JP2011109775A - Converter controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a converter controller to prevent breakdown of an auxiliary switch comprising an auxiliary circuit of a soft-switching converter. <P>SOLUTION: An FC soft-switching converter 250 includes a free-wheel circuit 22c that includes a free-wheel diode D6. In a second series-connected body of an auxiliary circuit 22b, an anode of a diode D2 is connected to the connecting portion of a diode D3 of a first series-connected body and a snubber capacitor C2. A cathode of the diode D2 is connected to an electrode at one end of a second switching element S2. An electrode at the other end of the second switching element S2 is connected to the connecting portion of a coil L2 and the free-wheel diode D6. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a converter control device that controls an output voltage of a fuel cell.

  In fuel cell systems mounted on automobiles, various hybrid fuel cell systems with fuel cells and batteries as power sources have been proposed in order to respond to sudden load changes exceeding the power generation capacity of fuel cells. Has been.

  In the hybrid fuel cell system, the output voltage of the fuel cell and the output voltage of the battery are controlled by a DC / DC converter. As a DC / DC converter that performs such control, a type that performs voltage conversion by causing a switching element such as a power transistor, IGBT, or FET to perform PWM operation is widely used. DC / DC converters are required to have further lower loss, higher efficiency, and lower noise in accordance with power saving, downsizing, and higher performance of electronic devices, and in particular, switching loss and switching surge associated with PWM operation. Reduction is desired.

  One of the techniques for reducing such switching loss and switching surge is soft switching technique. Here, soft switching is a switching method for realizing ZVS (Zero Voltage Switching) or ZCS (Zero Current Switching), and has low switching loss and stress applied to the power semiconductor device. On the other hand, a switching method in which the voltage / current is directly turned on / off by the switching function of the power semiconductor device is called hard switching. In the following description, a method in which both or one of ZVS / ZCS is realized is called soft switching, and the other is called hard switching.

  Soft switching is realized by, for example, a common buck-boost type DC / DC converter including an inductor, a switching element, and a diode to which an auxiliary circuit for reducing switching loss is added (so-called soft switching converter) (for example, a patent) Reference 1).

JP 2005-102438 A

Ｌ；補助コイルのインダクタンス値 FIG. 19 is a diagram for explaining a mechanism for generating a surge voltage in the auxiliary circuit of the soft switch converter.
When the auxiliary switch (for example, IGBT) 2 of the auxiliary circuit 1 is in an ON state and a current flows through the auxiliary coil 3 (that is, energized), an abnormality occurs in the auxiliary circuit 1 and the auxiliary switch 2 is turned off. Then, the current flowing through the auxiliary coil 3 is abruptly interrupted. When such a sudden current interruption occurs, the current change rate di / dt becomes very large and a large surge voltage ΔV is generated (see the following formula (A)).
If the surge voltage exceeds the voltage rating of the auxiliary switch 2, the element is destroyed, and in the worst case, the system must be stopped.

L: Inductance value of auxiliary coil

  The present invention has been made in view of the circumstances described above, and an object of the present invention is to provide a converter control device capable of preventing the auxiliary switch constituting the auxiliary circuit of the soft switching converter from being destroyed.

  In order to solve the above problems, a converter control device according to the present invention is a control device for a soft switching converter having an auxiliary circuit for controlling an output voltage of a fuel cell, and an auxiliary coil constituting the auxiliary circuit is energized. In the state, when an auxiliary switch constituting the auxiliary circuit is turned off, a free wheel circuit is provided for continuing to flow a current in the same direction as the energization.

  According to such a configuration, even if an auxiliary switch has an open failure or the like when the auxiliary coil constituting the auxiliary circuit is energized, and the auxiliary switch is switched from on to off, the current is supplied in the same direction as when energized. Due to the presence of the freewheel circuit for continuing the flow of current, it is possible to continue the flow of current to the auxiliary coil, thereby preventing the occurrence of a surge voltage that would destroy the auxiliary switch.

  Here, in the above configuration, the auxiliary coil has one end connected to the high potential side of the fuel cell and the other end connected to one pole of the auxiliary switch. It is preferable that the free wheel diode includes an anode terminal connected to a low potential side of the fuel cell and a cathode terminal connected to a connection portion of the auxiliary coil and the auxiliary switch.

  In the above configuration, the main booster circuit of the soft switching converter has one end connected to the high potential side terminal of the fuel cell and one end connected to the other end of the main coil. A main switch for switching, the other end of which is connected to a terminal on the low potential side of the fuel cell, a first diode whose cathode is connected to the other end of the main coil, an anode of the first diode, and the main switch A smoothing capacitor provided between the other end of the switch, and the auxiliary circuit is connected in parallel to the main switch, and connected to the other end of the main coil and a terminal on the low potential side of the fuel cell. A first series connection body including a second diode and a snubber capacitor, and a third portion connected between a connection portion between the second diode and the snubber capacitor and one end of the main coil, And a secondary series connection comprising the auxiliary switch and diode and the auxiliary coil is also preferred.

