JP5333007B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system.

  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).

By using a soft switching converter, the speed can be increased compared to a conventional converter capable of only hard switching, but there is a problem that the converter becomes large.
In view of such a problem, it is conceivable to eliminate a part of the components constituting the soft switching converter (specifically, a smoothing capacitor provided on the input side of the soft switching converter).

JP 2005-102438 A

  However, if the smoothing capacitor on the input side of the soft switching converter (hereinafter abbreviated as the input side capacitor) is abolished, the fuel cell outputs a large fluctuation in output current (current with a large ripple component) and soft switching A new problem arises that power loss in the converter increases.

  18 and 19 are diagrams illustrating the output current waveform of the fuel cell before and after the abolition of the input side capacitor. As shown in FIG. 18, when an input side capacitor is provided, an output current waveform with a small ripple component can be obtained, whereas when the input side capacitor is abolished, a ripple component of the output current is obtained. Becomes larger (see FIG. 19).

  As described above, when the ripple component of the FC current increases, a new problem arises that the effective current value increases and abnormal overheating occurs in the fuel cell.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a fuel cell system capable of suppressing abnormal overheating of the fuel cell regardless of the effective current value of the fuel cell. .

In order to solve the above problems, a fuel cell system according to the present invention includes a fuel cell, a cooling mechanism for cooling the fuel cell, and a main switch for controlling the output voltage of the fuel cell, and a smoothing capacitor is provided on the input side. a fuel cell system comprising a DC / DC converter and comprises a was DC / DC converter does not have to be, for the DC / DC converter, and a non-switching control mode for always turn off the main switch, the load When the DC / DC converter is set in the hard switching control mode, and the switching control means for switching between the hard switching control mode for turning on and off the main switch according to the request, the DC / DC A state in which the cooling performance of the cooling mechanism is higher than when the DC converter is set to the non-switching control mode. Characterized by comprising a cooling control means which cools the fuel cell.

  According to such a configuration, when the DC / DC converter is set to the hard switching control mode, the cooling performance of the cooling mechanism is improved compared to the case where the DC / DC converter is set to the non-switching control mode. Cool the fuel cell in the state. The ripple component of the FC current when the DC / DC converter is set to the hard switching control mode (see FIG. 4B) is the ripple component of the FC current when the DC / DC converter is set to the non-switching control mode (see FIG. 4B). 4), and the fuel cell 110 is likely to overheat. Therefore, the cooling performance of the cooling mechanism 200 is increased in accordance with the transition from the non-switching control mode to the hard switching control mode, thereby causing abnormal overheating of the fuel cell. Can be prevented.

  Here, in the above configuration, the cooling mechanism includes a radiator for cooling the refrigerant, a circulation channel for circulating the refrigerant from the fuel cell via the radiator, and the fuel cell. A bypass flow path for bypassing the radiator; a flow rate of the refrigerant that is provided at a connection point between the circulation path and the bypass flow path and that is sent to the radiator side; and a flow rate of the refrigerant that is sent to the bypass flow path side. The cooling control means, when the DC / DC converter is set in a hard switching control mode, than when the DC / DC converter is set in a non-switching control mode. It is preferable that the opening degree of the valve is adjusted so that the flow rate of the refrigerant sent to the radiator side is increased.

Another fuel cell system according to the present invention includes a fuel cell, a cooling mechanism for cooling the fuel cell, a main booster circuit and an auxiliary circuit for controlling the output voltage of the fuel cell , and smoothing. A fuel cell system comprising a soft switching converter having no capacitor on the input side , wherein the main switch constituting the main booster circuit and the auxiliary switch constituting the auxiliary circuit are always turned off for the soft switching converter A non-switching control mode; a hard switching control mode in which the main switch is turned on and off in response to a load request; and the auxiliary switch and the main switch in response to a load request Switching control means for switching between soft switching control modes for turning on and off, and When the soft switching converter is set to the soft switching control mode, the cooling performance of the cooling mechanism is improved as compared with the case where the soft switching converter is set to the non-switching control mode or the hard switching control mode. And cooling control means for cooling the fuel cell in a state.

  Here, in the above configuration, it is preferable that the cooling control unit sets the cooling performance of the cooling mechanism high in the order of the non-switching control mode, the hard switching control mode, and the soft switching control mode. .

  In the above configuration, the cooling mechanism includes a radiator for cooling the refrigerant, a circulation channel for circulating the refrigerant from the fuel cell via the radiator, and the fuel cell from the fuel cell. A bypass flow path for bypassing the radiator, a flow rate of the refrigerant sent to the radiator side and a flow rate of the refrigerant sent to the bypass flow path side are controlled at a connection point between the circulation path and the bypass flow path The cooling control means, when the soft switching converter is set to the soft switching control mode, the soft switching converter is set to the non-switching control mode or the hard switching control mode. Opening of the valve so that the flow rate of the refrigerant sent to the radiator side becomes larger than the case Mode of adjustment preferred.

