JP6174546B2 - Control method for fuel cell system and fuel cell vehicle - Google Patents

Description

  The present invention relates to a control method for a fuel cell system that supplies power from two power sources of a fuel cell and a power storage device to a load such as a drive motor, and a fuel cell vehicle in which the control method is implemented.

  Conventionally, as shown in FIG. 1 of Patent Document 1, for example, a boost converter is provided between an inverter that drives a drive motor and an output terminal of a fuel cell, and between the inverter and an input / output terminal of a power storage device. There is known a fuel cell vehicle equipped with a fuel cell system in which a load (the inverter and the drive motor) is driven.

  In Patent Document 1, a drive request load end voltage (motor required voltage, motor drive request voltage, power supplied from the two power sources (the fuel cell and the power storage device) to the load in order to cause the load to exhibit a predetermined driving force. If the fuel cell voltage is higher than the drive required load end voltage based on the correlation between the fuel required voltage and the fuel cell voltage, do not perform boosting by the boost converter on the fuel cell side. A technique is disclosed in which the switching loss of the boost converter on the fuel cell side is reduced directly ([0011] and [0012] of Patent Document 1).

International Publication No. 2009/084650 Pamphlet

  Incidentally, in the fuel cell system, it is always desired to improve the efficiency of the fuel cell system.

  However, since Patent Document 1 does not disclose a technique for reducing the switching loss of the converter on the power storage device side, there is room for improvement.

  The present invention has been made in consideration of the above-described problems, and further provides a fuel cell system in the relationship between the first voltage conversion device on the fuel cell side, the second voltage conversion device on the power storage device side, and the load. An object of the present invention is to provide a fuel cell system control method and a fuel cell vehicle that can improve the efficiency of the fuel cell system.

  A fuel cell system according to the present invention includes a fuel cell that outputs a fuel cell voltage, a power storage device that outputs a power storage device voltage, a load that includes an inverter and a motor driven through the inverter, and the fuel cell of the fuel cell A first voltage conversion device that converts the voltage into a load end voltage and applies it to the DC end side of the inverter; and a voltage conversion of the power storage device voltage of the power storage device and applies the voltage to the DC end side of the inverter as the load end voltage A control method of a fuel cell system comprising: a motor control setting step for setting a motor rotational speed or a motor power of the motor based on a request for the load of the fuel cell system; A low load determination step of determining whether the motor rotation speed or the motor electric power is a low load lower than a threshold value Have if it is determined that a low load, in the power storage device voltage and the fuel cell voltage, and the voltage drop step of lowering the higher voltage.

  According to the present invention, when the load is determined to be low, a voltage lowering step for lowering the higher one of the power storage device voltage and the fuel cell voltage is provided, so the low voltage is supplied to the load. This can reduce the load loss. As a result, the efficiency of the fuel cell system can be improved.

  In this case, after the voltage reduction step, the voltage conversion operation of the first and second voltage conversion devices is stopped, and control is performed so as to have a voltage conversion stop step of directly connecting the fuel cell and the power storage device to the load. It is preferable. In a region where the load is determined to be low and the loss can be reduced by supplying a low voltage, the voltage conversion of the first and second voltage converters is stopped. As a result, a low voltage can be supplied to the load, load loss can be reduced, and loss due to voltage conversion can be eliminated. Therefore, the efficiency of the fuel cell system can be further improved.

  Furthermore, after the voltage lowering step and before the voltage conversion stop step, a voltage difference grasping step for grasping a voltage difference between the fuel cell voltage and the power storage device voltage, and the grasped voltage difference are the first and first voltage differences. Since the voltage difference control step of controlling the voltage converter so as to be within a predetermined value that allows the stoppage of the voltage converter is performed, the voltage difference between the fuel cell voltage and the power storage device voltage is reduced and directly connected. The direct connection can be made smoothly without impairing the controllability of the fuel cell or power storage device.

  In this case, when it is determined in the voltage difference grasping step that the power storage device voltage is higher than the fuel cell voltage, the voltage difference control step reduces the SOC of the power storage device. The voltage difference between the fuel cell voltage and the power storage device voltage can be reduced by the method.

  When the voltage difference grasping step finds that the fuel cell voltage is higher than the power storage device voltage, the voltage difference control step reduces the membrane water content and / or stoichiometric ratio of the fuel cell. Thus, the voltage difference between the fuel cell voltage and the power storage device voltage can be reduced by a simple method.

