JP7547738B2 - Snubber circuit and power conversion device - Google Patents

Description

The present invention relates to a snubber circuit and a power conversion device.

Conventionally, various techniques have been proposed for reducing switching loss while preventing element destruction due to surge voltages (see, for example, Japanese Patent Application Laid-Open No. 2003-233634).
Patent Document 1: JP 2016-144340 A

In recent years, there has been a demand to further reduce switching losses.

In order to solve the above problem, a first aspect of the present invention provides a snubber circuit. The snubber circuit may have a positive capacitor, a first diode, and a negative capacitor connected in series between a positive terminal and a negative terminal, and may have N parallel charging paths (where N is an integer of 1 or more) that pass a current from the positive terminal side to the negative terminal side. The snubber circuit may have a second diode connected between a negative capacitor in a k-th charging path (where k is an integer of 0≦k<N) among the N charging paths and a positive capacitor or a positive terminal in the k+1-th charging path among the N charging paths, and may have N+1 parallel discharge paths that pass a current from the negative terminal side to the positive terminal side through at least one of the negative capacitor and the positive capacitor. The snubber circuit may have at least one auxiliary capacitor connected in parallel to at least one of the N first diodes included in the N charging paths and the N+1 second diodes included in the N+1 discharge paths. The capacitance of one of the at least one auxiliary capacitors may change depending on the applied voltage.

Each of the at least one auxiliary capacitor may have a capacitance that changes depending on the applied voltage.

An auxiliary capacitor whose capacitance changes depending on the applied voltage can have a smaller capacitance as the applied voltage increases.

The auxiliary capacitor, whose capacitance changes according to the applied voltage, may have a larger rate of change in capacitance according to the applied voltage than the positive and negative capacitors.

Auxiliary capacitors whose capacitance changes depending on the applied voltage may have a capacitance decrease of 10% or more with increasing applied voltage within the rated voltage range.

The auxiliary capacitor, whose capacitance changes depending on the applied voltage, may be a high dielectric constant capacitor.

The auxiliary capacitor, whose capacitance changes depending on the applied voltage, may be a ceramic capacitor.

The auxiliary capacitor, whose capacitance changes depending on the applied voltage, may have a barium titanate-based dielectric layer.

The capacitance of the auxiliary capacitor may be smaller than the capacitance of each positive capacitor and each negative capacitor.

The capacitance of the auxiliary capacitor may be 1/1000 to 1/100 of the capacitance of each positive capacitor and each negative capacitor.

Each auxiliary capacitor may be connected in parallel with either the first diode or the second diode.

Each auxiliary capacitor may be connected in parallel with either one of the N first diodes or each of the N+1 second diodes.

In a second aspect of the present invention, a power conversion device is provided. The power conversion device may include the snubber circuit of the first aspect. The power conversion device may include a switch circuit connected to the positive terminal and the negative terminal.

Note that the above summary of the invention does not list all of the necessary features of the present invention. Also, subcombinations of these features may also be inventions.

1 is a circuit diagram of a power conversion device 1 according to a first embodiment. 4 shows the current flow when the switching element 11 is turned off in the comparative example. 4 shows the current flow when the switching element 11 is turned on in the comparative example. The current flow in mode (1) is shown. The current flow in mode (2) is shown. The current flow in mode (3) is shown. The current flow in mode (4) is shown. The current flow in mode (5) is shown. This indicates the voltage applied to the switching element 11 when the switching element 11 is turned off and non-conductive. 1 shows a power conversion device 1A according to a second embodiment. 1 shows the current flow in mode (1 A). 3 shows the current flow in mode (2A). 3 shows the current flow in mode (3A). 3 shows the current flow in mode (4A). 3 shows the current flow in mode (5A). 13 shows operational waveforms when a switching element 11 is turned off in a power conversion device 1A according to a modified example.

The present invention will be described below through embodiments of the invention, but the following embodiments do not limit the invention according to the claims. Furthermore, not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention.

[1. First embodiment]
[1.1. Circuit configuration of power conversion device]
FIG. 1 is a circuit diagram of a power conversion device 1 according to the first embodiment. The power conversion device 1 is one phase of a circuit that converts DC power into multi-phase AC power. The power conversion device 1 outputs a converted voltage from the power output terminal 19 by switching the connection between each electrode of the power supply capacitor 10 and the power supply output terminal 19. The return path of the output AC current may be the power supply output terminal 19 of another phase. An inductive load (not shown) may be connected to the power supply output terminal 19. The power conversion device 1 includes a power supply capacitor 10, a switch circuit 3, and a snubber circuit 2. The power conversion device 1 may convert DC power into single-phase AC power by the switch circuit 3. In this case, the power conversion device 1 includes two power supply capacitors 10 connected in series, and the return path of the AC current output from the power supply output terminal 19 may be the midpoint of the power supply capacitor 10.

The power supply capacitor 10 functions as a DC power supply. One terminal of the power supply capacitor 10 is connected to a positive wiring 101, and the other terminal is connected to a negative wiring 102. Note that although one power supply capacitor 10 is illustrated in FIG. 1, the power conversion device 1 may be provided with multiple power supply capacitors 10 connected in series or parallel.

The switch circuit 3 is connected between the positive wiring 101 and the negative wiring 102. As a result, the switch circuit 3 is connected between the positive terminal 201 and the negative terminal 202 of the snubber circuit 2 described below. The switch circuit 3 according to this embodiment may be a DC/AC inverter, and has switching elements 11, 12 as the upper arm and the lower arm of the power conversion device 1, and free wheel diodes 13, 14.

The switching elements 11 and 12 are connected in series between the negative wiring 102 and the positive wiring 101. The switching elements 11 and 12 have drain terminals connected to the positive wiring 101 side and source terminals connected to the negative wiring 102 side. A gate drive circuit (not shown) is connected to the gate terminals of the switching elements 11 and 12, and controls the on/off of the switching elements 11 and 12. For example, the switching elements 11 and 12 may be controlled to be alternatively connected with a dead time in which both are off. The switching elements 11 and 12 may be controlled by a PWM method. A power supply output terminal 19 is connected to the midpoint of the switching elements 11 and 12.

The switching elements 11 and 12 may be silicon semiconductor elements based on silicon, or may be wide band gap semiconductor elements. A wide band gap semiconductor element is a semiconductor element with a larger band gap than a silicon semiconductor element, and is, for example, a semiconductor element containing SiC, GaN, diamond, gallium nitride material, gallium oxide material, AlN, AlGaN, or ZnO. The switching elements 11 and 12 may be MOSFETs, or may be semiconductor elements of other structures, such as IGBTs or bipolar transistors.

The free wheel diodes 13 and 14 are connected in inverse parallel to the switching elements 11 and 12 so that the positive wiring 101 side serves as the cathode. The free wheel diodes 13 and 14 may be Schottky barrier diodes. The free wheel diodes 13 and 14 may be silicon semiconductor elements or wide band gap semiconductor elements.