  Furthermore, in the above configuration, the cooling control means increases the flow rate of the refrigerant sent to the radiator in the order of the non-switching control mode, the hard switching control mode, and the soft switching control mode. Also preferred is an aspect of adjusting the opening of the valve.

Furthermore, the main booster circuit has a main coil having one end connected to a high potential side terminal of the fuel cell, one end connected to the other end of the main coil, and the other end being a low potential side of the fuel cell. A main switch for switching and a first diode with a cathode connected to the other end of the main coil, the auxiliary circuit is connected in parallel to the main switch, and A first series connection body including a second diode and a snubber capacitor, connected to the other end of the main coil and a terminal on the low potential side of the fuel cell; and a connection portion between the second diode and the snubber capacitor; An aspect having a second series connection body including a third diode, an auxiliary coil, and the auxiliary switch connected between one end of the main coil is also preferable.

  According to the present invention, abnormal overheating of the fuel cell can be suppressed regardless of the effective current value of the fuel cell.

It is a system configuration figure of the FCHV system concerning this embodiment. It is a figure which shows the circuit structure of the multiphase FC soft switching converter which concerns on the same embodiment. It is a figure which shows the circuit structure of the conventional multiphase FC soft switching converter. It is a figure which shows the circuit structure for 1 phase of FC soft switching converter. It is a figure which shows the fluctuation | variation of FC electric current at the time of soft switching control mode. It is a figure which shows the fluctuation | variation of FC electric current at the time of hard switching control mode. It is a figure which shows the fluctuation | variation of FC electric current at the time of non-switching control mode. It is the figure which illustrated the cooling control table. 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 which shows the voltage and electric current behavior in the transition process from mode 2 to mode 3. It is a flowchart which shows a cooling control process. It is the figure which illustrated the cooling control table which concerns on a modification. It is a flowchart which shows the cooling control process which concerns on a modification. It is the figure which illustrated the output current waveform of the fuel cell before the abolition of the input side capacitor. It is the figure which illustrated the output current waveform of the fuel cell after the abolition of the input side capacitor.

A. Embodiments Hereinafter, embodiments 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 present 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 The FCHV system 100 includes an FC converter 2500 between the fuel cell 110 and the inverter 140, and a DC / DC converter (hereinafter referred to as a battery converter) 180 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 2500 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 2500 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 2500, 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 160 determines the distribution of the output power between the fuel cell 110 and the battery 120, and calculates the 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 operations of the FC converter 2500 and the battery converter 180 so that the required power is obtained.

  The FC cooling mechanism 200 is a mechanism that cools the fuel cell 110 by circulating a cooling medium (for example, cooling water) through the cooling flow path. The FC cooling mechanism 200 includes a refrigerant flow path 230 connected to the fuel cell 110, a cooling pump 210 provided in the refrigerant flow path 230, a radiator 260 that cools the refrigerant discharged from the fuel cell 110, and the radiator 260. A bypass flow path 240 for bypassing, a flow rate of refrigerant sent to the radiator 260 side, and a three-way valve 250 for controlling the flow rate of refrigerant sent to the bypass flow path 240 side are provided. The cooling pump 210 drives the motor M to circulate the refrigerant in the refrigerant flow path of the fuel cell 110 to the fuel cell 110, and the refrigerant flow path 230 detects the temperature of the refrigerant (reflecting the FC temperature). 270 is provided.

A-2. Configuration of FC Converter As shown in FIG. 1, the FC converter 2500 has a circuit configuration as a three-phase resonant converter composed of a U phase, a V phase, and a W phase. The circuit configuration of the three-phase resonant 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. In the present embodiment, a multi-phase soft switching converter (hereinafter referred to as a multi-phase FC soft switching converter) provided with a freewheel circuit (details will be described later) is employed as the FC converter 2500.

A-2-1. 2. Description of Multi-Phase FC Soft Switching Converter FIG. 2A is a diagram showing a circuit configuration of a multi-phase FC soft switching converter 2500 mounted on the FCHV system 100 according to the present embodiment, and FIG. It is a figure which shows the circuit structure of FC soft switching converter 2500 '.

  2A and 2B, the multiphase FC soft switching converter 2500 according to the present embodiment has a configuration in which the input side capacitor C1 is removed from the conventional multiphase FC soft switching converter 2500 ′. have.

