Inverter device and inverter module

Abstract

To realize efficiency improvement in an inverter device capable of outputting power of a single-phase three-wire system during independent operation independent of a commercial power system in addition to interlocked operation.SOLUTION: The present invention relates to an inverter device by which inputted DC power is converted into AC power of a single-phase two-wire system or a single-phase three-wire system and outputted. The inverter device comprises: a first phase output terminal, a second phase output terminal and a neutral output terminal; an inverter unit which converts the DC power into the AC power; a first phase power line which connects the inverter unit with the first phase output terminal and to which first phase power of the AC power is supplied; a second phase power line which connects the inverter unit with the second phase output terminal and to which second phase power of the AC power is supplied; a neutral power line which connects the inverter unit with the neutral output terminal; a short circuit which is connected between the first phase power line and the second phase power line and capable of short-circuiting the first phase power line and the second phase power line; and a control unit which controls the inverter unit and the short circuit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an inverter device and an inverter module. [Background technology]

[0002] BACKGROUND ART Conventionally, a single-phase two-wire inverter device is known as an inverter device that converts DC power into AC power.

[0003] As a means for improving the efficiency of such single-phase two-wire inverter devices, it has been proposed to provide a short-circuitable circuit called an HERIC circuit between the output lines (see, for example, Patent Document 1).

[0004] On the other hand, high efficiency is also required for inverter devices that can output single-phase three-wire power during stand-alone operation independent of the commercial power grid in addition to operating in grid-connected mode with the commercial power grid. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] German Patent Application Publication No. 102008048841 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in consideration of the above-mentioned problems, and aims to achieve high efficiency in an inverter device that can output single-phase three-wire power during grid-connected operation with a commercial power grid as well as during stand-alone operation independent of the commercial power grid. [Means for solving the problem]

[0007] To solve the above problems, the present invention provides: An inverter device that converts input DC power into single-phase two-wire or single-phase three-wire AC power and outputs it, a first phase output terminal, a second phase output terminal, and a neutral output terminal; an inverter unit that converts the DC power into the AC power; a first-phase power line connecting the inverter unit and the first-phase output terminal and through which first-phase power of the AC power is supplied; a second-phase power line connecting the inverter unit and the second-phase output terminal and through which second-phase power of the AC power is supplied; a neutral power line connecting the inverter unit and the neutral output terminal; a short circuit connected between the first-phase power line and the second-phase power line, capable of short-circuiting the first-phase power line and the second-phase power line; The power supply device is characterized by comprising a control unit that controls the inverter unit and the short circuit.

[0008] According to the present invention, by providing a short-circuit circuit that is connected between a first-phase power line and a second-phase power line and that can short-circuit the first-phase power line and the second-phase power line, it is possible to provide an inverter device that achieves high efficiency as a single-phase two-wire inverter device during grid-connected operation with a commercial power grid, and that can output single-phase three-wire power during stand-alone operation independent of the commercial power grid.

[0009] In addition, in the present invention, The inverter unit a positive input terminal connected to the positive terminal of a DC power supply and a negative input terminal connected to the negative terminal of the DC power supply; a first phase leg in which a first switching element connected to the positive input terminal and a second switching element connected to the negative input terminal are connected in series; a neutral leg in which a third switching element connected to the positive input terminal and a fourth switching element connected to the negative input terminal are connected in series; a second phase leg in which a fifth switching element connected to the positive input terminal and a sixth switching element connected to the negative input terminal are connected in series; and the first phase leg has a first phase connection point, to which the first phase power line is connected, at a midpoint between the first switching element and the second switching element; the neutral leg has a neutral connection point to which the neutral power line is connected at a midpoint between the third switching element and the fourth switching element, The second phase leg may have a second phase connection point, to which the second phase power line is connected, at a midpoint between the fifth switching element and the sixth switching element.

[0010] In this way, a three-arm inverter device having a first phase leg, a second phase leg, and a neutral leg can achieve high efficiency during grid-connected operation and output single-phase three-wire power during stand-alone operation.

[0011] In addition, in the present invention, the short circuit includes a first short-circuit switching element that turns on and off a current flowing from the first-phase power line side to the second-phase power line side, and a second short-circuit switching element that turns on and off a current flowing from the second-phase power line side to the first-phase power line side, When operating in connection with a commercial power system, the PWM control of the first switching element to the sixth switching element by the control unit in one half cycle of the frequency of the AC power to be output is turning on the first switching element and turning off the second switching element; turning off the third switching element and the fourth switching element; turning off the fifth switching element and turning on the sixth switching element; an eleventh mode in which the first short-circuiting switching element is turned off and the second short-circuiting switching element is turned on; The first switching element is turned from on to off, and the second switching element is turned off; turning off the third switching element and the fourth switching element; Turning off the fifth switching element and turning off the sixth switching element; a twelfth mode in which the first short-circuiting switching element is turned off and the second short-circuiting switching element is turned on; turning off the first switching element and the second switching element; turning off the third switching element and the fourth switching element; turning off the fifth switching element and the sixth switching element; a thirteenth mode in which the first short-circuiting switching element is turned off and the second short-circuiting switching element is turned on; The first switching element is turned on from off, and the second switching element is turned off; turning off the third switching element and the fourth switching element; turning off the fifth switching element, and turning on the sixth switching element; a fourteenth mode in which the first short-circuiting switching element is turned off and the second short-circuiting switching element is turned on; and the 11th mode, the 12th mode, the 13th mode, and the 14th mode It may also include control for repeating transitions in order.

[0012] According to this, during grid-connected operation in mode 13, the first-phase power line and the second-phase power line are short-circuited by the short circuit, thereby achieving high efficiency. One half cycle of the frequency of the AC power to be output may be either the first half cycle or the second half cycle.

[0013] In addition, in the present invention, When operating in connection with a commercial power system, the PWM control of the first switching element to the sixth switching element by the control unit in the other half cycle of the frequency of the AC power to be output is turning off the first switching element and turning on the second switching element; turning off the third switching element and the fourth switching element; turning on the fifth switching element and turning off the sixth switching element; a fifteenth mode in which the first short-circuiting switching element is turned on and the second short-circuiting switching element is turned off; turning off the first switching element and turning off the second switching element; turning off the third switching element and the fourth switching element; The fifth switching element is turned from on to off, and the sixth switching element is turned off; a sixteenth mode in which the first short-circuit switching element is turned on and the second short-circuit switching element is turned off; turning off the first switching element and the second switching element; turning off the third switching element and the fourth switching element; turning off the fifth switching element and the sixth switching element; a seventeenth mode in which the first short-circuiting switching element is turned on and the second short-circuiting switching element is turned off; turning off the first switching element, and turning on the second switching element; turning off the third switching element and the fourth switching element; The fifth switching element is turned on from off, and the sixth switching element is turned off; an eighteenth mode in which the first short-circuiting switching element is turned on and the second short-circuiting switching element is turned off; and may include control of repeating transitions in the order of the 15th mode, the 16th mode, the 17th mode, and the 18th mode.

[0014] According to this, during grid-connected operation in mode 17, the first-phase power line and the second-phase power line are short-circuited by the short circuit, thereby achieving high efficiency. If one half cycle is the first half cycle, the other half cycle is the second half cycle, and if one half cycle is the second half cycle, the other half cycle is the first half cycle.

[0015] In addition, in the present invention, the short circuit includes a first short-circuit switching element that turns on and off a current flowing from the first-phase power line side to the second-phase power line side, and a second short-circuit switching element that turns on and off a current flowing from the second-phase power line side to the first-phase power line side, When operating independently from a commercial power system, the PWM control of the first switching element to the sixth switching element by the control unit in one half cycle of the frequency of the AC power to be output is turning on the first switching element and turning off the second switching element; turning off the third switching element and turning on the fourth switching element; turning off the fifth switching element and the sixth switching element; a 21st mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning on the first switching element and turning off the second switching element; turning on the third switching element and turning off the fourth switching element; turning off the fifth switching element and the sixth switching element; a 22nd mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning off the first switching element and the second switching element; turning on the third switching element and turning off the fourth switching element; turning off the fifth switching element and turning on the sixth switching element; a 23rd mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning off the first switching element and the second switching element; turning off the third switching element and turning on the fourth switching element; turning off the fifth switching element and turning on the sixth switching element; a 24th mode in which the first short-circuiting switching element is turned off and the second short-circuiting switching element is turned off; and may include control of repeating transitions in the order of the 21st mode, the 22nd mode, the 23rd mode, the 22nd mode, the 21st mode, and the 24th mode.

[0016] This makes it possible to provide an inverter device that can output single-phase three-wire AC power during stand-alone operation. If one half cycle is the first half cycle, the other half cycle is the second half cycle, and if one half cycle is the second half cycle, the other half cycle is the first half cycle.

[0017] In addition, in the present invention, When operating independently from a commercial power system, the PWM control of the first switching element to the sixth switching element by the control unit in one half cycle of the frequency of the AC power to be output is turning off the first switching element and the second switching element; turning off the third switching element and turning on the fourth switching element; turning on the fifth switching element and turning off the sixth switching element; a 25th mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning off the first switching element and the second switching element; turning on the third switching element and turning off the fourth switching element; turning on the fifth switching element and turning off the sixth switching element; a 26th mode in which the first short-circuiting switching element is turned off and the second short-circuiting switching element is turned off; turning off the first switching element and turning on the second switching element; turning on the third switching element and turning off the fourth switching element; turning off the fifth switching element and the sixth switching element; a 27th mode in which the first short-circuiting switching element is turned off and the second short-circuiting switching element is turned off; turning off the first switching element and turning on the second switching element; turning off the third switching element and turning on the fourth switching element; turning off the fifth switching element and the sixth switching element; a 28th mode in which the first short-circuiting switching element is turned off and the second short-circuiting switching element is turned off; and may include control of repeating transitions in the order of the 25th mode, the 26th mode, the 27th mode, the 26th mode, the 25th mode, and the 28th mode.