  Another converter control device according to the present invention is a control device for a multiphase soft switching converter provided with an auxiliary circuit for controlling the output voltage of the fuel cell for each phase, and constitutes the auxiliary circuit for each phase. The auxiliary coil is common to all phases of the auxiliary circuit, and one or more auxiliary coils that are turned on to form an energized state of the auxiliary coil when the auxiliary coil constituting the auxiliary circuit is energized. When a phase auxiliary switch is turned off, a free wheel circuit is provided for continuing to flow a current in the same direction as in the energization.

  Another converter control device according to the present invention is a control device for a soft switching converter including an auxiliary circuit for controlling an output voltage of a fuel cell, wherein the gate resistance of a semiconductor element constituting an auxiliary switch of the auxiliary circuit A resistance control circuit for changing the value is provided, and the gate resistance value when the auxiliary switch is turned off is larger than the gate resistance value when turned on and larger than the element breakdown resistance threshold value. Here, in the above configuration, the semiconductor device further includes detection means for detecting a transition from turn-on to turn-off of the auxiliary switch, and the resistance control circuit detects the transition when the detection means detects the transition. The gate resistance value may be set to a value larger than the set element breakdown resistance threshold value.

  According to the present invention, it is possible to prevent the auxiliary switch constituting the auxiliary circuit of the soft switching converter from being destroyed.

It is a system configuration figure of the FCHV system concerning a 1st embodiment. It is a figure which shows the circuit structure for 1 phase of the conventional FC soft switching converter. It is a flowchart which shows a soft switching process. FIG. 6 is a diagram showing an operation in mode 1. FIG. 6 is a diagram illustrating an operation in mode 2. FIG. 6 is a diagram illustrating an operation in mode 3. FIG. 10 is a diagram illustrating an operation in mode 4. FIG. 10 is a diagram illustrating an operation in mode 5. FIG. 10 is a diagram illustrating an operation in mode 6. It is the figure which illustrated the relationship of the snubber capacitor voltage Vc of mode 5, the element voltage Ve, and the element current Ie. It is a figure for demonstrating the problem of the conventional FC soft switching converter. It is a figure which shows the circuit structure for 1 phase of the FC soft switching converter which concerns on 1st Embodiment. It is a figure which shows the circuit structure for 1 phase of the FC soft switching converter which concerns on the same embodiment. It is a figure which shows the circuit structure for 1 phase of the FC soft switching converter which concerns on the modification 1. FIG. It is a figure which shows the circuit structure for 1 phase of the FC soft switching converter which concerns on the modification 2. FIG. It is a figure which shows the circuit structure of the FC soft switching converter which concerns on the modification 3. It is a system configuration figure of the FCHV system concerning a 2nd embodiment. It is a figure which shows the circuit structure of the gate voltage control circuit which concerns on the same embodiment. 7 is a diagram illustrating a circuit configuration of a gate voltage control circuit according to Modification 1. FIG. It is a figure for demonstrating the generation | occurrence | production mechanism of the surge voltage in the auxiliary circuit of a soft switching converter.

A. First Embodiment Hereinafter, an embodiment according to the present invention will be described with reference to the drawings.
FIG. 1 shows a configuration of an FCHV system mounted on a vehicle according to the first embodiment. In the following description, a fuel cell vehicle (FCHV) is assumed as an example of the vehicle, but the present invention can also be applied to an electric vehicle. Further, the present invention can be applied not only to vehicles but also to various moving bodies (for example, ships, airplanes, robots, etc.), stationary power sources, and portable fuel cell systems.

A-1. Overall System Configuration FIG. 1 is an overall system diagram of an FCHV system 100.
In the FCHV system 100, an FC converter 250 is provided between the fuel cell 110 and the inverter 140, and a DC / DC converter (hereinafter referred to as a battery converter) 180 is provided between the battery 120 and the inverter 140.

  The fuel cell 110 is a solid polymer electrolyte cell stack in which a plurality of unit cells are stacked in series. The fuel cell 110 is provided with a voltage sensor V0 for detecting the output voltage Vfcmes of the fuel cell 110 and a current sensor I0 for detecting the output current Ifcmes. In the fuel cell 110, the oxidation reaction of the formula (1) occurs in the anode electrode, the reduction reaction of the formula (2) occurs in the cathode electrode, and the electromotive reaction of the formula (3) occurs in the fuel cell 110 as a whole.

H ₂ → 2H ⁺ + 2e ⁻ (1)
(1/2) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (2)
H ₂ + (1/2) O ₂ → H ₂ O (3)

  The unit cell has a structure in which a MEA in which a polymer electrolyte membrane or the like is sandwiched between two electrodes, a fuel electrode and an air electrode, is sandwiched between separators for supplying fuel gas and oxidizing gas. The anode electrode is provided with an anode electrode catalyst layer on the porous support layer, and the cathode electrode is provided with a cathode electrode catalyst layer on the porous support layer.

