Power conversion device and control method thereof

Abstract

To suppress dV / dt at the time of switching of an output point.SOLUTION: A power converter for converting DC to AC and vice versa includes: a first flying capacitor circuit connected between a pair of DC input points and a first output point; a second flying capacitor circuit connected between a pair of DC input points and a second output point; an AC filter connected to the first output point and the second output point; and a control circuit. A plurality of first semiconductor switching elements and a plurality of second semiconductor switching elements of the second flying capacitor circuit are an element that performs switching according to a polarity of an AC voltage. The control circuit turns on the plurality of first semiconductor switching elements or the plurality of second semiconductor switching elements in turn from the DC input point toward the second output point or from the second output point toward the DC input point.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to a power conversion device and a control method thereof.

Background Art

[0002] In recent years, due to the response to environmental problems, there has been an increasing demand for further higher efficiency and miniaturization in power conversion devices. In order to meet such demands, a multilevel power conversion device capable of outputting three or more voltages is known. There are several types of multilevel power conversion devices. One of them is a multilevel power conversion device using a flying capacitor circuit (see, for example, Patent Document 1).

[0003] FIG. 1 is a configuration example of a multilevel power conversion device using a flying capacitor circuit, and shows a 7-level inverter configuration as an example. The flying capacitor circuit shown in FIG. 1 is composed of 12 semiconductor switching elements Sp1 to Sp6, Sn1 to Sn6 and 5 flying capacitors FC1 to FC5. In FIG. 1, the description of FC3, FC4 and Sp3 to Sp5, Sn3 to Sn5 is omitted. Also, Lac and Cac are AC filters. By adding and subtracting different voltage values held in each flying capacitor by switching of each semiconductor switching element, the output voltage VL can be controlled to a 7-level AC voltage.

[0004] However, since the circuit shown in FIG. 1 has a half-bridge configuration, a DC voltage about twice the AC voltage value of the output is required. For example, when the AC voltage is 200V, the DC voltage Edc needs to be about 800V (±400V). In order to cope with a higher voltage, it is necessary to increase the number of series-connected semiconductor switching elements and capacitors, so there is a risk that the device will become larger and more expensive.

[0005] As a circuit for dealing with such problems, a flying capacitor type multilevel circuit of a hybrid bridge (hereinafter also referred to as a flying capacitor totem pole circuit) is known (see, for example, Non-Patent Document 1).

[0006] FIG. 2 is a configuration diagram of a flying capacitor totem pole circuit, and shows a 4-level inverter configuration as an example. This flying capacitor totem pole circuit includes a flying capacitor circuit connected between a DC input terminal (between P and N) and an AC terminal U, and a low-frequency conversion circuit connected between the DC input terminal (between P and N) and an AC terminal V. The flying capacitor circuit is composed of semiconductor switching elements Sal to Sa3, Sbl to Sb3 and flying capacitors FC1, FC2. The low-frequency conversion circuit is composed of semiconductor switching elements Sp, Sn.

[0007] FIG. 3 shows an example of the operation waveforms of the flying capacitor totem pole circuit. By turning on and off the gates G of the semiconductor switching elements Sp, Sn of the low-frequency conversion circuit according to the polarity of an AC voltage (for example, commercial frequency 50 Hz or 60 Hz), the potential V104 at the output point 104 (AC terminal V) changes stepwise.

[0008] When the AC voltage applied between the UV terminals is positive, the potential V104 is 0 due to the turning on of the semiconductor switching element Sn. Therefore, the gate commands of the semiconductor switching elements Sal to Sa3, Sbl to Sb3 of the flying capacitor circuit are controlled so that the potential V103 at the output point 103 becomes sinusoidal between 0 and Edc in 4 levels. On the other hand, when the AC voltage applied between the UV terminals is negative, the potential V104 is Edc due to the turning on of the semiconductor switching element Sp. Therefore, the gate commands of the semiconductor switching elements Sal to Sa3, Sbl to Sb3 of the flying capacitor circuit are controlled with an offset of Edc in advance so that the difference between the potential V103 and the potential V104 becomes sinusoidal between 0 and -Edc in 4 levels.