[0018] This makes it possible to provide an inverter device that can output single-phase three-wire AC power during stand-alone operation. If one half cycle is the first half cycle, the other half cycle is the second half cycle, and if one half cycle is the second half cycle, the other half cycle is the first half cycle.

[0019] In addition, in the present invention, the short circuit includes a first short-circuit switching element that turns on and off a current flowing from the first-phase power line side to the second-phase power line side, and a second short-circuit switching element that turns on and off a current flowing from the second-phase power line side to the first-phase power line side, When operating independently from a commercial power system, the PWM control of the first switching element to the sixth switching element by the control unit in one half cycle of the frequency of the AC power to be output is turning on the first switching element and turning off the second switching element; turning off the third switching element and turning on the fourth switching element; turning off the fifth switching element and the sixth switching element; a 21st mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning on the first switching element and turning off the second switching element; turning on the third switching element and turning off the fourth switching element; turning off the fifth switching element and the sixth switching element; a 22nd mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning off the first switching element and the second switching element; turning on the third switching element and turning off the fourth switching element; turning off the fifth switching element and turning on the sixth switching element; a 23rd mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning off the first switching element and the second switching element; turning off the third switching element and turning on the fourth switching element; turning off the fifth switching element and turning on the sixth switching element; a 24th mode in which the first short-circuiting switching element is turned off and the second short-circuiting switching element is turned off; and may include control of repeating transitions in the order of the 21st mode, the 22nd mode, the 23rd mode, and the 24th mode.

[0020] This makes it possible to provide an inverter device that can output single-phase three-wire AC power during stand-alone operation. This reduces the number of switching operations and improves efficiency. If one half-cycle is the first half-cycle, the other half-cycle is the second half-cycle, and if one half-cycle is the second half-cycle, the other half-cycle is the first half-cycle.

[0021] In addition, in the present invention, When operating independently from a commercial power system, the PWM control of the first switching element to the sixth switching element by the control unit in one half cycle of the frequency of the AC power to be output is turning off the first switching element and the second switching element; turning off the third switching element and turning on the fourth switching element; turning on the fifth switching element and turning off the sixth switching element; a 25th mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning off the first switching element and the second switching element; turning on the third switching element and turning off the fourth switching element; turning on the fifth switching element and turning off the sixth switching element; a 26th mode in which the first short-circuiting switching element is turned off and the second short-circuiting switching element is turned off; turning off the first switching element and turning on the second switching element; turning on the third switching element and turning off the fourth switching element; turning off the fifth switching element and the sixth switching element; a 27th mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning off the first switching element and turning on the second switching element; turning off the third switching element and turning on the fourth switching element; turning off the fifth switching element and the sixth switching element; a 28th mode in which the first short-circuiting switching element is turned off and the second short-circuiting switching element is turned off; and may include control of repeating transitions in the order of the 25th mode, the 26th mode, the 27th mode, and the 28th mode.

[0022] This makes it possible to provide an inverter device capable of outputting single-phase three-wire AC power during stand-alone operation. This reduces the number of switching operations and improves efficiency. If one half-cycle is the first half-cycle, the other half-cycle is the second half-cycle, and if one half-cycle is the second half-cycle, the other half-cycle is the first half-cycle.

[0023] In addition, in the present invention, An inverter module that converts input DC power into single-phase two-wire or single-phase three-wire AC power and outputs it, a first phase output terminal, a second phase output terminal, and a neutral output terminal; an inverter unit that converts the DC power into the AC power; a first-phase power line connecting the inverter unit and the first-phase output terminal and through which first-phase power of the AC power is supplied; a second-phase power line connecting the inverter unit and the second-phase output terminal and through which second-phase power of the AC power is supplied; a neutral power line connecting the inverter unit and the neutral output terminal; a short circuit connected between the first-phase power line and the second-phase power line, capable of short-circuiting the first-phase power line and the second-phase power line; Equipped with The inverter unit a positive input terminal connected to the positive terminal of a DC power supply and a negative input terminal connected to the negative terminal of the DC power supply; a first phase leg in which a first switching element connected to the positive input terminal and a second switching element connected to the negative input terminal are connected in series; a neutral leg in which a third switching element connected to the positive input terminal and a fourth switching element connected to the negative input terminal are connected in series; a second phase leg in which a fifth switching element connected to the positive input terminal and a sixth switching element connected to the negative input terminal are connected in series; and the first phase leg has a first phase connection point, to which the first phase power line is connected, at a midpoint between the first switching element and the second switching element; the neutral leg has a neutral connection point to which the neutral power line is connected at a midpoint between the third switching element and the fourth switching element, The second phase leg may have a second phase connection point, to which the second phase power line is connected, at a midpoint between the fifth switching element and the sixth switching element.

[0024] In this way, by configuring an inverter device that converts input DC power into single-phase two-wire or single-phase three-wire AC power and outputs it as an inverter module, it is possible to improve efficiency during grid-connected operation, reduce variation in the characteristics of inverter devices that are capable of single-phase three-wire output during stand-alone operation, improve heat dissipation, and make it easier to assemble the inverter device.

[0025] In addition, in the present invention, A temperature detector for detecting temperature may be disposed in an area surrounded by the first phase leg, the second phase leg, and the short circuit.

[0026] This makes it possible to provide an inverter module that can accurately control the temperature according to the heat generation state, such as by reducing the output when abnormal heat generation occurs, by detecting the temperature using the temperature detection unit. [Effects of the Invention]

[0027] According to the present invention, it is possible to improve the efficiency of a single-phase three-wire inverter device. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a diagram showing an outline of a circuit configuration of an inverter device according to a first embodiment of the present invention. [Figure 2] FIG. 1 is a diagram illustrating a configuration of a HERIC circuit according to a first embodiment of the present invention. [Figure 3]1 is a diagram showing a schematic configuration of a system including a power conditioner having an inverter device according to a first embodiment of the present invention. [Figure 4] 4 is a flowchart illustrating switching control between grid-connected operation and independent operation of the inverter device according to the first embodiment of the present invention. [Figure 5] 4 is a timing chart of switching control during grid-connected operation of the inverter device according to the first embodiment of the present invention. [Figure 6] FIG. 3 is a diagram showing current paths in mode 11 of the inverter device according to the first embodiment of the present invention. [Figure 7] FIG. 3 is a diagram showing a current path in mode 12 of the inverter device according to the first embodiment of the present invention. [Figure 8] FIG. 3 is a diagram showing a current path in mode 13 of the inverter device according to the first embodiment of the present invention. [Figure 9] FIG. 3 is a diagram showing a current path in mode 14 of the inverter device according to the first embodiment of the present invention. [Figure 10] 4 is a timing chart of switching control during independent operation of the inverter device according to the first embodiment of the present invention. [Figure 11] 4 is a timing chart showing details of switching control during self-sustained operation of the inverter device according to the first embodiment of the present invention. [Figure 12] FIG. 2 is a diagram showing current paths in mode 21 of the inverter device according to the first embodiment of the present invention. [Figure 13] FIG. 3 is a diagram showing a current path in mode 22 of the inverter device according to the first embodiment of the present invention. [Figure 14] FIG. 4 is a diagram showing a current path in mode 23 of the inverter device according to the first embodiment of the present invention. [Figure 15] FIG. 2 is a diagram showing a current path in mode 24 of the inverter device according to the first embodiment of the present invention. [Figure 16] FIG. 10 is a diagram showing an outline of a circuit configuration of an inverter module according to a second embodiment of the present invention. [Figure 17] FIG. 10 is a diagram showing a device layout of an inverter module according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] [Application example] Hereinafter, application examples of the present invention will be described with reference to the drawings. FIG. 1 shows an outline of the circuit configuration of an inverter device 10 to which the present invention is applied.

[0030] Inverter device 10 generally includes a single-phase three-wire inverter 11, a HERIC circuit 12 capable of short-circuiting between a U-phase power line Liu and a W-phase power line Liw of inverter 11, and a control unit .

[0031] The single-phase three-wire inverter 11 is a three-arm inverter in which three legs, an O-phase midpoint leg Lgo, a U-phase leg Lgu, and a W-phase leg Lgw, are connected in parallel. The O-phase midpoint leg Lgo has switches SW3 and SW4 connected in series, the U-phase leg Lgu has switches SW1 and SW2 connected in series, and the W-phase leg Lgw has switches SW5 and SW6 connected in series.

[0032] A HERIC circuit 12 is connected between the U-phase power line Liu and the W-phase power line Liw. The HERIC circuit 12 includes a switch SWuwn and a switch SWuwp.

[0033] When converting the DC voltage output from the DC power supply Sd into a 50 Hz sine curve AC commercial voltage, the switches of the inverter 11 and the HERIC circuits 12 and 13 are controlled in the first and second halves of the cycle as shown in Fig. 5. Here, the control unit 14 performs PWM control to control the output voltage by controlling the on / off duty ratio of the switches SW1 to Sw6 of the inverter 11.