  As described in the section of the problem to be solved, if the smoothing capacitor on the input side of the multi-phase FC soft switching converter 2500 is removed, the ripple component of the FC current increases (see FIG. B), and the current effective There is a problem that the value increases and abnormal overheating occurs in the fuel cell 110.

  Thus, in the present embodiment, when the ripple component of the FC current increases and the effective current value increases, the cooling performance of the cooling mechanism 200 that cools the fuel cell 110 is improved, thereby causing abnormal overheating of the fuel cell 110 in advance. To prevent.

In this embodiment, as will be described later, the control mode of the FC soft switching converter 250 is switched between the soft switching control mode, the hard switching control mode, and the non-switching control mode in accordance with the required power of the load 140 and the like.
Here, since the ripple component of the FC current greatly varies depending on each control mode (that is, the current effective value varies greatly), in the present embodiment, according to switching of the control mode of the FC soft switching converter 250 (for example, “Non-switching control mode” → “Hard switching control mode”), control for changing the cooling performance of the cooling mechanism 200 is performed, thereby preventing abnormal overheating of the fuel cell 110 in advance.

  Before describing the details of the control mode of the FC soft switching converter 250, the basic configuration of the FC soft switching converter 250 will be described first.

A-2-2. Basic Configuration of FC Soft Switching Converter FIG. 3 is a diagram showing a circuit configuration for one phase of a multi-phase FC soft switching converter 2500.
In the following description, the U-phase, V-phase, and W-phase FC soft switching converters constituting the multi-phase FC soft switching converter 2500 are referred to as FC soft switching converters 250a, 25b, and 250c, respectively, and need not be particularly distinguished. In some cases, it is simply called FC soft switching converter 250. Further, the voltage before boosting input to the FC soft switching converter 250 is called a converter input voltage Vin, and the voltage after boosting output from the FC soft switching converter 250 is called a converter output voltage Vout.

As shown in FIG. 3, each FC soft switching converter 250 includes a main boosting circuit 22a for performing a boosting operation, an auxiliary circuit 22b for performing a soft switching operation, and a freewheel circuit 22c. .
The main booster circuit 22a switches the energy stored in the coil L1 to the load 130 via the diode D5 by the switching operation of the switching circuit including the first switching element S1 made of IGBT (Insulated Gate Bipolar Transistor) 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 cathode terminal 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 anode terminal of the diode D5 and the other end of the first switching element S1. .

  Here, the voltage VH applied to the capacitor C3 becomes the converter output voltage Vout of the FC soft switching converter 250, and the output voltage VL of the fuel cell 110 becomes the converter input voltage Vin of the FC soft switching converter 250.

  The auxiliary circuit 22b includes a first series connection body including a clamp diode D3 connected in parallel to the first switching element S1 and a snubber capacitor C2 connected in series to the clamp diode D3. In the first series connection body, the cathode terminal of the clamp diode D3 is connected to the other end of the coil L1, and the anode terminal of the clamp 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. A voltage sensor Sv2 that detects the voltage across the snubber capacitor C2 is provided.

Further, the auxiliary circuit 22b includes a diode D2, a second switching element S2, a diode D1, and a second series connection body configured by an auxiliary coil L2 common to each phase.
In the second series connection body, 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. Moreover, the pole of the other end of the second switching element S2 is connected to a connection site between the auxiliary coil L2 and the freewheel circuit 22c. The anode terminal of the freewheel diode D6 is connected to the low potential side of the fuel cell 110, while the cathode terminal of the freewheel diode D6 is connected to the auxiliary coil L2. This free wheel circuit 22c includes a common free wheel diode D6 for each phase, and even if the second switching element S2 has an open failure while the auxiliary coil L2 is energized, the second switching element S2 is provided. This is a circuit for realizing a fail-safe function provided in order to prevent the occurrence of a surge voltage that would break down. Note that the present invention can also be applied to a configuration that does not include the freewheel circuit 22c.
The above is the basic configuration of the FC soft switching converter 250. Hereinafter, details of each control mode of the FC soft switching converter 250 will be described.

A-2-3-1. Outline of Soft Switching Control In the FC soft switching converter 250, the controller 160 adjusts the switching duty ratio of the first switching element S1 of each phase, so that the boosting ratio by the FC soft switching converter 250, that is, the converter for the converter input voltage Vin. The ratio of the output voltage Vout is controlled. Moreover, soft switching control is implement | achieved by interposing the switching operation of 2nd switching element S2 of the auxiliary circuit 12b in switching operation of 1st switching element S1.