At least two of the switching elements 11, 12 and the free wheel diodes 13, 14 may be modularized as a semiconductor module 5. In the present embodiment, as an example, the switching elements 11, 12 and the free wheel diodes 13, 14 are modularized as a semiconductor module 5. In this case, the drain terminal of the positive switching element 11 may be the positive terminal 51 of the semiconductor module 5, and the source terminal of the negative switching element 12 may be the negative terminal 52 of the semiconductor module 5.

[1.1.1. Snubber circuit 2]
The snubber circuit 2 absorbs a surge voltage that occurs when the switching elements 11 and 12 cut off the current, thereby protecting each element of the power conversion device 1. The snubber circuit 2 may be connected between the positive side wiring 101 and the negative side wiring 102 via the positive side terminal 201 and the negative side terminal 202. Note that a wiring (for example, a wiring including the positive side wiring 101 and the negative side wiring 102) between the snubber circuit 2 and the power supply capacitor 10 may have a wiring inductance 1011 depending on the wiring length. Also, a wiring (for example, a wiring including the positive side wiring 101 and the negative side wiring 102) between the snubber circuit 2 and the switching elements 11 and 12 may have a wiring inductance 1012 depending on the wiring length.

The snubber circuit 2 has N parallel charge paths 21, N+1 parallel discharge paths 22, and at least one auxiliary capacitor 252. The number N is an integer equal to or greater than 1, and is 3 in this embodiment as an example. In this embodiment, the three charge paths 21 are described as a first charge path 21(1), a second charge path 21(2), and a third charge path 21(3) from the left side of the figure as an example. The four discharge paths 22 are described as a first discharge path 22(1), a second discharge path 22(2), a third discharge path 22(3), and a fourth discharge path 22(4) from the left side of the figure as an example.

Each charging path 21 has a positive side capacitor 211, a first diode 212, and a negative side capacitor 213 connected in series between the positive side terminal 201 and the negative side terminal 202. The positive side capacitor 211 and the negative side capacitor 213 each function as a snubber capacitor and may absorb an instantaneous surge voltage (for example, a surge voltage applied to the element for a period greater than 10 ns and less than 10 μs) that occurs when the switching elements 11 and 12 are driven. For example, the positive side capacitor 211 and the negative side capacitor 213 may suppress vibrations greater than 100 kHz and less than 100 MHz. For example, the positive side capacitor 211 and the negative side capacitor 213 may be a film capacitor or a multilayer ceramic capacitor.

The first diode 212 is disposed with its anode facing the positive terminal 201 and its cathode facing the negative terminal 202. This allows each charging path 21 to pass a current from the positive terminal 201 to the negative terminal 202.

Each discharge path 22 has a second diode 221. The second diode 221 is connected between the negative terminal 202 or the negative capacitor 213 in the k-th charge path 21 (where k is an integer such that 0≦k≦N) among the N charge paths 21, and the positive capacitor 211 or the positive terminal 201 in the k+1-th charge path 21 among the N charge paths 21. For example, the second diode 221 of the first discharge path 22(1) is connected between the negative terminal 202 and the positive capacitor 211 of the first charge path 21(1). The second diode 221 of the second discharge path 22(2) is connected between the negative capacitor 213 of the first charge path 21(1) and the positive capacitor 211 of the second charge path 21(2). The second diode 221 of the third discharge path 22(3) is connected between the negative capacitor 213 of the second charge path 21(2) and the positive capacitor 211 of the third charge path 21(3). The second diode 221 of the fourth discharge path 22(4) is connected between the negative capacitor 213 of the third charge path 21(3) and the positive terminal 201. The second diode 221 is arranged with its anode facing the kth charge path 21(k) or the negative terminal 202 and its cathode facing the k+1th charge path 21(k+1) or the positive terminal 201. As a result, each discharge path 22 passes a current from the negative terminal 202 to the positive terminal 201 via at least one of the negative capacitor 213 and the positive capacitor 211.

The wiring inductance of each charging path 21 may be smaller than the wiring inductance of each discharging path 22. For example, the wiring length of each charging path 21 may be shorter than the wiring length of each discharging path 22. As an example, the wiring length of each charging path 21 connecting the positive terminal 201 and the negative terminal 202 may be shorter than the wiring length of each discharging path 22 connecting the positive terminal 201 and the negative terminal 202.

The auxiliary capacitor 252 is connected in parallel to at least one of the N+1 second diodes 221 included in the N+1 discharge paths 22. In this embodiment, as an example, the snubber circuit 2 includes N+1 auxiliary capacitors 252, and each auxiliary capacitor 252 is connected in parallel to each of the N+1 second diodes 221.

The capacitance of each auxiliary capacitor 252 may be smaller than the capacitance of each positive side capacitor 211 and the capacitance of each negative side capacitor 213. For example, the capacitance of the auxiliary capacitor 252 may be 1/1000 to 1/100 of the capacitance of each positive side capacitor 211 and the capacitance of each negative side capacitor 213. The capacitances of each auxiliary capacitor 252 may be equal to each other or different.

The charging voltage of each auxiliary capacitor 252 may be lower than the charging voltage of the negative side capacitor 213 at the timing when the switching elements 11 and 12 cut off the current. This allows each auxiliary capacitor 252 to draw a current flowing from the positive terminal 201 toward the first diode 212.

[1.2. Operation of snubber circuit 2]
[1.2(1). Operation of snubber circuit according to comparative example]
Before describing the operation of the snubber circuit 2 according to this embodiment, the operation of a snubber circuit 200 according to a comparative example (see FIGS. 2 and 3) will be described. The snubber circuit 200 differs from the snubber circuit 2 in that the auxiliary capacitor 252 is not provided.

First, we will explain the operation when switching element 11 is turned off from a state in which switching element 11 is on and switching element 12 is off. When switching element 11 is on and switching element 12 is off, the output current flows through the power supply capacitor 10, the positive side wiring 101, the switching element 11, and the power supply output terminal 19. At this time, the output current flows through the wiring inductance 1012 and energy is stored.

Figure 2 shows the current flow when the switching element 11 is turned off from this state in a comparative example. Note that the dashed arrows in the figure indicate the current flow, and the solid arrows indicate the voltages of the power supply capacitor 10, the positive side capacitor 211, the negative side capacitor 213, etc., and the voltages generated by the wiring inductance 1012, etc.

When the switching element 11 is turned off, the output current is commutated and flows from the power supply capacitor 10 and the positive wiring 101 to the positive capacitor 211, the first diode 212, and the negative capacitor 213 of each charging path 21, and is output from the power supply output terminal 19 via the freewheeling diode 14. As a result, the current energy of the wiring inductance 1012 is absorbed by charging the positive capacitor 211 and the negative capacitor 213 of the charging path 21. Then, the output current is finally commutated to the path of the power supply capacitor 10, the negative wiring 102, the freewheeling diode 14, and the power supply output terminal 19. This completes the commutation associated with the turn-off operation of the switching element 11.