  The fuel cell 110 is provided with a system for supplying fuel gas to the anode electrode, a system for supplying oxidizing gas to the cathode electrode, and a system for supplying coolant (all not shown). By controlling the supply amount of the fuel gas and the supply amount of the oxidizing gas according to the signal, it is possible to generate desired power.

  The FC converter 250 plays a role of controlling the output voltage Vfcmes of the fuel cell 110, and converts the output voltage Vfcmes input to the primary side (input side: fuel cell 110 side) into a voltage value different from the primary side ( Step-up or step-down) and output to the secondary side (output side: inverter 140 side). Conversely, the voltage input to the secondary side is converted to a voltage different from the secondary side and output to the primary side. A bidirectional voltage converter. The FC converter 250 controls the output voltage Vfcmes of the fuel cell 110 to be a voltage corresponding to the target output.

  The battery 120 is connected in parallel to the fuel cell 110 with respect to the load 130, and stores a surplus power storage source, a regenerative energy storage source during regenerative braking, and an energy buffer when the load fluctuates due to acceleration or deceleration of the fuel cell vehicle. Function as. As the battery 120, for example, a secondary battery such as a nickel / cadmium storage battery, a nickel / hydrogen storage battery, or a lithium secondary battery is used.

  The battery converter 180 plays a role of controlling the input voltage of the inverter 140 and has a circuit configuration similar to that of the FC converter 250, for example. Note that a step-up converter may be employed as the battery converter 180, but a step-up / step-down converter capable of step-up and step-down operations may be employed instead, and the input voltage of the inverter 140 can be controlled. Any configuration can be adopted.

  The inverter 140 is, for example, a PWM inverter driven by a pulse width modulation method, and converts DC power output from the fuel cell 110 or the battery 120 into three-phase AC power in accordance with a control command from the controller 160, thereby obtaining a traction motor. The rotational torque of 131 is controlled.

  The traction motor 131 is the main power of the vehicle, and generates regenerative power during deceleration. The differential 132 is a reduction device that reduces the high-speed rotation of the traction motor 131 to a predetermined number of rotations and rotates the shaft on which the tire 133 is provided. The shaft is provided with a wheel speed sensor (not shown) and the like, thereby detecting the vehicle speed of the vehicle. In the present embodiment, all devices (including the traction motor 131 and the differential 132) that can operate by receiving power supplied from the fuel cell 110 are collectively referred to as a load 130.

  The controller 160 is a computer system for controlling the FCHV system 100 and includes, for example, a CPU, a RAM, a ROM, and the like. The controller 160 inputs various signals (for example, a signal representing the accelerator opening, a signal representing the vehicle speed, a signal representing the output current and output terminal voltage of the fuel cell 110) supplied from the sensor group 170, and the load. The required power of 130 (that is, the required power of the entire system) is obtained.

  The required power of the load 130 is, for example, the total value of the vehicle running power and the auxiliary machine power. Auxiliary power is the power consumed by in-vehicle accessories (humidifiers, air compressors, hydrogen pumps, cooling water circulation pumps, etc.), and equipment required for vehicle travel (transmissions, wheel control devices, steering devices, and suspensions) Power consumed by devices, etc., and power consumed by devices (air conditioners, lighting fixtures, audio, etc.) disposed in the passenger space.

  Then, the controller (converter control device) 160 determines the distribution of output power between the fuel cell 110 and the battery 120 and calculates a power generation command value. When the controller 160 obtains the required power for the fuel cell 110 and the battery 120, the controller 160 controls the operation of the FC converter 250 and the battery converter 180 so that the required power is obtained.

A-2. Configuration of FC Converter As shown in FIG. 1, the FC converter 250 has a circuit configuration as a three-phase bridge type converter configured by a U phase, a V phase, and a W phase. The circuit configuration of the three-phase bridge type converter combines an inverter-like circuit part that once converts an input DC voltage into AC, and a part that rectifies the AC again to convert it to a different DC voltage. The present embodiment employs a step-up type soft switching converter (hereinafter referred to as an FC soft switching converter) as the FC converter 250, and is characterized in that a freewheel circuit described later is set. Hereinafter, the features of the present embodiment will be described in detail in comparison with a conventional FC soft switching converter that does not include a freewheel circuit.

A-2-1. 2. Description of Conventional FC Soft Switching Converter FIG. 2 is a diagram showing a circuit configuration for one phase of a conventional FC soft switching converter 150 mounted on the FCHV system 100. In the following description, a converter for one phase constituting the FC soft switching converter 150 is referred to as an FC soft switching converter 150. Further, the voltage before boosting input to the FC soft switching converter 150 is called a converter input voltage Vin, and the voltage after boosting output from the FC soft switching converter 150 is called a converter output voltage Vout.