[0034] The inverter device 10 outputs single-phase two-wire AC power during grid-connected operation with the commercial power system, and outputs single-phase three-wire AC power during stand-alone operation independent of the commercial power system.

[0035] In the first half cycle of grid-connected operation, the current path of the inverter device 10 repeatedly transitions through four modes in the order of mode 11, mode 12, mode 13, and mode 14. During grid-connected operation, the switches SW3 and SW4 are always off, the switch SWuwn is off, and the switch SWuwp is on.

[0036] In mode 11, switches SW1 and SW6 are turned on, and switches SW2 and SW5 are turned off. In mode 12, switches SW1 and SW6 are turned from on to off, and switches SW4 and SW5 are turned off. In mode 13, switches SW1, SW2, SW5, and SW6 are turned off, and HERIC circuit 12 shorts U-phase power line Liu and W-phase power line Liw. Then, in mode 14, switches SW1 and SW6 are turned from off to on, the parasitic capacitance of switch SWuwn of HERIC circuit 12 is charged, and HERIC circuit 12 is disconnected. In the second half of the frequency during grid-connected operation, PWM control is performed to sequentially transition through four modes, modes 15 to 18, in which switches SW1 and SW2 of the U-phase leg Lgu in the first half and switches SW5 and SW6 of the W-phase leg Lgw are switched on and off, respectively, and switch SWuwn of HERIC circuit 12 is turned on and switch SWuwp is turned off.

[0037] During the first half cycle of the independent operation, the current path of the inverter device 10 repeatedly transitions through four modes in the order of mode 21, mode 22, mode 23, and mode 24. During the independent operation, the switches SWuwn and SWuwp that constitute the HERIC circuit 12 are both always off, and no short circuit is formed between the U-phase power line Liu and the W-phase power line Liw.

[0038] In mode 21, switches SW1 and SW5 are on, switches SW2 and SW5 are off, switch SW3 is on, and switch SW4 is off. In mode 22, switches SW1 and SW5 are on, switches SW2 and SW5 are off, switch SW3 is off, and switch SW4 is on. In mode 23, switches SW1, SW5, SW2, and SW5 are off, switch SW3 is off, and switch SW4 is on. In mode 24, switches SW1, SW5, SW2, and SW5 are off, switch SW3 is on, and switch SW4 is off. In the second half of the frequency during grid-connected operation, PWM control is performed to repeatedly transition through four modes, modes 25 to 28, in which the on / off states of switches SW1 and SW2 of the U-phase leg Lgu and switches SW5 and SW6 of the W-phase leg Lgw are interchanged in the first half.

[0039] In this way, the inverter device 10 enables efficient operation by the HERIC circuit 12 during grid-connected operation in which single-phase two-wire power is output, and also enables output of single-phase three-wire power, which is in high demand, during stand-alone operation.

[0040] Example 1 The configuration of an inverter device 10 according to a first embodiment of the present invention will be described below with reference to the drawings. However, the configurations of the device and system described in this embodiment may be modified as appropriate depending on various conditions. In other words, the scope of the present invention is not intended to be limited to the following embodiment.

[0041] FIG. 1 is a circuit diagram showing a schematic configuration of an inverter device 10. As shown in FIG. The inverter device 10 is a power converter that converts DC power into AC power. Its input terminals Ip and In are connected to the positive and negative terminals of a DC power source Sd, respectively. The inverter device 10 supplies the converted AC power to loads RLiu and RLiw connected between output terminals Ou and Oo, and between output terminals Ow and Oo, respectively, and can also be connected to a commercial power grid. The output terminal Oo is grounded. Here, the input terminals Ip and In correspond to the positive and negative input terminals of the present invention, respectively. The output terminals Ou, Ow, and Ou correspond to the first-phase output terminal, second-phase output terminal, and neutral output terminal, respectively.

[0042] Inverter device 10 generally includes a single-phase three-wire inverter 11, an HERIC circuit 12 capable of short-circuiting between a U-phase power line Liu and a W-phase power line Liw of inverter 11, and a control unit 14. Here, inverter 11 and control unit 14 correspond to the inverter unit and control unit, respectively, of the present invention. Also, HERIC circuit 12 corresponds to the short-circuit circuit of the present invention.

[0043] (inverter) The single-phase three-wire inverter 11 is a three-arm inverter in which a leg consisting of two switches connected in series is connected in parallel to a DC power supply Sd. That is, the inverter 11 is configured such that three legs, an O-phase midpoint leg Lgo, a U-phase leg Lgu, and a W-phase leg Lgw, are connected in parallel between a positive input line Lip and a negative input line Lin, in that order from the input terminals Ip and In. Here, the switches are made of semiconductor switching elements ranging from n-channel enhancement-type MOSFETs (Metal-Oxide-Semiconductor Field Effect Transistors) to An IGBT (Insulated Gate Bipolar Transistor) can also be used as the semiconductor switching element, but in this case, a free-wheeling diode connected in reverse parallel to the IGBT is used. Here, the O-phase midpoint leg Lgo, the U-phase leg Lgu, and the W-phase leg Lgw correspond to the neutral leg, the first phase leg, and the second phase leg of the present invention, respectively.

[0044] The U-phase leg Lgu is composed of switches SW1 and SW2. The drain terminal of switch SW1 is connected to the positive input line Lip, the source terminal of switch SW1 is connected to the drain terminal of switch SW2, and the source terminal of switch SW2 is connected to the negative input line Lin. The O-phase midpoint leg Lgo is composed of switches SW3 and SW4. The drain terminal of switch SW3 is connected to the positive input line Lip, the source terminal of switch SW3 is connected to the drain terminal of switch SW4, and the source terminal of switch SW4 is connected to the negative input line Lin. The W-phase leg Lgw is composed of switches SW5 and SW6. The drain terminal of switch SW5 is connected to the positive input line Lip, the source terminal of switch SW5 is connected to the drain terminal of switch SW6, and the source terminal of switch SW6 is connected to the negative input line Lin. Here, switches SW1 and SW2 correspond to the first and second switching elements of the present invention. Also, switches SW3 and SW4 correspond to the third and fourth switching elements of the present invention. The switches SW5 and SW6 correspond to the fifth and sixth switching elements of the present invention.

[0045] An O-phase neutral conductor Lio is drawn from the midpoint of the O-phase midpoint leg Lgo, i.e., midpoint Cpo between the source terminal of switch SW3 and the drain terminal of switch SW4. A U-phase power line Liu is drawn from the midpoint of the U-phase leg Lgu, i.e., midpoint Cpu between the source terminal of switch SW1 and the drain terminal of switch SW2. A W-phase power line Liw is drawn from the midpoint of the W-phase leg Lgw, i.e., midpoint Cpw between the source terminal of switch SW5 and the drain terminal of switch SW6. Here, midpoint Cpo and O-phase neutral conductor Lio correspond to the neutral connection point and neutral power line of the present invention, respectively. Also, midpoint Cpu and U-phase power line Liu correspond to the first-phase connection point and first-phase power line of the present invention, respectively. Also, midpoint Cpw and W-phase power line Liw correspond to the second-phase connection point and second-phase power line of the present invention, respectively.

[0046] A HERIC circuit 12 is connected between the U-phase power line Liu and the W-phase neutral line Liw. On the output terminals Ou and Ow sides of the HERIC circuit 12, a reactor Lu and a reactor Lw are connected in series to the U-phase power line Liu and the W-phase power line Liw, respectively. The O-phase neutral line Lio is connected to the output terminal Oo via a reactor Lo connected in series.

[0047] A capacitor Cu is connected between the output terminal Ou of the reactor Lu in the U-phase power line Liu and the output terminal Oo of the reactor Lo in the O-phase neutral line Lio. A capacitor Cw is connected between the output terminal Lo of the O-phase neutral line Lio and the W-phase power line Liw. That is, capacitor Cu and HERIC circuit 12 are connected in parallel between the U-phase power line Liu and the O-phase neutral line Lio, in this order from the output terminal Ou and output terminal Oo. Capacitor Cw and HERIC circuit 13 are connected in parallel between the O-phase neutral line Lio and the W-phase power line Liw, in this order from the output terminal Oo and output terminal Ow.

[0048] A load RLu is connected between the output terminal Ou of the U-phase power line Liu and the output terminal Oo of the O-phase neutral line Lio, and a load RLw is connected between the output terminal Ou of the O-phase power line Liu and the output terminal Ow of the W-phase power line Liw.

[0049] (HERIC circuit) The HERIC circuit 12 includes switches SWuwn and SWuwp, which are made up of n-channel enhancement-type MOSFETs. Although not shown in FIG. 1, the HERIC circuit 12 also includes a gate drive circuit that drives the gates of the switches SWuwn and SWuwp. The gate drive circuit controls the on / off of the switches SWuwn and SWuwp based on instructions from a control unit 14 that controls the operation of the inverter device 10.

[0050] The drain terminal of the switch SWuwn in the HERIC circuit 12 is connected to the U-phase power line Liu. The source terminal of switch SWuwn is connected to the source terminal of switch SWuwp, and the drain terminal of switch SWuwp is connected to W-phase power line Liw. Here, switches SWuwn and SWuwp correspond to the first short-circuit switching element and second short-circuit switching element of the present invention, respectively.