Figure 3 shows the current flow when switching element 11 is turned on again after the turn-off operation of switching element 11 has been completed in a comparative example.

When the switching element 11 is turned on again, the output current flowing through the power supply capacitor 10, the negative wiring 102, the free wheel diode 14, and the power supply output terminal 19 is diverted to the power supply capacitor 10, the negative wiring 102, the second diode 221 of each discharge path 22, the switching element 11, and the power supply output terminal 19, and the energy stored in the positive side capacitor 211 and/or the negative side capacitor 213 on the anode/cathode side of the second diode 221 during the turn-off operation is released. Then, the output current is finally diverted to the power supply capacitor 10, the positive side wiring 101, the switching element 11, and the power supply output terminal 19. This completes the diverting operation associated with the turn-on operation of the switching element 11.

Here, the voltages of the positive side capacitor 211 and the negative side capacitor 213 during the turn-off and turn-on operations of the switching element 11 will be described. The relationship between the voltages of the positive side capacitor 211 and the negative side capacitor 213 of each charging path 21 during the turn-off operation is expressed by the following formula (1). In the formula, E is the voltage of the power supply capacitor 10, and V _dc-off is the inter-terminal voltage between the positive side wiring 101 and the negative side terminal 202 during the turn-off operation. Furthermore, V _p(1) to V _p(3) are the voltages of the positive side capacitor 211 in the first charging path 21(1) to the third charging path 21(3). Furthermore, V _N(1) to V _N(3) are the voltages of the negative side capacitor 213 in the first charging path 21(1) to the third charging path 21(3).

E≦(V _p (1) + V _N (1))
=(V _p (2) + V _N (2))
=(V _p (3) + V _N (3))
=V _dc-off …(1)

The voltage relationship between the positive side capacitor 211 and the negative side capacitor 213 of each charging path 21 during a turn-on operation is expressed by the following formula (2): where V _dc-oN is the inter-terminal voltage between the positive side wiring 101 and the negative side terminal 202 during a turn-on operation.

E≧V _p (1)
=(V _N (1) + V _p (2))
=(V _N (2) + V _p (3))
= V _N (3)
=V _dc-oN ...(2)

From equations (1) and (2), the relationship between the voltages of each positive side capacitor 211 and each negative side capacitor 213 is expressed by the following equation (3) (see also the voltages shown in Figures 2 and 3). In this equation, Vdc is the terminal voltage between the positive side terminal 51 and the negative side terminal 52 in a steady state.

E=V _dc ≒V _p (1)
= V _N (3)
=1.5×V _p (2)
=1.5× _VN (2)
= 3 × V _N (1)
=3×V _p (3) …(3)

From equation (3), it can be seen that the charging voltage in each charging path 21 when the capacitor current is cut off (4E/3 as an example in FIG. 3) is higher than the discharging voltage in each discharging path 22 (E as an example in FIG. 3). Note that the same effect can be obtained in the turn-on and turn-off operations of the switching element 12 when the output current is in the opposite direction due to the symmetry of the circuit, so a detailed explanation is omitted.

The snubber circuit 200 according to the above comparative example is provided with N parallel charging paths 21 each having a positive side capacitor 211 and a negative side capacitor 213. Therefore, when the current is interrupted by the semiconductor module 5, the energy stored in the wiring inductance 1012 passes through each charging path 21 to charge the positive side capacitor 211 and the negative side capacitor 213 to a voltage higher than the voltage between the positive side wiring 101 and the negative side terminal 202. This prevents element destruction due to surge voltage.

The snubber circuit 200 is also provided with N+1 discharge paths 22 that pass current from the negative terminal 202 to the positive terminal 201 via at least one of the negative capacitor 213 and the positive capacitor 211. Therefore, when a current is passed by the semiconductor module 5, the energy stored in the positive capacitor 211 and the negative capacitor 213 is discharged, and the discharge voltage of each discharge path 22 drops to the voltage between the positive terminal 201 and the negative terminal 202.

Here, when the current is interrupted, the charging voltage in each of the N charging paths 21 is higher than the discharging voltage in each of the discharging paths 22, so the energy that has charged the charging paths 21 when the current is interrupted cannot further charge the charging paths 21 even if it is discharged by the discharging paths 22. Therefore, the energy that has charged the positive side capacitor 211 and the negative side capacitor 213 when the current is interrupted is charged and discharged by the resonant operation of the wiring inductance 1011 and the positive side capacitor 211 or the negative side capacitor 213, and is stored in the positive side capacitor 211 and the negative side capacitor 213 and regenerated without being consumed as circuit loss. This reduces circuit loss due to the resonant operation.

In this way, it is possible to prevent element destruction due to surge voltage when current is interrupted and reduce circuit loss, so that the allowable inductance of the wiring connected to the positive terminal 51 and the negative terminal 52 of the semiconductor module 5 can be increased. In other words, the degree of freedom in the wiring length of the positive wiring 101 and the negative wiring 102 can be increased.

As described above, in the comparative snubber circuit 200, the charging voltage in each charging path 21 when the current is interrupted is 4E/3 (V). Therefore, of the surge voltage that occurs instantaneously between the positive wiring 101 and the negative wiring 102, the voltage ΔV1 that occurs due to the wiring inductance 1012 is generated in a form that is added to 4E/3 (V) based on 4E/3 (V).

In contrast, when a single snubber capacitor is connected between the positive wiring 101 and the negative wiring 102, the charging voltage of the snubber capacitor is E (V), and the surge voltage, ΔV1, generated by the wiring inductance 1012, is generated in a form that is added to E (V). Therefore, in the snubber circuit 200 of the comparative example, the total surge voltage that is instantaneously generated between the positive wiring 101 and the negative wiring 102 due to the wiring inductance 1012, that is, the total voltage of the voltage ΔV1 and the base voltage, becomes larger than when a single snubber capacitor is connected between the positive wiring 101 and the negative wiring 102.

[1.2(2. Operation of the snubber circuit 2 according to this embodiment]
Next, an operation of the snubber circuit 2 according to the present embodiment will be described. Unless otherwise specified, the charging voltages of the positive side capacitor 211 and the negative side capacitor 213 in the snubber circuit 2 may be the same as those in the snubber circuit 200 described above.

When switching element 11 is on and switching element 12 is off, the output current flows through the power supply capacitor 10, the positive side wiring 101, the switching element 11, and the power supply output terminal 19. At this time, the output current flows through the wiring inductance 1012 and energy is accumulated. When switching element 11 is turned off from this state, current may flow through snubber circuit 2 in modes (1) to (5).