As shown in FIG. 2, the FC soft switching converter 150 includes a main boosting circuit 12a for performing a boosting operation and an auxiliary circuit 12b for performing a soft switching operation.
The main booster circuit 12a switches the energy stored in the coil L1 to the load 130 via the diode D5 by the switching operation of the switching circuit composed of the first switching element S1 made of IGBT (Insulated Gate Bipolar Transistor) and the like and the diode D4. The output voltage of the fuel cell 110 is boosted by releasing.

More specifically, one end of the coil L1 is connected to the high potential side terminal of the fuel cell 110, one pole of the first switching element S1 is connected to the other end of the coil L1, and the other end of the first switching element S1. Is connected to the low potential side terminal of the fuel cell 110. The anode of the diode D5 is connected to the other end of the coil L1, and the capacitor C3 functioning as a smoothing capacitor is connected between the cathode of the diode D5 and the other end of the first switching element S1. The main booster circuit 12a is provided with a smoothing capacitor C1 on the side of the fuel cell 110, whereby the ripple of the output current of the fuel cell 110 can be reduced.
Here, the voltage VH applied to the capacitor C3 becomes the converter output voltage Vout of the FC soft switching converter 150, and the voltage VL applied to the smoothing capacitor C1 is the output voltage of the fuel cell 110 and the converter input voltage of the FC soft switching converter 150. Vin.

  The auxiliary circuit 12b includes a first series connection body including a diode D3 connected in parallel to the first switching element S1 and a snubber capacitor C2 connected in series to the diode D3. In the first series connection body, the anode of the diode D3 is connected to the other end of the coil L1, and the cathode of the diode D3 is connected to one end of the snubber capacitor C2. Further, the other end of the snubber capacitor C2 is connected to a terminal on the low potential side of the fuel cell 110.

  Further, the auxiliary circuit 12b includes a second series connection body in which a coil L2, which is an inductive element, a diode D2, and a switching circuit including the second switching element S2 and the diode D1 are connected in series. In the second series connection body, one end of the coil L2 is connected to a connection portion between the diode D3 and the snubber capacitor C2 of the first series connection body. Furthermore, the anode of the diode D2 is connected to the other end of the coil L2, while the cathode of the diode D2 is connected to the pole of one end of the second switching element S2. The other end of the second switching element S2 is connected to one end of the coil L1. In addition, about the circuit topology of this 2nd serial connection body, the aspect which changed suitably the serial order of the switching circuit by the coil L2, the diode D2, the 2nd switching element S2, etc. can also be employ | adopted. For example, by switching the order of the switching circuit including the coil L2 and the second switching element S2, the coil L1 and the coil L2 can be integrated in an actual mounting circuit, and the modularization of the semiconductor element is facilitated.

  In the FC soft switching converter 150 configured as described above, the controller 160 adjusts the switching duty ratio of the first switching element S1, so that the boost ratio by the FC soft switching converter 150, that is, the converter output voltage with respect to the converter input voltage Vin. The ratio of Vout is controlled. Also, soft switching is realized by interposing the switching operation of the second switching element S2 of the auxiliary circuit 12b in the switching operation of the first switching element S1.

  Next, the soft switching operation by the FC soft switching converter 150 will be described with reference to FIGS. Here, FIG. 3 is a flowchart of one cycle of processing (hereinafter referred to as soft switching processing) of the FC soft switching converter 150 through the soft switching operation. The controller 160 sequentially executes steps S101 to S106 shown in FIG. To form a cycle. In the following description, modes representing the current and voltage states of the FC soft switching converter 150 are expressed as mode 1 to mode 6, respectively, and the states are shown in FIGS. 4 to 7, the current flowing through the circuit is indicated by arrows.

<Soft switching operation>
First, the initial state in which the soft switching process shown in FIG. 3 is performed is a state in which power required for the load 130 is supplied from the fuel cell 110, that is, both the first switching element S1 and the second switching element S2 are turned off. Thus, a current is supplied to the load 130 via the coil L1 and the diode D5.

(Mode 1; see Fig. 4)
In step S101, the first switching element S1 is kept off, while the second switching element S2 is turned on. When such a switching operation is performed, the current flowing to the load 130 side through the coil L1, the diode D3, the coil L2, and the second switching element S2 due to the potential difference between the output voltage VH and the input voltage VL of the FC soft switching converter 150. It gradually shifts to the auxiliary circuit 12b side. In FIG. 4, the state of current transfer from the load 130 side to the auxiliary circuit 12b side is indicated by white arrows.

Ｉｐ；相電流
Ｌ２ｉｄ；コイルＬ２のインダクタンス Furthermore, by turning on the second switching element S2, current circulation occurs in the direction of the arrow _Dm11 shown in FIG. Here, the current changing speed of the second switching element S2 increases according to the voltage across the coil L2 (VH−VL) and the inductance of the coil L2, but the current flowing through the second switching element S2 is suppressed by the coil L2. Therefore, as a result, soft turn-off of the current (see arrow D _m12 shown in FIG. 4) flowing to the load 130 side via the diode D5 is realized.
Here, the transition completion time tm1 from mode 1 to mode 2 is expressed by the following equation (4).