A-2-3-2. Overview of Hard Switching Control On the other hand, in the FC soft switching converter 250, if the auxiliary circuit 22b is not functioned (that is, the second switching element S2 of the auxiliary circuit 22b is always turned off), hard switching control is realized. As is well known, since hard switching has a larger switching loss than soft switching, hard switching is not usually performed.
However, as explained in the section of the problem to be solved by the invention, when the element temperature is low, such as at a low temperature start, the breakdown voltage becomes low. Therefore, the FC soft switching converter 250 is used with the operation performance lowered. There is a problem of having to.

  Therefore, in this embodiment, as the low-temperature countermeasure control, the control of the FC soft switching converter 250 is switched from the soft switching control to the hard switching control to increase the switching loss, thereby realizing the rapid warming up of the element temperature.

A-2-3-3. Outline of Non-Switching Control Further, in the FC soft switching converter 250, not only the auxiliary circuit 22b but also the main boost circuit auxiliary circuit 22a does not function (that is, the second switching element S2 of the auxiliary circuit 22b and the first of the main boost circuit 22a). By keeping the switching element S1 off at all times, non-switching control without performing the converter operation is realized. As will be described later, in the low load region, the effect of converter loss (power loss due to switching) due to hard switching control or soft switching control is large, so that the required power of the load 130 (for example, when the rotational speed of the traction motor 131 is low) Etc.), the operation of the FC switching converter 250 is stopped to reduce the converter loss.

A-2-3-4. Fluctuation of FC Current in Each Control Mode FIGS. 4A to 4C are diagrams illustrating FC current fluctuations in the soft switching control mode, the hard switching control mode, and the non-switching control mode, respectively.

  4A to 4C, the fluctuation of the FC current detected by the current sensor 290 (see FIG. 3) increases in the order of the non-switching control mode → the hard switching control mode → the soft switching control mode. Become. This is because, in the non-switching control mode, the output current of the fuel cell 110 includes almost no ripple component, whereas in the hard switching control mode, the ripple component RC1 due to the coil L1 is included, and in the soft switching control mode, the coil This is because the ripple component RC1 due to L1 and the ripple component RC2 due to the coil L2 are included. As described above, if the ripple component of the FC current increases and the effective current value increases, the fuel cell 110 may overheat. Therefore, by increasing the cooling performance of the cooling mechanism 200 according to switching of the switching control mode. Then, abnormal overheating of the fuel cell 110 is prevented in advance.

  Specifically, the flow rate of the refrigerant sent to the radiator 260 by controlling the opening of the three-way valve 250 of the cooling mechanism 200 according to the switching of the switching control mode (in other words, the flow rate of the refrigerant bypassing the radiator 260). Adjust.

  FIG. 5 is a diagram exemplifying a cooling control table TA1 showing the relationship between the switching timing of the switching control mode, the valve opening degree of the three-way valve 250, and the flow rate of refrigerant sent to the radiator 260 (hereinafter referred to as the cooling flow rate of refrigerant). It is. In FIG. 5, for the sake of convenience, the non-switching control mode (= Non-Switch), the hard switching control mode (= Hard-Switch), and the soft switching control mode (= Soft-Switch) are abbreviated.

  As described above, the fuel cell 110 has a current effective value that increases in the order of the non-switching control mode → the hard switching control mode → the soft switching control mode (that is, it is easily overheated). The valve opening is adjusted so that the cooling performance of 200 is enhanced.

Specifically, when switching from the non-switching control mode to the hard switching control mode, by setting the valve opening degree O01 = the current opening degree (the current valve opening degree in the non-switching control mode) + 5%, The cooling flow rate is increased from F0 to F1 (> F0). When switching from the non-switching control mode to the soft switching control mode, the cooling flow rate of the refrigerant is set by setting the valve opening degree O02 = the current opening degree (the current valve opening degree in the non-switching control mode) + 10%. Increase from F0 to F2 (> F1). As described above, the refrigerant cooling flow rate F2 when switching from the non-switching control mode to the soft switching control mode is larger than the refrigerant cooling flow rate F1 when switching from the non-switching control mode to the hard switching control mode. This is because the ripple component in the control mode is larger than the ripple component in the hard switching control mode and is easily overheated. Further, when switching from the hard switching control mode to the soft switching control mode, the cooling flow rate of the refrigerant is set by setting the valve opening degree O03 = the current opening degree (the current valve opening degree in the hard switching control mode) + 5%. Is increased from F1 to F2. In the present embodiment, by adjusting the cooling flow rate of the refrigerant using the cooling control table TA1 described above (in other words, by controlling the cooling performance of the cooling mechanism 200), abnormal overheating of the fuel cell 110 is prevented. It is possible to prevent it in advance. The cooling control table TA1 is stored in the memory of the controller 160. The value registered in the cooling control table TA1 may be a fixed value, but may be set / changed as appropriate.
Next, the soft switching operation by the FC soft switching converter 250 will be described with reference to FIG.