FIG. 4 shows the current flow in mode (1).
When the switching element 11 is turned off, the output current is commutated and flows from the power supply capacitor 10 and the positive side wiring 101 into each charging path 21. At this time, the charging voltage _Vm of each auxiliary capacitor 252 is lower than the charging voltage _Vn of the negative side capacitor 213, and in this embodiment, it is 0 (V) as an example. Therefore, the current that has flowed into the positive side capacitor 211 of the charging path 21 flows toward the auxiliary capacitor 252, rather than toward the first diode 212 and the negative side capacitor 213. As a result, the current energy of the wiring inductance 1012 is absorbed by charging the positive side capacitor 211 and the auxiliary capacitor 252.

Thus, in the snubber circuit 2 according to this embodiment, in the initial stage when the current is interrupted, the series circuit of the positive side capacitor 211 and the auxiliary capacitor 252 functions as a charging path (also called a bypass charging path), and the charging voltage in each bypass charging path is E(V). Therefore, the voltage ΔV1 of the surge voltage generated by the wiring inductance 1012 is generated in a form that is added to E(V) with E(V) as the base.

The voltage _Vm of the auxiliary capacitor 252 may rise up to E/3 (V).

As a result, the total voltage of the positive side capacitor 211 and auxiliary capacitor 252 in series with the negative side capacitor 213 in the detouring charging path rises to the voltage of the positive side capacitor 211 in series in the same charging path 21 as the negative side capacitor 213. As an example, the total voltage of the voltage 2E/3 (V) of the positive side capacitor 211 in the detouring charging path including the positive side capacitor 211 in charging path 21(2) and the negative side capacitor 213 in charging path 21(1) and the voltage V _m (V) of the auxiliary capacitor 252 rises to the voltage E (V) of the positive side capacitor 211 in charging path 21(1).

In other words, the total voltage of the negative capacitor 213 and auxiliary capacitor 252 in the bypass charging path into which current flows from the positive capacitor 211 rises to the voltage of the negative capacitor 213 in the same charging path 21 as the positive capacitor 211. As an example, the total voltage of the voltage E/3 (V) of the negative capacitor 213 in the bypass charging path into which current flows from the positive capacitor 211 of charging path 21(2) and the auxiliary capacitor (V) rises to the voltage 2E/3 (V) of the negative capacitor 213 in charging path 21(2).

As a result, the voltage between the positive wiring 101 and the negative wiring 102 increases from E (V) to 4E/3 (V).

5 shows the current flow in mode (2). When the voltage _Vm of the auxiliary capacitor 252 reaches E/3 (V), the potential of the anode side of the first diode 212 in each charging path 21 becomes higher than the cathode side, and the first diode 212 becomes conductive, and the current flowing into the positive side capacitor 211 of the charging path 21 flows into the negative side capacitor 213, which has a larger capacity than the auxiliary capacitor 252. As a result, the current energy of the wiring inductance 1012 is absorbed by charging the positive side capacitor 211 and the negative side capacitor 213. Note that the current flowing into the positive side capacitor 211 may also flow slightly into the auxiliary capacitor 252 to slightly increase the voltage _Vm of the auxiliary capacitor 252. As a result, the current energy of the wiring inductance 1012 is completely absorbed by the positive side capacitor 211, the negative side capacitor 213, and the auxiliary capacitor 252, and charging is completed. In addition, in mode (2), the energy of the current flowing into the positive side capacitor 211 generates a voltage ΔV2 due to the wiring inductance 1011.

Figure 6 shows the current flow in mode (3). When the current energy of the wiring inductance 1012 is completely absorbed and charging is completed, the charging voltage in the bypass charging path is 4E/3 (V) or more, so discharging occurs via the bypass charging path. However, since the capacitance of each auxiliary capacitor 252 is smaller than the capacitance of the positive side capacitor 211 and the negative side capacitor 213, discharging may occur mainly from the auxiliary capacitor 252. As a result, the voltage of each auxiliary capacitor 252 becomes 0 (V), and the voltage between the positive side wiring 101 and the negative side wiring 102 decreases from 4E/3 (V) to E (V).

7 shows the flow of current in mode (4). When the voltage between the positive side wiring 101 and the negative side wiring 102 decreases to E (V) and the voltage _Vm of the auxiliary capacitor 252 becomes 0 (V), a current is drawn from the snubber circuit 2 due to the self-induction effect of the wiring inductance 1011, and as a result, discharge is performed from the positive side capacitor 211 and the negative side capacitor 213 of each discharge path 22. As a result, the voltage between the positive side wiring 101 and the negative side wiring 102 may decrease from E (V) to E-ΔVs.

FIG. 8 shows the flow in mode (5). When the voltage between the positive wiring 101 and the negative wiring 102 decreases to E-ΔVs due to discharge from the positive capacitor 211 and the negative capacitor 213, the current from the wiring inductance 1011 flows again into each charging path 21 due to the difference with the DC electromotive force E. At this time, the charging voltage _Vm of each auxiliary capacitor 252 is lower than the charging voltage _Vn of the negative capacitor 213, and is 0 (V) as an example in this embodiment. Therefore, the current that has flowed into the positive capacitor 211 of the charging path 21 does not flow toward the first diode 212 and the negative capacitor 213, but flows again toward the auxiliary capacitor 252. As a result, the current energy of the wiring inductance 1011 is temporarily absorbed by charging the positive capacitor 211 and the auxiliary capacitor 252. The energy of the current flowing into the charging path 21 in mode (5) may generate a voltage ΔV3 due to the wiring inductance 1012.

Thereafter, the charging and discharging of modes (2) to (5) is repeated due to resonance between the wiring inductance 1011 and the auxiliary capacitor 252, etc., and as a result, the voltage _Vm of the auxiliary capacitor 252 converges to approximately ΔVs/2 (V). This completes the commutation associated with the turn-off operation of the switching element 11. The energy lost due to this resonance is approximately ΔVs/2 (V), which may be smaller than the energy equivalent to, for example, E/3 (V).

Then, when the switching element 11 is turned on again, as in the comparative example, the energy stored in the positive side capacitor 211, the negative side capacitor 213, and the auxiliary capacitor 252 during the turn-off operation is released, completing the commutation associated with the turn-on operation of the switching element 11. As a result, in this embodiment, as an example, the charging voltage _Vm of each auxiliary capacitor 252 may become 0 (V).

According to the above snubber circuit 2, since the auxiliary capacitor 252 is connected in parallel to at least one of the multiple first diodes 212 and the multiple second diodes 221, when the wiring inductance 1012 generates a voltage ΔV1, the current flowing from the positive side wiring 101 to the negative side wiring 102 is drawn from the positive side capacitor 211 to the auxiliary capacitor 252 to charge the auxiliary capacitor 252. Therefore, the base voltage of the voltage ΔV1 generated by the wiring inductance 1012 can be the total voltage (=E) of the positive side capacitor 211 and the auxiliary capacitor 252, rather than the total voltage (=4E/3) of the positive side capacitor 211 and the negative side capacitor 213. Therefore, the surge voltage that occurs instantaneously between the positive side wiring 101 and the negative side wiring 102 can be reduced.