Ip; phase current L2id; inductance of coil L2

Ｃ２ｄ；コンデンサＣ２の容量 (Mode 2; see FIG. 5)
When the transition completion time elapses and the process proceeds to step S102, the current flowing through the diode D5 becomes zero, and the current flows into the auxiliary circuit 12b via the coil L1 and the diode D3 (see arrow D _m21 shown in FIG. 5). Instead, due to the potential difference between the snubber capacitor C2 and the voltage VL of the fuel cell 110, the charge charged in the snubber capacitor C2 flows _{toward the} auxiliary circuit 12b (see arrow D _m22 shown in FIG. 5). The voltage applied to the first switching element S1 is determined according to the capacitance of the snubber capacitor C2. Here, in mode 2, when the first switching element S1 is turned off, the charge charged in the snubber capacitor C2 flows into the auxiliary circuit 12b, so that the voltage applied to the snubber capacitor C2 decreases (VH → 0). go. At this time, current continues to flow until the voltage of the snubber capacitor C2 becomes zero due to LC resonance of the coil L2 and the snubber capacitor C2. Here, since the anode of the diode D2 is connected to one end of the coil L2, the LC resonance stops at a half wave. For this reason, the snubber capacitor C2 holds 0 V after discharging. A part of the current flowing through the auxiliary circuit 12b flows to the auxiliary circuit 12b side through the diode D4.
Here, the transition completion time tm2 from mode 2 to mode 3 is expressed by the following equation (5).

C2d: capacitance of capacitor C2

(Mode 3; see FIG. 6)
When the transition completion time elapses and the charge of the snubber capacitor C2 is completely discharged, the first switching element S2 is turned on, and the process proceeds to step S103. When the voltage of the snubber capacitor C2 is zero, the voltage applied to the first switching element S1 is also zero. In such a state, the current Il1 flowing in the coil L1 is the sum of the current Idm31 flowing on the auxiliary circuit 12b side indicated by the arrow Dm31 and the current Idm32 flowing through the first switching element S1 indicated by the arrow Dm32 (the following equation (6) reference).

Here, the current Idm31 flowing through the first switching element S1 is determined according to the decreasing rate of the current Idm31 flowing through the auxiliary circuit 12b. The current change rate of the current Idm31 flowing on the auxiliary circuit 12b side is expressed by the following equation (7). That is, since the current Idm31 flowing to the auxiliary circuit 12b side decreases at the changing speed of the following formula (7), even if the first switching element S1 is turned on, the current flowing to the first switching element S1 suddenly rises. However, ZCS (Zero Current Switching) is realized.

Ｔｃｏｎ；制御周期
なお、制御周期とは、ステップＳ１０１〜ステップＳ１０６までの一連の処理を一周期（一サイクル）としたときのソフトスイッチング処理の時間周期を意味する。 (Mode 4; see FIG. 7)
In step S104, as the state in step S103 continues, the amount of current flowing into coil L1 is increased to gradually increase the energy stored in coil L1 (see arrow D _{m42 in} FIG. 7). . Here, a diode D2 having an anode connected to one end of the coil L2 and a cathode connected to one end of the second switching element S2 exists between the coil L2 and the second switching element S2 in the auxiliary circuit 12b. Therefore, no reverse current flows through the coil L2 (see arrow D _m41 shown in FIG. 7), and the snubber capacitor C2 is not charged via the second switching element S2. At this time, since the first switching element S1 is turned on, the snubber capacitor C2 is not charged via the diode D3. Therefore, the current of the coil L1 is equal to the current of the first switching element S1, and the energy stored in the coil L1 is gradually increased. Here, the turn-on time Ts1 of the first switching element S1 is represented by the following formula (8).

Tcon; control period The control period means a time period of the soft switching process when a series of processes from step S101 to step S106 is defined as one period (one cycle).

(Mode 5; see FIG. 8)
When desired energy is stored in the coil L1 in step S104, the first switching element S1 and the second switching element S2 are turned off, and a current flows through a path indicated by an arrow D _m51 in FIG. Here, FIG. 10 shows the voltage of the snubber capacitor C2 in mode 5 (hereinafter referred to as snubber capacitor voltage) Vc, the voltage applied to the first switching element S1 (hereinafter referred to as element voltage) Ve, and the current flowing through the first switching element S1 (hereinafter referred to as “voltage”). , Element current) Ie. When the above switching operation is performed, in the mode 2, the electric charge is extracted and the snubber capacitor C2 in the low voltage state is charged, so that the snubber capacitor voltage Vc becomes the converter output voltage VH of the FC soft switching converter 150. Ascend toward. At this time, the rising speed of the device voltage Ve is suppressed by charging the snubber capacitor C2 (that is, the rising of the device voltage is slowed down), and the region where the tail current exists in the device current Ie (see α shown in FIG. 10). It is possible to reduce the switching loss at the.