A-3. FIG. 6 is a flowchart showing a process of one cycle of the FC soft switching converter 25 (hereinafter referred to as a soft switching process) through the soft switching operation. The controller 160 performs step S101 shown in FIG. A cycle is formed by sequentially executing S106. In the following description, modes representing the current and voltage states of the FC soft switching converter 25 are expressed as modes 1 to 6, respectively, and the states are shown in FIGS. Moreover, in FIGS. 7-12, the electric current which flows through a circuit is shown by the arrow.

  First, the initial state in which the soft switching process shown in FIG. 6 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. 7)
In step S101, the first switching element S1 is kept turned 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 second switching element S2, and the auxiliary coil L2 due to the potential difference between the output voltage VH of the FC soft switching converter 150 and the input voltage VL. Then, it gradually shifts to the auxiliary circuit 12b side. In FIG. 7, 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；補助コイルＬ２のインダクタンス Further, when the second switching element S2 is turned on, current circulation occurs in the direction of the arrow Dm11 shown in FIG. Here, the current change rate of the second switching element S2 increases according to the voltage across the auxiliary coil L2 (VH−VL) and the inductance of the auxiliary coil L2, but the current flowing through the second switching element S2 is the auxiliary coil L2. As a result, soft turn-off of the current (see arrow Dm12 shown in FIG. 7) flowing to the load 130 side via the diode D5 is realized.
Here, the transition completion time tmode1 from mode 1 to mode 2 is represented by the following equation (4).

Ip; phase current L2id; inductance of auxiliary coil L2

(Mode 2; refer to FIG. 8)
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 D5 (see arrow Dm21 shown in FIG. 8). 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 Dm22 shown in FIG. 8). The voltage applied to the first switching element S1 is determined according to the capacitance of the snubber capacitor C2.

Here, FIG. 14 is a diagram showing the voltage / current behavior in the transition process from mode 2 to mode 3, where the voltage of the fuel cell 110 is a thick solid line, the voltage of the snubber capacitor C2 is a thin solid line, and the current of the snubber capacitor C2 is shown. It is indicated by a broken line.
After the energization of the path Dm21 shown in FIG. 8 is started (see FIG. 14A), the path Dm22 shown in FIG. 8 is caused by the potential difference between the voltage VH of the snubber capacitor C2 and the voltage VL of the fuel cell 110. Energization, that is, energization of the auxiliary coil L2 is started (see FIG. 14B). Here, as shown in FIG. 14, the current of the snubber capacitor C <b> 2 continues to rise until the voltage of the snubber capacitor C <b> 2 reaches the voltage VL of the battery 110.

左辺；補助コイルＬ２に蓄積されたエネルギ
右辺；スナバコンデンサＣ２に残存するエネルギ More specifically, although the electric charge accumulated in the snubber capacitor C2 begins to be regenerated on the power source side due to the potential difference between the voltage VH of the snubber capacitor C2 and the voltage VL of the fuel cell 110 (arrow Dm22 shown in FIG. 8), the original potential difference is ( VH−VL), the flow of electric charge (discharge) accumulated in the snubber capacitor C2 stops when the power supply voltage (that is, the voltage VL of the fuel cell 110) is reached (timing Tt1 shown in FIG. 14). Due to the characteristic of the auxiliary coil L2 (that is, the characteristic of continuing to flow current), the charge continues to flow even when the voltage of the snubber capacitor C2 becomes VL or less (see (C) shown in FIG. 14). At this time, if the following expression (4) ′ is satisfied, all the charges of the snubber capacitor C2 flow (discharge).

Left side; right side of energy stored in auxiliary coil L2; energy remaining in snubber capacitor C2

  When the electric charge accumulated in the snubber capacitor C2 is exhausted, a free wheel operation is performed along the path Dm23 shown in FIG. 8, and energization is continued (see (D) shown in FIG. 14). Thereby, all the energy accumulated in the auxiliary coil L2 is released. Since the anode of the diode D2 is connected to one end of the auxiliary coil L2, the LC resonance stops at a half wave. For this reason, the snubber capacitor C2 holds 0 V after discharging.

Ｃ２ｄ；コンデンサＣ２の容量 Here, the transition completion time tmode2 from mode 2 to mode 3 is expressed by the following equation (5).

