voltage of the DC power supply 100 is E [V], the potential of the first input point 101 is E [V], and the potential of the second input point 102 is 0 [V]. Here, the voltage across each of the first capacitor C1 and the second capacitor C2 charged to the reference voltage is E / 4 [V]. Hereinafter, the potential difference between the first output point 103 and the second output point 104, that is, the voltage generated between the first output point 103 and the second output point 104 will be described as the output voltage V2 of the power converter 1. The output voltage V2 generated between the first output point 103 and the second output point 104 is also referred to as “second output voltage V2”.

  Since the third output point 105 and the fourth output point 106 are electrically connected to the system power supply 7, the potential difference between the third output point 105 and the fourth output point 106, that is, the third output point 105-the fourth output. The output voltage V1 generated between the points 106 is equal to the output voltage of the system power supply 7. The potential difference between the first output point 103 and the third output point 105 and the potential difference between the second output point 104 and the fourth output point 106 are absorbed by the filter circuit 5. The output voltage V1 generated between the third output point 105 and the fourth output point 106 is also referred to as “first output voltage V1”.

  The operation modes of the power conversion device 1 include the first to eighth modes. As a result, the power conversion device 1 converts the DC voltage (E [V]) applied between the first input point 101 and the second input point 102 into an AC voltage, and the first output point 103 and the first input point 103 An output voltage V2 is generated between the two output points 104. In the following description, the first to twelfth switching elements Q1 to Q12 are assumed to be in the “off” state when the on / off state is not mentioned. Further, it is assumed that the voltage drop in the first to twelfth switching elements Q1 to Q12 and the voltage drop in each of the first to twelfth diodes D1 to D12 and the first to fourth protection diodes D101 to D104 are negligible. To do.

  Here, the control unit 6 controls each of the first to twelfth switching elements Q1 to Q12 according to the following two conditions.

  The first condition is that a one-to-one pair is set between the first to fourth switching elements Q1 to Q4 of the first conversion circuit 11 and the fifth to eighth switching elements Q5 to Q8 of the second conversion circuit 12. On / off is switched for each pair. Here, the first and eighth switching elements Q1, Q8 are paired, the second, seventh switching elements Q2, Q7 are paired, the third, sixth switching elements Q3, Q6 are paired, and the fourth, fifth Switching elements Q4 and Q5 form a pair.

  The second condition is that the second switching element Q2 and the third switching element Q3 are not simultaneously turned on or off. Further, in the first to fourth modes, the first switching element Q1 and the eleventh switching element Q11, and in the fifth to eighth modes, the fourth switching element Q4 and the ninth switching element Q9, Are not simultaneously turned on or off. The condition that the two conditions are not turned off at the same time is applied except for the dead time described in “(2.4.2) Dead time”.

  First, in the first mode shown in FIG. 2A, the first and second switching elements Q1 and Q2, the seventh and eighth switching elements Q7 and Q8, and the twelfth switching element Q12 are on. . That is, the second bidirectional switch 14 is in a half-on state. In this state, as shown in FIG. 2A, the first input point 101 is electrically connected to the first output point 103 via the first switching element Q1 and the second switching element Q2. The second input point 102 is electrically connected to the second output point 104 via the eighth switching element Q8 and the seventh switching element Q7. At this time, among the semiconductor elements (switching elements, diodes), there are a total of four elements, i.e., first, second, seventh, and eighth switching elements Q1, Q2, Q7, and Q8, and the twelfth switching element Q12. There is no current flowing through.

  Accordingly, the first output point 103 has the same potential (E [V]) as the first input point 101, and the second output point 104 has the same potential (0 [V]) as the second input point 102. Therefore, the output voltage V2 of the power conversion device 1 generated between the first output point 103 and the second output point 104 becomes E (= E-0) [V]. Further, at this time, the potential of the third output point 105 becomes a potential obtained by subtracting the voltage across the inductor L1 from the potential of the first output point 103, and the potential of the fourth output point 106 becomes the potential of the second output point 104 to the inductor. The potential is the sum of the voltages at both ends of L2.

  Next, in the second mode shown in FIG. 2B, the first and third switching elements Q1 and Q3, the sixth and eighth switching elements Q6 and Q8, and the twelfth switching element Q12 are turned on. is there. That is, the second bidirectional switch 14 is in a half-on state. In this state, as shown in FIG. 2B, the first input point 101 is electrically connected to the first output point 103 via the first switching element Q1, the first capacitor C1, and the third switching element Q3. Is done. The second input point 102 is electrically connected to the second output point 104 via the eighth switching element Q8, the second capacitor C2, and the sixth switching element Q6. At this time, among the semiconductor elements (switching elements, diodes), there are a total of four elements, that is, the first, third, sixth, and eighth switching elements Q1, Q3, Q6, and Q8, and the twelfth switching element Q12. There is no current flowing through.

  Therefore, the potential of the first output point 103 is lower than the potential (E [V]) of the first input point 101 by the voltage across the first capacitor C1 (E / 4 [V]), that is, 3E / 4 ( = EE-4) [V]. The potential of the second output point 104 is higher than the potential of the second input point 102 (0 [V]) by the voltage across the second capacitor C2 (E / 4 [V]), that is, E / 4 ( = 0 + E / 4) [V]. Therefore, the output voltage V2 of the power converter 1 generated between the first output point 103 and the second output point 104 is E / 2 (= 3E / 4-E / 4) [V]. Further, at this time, the potential of the third output point 105 becomes a potential obtained by subtracting the voltage across the inductor L1 from the potential of the first output point 103, and the potential of the fourth output point 106 becomes the potential of the second output point 104 to the inductor. The potential is the sum of the voltages at both ends of L2.

  Next, in the third mode shown in FIG. 3A, the second switching element Q2, the seventh switching element Q7, and the eleventh and twelfth switching elements Q11 and Q12 are in an on state, respectively. That is, the second bidirectional switch 14 is in an all-on state. At this time, the second output point 104 passes through the seventh switching element Q7, the second capacitor C2, the eleventh switching element Q11, the twelfth switching element Q12, the first capacitor C1, and the second switching element Q2. And electrically connected to the first output point 103. At this time, among the semiconductor elements (switching elements, diodes), there are a total of four elements, ie, the second, seventh, eleventh and twelfth switching elements Q2, Q7, Q11 and Q12.

  Accordingly, the potential at the first output point 103 is determined by the voltage across the first capacitor C1 (E / 4 [V]) and the voltage across the second capacitor C2 (E / 4 [V]) from the potential at the second output point 104. ) And a higher potential. Therefore, the output voltage V2 of the power conversion device 1 generated between the first output point 103 and the second output point 104 is E / 2 (= E / 4 + E / 4) [V]. Further, at this time, the potential of the third output point 105 becomes a potential obtained by subtracting the voltage across the inductor L1 from the potential of the first output point 103, and the potential of the fourth output point 106 becomes the potential of the second output point 104 to the inductor. The potential is the sum of the voltages at both ends of L2. In this state, since the second bidirectional switch 14 is fully on, the conversion circuit 10 can cause a bidirectional current to flow between the first output point 103 and the second output point 104. it can.

  Next, in the fourth mode shown in FIG. 3B, the third switching element Q3, the sixth switching element Q6, and the eleventh and twelfth switching elements Q11 and Q12 are in an on state, respectively. That is, the second bidirectional switch 14 is in an all-on state. In this state, the second output point 104 is electrically connected to the first output point 103 via the sixth switching element Q6, the eleventh switching element Q11, the twelfth switching element Q12, and the third switching element Q3. Connected to. At this time, among the semiconductor elements (switching elements, diodes), there are a total of four elements, ie, third, sixth, eleventh, and twelfth switching elements Q3, Q6, Q11, and Q12.