(Mode 6; see FIG. 9)
When the snubber capacitor C2 is charged to the voltage VH, the energy stored in the coil L1 is released to the load 130 (see arrow D _m61 shown in FIG. 9). Here, the turn-off time Ts2 of the first switching element S1 is expressed by the following formula (9).

  By performing the soft switching process described above, the switching loss of the FC soft switching converter 150 can be suppressed as much as possible, and the output voltage of the fuel cell 110 can be increased to a desired voltage and supplied to the load 130. It becomes.

<Problems of conventional FC soft switching converter>
FIG. 11 is a diagram for explaining a problem of the conventional FC soft switching converter 150, and shows a state in the mode 1 described above.
When the second switching element S2 is turned on and the second switching element S2 is switched from on to off due to an open failure or the like in a state where current circulation occurs in the direction of the arrow _Dm11 and the coil L2 is energized. The current flowing through the coil L2 is suddenly interrupted. When such a sudden current interruption occurs, the current change rate di / dt becomes very large, a large surge voltage ΔV is generated, the element is destroyed, and in the worst case, the system must be stopped. (See the section on the problem to be solved by the invention). In the above description, the case where the second switching element S2 has an open failure is illustrated as an example in which the current flowing through the coil L2 is suddenly interrupted. However, it will be understood that the present invention is not limited to this. In the present embodiment, in order to prevent the occurrence of such a surge voltage ΔV, a free wheel circuit that can continue to pass current through the coil L2 even if the second switching element S2 is turned off while the coil L2 is energized. Set.

A-2-2. Description of FC Soft Switching Converter 250 of the Present Embodiment FIG. 12 is a diagram showing a circuit configuration for one phase of the FC soft switching converter 250. 2 corresponding to those in FIG. 2 are denoted by the same reference numerals, and detailed description thereof is omitted.
As apparent from comparison between FIG. 12 and FIG. 2, the soft switching converter 250 according to the present embodiment includes an auxiliary circuit 22b in which the arrangement order of the coil L2 and the second switching element S2 of the auxiliary circuit 12b shown in FIG. One of the features is that a free wheel circuit 22c including the free wheel diode D6 is formed.

  In the second series connection body of the auxiliary circuit 22b according to the present embodiment, the anode terminal of the diode D2 is connected to the connection portion between the diode D3 of the first series connection body and the snubber capacitor C2. Furthermore, the cathode terminal of the diode D2 is connected to the pole at one end of the second switching element (auxiliary switch) S2. The pole at the other end of the second switching element S2 is connected to a connection site of the freewheel diode D6 that forms the freewheel circuit 22c with the coil L2. The anode of the freewheel diode D6 is connected to the low potential side of the fuel cell 110, while the cathode of the freewheel diode D6 is connected to the coil L2.

According to such a configuration, even when the coil L2 is energized (second switching element; on), an open failure or the like occurs in the second switching element S2, and the second switching element S2 is switched from on to off. Due to the presence of the freewheel diode D6, current circulation occurs in the direction of the arrow _Dm71 (the same direction as when the coil L2 is energized) as shown in FIG. 13, and the current continues to flow through the coil L2. Thus, it is possible to prevent the occurrence of a surge voltage that destroys the second switching element S2.

<Modification 1>
FIG. 14A is a diagram illustrating a circuit configuration of the FC soft switching converter 350 according to the first modification.
14A and 2, the soft switching converter 350 according to the first modification includes a coil L2 and a second switching element S2 of the auxiliary circuit 12b illustrated in FIG. 2 and a Zener diode. It is characterized in that a free wheel circuit 22c including D7 (or varistor V1) is formed.

  In the second series connection body of the auxiliary circuit 22b according to the present embodiment, one end of the coil L2 and one pole of the second switching element (auxiliary switch S2) are connected. Further, the cathode of the Zener diode D7 (or one end of the varistor V1) is connected to the connection portion of the coil L2 and the second switching element S2, while the anode of the Zener diode D7 (or the other end of the varistor V1) is connected to the fuel cell 110. Is connected to the low potential side.

According to such a configuration, even when the coil L2 is energized (second switching element; on), an open failure or the like occurs in the second switching element S2, and the second switching element S2 is switched from on to off. Due to the presence of the Zener diode D7 (or varistor V1), a current can flow in the direction of the arrow _{Dv1 in} FIG. 14A (that is, the current of the coil L2 can be freewheeled), thereby the second switching element S2. It is possible to prevent the generation of a surge voltage that destroys the battery.

<Modification 2>
FIG. 14B is a diagram illustrating a circuit configuration of the FC soft switching converter 450 according to the second modification.
14B and 14A, the soft switching converter 450 according to the modified example 2 has a free wheel circuit 22c including a Zener diode D7 (or varistor V1) connected in parallel to the coil L2. There is a feature.