[0051] The specific configuration of the HERIC circuit is not limited to the HERIC circuit 12. 2(A) to 2(D) show specific examples of HERIC circuits.

[0052] 2A is a diagram showing the basic configuration of the HERIC circuit Hr1. A series-connected switch S1 and diode D1, and a series-connected diode D2 and switch S2 are connected in parallel between the U-phase power line Liu and the W-phase power line Liw. The cathode and anode terminals of diode D1 are connected to the U-phase power line Liu side and the W-phase power line Liw side, respectively. The cathode and anode terminals of diode D2 are connected to the W-phase power line Liw side and the U-phase power line Liu side, respectively. Semiconductor switching elements such as IGBTs and MOSFETs can be used as switches S1 and S2.

[0053] Here, when the U-phase power line Liu is at a higher potential than the W-phase power line Liw, no current flows even if switch S1 is closed because diode D1 is connected in the reverse direction. When the W-phase power line Liw and power line Liu are at the same potential, diode D1 turns on, commutating the load current and shorting out the power lines Liu and Liw.

[0054] 2B is a diagram showing the basic configuration of HERIC circuit Hr2. HERIC circuit Hr2 has the same configuration as HERIC circuit Hr1, except that the midpoint between switch S1 and diode D1 is connected to the midpoint between switch S2 and diode D2 by connection line Sc1.

[0055] Here, when the U-phase power line Liu is at a higher potential than the W-phase power line Liw, no current flows even if switch S1 is closed because diode D1 is connected in the reverse direction. When the W-phase power line Liw becomes equipotential with the U-phase power line Liu, diode D1 turns on, commutating the load current and shorting the power lines Liu and Liw.

[0056] In the HERIC circuit Hr3 shown in FIG. 2(C), switches SW31 and SW32, each composed of an n-channel enhancement-mode MOSFET, are connected in series between the power lines Liu and Liw. The drain terminal of switch SW31 in the HERIC circuit Hr3 is connected to the U-phase power line Liu, the source terminal of switch SW31 is connected to the source terminal of switch SW32, and the drain terminal of switch SW32 is connected to the W-phase power line Liw. This HERIC circuit Hr3 has the same configuration as the HERIC circuit 12 shown in FIG. 1. This HERIC circuit Hr3 has the same functions as the HERIC circuit Hr2 shown in FIG. 2(B).

[0057] The HERIC circuit Hr4 shown in Figure 2(D) has switches SW41 and SW42, each composed of an n-channel enhancement-type MOSFET, connected in series between the power lines Liu and Liw. The source terminal of switch SW41 in the HERIC circuit Hr4 is connected to the U-phase power line Liu, the drain terminal of switch SW41 is connected to the drain terminal of switch SW42, and the source terminal of switch SW42 is connected to the W-phase power line Liw. This HERIC circuit Hr4 has the same functions as the HERIC circuit Hr3 shown in Figure 2(C).

[0058] (System Configuration) FIG. 3 shows an example of a system configuration including the inverter device 10. Here, a system including a power conditioner 1 having an inverter device 10 will be described.

[0059] The power conditioner 1 converts power output from distributed power sources such as storage batteries, solar cells, and fuel cells into single-phase three-wire or single-phase two-wire AC power and outputs it using an inverter device 10. The power conditioner 1 can operate in two modes: grid-connected operation, in which it operates in connection with the commercial power grid 2, and stand-alone operation, in which it operates independently from the commercial power grid 2 when the power supply from the commercial power grid 2 is stopped due to a power outage or the like.

[0060] The power line connected to the commercial power grid 2 is connected to a full-load distribution panel 4 via a contract breaker 3 installed at the consumer's home. The contract breaker 3 is a circuit breaker that interrupts the electrical circuit connecting the commercial power grid 2 to the consumer when a current greater than the contract value flows. The full-load distribution panel 4 includes a molded-case circuit breaker 41, an automatic transfer switch 42, and a ground fault circuit interrupter 43. The molded-case circuit breaker 41 is a circuit breaker for protecting low-voltage wiring. The automatic transfer switch 42 connects the grid side or the isolated side to the main distribution panel 5. When power supply from the commercial power grid 2 is interrupted due to a power outage or the like, the automatic transfer switch 42 automatically switches from the grid side to the isolated side, and when power supply from the commercial power grid 2 is resumed, the automatic transfer switch 42 automatically switches back to the grid side. The grid side of the automatic transfer switch 42 is connected to the commercial power grid 2 and the interconnection terminal, which is the output terminal of the power conditioner 1 during grid-connected operation. An independent terminal, which is the output terminal during independent operation of the power conditioner 1, is connected to the independent side of the automatic transfer switch 42. The earth leakage breaker 43 is provided in an electric circuit connecting the interconnection terminal of the power conditioner 1 and the power line connected to the commercial power system 2, and is a circuit breaker for preventing accidents such as electric leakage.

[0061] The main distribution panel 5 has an earth leakage circuit breaker 51 and branch breakers 52a, 52b, and 52c. The earth leakage circuit breaker 51 connected to the automatic transfer switch 42 of the full-load distribution panel 4 is connected to the loads 6a, 6b, and 6c via the branch breakers 52a, 52b, and 52c, respectively. Although FIG. 3 shows three branch breakers 52 and loads 6, the number of branch breakers 52 and loads 6 is not limited to this. The earth leakage circuit breaker 51 is a circuit breaker for preventing accidents such as electric leakage, and the branch breakers 52a, 52b, and 52c are circuit breakers for interrupting an electric circuit when an excessive current flows according to the connected loads 6a, 6b, and 6c.

[0062] (Switching between grid-connected operation and stand-alone operation) 4 shows a control procedure for switching between grid-connected operation and stand-alone operation of the power conditioner 1 including the inverter device 10. The power conditioner 1 including the inverter device 10 outputs AC power in a single-phase two-wire system from the grid-connected terminal during grid-connected operation, and outputs AC power in a single-phase three-wire system from the stand-alone terminal during stand-alone operation.

[0063] First, when the power conditioner 1 starts operation, it performs a self-diagnosis to determine whether or not there is a malfunction in the inverter device 10, the control unit 14, etc. (Step S1). Since a known technique can be appropriately adopted for the self-diagnosis, a detailed description thereof will not be given.

[0064] The self-diagnosis in step S1 determines whether there is an abnormality (step S2), and if it is determined that there is no abnormality, abnormality processing is performed in step S15 and the processing ends. If the self-diagnosis in step S1 determines that there is a normality, the interconnection relay of the power conditioner 1 is turned on to output from the interconnection terminal (step S3).

[0065] When the grid-connection relay is turned on, the power conditioner 1 performs grid-connected operation (step S4). At this time, the automatic transfer switch 42 is connected to the grid side.

[0066] Then, the power conditioner 1 monitors whether or not there is a power outage in the commercial power grid (step S5), and if there is no power outage in the commercial power grid, the power conditioner 1 continues the grid-connected operation in step S4. If there is a power outage in the commercial power grid, the power conditioner 1 stops the grid-connected operation (step S6). At this time, the automatic transfer switch 42 is switched from the grid side to the isolated side (step S7).

[0067] At this stage, the power conditioner 1 performs a self-diagnosis (step S8).

[0068] The self-diagnosis in step S8 determines whether there is an abnormality (step S9), and if it is determined that there is no normality, the abnormality processing in step S15 is performed and the processing ends. If the self-diagnosis in step S8 determines that there is a normality, the power conditioner's independent relay is turned on to output from the independent terminal (step S10).

[0069] When the isolation relay is turned on, the power conditioner 1 performs an isolated operation (step S11).

[0070] Then, the power conditioner 1 monitors whether or not power has been restored to the commercial power grid (restart of power supply that had been stopped) (step S12), and if power has not been restored to the commercial power grid, the power conditioner 1 continues the isolated operation in step S11. If power has been restored to the commercial power grid, the power conditioner 1 stops the isolated operation (step S13), turns off the isolated relay (step S14), and returns to step S1. At this time, the automatic transfer switch 42 is switched from the isolated side to the grid side.

[0071] (PWM control during grid-connected operation) The following describes switching control of the inverter 11 and the HERIC circuit 12 for converting input DC power into AC power in the inverter device 10 during grid-connected operation.

[0072] The control unit 14 controls the switching of the inverter 11 and the HERIC circuit 12 based on a command value (for example, a 50 Hz sine curve) related to the AC voltage waveform to be output. Here, the control unit 14 performs PWM control to control the output voltage by controlling the on / off duty ratio of the switches SW1, SW2, SW5, and SW6 of the inverter 11. During grid-connected operation, SW3 and SW4, which constitute the O-phase midpoint leg Lgo, are always off, and the inverter 11 outputs single-phase two-wire power.

[0073] Fig. 5 shows a portion of a timing chart of control signals for each switch of the inverter 11 and the HERIC circuit 12 in the power conversion process by the inverter device 10. Fig. 5 shows the control signals for each switch in the first half cycle when outputting an AC voltage that forms a sine curve with a frequency of 50 Hz, the same as commercial power. PWM1 to 6 indicate control signals for switches SW1 to SW6, and PWMp and PWMn indicate control signals for switches SWuwp and SWuwn.

