Power Conversion Equipment

Abstract

To provide power conversion equipment of which the miniaturization and improved cooling performance can be materialized.SOLUTION: Power conversion equipment for converting a direct current to an alternating current or an alternating current to a direct current comprises: a flying capacitor circuit connected between a pair of DC input points and a first output point; a low frequency conversion circuit connected between the 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 substrate having a first surface and a second surface opposite the first side, the flying capacitor circuit includes a first switching element group including a plurality of cascaded semiconductor switching elements and at least one first capacitor, and the low frequency conversion circuit includes a second switching element group including a plurality of cascaded semiconductor switching elements, and the first switching element group and the second switching element group are arranged on the first surface.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to a power conversion device. [Background technology]

[0002] In recent years, in response to environmental issues, there is an increasing demand for power conversion devices to be more efficient and compact. To meet such demands, multilevel power conversion devices capable of outputting three or more voltage values ​​are 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 shows 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-Sp6, Sn1-Sn6 and 5 flying capacitors FC1-FC5. Note that FC3, FC4 and Sp3-Sp5, Sn3-Sn5 are omitted in FIG. 1. Also, Lac and Cac are AC filters. By adding or subtracting different voltage values ​​held in each flying capacitor by switching each semiconductor switching element, the output voltage VL can be controlled to a 7-level AC voltage.

[0004] However, because the circuit shown in Fig. 1 has a half-bridge configuration, it requires a DC voltage that is approximately twice the output AC voltage. For example, if the AC voltage is 200V, a DC voltage Edc of approximately 800V (±400V) is required. To handle higher voltages, it is necessary to increase the number of semiconductor switching elements and capacitors connected in series, which may result in a larger device and higher costs.

[0005] As a circuit that addresses such a problem, a mixed-bridge flying capacitor type multilevel circuit (hereinafter also referred to as a flying capacitor totem pole circuit) is known (for example, see Non-Patent Document 1).

[0006] 2 is a configuration diagram of a flying capacitor totem pole circuit, and shows a four-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 P) and an AC terminal U, and a low-frequency conversion circuit connected between the DC input terminal (between P and P) 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 and FC2. The low-frequency conversion circuit is composed of semiconductor switching elements Sp and Sn.

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

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

[0009] Therefore, the output voltage range at output point 103 of the flying capacitor circuit is four levels, from 0 to Edc, so that the same voltage level can be achieved with half the number of series connections compared to a conventional half-bridge seven-level inverter circuit. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] International Publication No. 2015 / 037537 [Non-patent literature]

[0011] [Non-Patent Document 1] Qingyun Huang and others, ``3kW Four-Level Flying Capacitor Totem-Pole Bridgeless PFC Rectifier with 200V GaN Devices'', 2019 IEEE Energy Conversion Congress and Exposition (ECCE), Baltimore, MD, USA, 2019, pp.81-88, DOI:10.1109 / ECCE.2019.8913025. Summary of the Invention [Problem to be solved by the invention]

[0012] In a conventional low-frequency conversion circuit using a flying capacitor totem pole circuit, as shown in Fig. 2, two semiconductor switching elements Sp and Sn are connected in parallel, so heat is concentrated in each of the semiconductor switching elements Sp and Sn. As a countermeasure against heat generation, it is possible to reduce the on-resistance of each of the semiconductor switching elements Sp and Sn by configuring each of the semiconductor switching elements Sp and Sn as a parallel configuration of multiple switching elements. However, if a package according to the withstand voltage of the DC voltage Edc is adopted, there is a risk that the element cost and device size will increase depending on the number of parallel connections.