[0009] Therefore, since the output voltage range at the output point 103 of the flying capacitor circuit has four levels from 0 to Edc, it is possible to achieve the same voltage levels with half the number of series elements as compared to the conventional seven-level inverter circuit of a half bridge.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Non-Patent Documents

[0011]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0012] As described above, in the flying capacitor totem-pole circuit, the potential of the output point 104 (AC terminal V) is changed stepwise by the low-frequency conversion circuit. At this time, since the potential V104 of the output point 104 changes directly from 0 to Edc or from Edc to 0, the dV / dt (amount of voltage (potential) change per unit time) during switching becomes large. Therefore, the leakage current flowing through the stray capacitance between the ground and the current wiring increases, and there is concern about the influence of noise. For example, there is a risk that external devices may malfunction due to noise intrusion.

[0013] The present disclosure provides a power conversion device capable of suppressing dV / dt during switching of an output point.

Means for Solving the Problem

[0014] In one aspect of the present disclosure, a power conversion device that converts direct current to alternating current or alternating current to direct current, a first input point and a second input point, which are a pair of direct current input points, a first output point, a second output point, a first flying capacitor circuit connected between the pair of direct current input points and the first output point, a second flying capacitor circuit connected between the pair of direct current input points and the second output point, an AC filter connected to the first output point and the second output point, a control circuit, and is provided with, the first flying capacitor circuit includes a plurality of semiconductor switching elements and at least one capacitor, the second flying capacitor circuit a plurality of first semiconductor switching elements connected in series between the first input point and the second output point, a plurality of second semiconductor switching elements connected in series between the second input point and the second output point, at least one first connection portion connecting adjacent elements among the plurality of first semiconductor switching elements, at least one second connection portion connecting adjacent elements among the plurality of second semiconductor switching elements, and at least one capacitor connected between a paired first connection portion and second connection portion among the at least one first connection portion and the at least one second connection portion, and has, the plurality of first semiconductor switching elements and the plurality of second semiconductor switching elements are elements that switch according to the polarity of an alternating voltage, The control circuit turns on the plurality of first semiconductor switching elements or the plurality of second semiconductor switching elements in order from the DC input point toward the second output point or from the second output point toward the DC input point. A power conversion device is provided.

Effects of the Invention

[0015] According to one aspect of the present disclosure, it is possible to suppress dV / dt during switching of the output point.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

DETAILED DESCRIPTION OF THE INVENTION

[0017] Embodiments will be described below.

[0018] <Circuit Configuration of Power Conversion Device> FIG. 4 is a diagram showing an example of a power conversion device according to the present embodiment. The power conversion device 1 shown in FIG. 4 has a circuit configuration for suppressing the dV / dt at the output point 204. The power conversion device 1 includes a DC power supply 10, input points 201 and 202, a flying capacitor totem pole circuit 2, output points 203 and 204, an AC filter 11, and a control circuit 12. The flying capacitor totem pole circuit 2 has a flying capacitor circuit 20 and a low-frequency conversion circuit 30.

[0019] The flying capacitor circuit 20 is an example of a first flying capacitor circuit, and the low-frequency conversion circuit 30 is an example of a second flying capacitor circuit. The input points 201 and 202 are examples of a pair of DC input points, the input point 201 is an example of a first input point, and the input point 202 is an example of a second input point. The output point 203 is an example of a first output point, and the output point 204 is an example of a second output point.

[0020] Here, in the illustration of the semiconductor switching elements 21, 22, 31, and 32 used in the flying capacitor totem pole circuit 2, the diodes connected in antiparallel (including the internally generated diodes such as body diodes) are omitted. Also, the flying capacitor totem pole circuit 2 according to this embodiment is, as an example, a 5-level inverter that outputs a 5-level AC voltage as the pulse voltage VL, but it may also be a multi-level inverter with 7 or more levels. Further, the power conversion device 1 may operate as a device that converts DC to AC or as a device that converts AC to DC.

[0021] The DC power supply 10 supplies DC power of the DC voltage Edc to the flying capacitor totem pole circuit 2 via a pair of DC input points, i.e., input points 201 and 202. The DC power supply 10 may be a rectifier circuit that converts the AC supplied from the power system into DC. Note that one or more smoothing capacitors (not shown) for smoothing the DC voltage Edc supplied from the DC power supply 10 may be provided between the DC power supply 10 and the flying capacitor totem pole circuit 2.

[0022] The flying capacitor circuit 20 is connected between a pair of input points 201 and 202 and an output point 203, and shifts the potential of the output point 203. The flying capacitor circuit 20 is a flying capacitor type multi-level circuit including a plurality of semiconductor switching elements 21 (21 1 , 21 2 ), a plurality of semiconductor switching elements 22 (22 1 , 22 2 ), and at least one capacitor 25. By adding and subtracting the voltages held by the capacitor 25, a multi-level (3-level in this embodiment) voltage is applied to the output point 203 as seen from the N potential.

[0023] In this embodiment, the flying capacitor circuit 20 has the same circuit configuration as the low-frequency conversion circuit 30. However, the number of cascaded semiconductor switching elements and capacitors may be different depending on the number of levels output from the output point 203.

[0024] The low-frequency conversion circuit 30 is connected between a pair of input points 201 and 202 and an output point 204, and shifts the potential of the output point 204 at a frequency lower than the frequency at which the potential of the output point 203 shifts. The low-frequency conversion circuit 30 has a plurality of semiconductor switching elements 31 (31 1 , 31 2 ) on the first wiring 26, and a plurality of semiconductor switching elements 32 (32 1 , 32 2 ) on the second wiring 27. Further, the low-frequency conversion circuit 30 has at least one capacitor 33 on a third wiring 28 that connects connection points between the semiconductor switching elements 31 on the first wiring 26 and connection points between the semiconductor switching elements 32 on the second wiring 27. The low-frequency conversion circuit 30 turns on and off the plurality of semiconductor switching elements 31 and 32 at the commercial frequency (50 Hz or 60 Hz) according to, for example, the polarity of the alternating voltage.

[0025] The plurality of semiconductor switching elements 31 arranged on the first wiring 26 are an example of a plurality of first semiconductor switching elements, and are connected in series between the input point 201 and the output point 204. The plurality of semiconductor switching elements 32 arranged on the second wiring 27 are an example of a plurality of second semiconductor switching elements, and are connected in series between the input point 202 and the output point 204.

[0026] The low-frequency conversion circuit 30 has connection portions 13 and 14 connected via the capacitor 33 on the third wiring 28. The connection portion 13 is an example of at least one first connection portion that connects between adjacent elements among the plurality of semiconductor switching elements 31. The connection portion 14 is an example of at least one second connection portion that connects between adjacent elements among the plurality of semiconductor switching elements 32. The capacitor 33 is an example of at least one capacitor connected between a paired first connection portion and second connection portion among at least one first connection portion and at least one second connection portion.

[0027] Incidentally, the number of series connections of each of the semiconductor switching elements 31 and 32 is arbitrarily determined by the magnitude of the DC voltage Edc and the breakdown voltage of the elements to be used. For example, in the case of a DC voltage of 400 V, two elements with a breakdown voltage of 300 V connected in series may be used, or three elements with a breakdown voltage of 200 V may be used.

[0028] Since the packages of low breakdown voltage devices are small and the on-resistance is also small, increasing the number does not change the size or efficiency. At least one capacitor 33 is required between the series-connected semiconductor switching elements. For example, when the number of series connections of the semiconductor switching elements 31 and 32 is 4, three capacitors 33 are required. In addition, the capacitor 33 may be connected in two or more series or two or more parallel according to the breakdown voltage or capacitance.

[0029] Also, the voltage of the capacitor 33 becomes a constant value. For example, the voltage of the capacitor 33 in FIG. 4 is 1×Edc / 2. The size of the capacitor 33 in this embodiment is about the same as the size of the capacitor provided as a snubber capacitor, and the volume occupied by the entire power conversion device is extremely small.

[0030] The AC filter 11 is connected to the output points 203 and 204 of the flying capacitor totem pole circuit 2. When the power conversion device 1 outputs AC power, the AC filter 11 sinusoidizes the multilevel voltage output from the flying capacitor totem pole circuit 2. Incidentally, when the power conversion device 1 outputs DC power, the AC filter 11 functions as a low-pass filter that removes high frequencies.

[0031] In this embodiment, the AC filter 11 is an LC filter formed by an inductor (L) and a capacitor (C).

[0032] <First Example of dV / dt Suppression Control> FIG. 5 shows the series-connected elements (31 1 and 31 2 , 32 1 and 322 ) is the overall operation waveform of the five-level inverter when driven by the same gate signal. FIG. 6 is the operation waveform when dV / dt suppression control is applied at the zero-crossing points (points A and B in FIG. 5). 31 1 , 31 2 , 32 1 , 32 2 represents the gate signals of the respective semiconductor switching elements, V31 1 , V31 2 , V32 1 , V32 2 represents the voltages applied to the respective semiconductor switching elements. The applied voltage V31 of the semiconductor switching element 31 is positive on the DC power supply side, and the applied voltage V32 of the semiconductor switching element 32 is positive on the AC filter side. Also, V204 is the voltage waveform of the output point 204 viewed from the ground potential.

[0033] The control circuit 12 turns on and off a plurality of semiconductor switching elements 31, 32, for example, at the commercial frequency (50 Hz or 60 Hz) according to the polarity of the AC voltage. As a result, the potential V204 of the output point 204 changes stepwise.

[0034] When the AC voltage Vout is positive, the potential V204 is 0 due to the on state of the semiconductor switching element 32. Therefore, the control circuit 12 controls the gate commands of the semiconductor switching elements 21, 22 of the flying capacitor circuit so that the potential V203 of the output point 203 becomes sinusoidal between the three levels of 0 to Edc. On the other hand, when the AC voltage Vout is negative, the potential V204 is Edc due to the on state of the semiconductor switching element 31. At this time, the control circuit 12 controls the gate commands of the semiconductor switching elements 21, 22 of the flying capacitor circuit with an offset of Edc in advance so that the difference between the potential V203 and the potential V204 becomes sinusoidal between the three levels of 0 to -Edc.

[0035] The control circuit 12 increases or decreases the voltage at the output point 204 stepwise (= DC voltage / number of elements in one arm. In the circuit of FIG. 3, Edc / 2) by shifting the ON signal of the gates of the semiconductor switching elements connected in series. Thereby, dV / dt can be suppressed. In FIG. 6, the control circuit 12 suppresses dV / dt by shifting the turn-on timing of the gate signal at both point A and point B to increase or decrease the voltage at the output point 204 by Edc / 2 each time.

[0036] FIG. 7 is a diagram showing the current path at point A (corresponding to (a) to (d) in FIG. 6). Also, in order to show the current path, FIG. 7 shows a diagram in which a diode whose illustration is omitted in FIG. 4 is connected in anti-parallel to the semiconductor switching element. Hereinafter, each state will be described.

[0037] (a): Since the semiconductor switching element 31 is OFF and the semiconductor switching element 32 is ON, the voltage at the output point 204 becomes 0. Also, a positive current is flowing (assuming the direction of the current flowing from the output point 204 to the DC power supply 10 (input point 202) as positive).

[0038] (a) ⇒ (b): At this timing, the direction of the current changes from positive to negative.

[0039] (b): This period is a dead time period for preventing power supply short circuit. Since the semiconductor switching element 32 is turned off, the current flows through the diode connected in anti-parallel to the semiconductor switching element 32, and the voltage at the output point 204 becomes 0.

[0040] (c): When the semiconductor switching element 31 2 is turned on, the current path changes. At this time, since it passes through the capacitor 33, the voltage at the output point 204 becomes Edc / 2.

[0041] (d): When the semiconductor switching element 31 1 is turned on, the current passes through two elements of the semiconductor switching element 31. Therefore, the voltage at the output point 204 becomes Edc.

[0042] Thus, in the transition from (c) to (d), the control circuit 12 turns on these semiconductor switching elements 31 2 , 31 1 in this order.

[0043] FIG. 8 is a diagram showing the current path at point B (corresponding to (e) to (h) in FIG. 6). Further, FIG. 8 shows the current path as a diagram in which a diode omitted in FIG. 4 is connected in anti-parallel to the semiconductor switching element. Hereinafter, each state will be described.

[0044] (e): Since the semiconductor switching element 31 is on and the semiconductor switching element 32 is off, the voltage at the output point 204 becomes Edc. Also, a negative current is flowing.

[0045] (e) ⇒ (f): At this timing, the direction of the current changes from negative to positive.

[0046] (f): This period is a dead time period for preventing a power short circuit. Since the semiconductor switching element 31 is turned off, the current flows through the diode connected in anti-parallel to the semiconductor switching element 31, and the voltage at the output point 204 remains Edc.

[0047] (g): When the semiconductor switching element 32 1 turns on, the current path changes. At this time, since it passes through the capacitor 33, the voltage at the output point 204 becomes Edc / 2.

[0048] (h): When the semiconductor switching element 32 2 turns on, the current passes through the two elements of the semiconductor switching element 32. Therefore, the voltage at the output point 204 becomes 0.

[0049] Thus, in the transition from (g) to (h), the control circuit 12 turns on these semiconductor switching elements 32 1 , 32 2 in this order.

[0050] In the description of FIG. 6, as an example, when at point A, the order of turning on the semiconductor switching element 31 is 31 2 →31 1 in this order (the order from the input point 201 to the output point 204). However, when at point A, even if the order of turning on the semiconductor switching element 31 is reversed to 31 1 →31 2 (the order from the output point 204 to the input point 201), the voltage at the output point 204 rises by Edc / 2 every time, and the same result can be obtained. Similarly at point B, even if the order of turning on the semiconductor switching element 32 is reversed to 32 2 →32 1 (the order from the output point 204 to the input point 202), the voltage at the output point 204 decreases by Edc / 2 every time, and the same result can be obtained.

[0051] Also, even if the number of series-connected semiconductor switching elements 31 and 32 in the low-frequency conversion circuit 30 is 3 or more, the same result can be obtained. In this case as well, the semiconductor switching elements on the DC power supply 10 side can be turned on in order from the semiconductor switching element on the DC power supply 10 side to the semiconductor switching element on the AC filter 11 side, or from the semiconductor switching element on the AC filter 11 side to the semiconductor switching element on the DC power supply 10 side.

[0052] <Second Example of dV / dt Suppression Control> In the first example of suppression control, it is control based on the premise that the power factor is 1 and the positive and negative of the AC current change at the zero-crossing point of the AC voltage. However, there may be a case where the current lags and the positive and negative of the AC current do not change at the zero-crossing point of the AC voltage. At this time, even if the operation of the first example of suppression control is performed, the dV / dt suppression effect is small. In the second example of suppression control, the dV / dt of the voltage at the output point 204 is suppressed by shifting the off timing of the gate signal.

[0053] Figure 9 shows the operating waveforms when applying suppression control to dV / dt by shifting the off-timing of the gate signal at the zero-crossing points (points A and B in Figure 5). The meanings of the symbols in the figure are the same as those in Figure 6. In Figure 9, by shifting the turn-off timing of the gate signal at both point A and point B, the voltage at the output point 204 is increased or decreased by Edc / 2 each time, thereby suppressing dV / dt.

[0054] Figure 10 shows the current path at point A (corresponding to (a) to (d) in Figure 9). Also, in order to show the current path, Figure 10 shows a diagram in which the diodes omitted in Figure 4 are connected in anti-parallel to the semiconductor switching elements. Hereinafter, each state will be described.

[0055] (a): Since the semiconductor switching element 31 is off and the semiconductor switching element 32 is on, the voltage at the output point 204 becomes 0. Also, a positive current is flowing (assuming the direction of the current flowing from the output point 204 to the DC power supply 10 (input point 202) as positive).

[0056] (b): When the semiconductor switching element 32 2 is turned off, since a positive current is flowing, current flows through the diode connected in anti-parallel to the semiconductor switching element 31 2 . At this time, since it passes through the capacitor 33, the voltage at the output point 204 becomes Edc / 2.

[0057] (c): This period is a dead time period for preventing power supply short circuit. At this time, when the semiconductor switching element 32 1 is turned off, the current passes through the diode connected in anti-parallel to the semiconductor switching element 31. Therefore, the voltage at the output point 204 becomes Edc.

[0058] (d): When the semiconductor switching element 31 is turned on, the current starts to flow through the semiconductor switching element 31, and the voltage at the output point 204 remains unchanged at Edc. Also, after this, even when the current becomes negative, the current flows through the semiconductor switching element 31, and the voltage at the output point 204 remains unchanged at Edc.

[0059] Thus, in the transition from (b) to (c), the control circuit 12 turns off these semiconductor switching elements 32 2 , 32 1 in this order.

[0060] FIG. 11 shows the current path at point B (corresponding to (e) to (h) in FIG. 9). Further, FIG. 11 shows the current path as a diagram in which the diodes omitted in FIG. 4 are connected in anti-parallel to the semiconductor switching elements. Hereinafter, each state will be described.

[0061] (e): Since the semiconductor switching element 31 is on and the semiconductor switching element 32 is off, the voltage at the output point 204 becomes Edc. Also, a negative current is flowing.

[0062] (f): When the semiconductor switching element 31 1 is turned off, since a negative current is flowing, current flows through the diode connected in anti-parallel to the semiconductor switching element 32 1 . At this time, since it passes through the capacitor 33, the voltage at the output point 204 becomes Edc / 2.

[0063] (g): This period is a dead time period for preventing power supply short circuit. At this time, when the semiconductor switching element 31 2 is turned off, the current passes through the diode connected in anti-parallel to the semiconductor switching element 32. Therefore, the voltage at the output point 204 becomes 0.

[0064] (h): When the semiconductor switching element 32 is turned on, the current starts to flow through the semiconductor switching element 32, and the voltage at the output point 204 remains 0. Also, after this, even when the current becomes positive, the current flows through the semiconductor switching element 32, and the voltage at the output point 204 remains 0.

[0065] Thus, in the transition from (g) to (h), the control circuit 12 turns off the semiconductor switching elements 31 1 , 312 Turn off these elements in the order of

[0066] In the description of FIG. 9, as an example, when at point A, the order of turning off the semiconductor switching element 32 is 32 2 →32 1 in this order (the order from the input point 202 to the output point 204). However, when at point A, even if the order of turning off the semiconductor switching element 32 is reversed to 32 1 →32 2 (the order from the output point 204 to the input point 202), the voltage at the output point 204 rises by Edc / 2 every time, and a similar result can be obtained. Similarly, at point B, even if the order of turning off the semiconductor switching element 31 is reversed to 31 2 →31 1 (the order from the input point 202 to the output point 204), the voltage at the output point 204 decreases by Edc / 2 every time, and a similar result can be obtained.

[0067] Also, even if the number of series-connected semiconductor switching elements 31 and 32 in the low-frequency conversion circuit 30 is 3 or more, a similar result can be obtained. In this case as well, the order of turning off may be from the semiconductor switching element on the DC power supply 10 side to the semiconductor switching element on the AC filter 11 side, or from the semiconductor switching element on the AC filter 11 side to the semiconductor switching element on the DC power supply 10 side.

[0068] Note that in the first example of the suppression control, the turning-off timing is performed simultaneously, and in the second example of the suppression control, the turning-on timing is performed simultaneously. However, in preparation for the case where the positive and negative states of the current are unknown, control may be performed to shift both the turning-off timing and the turning-on timing (it may also be a control combining the first and second examples of the suppression control).

[0069] Although the embodiments have been described above, the technology of the present disclosure is not limited to the above embodiments. Various modifications and improvements such as combinations or substitutions with part or all of other embodiments are possible.

Description of Reference Numerals

[0070] 1 Power conversion device 2 Flying capacitor totem pole circuit 10 DC power supply 11 AC filter 12 Control circuit 13, 14 Connection part 20 Flying capacitor circuit 21, 22 Semiconductor switching element 25 Capacitor 26 First wiring 27 Second wiring 28 Third wiring 30 Low-frequency conversion circuit 31, 32 Semiconductor switching element 33 Capacitor 201, 202 Input point 203, 204 Output point

Claims

1. A power conversion device for converting direct current to alternating current or alternating current to direct current, comprising: a first input point and a second input point which are a pair of direct current input points; a first output point; a second output point; a first flying capacitor circuit connected between the pair of direct current input points and the first output point; a second flying capacitor circuit connected between the pair of direct current input points and the second output point; an AC filter connected to the first output point and the second output point; a control circuit, wherein the first flying capacitor circuit includes a plurality of semiconductor switching elements and at least one capacitor; wherein the second flying capacitor circuit includes a plurality of first semiconductor switching elements connected in series between the first input point and the second output point; a plurality of second semiconductor switching elements connected in series between the second input point and the second output point; at least one first connection portion connecting adjacent elements among the plurality of first semiconductor switching elements; at least one second connection portion connecting adjacent elements among the plurality of second semiconductor switching elements; and at least one capacitor connected between a paired first connection portion and second connection portion among the at least one first connection portion and the at least one second connection portion; wherein the plurality of first semiconductor switching elements and the plurality of second semiconductor switching elements are elements that switch so that the polarity of the alternating voltage changes; and the control circuit turns on the plurality of first semiconductor switching elements or the plurality of second semiconductor switching elements in the order from the direct current input point to the second output point or in the order from the second output point to the direct current input point when switching the polarity. A power conversion device.

2. When the potential of the second output point transitions between the potential of the first input point and the potential of the second input point, the control circuit turns on the plurality of first semiconductor switching elements or the plurality of second semiconductor switching elements in the order from the direct current input point to the second output point or in the order from the second output point to the direct current input point. The power conversion device according to Claim 1.

3. The control circuit After turning off the plurality of second semiconductor switching elements in the order from the DC input point to the second output point or in the order from the second output point to the DC input point, the plurality of first semiconductor switching elements are turned on in the order from the DC input point to the second output point or in the order from the second output point to the DC input point. Or After turning off the plurality of first semiconductor switching elements in the order from the DC input point to the second output point or in the order from the second output point to the DC input point, the plurality of second semiconductor switching elements are turned on in the order from the DC input point to the second output point or in the order from the second output point to the DC input point. The power conversion device according to claim 1 or 2.

4. A power conversion device that converts DC to AC or AC to DC, A first input point and a second input point, which are a pair of DC input points, A first output point, A second output point, A first flying capacitor circuit connected between the pair of DC input points and the first output point, A second flying capacitor circuit connected between the pair of DC input points and the second output point, An AC filter connected to the first output point and the second output point, A control circuit, and comprising, The first flying capacitor circuit, Includes a plurality of semiconductor switching elements and at least one capacitor, The second flying capacitor circuit, A plurality of first semiconductor switching elements connected in series between the first input point and the second output point, A plurality of second semiconductor switching elements connected in series between the second input point and the second output point, At least one first connection portion connecting adjacent elements among the plurality of first semiconductor switching elements, At least one second connection portion connecting adjacent elements among the plurality of second semiconductor switching elements, Among the at least one first connection portion and the at least one second connection portion, at least one capacitor connected between the paired first connection portion and the second connection portion, The plurality of first semiconductor switching elements and the plurality of second semiconductor switching elements are elements that switch so that the polarity of the AC voltage is switched. When switching the polarity, the control circuit turns off the plurality of first semiconductor switching elements or the plurality of second semiconductor switching elements in the order from the DC input point to the second output point or in the order from the second output point to the DC input point. Power conversion device.

5. When the potential of the second output point transitions between the potential of the first input point and the potential of the second input point, the control circuit turns off the plurality of first semiconductor switching elements or the plurality of second semiconductor switching elements in the order from the DC input point to the second output point or in the order from the second output point to the DC input point. The power conversion device according to claim 4.

6. A control method for a power conversion device that converts DC to AC or AC to DC, wherein the power conversion device includes a first input point and a second input point which are a pair of DC input points, a first output point, a second output point, a first flying capacitor circuit connected between the pair of DC input points and the first output point, a second flying capacitor circuit connected between the pair of DC input points and the second output point, an AC filter connected to the first output point and the second output point, and a control circuit. The first flying capacitor circuit includes a plurality of semiconductor switching elements and at least one capacitor. The second flying capacitor circuit includes a plurality of first semiconductor switching elements connected in series between the first input point and the second output point, a plurality of second semiconductor switching elements connected in series between the second input point and the second output point, at least one first connection portion connecting adjacent elements among the plurality of first semiconductor switching elements, at least one second connection portion connecting adjacent elements among the plurality of second semiconductor switching elements, and at least one capacitor connected between a paired first connection portion and second connection portion among the at least one first connection portion and the at least one second connection portion. When switching the plurality of first semiconductor switching elements and the plurality of second semiconductor switching elements so that the polarity of the AC voltage is switched, When switching the polarity, turning on the plurality of first semiconductor switching elements or the plurality of second semiconductor switching elements in the order from the DC input point to the second output point or in the order from the second output point to the DC input point. A control method for a power conversion device.

7. A control method for a power conversion device that converts DC to AC or AC to DC, wherein the power conversion device comprises a first input point and a second input point which are a pair of DC input points, a first output point, a second output point, a first flying capacitor circuit connected between the pair of DC input points and the first output point, a second flying capacitor circuit connected between the pair of DC input points and the second output point, an AC filter connected to the first output point and the second output point, and a control circuit. The first flying capacitor circuit includes a plurality of semiconductor switching elements and at least one capacitor. The second flying capacitor circuit comprises a plurality of first semiconductor switching elements connected in cascade between the first input point and the second output point, a plurality of second semiconductor switching elements connected in cascade between the second input point and the second output point, at least one first connection portion connecting adjacent elements among the plurality of first semiconductor switching elements, at least one second connection portion connecting adjacent elements among the plurality of second semiconductor switching elements, and at least one capacitor connected between a paired first connection portion and second connection portion among the at least one first connection portion and the at least one second connection portion. When switching the plurality of first semiconductor switching elements and the plurality of second semiconductor switching elements so that the polarity of the AC voltage is switched, when switching the polarity, turning off the plurality of first semiconductor switching elements or the plurality of second semiconductor switching elements in the order from the DC input point to the second output point or in the order from the second output point to the DC input point. A control method for a power conversion device.

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