[0074] The inverter 11 is subjected to PWM control using unipolar modulation. The on / off of each switch is controlled according to a duty ratio determined by the PWM control. In the first half cycle, a voltage is output to the output terminal Ou of the U-phase power line Liu and the output terminal Oo of the O-phase neutral line Lio, and the voltage applied to the load RLiu is either positive or zero on the output terminal Ou side relative to the output terminal Oo side. A voltage is output to the output terminal Oo of the O-phase neutral line Lio and the output terminal Ow of the W-phase power line Liw, and the voltage applied to the load Rlw is either positive or zero on the output terminal Oo side relative to the output terminal Ow side. In the second half cycle, the voltage applied to the load RLiu is negative or zero on the output terminal Ou side relative to the output terminal Oo side, and the voltage applied to the load RLiu is negative or zero on the output terminal Ou side relative to the output terminal Oo side, and the voltage applied to the load Rlw is negative or zero on the output terminal Oo side relative to the output terminal Ow side.

[0075] In the first half cycle, the current path of the inverter device 10 repeatedly transitions through four modes in the order of mode 11, mode 12, mode 13, and mode 14. Of these four modes, mode 11 and mode 13 are steady states. Mode 12 is a transient state in which mode 11 transitions to mode 13, and mode 14 is a transient state in which mode 13 transitions to mode 14. Here, mode 11, mode 12, mode 13, and mode 14 correspond to the 11th mode, 12th mode, 13th mode, and 14th mode of the present invention, respectively.

[0076] 6 shows the current path of the inverter device 10 in mode 11. Here, switch SW1 is on, switch SW2 is off, switch SW3 is off, switch SW4 is off, switch SW5 is off, switch SW6 is on, switch SWuwp is on, and switch SWuwn is off. At this time, current input from the positive terminal of DC power supply Sd through input terminal Ip to positive input line Lip passes through switch SW1, U-phase power line Liu, reactor Lu, load RLu, load RLw, reactor Lw, W-phase power line Liw, switch SW6, negative input line Lin, and returns from input terminal In to the negative terminal of DC power supply Sd.

[0077] FIG. 7 shows the current path of the inverter device 10 in mode 12. When the switches SW1 and SW6 are switched from on to off, a current transiently flows from the positive terminal of the DC power supply Sd through the input terminal Ip and input to the positive input line Lip, as shown by the dashed line. The current then flows through the switch SW1, the U-phase power line Liu, the reactor Lu, the load RLiu, the load RLw, the reactor Lw, the W-phase power line Liw, the switch SW6, and the negative input line Lin, and returns from the input terminal In to the negative terminal of the DC power supply Sd, similar to the path shown in mode 11 in FIG. 6. This current charges the parasitic capacitance of the MOSFETs, which are switching elements constituting the switches SW1 and SW6 that have switched from on to off. Along with the current shown by the dashed line, the HERIC circuit 12 is short-circuited, and current flows through the path shown by the solid line. That is, current flows from reactor Lu, load RLu, load RLw, and reactor Lw to the W-phase power line, switch SWuwp, switch SWuwn, and U-phase power line Liu. Here, switch SW2 is off, switch SW3 is on, switch SW4 is off, switch SW5 is off, switch SWuwp is on, and switch SWuwn is off. Although switch SWuwn of HERIC circuit 12 is off, the parasitic diode of the MOSFET, which is a switching element, is conductive, and current flows from the W-phase power line Liw to the U-phase power line Liu.

[0078] 8 shows the current path of inverter device 10 in mode 13. Here, switches SW1 to SW6 are all off, switch SWuwp is on, and switch SWuwn is off. At this time, HERIC circuit 12 is short-circuited, and current flows from reactor Lu, load RLu, load RLw, and reactor Lw to the W-phase power line, switch SWuwp, switch SWuwn, and U-phase power line Liu. Although switch SWuwn of HERIC circuit 12 is off, the parasitic diode of the MOSFET, which is a switching element, is conductive, and current flows from W-phase neutral line Liw to U-phase power line Liu.

[0079] 9 shows the current path of the inverter device 10 in mode 14. At this time, similar to mode 13 shown in FIG. 8, current flows along the path shown by the solid lines, that is, from the reactor Lu, load RLu, load RLw, and reactor Lw to the W-phase power line, switch SWuwp, switch SWuwn, and U-phase power line Liu. When the switches SW1 and SW6 are turned on from off, current transiently flows as shown by the dashed lines to the switch SWuwn, switch SWuwp, W-phase power line Liw, switch SW6, negative input line Lin, DC power supply Sd, positive input line Lip, switch SW1, U-phase power line Liu, and switch SWuwn. This current causes the MOSFET, which is a switching element constituting the switch SWuwn, to The parasitic capacitance is charged and the switch SWuwn is automatically shut off. After passing through this transient mode 14, the system transitions again to the steady state mode 11, and in the first half of the commercial frequency, the transitions are repeated in the order of mode 11, mode 12, mode 13, and mode 14.

[0080] The control of each switch during the second half cycle of the commercial frequency will be briefly described. In this case, SW3 and SW4, which constitute the O-phase midpoint leg Lgo, are always off. This control repeats transitions in the order of mode 15, mode 16, mode 17, and mode 18. Mode 15 is a mode in which, in mode 11, the on / off states of switches SW1 and SW5 are interchanged, the on / off states of switches SW2 and SW6 are interchanged, and switch SWuwn is turned on and SWuwp is turned on. Mode 16 is a transient state in which switches SW2 and SW5 transition from on to off, and switches SW1, SW3, SW4, SW6, SWuwn, and SWuwp are in the same switching states as in mode 15. Mode 17 is a mode in which switches SW1, SW2, SW3, SW4, SW5, and SW6 are all off, switch SWuwn is turned on, and switch SWuwp is turned on. Mode 18 is a transitional state in which switches SW2 and SW5 transition from off to on, and switches SW1, SW3, SW4, SW6, SWuwn, and SWuwn are in the same switching states as in mode 17. Here, modes 15, 16, 17, and 18 correspond to the 15th, 16th, 17th, and 18th modes of the present invention, respectively. Here, the first and second half cycles of the commercial frequency correspond to one half cycle and the other half cycle of the frequency of AC power to be output, respectively, of the present invention.

[0081] In this way, it is possible to realize a single-phase two-wire inverter device 10 using a HERIC circuit, and high efficiency is possible.

[0082] (PWM control during stand-alone operation) The following describes switching control of the inverter 11 and the HERIC circuit 12 for converting input DC power into AC power in the inverter device 10 during stand-alone operation.

[0083] As in grid-connected operation, the control unit 14 controls the switching of the inverter 11 and the HERIC circuit 12 based on command values ​​related to the AC voltage waveform to be output. The control unit 14 performs PWM control, which controls the output voltage by controlling the on / off duty ratio of the switches SW1, SW2, SW3, SW4, SW5, and SW6 of the inverter 11. During isolated operation, the switches SW3 and SW4 that constitute the O-phase midpoint leg Lgo are on / off controlled, and the inverter 11 outputs single-phase three-wire power. Also, during isolated operation, the switches SWuwn and SWuwp that constitute the HERIC circuit 12 are always off.

[0084] In the first half cycle, the current path of the inverter device 10 repeatedly transitions through four modes in the order of mode 21, mode 22, mode 23, mode 22, mode 21, and mode 24. All of these four modes are steady states.

[0085] FIG. 10 shows a part of a timing chart of control signals for each switch of the inverter 11 and the HERIC circuit 12 in the power conversion process by the inverter device 10. FIG. 10 shows the control signals for each switch in the first half cycle when an AC voltage that draws a sine curve with a frequency of 50 Hz is output. PWM1 to 6 indicate the control signals for the switches SW1 to 6, and PWMp and PWMn indicate the control signals for the switches SWuwp and SWuwn. Also, FIG. 11 shows the control signals for the inverter 11 and the HERIC circuit 12 shown in FIG. 2 shows an enlarged portion of a timing chart of control signals for each switch in FIG.

[0086] The inverter 11 is subjected to PWM control using unipolar modulation. The on / off of each switch is controlled according to a duty ratio determined by the PWM control. In the first half cycle, a voltage is output to the output terminal Ou of the U-phase power line Liu and the output terminal Oo of the O-phase neutral line Lio, and the voltage applied to the load RLiu is either positive or zero on the output terminal Ou side relative to the output terminal Oo side. A voltage is output to the output terminal Oo of the O-phase neutral line Lio and the output terminal Ow of the W-phase power line Liw, and the voltage applied to the load Rlw is either positive or zero on the output terminal Oo side relative to the output terminal Ow side. In the second half cycle, the voltage applied to the load RLiu is negative or zero on the output terminal Ou side relative to the output terminal Oo side, and the voltage applied to the load RLiu is negative or zero on the output terminal Ou side relative to the output terminal Oo side, and the voltage applied to the load Rlw is negative or zero on the output terminal Oo side relative to the output terminal Ow side.

[0087] 12 shows the current paths of the inverter device 10 in mode 21. The path of current Iu flowing through load RLiu is shown by a dashed line, and the path of current Iw flowing through load RLw is shown by a solid line. Here, switch SW1 is on, switch SW2 is off, switch SW3 is off, switch SW4 is on, switch SW5 is off, switch SW6 is off, switch SWuwp is off, and switch SWuwn is off. At this time, current input from the positive terminal of DC power supply Sd through input terminal Ip to positive input line Lip passes through switch SW1, U-phase power line Liu, reactor Lu, load RLiu, reactor Lo, O-phase neutral line Lio, switch SW4, negative input line Lin, and returns from input terminal In to the negative terminal of DC power supply Sd. On the other hand, the current input from the negative terminal of the DC power supply Sd through the input terminal In to the negative input line Lin passes through the switch SW4, the O-phase neutral line Lio, the reactor Lo, the load RLw, the reactor Lw, the W-phase power line Liw, the switch SW5, and the positive input line Lip, and is input from the input terminal Ip to the positive terminal of the DC power supply Sd.