C2d: capacitance of capacitor C2

(Mode 3; see FIG. 9)
When the operation of flowing the current through the path Dm22 shown in FIG. 8 is finished and the electric charge of the snubber capacitor C2 is completely discharged or reaches the minimum voltage (MIN voltage), the first switching element S1 is turned on, and the process proceeds to step S103. In a state where the voltage of the snubber capacitor C2 becomes zero, the voltage applied to the first switching element S1 is also zero, so that ZVS (Zero Voltage Switching) is realized. 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 to the auxiliary circuit 12b side is expressed by the following equation (7). That is, the current Idm31 flowing to the auxiliary circuit 12b side decreases at the change rate of the following equation (7), so the first switching Even if the element S1 is turned on, the current flowing through the first switching element S1 does not suddenly rise, and 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. 10)
In step S104, the state of step S103 is continued to increase the amount of current flowing into the coil L1 and gradually increase the energy stored in the coil L1 (see arrow Dm42 in FIG. 10). Here, since the auxiliary circuit 12b includes the diode D2, no reverse current flows through the auxiliary coil L2, 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 approximately 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. 11)
When desired energy is stored in the coil L1 in step S104, the first switching element S12 is turned off, and a current flows through a path indicated by an arrow Dm51 in FIG. Here, FIG. 13 is a diagram illustrating the relationship among the voltage Vc of the snubber capacitor C2, the voltage Ve applied to the first switching element S1, and the current Ie flowing through the first switching element S1 in mode 5. When the above switching operation is performed, the charge is removed from the snubber capacitor C2, which is in a low voltage state in mode 2, so that the voltage Vc of the snubber capacitor C2 becomes the converter output voltage of the FC soft switching converter 150. Rise toward VH. At this time, the rising speed of the voltage Ve applied to the first switching element S1 is suppressed by charging the snubber capacitor C2 (that is, the rising of the voltage is slowed down), and switching loss at the time of turn-off (see α shown in FIG. 13). It is possible to perform a ZVS operation for reducing the above.

(Mode 6; see FIG. 12)
When the snubber capacitor C2 is charged to the voltage VH, the energy stored in the coil L1 is released to the load 130 side (see arrow Dm61 shown in FIG. 12). Here, the turn-off time Ts2 of the first switching element S1 is approximately represented 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.

A-3. Fuel Cell Cooling Control Operation FIG. 15 is a flowchart showing a cooling control process executed by the controller 160.
The controller 160 first determines whether or not the switching timing of the switching control mode of the FC soft switching converter 250 has arrived based on the required power of the load 130 and sensor signals received from various sensors (accelerator opening sensor or the like). (Step S1). If the controller 160 determines that the switching timing of the switching control mode has not arrived (step S1; NO), the controller 160 ends the process without executing the following steps.

  On the other hand, when the controller 160 determines that the switching timing of the switching control mode has arrived (step S1; YES), the controller 160 refers to the cooling control table TA1 and determines whether it is any switching timing registered in the table TA1. Is determined (step S2). Specifically, the controller 160 switches from the non-switching control mode (Non-Switch) to the hard switching control mode (Hard-Switch), and from the non-switching control mode (Non-Switch) to the soft-switching control mode (Soft-Switch). ), Whether the switching from the hard switching control mode (Hard-Switch) to the soft switching control mode (Soft-Switch) is determined. If the controller 160 determines that it is not any switching timing registered in the cooling control table TA1 (for example, switching timing from the soft switching control mode to the hard switching control mode) (step S2; NO), the following processing is performed. The process is terminated without executing.

  On the other hand, when controller 160 determines that it is any switching timing registered in cooling control table TA1 (step S2; YES), it proceeds to step S3, and switching timing from the non-switching control mode to the hard switching control mode. Is determined (step S3). When the controller 160 determines that it is the switching timing from the non-switching control mode to the hard switching control mode (step S3; YES), the valve opening degree of the three-way valve 250 is set to the valve opening degree O01 = the current opening degree (non-switching control mode). Is set to + 5% (step S4), the cooling flow rate of the refrigerant is increased from F0 to F1 (> F0) to improve the cooling performance of the cooling mechanism 200, and then the process ends.

  On the other hand, if the controller 160 determines that it is not the switching timing from the non-switching control mode to the hard switching control mode (step S3; NO), the controller 160 proceeds to step S5 and is the switching timing from the non-switching control mode to the soft switching control mode. Determine whether or not. When the controller 160 determines that it is the switching timing from the non-switching control mode to the soft switching control mode (step S5; YES), the valve opening degree of the three-way valve 250 is set to the valve opening degree O02 = the current opening degree (non-switching control mode). Is set to + 10% (step S6), the cooling flow rate of the refrigerant is increased from F0 to F2 (> F1), and the process is terminated. As described above, the refrigerant cooling flow rate F2 when switching from the non-switching control mode to the soft switching control mode is larger than the refrigerant cooling flow rate F1 when switching from the non-switching control mode to the hard switching control mode. This is because the ripple component in the switching control mode is larger than the ripple component in the hard switching control mode and is easily overheated.