In addition, since each auxiliary capacitor 252 is connected in parallel to each of the N+1 second diodes 221, even if there is a difference in the wiring path length of the bypass charging path passing through the auxiliary capacitor 252, the energy of the voltage ΔV1 generated by the wiring inductance 1012 can be absorbed early by the bypass charging path with a shorter path length, and the surge voltage can be reliably reduced.

In addition, since the capacitance of the auxiliary capacitor 252 is smaller than the capacitance of each positive side capacitor 211 and each negative side capacitor 213, the energy loss due to resonance between the wiring inductance 1011 and the auxiliary capacitor 252 can be reduced.

In addition, since the capacity of the auxiliary capacitor 252 is 1/1000 or more of the capacity of each positive side capacitor 211 and each negative side capacitor 213, the surge voltage can be reliably reduced by drawing in current compared to when the capacity is less than 1/1000. In addition, compared to when the capacity of the auxiliary capacitor 252 is more than 1/100 of the capacity of each positive side capacitor 211 and each negative side capacitor 213, the energy loss due to resonance between the wiring inductance 1011 and the auxiliary capacitor 252 can be reliably reduced.

In addition, since the wiring inductance of each charging path 21 is smaller than the wiring inductance of each discharging path 22, the surge voltage can be reliably reduced by the charging path 21. In addition, the wiring inductance of the discharging path 22 can prevent an excessive inrush current from occurring when a current flows due to discharging.

[1.3. Operating waveform]
9 shows the voltage applied to the switching element 11 when the switching element 11 is turned off and non-conductive. In the figure, the vertical axis represents voltage and the horizontal axis represents time. The graph in the figure shows the operating waveforms when a single snubber capacitor is connected between the positive wiring 101 and the negative wiring 102. In the figure, the graph in the center shows the operating waveforms when a single snubber capacitor is connected between the positive wiring 101 and the negative wiring 102. The graph on the right side of the figure shows the operation waveforms when the snubber circuit 200 according to the comparative example is connected between the positive wiring 101 and the negative wiring 102. 4 shows the operational waveforms when

As shown in the graph on the left in the figure, when a single snubber capacitor is connected, the voltage ΔV1 caused by the wiring inductance 1012 is generated in a form superimposed on the voltage E (V) of the power supply capacitor 10, and the energy of the voltage ΔV2 caused by the wiring inductance 1011 is lost due to resonance between the wiring inductance 1011 and the snubber capacitor.

Also, as shown in the graph in the center of the figure, when the snubber circuit 200 according to the comparative example is connected, the voltage ΔV1 (the peak value of the voltage generated in the wiring inductance 1012 by commutation to the snubber circuit 200 during the turn-off operation of the switching element 11 or 12) is generated in a form that is superimposed on the voltage 4E/3 (V) of the charging path 21. Also, since there is no resonance between the wiring inductance 1011 and the snubber capacitor, the energy of the voltage ΔV2 is regenerated without being lost.

As shown in the graph on the right side of the figure, when the snubber circuit 2 according to this embodiment is connected, unlike when the comparative example 200 is connected, the voltage ΔV1 is not generated in a form superimposed on the voltage 4E/3 (V) of the charging path 21, but is generated in a form superimposed on the voltage E (V) of the power supply capacitor 10, preventing element destruction. Also, because the capacity of the auxiliary capacitor 252 that resonates with the wiring inductance 1011 is small, the energy of the voltage ΔV2 is regenerated with almost no loss.

The dashed line portion in this graph may be the total voltage of the positive side capacitor 211 and the auxiliary capacitor 252 in the bypass charging path. The slope of the dashed line portion may change depending on the capacity of the auxiliary capacitor 252. For example, when the capacity of the auxiliary capacitor 252 is small, the slope of the dashed line portion may become large and approach the slope of the solid line graph in the rising portion.

Here, the time ΔT1 from when the voltage applied to the switching element 11 reaches the power supply voltage E until it becomes the total voltage of the positive side capacitor 211 and the negative side capacitor 213 connected in series with each other, and the time ΔT2 from the end of the time ΔT1 until the charging of the positive side capacitor 211 or the negative side capacitor is completed may be ΔT1≦ΔT2<5×ΔT1. The end timing of the time ΔT1 may be the timing when the voltage applied to the switching element 11 returns to the total voltage of the positive side capacitor 211 and the negative side capacitor 213 connected in series with each other (a voltage with an initial value of 4E/3 as an example in this embodiment) after reaching the power supply voltage E and becoming a peak value E+ΔV1. This timing may be the timing when the current energy stored in the wiring inductance 1012 becomes zero, or the timing when the current energy is completely absorbed by the snubber circuit 2. The end timing of the time ΔT2 may be the timing when the energy of the wiring inductance 1011 is absorbed by the series voltage V of the positive side capacitor 211 and the auxiliary capacitor 252 and reaches 0 (A). Times ΔT1 and ΔT2 may be adjustable by the capacitance of the positive side capacitor 211, the negative side capacitor 213, and the auxiliary capacitor 252.

As described above, according to the snubber circuit 2 of this embodiment, since the times ΔT1 and ΔT2 are ΔT2<5×ΔT1, the energy stored in the auxiliary capacitor 252 is smaller than when ΔT2≧5×ΔT1, and therefore the loss due to resonance between the wiring inductance 1011 and the auxiliary capacitor 252 can be reduced.

[2. Second embodiment]
10 shows a power conversion device 1A according to the second embodiment. A snubber circuit 2A of the power conversion device 1A may have at least one auxiliary capacitor 251 connected in parallel to at least one of the N first diodes 212 included in the N charging paths 21. In the present embodiment, as an example, the snubber circuit 2 includes N auxiliary capacitors 251, and each auxiliary capacitor 251 is connected in parallel to each of the N first diodes 212. When the auxiliary capacitor 251 has positive and negative polarities, each auxiliary capacitor 251 may have a negative electrode connected to the anode side of the first diode and a positive electrode connected to the cathode side.

The capacitance of each auxiliary capacitor 251 may be smaller than the capacitance of each positive side capacitor 211 and the capacitance of each negative side capacitor 213. For example, the capacitance of the auxiliary capacitor 251 may be 1/1000 to 1/100 of the capacitance of each positive side capacitor 211 and the capacitance of each negative side capacitor 213. The capacitances of each auxiliary capacitor 251 may be equal to each other or different.

Furthermore, the charging voltage _Vm of each auxiliary capacitor 251 may be lower than the charging voltage _Vn of the negative side capacitor 213, and may be, for example, a negative voltage, at the timing when the switching elements 11, 12 cut off the current. In this embodiment, as an example, the absolute value of the voltage _Vm of each auxiliary capacitor 251 may be equal to the voltage _Vn of the negative side capacitor 213. As a result, each auxiliary capacitor 251 may draw a current flowing from the positive terminal 201 side toward the first diode 212.