[0088] FIG. 13 shows the current paths of the inverter device 10 in mode 22. The path of current Iu flowing through load RLiu is indicated by a dashed line, and the path of current Iw flowing through load RLw is indicated by a solid line. Here, switch SW1 is on, switch SW2 is off, switch SW3 is on, switch SW4 is off, switch SW5 is off, switch SW6 is off, switch SWuwp is off, and switch SWuwn is off. At this time, the current flowing through load RLiu passes through reactor Lo, O-phase neutral conductor Lio, switch SW3, positive input line Lip, switch SW1, U-phase power line Liu, reactor Lu, load RLiu, and reactor Lo. Meanwhile, the current flowing through load RLw passes through reactor Lw, W-phase power line Liw, switch SW5, positive input line Lip, switch SW3, O-phase neutral conductor Lio, reactor Lo, load RLw, and reactor Lw.

[0089] 14 shows the current paths of the inverter device 10 in mode 23. The path of current Iu flowing through load RLi is indicated by a dashed line, and the path of current Iw flowing through load RLw is indicated by a solid line. Here, switch SW1 is off, switch SW2 is off, switch SW3 is on, switch SW4 is off, switch SW5 is off, switch SW6 is on, switch SWuwp is off, and switch SWuwn is off. At this time, current input from the positive terminal of DC power supply Sd through input terminal Ip to positive input line Lip passes through switch SW3, O-phase neutral line Lio, reactor Lo, load RLw, reactor Lw, W-phase power line Liw, switch SW6, negative input line Lin, and returns from input terminal In to the negative terminal of DC power supply Sd. On the other hand, the current input from the negative terminal of the DC power supply Sd to the negative input line Lin via the input terminal In passes through the switch SW2, the U-phase power line Liu, the reactor Lu, the load RLiu, the reactor Lo, the O-phase neutral line Lio, the switch SW3, and the positive input line Lip, and reaches the input terminal I The input is from p to the positive terminal of the DC power supply Sd.

[0090] FIG. 15 shows the current paths of the inverter device 10 in mode 24. The path of current Iu flowing through load RLiu is indicated by a dashed line, and the path of current Iw flowing through load RLw is indicated by a solid line. Here, switch SW1 is off, switch SW2 is off, switch SW3 is off, switch SW4 is on, switch SW5 is off, switch SW6 is on, switch SWuwp is off, and switch SWuwn is off. At this time, the current flowing through load RLiu passes through reactor Lo, O-phase neutral conductor Lio, switch SW4, negative input line Lin, switch SW2, U-phase power line Liu, reactor Lu, load RLiu, and reactor Lo. Meanwhile, the current flowing through load RLiu passes through reactor Lw, W-phase power line Liw, switch SW6, negative input line Lin, switch SW4, O-phase neutral conductor Lio, reactor Lo, load RLiw, and reactor Lw. Here, modes 21, 22, 23, and 24 correspond to the 21st mode, 22nd mode, 23rd mode, and 24th mode of the present invention, respectively.

[0091] Control of each switch during the second half cycle of the commercial frequency will be briefly described. Even in this case, the switches SWuwn and SWuwp constituting the HERIC circuit 12 are always off. This control repeats transitions in the order of mode 25, mode 26, mode 27, mode 26, mode 25, and mode 28. Modes 25 to 28 are modes in which the on / off states of switches SW1 and SW5 are swapped, and the on / off states of switches SW2 and SW6 are swapped, respectively, in modes 21 to 24. However, if the switching states of the switches are all off, swapping their on / off states does not change the switching states from before the swapping, and all remain off. Here, modes 25, 26, 27, and 28 correspond to the 25th, 26th, 27th, and 28th modes of the present invention, respectively. Furthermore, the first and second half cycles of the commercial frequency correspond to one half cycle and the other half cycle of the frequency of the AC power to be output, respectively, of the present invention.

[0092] In this way, the inverter device 10 enables efficient operation by the HERIC circuit 12 during grid-connected operation in which single-phase two-wire power is output, and also enables output of single-phase three-wire power, which is in high demand, during stand-alone operation.

[0093] In the PWM control during isolated operation described above, the mode transitions are repeated in the order of mode 21, mode 22, mode 23, mode 22, mode 21, and mode 24 in the first half of the commercial frequency. However, the mode transitions may also be repeated in the order of mode 21, mode 21, mode 22, mode 22, mode 23, and mode 24. In this case, "mode 21, mode 2" and "mode 22, mode 22" mean that the periods of mode 21 and mode 22 are doubled, respectively. This type of PWM control reduces the number of switching operations, improving efficiency. In this case, the second half of the commercial frequency is mode 25, mode 25, mode 26, mode 26, mode 27, and mode 28.

[0094] Example 2 Hereinafter, a description will be given of a single-phase three-wire inverter module 20 according to the second embodiment. Fig. 16 shows a circuit configuration of the inverter module 20. The inverter module 20 is a modularized version of the inverter device 10 according to the first embodiment.

[0095] The inverter module 20 has input terminals DC+ and DC- and output terminals OUT1, OUT2, and OUT3. The inverter module 20 generally includes a single-phase three-wire inverter 21, a HERIC circuit 22 capable of short-circuiting between the U-phase power line Liu and the W-phase power line Liw of the inverter 21, and a thermistor TH. Here, the thermistor TH detects the temperature of the present invention. It corresponds to the temperature detection unit that outputs the temperature.

[0096] The single-phase three-wire inverter 61 is a three-arm inverter in which a leg, consisting of two switches connected in series, is connected in parallel to the input terminals DC+ and DC-. That is, the inverter 61 has three legs, an O-phase midpoint leg MLgo, a U-phase leg MLgu, and a W-phase leg MLgw, connected in parallel between the positive input line Lip and the negative input line Lin, in that order from the input terminals DC+ and DC-. Here, the switches are configured with semiconductor switching elements, such as PNP transistors and freewheeling diodes, but are not limited to this. The switches can also be configured by combining an n-channel enhancement-type MOSFET, an IGBT, and a freewheeling diode connected in anti-parallel as the semiconductor switching elements.

[0097] The O-phase midpoint leg MLo is composed of switches Q1 and Q4. The collector terminal of switch Q1 is connected to the positive input line Lip, the emitter terminal of switch Q1 is connected to the collector terminal of switch Q4, and a gate terminal connection line G1 and an emitter terminal connection line E1 of switch Q1 are extended. A freewheeling diode D1 is connected in anti-parallel to switch Q1. The emitter terminal of switch Q4 is connected to the negative input line Lin, and a gate terminal connection line G4 and an emitter terminal connection line E4 of switch Q4 are extended. A freewheeling diode D4 is connected in anti-parallel to switch Q4. The U-phase leg MLgu is composed of switches Q2 and Q5. The collector terminal of switch Q2 is connected to the positive input line Lip, and the emitter terminal of switch Q2 is connected to the collector terminal of switch Q5, and a gate terminal connection line G2 and an emitter terminal connection line E2 of switch Q2 are extended. A freewheel diode D2 is connected in anti-parallel to the switch Q2. The emitter terminal of the switch Q5 is connected to the negative input line Lin, and a gate terminal connection line G5 and an emitter terminal connection line E5 of the switch Q5 are drawn out. A freewheel diode D5 is connected in anti-parallel to the switch Q5. The W-phase leg MLgw is composed of switches Q3 and Q6. The collector terminal of the switch Q3 is connected to the positive input line Lip, and the emitter terminal of the switch Q3 is connected to the collector terminal of the switch Q6, and a gate terminal connection line G3 and an emitter terminal connection line E3 of the switch Q3 are drawn out. A freewheel diode D3 is connected in anti-parallel to the switch Q3. The emitter terminal of the switch Q6 is connected to the negative input line Lin, and a gate terminal connection line G6 and an emitter terminal connection line E6 of the switch Q6 are drawn out. A freewheel diode D6 is connected in anti-parallel to the switch Q6.

[0098] An O-phase neutral wire Lio is drawn from the midpoint of the O-phase midpoint leg MLgo, i.e., the midpoint between the emitter terminal of switch Q1 and the drain terminal of switch Q4, and connected to output terminal OUT1. A U-phase power line Liu is drawn from the midpoint of the U-phase leg MLgu, i.e., the midpoint between the emitter terminal of switch Q2 and the collector terminal of switch Q52, and connected to output terminal OUT2. A W-phase power line Liw is drawn from the midpoint of the W-phase leg MLgw, i.e., the midpoint between the emitter terminal of switch Q3 and the connector terminal of switch Q6, and connected to output terminal OUT3.

[0099] A HERIC circuit 22 is connected between the U-phase power line Liu and the W-phase power line Liw. The emitter terminal of switch Q7 is connected to the U-phase power line Liu, and the collector terminal of switch Q7 is connected to the collector terminal of switch Q8, from which a gate terminal connection line G7 and an emitter terminal connection line E7 of switch Q7 are drawn. A freewheeling diode D7 is connected in anti-parallel to switch Q7. The emitter terminal of switch Q8 is connected to the W-phase power line Liw, from which a gate terminal connection line G8 and an emitter terminal connection line E8 of switch Q8 are drawn. A freewheeling diode D8 is connected in anti-parallel to switch Q8. A connection line C7 is drawn from the midpoint between the collector terminal of switch Q7 and the collector terminal of switch Q8. Here, the switches constituting HERIC circuit 22 are semi-conductors. The semiconductor switching element is a PNP transistor and a free wheel diode, but this is not limited to this. The switch can also be configured by combining an n-channel enhancement type MOSFET, an IGBT, and a free wheel diode connected in anti-parallel. The thermistor TH is connected to output terminals TH1 and TH2.