[0013] The present disclosure provides a power conversion device that can achieve miniaturization and improved cooling performance. [Means for solving the problem]

[0014] In one aspect of the present disclosure, A power conversion device for converting DC to AC or AC to DC, A pair of DC input points, a first input point and a second input point; A first output point; A second output point; and a flying capacitor circuit connected between the pair of DC input points and the first output point, for shifting a potential of the first output point; a low-frequency conversion circuit connected between the pair of DC input points and the second output point, the low-frequency conversion circuit shifting the potential of the second output point at a frequency lower than a frequency at which the potential of the first output point is shifted; an AC filter connected to the first output point and the second output point; a substrate having a first surface and a second surface opposite the first surface; the flying capacitor circuit includes a first switching element group including a plurality of semiconductor switching elements connected in cascade and at least one first capacitor; the low-frequency conversion circuit includes a second switching element group including a plurality of semiconductor switching elements connected in cascade; A power conversion device is provided, wherein the first group of switching elements and the second group of switching elements are arranged on the first surface. Effect of the Invention

[0015] According to one aspect of the present disclosure, miniaturization and improved cooling performance can be achieved. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 illustrates a prior art flying capacitor inverter. [Diagram 2] FIG. 1 illustrates a prior art flying capacitor totem pole circuit. [Diagram 3] FIG. 1 is a diagram showing operational waveforms of a flying capacitor totem pole circuit according to the prior art; [Figure 4]1 is a diagram illustrating an example of a circuit configuration of a power conversion device including a flying capacitor totem pole circuit according to a first embodiment. [Diagram 5] 1 is a perspective view showing an example of mounting a flying capacitor totem pole circuit on a substrate according to a first embodiment; [Figure 6] 1 is a diagram (cross-sectional view) showing an example of mounting the flying capacitor totem-pole circuit on a substrate according to a first embodiment. FIG. [Figure 7] 3A to 3C are diagrams illustrating an example of a cooling structure when the flying capacitor totem pole circuit according to the first embodiment is mounted on a substrate. [Figure 8] FIG. 11 is a diagram illustrating an example of a circuit configuration of a power conversion device including a flying capacitor totem pole circuit according to a second embodiment. [Figure 9] FIG. 11 is a perspective view showing an example of mounting a flying capacitor totem pole circuit on a substrate according to a second embodiment. [Figure 10] FIG. 11 is a diagram (cross-sectional view) showing an example of mounting a flying capacitor totem-pole circuit on a substrate according to a second embodiment. [Figure 11] 11A to 11C are diagrams illustrating an example of a cooling structure when a flying capacitor totem pole circuit according to a second embodiment is mounted on a substrate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] An embodiment will be described below.

[0018] First Embodiment Fig. 4 is a diagram showing an example of a power conversion device according to the first embodiment. The power conversion device 1 shown in Fig. 4 has a seven-level output inverter configuration similar to the conventional circuit (Fig. 2). The difference between the power conversion device 1 (Fig. 1) and the conventional circuit (Fig. 2) is that semiconductor switching elements 31 and 32 are connected in cascade in a low-frequency conversion circuit 30. The configuration of the power conversion device 1 will be described in more detail below.

[0019] 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 drive circuit 15. The flying capacitor totem pole circuit 2 has a flying capacitor circuit 20 and a low-frequency conversion circuit 30.

[0020] The input points 201 and 202 are an example 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.

[0021] Here, in the illustration of the semiconductor switching elements 21, 22, 31, and 32 used in the flying capacitor totem pole circuit 2, diodes (including diodes generated inside such as body diodes) connected in anti-parallel are omitted. In addition, the flying capacitor totem pole circuit 2 according to the present embodiment is, as an example, a 7-level inverter that outputs 7-level AC voltage as the pulse voltage VL, but may be a multilevel inverter having 5 or more levels. In addition, the power conversion device 1 may operate as a device that converts DC to AC, or may operate as a device that converts AC to DC.

[0022] The DC power supply 10 supplies DC power of a DC voltage Edc to the flying capacitor totem pole circuit 2 via a pair of DC input points, 201 and 202. The DC power supply 10 may be a rectifier circuit that converts AC supplied from a power system into DC. Note that one or more smoothing capacitors (not shown) that smooth 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.