  Therefore, the potential at the first output point 103 is the same as that at the second output point 104. Therefore, the output voltage V2 of the power conversion device 1 generated between the first output point 103 and the second output point 104 is 0 [V]. Further, at this time, the potential of the third output point 105 becomes a potential obtained by subtracting the voltage across the inductor L1 from the potential of the first output point 103, and the potential of the fourth output point 106 becomes the potential of the second output point 104 to the inductor. The potential is the sum of the voltages at both ends of L2. In this state, since the second bidirectional switch 14 is fully on, the conversion circuit 10 can cause a bidirectional current to flow between the first output point 103 and the second output point 104. it can.

  On the other hand, in the fifth to eighth modes, the power conversion device 1 switches the operation between the first conversion circuit 11 and the second conversion circuit 12 based on the first to fourth modes, and the first The bi-directional switch 13 and the second bi-directional switch 14 perform operations that are interchanged. That is, in the fifth to eighth modes and the first to fourth modes, the operation of the conversion circuit 10 is the first conversion circuit 11 and the first bidirectional switch 13, and the second conversion circuit 12 and the second mode. The direction switch 14 is replaced with a symmetrical operation.

  That is, in the fifth mode shown in FIG. 4A, the operation of the conversion circuit 10 is symmetric to the fourth mode. Therefore, in the fifth mode, the second switching element Q2, the seventh switching element Q7, and the ninth and tenth switching elements Q9 and Q10 are in the ON state. That is, the first bidirectional switch 13 is fully turned on. In this state, as shown in FIG. 4A, the first output point 103 passes through the second switching element Q2, the ninth switching element Q9, the tenth switching element Q10, and the seventh switching element Q7. The two output points 104 are electrically connected. At this time, among the semiconductor elements (switching elements, diodes), there are a total of four elements, ie, the second, seventh, ninth, and tenth switching elements Q2, Q7, Q9, and Q10.

  Therefore, the potential at the first output point 103 is the same as that at the second output point 104. Therefore, the output voltage V2 of the power conversion device 1 generated between the first output point 103 and the second output point 104 is 0 [V]. Further, at this time, the potential at the third output point 105 is a potential obtained by adding the voltage across the inductor L1 to the potential at the first output point 103, and the potential at the fourth output point 106 is changed from the potential at the second output point 104 to the inductor. The potential is obtained by subtracting the voltage across L2. In this state, since the first bidirectional switch 13 is fully on, the conversion circuit 10 can cause a bidirectional current to flow between the first output point 103 and the second output point 104. it can.

  Next, in the sixth mode shown in FIG. 4B, the operation of the conversion circuit 10 is symmetric to the third mode. Therefore, in the sixth mode, the third switching element Q3, the sixth switching element Q6, and the ninth and tenth switching elements Q9 and Q10 are in the ON state. That is, the first bidirectional switch 13 is fully turned on. In this state, the first output point 103 includes the third switching element Q3, the first capacitor C1, the ninth switching element Q9, the tenth switching element Q10, the second capacitor C2, and the sixth switching element Q6. And is electrically connected to the second output point 104. At this time, among the semiconductor elements (switching elements, diodes), there are a total of four elements, that is, third, sixth, ninth, and tenth switching elements Q3, Q6, Q9, and Q10.

  Accordingly, the potential at the first output point 103 is determined by the voltage across the first capacitor C1 (E / 4 [V]) and the voltage across the second capacitor C2 (E / 4 [V]) from the potential at the second output point 104. ) And a lower potential. Therefore, the output voltage V2 of the power converter 1 generated between the first output point 103 and the second output point 104 becomes −E / 2 (= −E / 4−E / 4) [V]. Further, at this time, the potential at the third output point 105 is a potential obtained by adding the voltage across the inductor L1 to the potential at the first output point 103, and the potential at the fourth output point 106 is changed from the potential at the second output point 104 to the inductor. The potential is obtained by subtracting the voltage across L2. In this state, since the first bidirectional switch 13 is fully on, the conversion circuit 10 can cause a bidirectional current to flow between the first output point 103 and the second output point 104. it can.

  Next, in the seventh mode shown in FIG. 5A, the operation of the conversion circuit 10 is symmetric to the second mode. Therefore, in the seventh mode, the second and fourth switching elements Q2 and Q4, the fifth and seventh switching elements Q5 and Q7, and the tenth switching element Q10 are in an ON state. That is, the first bidirectional switch 13 is in a half-on state. In this state, as shown in FIG. 5A, the first input point 101 is electrically connected to the second output point 104 via the fifth switching element Q5, the second capacitor C2, and the seventh switching element Q7. Is done. The second input point 102 is electrically connected to the first output point 103 via the fourth switching element Q4, the first capacitor C1, and the second switching element Q2. At this time, among the semiconductor elements (switching elements, diodes), there are a total of four elements, ie, the second, fourth, fifth, and seventh switching elements Q2, Q4, Q5, and Q7, and the tenth switching element Q10. There is no current flowing through.

  Therefore, the potential of the first output point 103 is higher than the potential of the second input point 102 (0 [V]) by the voltage across the first capacitor C1 (E / 4 [V]), that is, E / 4 ( = 0 + E / 4) [V]. The potential of the second output point 104 is lower than the potential of the first input point 101 (E [V]) by the voltage across the second capacitor C2 (E / 4 [V]), that is, 3E / 4 ( = EE-4) [V]. Therefore, the output voltage V2 of the power conversion device 1 generated between the first output point 103 and the second output point 104 is −E / 2 (= E / 4-3E / 4) [V]. Further, at this time, the potential at the third output point 105 is a potential obtained by adding the voltage across the inductor L1 to the potential at the first output point 103, and the potential at the fourth output point 106 is changed from the potential at the second output point 104 to the inductor. The potential is obtained by subtracting the voltage across L2.

  Next, in the eighth mode shown in FIG. 5B, the operation of the conversion circuit 10 is symmetric with respect to the first mode. Therefore, in the eighth mode, the third and fourth switching elements Q3 and Q4, the fifth and sixth switching elements Q5 and Q6, and the tenth switching element Q10 are in an ON state. That is, the first bidirectional switch 13 is in a half-on state. In this state, as shown in FIG. 5B, the first input point 101 is electrically connected to the second output point 104 via the fifth switching element Q5 and the sixth switching element Q6. The second input point 102 is electrically connected to the first output point 103 via the fourth switching element Q4 and the third switching element Q3. At this time, among the semiconductor elements (switching elements, diodes), there are a total of four elements, that is, the third, fourth, fifth, and sixth switching elements Q3, Q4, Q5, and Q6, and the tenth switching element Q10. There is no current flowing through.

  Therefore, the first output point 103 has the same potential (0 [V]) as the second input point 102, and the second output point 104 has the same potential (E [V]) as the first input point 101. Therefore, the output voltage V2 of the power conversion device 1 generated between the first output point 103 and the second output point 104 is −E (= 0−E) [V]. Further, at this time, the potential at the third output point 105 is a potential obtained by adding the voltage across the inductor L1 to the potential at the first output point 103, and the potential at the fourth output point 106 is changed from the potential at the second output point 104 to the inductor. The potential is obtained by subtracting the voltage across L2.