[2.1. Operation of the snubber circuit 2A according to this embodiment]
Next, the operation of the snubber circuit 2A according to this embodiment will be described. Unless otherwise specified, the charging voltages of the positive side capacitor 211 and the negative side capacitor 213 in the snubber circuit 2A may be the same as those in the snubber circuits 2 and 200 described above.

When switching element 11 is on and switching element 12 is off, the output current flows through the power supply capacitor 10, the positive side wiring 101, the switching element 11, and the power supply output terminal 19. At this time, the output current flows through the wiring inductance 1012 and energy is accumulated. When switching element 11 is turned off from this state, current may flow through snubber circuit 2A in modes (1A) to (5A).

FIG. 11 shows the current flow in mode (1A).
When the switching element 11 is turned off, the output current is commutated and flows from the power supply capacitor 10 and the positive side wiring 101 into each charging path 21. At this time, the charging voltage _Vm of each auxiliary capacitor 251 is lower than the charging voltage _Vn of the negative side capacitor 213, and in this embodiment, it is −E/3 (V) as an example. Therefore, the current that has flowed into the positive side capacitor 211 of the charging path 21 does not flow into the first diode 212, but flows into the negative side capacitor 213 via the auxiliary capacitor 251. As a result, the current energy of the wiring inductance 1012 is absorbed by charging the positive side capacitor 211, the auxiliary capacitor 251, and the negative side capacitor 213.

Thus, in the snubber circuit 2A according to this embodiment, in the initial stage when the current is interrupted, the series circuit of the positive side capacitor 211, the auxiliary capacitor 251, and the negative side capacitor 213 functions as a bypass charging path, and the charging voltage in each bypass charging path is E(V). Therefore, the voltage ΔV1 generated by the wiring inductance 1012, which is part of the surge voltage, is generated in a form that is added to E(V) based on E(V).

The voltage _Vm of the auxiliary capacitor 251 may rise to 0 (V). As a result, the voltage between the positive side wiring 101 and the negative side wiring 102 rises from E (V) to 4E/3 (V).

FIG. 12 shows the flow of current in mode (2A). When the voltage _Vm of the auxiliary capacitor 251 reaches 0 (V), the current flowing into the positive side capacitor 211 of the charging path 21 flows to the negative side capacitor 213 via the first diode 212. As a result, the current energy of the wiring inductance 1012 is absorbed by charging the positive side capacitor 211 and the negative side capacitor 213. Note that the current flowing into the positive side capacitor 211 may also flow slightly into the auxiliary capacitor 251 to slightly increase the voltage _Vm of the auxiliary capacitor 251. As a result, the current energy of the wiring inductance 1012 is completely absorbed by the positive side capacitor 211, the negative side capacitor 213, and the auxiliary capacitor 251, and charging is completed. Note that the energy of the current flowing into the positive side capacitor 211 in mode (2A) generates a voltage ΔV2 due to the wiring inductance 1011.

13 shows the current flow in mode (3A). When the current energy of the wiring inductance 1012 is completely absorbed and charging is completed, the charging voltage in the bypass charging path is 4E/3 (V) or more, so discharging occurs via the bypass charging path. However, since the capacitance of each auxiliary capacitor 251 is smaller than the capacitance of the positive side capacitor 211 and the negative side capacitor 213, discharging may occur mainly from the auxiliary capacitor 251. As a result, the voltage _Vm of each auxiliary capacitor 251 becomes -E/3 (V), and the voltage between the positive side wiring 101 and the negative side wiring 102 decreases from 4E/3 (V) to E (V).

14 shows the flow of current in mode (4A). When the voltage between the positive side wiring 101 and the negative side wiring 102 decreases to E (V) and the voltage _Vm of the auxiliary capacitor 251 becomes -E/3 (V), a current is drawn from the snubber circuit 2A due to the self-induction effect of the wiring inductance 1011, and as a result, discharge is performed from the positive side capacitor 211 and the negative side capacitor 213 of each discharge path 22. As a result, the voltage between the positive side wiring 101 and the negative side wiring 102 may decrease from E (V) to E-ΔVs.

FIG. 15 shows the flow in mode (5A). When the voltage between the positive wiring 101 and the negative wiring 102 decreases to E-ΔVs due to discharge from the positive capacitor 211 and the negative capacitor 213, the current from the wiring inductance 1011 flows again into each charging path 21 due to the difference with the DC electromotive force E. At this time, the charging voltage _Vm of each auxiliary capacitor 251 is lower than the charging voltage _Vn of the negative capacitor 213, and is −E/3 (V) in this embodiment as an example. Therefore, the current that has flowed into the positive capacitor 211 of the charging path 21 does not flow into the first diode 212, but flows again to the negative capacitor 213 via the auxiliary capacitor 251. As a result, the current energy of the wiring inductance 1011 is temporarily absorbed by charging the positive capacitor 211 and the auxiliary capacitor 251.

Thereafter, charging and discharging in modes (2A) to (5A) are repeated due to resonance between the wiring inductance 1011 and the auxiliary capacitor 251, etc., and as a result, the voltage _Vm of the auxiliary capacitor 251 converges to approximately ΔVs/2 (V). This completes the commutation associated with the turn-off operation of the switching element 11. The energy lost due to this resonance is approximately ΔVs/2 (V), which may be smaller than the energy equivalent to, for example, E/3 (V).

Then, when the switching element 11 is turned on again, as in the comparative example, the energy stored in the positive side capacitor 211, the negative side capacitor 213, and the auxiliary capacitor 251 during the turn-off operation is released, completing the commutation associated with the turn-on operation of the switching element 11. As a result, in this embodiment, as an example, the charging voltage _Vm of each auxiliary capacitor 251 may become −E/3 (V).

As described above, the snubber circuit 2A according to the second embodiment can achieve the same effects as the snubber circuit 2 according to the first embodiment.

In the above embodiment, the resonance between the wiring inductance 1011 and the auxiliary capacitor 252 causes repeated charging and discharging, resulting in energy loss. A modified example that improves this problem will be described below.

3. Modifications
In this modification, any one of the at least one auxiliary capacitor 251 provided in the snubber circuit 2A is a capacitor whose capacitance changes in response to an applied voltage (also referred to as a variable capacitance capacitor). In this modification, as an example, each of the N+1 auxiliary capacitors 251 provided in the snubber circuit 2A may be a variable capacitance capacitor.

The capacitance of a variable capacitance capacitor may be smaller the greater the applied voltage. For example, the capacitance of a variable capacitance capacitor may be smaller the greater the applied voltage within the rated voltage range of the capacitor. As an example, if the rated voltage range of a variable capacitance capacitor includes 133 (V) to 267 V (= 400/3 (V) to 2 * 400/3 (V)), the capacitance when a voltage of 267 (V) is applied may be 1/2 the capacitance when a voltage of 133 (V) is applied.

