JP7647376B2 - Power Conversion Equipment - Google Patents

Description

This disclosure relates to a power conversion device.

In recent years, in response to environmental issues, there has been an increasing demand for power conversion devices to be more efficient and compact. To meet these 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 these is a multilevel power conversion device that uses a flying capacitor circuit (see, for example, Patent Document 1).

Figure 1 shows an example of the configuration 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 Figure 1 is composed of 12 semiconductor switching elements Sp1 to Sp6, Sn1 to Sn6 and five flying capacitors FC1 to FC5. Note that FC3, FC4 and Sp3 to Sp5, Sn3 to Sn5 are omitted in Figure 1. Also, Lac and Cac are AC filters. By adding or subtracting the 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.

However, because the circuit shown in Figure 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 200 V, a DC voltage Edc of approximately 800 V (±400 V) is required. To handle higher voltages, it is necessary to increase the number of semiconductor switching elements and capacitors connected in series, which can lead to larger equipment and higher costs.

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

Figure 2 is a configuration diagram of a flying capacitor totem pole circuit, showing a four-level inverter configuration as an example. This flying capacitor totem pole circuit comprises a flying capacitor circuit connected between the DC input terminal (between P and N) and the AC terminal U, and a low-frequency conversion circuit connected between the DC input terminal (between P and N) and the 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.

Figure 3 shows an example of the operating waveforms of a 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-like manner.

When the AC voltage applied between the U and U 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, 0 to Edc. On the other hand, when the AC voltage applied between the U and U 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, 0 to -Edc.

Therefore, the output voltage range at the 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.

International Publication No. 2015/037537

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.

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 multiple switching elements in parallel. 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.

This disclosure provides a power conversion device that can achieve compact size and improved cooling performance.

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, in which the first group of switching elements and the second group of switching elements are arranged on the first surface.

According to one aspect of the present disclosure, it is possible to achieve miniaturization and improved cooling performance.

FIG. 1 illustrates a prior art flying capacitor inverter. FIG. 1 illustrates a prior art flying capacitor totem pole circuit. FIG. 1 is a diagram showing operational waveforms of a flying capacitor totem pole circuit according to the prior art. 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. FIG. 2 is a perspective view showing an example of mounting the flying capacitor totem pole circuit on a substrate according to the first embodiment; FIG. 2 is a diagram (cross-sectional view) showing an example of mounting the flying capacitor totem pole circuit on a substrate according to the first embodiment. 1A to 1C are diagrams illustrating an example of a cooling structure for mounting the flying capacitor totem pole circuit according to the first embodiment on a substrate. 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. FIG. 11 is a perspective view showing an example of a substrate mounting of a flying capacitor totem pole circuit according to a second embodiment. FIG. 11 is a cross-sectional view showing an example of mounting a flying capacitor totem pole circuit on a substrate according to a second embodiment. 13A to 13C are diagrams illustrating an example of a cooling structure for mounting a flying capacitor totem pole circuit according to a second embodiment on a substrate.

The following describes the embodiment.

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 series in the low-frequency conversion circuit 30. The configuration of the power conversion device 1 will be described in more detail below.

The power conversion device 1 includes a DC power supply 10, input points 201, 202, a flying capacitor totem pole circuit 2, output points 203, 204, an AC filter 11, and a drive circuit 15. The flying capacitor totem pole circuit 2 includes a flying capacitor circuit 20 and a low-frequency conversion circuit 30.

Input points 201 and 202 are an example of a pair of DC input points, where input point 201 is an example of a first input point and input point 202 is an example of a second input point. Output point 203 is an example of a first output point and output point 204 is an example of a second output point.

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 anti-parallel (including diodes generated inside such as body diodes) are omitted. In addition, the flying capacitor totem pole circuit 2 according to this embodiment is, as an example, a 7-level inverter that outputs 7 levels of AC voltage as the pulse voltage VL, but it may also be a multilevel inverter with 5 or more levels. In addition, the power conversion device 1 may operate as a device that converts DC to AC, or as a device that converts AC to DC.

The DC power supply 10 supplies DC power of DC voltage Edc to the flying capacitor totem pole circuit 2 via a pair of DC input points, input points 201 and 202. The DC power supply 10 may be a rectifier circuit that converts AC supplied from the power system to 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.

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 is a flying capacitor type multilevel circuit including a plurality of semiconductor switching elements 21 ( ₂₁₁ , ₂₁₂ , ₂₁₃ ), a plurality of semiconductor switching elements 22 ( ₂₂₁ , ₂₂₂ , ₂₂₃ ), and at least one capacitor 25 ( ₂₅₁ , ₂₅₂ ). By adding or subtracting the voltage held by the capacitor 25, a multilevel (five levels in this embodiment) voltage is applied to the output point 203 as viewed from the N potential.