[0100] Switches Q1, Q2, Q3, Q4, Q5, and Q6 constituting the inverter 21 of the inverter module 20 correspond to the switches SW3, SW1, SW5, SW4, SW2, and SW6, respectively, of the inverter device 10 shown in Example 1. Furthermore, switches Q7 and Q8 constituting the HERIC circuit 12 of the inverter module 20 correspond to the switches SWuwp and SWuwn, respectively, of the inverter device 10 shown in Example 1.

[0101] FIG. 17 is a diagram showing an example of the arrangement of each device and pin in the inverter module 20. FIG. 17 shows the approximate arrangement of the O-phase midpoint leg MLgo, the U-phase leg MLgu, the W-phase leg MLgw, the HERIC circuit 12, and the thermistor TH, as well as the arrangement of the pins connected to the terminals of each device. In the following description, up, down, left, and right refer to the up, down, left, and right of FIG. 17. As shown in FIG. 17, in the inverter module 20, the O-phase midpoint leg MLgo is located at the left end, the U-phase leg MLgu is located adjacent to it on the right, and the W-phase leg MLgw is located at the right end. The HERIC circuit 12 is located above the U-phase leg MLgu and the W-phase leg MLgw, and the thermistor TH is located below the U-phase leg MLgu and the W-phase leg MLgw. In this way, by placing the thermistor TH in the area surrounded by the U-phase leg MLgu, the W-phase leg MLgw, and the HERIC circuit 12, which generates a large amount of heat, and measuring the temperature of the inverter module 20, it is possible to accurately control the inverter module 20 in response to the heat generation state, such as by reducing the output power in the event of abnormal heat generation.

[0102] By using the single-phase three-wire HERIC inverter module 20 in this way, it is possible to suppress variations in the characteristics of the inverter device, improve heat dissipation, and facilitate assembly.

[0103] <Appendix 1> An inverter device (10) that converts input DC power into single-phase two-wire or single-phase three-wire AC power and outputs the AC power, a first phase output terminal (Ou), a second phase output terminal (Ow) and a neutral output terminal (Oo); an inverter unit (11) that converts the DC power into AC power; a first-phase power line (Liu) connecting the inverter unit (11) and the first-phase output terminal (Ou) and receiving first-phase power of the AC power; a second-phase power line (Liw) connecting the inverter unit (11) and the second-phase output terminal (Ow) and receiving second-phase power of the AC power; a neutral power line (Lio) connecting the inverter unit (11) and the neutral output terminal (Oo); a short-circuit (12) connected between the first-phase power line (Liu) and the second-phase power line (Liw) and capable of short-circuiting the first-phase power line (Liu) and the second-phase power line (Liw); An inverter device (10) comprising the inverter unit (11) and a control unit (14) that controls the short circuit. [Explanation of symbols]

[0104] 10: Inverter device 11: Inverter 12:HERIC circuit Ou, Ow, Oo: Output terminals Liu :U-phase power line Liw :W phase power line Lio :O phase neutral line

Claims

1. An inverter device that converts input DC power into single-phase two-wire or single-phase three-wire AC power and outputs it, a first phase output terminal, a second phase output terminal, and a neutral output terminal; an inverter unit that converts the DC power into the AC power; a first-phase power line connecting the inverter unit and the first-phase output terminal and through which first-phase power of the AC power is supplied; a second-phase power line connecting the inverter unit and the second-phase output terminal and through which second-phase power of the AC power is supplied; a neutral power line connecting the inverter unit and the neutral output terminal; a short circuit connected between the first-phase power line and the second-phase power line, capable of short-circuiting the first-phase power line and the second-phase power line; a control unit that controls the inverter unit and the short circuit, The inverter unit a positive input terminal connected to the positive terminal of a DC power supply and a negative input terminal connected to the negative terminal of the DC power supply; a first phase leg in which a first switching element connected to the positive input terminal and a second switching element connected to the negative input terminal are connected in series; a neutral leg in which a third switching element connected to the positive input terminal and a fourth switching element connected to the negative input terminal are connected in series; a second phase leg in which a fifth switching element connected to the positive input terminal and a sixth switching element connected to the negative input terminal are connected in series; and the first phase leg has a first phase connection point, to which the first phase power line is connected, at a midpoint between the first switching element and the second switching element; the neutral leg has a neutral connection point to which the neutral power line is connected at a midpoint between the third switching element and the fourth switching element, the second phase leg has a second phase connection point, to which the second phase power line is connected, at a midpoint between the fifth switching element and the sixth switching element; the short circuit includes a first short-circuit switching element that switches on and off a current flowing from the first-phase power line side to the second-phase power line side, and a second short-circuit switching element that switches on and off a current flowing from the second-phase power line side to the first-phase power line side, When operating in connection with a commercial power system, the PWM control of the first switching element to the sixth switching element by the control unit in one half cycle of the frequency of the AC power to be output is turning on the first switching element and turning off the second switching element; turning off the third switching element and the fourth switching element; turning off the fifth switching element and turning on the sixth switching element; an eleventh mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned on; The first switching element is turned from on to off, and the second switching element is turned off; turning off the third switching element and the fourth switching element; turning off the fifth switching element and turning off the sixth switching element; a twelfth mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned on; turning off the first switching element and the second switching element; turning off the third switching element and the fourth switching element; turning off the fifth switching element and the sixth switching element; a thirteenth mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned on; The first switching element is turned on from off, and the second switching element is turned off; turning off the third switching element and the fourth switching element; turning off the fifth switching element, and turning on the sixth switching element; a fourteenth mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned on; and includes control for repeating transitions in the order of the 11th mode, the 12th mode, the 13th mode, and the 14th mode.

2. When operating in connection with a commercial power system, the PWM control of the first switching element to the sixth switching element by the control unit in the other half cycle of the frequency of the AC power to be output is turning off the first switching element and turning on the second switching element; turning off the third switching element and the fourth switching element; The fifth switching element is turned on and the sixth switching element is turned off, a fifteenth mode in which the first short-circuiting switching element is turned on and the second short-circuiting switching element is turned off; turning off the first switching element and turning off the second switching element; turning off the third switching element and the fourth switching element; The fifth switching element is turned from on to off, and the sixth switching element is turned off; a sixteenth mode in which the first short-circuiting switching element is turned on and the second short-circuiting switching element is turned off; turning off the first switching element and the second switching element; turning off the third switching element and the fourth switching element; turning off the fifth switching element and the sixth switching element; a seventeenth mode in which the first short-circuit switching element is turned on and the second short-circuit switching element is turned off; turning off the first switching element, and turning on the second switching element; turning off the third switching element and the fourth switching element; The fifth switching element is turned from off to on, and the sixth switching element is turned off; an eighteenth mode in which the first short-circuit switching element is turned on and the second short-circuit switching element is turned off; 2. The inverter device according to claim 1, wherein the inverter device includes a control for repeating transitions in the order of the 15th mode, the 16th mode, the 17th mode, and the 18th mode.

3. When operating independently from a commercial power grid, the PWM control of the first switching element to the sixth switching element by the control unit in either half cycle of the frequency of the AC power to be output is turning on the first switching element and turning off the second switching element; turning off the third switching element and turning on the fourth switching element; turning off the fifth switching element and the sixth switching element; a 21st mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning on the first switching element and turning off the second switching element; turning on the third switching element and turning off the fourth switching element; turning off the fifth switching element and the sixth switching element; a 22nd mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning off the first switching element and the second switching element; turning on the third switching element and turning off the fourth switching element; turning off the fifth switching element and turning on the sixth switching element; a 23rd mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning off the first switching element and the second switching element; turning off the third switching element and turning on the fourth switching element; turning off the fifth switching element and turning on the sixth switching element; a 24th mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; and includes control of repeating transitions in the order of the 21st mode, the 22nd mode, the 23rd mode, the 22nd mode, the 21st mode, and the 24th mode.

4. When operating independently from a commercial power system, the PWM control of the first switching element to the sixth switching element by the control unit in one half cycle of the frequency of the AC power to be output is turning off the first switching element and the second switching element; turning off the third switching element and turning on the fourth switching element; The fifth switching element is turned on and the sixth switching element is turned off, a 25th mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning off the first switching element and the second switching element; turning on the third switching element and turning off the fourth switching element; The fifth switching element is turned on and the sixth switching element is turned off, a 26th mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning off the first switching element and turning on the second switching element; turning on the third switching element and turning off the fourth switching element; turning off the fifth switching element and the sixth switching element; a 27th mode in which the first short-circuiting switching element is turned off and the second short-circuiting switching element is turned off; turning off the first switching element and turning on the second switching element; turning off the third switching element and turning on the fourth switching element; turning off the fifth switching element and the sixth switching element; a 28th mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; and includes control of repeating transitions in the order of the 25th mode, the 26th mode, the 27th mode, the 26th mode, the 25th mode, and the 28th mode.