  In the second series connection body of the auxiliary circuit 22b according to the present embodiment, one end of the coil L2 and one pole of the second switching element (auxiliary switch S2) are connected. Further, the cathode of the Zener diode D7 (or one end of the varistor V1) is connected to the connection site between the coil L2 and the second switching element S2, while the anode of the Zener diode D7 (or the other end of the varistor V1) is connected to the coil L2. Connected to the other end.

  Even with this configuration, even when the coil L2 is energized (second switching element; on), even if an open failure occurs in the second switching element S2, and the second switching element S2 is switched from on to off, Due to the presence of the Zener diode D7 (or varistor V1), a current can flow in the direction of the arrow Dv2 in FIG. 14B (that is, the current of the coil L2 can be freewheeled), thereby destroying the second switching element S2. Such a surge voltage can be prevented from occurring.

<Modification 3>
In the above-described embodiment, the FC soft switching converter 250 has been described with respect to the case where the U-phase, V-phase, and W-phase interleave configurations are adopted and the auxiliary circuit 22b and the freewheel circuit 22c are provided for each phase. In order to reduce the number of points and the cost, some of these circuit elements may be shared.

FIG. 15 is a diagram illustrating a circuit configuration of the FC soft switching converter 550 according to the third modification.
In the third modification, by utilizing the fact that the operation time of the auxiliary circuit 32b is shorter than the operation time of the main booster circuit 32a, the coil L2 is shared by the auxiliary circuit 32b provided in each phase, and The freewheel circuit 32c (here, the freewheel diode D6) is shared. Since other configurations are the same as those of the first embodiment, the corresponding parts are denoted by the same reference numerals, and detailed description thereof is omitted. In this way, by sharing a part of the circuit elements, the cost increase of the entire circuit may be suppressed.
Note that a part having a low withstand voltage may be set in a part of the coil L2, and the inside of the coil L2 may be short-circuited before the voltage generated in the coil L2 reaches the element breakdown voltage to prevent the generation of a surge voltage.

B. Second Embodiment FIG. 16 is an overall system diagram of an FCHV system 300 according to a second embodiment, and FIG. 17 is a diagram showing a circuit configuration of a gate voltage control circuit 500.
The FCHV system 300 includes a gate voltage control circuit 500 instead of the freewheel circuit 32c. Since other configurations are the same as those of the FCHV system 100 shown in FIG. 1, the same reference numerals are given to corresponding portions, and detailed description thereof is omitted.

  The gate voltage control circuit 500 includes a circuit driving power supply 510, a turn-on control unit 520, a turn-off control unit 530, and a drive circuit 540. The turn-on control unit 520 includes a switch W1 for turning on the second switching element S2 and a gate resistor R1 for turn-on, while the turn-off control unit 530 includes a switch W2 for turning off the second switching element S2. W3 and gate resistors R2 and R3 for turn-off are provided. The resistance value of the gate resistor R3 is set larger than the resistance value of the gate resistor R2. Here, since the surge voltage ΔV is proportional to the current change rate di / dt (see the section of the problem to be solved by the invention), in the present embodiment, the gate resistance R3 for turning off the second switching element S2 is set large. The surge voltage ΔV is reduced by reducing the current change rate di / dt. For the gate resistor R3, a resistance value (element breakdown resistance threshold value) may be set so that the surge voltage ΔV does not exceed the withstand voltage of the switching element S2. Such a gate resistor also functions as an energy emission source that consumes energy as a switching loss.

The drive circuit (resistance control circuit) 540 is a circuit that controls turn-on and turn-off of the second switching element S2 and controls a gate resistance value for turn-off in accordance with a signal given from the controller 160. When the system is normal, when the second switching element S2 is turned on, the drive circuit 440 turns on the switch W1, while when the second switching element S2 is turned off, the drive circuit 540 includes the switches W2 and W3. Turn on.
On the other hand, when the drive circuit 540 detects that the coil L2 is energized and the second switching element S2 is turned off, the drive circuit 540 should prevent element destruction of the second switching element S2 due to generation of the surge voltage ΔV. , The resistance is switched to a high resistance only by the resistance R3. More specifically, the drive circuit (detection means) 540 detects the current flowing through the coil L2, and grasps the voltage between the collector and the emitter of the second switching element S2 to detect the switching state (on / off state). ) Is detected. When the drive circuit 540 detects that the coil L2 is energized and the second switching element S2 is turned off in this state, the drive circuit 540 turns off the switch S2 and turns the gate resistance R2 and R3 from a low resistance in parallel. Switch to a high resistance only resistor R3.

  According to such a configuration, the gate voltage R3 for turning off the second switching element S2 is set large, and the current change rate di / dt is reduced to reduce the surge voltage ΔV. Thus, even when the above-described surge voltage ΔV is generated, it is possible to prevent the second switching element S2 from being destroyed.

  The second switching element S2 may be a switching element that does not turn off even when a circuit abnormality occurs, that is, a normally on type switching element.