The capacitance-changing capacitor may have a capacitance decrease rate of 10% or more (preferably 15% or more) with respect to an increase in applied voltage within the range of the rated voltage (the rated voltage of the capacitor, as an example). The capacitance-changing capacitor may have a larger change rate of capacitance according to the applied voltage compared to the positive side capacitor 211 and the negative side capacitor 213. For example, for the positive side capacitor 211, the capacitance decrease rate with respect to an increase in applied voltage within the range of its rated voltage is set to rate (1), for the negative side capacitor 213, the capacitance decrease rate with respect to an increase in applied voltage within the range of its rated voltage is set to rate (2), and for the auxiliary capacitor 25, the capacitance decrease rate with respect to an increase in applied voltage within the range of its rated voltage is set to rate (3). In this case, rate (3) may be greater than each of rate (1) and rate (2).

The capacitance-changing capacitor may be a high dielectric constant capacitor, for example a capacitor having temperature characteristics of B characteristics or X5R characteristics. The capacitance-changing capacitor may be a ceramic capacitor. The capacitance-changing capacitor may have a ferroelectric, for example a barium titanate-based dielectric layer. The dielectric layer of the capacitance-changing capacitor may have a relative dielectric constant of 1000 to 20000 at room temperature.

The high dielectric constant capacitor may be a different capacitor than the low dielectric constant capacitor. The low dielectric constant capacitor may have a dielectric layer made of a normal dielectric material, for example a titanium oxide or calcium zirconate based material. The dielectric layer of the low dielectric constant capacitor may have a relative dielectric constant of 20 to 300 at room temperature.

According to the snubber circuit 2A of this modified example, one of at least one auxiliary capacitor 251 provided in the snubber circuit 2A is a capacitance-varying capacitor having a variable capacitance according to the applied voltage, so when the voltage of the auxiliary capacitor 251 converges due to repeated charging and discharging caused by resonance between the wiring inductance 1011 and the auxiliary capacitor 251, the capacitance of the auxiliary capacitor 251 when a peak voltage due to resonance is applied differs from the capacitance of the auxiliary capacitor 251 when the voltage has converged. This makes it possible to reduce energy loss due to resonance.

In addition, each of the N+1 auxiliary capacitors 251 provided in the snubber circuit 2A is a variable capacitance capacitor, which further reduces energy loss due to resonance.

In addition, since the capacitance of a capacitance-varying capacitor decreases as the applied voltage increases, the capacitance when a peak voltage due to resonance is applied is smaller than the capacitance when the voltage converges. Therefore, it is possible to reliably reduce energy loss due to resonance.

In addition, the capacitance-varying capacitor has a larger rate of change in capacitance in response to the applied voltage compared to the positive side capacitor 211 and the negative side capacitor 213, so it is possible to reliably reduce energy loss due to resonance.

In addition, since the capacitance of a variable capacitance capacitor decreases by 10% or more in response to an increase in applied voltage within the rated voltage range, energy loss due to resonance can be reduced compared to when the decrease rate is less than 10%.

In addition, since the capacitance-changing capacitor is a high-dielectric constant capacitor, it is possible to reliably reduce energy loss due to resonance compared to a low-dielectric constant capacitor.

[3.1. Operating waveform]
16 shows an operation waveform when the switching element 11 is turned off in the power conversion device 1A according to the modified example. More specifically, FIG. 16 shows a voltage applied to the switching element 11 (as an example, a drain-source voltage Vds ), the waveform of the charging voltage of the charging path 21, and the waveform of the charging voltage _Vm of the auxiliary capacitor 251. In the figure, the vertical axis represents voltage, and the horizontal axis represents time.

During the period up to time t1 when the switching element 11 is in the on state, the drain-source voltage Vds of the switching element 11 is 0 (V), and the charging voltage _Vm of the auxiliary capacitor 251 is −E/3 (V). In addition, the charging voltage of the charging path 21, that is, the charging voltage of the positive side capacitor 211, the negative side capacitor 213, and the auxiliary capacitor 251 as a whole, is E (V).

When the switching element 11 starts to turn off at time t1, the drain-source voltage Vds of the switching element 11 rises. The drain-source voltage Vds increases in a form in which the voltage ΔV1 generated by the wiring inductance 1012 is added to the charging voltage E (V) of the charging path 21, and reaches a peak voltage Vp at time t2.

In addition, when turn-off begins, a current flows through snubber circuit 2A in mode (1A), discharging auxiliary capacitor 251.

When the charging voltage _Vm of the auxiliary capacitor 251 becomes 0 (V) at time t3, a current flows in the snubber circuit 2A in mode (2A). As a result, the current energy of the wiring inductance 1012 is absorbed by charging the positive side capacitor 211 and the negative side capacitor 213 of the charging path 21.

At time t4, when the current energy of the wiring inductance 1012 is completely absorbed and charging of the positive side capacitor 211, the negative side capacitor 213, and the auxiliary capacitor 251 is completed, a current flows in mode (3A) through the snubber circuit 2A. As a result, discharge mainly occurs from the auxiliary capacitor 251.

At time t5, the voltage _Vm of the auxiliary capacitor 251 becomes -E/3 (V), and the charging voltage of the charging path 21 decreases from 4E/3 (V) to E (V). As a result, a current flows through the snubber circuit 2A in mode (4A), and current is drawn from the snubber circuit 2A due to the self-induction effect of the wiring inductance 1011, causing discharging from the positive side capacitor 211 and the negative side capacitor 213 of each discharge path 22. This causes the charging voltage of the charging path 21 to decrease below E (V). In this operation example, the charging voltage _Vm of the auxiliary capacitor 251 decreases to the negative peak voltage Vc2.

When the voltage between the positive wiring 101 and the negative wiring 102 decreases due to discharge from the positive capacitor 211 and the negative capacitor 213, a current flows in the snubber circuit 2A in mode (5A). As a result, the current from the wiring inductance 1011 flows again into each charging path 21 due to the difference with the DC electromotive force E, and the current energy is temporarily absorbed by charging the positive capacitor 211 and the auxiliary capacitor 251.

Thereafter, current flows through the snubber circuit 2A in modes (2A) to (5A), repeating charging and discharging, and at time t6, the voltage _Vm of the auxiliary capacitor 251 converges to Vc1, thereby completing the commutation associated with the turn-off operation of the switching element 11.

In the above operation, the energy loss E _LOSS due to resonance during the period from time t5 to time t6 is expressed by the following equation (1): In the equation, “C ₀ ” is the capacitance of the auxiliary capacitor 251.

E _LOSS =1/2*C ₀ *Vc2 ² -1/2*C ₀ *Vc1 ^2... (1)

Here, voltage Vc1 may be -E/3 (V). Voltage Vc2 corresponds to the voltage fluctuation range and may be 2 x (-E/3) (V). In this modified example, voltage E (V) may be 400 (V), as an example.