  In short, the power conversion device 1 changes the output voltage V2 generated between the first output point 103 and the second output point 104 in a plurality of stages by switching the first to eighth modes.

  More specifically, the first conversion circuit 11 uses the first capacitor C1 as a flying capacitor, and switches each of the first to fourth and ninth to twelfth switching elements Q1 to Q4 and Q9 to Q12 on / off. The potential at the first output point 103 is switched. The first capacitor C1 is charged in the second and seventh modes and discharged in the third and sixth modes in principle. However, if the first to eighth modes are switched at a relatively high frequency, the first capacitor C1 can be The voltage across one capacitor C1 can be regarded as substantially constant (E / 4 [V]).

  The second conversion circuit 12 uses the second capacitor C2 as a flying capacitor, and switches the potential of the second output point 104 by switching each of the fifth to twelfth switching elements Q5 to Q12. In principle, the second capacitor C2 is charged in the second and seventh modes and discharged in the third and sixth modes. If the first to eighth modes are switched at a relatively high frequency, the second capacitor C2 is charged in the basic operation. The voltage across the two capacitors C2 can be regarded as substantially constant (E / 4 [V]).

  In short, the control unit 6 charges and discharges the capacitor by switching a pair of modes in which the output voltage V2 is the same and the directions of the currents flowing through the capacitors (the first capacitor C1 and the second capacitor C2) are reversed. And switching.

  Specifically, when the output voltage V2 is set to E / 2 [V], the control unit 6 switches the second mode and the third mode as a pair of modes so that the capacitor (the first capacitor C1 and second capacitor C2) are switched between charging and discharging. In addition, when the output voltage V2 is set to −E / 2 [V], the control unit 6 switches the seventh mode and the sixth mode as a pair of modes, so that the capacitor (the first capacitor C1 and the first mode) Switching between charging and discharging of the second capacitor C2).

  Here, since each of the first capacitor C1 and the second capacitor C2 is charged in the second and seventh modes in principle, the second mode and the seventh mode are hereinafter referred to as “charging mode”. Call. Since each of the first capacitor C1 and the second capacitor C2 is discharged in the third and sixth modes in principle, the third mode and the sixth mode are also referred to as “discharge modes” below. In the following description, the control unit 6 outputs a “charge command” when selecting the charge mode, and outputs a “discharge command” when selecting the discharge mode.

  That is, when the output voltage V2 is set to E / 2 [V], the control unit 6 outputs a charge command when charging the capacitors (the first capacitor C1 and the second capacitor C2), and is in the charging mode. 2 mode is selected. When the output voltage V2 is set to E / 2 [V], the controller 6 outputs a discharge command when discharging the capacitors (the first capacitor C1 and the second capacitor C2), and the third mode is the discharge mode. Select a mode.

  Similarly, when the output voltage V2 is set to −E / 2 [V], the control unit 6 outputs a charge command when charging the capacitors (the first capacitor C1 and the second capacitor C2), and in the charge mode. A certain seventh mode is selected. When the output voltage V2 is set to −E / 2 [V], the control unit 6 outputs a discharge command when discharging the capacitors (the first capacitor C1 and the second capacitor C2), and is in the sixth discharge mode. Select the mode.

  In this way, the control unit 6 switches between the charging mode and the discharging mode in which the output voltage V2 is the same and the direction of the current flowing through the capacitor is reversed as a pair of modes, thereby charging and discharging the capacitor. Switch. However, the capacitor is charged in the charge mode and the capacitor is discharged in the discharge mode because the forward current described in the column “(2.4.1) Forward current and reverse current” is applied to the conversion circuit 10. Limited to flowing conditions. In the state where the reverse current described in the column “(2.4.1) Forward current and reverse current” flows through the conversion circuit 10, the capacitor is discharged in the charge mode and the capacitor is charged in the discharge mode. The This point will be described later. Hereinafter, the description will be made assuming that the current flowing through the conversion circuit 10 is a forward current unless otherwise specified.

  As described above, in the first to eighth modes, the power conversion device 1 outputs the voltage having the first output point 103 as the high potential side and the second output point 104 as the low potential side as the output voltage V2. Will do. In the first to fourth modes, the power conversion device 1 converts the output voltage V2 generated between the first output point 103 and the second output point 104 to E [V] (first mode), E / Switching is performed in three stages of 2 [V] (second and third modes) and 0 [V] (fourth mode). In the fifth to eighth modes, the power conversion device 1 sets the output voltage V2 generated between the first output point 103 and the second output point 104 to 0 [V] (fifth mode), −E / Switching is performed in three stages: 2 [V] (sixth and seventh modes) and -E [V] (eighth mode).

  Therefore, the power converter 1 switches the output voltage V2 to E [V], E / 2 [V], 0 [V], -E / 2 [V] by switching the first to eighth modes. ] And -E [V]. The power conversion apparatus 1 generates the first output voltage V1 that is an AC voltage between the third output point 105 and the fourth output point 106 by appropriately switching the five-stage second output voltage V2.

  Here, the output voltage V1 is equal to the output voltage of the system power supply 7, and has a sinusoidal waveform as shown in FIG. In FIG. 6, the horizontal axis represents the time axis and the vertical axis represents the voltage value. Here, in the period T1 to T3 in which the output voltage V1 varies in the range of 0 [V] to E [V] (that is, the period corresponding to the positive half-wave in the sine wave), the power converter 1 Switch the first to fourth modes. In the period in which the output voltage V1 fluctuates in the range of 0 [V] to -E [V] (that is, the period corresponding to the negative half-wave in the sine wave) T4 to T6, the power conversion device 1 Switch the mode of ~ 8.

  Table 1 summarizes the first to eighth modes described above.

  Here, the control unit 6 switches on / off each of the first to twelfth switching elements Q1 to Q12 by the PWM signal to realize the first to eighth modes.

  More specifically, in the period T1 and T3 when the output voltage V1 varies in the range of 0 [V] to E / 2 [V] in FIG. 6, the control unit 6 performs the operation of switching the second to fourth modes. repeat. Here, the controller 6 balances the discharge and charge of the first capacitor C1 and the second capacitor C2 by adjusting the time length in the second mode and the third mode.

  Further, in FIG. 6, the control unit 6 repeats the operation of switching the first to third modes during the period T <b> 2 when the output voltage V <b> 1 varies in the range of E / 2 [V] to E [V]. Here, the controller 6 balances the discharge and charge of the first capacitor C1 and the second capacitor C2 by adjusting the time length in the second mode and the third mode.

  In FIG. 6, the control unit 6 repeats the operation of switching the fifth to seventh modes during the periods T4 and T6 in which the output voltage V1 varies in the range of 0 [V] to -E / 2 [V]. Here, the control unit 6 balances the discharge and charging of the first capacitor C1 and the second capacitor C2 by adjusting the time length in the sixth mode and the seventh mode.

  Furthermore, in the period T5 in which the output voltage V1 varies in the range of −E / 2 [V] to −E [V] in FIG. 6, the control unit 6 repeats the operation of switching the sixth to eighth modes. Here, the control unit 6 balances the discharge and charging of the first capacitor C1 and the second capacitor C2 by adjusting the time length in the sixth mode and the seventh mode.

  In the present embodiment, the control unit 6 switches the first to eighth modes described above while changing the duty ratio of the PWM signal, so that the waveform of the output voltage V1 approximates a sine wave. The output voltage V2 generated between the output point 103 and the second output point 104 is controlled. In short, the power conversion device 1 changes the output voltage V2 generated between the first output point 103 and the second output point 104 in five steps by the control unit 6 to thereby generate a sinusoidal AC voltage (output voltage V1). ) Occurs between the third output point 105 and the fourth output point 106.