5. When operating independently from a commercial power grid, the PWM control of the first switching element to the sixth switching element by the control unit in either half cycle of the frequency of the AC power to be output is turning on the first switching element and turning off the second switching element; turning off the third switching element and turning on the fourth switching element; turning off the fifth switching element and the sixth switching element; a 21st mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning on the first switching element and turning off the second switching element; turning on the third switching element and turning off the fourth switching element; turning off the fifth switching element and the sixth switching element; a 22nd mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning off the first switching element and the second switching element; turning on the third switching element and turning off the fourth switching element; turning off the fifth switching element and turning on the sixth switching element; a 23rd mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning off the first switching element and the second switching element; turning off the third switching element and turning on the fourth switching element; turning off the fifth switching element and turning on the sixth switching element; a 24th mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; 3. The inverter device according to claim 1, wherein the inverter device includes control for repeating transitions in the order of the 21st mode, the 22nd mode, the 23rd mode, and the 24th mode.

6. When operating independently from a commercial power system, the PWM control of the first switching element to the sixth switching element by the control unit in one half cycle of the frequency of the AC power to be output is turning off the first switching element and the second switching element; turning off the third switching element and turning on the fourth switching element; The fifth switching element is turned on and the sixth switching element is turned off, a 25th mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning off the first switching element and the second switching element; turning on the third switching element and turning off the fourth switching element; The fifth switching element is turned on and the sixth switching element is turned off, a 26th mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning off the first switching element and turning on the second switching element; turning on the third switching element and turning off the fourth switching element; turning off the fifth switching element and the sixth switching element; a 27th mode in which the first short-circuiting switching element is turned off and the second short-circuiting switching element is turned off; turning off the first switching element and turning on the second switching element; turning off the third switching element and turning on the fourth switching element; turning off the fifth switching element and the sixth switching element; a 28th mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; and includes control for repeating transitions in the order of the 25th mode, the 26th mode, the 27th mode, and the 28th mode.

7. An inverter device that converts input DC power into single-phase two-wire or single-phase three-wire AC power and outputs the converted power, a first phase output terminal, a second phase output terminal, and a neutral output terminal; an inverter unit that converts the DC power into the AC power; a first-phase power line connecting the inverter unit and the first-phase output terminal and through which first-phase power of the AC power is supplied; a second-phase power line connecting the inverter unit and the second-phase output terminal and through which second-phase power of the AC power is supplied; a neutral power line connecting the inverter unit and the neutral output terminal; a short circuit connected between the first-phase power line and the second-phase power line, capable of short-circuiting the first-phase power line and the second-phase power line; a control unit that controls the inverter unit and the short circuit, The inverter unit a positive input terminal connected to the positive terminal of a DC power supply and a negative input terminal connected to the negative terminal of the DC power supply; a first phase leg in which a first switching element connected to the positive input terminal and a second switching element connected to the negative input terminal are connected in series; a neutral leg in which a third switching element connected to the positive input terminal and a fourth switching element connected to the negative input terminal are connected in series; a second phase leg in which a fifth switching element connected to the positive input terminal and a sixth switching element connected to the negative input terminal are connected in series; and the first phase leg has a first phase connection point, to which the first phase power line is connected, at a midpoint between the first switching element and the second switching element; the neutral leg has a neutral connection point to which the neutral power line is connected at a midpoint between the third switching element and the fourth switching element, the second phase leg has a second phase connection point, to which the second phase power line is connected, at a midpoint between the fifth switching element and the sixth switching element; the short circuit includes a first short-circuit switching element that switches on and off a current flowing from the first-phase power line side to the second-phase power line side, and a second short-circuit switching element that switches on and off a current flowing from the second-phase power line side to the first-phase power line side, When operating independently from a commercial power system, the PWM control of the first switching element to the sixth switching element by the control unit in one half cycle of the frequency of the AC power to be output is turning on the first switching element and turning off the second switching element; turning off the third switching element and turning on the fourth switching element; turning off the fifth switching element and the sixth switching element; turning off the first short-circuit switching element and the second short-circuit switching element; The 21st mode, turning on the first switching element and turning off the second switching element; turning on the third switching element and turning off the fourth switching element; turning off the fifth switching element and the sixth switching element; a 22nd mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning off the first switching element and the second switching element; turning on the third switching element and turning off the fourth switching element; turning off the fifth switching element and turning on the sixth switching element; a 23rd mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning off the first switching element and the second switching element; turning off the third switching element and turning on the fourth switching element; turning off the fifth switching element and turning on the sixth switching element; a 24th mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; and includes control for repeating transitions in the order of the 21st mode, the 22nd mode, the 23rd mode, the 22nd mode, the 21st mode, and the 24th mode.

8. When operating independently from a commercial power grid, the PWM control of the first switching element to the sixth switching element by the control unit in either half cycle of the frequency of the AC power to be output is turning off the first switching element and the second switching element; turning off the third switching element and turning on the fourth switching element; The fifth switching element is turned on and the sixth switching element is turned off, a 25th mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning off the first switching element and the second switching element; turning on the third switching element and turning off the fourth switching element; The fifth switching element is turned on and the sixth switching element is turned off, a 26th mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning off the first switching element and turning on the second switching element; turning on the third switching element and turning off the fourth switching element; turning off the fifth switching element and the sixth switching element; a 27th mode in which the first short-circuiting switching element is turned off and the second short-circuiting switching element is turned off; turning off the first switching element and turning on the second switching element; turning off the third switching element and turning on the fourth switching element; turning off the fifth switching element and the sixth switching element; a 28th mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; and includes control of repeating transitions in the order of the 25th mode, the 26th mode, the 27th mode, the 26th mode, the 25th mode, and the 28th mode.

9. An inverter device that converts input DC power into single-phase two-wire or single-phase three-wire AC power and outputs it, a first phase output terminal, a second phase output terminal, and a neutral output terminal; an inverter unit that converts the DC power into the AC power; a first-phase power line connecting the inverter unit and the first-phase output terminal and through which first-phase power of the AC power is supplied; a second-phase power line connecting the inverter unit and the second-phase output terminal and through which second-phase power of the AC power is supplied; a neutral power line connecting the inverter unit and the neutral output terminal; a short circuit connected between the first-phase power line and the second-phase power line, capable of short-circuiting the first-phase power line and the second-phase power line; a control unit that controls the inverter unit and the short circuit, The inverter unit a positive input terminal connected to the positive terminal of a DC power supply and a negative input terminal connected to the negative terminal of the DC power supply; a first phase leg in which a first switching element connected to the positive input terminal and a second switching element connected to the negative input terminal are connected in series; a neutral leg in which a third switching element connected to the positive input terminal and a fourth switching element connected to the negative input terminal are connected in series; a second phase leg in which a fifth switching element connected to the positive input terminal and a sixth switching element connected to the negative input terminal are connected in series; and the first phase leg has a first phase connection point, to which the first phase power line is connected, at a midpoint between the first switching element and the second switching element; the neutral leg has a neutral connection point to which the neutral power line is connected at a midpoint between the third switching element and the fourth switching element, the second phase leg has a second phase connection point, to which the second phase power line is connected, at a midpoint between the fifth switching element and the sixth switching element; the short circuit includes a first short-circuit switching element that switches on and off a current flowing from the first-phase power line side to the second-phase power line side, and a second short-circuit switching element that switches on and off a current flowing from the second-phase power line side to the first-phase power line side, When operating independently from a commercial power system, the PWM control of the first switching element to the sixth switching element by the control unit in one half cycle of the frequency of the AC power to be output is turning on the first switching element and turning off the second switching element; turning off the third switching element and turning on the fourth switching element; turning off the fifth switching element and the sixth switching element; a 21st mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning on the first switching element and turning off the second switching element; turning on the third switching element and turning off the fourth switching element; turning off the fifth switching element and the sixth switching element; a 22nd mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning off the first switching element and the second switching element; turning on the third switching element and turning off the fourth switching element; turning off the fifth switching element and turning on the sixth switching element; a 23rd mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning off the first switching element and the second switching element; turning off the third switching element and turning on the fourth switching element; turning off the fifth switching element and turning on the sixth switching element; turning off the first short-circuit switching element and the second short-circuit switching element; The 24th mode, and includes control for repeating transitions in the order of the 21st mode, the 22nd mode, the 23rd mode, and the 24th mode.

10. When operating independently from a commercial power grid, the PWM control of the first switching element to the sixth switching element by the control unit in either half cycle of the frequency of the AC power to be output is turning off the first switching element and the second switching element; turning off the third switching element and turning on the fourth switching element; The fifth switching element is turned on and the sixth switching element is turned off, a 25th mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning off the first switching element and the second switching element; turning on the third switching element and turning off the fourth switching element; The fifth switching element is turned on and the sixth switching element is turned off, a 26th mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; turning off the first switching element and turning on the second switching element; turning on the third switching element and turning off the fourth switching element; turning off the fifth switching element and the sixth switching element; a 27th mode in which the first short-circuiting switching element is turned off and the second short-circuiting switching element is turned off; turning off the first switching element and turning on the second switching element; turning off the third switching element and turning on the fourth switching element; turning off the fifth switching element and the sixth switching element; a 28th mode in which the first short-circuit switching element is turned off and the second short-circuit switching element is turned off; and includes control for repeating transitions in the order of the 25th mode, the 26th mode, the 27th mode, and the 28th mode.

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