The multiple semiconductor switching elements 21 ( ₂₁₁ , ₂₁₂ , ₂₁₃ ) and the multiple semiconductor switching elements 22 ( ₂₂₁ , ₂₂₂ , ₂₂₃ ) are an example of a first switching element group including multiple switching elements connected in cascade. The multiple semiconductor switching elements 21 ( ₂₁₁ , ₂₁₂ , ₂₁₃ ) are an example of first semiconductor switching elements, and the multiple semiconductor switching elements 22 ( ₂₂₁ , ₂₂₂ , ₂₂₃ ) are an example of second semiconductor switching elements. At least one capacitor 25 ( ₂₅₁ , ₂₅₂ ) is an example of a first capacitor.

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 has a plurality of semiconductor switching elements 31 ( ₃₁₁ , ₃₁₂ , ₃₁₃ ) on the first wiring 26, and a plurality of semiconductor switching elements 32 ( ₃₂₁ , ₃₂₂ , ₃₂₃ ) on the second wiring 27. The low-frequency conversion circuit 30 turns on and off the plurality of semiconductor switching elements 31, 32 at a commercial frequency (50 Hz or 60 Hz) depending on the polarity of the AC voltage, for example.

The multiple semiconductor switching elements 31 ( ₃₁₁ , ₃₁₂ , ₃₁₃ ) and the multiple semiconductor switching elements ₃₂ (321, ₃₂₂ , ₃₂₃ ) are an example of a second switching element group including multiple switching elements connected in cascade.

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.

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.

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

The AC filter 11 is connected to the 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.

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

The drive circuit 15 switches the multiple semiconductor switching elements 31 ( ₃₁₁ , ₃₁₂ , ₃₁₃ ) and the multiple semiconductor switching elements 32 ( ₃₂₁ , ₃₂₂ , ₃₂₃ ) in a complementary manner. 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. 3. For example, the drive circuit 15 drives the multiple semiconductor switching elements ₃₁₁ , ₃₁₂ , ₃₁₃ with a common gate signal, and drives the multiple semiconductor switching elements ₃₂₁ , ₃₂₂ , ₃₂₃ with a common gate signal.

The drive circuit 15 turns on and off multiple semiconductor switching elements 31 and 32 at, for example, a commercial frequency (50 Hz or 60 Hz) depending on 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. 3.

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 at 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 providing an offset of Edc in advance so that the difference between the potential V203 and the potential V204 becomes sinusoidal between three levels from 0 to -Edc.

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

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, 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, 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, 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 made smaller and thinner.

On the other hand, in order to operate the flying capacitor circuit 20 at high frequencies, it is necessary to configure the components with the shortest distance possible, so cooling becomes an issue. In the flying capacitor circuit 20, it is possible to disperse heat by using low-voltage switching elements for each of the semiconductor switching elements 21 ( ₂₁₁ , ₂₁₂ , ₂₁₃ ) and the semiconductor switching elements 22 ( ₂₂₁ , ₂₂₂ , ₂₂₃ ). In the low-frequency conversion circuit 30, it is also possible to disperse heat by using low-voltage switching elements for each of the semiconductor switching elements 31 ( ₃₁₁ , ₃₁₂ , ₃₁₃ ) and the semiconductor switching elements 32 ( ₃₂₁ , ₃₂₂ , ₃₂₃ ).

Figures 5 and 6 show an example of a configuration in which the seven-level flying capacitor totem pole circuit 2 and AC filter 11 shown in Figure 4 are mounted on a substrate 310. Figure 5 is a perspective view of the substrate 310 in a plan view from above. Figure 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.

All the semiconductor switching elements 21 ( ₂₁₁ , 212, 213), 22 (221, ₂₂₂ , ₂₂₃ ), 31 ( ₃₁₁ , ₃₁₂ , ₃₁₃ ), and 32 ( ₃₂₁ , ₃₂₂ , ₃₂₃ ) are arranged on the first main surface 313. Components other than _the semiconductor switching elements ( _{e.g., flying capacitors 25 (251 , 252} ), AC filter 11, and drive circuit 15) are arranged on _the second main surface 314.

The semiconductor switching elements 21 and 22 of the flying capacitor circuit 20 are arranged in parallel so that the distance between two semiconductor switching elements (e.g., ₂₁₃ and ₂₂₃ , ₂₁₂ and ₂₂₂ , ₂₁₁ and ₂₂₁ ) that perform complementary switching operation is minimized. Complementary switching operation refers to the gate signals of two corresponding elements switching in an opposite relationship of on or off.

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 via a number of vias (not shown). This allows the wiring between the elements to be shortened, and the surge voltage associated with switching to be reduced.

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, they can be arranged in the space behind the AC filter 11, thereby making the circuit more compact. As shown in FIG. 5, the flying capacitor circuit 20 and the low-frequency conversion circuit 30 can be arranged in a straight line in a plan view, thereby making the circuit more compact. Here, the number of switching elements in series in the low-frequency conversion circuit 30 is set to "3", the same as in the flying capacitor circuit 20, and the switching elements are arranged at equal intervals, thereby dispersing heat.

In FIG. 6, the semiconductor switching element 21 is arranged on a first straight line 16, and the semiconductor switching element 22 is arranged on a second straight line 17 parallel to the first straight line 16. The semiconductor switching element 31 is arranged on a third straight line 18, and the semiconductor switching element 32 is arranged on a fourth straight line 19 parallel to the third straight line 18.

In the example shown in FIG. 6, the first line 16 is collinear with the third line 18, but may also be collinear with the fourth line 19. In the example shown in FIG. 6, the second line 17 is collinear with the fourth line 19, but may also be collinear with the third line 18.

Figure 7 is a diagram showing an example of a cooling structure by mounting the flying capacitor totem pole circuit of 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.

Here, by using devices with the same height as the semiconductor switching elements 21 and 22 of the flying capacitor circuit 20 for the semiconductor switching elements 31 and 32 of the low-frequency conversion circuit 30, the heights of the heat sink 300 and the thermal sheet 320 can be aligned. This reduces the number of steps and the cost of the heat sink 300.

In this way, according to the first embodiment, by configuring multiple 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 distribute each semiconductor switching element, which is a heat source. Therefore, it is possible to cool each semiconductor switching element while suppressing increases in size and cost.

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 technology according to the second embodiment, when 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 voltage imbalance is suppressed, improving the cooling performance and reducing the size of the device. The second embodiment will be described below, but the description of the configuration, action, and effect similar to those of the first embodiment will be omitted or simplified by invoking the above description.

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 ₁ , 33 ₂ ) for preventing voltage imbalance is included. The configuration of the power conversion device 3 will be described in more detail below.

The power conversion device 3 includes a DC power supply 10, input points 201, 202, a flying capacitor totem pole circuit 4, output points 203, 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.

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

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.

The voltages of the multiple capacitors 33 (33 ₁ , 33 ₂ ) are different 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 multiple capacitors 33 are at a constant voltage, 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.

Figures 9 and 10 show an example of a configuration in which the seven-level flying capacitor totem pole circuit 4 and AC filter 11 shown in Figure 8 are mounted on a substrate 310. Figure 9 is a perspective view of the substrate 310 in a plan view from above. Figure 6 is a cross-sectional view of the substrate 310. The power conversion device 3 includes a 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.

All the semiconductor switching elements 21 ( ₂₁₁ , 212, 213), 22 (221, ₂₂₂ , ₂₂₃ ), 31 ( ₃₁₁ , ₃₁₂ , ₃₁₃ ), 32 ( ₃₂₁ , ₃₂₂ , ₃₂₃ ) and _a plurality of capacitors 33 ( ₃₃₁ , ₃₃₂ ) are arranged on the first main surface 313. Components other than _the semiconductor switching elements (e.g., flying capacitors 25 ( ₂₅₁ , ₂₅₂ ), the AC filter 11, and _the drive circuit 15) are arranged on the second main surface 314.

In the example shown in Figures 9 and 10, 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, etc. are arranged).

Figure 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 in Figure 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 less than the thickness of the semiconductor switching elements 21, 22, 31, and 32. In this way, by arranging the capacitor 33 so as not to come into contact with the thermal sheet 320, it is possible to prevent heat from reaching the capacitor 33 via the thermal sheet 320.

In this way, according to the second embodiment, by configuring multiple 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 distribute each semiconductor switching element, which is a heat source. Therefore, it is possible to cool each semiconductor switching element while suppressing increases in size and cost.

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 are possible, such as combinations or substitutions with part or all of other embodiments.

REFERENCE SIGNS LIST 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 portion 15 Drive circuit 16 First line 17 Second line 18 Third line 19 Fourth line 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 40 Low-frequency conversion circuit 201, 202 Input point 203, 204 Output point 300 Heat sink 310 Substrate 311 Copper foil 312 Insulating layer 313 First main surface 314 Second main surface 320 Thermal sheet

Claims (8)

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. 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. 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. 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. The power conversion device according to any one of claims 1 to 4, further comprising a heat sink that contacts each surface of the first switching element group and the second switching element group via a heat conductive component. 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. The power conversion device according to claim 6, wherein the second capacitor is disposed on the first surface. 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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