  On the other hand, the controller 160 does not have the switching timing from the non-switching control mode to the hard switching control mode (step S3; NO), and is not the switching timing from the non-switching control mode to the soft switching control mode (step S5; NO), it is determined that it is the switching timing from the hard switching control mode to the soft switching control mode, and the valve opening degree of the three-way valve 250 is set to the valve opening degree O03 = the current opening degree (the current valve opening degree in the hard switching control mode) ) + 5% (step S7), the cooling flow rate of the refrigerant is increased from F1 to F2 to improve the cooling performance of the cooling mechanism 200, and then the process ends.

  As described above, according to the present embodiment, it is possible to suppress the occurrence of abnormal overheating of the fuel cell by increasing the cooling performance of the cooling mechanism 200 in accordance with the switching of the switching control mode of the FC switching converter. It becomes possible.

B. Modification <Modification 1>
FIG. 16 is a cooling control table TA2 according to the first modification, and illustrates the relationship among the switching control mode, the valve opening degree of the three-way valve 250, and the flow rate of refrigerant sent to the radiator 260 (that is, the cooling flow rate of refrigerant). FIG.
As shown in FIG. 16, the valve opening degree of the three-way valve 250 is set so that the cooling flow rate of the refrigerant increases as the current execution value of the fuel cell 110 (in other words, the ripple component of the FC current) increases. The Specifically, when the non-switching control mode (Non-Switch) in which the ripple component of the FC current is the smallest is set, the valve opening of the three-way valve 250 is set to the valve opening O11. The cooling flow rate is F11. On the other hand, when the hard switching control mode (Hard-Switch) in which the ripple component of the FC current is larger than that in the non-switching control mode is set, the valve opening degree of the three-way valve 250 is set to the valve opening degree O12 (> O12). Thus, the cooling flow rate of the refrigerant becomes F12 (> F11). Further, when the soft switching control mode (Soft-Switch) in which the ripple component of the FC current is larger than that in the hard switching control mode is set, the valve opening degree of the three-way valve 250 is set to the valve opening degree O13 (> O12). Thus, the cooling flow rate of the refrigerant becomes F13 (> F12).

When such a cooling control table TA2 is used, the cooling control process shown in FIG. 17 is performed. Of the steps shown in FIG. 17, steps corresponding to FIG. 15 are denoted by the same reference numerals and description thereof is omitted.
The controller 160 first determines whether or not the switching timing of the switching control mode of the FC soft switching converter 250 has arrived based on the required power of the load 130 and sensor signals received from various sensors (accelerator opening sensor or the like). (Step S1). If the controller 160 determines that the switching timing of the switching control mode has not arrived (step S1; NO), the controller 160 ends the process without executing the following steps.

  On the other hand, when determining that the switching timing of the switching control mode has arrived (step S1; YES), the controller 160 determines which switching control mode to switch to based on the required power and each sensor signal. When controller 160 determines that it should switch to the non-switching control mode (for example, hard switching control mode → non-switching control mode), it refers to cooling control table TA2 and sets the valve opening of three-way valve 250 to valve opening O11. Thereby, the cooling flow rate of the refrigerant is adjusted to F11 (step S2a), and the process is terminated.

  When the controller 160 determines that the hard switching control mode should be switched (for example, the soft switching control mode → the hard switching control mode), the controller 160 refers to the cooling control table TA2 and changes the valve opening of the three-way valve 250 to the valve opening O12. By setting, the cooling flow rate of the refrigerant is adjusted to F12 (step S3a), and the process ends.

  Further, when the controller 160 determines that the soft switching non-switching control mode should be switched (for example, the hard switching control mode → the soft switching control mode), the controller 160 refers to the cooling control table TA2 and determines the valve opening of the three-way valve 250 as the valve opening. By setting to O13, the cooling flow rate of the refrigerant is adjusted to F13 (step S4a), and the process ends.

  As described above, the cooling performance of the cooling mechanism 200 may be controlled using the cooling control table TA2 instead of the cooling control table TA1, and the occurrence of abnormal overheating of the fuel cell may be suppressed in advance.