[0023] The flying capacitor circuit 20 is connected between a pair of input points 201, 202 and an output point 203, and shifts the potential of the output point 203. The flying capacitor circuit 20 includes a plurality of semiconductor switching elements 21 (21 1 ,twenty one 2,twenty one 3 ), and a plurality of semiconductor switching elements 22 (22 1 ,twenty two 2 ,twenty two 3 ) and at least one capacitor 25 (25 1 ,twenty five 2 By adding or subtracting the voltage held by the capacitor 25, a multi-level voltage (5 levels in this embodiment) is applied to the output point 203 as viewed from the N potential.

[0024] A plurality of semiconductor switching elements 21 (21 1 ,twenty one 2 ,twenty one 3 ) and a plurality of semiconductor switching elements 22 (22 1 ,twenty two 2 ,twenty two 3 ) is an example of a first switching element group including a plurality of switching elements connected in series. 1 ,twenty one 2 ,twenty one 3 ) is an example of a first semiconductor switching element, and the plurality of semiconductor switching elements 22 (22 1 ,twenty two 2 ,twenty two 3 ) is an example of a second semiconductor switching element. At least one capacitor 25 (25 1 ,twenty five 2 ) is an example of a first capacitor.

[0025] The low-frequency conversion circuit 30 is connected between a pair of input points 201, 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 is shifted. The low-frequency conversion circuit 30 includes a plurality of semiconductor switching elements 31 (31) on the first wiring 26. 1 ,31 2 ,31 3 ), and a plurality of semiconductor switching elements 32 (32 1 ,32 2 ,32 3The low-frequency conversion circuit 30 turns on and off a plurality of semiconductor switching elements 31 and 32 at a commercial frequency (50 Hz or 60 Hz) according to the polarity of the AC voltage, for example.

[0026] A plurality of semiconductor switching elements 31 (31 1 ,31 2 ,31 3 ) and a plurality of semiconductor switching elements 32 (32 1 ,32 2 ,32 3 ) is an example of a second switching element group including a plurality of switching elements connected in cascade.

[0027] The multiple semiconductor switching elements 31 arranged on the first wiring 26 are an example of multiple third semiconductor switching elements, and are connected in cascade between the input point 201 and the output point 204. The multiple semiconductor switching elements 32 on the second wiring 27 are an example of multiple fourth semiconductor switching elements, and are connected in cascade between the input point 202 and the output point 204.

[0028] The number of semiconductor switching elements 31, 32 connected in series is determined arbitrarily depending on the magnitude of the DC voltage Edc and the withstand voltage of the element used. For example, in the case of a DC voltage of 400V, two elements with a withstand voltage of 300V may be connected in series, or three elements with a withstand voltage of 200V may be connected in series.

[0029] The packages of low-voltage devices are small and the on-resistance is also small, so even if the number of devices increases, the total on-resistance and size remain almost unchanged.

[0030] The AC filter 11 is connected to output points 203, 204 of the flying capacitor totem pole circuit 2. When the power conversion device 1 outputs AC power, the AC filter 11 converts the multilevel voltage output from the flying capacitor totem pole circuit 2 into a sine wave. 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] The drive circuit 15 includes a plurality of semiconductor switching elements 31 (31 1 ,31 2 ,31 3 ) and a plurality of semiconductor switching elements 32 (32 1 ,32 2 ,32 3 3. As a result, the potential V204 of the output point 204 changes in a step-like manner, similar to the potential V104 shown in FIG. 1 ,31 2 ,31 3 are driven by a common gate signal, and a plurality of semiconductor switching elements 32 1 ,32 2 ,32 3 are driven by a common gate signal.

[0033] The drive circuit 15 turns on and off the multiple semiconductor switching elements 31 and 32 at, for example, a 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 in a step-like manner, similar to the potential V104 shown in FIG.