  The fourth mode and the fifth mode are both modes in which the output voltage V2 is 0 [V] and do not contribute to the discharging and charging of the first capacitor C1 and the second capacitor C2. For this reason, it is conceivable to omit either the fourth mode or the fifth mode, but the power conversion device 1 is configured as the fourth mode in consideration of the positive / negative balance of the output voltage V1. By dividing the fifth mode, the switching loss can be reduced and the efficiency is improved.

  According to the power conversion device 1 of the present embodiment, the number of elements through which a current flows (hereinafter referred to as “the number of passing elements”) among the semiconductor elements (switching elements, diodes) In this mode, it is “4” or less.

  In particular, in the third and fourth modes in which the second bidirectional switch 14 is fully turned on, even if the eleventh switching element Q11 and the twelfth switching element Q12 are counted as separate elements, the number of passing elements is “ 4 ". Similarly, in the fifth and sixth modes in which the first bidirectional switch 13 is fully turned on, even if the ninth switching element Q9 and the tenth switching element Q10 are counted as separate elements, the number of passing elements is “4”. Therefore, when the first and second bidirectional switches 13 and 14 are each composed of one element, the number of passing elements in the third to sixth modes is “3”.

  Meanwhile, it is preferable that the control unit 6 determines whether to charge or discharge the first capacitor C1 and the second capacitor C2 according to the detection result of the detection circuit 63. In the present embodiment, the detection circuit 63 is included in the control unit 6, and the detection result of the detection circuit 63 is output to the microcomputer 62. The detection circuit 63 individually detects the voltage across the first capacitor C1 and the voltage across the second capacitor C2, and outputs an average value Vc of these two voltages to the microcomputer 62 as a detection result. The microcomputer 62 is configured to select whether to charge or discharge the capacitor according to the detection result of the detection circuit 63.

  More specifically, for example, during the periods T1 to T3 in which the output voltage V1 varies in the range of 0 [V] to E [V], the control unit 6 repeats the operation of switching the first to fourth modes. In these cases (periods T1 to T3), the microcomputer 62 determines whether to select the second mode (charge mode) or the third mode (discharge mode) according to the detection result of the detection circuit 63. To decide. That is, the microcomputer 62 compares the detection result (average value Vc) of the detection circuit 63 with the target voltage, and either the second mode (charge mode) or the third mode (discharge mode) is determined according to the comparison result. Select. The microcomputer 62 selects the third mode, which is the discharge mode, if the detection result of the detection circuit 63 is greater than the target voltage, and the charge mode, if the detection result of the detection circuit 63 is smaller than the target voltage. 2 mode is selected. Here, the target voltage is the same value as the reference voltage (E / 4 [V]).

  Similarly, during the period T4 to T6 in which the output voltage V1 varies in the range of 0 [V] to -E [V], the control unit 6 repeats the operation of switching the fifth to eighth modes. In these cases (periods T4 to T6), the microcomputer 62 determines which of the sixth mode (discharge mode) and the seventh mode (charge mode) is selected according to the detection result of the detection circuit 63. To decide. That is, the microcomputer 62 compares the detection result (average value Vc) of the detection circuit 63 with the target voltage (E / 4 [V]), and the seventh mode (charging mode) and the sixth mode are compared according to the comparison result. (Discharge mode) is selected. The microcomputer 62 selects the sixth mode that is the discharge mode if the detection result of the detection circuit 63 is larger than the target voltage, and the charge mode if the detection result of the detection circuit 63 is smaller than the target voltage. 7 mode is selected.

  Thus, the voltage across the first capacitor C1 and the voltage across the second capacitor C2 during the basic operation are each maintained at the reference voltage (E / 4 [V]).

  Moreover, it is preferable that the control part 6 switches charge and discharge of a capacitor (1st capacitor C1 and 2nd capacitor C2) with a predetermined switching period. The switching period here is set in accordance with, for example, the period of the PWM signal.

(2.3) Configuration of Power Conditioner As shown in FIG. 7, the power conditioner 20 according to the present embodiment includes the power conversion device 1 and the disconnector 9. The disconnector 9 is electrically connected between the first output point 103 (see FIG. 1) and the second output point 104 (see FIG. 1) and the system power supply 7. In the example of FIG. 7, the disconnector 9 is electrically connected between the third output point 105 and the fourth output point 106 and the system power supply 7. In other words, the resolver 9 is connected to the first output point 103 and the second output point 104 via the filter circuit 5 (see FIG. 1). The disconnector 9 may be located between the first output point 103 and the second output point 104 and the system power supply 7, and is required to be directly connected to the first output point 103 and the second output point 104. Instead, it may be connected to the subsequent stage of the filter circuit 5 as in this embodiment.

  Here, the circuit breaker 9 is electrically connected between the first contact point 91 electrically connected between the third output point 105 and the system power supply 7, and between the fourth output point 106 and the system power supply 7. And a second contact portion 92 connected to the. However, the circuit breaker 9 only needs to be electrically connected between at least one of the third output point 105 and the fourth output point 106 and the system power supply 7, and the first contact portion 91 and the second contact portion are required. Any of 92 may be omitted.

  The power conditioner 20 performs grid connection operation in a steady state, converts DC power input from the DC power supply 100 into AC power by the power conversion device 1, and outputs the AC power to the system power supply 7 and the load 8. Although detailed description is omitted, the power conditioner 20 performs a self-sustained operation in which the disconnector 9 is opened and AC power is output in a state disconnected from the system power supply 7 in the event of an abnormality such as a power failure of the system power supply 7. It is configured as follows.

  According to the power conditioner 20, the first converter circuit 11, the second converter circuit 12, and the system power supply 7 can be electrically disconnected by opening (disconnecting) the disconnector 9. Therefore, the power conditioner 20 opens the disconnector 9 during the start-up period after the power is turned on and before the power converter 1 starts the basic operation described above, so that the first output point 103 and the second output point are opened. A current path including the filter circuit 5 can be formed between the terminal 104 and the terminal 104.

  The current path here is a current path including the inductor L1, the third capacitor C3, and the inductor L2 that constitute the filter circuit 5. The power conversion device 1 uses the current path as a charging path, so that even if the third output point 105 and the fourth output point 106 are electrically insulated, the first capacitor C1 and the second capacitor C2 can be charged.

  Therefore, the power converter 1 can charge the first capacitor C1 and the second capacitor C2 even when the third output point 105 and the fourth output point 106 are not connected to the system power supply 7. In other words, the power conversion device 1 operates in a steady state even when no load is connected between the pair of output terminals (the third output point 105 and the fourth output point 106) (no load state). Necessary capacitors (first capacitor C1 and second capacitor C2) can be charged. The steady operation here is an operation of the power conversion device 1 after the start-up period has elapsed, that is, after each of the first capacitor C1 and the second capacitor C2 is charged to the reference voltage (E / 4 [V]). Therefore, it is synonymous with the basic operation described above.

(2.4) Detailed operation (2.4.1) Forward current and reverse current As described above, the power converter 1 of the present embodiment has the second bidirectional switch 14 in the third and fourth modes. In the fifth and sixth modes, the first bidirectional switch 13 is in the fully on state. That is, in any of the first to eighth modes, the element through which a current flows among the semiconductor elements (switching elements, diodes) is any one of the first to twelfth switching elements Q1 to Q12, and the diode (first to first modes). No current flows through the twelve diodes D1 to D12). Therefore, the power conversion device 1 can flow a bidirectional current between the first output point 103 and the second output point 104 in any of the first to eighth modes.