  In addition, an energization determination circuit that implements whether or not the coil L2 is energized (energization determination) is provided to control the gate resistances R1 to R3 so that the second switching element S2 cannot be turned off when the coil L2 is energized. May be.

<Modification 1>
Here, in the above-described second embodiment, the case where the transition from the turn-on to the turn-off of the second switching element S2 is detected and the gate resistance of the second switching element S2 is actively switched has been described. You may do it.

FIG. 18 is a diagram illustrating a gate voltage control circuit 600 according to the first modification.
The gate voltage control circuit 600 includes a power source 610 for driving the circuit, a gate resistance circuit 620, and a capacitor Cge connected between the gate (G) and the emitter (E) of the second auxiliary switch S2. .
The gate resistance circuit 620 includes resistors R1 and R2 connected in parallel, and a diode Dg whose cathode is connected to the resistor R2.

  According to this configuration, when the second switching element S2 is turned on (when the capacitor Cge is charged), the gate resistance R becomes a low resistance in which the resistors R1 and R2 are connected in parallel, while the second switching element S2 Is turned off (when the capacitor Cge is discharged), the gate resistance R is switched to a high resistance of only the resistor R1. Thus, by switching the gate resistance of the switching element S2 passively, the gate resistance R at the time of turn-off of the second switching element S2 is set large, and the current change rate di / dt is reduced to reduce the surge. It is possible to reduce the voltage ΔV. For the resistor R1, a resistance value (element breakdown resistance threshold value) may be set so that the surge voltage ΔV does not exceed the withstand voltage of the switching element S2.

DESCRIPTION OF SYMBOLS 100,300 ... FCHV system, 110 ... Fuel cell, 120 ... Battery, 130 ... Load, 140 ... Inverter, 150,250 ... FC converter, 160 ... Controller, 170 ... Sensor group, 180 ... Battery converter, 400 ... Gate voltage control Circuit, 410 ... Power supply, 420 ... Turn-on controller, 430 ... Turn-off controller, 440 ... Drive circuit, 22a ... Main booster circuit, 22b ... Auxiliary circuit, 22c ... Freewheel circuit, S1, S2 ... Switching elements, C1, C3 ... smoothing capacitor, C2 ... snubber capacitor, L1, L2, ... coil, D1, D2, D3, D4, D5 ... diode, D6 ... freewheeling diode

Claims (6)

A control device for a soft switching converter having an auxiliary circuit for controlling an output voltage of a fuel cell,
A converter control device comprising a freewheel circuit for continuing to flow a current in the same direction as the energization when the auxiliary switch constituting the auxiliary circuit is turned off while the auxiliary coil constituting the auxiliary circuit is energized. The auxiliary coil has one end connected to the high potential side of the fuel cell and the other end connected to one pole of the auxiliary switch,
The freewheeling circuit comprises a freewheeling diode;
2. The converter control device according to claim 1, wherein the free wheel diode has an anode terminal connected to a low potential side of the fuel cell and a cathode terminal connected to a connection portion of the auxiliary coil and the auxiliary switch. . The main booster circuit of the soft switching converter is
A main coil having one end connected to a terminal on the high potential side of the fuel cell;
A main switch for switching, with one end connected to the other end of the main coil and the other end connected to a terminal on the low potential side of the fuel cell;
A first diode having a cathode connected to the other end of the main coil;
A smoothing capacitor provided between the anode of the first diode and the other end of the main switch;
The auxiliary circuit is
A first series connection including a second diode and a snubber capacitor connected in parallel to the main switch and connected to the other end of the main coil and a terminal on the low potential side of the fuel cell;
3. A second series connection body including a third diode, an auxiliary coil, and the auxiliary switch connected between a connection portion of the second diode and the snubber capacitor and one end of the main coil. The converter control apparatus described in 1. A control device for a multi-phase soft switching converter having an auxiliary circuit for controlling the output voltage of a fuel cell for each phase,
The auxiliary coil constituting the auxiliary circuit of each phase is common to the auxiliary circuits of all phases,
When the auxiliary coil constituting the auxiliary circuit is energized and one or more auxiliary switches that have been turned on to form the energized state of the auxiliary coil are turned off, the auxiliary coil is turned in the same direction as the energized state. A converter control device provided with a freewheel circuit for keeping current flowing. A control device for a soft switching converter having an auxiliary circuit for controlling an output voltage of a fuel cell,
Comprising a resistance control circuit for varying a gate resistance value of a semiconductor element constituting an auxiliary switch of the auxiliary circuit;
A control device for a converter, wherein a gate resistance value when the auxiliary switch is turned off is larger than a gate resistance value when the auxiliary switch is turned on and larger than an element breakdown resistance threshold value. A detecting means for detecting a transition from turn-on to turn-off of the auxiliary switch;
The converter according to claim 5, wherein the resistance control circuit sets a gate resistance value of the semiconductor element to a value larger than a set element breakdown resistance threshold when the transition is detected by the detection unit. Control device.

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