[0034] When the AC voltage Vout is positive, the semiconductor switching element 32 is turned on and the potential V204 is 0. At this time, the drive circuit 15 controls the gate commands of the semiconductor switching elements 21 and 22 of the flying capacitor circuit so that the potential V203 of the output point 203 becomes sinusoidal between three levels from 0 to Edc. On the other hand, when the AC voltage Vout is negative, the semiconductor switching element 31 is turned on and the potential V204 is Edc. At this time, the drive circuit 15 controls the gate commands of the semiconductor switching elements 21 and 22 of the flying capacitor circuit by previously providing an offset of Edc so that the difference between the potential V203 and the potential V204 becomes sinusoidal between three levels from 0 to -Edc.

[0035] Since the loss in the semiconductor switching elements 31, 32 of the low-frequency arm is only the conduction loss, inexpensive Si (silicon) elements can be used for the semiconductor switching elements 31, 32 (however, a withstand voltage corresponding to the DC voltage Edc is required), thereby reducing the cost of the power conversion device 1.

[0036] In the flying capacitor totem pole circuit 2, the flying capacitor circuit 20 is operated at a high frequency, and the semiconductor switching elements 31 and 32 of the low-frequency conversion circuit 30 shift the potential of the AC end (output point 204). This reduces the number of switching elements 21 and 22 connected in series in the flying capacitor circuit 20 while miniaturizing the AC filter 11. In particular, by using low-voltage gallium nitride (GaN) elements that can operate at high speed and with low loss as the switching elements 21 and 22 to operate the flying capacitor circuit 20 at a high frequency, it is possible to miniaturize the capacitors 25. As a result, by configuring these circuits on a substrate, the power conversion device can be significantly reduced in size and thickness.

[0037] On the other hand, in order to operate the flying capacitor circuit 20 at high frequencies, it is necessary to minimize the distance between components, so cooling becomes an issue. 1 ,twenty one 2 ,twenty one 3 ) and the semiconductor switching element 22 (22 1 ,twenty two 2 ,twenty two 3 ) can disperse heat by using a low-voltage switching element for each of the low-frequency conversion circuit 30. 1 ,31 2 ,31 3 ) and the semiconductor switching element 32 (32 1 ,32 2 ,32 3 ) using low-voltage switching elements for each of these, it is possible to disperse heat.

[0038] 5 and 6 show a configuration example in which the seven-level flying capacitor totem pole circuit 2 and the AC filter 11 shown in FIG. 4 are mounted on a substrate 310. FIG. 5 is a perspective view in a plan view from above the substrate 310. FIG. 6 is a cross-sectional view of the substrate 310. The power conversion device 1 includes the substrate 310. The substrate 310 is, for example, a printed circuit board. The substrate 310 has a first main surface 313 and a second main surface 314 opposite to the first main surface 313.

[0039] On the first main surface 313, all of the semiconductor switching elements 21 (21 1 ,twenty one 2 ,twenty one 3 ),22(22 1 ,twenty two 2 ,twenty two 3 ),31(31 1 ,31 2 ,31 3 ),32(32 1 ,32 2 ,32 3 On the second main surface 314, components other than the semiconductor switching elements (flying capacitors 25 (25 1 ,twenty five 2 ), an AC filter 11 and a drive circuit 15, etc. are arranged.

[0040] The semiconductor switching elements 21 and 22 of the flying capacitor circuit 20 are two semiconductor switching elements (for example, 21 3 and 22 3 ,twenty one 2 and 22 2 ,twenty one 1 and 22 1 The gate signals of two corresponding elements are switched on or off in an opposite manner.

[0041] The semiconductor switching elements 21, 22 are arranged on the first main surface 313. On the other hand, the flying capacitor 25 is arranged on the second main surface 314, and is connected between the connection portion between adjacent switching elements 21 and the connection portion between adjacent switching elements 22 through a plurality of vias (not shown). This makes it possible to shorten the wiring between the elements, and reduce the surge voltage associated with switching.