If the capacitance _C0 of the auxiliary capacitor 251 is constant regardless of the applied voltage, the loss energy E _LOSS is calculated as follows: However, the capacitance _C0 may be a capacitance necessary to reduce the surge voltage caused by turning off the switching element 11, and may be a capacitance that can be discharged from time t1 to time t2 or later.

E _LOSS =1/2*C ₀ *(-2E/3) ² -1/2*C ₀ *(-E/3) ²
=1/2*C ₀ *(-800/3) ² -1/2*C ₀ *(-400/3) ²
= 26667 × C ₀

In contrast, in this modification, the capacitance of the auxiliary capacitor 251 changes depending on the applied voltage. As an example, when the capacitance _{C0_Vc2} when the applied voltage is 2E/3 is half the capacitance _{C0_Vc1} when the applied voltage is E/3, that is, when _{C0_Vc2} = _{C0_Vc1} /2, the loss energy E _LOSS is calculated as follows: However, the capacitance _{C0_Vc1} may be a capacitance required to reduce a surge voltage accompanying the turn-off of the switching element 11, and may be a capacitance that can be discharged from time t1 to time t2 or later when the applied voltage is E/3.

E _LOSS =1/2*C _{0_Vc2} *(-2E/3) ² -1/2*C _{0_Vc1} *(-E/3) ²
=1/4*C _{0_Vc1} *(-800/3) ² -1/2*C _{0_Vc1} *(-400/3) ²
=8889× _{C0_Vc1}

As shown by this result, in this modified example, the energy loss E _LOSS due to resonance can be reduced to approximately 1/3.

In this modified example, a capacitance-varying capacitor is applied to at least one auxiliary capacitor 251 of the snubber circuit 2A, but it may also be applied to at least one auxiliary capacitor 252 of the snubber circuit 2.

[4. Other Modifications]
According to the above embodiment and modified example, the snubber circuit 2, 2A has been described as having only one of the auxiliary capacitor 252 and the auxiliary capacitor 251, but may have both. In this case, at least one of the auxiliary capacitor 252 and the auxiliary capacitor 251 may be a variable capacitance capacitor.

In addition, although the auxiliary capacitor 252 has been described as being connected in parallel to each of the N+1 second diodes 221, it may be connected in parallel to only some of the second diodes 221. In addition, although the auxiliary capacitor 251 has been described as being connected in parallel to each of the N first diodes 212, it may be connected in parallel to only some of the first diodes 212.

The present invention has been described above using an embodiment, but the technical scope of the present invention is not limited to the scope described in the above embodiment. It is clear to those skilled in the art that various modifications and improvements can be made to the above embodiment. It is clear from the claims that forms incorporating such modifications or improvements can also be included in the technical scope of the present invention.

The order of execution of each process, such as operations, procedures, steps, and stages, in the devices, systems, programs, and methods shown in the claims, specifications, and drawings is not specifically stated as "before" or "prior to," and it should be noted that the processes may be performed in any order, unless the output of a previous process is used in a later process. Even if the operational flow in the claims, specifications, and drawings is explained using "first," "next," etc. for convenience, it does not mean that it is necessary to perform the processes in this order.

1 Power conversion device, 2 Snubber circuit, 3 Switch circuit, 5 Semiconductor module, 10 Power supply capacitor, 11 Switching element, 12 Switching element, 13 Freewheeling diode, 14 Freewheeling diode, 19 Power supply output terminal, 21 Charging path, 22 Discharging path, 51 Positive terminal, 52 Negative terminal, 101 Positive wiring, 102 Negative wiring, 200 Snubber circuit, 201 Positive terminal, 202 Negative terminal, 211 Positive capacitor, 212 First diode, 213 Negative capacitor, 221 Second diode, 251 Auxiliary capacitor, 252 Auxiliary capacitor, 1011 Wiring inductance, 1012 Wiring inductance

Claims (12)

N (N is an integer of 1 or more) parallel charging paths each including a positive-side capacitor, a first diode, and a negative-side capacitor connected in series between a positive terminal and a negative terminal, and each of the N (N is an integer of 1 or more) parallel charging paths passing a current from the positive terminal side to the negative terminal side;
a second diode connected between the negative terminal and the positive capacitor in a first charging path among the N charging paths, a second diode connected between the negative capacitor in a k-th charging path (where k is an integer satisfying 1≦k≦N−1 ) among the N charging paths and the positive capacitor in the k+1 -th charging path among the N charging paths, and a second diode connected between the negative capacitor and the positive terminal in the N-th charging path among the N charging paths, and N+1 discharge paths in parallel that allow a current to flow from the negative terminal side to the positive terminal side via at least one of the negative capacitor and the positive capacitor;
at least one auxiliary capacitor connected in parallel to at least one of the N first diodes included in the N charging paths and the N+1 second diodes included in the N+1 discharging paths;
Equipped with
Any one of the at least one auxiliary capacitors is a snubber circuit whose capacitance changes in response to an applied voltage. Each of the at least one auxiliary capacitor has a capacitance that changes in response to an applied voltage.
2. The snubber circuit according to claim 1. The auxiliary capacitor, whose capacitance changes according to an applied voltage, has a smaller capacitance as the applied voltage increases.
3. A snubber circuit according to claim 1 or 2. the auxiliary capacitor, whose capacitance changes in response to an applied voltage, has a larger fluctuation rate of capacitance in response to an applied voltage than the positive-side capacitor and the negative-side capacitor;
A snubber circuit according to any one of claims 1 to 3. the auxiliary capacitor, the capacitance of which changes in response to an applied voltage, is a high dielectric constant capacitor;
A snubber circuit according to any one of claims 1 to 4 . The auxiliary capacitor, the capacitance of which changes in response to an applied voltage, is a ceramic capacitor.
A snubber circuit according to any one of claims 1 to 5 . The auxiliary capacitor, the capacitance of which changes in response to an applied voltage, has a barium titanate-based dielectric layer.
7. The snubber circuit according to claim 6 . The capacitance of the auxiliary capacitor is smaller than the capacitance of each positive side capacitor and the capacitance of each negative side capacitor.
A snubber circuit according to any one of claims 1 to 7 . The capacitance of the auxiliary capacitor is 1/1000 to 1/100 of the capacitance of each positive side capacitor and the capacitance of each negative side capacitor.
9. The snubber circuit according to claim 8 . Each auxiliary capacitor is connected in parallel with either the first diode or the second diode.
The snubber circuit according to any one of claims 1 to 9 . Each auxiliary capacitor is connected in parallel to either one of the N first diodes and the N+1 second diodes.
The snubber circuit according to any one of claims 1 to 10 . A snubber circuit according to any one of claims 1 to 11 ,
a switch circuit connected to the positive terminal and the negative terminal;
A power conversion device comprising: