JP2011250506A - Snubber circuit, chopper circuit, dc/dc converter, and fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology concerning a snubber circuit.SOLUTION: A snubber circuit is connected to a snubber capacitor on a cathode side of a snubber diode. Capacitance of the snubber capacitor and junction capacitance of the snubber diode are so adjusted as to cancel out a charged electric charge with an accumulated electric charge based on a recovery characteristic of the snubber diode by a reverse bias caused by the charged electric charge of the snubber capacitor after stopping electrification of the snubber circuit.

Description

  The present invention relates to a snubber circuit technology in which a snubber capacitor is connected to the cathode side of a snubber diode.

  As a snubber circuit, there is a circuit configuration in which a snubber capacitor is connected to the cathode side of a snubber diode (Patent Document 1 below). Snubber circuits are generally provided to absorb transient electromotive force.

JP 2009-165242 A

  However, in the snubber circuit according to the above technique, immediately after the system is operated and immediately after the system is stopped, the switching element S2 is turned off, and one of the charges charged in the snubber capacitor is connected to the cathode of the snubber diode. As a result, there is a problem that the charge remains in the capacitor for a certain period even after the system is stopped.

  The present invention has been made to solve the above-described problems, and an object thereof is to prevent a charge from remaining in a snubber capacitor in a snubber circuit after energization for a long period of time.

In order to solve at least a part of the problems described above, the present invention can take the following forms or application examples.
[Application Example 1]
A snubber circuit in which a snubber capacitor is connected to the cathode side of the snubber diode, and the accumulated charge due to the recovery characteristic of the snubber diode caused by a reverse bias caused by the charge charge of the snubber capacitor after stopping the energization of the snubber circuit, A snubber circuit in which the capacitance of the snubber capacitor and the junction capacitance of the snubber diode are adjusted so as to at least cancel the charged charges.
According to this snubber circuit, no charge remains in the snubber capacitor after the energization is stopped.

[Application Example 2]
The snubber circuit according to Application Example 1, wherein the snubber capacitor has a capacitance C _C , a snubber diode junction capacitance C _D, and is applied to the snubber capacitor during operation of the snubber circuit. The maximum voltage V1 and the minimum reverse bias voltage V2 applied to the snubber diode when the snubber circuit stops the energization with the V1 applied to the snubber capacitor are represented by C _C × V1 <C _D × V2
Snubber circuit having a correlation of
According to the snubber circuit, it is possible to make the circuit design determines the C _C and C _D so as to have the relationship of the above formula.

[Application Example 3]
A chopper circuit that controls the effective value of voltage or current by repeatedly switching on and off of the current of the main switching element, the snubber circuit having a snubber capacitor connected to the cathode side of the snubber diode, and energizing the snubber circuit Junction between the snubber capacitor capacitance and the snubber diode so as to at least cancel the charged charge by the accumulated charge due to the recovery characteristic of the snubber diode caused by the reverse bias due to the charged charge of the snubber capacitor after stopping Chopper circuit with adjusted capacitance.
According to this chopper circuit, no charge remains in the snubber capacitor after the energization is stopped.

[Application Example 4]
The chopper circuit according to Application Example 3, which includes an auxiliary switching element, and the chopper circuit controls the main switching element by controlling a switching timing of the auxiliary switching element. A chopper circuit that uses a soft switching operation to control the voltage applied to the.
This chopper circuit can be applied to a soft switching circuit, for example, a soft switching converter.

[Application Example 5]
A soft switching operation is provided that includes a main switching element and an auxiliary switching element, and controls a voltage applied to the main switching element when the main switching element is switched by controlling a switching timing of the auxiliary switching element. A DC / DC converter,
A snubber circuit in which a snubber capacitor is connected to the cathode side of the snubber diode, and the accumulated charge due to the recovery characteristic of the snubber diode caused by a reverse bias caused by the charged charge of the snubber capacitor after stopping the energization of the snubber circuit, A DC / DC converter in which a capacitance of the snubber capacitor and a junction capacitance of the snubber diode are adjusted so as to at least cancel charged charges.
According to this DC / DC converter, no charge remains in the snubber capacitor after energization is stopped.

[Application Example 6]
A fuel cell system, comprising: a fuel cell that supplies power to a load; and a DC / DC converter that performs voltage control of the power by using a chopper circuit including a switching element, wherein the DC / DC converter includes: A snubber circuit having a snubber capacitor connected to the cathode side of the snubber diode, and the accumulated charge due to the recovery characteristic of the snubber diode caused by a reverse bias caused by the charge charge of the snubber capacitor after the snubber circuit is deenergized, A fuel cell system in which a capacitance of the snubber capacitor and a junction capacitance of the snubber diode are adjusted so as to at least cancel the charged charges.
According to this fuel cell system, no charge remains in the snubber capacitor after energization is stopped.

  Note that the present invention can be realized in various modes. For example, the present invention can be realized in the form of a soft switching method and apparatus, a power conversion system, an integrated circuit for realizing the functions of the method or apparatus, a computer program, a recording medium on which the computer program is recorded, and the like.

It is explanatory drawing explaining the structure of the fuel cell system 10 mounted in the vehicle as 1st Example. 3 is an explanatory diagram showing a circuit configuration of a soft switching converter 50. FIG. It is a state transition diagram explaining a soft switching process. It is explanatory drawing explaining the initial state in a soft switching process. It is explanatory drawing explaining the mode 1 in a soft switching process. It is explanatory drawing explaining the mode 2 in a soft switching process. It is explanatory drawing explaining the mode 3 in a soft switching process. It is explanatory drawing explaining the mode 4 in a soft switching process. It is explanatory drawing explaining the mode 5 in a soft switching process. It is explanatory drawing explaining the mode 6 in a soft switching process. It is explanatory drawing explaining the relationship between the snubber capacitor | condenser C2 and the snubber diode D3. It is explanatory drawing explaining the modification 2. FIG.

Next, embodiments of the present invention will be described based on examples.
A. First embodiment:
(A1) Configuration of fuel cell system:
FIG. 1 is an explanatory view illustrating the configuration of a fuel cell system 10 mounted on a vehicle as a first embodiment. In the present embodiment, a fuel cell vehicle (FCHV) is assumed as an example of the vehicle, but the present invention is also applicable to an electric vehicle and a hybrid vehicle.

  The fuel cell system 10 includes a control unit 20, a power supply device 30, and a load LOAD. The power supply device 30 supplies DC power to the load LOAD. The load LOAD is mainly a vehicle driving motor, and other loads include loads such as peripheral devices (lighting, audio, etc.). These loads include loads that operate with direct current, loads that operate with alternating current through an inverter, and the like. The power supply device 30 and the control unit 20 are connected by a wire harness WH. For example, if the vehicle is running, the control unit 20 calculates the power required for the vehicle driving motor based on the driver's accelerator operation, and outputs the power output from the power supply device 30 to the load LOAD according to the calculation result. Control. The power supply device 30 includes a fuel cell FC and a soft switching converter 50.

  The fuel cell FC employs a power generation system that generates electric power from supplied fuel gas (for example, hydrogen gas) and oxidizing gas, and has a single cell equipped with a membrane-electrode assembly (MEA) or the like. It has a stack structure in which a plurality are stacked in series. As the fuel cell FC, various types of fuel cells such as a solid polymer type, a phosphoric acid type and a molten carbonate type can be used. The soft switching converter 50 is a DC / DC converter (boost converter) that boosts the voltage of the DC power supplied from the fuel cell FC. The soft switching converter 50 includes a switching element S1 and a switching element S2, which will be described later, and is configured by a chopper circuit that controls the power supplied to the load LOAD by the switching operation of the switching elements S1 and S2.

  The control unit 20 is configured as a microcomputer having a CPU, RAM, and ROM therein. The control unit 20 outputs a gate signal for controlling the switching timing of the switching element S1 and the switching element S2 included in the soft switching converter 50 to the soft switching converter 50 in accordance with the calculation based on the above-described acceleration or the like. . Specifically, an S1 gate signal that controls the switching timing of the switching element S1 and an S2 gate signal that controls the switching timing of the switching element S2 are output to the soft switching converter 50 via the wire harness WH. is doing. That is, the control unit 20 controls the power supplied from the power supply device 30 to the load LOAD by outputting the S1 gate signal and the S2 gate signal to the soft switching converter 50.

(A2) Configuration and operation of soft switching converter:
Next, the configuration and operation of the soft switching converter 50 will be described. FIG. 2 is an explanatory diagram showing a circuit configuration of the soft switching converter 50. The soft switching converter controls the timing of the switching operation of the auxiliary switching element (switching element S2 in this embodiment) constituting the circuit, so that the main switching element (switching element S1 in this embodiment) performs the switching operation. This is a converter using a soft switching operation that reduces the voltage applied to both ends of the main switching element and reduces power loss due to switching of the switching element S1. The detailed operation principle of the soft switching converter is disclosed in Japanese Unexamined Patent Application Publication No. 2009-165245.

  The soft switching converter 50 is configured by a chopper circuit including a main circuit 51 and an auxiliary circuit 52. The main circuit 51 includes a reactor L1, a diode D5, a switching element S1, a diode D4, a filter capacitor C1, a smoothing capacitor C3, and a discharge resistor R. Reactor L1 has one end connected to the positive electrode of DC power supply E, which is fuel cell FC (FIG. 1). The diode D5 has an anode connected to the other end of the reactor L1, and a cathode connected to one end of the load LOAD.

  The switching element S1 has one end connected to the other end of the reactor L1 and the other end connected to the negative electrode of the DC power supply E and the other pole of the load LOAD, according to the S1 gate signal transmitted from the control unit 20 Turn on and off. In this embodiment, the switching element S1 uses an insulated gate bipolar transistor. In addition, a semiconductor element such as a thyristor or a diode can be used as the switching element S1. A diode D4 is connected to the switching element S1 in parallel to protect the switching element S1. The switching element S1 corresponds to a main switching element described in the claims. The filter capacitor C1 is connected between the positive electrode and the negative electrode of the DC power supply E. The smoothing capacitor C3 is connected in parallel to the load LOAD. The filter capacitor C1 and the smoothing capacitor C3 stabilize the input / output of the soft switching converter 50, respectively. The discharge resistor R is a resistor for discharging the charges charged in the filter capacitor C1 and the smoothing capacitor C3 after the system of the fuel cell system 10 is stopped.

  On the other hand, the auxiliary circuit 52 includes a reactor L2, a diode D1, a switching element S2, a diode D2, a snubber diode D3, and a snubber capacitor C2. Reactor L2 has one end connected to the high potential side of reactor L1. The diode D2 is connected between the switching element S2 and the snubber diode D3. One end of the switching element S <b> 2 is connected to the anode of the diode D <b> 2 and is turned on / off according to the S <b> 2 gate signal transmitted from the control unit 20. The snubber diode D3 has an anode connected to one end of the switching element S1 and a cathode connected to the other end of the switching element S2. The snubber capacitor C2 has one end connected to the cathode of the snubber diode D3 and the other end connected to the switching element S1. The diode D1 is connected in parallel to protect the switching element S2. The switching element S2 corresponds to an auxiliary switching element described in the claims. The snubber diode D3 and the snubber capacitor C2 are for absorbing a transient counter electromotive force generated when the switching element S1 is turned off.

  Next, the soft switching operation of the soft switching converter 50 will be described. FIG. 3 is a state transition diagram illustrating a one-cycle process for boosting by the soft switching operation of the soft switching converter 50 (hereinafter also referred to as “soft switching process”).

  In the soft switching process, each process in the states S101 to S106 is sequentially performed by the control unit 20 to form one cycle, and the current and voltage states in the soft switching converter 50 by each process are set as mode 1 to mode 6, respectively. FIG. 4 shows the initial state, and FIGS. 5 to 10 show the states of mode 1 to mode 6, respectively. Hereinafter, the soft switching processing in the soft switching converter 50 will be described based on these drawings. 4 to 10, the symbols of the main circuit 51 and the auxiliary circuit 52 are omitted for the sake of brevity, but each circuit may be cited in the description of each mode. .

  The initial state (see FIG. 4) immediately before the soft switching process shown in FIG. 3 is performed is a state in which power is supplied from the fuel cell FC to the load LOAD, that is, the switching elements S1 and S2 are both turned off. In this state, current flows to the load LOAD side via the reactor L1 and the diode D5. Therefore, when one cycle of the soft switching process is completed, the same state as this initial state is reached.

  In the soft switching process (see FIG. 3), a transition is made from the initial state to the mode 1 (see FIG. 5), and the current / voltage state of mode 1 shown in FIG. 5 is formed (state S101). Specifically, the switching element S2 is turned on while the switching element S1 is turned off. As a result, the current flowing to the load LOAD side via the reactor L1 and the diode D5 gradually shifts to the auxiliary circuit 52 side due to the potential difference between the outlet voltage VH and the inlet voltage VL of the soft switching converter 50. .

  If the state of mode 1 continues for a predetermined time, the current flowing through the diode D5 becomes zero, and instead, the electric charge stored in the snubber capacitor C2 is replaced by the potential difference between the snubber capacitor C2 and the voltage VL of the fuel cell FC. (State S102: state of mode 2 shown in FIG. 6). In mode 2, the charge of the snubber capacitor C2 that affects the voltage applied to the switching element S1 when turning on the switching element S1 flows into the diode D2 → the switching element S2 → the reactor L2 of the auxiliary circuit 52, so that the snubber capacitor The voltage applied to C2 decreases. At this time, the current continues to flow until the voltage of the snubber capacitor C2 becomes zero due to the half-wave resonance of the reactor L2 and the snubber capacitor C2. The electric charge of the snubber capacitor C2 determines the voltage across the switching element S1 connected in parallel with the snubber capacitor C2. As a result, when the switching element S1 is turned on in the state S103 (FIG. 3), it is possible to reduce the applied voltage across the switching element S1.

  Further, in the state S103, the switching element S1 is turned on at the timing when the electric charge of the snubber capacitor C2 is completely discharged, and the mode 3 current / voltage state shown in FIG. 7 is formed. That is, when the voltage of the snubber capacitor C2 is zero, the voltage applied to both ends of the switching element S1 is also zero. When the switching element S1 is turned on in this state, the switching element S1 is in a zero voltage state, and a current starts to flow from that state. Therefore, power loss due to switching in the switching element S1 (hereinafter referred to as “switching loss”) Is theoretically zero.

  And in state S104, the state of state S103 continues, the current amount which flows into reactor L1 is increased, and the energy stored in reactor L1 is gradually increased. This state is the current / voltage state of mode 4 shown in FIG. Thereafter, in a state where desired energy is stored in reactor L1, switching element S1 and switching element S2 are turned off in state S105. Then, the electric charge is discharged in mode 2 to charge the snubber capacitor C2, which is in a low voltage state, and reaches the same voltage as the outlet voltage VH of the soft switching converter 50. This state is the current / voltage state of mode 5 shown in FIG. When the electric charge is charged until the snubber capacitor C2 reaches the voltage VH, the energy stored in the reactor L1 in the state S106 is released to the load LOAD side. This state is the current / voltage state of mode 6 shown in FIG. Note that when the transition from the mode 4 state to the mode 5 state occurs, the voltage applied to the switching element S1 when the switching elements S1 and S2 are turned off can be delayed by the snubber capacitor C2, so that the tail current in the switching element S1 Switching loss due to can be further reduced.

  As described above, by performing the soft switching process with the processes in the states S101 to S106 as one cycle, the switching loss in the soft switching converter 50 is suppressed as much as possible, and the output voltage of the fuel cell FC is boosted to the load LOAD. Supply is possible.

(A3) Relationship between snubber capacitor C2 and snubber diode D3 after system stop:
Next, the relationship between the snubber capacitor C2 and the snubber diode D3 of the fuel cell system 10 after the system is stopped will be described. FIG. 11A is an explanatory diagram for explaining the state of the fuel cell system 10 immediately after the system is stopped. The stop of the fuel cell system 10 means a stop of power generation by the fuel cell FC and a state in which the switching element S1 and the switching element S2 stop the switching operation. At this time, the switching element S1 and the switching element S2 are stopped in a turn-off state. When the fuel cell system 10 stops, the charge charged in the smoothing capacitor C3 during system operation is discharged by the discharge resistor R. As the electric charge of the smoothing capacitor C3 is discharged, the outlet voltage VH gradually decreases. When the voltage drops to VH = VL, the diode D5 is turned on, and the charge charged in the filter capacitor C1 is gradually discharged by the discharge resistor R.

  On the other hand, since the snubber capacitor C2 is connected to the cathode side of the snubber diode D3 and the switching element S2 is turned off, the charge charged in the snubber capacitor C2 is discharged to the discharge resistor R. It will never be done. Therefore, in the fuel cell system 10 of this embodiment, the charge of the filter capacitor C1 is discharged using the recovery characteristic of the snubber diode D3. This will be described in detail below.

  In general, when a reverse bias is applied to a diode from a state in which a forward bias is applied, an apparent current flows in the reverse bias direction due to accumulated carriers (charges). Such a characteristic of the diode is called a recovery characteristic. In the present embodiment, in order to discharge the charge charged in the snubber capacitor C2 using the recovery characteristics of the diode, it is substantially the same as the charge that negates the maximum charge amount charged in the snubber capacitor C2 during the soft switching process. The circuit was designed on condition that the same charge was accumulated in the snubber diode D3 immediately after the system stopped.

The voltage applied to the snubber capacitor C2 during the soft switching process is the outlet voltage VH as described in the soft switching process. The outlet voltage VH constantly changes depending on the amount of power required by the load LOAD, but the maximum value of the output voltage VH (hereinafter also referred to as the maximum outlet voltage VH _max ) depends on the specifications of the fuel cell system 10 and the required power of the load. Can be determined by. Therefore, the maximum amount of charge Q _C2max charged in the snubber capacitor C2 immediately after the system is stopped can be calculated as Q _C2max = VH _max × C _{C2 where the} capacitance of the snubber capacitor C2 is C _C2 .

Next, the amount of charge that can be discharged (cancelled) by the snubber capacitor C2 by the recovery characteristic of the snubber diode D3 will be described. FIGS. 11B and 11C are explanatory diagrams for explaining the recovery characteristics of the snubber diode D3. As shown in FIG. 11B, if the potential on the anode side of the snubber diode D3 is VH _max before the system is stopped, the snubber capacitor C2 is charged with a charge of VH _max × C _C2 . When the system stops in this state, immediately after the system stops, the boosting by the switching element S1 stops, and the anode side potential of the snubber diode D3 immediately enters the inlet due to the influence of the charge charged in the filter capacitor C1. The voltage becomes VL (see FIG. 11C).

On the other hand, the cathode potential of the snubber diode D3 is a _{VH max} the charge of _{C C2} × _{VH max} is charged in the snubber capacitor C2. That is, immediately after the system is stopped, VH _max −VL is applied to the snubber diode D3 as a reverse bias. Thus, charge accumulated in the snubber diode D3 immediately after the system is stopped, the junction capacitance of the snubber diode D3 When _{C D3,} can be calculated as _{C D3 × (VH max -VL)} . The inlet voltage VL constantly changes during one cycle of the soft switching process. If the system is stopped at the maximum value (hereinafter also referred to as the maximum inlet voltage VL _max ), the accumulation of the snubber diode D3 functioning as a recovery characteristic. The charge is C _D3 × (VH _max −VL _max ). This state is the minimum charge amount as the accumulated charge amount of the snubber diode D3 when the snubber capacitor C2 is charged with _QC2max .

Therefore, in the fuel cell system 10 according to the present embodiment, as shown in the following formula (1), “the minimum accumulated charge amount of the snubber diode D3 is larger than the maximum charge amount charged in the snubber capacitor C2”. Under the conditions, the capacitance C _C2 of the snubber capacitor C2 and the junction capacitance C _D3 of the snubber diode D3 are adjusted and determined, and the snubber capacitor C2 and the snubber diode D3 are provided according to the conditions. As a result, the charge of the snubber capacitor C2 can be discharged (cancelled) by the accumulated charge of the snubber diode D3 regardless of the state of the fuel cell system 10 in the soft switching process (see FIG. 3). .

C _C2 × VH _max <C _D3 × (VH _max −VL _max ) (1)

  In Expression (1), “the minimum accumulated charge amount of the snubber diode D3 is larger than the maximum charge amount charged in the snubber capacitor C2”, but “the maximum charge amount charged in the snubber capacitor C2 and the snubber diode D3”. May be the same. Further, it includes the concept that the electric charge of the snubber capacitor C2 does not necessarily become zero due to variations in temperature and product specifications, and some electric charge remains to the extent that it does not matter. Therefore, the electric charge remaining in the snubber capacitor C2 can be represented as “ΔQ” and expressed as the following formula (2).

C _D3 × (VH _max −VL _max ) −VH _max × C _C2 = ΔQ (2)
−ε ₁ ≦ ΔQ ≦ ε ₂

As described above, the fuel cell system 10 includes the snubber capacitor C2 and the snubber diode D3 having the capacitance C _C2 and the junction capacitance C _D3 that satisfy the condition of the expression (1). The above equation (1) means a condition that “the minimum accumulated charge amount of the snubber diode D3 is larger than the maximum charge amount charged in the snubber capacitor C2”. Therefore, no matter what the state of the fuel cell system 10 stops, the charge of the snubber capacitor C2 is discharged (cancelled) by the charge stored in the snubber diode D3 immediately before the stop of the system, and the charge of the snubber capacitor C2 is charged. Can be zero.

As the correspondence relationship with the claims, the capacitance C _C2 corresponds to C _C described in the claims, the junction capacitance C _D3 corresponds to C _D described in the claims, and VH _max Corresponds to V1 described in the claims, and (VH _max -VL _max ) corresponds to V2 described in the claims.

B. Variations:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

(B1) Modification 1:
In the above embodiment, the capacitance C _C2 and the junction capacitance C _D3 are adjusted and determined based on the condition of the expression (1). However, the present invention is not limited to this, and the snubber capacitor is stopped after the system including the snubber circuit is stopped. if the C2 of charges than determining the electrostatic capacitance C _C2 and junction capacitance C _D3 so as to cancel the recovery characteristics of the snubber diode D3, determines the capacitance C _C2 and junction capacitance C _D3 by other conditions May be. For example, in the case of a snubber circuit having a circuit configuration in which the anode potential of the snubber diode D3 immediately becomes zero after the system is stopped, the maximum voltage applied to the snubber capacitor C2 is equal to the minimum voltage applied to the snubber diode D3 at that time. Therefore, the condition for canceling the charging charge of the snubber capacitor C2 by the recovery characteristic of the snubber diode D3 is capacitance C _C2 ≦ C _D3 . As described above, even if the conditions are set in accordance with the circuit configurations of various snubber circuits and the capacitance C _C2 and the junction capacitance C _D3 are adjusted, it is possible to obtain the same effect as in the above embodiment. .

(B2) Modification 2:
In the above embodiment, the snubber circuit having the circuit configuration shown in FIG. 2 has been described as an example. However, the present invention is not limited to this, and can be applied to snubber circuits having various circuit configurations in which a snubber capacitor is connected to the cathode side of the snubber diode. is there. For example, the present invention can be applied to the snubber circuit having the circuit configuration shown in FIG. In this case, the junction capacitance _{C D3a} of the snubber diodes D3a, the electrostatic capacitance _{C C2a} of the snubber capacitor C2a, the reverse bias charges accumulated in accordance recovery characteristics of the snubber diodes D3a, discharging the charge accumulated in the snubber capacitor C2a (cancel) to By adjusting in this way, it is possible to discharge the charge of the snubber capacitor C2a after the system is stopped.

  In addition, assuming that a snubber capacitor is connected to the cathode side of the snubber circuit, the above-described DC / DC converter, AC / DC converter, PFC circuit (power factor correction circuit: power factor correction circuit), UPS (UPS: Uninterruptible) Power Supply: Uninterruptible power supply), power conditioner, frequency converter, etc.

DESCRIPTION OF SYMBOLS 10 ... Fuel cell system 20 ... Control unit 30 ... Power supply device 50 ... Soft switching converter 51 ... Main circuit 52 ... Auxiliary circuit LOAD ... Load R ... Discharge resistance E ... DC power supply S1 ... Main switching element S2 ... Auxiliary switching element L1 ... Reactor L2 ... Reactor C1 ... Filter capacitor C2 ... Snubber capacitor C3 ... Smoothing capacitor D1 ... Diode D2 ... Diode D3 ... Snubber diode D4 ... Diode D5 ... Diode FC ... Fuel cell WH ... Wire harness VH ... Outlet voltage VL ... Inlet voltage C2a ... Snubber Capacitor D3a ... Snubber diode

Claims (6)

A snubber circuit in which a snubber capacitor is connected to the cathode side of the snubber diode,
The capacitance of the snubber capacitor is set so as to at least cancel the charged charge by accumulated charge due to the recovery characteristic of the snubber diode caused by a reverse bias caused by the charged charge of the snubber capacitor after the energization of the snubber circuit is stopped. A snubber circuit in which the junction capacitance of the snubber diode is adjusted. A snubber circuit according to claim 1,
And C _C is the capacitance of the snubber capacitor, and C _D is the junction capacitance of the snubber diode, and V1 is the maximum voltage applied to the snubber capacitor during operation of the snubber circuit, the snubber capacitor When the snubber circuit stops the energization with V1 applied, V2 which is the minimum reverse bias voltage applied to the snubber diode is C _C × V1 <C _D × V2
Snubber circuit with a correlation of A chopper circuit that controls the effective value of voltage or current by repeatedly switching the current on and off of the main switching element,
A snubber circuit in which a snubber capacitor is connected to the cathode side of the snubber diode, and the accumulated charge due to the recovery characteristic of the snubber diode caused by a reverse bias caused by the charged charge of the snubber capacitor after stopping the energization of the snubber circuit, A chopper circuit in which a capacitance of the snubber capacitor and a junction capacitance of the snubber diode are adjusted so as to at least cancel charged charges. A chopper circuit according to claim 3,
With an auxiliary switching element,
The chopper circuit uses a soft switching operation for controlling a voltage applied to the main switching element when switching the main switching element by controlling a switching timing of the auxiliary switching element. A soft switching operation is provided that includes a main switching element and an auxiliary switching element, and controls a voltage applied to the main switching element when the main switching element is switched by controlling a switching timing of the auxiliary switching element. A DC / DC converter,
A snubber circuit in which a snubber capacitor is connected to the cathode side of the snubber diode, and the accumulated charge due to the recovery characteristic of the snubber diode caused by a reverse bias caused by the charged charge of the snubber capacitor after stopping the energization of the snubber circuit, A DC / DC converter in which a capacitance of the snubber capacitor and a junction capacitance of the snubber diode are adjusted so as to at least cancel charged charges. A fuel cell system,
A fuel cell for supplying power to the load;
A DC / DC converter that performs voltage control of the power by using a chopper circuit including a switching element, and
The DC / DC converter includes a snubber circuit in which a snubber capacitor is connected to the cathode side of the snubber diode, and the recovery of the snubber diode caused by a reverse bias caused by the charge of the snubber capacitor after the snubber circuit is deenergized. A fuel cell system in which a capacitance of the snubber capacitor and a junction capacitance of the snubber diode are adjusted so as to at least cancel the charged charges by accumulated charges due to characteristics.

Images