[0042] The semiconductor switching elements 31, 32 of the low-frequency conversion circuit 30 are arranged in parallel and connected in cascade. As shown in Fig. 6, by arranging them in the space behind the AC filter 11, compactness can be achieved. As shown in Fig. 5, by arranging the flying capacitor circuit 20 and the low-frequency conversion circuit 30 on a straight line in a plan view, compactness can be achieved. Here, the number of switching elements in series of the low-frequency conversion circuit 30 is set to "3", the same as that of the flying capacitor circuit 20, and the switching elements are arranged at equal intervals, so that heat generation can be dispersed.

[0043] 6, semiconductor switching element 21 is arranged on a first line 16, and semiconductor switching element 22 is arranged on a second line 17 parallel to the first line 16. Semiconductor switching element 31 is arranged on a third line 18, and semiconductor switching element 32 is arranged on a fourth line 19 parallel to the third line 18.

[0044] In the example shown in Fig. 6, the first straight line 16 is collinear with the third straight line 18, but may be collinear with the fourth straight line 19. In the example shown in Fig. 6, the second straight line 17 is collinear with the fourth straight line 19, but may be collinear with the third straight line 18.

[0045] 7 is a diagram showing an example of a cooling structure by mounting the flying capacitor totem pole circuit according to the first embodiment on a board. The power conversion device 1 includes a thermal sheet 320 and a heat sink 300. The thermal sheet 320 is an example of a heat conductive part. The heat sink 300 contacts each surface of the semiconductor switching elements 21, 22, 31, and 32 via the thermal sheet 320. The semiconductor switching elements 21, 22, 31, and 32 are effectively cooled by dissipating heat from the surfaces of the semiconductor switching elements 21, 22, 31, and 32 to the heat sink 300 via the thermal sheet 320. The heat sink may be air-cooled or water-cooled.

[0046] Here, by using devices having the same height as the semiconductor switching elements 21, 22 of the flying capacitor circuit 20 for the semiconductor switching elements 31, 32 of the low-frequency conversion circuit 30, it is possible to align the heights of the heat sink 300 and the thermal sheet 320. This allows for a reduction in the number of steps required for the heat sink 300 and a reduction in cost.

[0047] As described above, according to the first embodiment, by configuring a plurality of low-voltage semiconductor switching elements connected in cascade in each of the upper and lower arms of the low-frequency conversion circuit 30, it is possible to disperse the semiconductor switching elements, which are heat sources. This makes it possible to cool each semiconductor switching element while suppressing increases in size and cost.

[0048] <Second embodiment> If the timing of turning on or off each semiconductor switching element connected in series is shifted, an imbalance occurs in the voltage applied to each semiconductor switching element, which may cause element destruction due to exceeding the withstand voltage. In the case where a plurality of semiconductor switching elements connected in series are configured in each of the upper and lower arms of the low-frequency conversion circuit 30, the technology according to the second embodiment suppresses the voltage imbalance, thereby improving the cooling performance and realizing a compact device. The second embodiment will be described below, but the description of the same configuration, action, and effect as the first embodiment will be omitted or simplified by invoking the above description.

[0049] FIG. 8 is a diagram showing an example of a power conversion device according to the second embodiment. The power conversion device 3 shown in FIG. 8 has a seven-level output inverter configuration similar to the conventional circuit (FIG. 2). The power conversion device 3 (FIG. 8) is different from the conventional circuit (FIG. 2) in that the semiconductor switching elements 31 and 32 are connected in series in the low-frequency conversion circuit 40, and at least one capacitor 33 (33) for preventing voltage imbalance is provided. 1 ,33 2 ) The configuration of the power conversion device 3 will be described in more detail below.

[0050] The power conversion device 3 includes a DC power supply 10, input points 201 and 202, a flying capacitor totem pole circuit 4, output points 203 and 204, an AC filter 11, and a drive circuit 15. The flying capacitor totem pole circuit 4 includes a flying capacitor circuit 20 and a low-frequency conversion circuit 40.

[0051] The low-frequency conversion circuit 40 has at least one capacitor 33 on a third wiring 28 that connects a connection point between the semiconductor switching elements 31 on the first wiring 26 and a connection point between the semiconductor switching elements 32 on the second wiring 27 .

[0052] The low-frequency conversion circuit 40 has connection parts 13, 14 connected via a capacitor 33 on the third wiring 28. The connection part 13 is an example of at least one first connection part that connects adjacent elements among the multiple semiconductor switching elements 31. The connection part 14 is an example of at least one second connection part that connects adjacent elements among the multiple semiconductor switching elements 32. The capacitor 33 is an example of at least one second capacitor connected between a pair of the first connection part and the second connection part among the at least one first connection part and the at least one second connection part.

[0053] Multiple capacitors 33 (33 1 ,33 2) has a different voltage value for each stage. For example, the voltage of the capacitor 331 is 1×Edc / 3, and the voltage of the capacitor 332 is 2×Edc / 3. When the semiconductor switching element 31 or 32 is switched, the voltage of the plurality of capacitors 33 is constant, so that the voltage applied when the semiconductor switching elements 31 and 32 are off is limited to about the rated voltage. The rated voltage here is a voltage obtained by dividing the DC voltage Edc by the number of elements in one arm, and corresponds to Edc / 3 in FIG. 8, for example. The size of the capacitor 33 in this embodiment is about the same as the size of a capacitor provided as a snubber capacitor, and the volume it occupies with respect to the entire power conversion device 3 is extremely small.

[0054] 9 and 10 show a configuration example in which the seven-level flying capacitor totem pole circuit 4 and the AC filter 11 shown in FIG. 8 are mounted on a substrate 310. FIG. 9 is a planar perspective view of the substrate 310 from above. FIG. 6 is a cross-sectional view of the substrate 310. The power conversion device 3 includes the substrate 310. The substrate 310 is, for example, a printed circuit board. The substrate 310 has a first main surface 313 and a second main surface 314 opposite to the first main surface 313.

[0055] On the first main surface 313, all of the semiconductor switching elements 21 (21 1 ,twenty one 2 ,twenty one 3 ),22(22 1 ,twenty two 2 ,twenty two 3 ),31(31 1 ,31 2 ,31 3 ),32(32 1 ,32 2 ,32 3 ) and a plurality of capacitors 33 (33 1 ,33 2 On the second main surface 314, components other than the semiconductor switching elements (flying capacitors 25 (25 1 ,twenty five 2 ), an AC filter 11 and a drive circuit 15, etc. are arranged.

[0056] 9 and 10, as an example, capacitor 33 is arranged on the same surface as semiconductor switching elements 21, 22, 31, and 32, but it may be arranged on the surface opposite to those semiconductor switching elements (the surface on which capacitor 25 and the like are arranged).

[0057] 11 is a diagram showing an example of a cooling structure by mounting a flying capacitor totem pole circuit according to the second embodiment on a board. The second embodiment has the same configuration as the first embodiment. However, as shown in FIG. 11, when the capacitor 33 is arranged on the same surface as the semiconductor switching elements 21, 22, 31, and 32, it is necessary to make the thickness of the capacitor 33 equal to or smaller than the thickness of the semiconductor switching elements 21, 22, 31, and 32. In this way, the capacitor 33 is arranged so as not to come into contact with the thermal sheet 320, so that it is possible to prevent heat from reaching the capacitor 33 via the thermal sheet 320.