<Modification 2>
In the above-described embodiment and Modification 1, the description has been made on the assumption of an FCHV system in which a soft switch converter is mounted. However, the present invention is not limited to this. Specifically, the present invention can also be applied to a general converter that does not have a soft switching function (that is, a hard switching type converter). When applied to a hard switching type converter, the switching control mode can be switched between the non-switching control mode and the hard switching control mode. Even in such a case, the occurrence of abnormal overheating of the fuel cell 110 can be prevented beforehand by controlling the cooling performance of the cooling mechanism 200. In addition, since the switching operation of specific switching control was demonstrated in this embodiment and the modification 1, the description beyond this is omitted.

DESCRIPTION OF SYMBOLS 100,300 ... FCHV system, 110 ... Fuel cell, 120 ... Battery, 130 ... Load, 140 ... Inverter, 2500 ... FC converter, 160 ... Controller, 170 ... Sensor group, 180 ... Battery converter, 250 ... FC soft switching converter, 400 ... Gate voltage control circuit 410 ... Power supply 420 ... Turn on control unit 430 ... Turn off control unit 440 ... Drive circuit 22a ... Main boost circuit 22b ... Auxiliary circuit 22c ... Free wheel circuit S1, S2 ... Switching Element, C3 ... smoothing capacitor, C2 ... snubber capacitor, L1, L2, ... coil, D1, D2, D3, D4, D5 ... diode, D6 ... freewheel diode, TA1, TA2 ... cooling control table.

Claims (7)

A fuel cell;
A cooling mechanism for cooling the fuel cell;
A fuel cell system comprising a main switch for controlling the output voltage of the fuel cell and a DC / DC converter having no smoothing capacitor on the input side ,
Switching control means for switching between a non-switching control mode in which the main switch is always turned off and a hard switching control mode in which the main switch is turned on and off in response to a load request for the DC / DC converter; ,
When the DC / DC converter is set in the hard switching control mode, the cooling performance of the cooling mechanism is increased in a state where the cooling performance of the cooling mechanism is improved as compared with the case where the DC / DC converter is set in the non-switching control mode. A fuel cell system comprising: cooling control means for cooling the fuel cell. The cooling mechanism is
A radiator for cooling the refrigerant;
A circulation channel for circulating the refrigerant from the fuel cell via the radiator;
A bypass flow path for bypassing the radiator from the fuel cell;
A valve that is provided at a connection point between the circulation path and the bypass flow path, and that controls a flow rate of the refrigerant sent to the radiator side and a flow rate of the refrigerant sent to the bypass flow path side;
The cooling control means includes
When the DC / DC converter is set to the hard switching control mode, the flow rate of the refrigerant sent to the radiator side is larger than when the DC / DC converter is set to the non-switching control mode. The fuel cell system according to claim 1, wherein the opening degree of the valve is adjusted as follows. A fuel cell;
A cooling mechanism for cooling the fuel cell;
A fuel cell system including a main boosting circuit and an auxiliary circuit for controlling the output voltage of the fuel cell, and a soft switching converter having no smoothing capacitor on the input side ,
For the soft switching converter, a non-switching control mode in which the main switch that constitutes the main booster circuit and the auxiliary switch that constitutes the auxiliary circuit are always turned off, and the auxiliary switch is always turned off, while responding to load demands. Switching control means for switching between a hard switching control mode for turning on and off the main switch and a soft switching control mode for turning on and off the auxiliary switch and the main switch according to the demand of the load;
When the soft switching converter is set to the soft switching control mode, the cooling performance of the cooling mechanism is improved compared to the case where the soft switching converter is set to the non-switching control mode or the hard switching control mode. And a cooling control means for cooling the fuel cell in a state where The cooling control means includes
4. The fuel cell system according to claim 3, wherein the cooling performance of the cooling mechanism is set higher in the order of the non-switching control mode, the hard switching control mode, and the soft switching control mode. The cooling mechanism is
A radiator for cooling the refrigerant;
A circulation channel for circulating the refrigerant from the fuel cell via the radiator;
A bypass flow path for bypassing the radiator from the fuel cell;
A valve that is provided at a connection point between the circulation path and the bypass flow path, and that controls a flow rate of the refrigerant sent to the radiator side and a flow rate of the refrigerant sent to the bypass flow path side;
The cooling control means includes
When the soft switching converter is set to the soft switching control mode, the refrigerant to be sent to the radiator side than when the soft switching converter is set to the non-switching control mode or the hard switching control mode. The fuel cell system according to claim 3, wherein the opening degree of the valve is adjusted so that the flow rate is increased. The cooling control means includes
The opening degree of the valve is adjusted so that the flow rate of the refrigerant sent to the radiator increases in the order of the non-switching control mode, the hard switching control mode, and the soft switching control mode. Fuel cell system. The main booster circuit
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 cathode having a cathode connected to the other end of the main coil;
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;
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 fuel cell system according to any one of claims 3 to 6.

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