  In the present embodiment, the current flowing through the conversion circuit 10 in the direction indicated by the thick arrow in FIGS. 2A, 2B, 3A, 3B, 4A, 4B, 5A, and 5B is referred to as “forward current” and is opposite to the forward current. The current flowing through the conversion circuit 10 is referred to as “reverse current”. That is, in the first to fourth modes in which the output voltage V1 varies in the range of 0 [V] to E [V], the current from the first output point 103 to the third output point 105 is the forward current. In the fifth to eighth modes in which the output voltage V1 varies in the range of 0 [V] to -E [V], the current from the second output point 104 to the fourth output point 106 is the forward current.

  In this way, the power conversion device 1 is configured so that the conversion circuit 10 supports bidirectional current, so that the output current I1 that flows between the third output point 105 and the fourth output point 106, the third output point 105, A phase difference can be set between the output voltage V <b> 1 generated between the fourth output points 106. If there is a phase difference between the output current I1 and the output voltage V1, as shown in FIG. 8, the output current I1 is different from the output voltage V1 (for example, the output voltage V1 is positive and the output current I1 is negative). A period will arise. FIG. 8 shows the first output voltage V1 generated between the third output point 105 and the fourth output point 106 and the output current I1 flowing through the third output point 105 or the fourth output point 106 with the horizontal axis as the time axis. Is shown. In the example of FIG. 8, the output current I1 is delayed with respect to the output voltage V1, the output current I1 and the output voltage V1 have different signs in the periods T11 and T13, and the output current I1 and the output voltage in the periods T12 and T14. V1 has the same sign.

  Here, in the periods T12 and T14 in which the output current I1 and the output voltage V1 have the same sign, the current flowing in the conversion circuit 10 is a forward current, but the period T11 in which the output current I1 and the output voltage V1 have different signs. , T13, the current flowing through the conversion circuit 10 is a reverse current. Therefore, when the power converter 1 sets a phase difference between the output current I1 and the output voltage V1, the conversion circuit 10 needs to support bidirectional current as in the present embodiment.

  In particular, when the power conversion device 1 is used for the power conditioner 20 (see FIG. 7) for the solar power generation device, the power conversion device is used for the purpose of detecting the isolated operation and suppressing the voltage rise of the system power supply 7. 1 may set a phase difference between the output current I1 and the output voltage V1. Moreover, when the power converter 1 is used for the power conditioner for the power storage device, the power converter 1 is supplied with power by setting a phase difference between the output current I1 and the output voltage V1. And switching between charging and discharging of the power storage device. The power converter 1 of this embodiment can respond to such a use because the conversion circuit 10 supports bidirectional current.

  Even if the power conversion device 1 that supports bidirectional current operates in the same mode, the first capacitor C1 and the first capacitor C1 and the second capacitor C2 depend on whether the current flowing through the first capacitor C1 and the second capacitor C2 is forward current or reverse current. The charging and discharging of the second capacitor C2 may be interchanged. That is, when forward current flows through the conversion circuit 10, the first capacitor C1 and the second capacitor C2 are charged in the second and seventh modes and discharged in the third and sixth modes, as a rule. The On the other hand, when a reverse current flows through the conversion circuit 10, the first capacitor C1 and the second capacitor C2 are discharged in the second and seventh modes and charged in the third and sixth modes. Will be.

(2.4.2) Dead time When the power conversion apparatus 1 switches the first to eighth modes, all the switching elements of the specific combination are turned off so that the switching elements of the specific combination are not turned on at the same time. There is a dead time. That is, in the power conversion device 1, the first to eighth modes are switched after a period (dead time) in which the on / off state of the switching element is different from any of the first to eighth modes. Below, operation | movement of the power converter device 1 in a dead time is demonstrated with reference to FIG. 9A, 9B, 10A, 10B. In the figure, a thick line arrow represents a current path, and a switching element with a dotted circle represents an on-state element.

  For example, between the first mode (see FIG. 2A) and the second mode (see FIG. 2B), as shown in FIG. 9A, the second, third, sixth, and seventh switching elements Q2, Q3, Q6 , Q7 are all set to a dead time. That is, only the first, eighth, and twelfth switching elements Q1, Q8, and Q12 are turned on during the dead time when switching between the first mode and the second mode. In this state, the return currents of the inductors L1 and L2 flow through the sixth diode D6, the second capacitor C2, the eighth switching element Q8, the first switching element Q1, the first capacitor C1, and the third diode D3. .

  Also, between the first mode (see FIG. 2A) and the third mode (see FIG. 3A), as shown in FIG. 9B, the first, eighth, and eleventh switching elements Q1, Q8, and Q11 are all. Set the dead time to turn off. That is, only the second, seventh, and twelfth switching elements Q2, Q7, and Q12 are turned on in the dead time when switching between the first mode and the third mode. In this state, the return currents of the inductors L1 and L2 pass through the seventh switching element Q7, the second capacitor C2, the eleventh diode D11, the twelfth switching element Q12, the first capacitor C1, and the second switching element Q2. Flowing.

  Further, between the second mode (see FIG. 2B) and the fourth mode (see FIG. 3B), as shown in FIG. 10A, the first, eighth, and eleventh switching elements Q1, Q8, and Q11 are all. Set the dead time to turn off. That is, only the third, sixth, and twelfth switching elements Q3, Q6, and Q12 are turned on during the dead time when switching between the second mode and the fourth mode. In this state, the return currents of the inductors L1 and L2 flow through the sixth switching element Q6, the eleventh diode D11, the twelfth switching element Q12, and the third switching element Q3.

  Further, between the third mode (see FIG. 3A) and the fourth mode (see FIG. 3B), as shown in FIG. 10B, the second, third, sixth and seventh switching elements Q2, Q3, Q6. , Q7 are all set to a dead time. That is, only the eleventh and twelfth switching elements Q11 and Q12 are turned on in the dead time when switching between the third mode and the fourth mode. In this state, the return currents of the inductors L1 and L2 flow through the sixth diode D6, the eleventh switching element Q11, the twelfth switching element Q12, and the third diode D3.

  Although only the dead time when the first to fourth modes are switched has been described here, the same dead time is set when the fifth to eighth modes are switched. Thus, setting the dead time prevents a specific combination of switching elements from being turned on simultaneously. Thereby, for example, it is possible to prevent a short circuit path from being formed between the first input point 101 and the second input point 102.

(2.4.3) Recovery Current Hereinafter, the recovery current of the parasitic diode (first to eighth diodes D1 to D8) will be described. Here, as a comparative example for explanation, a power conversion device 1A in which the first to fourth protection diodes D101 to D104 are omitted from the power conversion device 1 of the present embodiment is illustrated. As shown in FIG. 11A, the power conversion device 1A of the comparative example has the same configuration as the power conversion device 1 of the present embodiment, except that the conversion circuit 10A does not have the first to fourth protection diodes D101 to D104. .

  In the power conversion device 1A of the comparative example, there is a possibility that a short-circuit current flows between the first input point 101 and the second input point 102 due to the influence of the recovery current of the parasitic diode (first to eighth diodes D1 to D8). There is. This point will be described below with reference to FIGS. 11A and 11B. 11A and 11B show an operation in a state where a reverse current flows through the conversion circuit 10A in the power conversion device 1A of the comparative example. In the figure, a thick line arrow represents a current path, and a switching element with a dotted circle represents an on-state element.

  Here, the operation when the power conversion device 1A switches from the first mode (see FIG. 2A) to the third mode (see FIG. 3A) is illustrated, FIG. 11A shows the dead time, and FIG. 11B shows the third mode. Show. That is, in FIG. 11A, the on / off state of the switching element is the same as in the example of FIG. 9B, the direction of the current flowing through the conversion circuit 10A is different from the example of FIG. 9B, and the reverse current flows through the conversion circuit 10A. Is shown. FIG. 11B shows a state where the on / off state of the switching element is the same as in the example of FIG. 3A and the direction of the current flowing through the conversion circuit 10A is different from the example of FIG. ing.

  In the dead time between the first mode and the third mode, as shown in FIG. 11A, the return currents of the inductors L1 and L2 flow as reverse currents. In this state, the reverse current flows through the second switching element Q2, the first diode D1, the eighth diode D8, and the seventh switching element Q7. That is, the first and eighth switching elements Q1 and Q8 are in an off state, but current flows through the respective parasitic diodes (first and eighth diodes D1 and D8).

  And when dead time is complete | finished and it transfers to a 3rd mode, as shown to FIG. 11B, the path | route through which a reverse current flows changes by turning on the 11th switching element Q11. In this state, the reverse current flows through the second switching element Q2, the first capacitor C1, the twelfth switching element Q12, the eleventh switching element Q11, the second capacitor C2, and the seventh switching element Q7. At this time, if the recovery characteristics of the parasitic diodes (first and eighth diodes D1 and D8) are poor, the on states of the first and eighth diodes D1 and D8 may continue. That is, in the power conversion device 1A, since the recovery currents of the first and eighth diodes D1 and D8 continue to flow even after the dead time ends, the first and eighth diodes D1 and D8 are not immediately turned off. May remain on.

  In this case, the recovery currents of the first and eighth diodes D1 and D8 flow between the first input point 101 and the second input point 102 along a path indicated by a dotted arrow in FIG. 11B. That is, the recovery current flows through the first diode D1, the first capacitor C1, the twelfth switching element Q12, the eleventh switching element Q11, the second capacitor C2, and the eighth diode D8. Therefore, a short-circuit current flows between the first input point 101 and the second input point 102. When the short-circuit current flows, the current flowing through the conversion circuit 10A rises sharply, so that a surge voltage is generated due to the parasitic inductance of the conversion circuit 10A. As a result, stress may be applied to the components of the power conversion device 1A.

(2.4.4) Function of Protection Diode In the power conversion device 1 of the present embodiment, a short-circuit current flows due to the influence of the recovery current of the parasitic diode (first to eighth diodes D1 to D8) as in the comparative example. As measures against this, first to fourth protection diodes D101 to D104 are provided. That is, the first to fourth protection diodes D101 to D104 have a function of protecting the power conversion device 1 from a short circuit current. This point will be described below with reference to FIGS. 12A, 12B, 13A, and 13B. 12A, 12B, 13A, and 13B show an operation in a state where a reverse current flows through the conversion circuit 10 in the power conversion device 1 of the present embodiment. In the figure, a thick line arrow represents a current path, and a switching element with a dotted circle represents an on-state element.

  For example, in the dead time between the first mode and the second mode, as shown in FIG. 12A, the return currents of the inductors L1 and L2 flow as reverse currents. In this state, the reverse current flows through the first protection diode D101 and the fourth protection diode D104. That is, at least a part of the reverse current is replaced with a path including parasitic diodes (second and seventh diodes D2 and D7) as shown by dotted arrows in FIG. 12A, and the first and fourth protection diodes D101 and D104. Will flow. Therefore, when the dead time ends, the first and fourth protection diodes D101 and D104 having excellent recovery characteristics are turned off relatively quickly, and a short-circuit current is suppressed from flowing due to the influence of the recovery current.

  Further, in the dead time between the first mode and the third mode, as shown in FIG. 12B, the return currents of the inductors L1 and L2 flow as reverse currents. In this state, the reverse current flows through the first protection diode D101 and the fourth protection diode D104. That is, at least a part of the reverse current is replaced with a path including parasitic diodes (first and eighth diodes D1 and D8) as shown by dotted arrows in FIG. 12B, and the first and fourth protection diodes D101 and D104. Will flow. Therefore, when the dead time ends, the first and fourth protection diodes D101 and D104 having excellent recovery characteristics are turned off relatively quickly, and a short-circuit current is suppressed from flowing due to the influence of the recovery current.

  Further, in the dead time between the second mode and the fourth mode, as shown in FIG. 13A, the return currents of the inductors L1 and L2 flow as reverse currents. In this state, the reverse current flows through the first protection diode D101 and the fourth protection diode D104. That is, at least a part of the reverse current is replaced with a path including parasitic diodes (first and eighth diodes D1 and D8) as shown by dotted arrows in FIG. 13A, and the first and fourth protection diodes D101 and D104. Will flow. Therefore, when the dead time ends, the first and fourth protection diodes D101 and D104 having excellent recovery characteristics are turned off relatively quickly, and a short-circuit current is suppressed from flowing due to the influence of the recovery current.

  Further, in the dead time between the third mode and the fourth mode, as shown in FIG. 13B, the return currents of the inductors L1 and L2 flow as reverse currents. In this state, the reverse current flows through the second diode D2, the first capacitor C1, the twelfth switching element Q12, the eleventh switching element Q11, the second capacitor C2, and the seventh diode D7. That is, the reverse current flows through a path including parasitic diodes (second and seventh diodes D2 and D7). From this state, when the third switching element Q3 and the sixth switching element Q6 are turned on by shifting to the fourth mode, a short-circuit current may be generated in each of the first capacitor C1 and the second capacitor C2. That is, the recovery current of the second diode D2 may flow as a short-circuit current of the first capacitor C1 through the third switching element Q3. Similarly, the recovery current of the seventh diode D7 may flow as a short-circuit current of the second capacitor C2 through the sixth switching element Q6.

  However, the voltage across each of the first capacitor C1 and the second capacitor C2 is ¼ of the output voltage of the DC power supply 100. Therefore, the short-circuit current of each of the first capacitor C1 and the second capacitor C2 is about 1/4 of the short-circuit current of the DC power supply 100 flowing between the first input point 101 and the second input point 102. Further, each of the second, third, sixth, and seventh switching elements Q2, Q3, Q6, and Q7 has a lower withstand voltage than the first, fourth, fifth, and eighth switching elements Q1, Q4, Q5, and Q8. Therefore, the recovery characteristics of the parasitic diode can be improved. Therefore, the influence of the recovery current generated when the dead time between the third mode and the fourth mode ends on the components of the power conversion device 1 is suppressed to a small level.

  Here, only the dead time when the first to fourth modes are switched has been described. However, even in the dead time when the fifth to eighth modes are switched, the short-circuit current is affected by the recovery current of the parasitic diode as described above. Is suppressed from flowing. In the dead time when the fifth to eighth modes are switched, a part of the reverse current flows through the second protection diode D102 and the third protection diode D103 among the first to fourth protection diodes D101 to D104. It will be.

  In short, the power conversion device 1 of the present embodiment improves the recovery characteristics by flowing current to the first to fourth protection diodes D101 to D104 instead of the parasitic diodes (first to eighth diodes D1 to D8). ing. Thereby, the power converter device 1 of this embodiment can suppress that a short circuit current flows under the influence of the recovery current of a parasitic diode.

  By the way, the ratio of the current flowing through each of the first to fourth protection diodes D101 to D104 and the current flowing through the parasitic diode (each of the first to eighth diodes D1 to D8) is determined by the impedance on the current path. Here, the path in parallel with each of the first to fourth protection diodes D101 to D104 includes at least one parasitic diode and one switching element. Therefore, even if each of the first to fourth protection diodes D101 to D104 and each of the first to eighth diodes D1 to D8 have the same forward voltage, the first resistance diode D101 to D104 has the same value as the on-resistance of the switching element. Current easily flows through the protection diodes D101 to D104 of 1-4.

(3) Effect According to the power conversion device 1 of the present embodiment, the first conversion circuit 11 and the second conversion circuit 12 that are connected in parallel between both ends of the DC power supply 100 are provided. The circuit 12 is connected to the first bidirectional switch 13 and the second bidirectional switch 14. Here, the first conversion circuit 11 includes four switching elements (first to fourth switching elements Q1 to Q4) and one capacitor (first capacitor C1). Similarly, the second conversion circuit 12 includes four switching elements (fifth to eighth switching elements Q5 to Q8) and one capacitor (second capacitor C2).

  In this configuration, the current input from the DC power supply 100 to the power conversion device 1 is out of ten switching elements (first to eighth switching elements Q1 to Q8 and first and second bidirectional switches 13 and 14). It passes through at most four elements. Therefore, this power conversion device 1 has the advantage that the sum of the conduction loss (loss) of the switching elements is relatively small, and the power conversion efficiency can be further improved.

  Further, the power conversion device 1 generally requires a large heat radiating device (an air cooling device such as a heat sink or a fan) because the calorific value increases as the conduction loss increases. The power conversion device 1 of the present embodiment can be expected to reduce the size of the heat dissipation device by suppressing conduction loss.

  Compared with the configuration described in Patent Document 1, the power conversion device 1 of the present embodiment also has an advantage that the entire device can be reduced in size by the amount that does not require a voltage dividing capacitor. In other words, the power conversion device described in Patent Document 1 divides the DC voltage E by E / 2 by applying the DC voltage E to a series circuit of two DC capacitors. The capacitor is an essential configuration. On the other hand, since the power conversion device 1 of the present embodiment does not require a voltage dividing capacitor, the entire device can be reduced in size accordingly.

  Moreover, the power conversion device 1 further includes first to fourth protection diodes D101 to D104. Therefore, the power conversion device 1 of the present embodiment allows the current to flow through the first to fourth protection diodes D101 to D104 instead of the parasitic diodes (first to eighth diodes D1 to D8). It is possible to improve the recovery characteristics. Therefore, the power conversion device 1 of the present embodiment can suppress the short circuit current from flowing due to the influence of the recovery current of the parasitic diode.

  As in the present embodiment, each of the first to fourth protection diodes D101 to D104 is preferably a fast recovery diode. According to this configuration, each of the first to fourth protection diodes D101 to D104 has an excellent recovery characteristic as compared with a general rectifying diode, and further improves the recovery characteristic as the conversion circuit 10. be able to. Therefore, the power conversion device 1 can further suppress the short circuit current from flowing due to the influence of the recovery current of the parasitic diode. However, the fact that each of the first to fourth protection diodes D101 to D104 is a fast recovery diode is not an essential configuration for the power conversion device 1, and each of the first to fourth protection diodes D101 to D104 is a fast recovery diode. Not necessarily.

  Further, as in the present embodiment, the first bidirectional switch 13 is configured to be able to switch between operating states including an all-off state and an all-on state, and the second bidirectional switch is configured to switch between an all-off state and an all-off state. It is preferable that the operation state including the on state is switchable. The all-off state of the first bidirectional switch 13 is a state in which a bidirectional current is interrupted between the first connection point 201 and the second connection point 202. The all-on state of the first bidirectional switch 13 is a state in which bidirectional current passes between the first connection point 201 and the second connection point 202. The all-off state of the second bidirectional switch 14 is a state in which bidirectional current is interrupted between the third connection point 203 and the fourth connection point 204. The all-on state of the second bidirectional switch 14 is a state in which bidirectional current passes between the third connection point 203 and the fourth connection point 204.

  According to this configuration, the power conversion device 1 allows the bidirectional current to pass between the first connection point 201 and the second connection point 202 by turning on the first bidirectional switch 13 fully. Can create a unique state. In addition, the power conversion device 1 creates a state in which bidirectional current can pass between the third connection point 203 and the fourth connection point 204 by turning on the second bidirectional switch 14. be able to. Therefore, the power conversion device 1 is, for example, between the output current I1 flowing between the third output point 105 and the fourth output point 106 and the output voltage V1 generated between the third output point 105 and the fourth output point 106. Phase difference can be set.

  Further, as in the present embodiment, the operating state of the first bidirectional switch 13 is such that the current flowing from the second connection point 202 to the first connection point 201 is cut off, and the first connection point 201 to the second connection point. It is preferable to further include a half-on state in which the current flowing to 202 is passed. In this case, the operation state of the second bidirectional switch 14 cuts off the current flowing from the third connection point 203 to the fourth connection point 204 and passes the current flowing from the fourth connection point 204 to the third connection point 203. It is preferable to further include a half-on state.

  According to this configuration, the first bidirectional switch 13 is half-on in a mode in which the current flowing from the first connection point 201 to the second connection point 202 does not need to be interrupted as in the seventh and eighth modes. The state is fine. Therefore, the control unit 6 can continue to turn on the tenth switching element Q10 in the period (period T4 to T6) in which the operation for switching the fifth to seventh modes or the sixth to eighth modes is repeated. In other words, in the fifth and sixth modes, the first bidirectional switch 13 is fully turned on and the tenth switching element Q10 is turned on. Therefore, every time the mode is switched to the seventh or eighth mode, the tenth switching element. When Q10 is turned off, a switching loss may occur in the tenth switching element Q10. The power converter 1 of the present embodiment allows the first bidirectional switch 13 to keep the tenth switching element Q10 on when the fifth to seventh modes or the sixth to eighth modes are switched. The generated switching loss can be reduced.

  Similarly, in the mode in which the current flowing from the fourth connection point 204 to the third connection point 203 does not need to be interrupted as in the first and second modes, the second bidirectional switch 14 may be in a half-on state. . Therefore, the power conversion device 1 of the present embodiment is configured so that the twelfth switching element Q12 is continuously turned on when the first to third modes or the second to fourth modes are switched, so that the second bidirectional switch 14 can reduce the switching loss.

  Further, as in the present embodiment, the power conversion device 1 includes the first to fourth switching elements Q1 to Q4, the fifth to eighth switching elements Q5 to Q8, the first bidirectional switch 13, and the second bidirectional element. It is preferable to further include a control unit 6 that controls the switch 14. In this case, the control unit 6 controls the control target so that an output voltage is generated between the first output point 103 and the second output point 104. According to this configuration, the power conversion apparatus 1 controls the desired output by controlling the control target (first to eighth switching elements Q1 to Q8, first and second bidirectional switches 13 and 14) in the control unit 6. It is possible to output a voltage. It is not essential that the power conversion device 1 includes the control unit 6, and the control unit 6 may be omitted.

  In addition, the power conditioner 20 according to the present embodiment includes the power conversion device 1 and a disconnector 9 that is electrically connected between the first output point 103 and the second output point 104 and the system power supply 7. I have. According to this configuration, the first converter circuit 11 and the second converter circuit 12 and the system power supply 7 can be electrically disconnected by opening (disconnecting) the disconnector 9. Therefore, the power conditioner 20 performs grid connection operation in a steady state, and when the system power supply 7 is abnormal, such as a power failure, opens the disconnector 9 and outputs AC power in a state disconnected from the system power supply 7. You can perform autonomous operation.

(4) Modified Example As a modified example of the present embodiment, the bidirectional switch (each of the first bidirectional switch 13 and the second bidirectional switch 14) may not include the all-on state in the operation state. In other words, the bidirectional switch (each of the first bidirectional switch 13 and the second bidirectional switch 14) is a switch that passes current in at least one direction when turned on and cuts off current in either direction when turned off. I just need it. Specifically, the ninth switching element Q9 and the eleventh switching element Q11 are omitted from the configuration shown in FIG. 1 while leaving the ninth diode D9 and the eleventh diode D11. That is, in the first bidirectional switch 13, the ninth diode D9 and the tenth switching element Q10 are electrically connected in series between the first connection point 201 and the second connection point 202. . In the second bidirectional switch 14, the twelfth switching element Q12 and the eleventh diode D11 are electrically connected in series between the third connection point 203 and the fourth connection point 204.

  In the present modification, when the tenth switching element Q10 is off, the first bidirectional switch 13 is fully off. When the tenth switching element Q10 is on, the first bidirectional switch 13 is in a half-on state. Further, when the twelfth switching element Q12 is turned off, the second bidirectional switch 14 is fully turned off. When the twelfth switching element Q12 is on, the second bidirectional switch 14 is in a half-on state.

  Hereinafter, other modifications of the present embodiment will be listed.

  As described above, the power conversion device 1 is not limited to the configuration in which the conversion circuit 10 includes the first conversion circuit 11 and the second conversion circuit 12, the first bidirectional switch 13, and the second bidirectional switch 14. These can be changed as appropriate. The number of switching elements is not limited to 12 of the first to twelfth switching elements Q1 to Q12, and can be changed as appropriate.

  The first to eighth switching elements Q1 to Q8 and the ninth to twelfth switching elements Q9 to Q12 are not limited to depletion type n-channel MOSFETs, and other semiconductor switches may be used. For example, a power semiconductor device using a wide band gap semiconductor material such as IGBT (Insulated Gate Bipolar Transistor) or GaN (gallium nitride) is used.

  In the power converter 1, when each of the 1st-8th switching elements Q1-Q8 is IGBT, there also exists an advantage that the free-wheeling diode (FWD: Free Wheeling Diode) for circulating a load current becomes unnecessary. That is, there is an IGBT of a type in which a reflux diode connected in antiparallel is built in the IGBT. In the power conversion device 1, since the first to fourth protection diodes D101 to D104 function instead of the freewheeling diode, it is not necessary to use an IGBT of a type in which the freewheeling diode is built. If each of the first to eighth switching elements Q1 to Q8 is provided with a free-wheeling diode, eight diodes are required. However, by replacing the first to fourth protection diodes D101 to D104, four diodes are sufficient.

  Also, the specific configuration of the bidirectional switch (each of the first bidirectional switch 13 and the second bidirectional switch 14) is not limited to the configuration described above. The bidirectional switch may be a bidirectional gate (dual gate) structure bidirectional switch using a wide band gap semiconductor material such as GaN (gallium nitride).

DESCRIPTION OF SYMBOLS 1 Power converter 10 Conversion circuit 11 1st conversion circuit 12 2nd conversion circuit 13 1st bidirectional switch 14 2nd bidirectional switch 6 Control part 7 System power supply 9 Disconnector 20 Power conditioner 100 DC power supply 101 1st 1st input point 102 2nd input point 103 1st output point 104 2nd output point 201 1st connection point 202 2nd connection point 203 3rd connection point 204 4th connection point C1 1st capacitor C2 2nd capacitor D101-D104 1st 1 to 4 protective diodes Q1 to Q8 1st to 8th switching elements V1 (first) output voltage

Claims (6)

A first conversion circuit and a second conversion circuit electrically connected in parallel between a first input point on the high potential side of the DC power supply and a second input point on the low potential side of the DC power supply. Prepared,
The first conversion circuit includes a first switching element, a second switching element, a third switching element, a fourth switching element from the first input point side between the first input point and the second input point. First to fourth switching elements electrically connected in series in the order of the switching elements, and a second circuit electrically connected in parallel to the series circuit of the second switching element and the third switching element. 1 capacitor, and a connection point between the second switching element and the third switching element is a first output point,
The second conversion circuit includes a fifth switching element, a sixth switching element, a seventh switching element, an eighth switching element from the first input point side between the first input point and the second input point. In the order of the switching elements, the fifth to eighth switching elements electrically connected in series, and the sixth switching element and the seventh switching element are electrically connected in parallel with the series circuit. A second output point is a connection point between the sixth switching element and the seventh switching element,
Electrical connection between a first connection point that is a connection point of the first switching element and the second switching element and a second connection point that is a connection point of the seventh switching element and the eighth switching element. A first bidirectional switch connected electrically,
Electrical connection between a third connection point that is a connection point of the third switching element and the fourth switching element and a fourth connection point that is a connection point of the fifth switching element and the sixth switching element. A second bidirectionally connected switch;
Between the first input point and the first output point, the first switching element and the second switching element are electrically connected in parallel with each other, and the first output point to the first output point A first protection diode that passes current flowing to the input point;
Between the second input point and the first output point, the third switching element and the fourth switching element are electrically connected in parallel with the first input point to the first input point. A second protection diode for passing current flowing to the output point;
Between the first input point and the second output point, the fifth switching element and the sixth switching element are electrically connected in parallel, and from the second output point to the first A third protection diode that passes current flowing to the input point;
Between the second input point and the second output point, the seventh switching element and the eighth switching element are electrically connected in parallel with each other, and the second input point to the second input point And a fourth protection diode that allows a current flowing to the output point to pass therethrough,
A power conversion device configured to generate an output voltage between the first output point and the second output point. The power converter according to claim 1, wherein each of the first to fourth protective diodes is a fast recovery diode. The first bidirectional switch is between an all-off state that interrupts bidirectional current between the first connection point and the second connection point, and between the first connection point and the second connection point. It is configured to be able to switch between operating states including all on states that allow bidirectional current to pass through,
The second bidirectional switch includes a fully off state in which a bidirectional current is interrupted between the third connection point and the fourth connection point, and between the third connection point and the fourth connection point. The power conversion device according to claim 1, wherein the power conversion device is configured to be able to switch an operation state including an all-on state that allows a bidirectional current to pass therethrough. The operating state of the first bidirectional switch is a half-on state in which a current flowing from the second connection point to the first connection point is interrupted and a current flowing from the first connection point to the second connection point is allowed to pass. Including further states,
The operating state of the second bidirectional switch is a half-on state in which a current flowing from the third connection point to the fourth connection point is interrupted and a current flowing from the fourth connection point to the third connection point is allowed to pass. The power converter according to claim 3, further comprising a state. The first output point and the second output are controlled by the first to fourth switching elements, the fifth to eighth switching elements, the first bidirectional switch, and the second bidirectional switch. The power conversion device according to claim 1, further comprising a control unit that controls the control target so that the output voltage is generated between the points. The power conversion device according to any one of claims 1 to 5,
A power conditioner comprising: a disconnector electrically connected between the first output point and the second output point and a system power supply.

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