[0058] In this way, according to the second embodiment, by configuring a plurality of low-voltage semiconductor switching elements connected in cascade in each of the upper and lower arms of the low-frequency conversion circuit 30, it is possible to disperse the semiconductor switching elements, which are heat sources. Therefore, it is possible to cool each semiconductor switching element while suppressing increases in size and cost.

[0059] Although the embodiments have been described above, the technology of the present disclosure is not limited to the above-described embodiments. Various modifications and improvements, such as combinations with or substitutions for part or all of other embodiments, are possible. [Explanation of symbols]

[0060] 1,3 Power conversion device 2,4 Flying Capacitor Totem Pole Circuit 10 DC power supply 11 AC Filter 12 Control circuit 13,14 Connection part 15 Drive circuit 16 1st straight line 17 Second straight line 18 3rd straight line 19 4th straight line 20 Flying Capacitor Circuit 21, 22 Semiconductor switching elements 25 Capacitor 26 First wiring 27 Second wiring 28 Third wiring 30 Low-frequency conversion circuit 31,32 Semiconductor switching elements 33 Capacitor 40 Low-frequency conversion circuit 201,202 input points 203,204 output points 300 Heatsink 310 Substrate 311 Copper foil 312 Insulating layer 313 First principal surface 314 Second principal surface 320 Thermal Sheet

Claims

1. A power conversion device for converting DC to AC or AC to DC, A pair of DC input points, a first input point and a second input point; A first output point; A second output point; and a flying capacitor circuit connected between the pair of DC input points and the first output point, for shifting a potential of the first output point; a low-frequency conversion circuit connected between the pair of DC input points and the second output point, the low-frequency conversion circuit shifting the potential of the second output point at a frequency lower than a frequency at which the potential of the first output point is shifted; an AC filter connected to the first output point and the second output point; a substrate having a first surface and a second surface opposite the first surface; The flying capacitor circuit includes a first switching element group including a plurality of semiconductor switching elements connected in cascade and at least one first capacitor; the low-frequency conversion circuit includes a second switching element group including a plurality of semiconductor switching elements connected in cascade; The first switching element group and the second switching element group are arranged on the first surface.

2. The first switching element group includes: a plurality of first semiconductor switching elements connected in cascade between the first input point and the first output point; a plurality of second semiconductor switching elements connected in cascade between the second input point and the first output point; The second switching element group includes: a plurality of third semiconductor switching elements connected in cascade between the first input point and the second output point; The power conversion device according to claim 1 , further comprising: a plurality of fourth semiconductor switching elements connected in cascade between the second input point and the second output point.

3. the plurality of first semiconductor switching elements are arranged on a first straight line, the second semiconductor switching elements are arranged on a second straight line parallel to the first straight line, the third semiconductor switching elements are arranged on a third straight line, The power conversion device according to claim 2 , wherein the plurality of fourth semiconductor switching elements are arranged on a fourth straight line parallel to the third straight line.

4. the first straight line is collinear with the third straight line or the fourth straight line, 4. The power conversion device according to claim 3, wherein the second straight line is collinear with the fourth straight line when the first straight line is collinear with the third straight line, and is collinear with the third straight line when the first straight line is collinear with the fourth straight line.

5. The power conversion device according to claim 1 , further comprising a heat sink in contact with each surface of the first switching element group and the second switching element group via a heat conductive part.

6. The low-frequency conversion circuit includes: at least one first connection portion connecting adjacent elements among the plurality of third semiconductor switching elements; at least one second connection portion connecting adjacent elements among the plurality of fourth semiconductor switching elements; 5. The power conversion device according to claim 2, further comprising: at least one second capacitor connected between a pair of the first connection portion and the second connection portion among the at least one first connection portion and the at least one second connection portion.

7. The power converter according to claim 6 , wherein the second capacitor is disposed on the first surface.

8. a heat sink in contact with each surface of the first switching element group and the second switching element group via a heat conductive component; The power conversion device according to claim 7 , wherein the second capacitor is arranged so as not to contact the heat conducting component.

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