  Further, if the threshold value that is the determination value in the low load determination step is determined based on the total loss of the inverter and the motor, the efficiency of the entire fuel cell system is taken into consideration. The efficiency of the system can be improved.

  A fuel cell system according to the present invention includes a fuel cell that outputs a fuel cell voltage, a power storage device that outputs a power storage device voltage, a load that includes an inverter and a motor driven through the inverter, and the fuel cell of the fuel cell A voltage conversion device that converts a voltage or a power storage device voltage of the power storage device and applies the converted voltage to a DC terminal side of the inverter as a load terminal voltage, and a request for the load of the fuel cell system A motor control setting step for setting the motor rotation speed or motor power of the motor, and a low load for determining whether the set motor rotation speed or the motor power is a low load lower than a threshold value. In the determination step, when it is determined that the load is low, the fuel cell and the power storage device do not go through the voltage conversion device. Having a voltage drop step of lowering the voltage of the fuel cell or the electric storage device is connected to the DC end of the inverter.

  According to the present invention, when the load is determined to be low, the fuel cell or the power storage device connected to the DC terminal side of the inverter without going through the voltage conversion device among the fuel cell and the power storage device. Since the voltage lowering step for lowering the voltage is provided, a low voltage can be supplied to the load and load loss can be reduced. As a result, the efficiency of the fuel cell system can be improved.

  Furthermore, the fuel cell system according to the present invention is a fuel cell system control method comprising: a fuel cell that outputs a fuel cell voltage; and a load comprising an inverter and a motor driven through the inverter. A motor control setting step for setting the motor rotation speed or motor power of the motor based on the load request, and whether the set motor rotation speed or the motor power is a low load lower than a threshold value. A low load determination step for determining whether or not the load is low, and a voltage lowering step for reducing the fuel cell voltage to a required drive voltage of the motor or a lower limit voltage of the fuel cell when the load is determined to be low.

  According to the present invention, when the load is determined to be low, a voltage reduction step is provided to reduce the voltage to the motor drive request voltage or the lower limit voltage of the fuel cell, so that the low voltage can be supplied to the load. Load loss can be reduced. As a result, the efficiency of the fuel cell system can be improved.

  Each of the above inventions is suitable for implementation in a fuel cell vehicle.

  According to the present invention, when the load is determined to be low, a voltage lowering step is provided for lowering the higher one of the power storage device voltage and the fuel cell voltage, so that the low voltage can be supplied to the load. Load loss can be reduced. As a result, the effect that the efficiency of the fuel cell system can be improved is achieved.

1 is a schematic overall configuration diagram of a fuel cell vehicle to which a fuel cell system according to an embodiment of the present invention is applied. FIG. 2 is a schematic circuit diagram including a detailed configuration of an example of a boost converter and a step-up / down converter in the fuel cell automobile of FIG. 1. It is explanatory drawing of the power element as an example of a switching element. It is IV characteristic view of a fuel cell. It is a timing chart used for operation | movement description of this embodiment. It is a flowchart with which operation | movement description of this embodiment is provided. It is a characteristic view which shows the relationship between motor request | requirement electric power and the drive request | requirement load end voltage as a load end voltage. It is a characteristic view which shows the relationship between the motor electric power and load loss which used the load end voltage as a parameter. FIG. 9A is a conceptual diagram of a fuel cell vehicle to which a fuel cell system that is used in a directly connected state is applied after reducing the target remaining capacity of the power storage device in a low load state, and FIG. 9B is a diagram of FIG. 9A FIG. 9C is a conceptual diagram of a fuel cell vehicle in which a drive motor is driven only by the fuel cell, and FIG. 9D is a fuel cell in a low load state. FIG. 9E is a conceptual diagram of a fuel cell vehicle to which a fuel cell system that is used in a state where both are directly connected after the target membrane moisture content of the battery is reduced, and FIG. FIG. 9F is a conceptual diagram of a range extender type electric vehicle. FIG.

  Hereinafter, a control method for a fuel cell system according to the present invention will be described with reference to the accompanying drawings by citing preferred embodiments in relation to a fuel cell vehicle that implements the control method.

  FIG. 1 schematically shows a fuel cell vehicle 10 (hereinafter referred to as “FC vehicle 10” or “vehicle 10”) to which a fuel cell system 12 (hereinafter referred to as “FC system 12”) according to this embodiment is applied. FIG.

  FIG. 2 is a fuel cell side converter disposed between the primary side 1sf and the secondary side 2s, and is a chopper type boost converter 21 (hereinafter referred to as SUC21) as a voltage converter (boost). Step Up Converter) and a step-up / down converter 22 (hereinafter referred to as SUDC 22) as a chopper-type voltage converter (buck-boost) arranged between the primary side 1sb and the secondary side 2s side. SUDC: Step Up / 1 is a schematic circuit diagram of an FC automobile 10 including a detailed configuration of an example of a Down Converter.

  As shown in FIGS. 1 and 2, the FC automobile 10 includes an FC system 12, a drive motor 14 that is a motor / generator for running a vehicle, and an inverter 16 (hereinafter referred to as a load drive circuit) that drives the drive motor 14. It is referred to as “INV16.” INV: Inverter).

  The FC system 12 includes a fuel cell 18 (hereinafter referred to as “FC18”) disposed on one primary side 1sf and a high-voltage battery 20 (hereinafter referred to as “power storage device” disposed on the other primary side 1sb). BAT20 "), the SUC21, the SUDC22, a high voltage {power storage device voltage (BAT voltage) Vbat} input fuel cell auxiliary machine (hereinafter referred to as" FC auxiliary machine ") 31, and a high voltage input. Air conditioner 32, which is a vehicle interior air conditioner, a chopper-type step-down converter 23 (hereinafter referred to as “SDC 23”; SDC: Step Down Converter) as a step-down device, and an electronic control device 24 (hereinafter referred to as a control device). And “ECU 24.” ECU: Electronic Control Unit (ECU).

  The output end of FC18 is connected to the input end (primary side 1sf) of SUC21, and the output end (secondary side 2s) of SUC21 is connected to the DC end side of INV16 and one end (boost end side) side of SUDC22.

  The input / output end of the BAT 20 is connected to the input side (primary side 1sb) of the SDC 23, the other end side (step-down end side) of the SUDC 22, and the high-pressure auxiliary machine 35 (FC auxiliary machine 31, air conditioning auxiliary machine 32).

  A low voltage battery 29 having a voltage Vbb = + 12V and a low voltage auxiliary machine 33 such as a light are connected to the output end side (secondary side) of the SDC 23. The low pressure auxiliary machine 33, the SDC 23, and the ECU 24 are collectively referred to as a low pressure auxiliary machine (low pressure load) 33 '.

  The drive motor 14 is a combined power value of FC generated power (FC power) Pfc (Pfc = Vfc × Ifc) supplied from the FC 18 and BAT discharge power Pbatd (Pbatd = Vbat × Ibd) which is stored power supplied from the BAT 20. (Pfc + Pbatd) is supplied through the INV 16 to generate a driving force, and the wheel 28 is rotated through the transmission 26 by the driving force.

  The INV 16 has, for example, a three-phase full-bridge configuration, performs DC / AC conversion, and converts the load end voltage Vinv, which is a DC voltage obtained by boosting the FC voltage Vfc from the FC 18 via the SUC 21, into a three-phase AC voltage. Converted and supplied to the drive motor 14 (during power running).

  The INV 16 also converts the load end voltage Vinv, which is a DC voltage obtained by boosting the BAT voltage Vbat from the BAT 20 via the SUDC 22, into a three-phase AC voltage and supplies it to the drive motor 14 (during power running).

  That is, the drive motor 14 is driven by the power of the FC 18 and / or BAT 20 (during power running).

  In this embodiment, the INV 16 and the drive motor 14 are collectively referred to as a load 30. In addition to the load 30, the load includes a high-pressure auxiliary machine 35 such as an FC auxiliary machine 31 and an air conditioning auxiliary machine 32 and the low-pressure auxiliary machine 33 ′ described above.

  On the other hand, the load terminal voltage (DC terminal side voltage) Vinv generated at the input terminal (DC terminal side) of the INV 16 after AC / DC conversion accompanying the regenerative operation of the drive motor 14 is BAT voltage Vbat through the SUDC 22 operating as a step-down converter. And the SUDC 22 is directly connected (switching element 22b: off, switching element 22d: on) and supplied to the BAT 20 to charge the BAT 20.

  Further, when the power for driving the drive motor 14 by the FC 18 becomes surplus, the surplus power is supplied to the BAT 20 via the step-down SUC 21 or the direct connection SUC 21 through the step-down or direct connection SUDC 22. BAT20 is charged. The surplus power is also supplied to the high pressure auxiliary machine 35 (FC auxiliary machine 31, air conditioning auxiliary machine 32) and low pressure auxiliary machine 33 'according to the degree of surplus.

  The FC auxiliary unit 31 supplies an air pump (A / A) that supplies compressed air (oxidant gas) containing oxygen from a channel inlet to a cathode channel (not shown) of the FC 18 via a humidifier (HUM) 39. P) 31a, a membrane moisture meter 31b, and a water pump (not shown) for supplying a cooling medium (refrigerant) to the cooling flow path (not shown) of FC18.

  Furthermore, a hydrogen tank 37 for supplying hydrogen (fuel gas) to an anode flow path (not shown) of the FC 18 and the humidifier 39 are provided outside the FC 18. The humidifier 39 exchanges moisture and temperature between the oxidant gas supplied from the air pump 31a and the cathode off-gas discharged from the channel outlet of the cathode channel, and passes from the channel inlet to the cathode channel. A hollow fiber membrane part (not shown) for humidifying the supplied oxidant gas is included. Hydrogen and oxidant gas are referred to as reaction gases, respectively.

  The FC 18 has, for example, a stack structure in which fuel cell cells (hereinafter referred to as “FC cells”) formed by sandwiching an electrolyte membrane between an anode electrode and a cathode electrode from both sides, and through the anode flow path. The hydrogen-containing gas supplied to the anode electrode is hydrogen ionized on the electrode catalyst, moves to the cathode electrode through the electrolyte membrane, and electrons generated during the movement are taken out to an external circuit, It is used as electrical energy for generating a DC voltage (FC voltage Vfc). Since the oxidant gas (oxygen-containing gas) is supplied to the cathode electrode via the cathode channel, hydrogen ions, electrons, and oxygen gas react to generate water at the cathode electrode. .

  By generating water, the electrolyte membrane can be kept in a wet state, that is, the membrane moisture content (membrane humidity) Zm can be kept high, and the reaction can be smoothly performed. In order to maintain the membrane moisture content Zm within a predetermined range during the power generation period, the humidifier 39 humidifies the oxidant gas through the hollow fiber membrane part, and the humidified oxidant gas and the A / P 31a. The dried oxidant gas supplied by bypassing the hollow fiber membrane part is mixed and supplied to the cathode electrode. The membrane water content Zm can be adjusted by adjusting the mixing ratio.

  The membrane moisture content Zm is measured by a membrane moisture meter 31b that measures the impedance of the electrolyte membrane uniquely corresponding to the membrane moisture content Zm. The membrane moisture content Zm is managed and adjusted by controlling the amount of bypass of the humidifier 39 and the like so that the impedance of the electrolyte membrane is within a predetermined value range.

  The BAT 20 is a power storage device (energy storage) including a plurality of battery cells, and for example, a lithium ion secondary battery, a nickel hydrogen secondary battery, or the like can be used. A capacitor can also be used as the power storage device. In this embodiment, a lithium ion secondary battery is used. The BAT 20 has an BAT voltage (battery voltage) Vbat, a BAT current (battery current) Ib (discharge current Ibd, a charging current Ibc), a BAT temperature (battery temperature), and an SOC (State Of Charge) that is the remaining capacity of the BAT 20 as an ECU 24. Detected or managed by

  As described above, the FC power Pfc of the FC 18 is boosted to the load end voltage Vinv via the SUC 21 and supplied to the drive motor 14 via the INV 16 (during power running), and according to the power status of the FC system 12. Then, it is distributed from the FC 18 through the SUC 21 and the SUDC 22 to each device on the primary side 1sb (the high pressure auxiliary machine 35, the low pressure auxiliary machine 33 ′, and the BAT 20).

  On the other hand, the BAT discharge power Pbatd of the BAT 20 is boosted to the load end voltage Vinv through the SUDC 22 and supplied to the drive motor 14 through the INV 16 (at the time of power running), and also in accordance with the power status of the FC system 12. It is supplied to the high-pressure auxiliary equipment 35 (FC auxiliary equipment 31, air conditioning auxiliary equipment 32) and low-pressure auxiliary equipment 33 ′ (SDC 23, ECU 24, low-pressure auxiliary equipment 33), which are the devices on the side 1sb.

  Here, SUC21, SUDC22, and SDC23 can employ various configurations, but as is well known, basically, switching elements such as MOSFETs and IGBTs, diodes, reactors, and capacitors (including smoothing capacitors). The switching element is on / off-switched (duty controlled) by the ECU 24 based on the required power of the connected load.

  Specifically, as shown in FIG. 2, the SUC 21 is disposed between a reactor (inductor) 21a, a switching element 21b, a diode 21c (unidirectional current passing element, reverse current blocking element), and a primary side 1sf. The switching element 21b is switched to the switching state (duty control) through the ECU 24 that functions as a converter controller, and is configured to include the FC voltage. Vfc is boosted to a predetermined load end voltage Vinv.

  When the duty (drive duty) is set to 0 [%] and the switching element 21b is maintained in the off state (open state), the FC 18 and the load 30 are directly connected (FC directly connected state) through the reactor 21a and the diode 21c. Or the FC voltage Vfc is directly connected to the load end voltage Vinv (Vinv = Vfc−Vd≈Vfc, Vd << Vfc, Vd: forward drop voltage of the diode 21c). The diode 21c operates for boosting or direct coupling and for preventing backflow. Accordingly, the SUC 21 performs a backflow prevention operation and a direct connection operation (such as during power running) in addition to the boost operation (such as during power running).

  On the other hand, as shown in FIG. 2, the SUDC 22 is disposed between the reactor 22a, the switching elements 22b and 22d, the diodes 22c and 22e connected in parallel to the switching elements 22b and 22d, respectively, and the primary side 1sb. And a smoothing capacitor C2b disposed between the secondary sides 2s.

  At the time of boosting, the ECU 24 turns off the switching element 22d and switches (duty control) the switching element 22b, thereby boosting the BAT voltage Vbat (power storage device voltage) to a predetermined load end voltage Vinv (during power running) ).

  At the time of step-down, the ECU 24 turns off the switching element 22b and switches (duty control) the switching element 22d, so that the diode 22c functions as a flywheel diode when the switching element 22d is in the off-state. The end voltage Vinv is stepped down to the BAT voltage Vbat of the BAT 20 (during regenerative charging and / or charging by the FC 18).

  Further, the BAT 20 and the load 30 are directly connected (the BAT directly connected state or the BATVCU) by setting the switching element 22b to an off state with a duty of 0 [%] and the switching element 22d to an on state with a duty of 100 [%]. It is referred to as a directly connected state (powering, charging, or driving an auxiliary load).

  In the BAT direct connection state, the BAT voltage Vbat of the BAT 20 becomes the load end voltage Vinv (Vbat≈Vinv). Actually, the load end voltage Vinv at the time of power running by the BAT 20 in the BAT direct connection state is “Vbat−forward drop voltage of the diode 22e”, and the load end voltage Vinv at the time of charging (including during regenerative charging) is “Vbat = Vinv”. −On-voltage of the switching element 22d = Vbat (when the on-voltage of the switching element 22d is assumed to be 0 [V]) ”.

  As shown in FIG. 3, the above-described power elements such as MOSFETs or IGBTs are used for the switching elements 21b, 22b, and 22d connected between the low voltage side and the high voltage side.

  In the FC system 12, although not shown, the DC voltage of the SUC 21 or SUDC 22 when the SUC 21 is directly connected (consent with the direct connection of the FC 18) or when the SUDC 22 is directly connected (during powering) (with the direct connection of the BAT 20). In order to reduce the descent, a diode having an anode terminal connected to the primary side 1sf of the SUC 21 and a cathode terminal connected to the secondary side 2s and / or an anode terminal connected to the primary side 1sb of the SUDC 22 and the secondary side 2s A diode having a cathode terminal connected thereto may be provided.

  The FC 18 has a known current-voltage (IV) characteristic 70 in which the FC current Ifc increases as the FC voltage Vfc decreases from the FC open circuit voltage Vfcocv, as indicated by an IV (current-voltage) characteristic 70 in FIG. That is, the FC current Ifch when the FC voltage Vfc is a relatively low FC voltage Vfcl is larger than the FC current Ifcl when the FC voltage Vfc is a relatively high FC voltage Vfch. The FC power Pfc increases as the FC current Ifc increases (the FC voltage Vfc decreases). The low stoichiometric characteristics 70p and 70q indicated by broken lines will be described later.

  The FC voltage Vfc of the FC 18 is the step-up ratio (Vinv / Vbat) of the SUDC 22 in the step-up state (switching state) or the step-down ratio (Vbat / Vinv) of the SUDC 22 in the step-down state (switching state) when the SUC 21 is directly connected. The determined load end voltage Vinv {the command voltage (target voltage) of SUDC22. } And the FC voltage Vfc is determined, the FC current Ifc is controlled (determined) along the IV characteristic 70.

  Further, when the SUC 21 is boosted and when the SUDC 22 is directly connected, the voltage on the primary side 1 sf of the SUC 21, that is, the FC voltage Vfc is set as the command voltage (target voltage) of the SUC 21, and the FC current Ifc is determined along the IV characteristic 70. Then, the step-up ratio (Vinv / Vfc) of the SUC 21 is determined so that the desired load end voltage Vinv is obtained.

  In this embodiment, when the SUC 21 is boosted, feedback (F / B) in which the duty of the switching element 21b is adjusted by the ECU 24 as a converter controller so that the FC voltage Vfc becomes a command value (set value, target value). However, since there is a unique relationship based on the IV characteristic 70 between the FC voltage Vfc and the FC current Ifc, the ECU 24 controls the FC current Ifc to be a command value (set value, target value). It is also possible to perform feedback (F / B) control for adjusting the duty of the switching element 21b.

  The ECU 24 is connected to the drive motor 14, INV 16, FC 18, BAT 20, SUC 21, SUDC 22, SDC 23, FC auxiliary machine 31, air conditioning auxiliary machine 32, low pressure auxiliary machine 33 ′, etc. via the communication line 68 (see FIG. 2). To control. In the control, a program stored in a memory (ROM) of the ECU 24 is executed, and various sensors (a voltage sensor, a current sensor, a temperature sensor, a pressure sensor, a hydrogen concentration sensor (not shown) including a membrane moisture meter 31b, Detection values of various rotation speed sensors, accelerator pedal opening sensors, and the like, and on / off information of various switches (such as an air conditioning switch and an ignition switch) are used.

  The ECU 24 is a computer including a microcomputer, a CPU (central processing unit), a ROM (including EEPROM) as a memory, a RAM (random access memory), an A / D converter, a D / A converter, etc. Input / output device, a timer as a time measuring unit, etc., and when the CPU reads and executes a program recorded in the ROM, various function realization units (function realization means), for example, a control unit, a calculation unit, It functions as a processing unit. Note that the ECU 24 can be composed of a plurality of ECUs for each of the drive motor 14, the FC 18 and the FC auxiliary machine 31, the BAT 20, the SUC 21, the SUDC 22, and the SDC 23, instead of being composed of only one ECU.

  The ECU 24 determines the load (load power) required for the FC system 12 as a whole of the FC vehicle 10 determined based on the input values from various switches and various sensors in addition to the state of the FC 18, the state of the BAT 20, and the state of the drive motor 14. , While arbitrating the load (load power) that the FC 18 should bear, the load (load power) that the BAT 20 should bear, and the load (load power) that the regenerative power source (drive motor 14) should bear The drive motor 14, INV16, FC18, BAT20, SUC21, SUDC22 and SDC23 are controlled. That is, the ECU 24 performs energy management control of the entire fuel cell vehicle 10 including the FC 18, the BAT 20, the load 30, the high pressure auxiliary machine 35, and the low pressure auxiliary machine 33 '.

  The FC automobile 10 to which the fuel cell system 12 according to this embodiment is applied is basically configured as described above.

  Next, an example of control processing by the ECU 24 will be described with reference to the timing chart of FIG. 5 and the flowchart of FIG. The execution subject of the program according to the flowchart shown in FIG.

  In FIG. 5, the items on the vertical axis indicate the motor power Pm [kW] of the drive motor 14, the voltage drop determination flag Flow, SOC (State Of Charge) [%] which is the remaining capacity of the BAT 20, and the BAT voltage Vbat in order from the top. [V], membrane moisture content Zm [%], and FC voltage Vfc [V] are shown, and each waveform shows a change with time.

  However, in FIG. 5, for convenience of understanding, the waveform of the SOC and the waveform of the BAT voltage Vbat related to the voltage reduction processing of the BAT voltage Vbat of the BAT 20 and the water content of the membrane related to the voltage reduction processing of the FC voltage Vfc of the FC18 are shown. Although the waveform of the rate Zm and the waveform of the FC voltage Vfc are drawn on the same time axis, in reality, the voltage reduction processing of the BAT voltage Vbat and the voltage reduction processing of the FC voltage Vfc are performed on the same time axis. Note that the voltage drop process is performed only for one of the higher voltages at time t2.

  That is, when the BAT voltage Vbat is higher than the FC voltage Vfc at time t2 (Vbat> Vfc), the voltage reduction processing of the BAT voltage Vbat described with reference to the SOC waveform and the BAT voltage Vbat waveform is performed. On the other hand, when the FC voltage Vfc is higher than the BAT voltage Vbat (Vfc> Vbat) at time t2, the voltage drop of the FC voltage Vfc described with reference to the waveform of the membrane moisture content Zm and the waveform of the FC voltage Vfc Processing is performed.

  In FIG. 5, the waveform shown by the solid line and the waveform shown by the alternate long and short dash line are the same items, and the waveform indicated by the solid line is the waveform after the countermeasure (Example) and the waveform indicated by the alternate long and short dash line is the countermeasure. The previous (comparative example) waveform is shown. When the waveform after the countermeasure is shown, “a” is added to the end of the code, and when the waveform before the countermeasure is shown, “b” is added to the end of the code.

  In FIG. 5, in the vicinity of time t1, the motor power Pm is a negative value of 0 [kW] or less, the drive motor 14 is in the regenerative power generation state, and the BAT 20 is regeneratively charged. Show.

  Therefore, in step S1 of the flowchart of FIG. 6, the ECU 24 receives input values {Vfc, Ifc, Vbat, Ib, Vinv, I2 (input / output current for INV16, see FIGS. 1 and 2) from various switches and sensors. , Im (motor current flowing through the drive motor 14, usually for two phases, see FIG. 2), Nm (rotation speed of the drive motor 14), θp (operation amount of an accelerator pedal not shown), etc.} The motor required power Pmreq [kW] for 14 is calculated.

  More specifically, the required motor power Pmreq [kW] of the drive motor 14 is calculated based on the motor rotation speed Nm [rpm] and the required torque Treq [N · m] based on the accelerator pedal operation amount θp.

  FIG. 7 shows the required motor power Pmreq and the required drive load end voltage Vinvd [also referred to as the required drive voltage] Vinvd [as the load end voltage Vinv of the inverter 16 which is the lowest voltage for realizing the required motor power Pmreq. A characteristic 72 representing the relationship with V] is shown. The characteristic 72 is stored in advance in a storage device in the ECU 24.

  In step S1, the drive request load end voltage Vinvd [V] is further calculated with reference to the characteristic 72 of FIG. 7 based on the motor required power Pmreq [kW]. The drive request load end voltage Vinvd is the minimum voltage to the drive motor 14 that secures the motor request power Pmreq, and is higher than the drive request load end voltage Vinvd when priority is given to the efficiency of the load 30. The control may be changed so that the efficiency required load end voltage Vinvη is applied to INV16. The efficiency required load end voltage Vinvη can be obtained in advance according to the motor rotational speed Nm and the motor torque. By applying a higher voltage as the load end voltage Vinv, the power loss at the load 30 proportional to the square of the motor current Im (load current) flowing through the drive motor 14 through the inverter 16 can be reduced. The system efficiency of the battery system 12 can be improved.

  Next, in step S2, the actual motor power Pm (Pm = Im × Vinv) is detected.

  Further, in step S3, the moving average motor power Pmmean is calculated from the motor power Pm. The reason why the moving average is calculated is to perform stable control that does not cause hunting.

  Next, in step S4, the moving average motor power Pmmean determines that the load 30 is a low load, and the load loss is reduced when the load end voltage Vinv is reduced (total loss of the inverter 16 and the drive motor 14). It is determined whether or not Pmloss is lower than the threshold power Pmth at which it becomes smaller.

  FIG. 8 is a characteristic diagram showing the relationship between the motor power Pm and the load loss Pmloss using the load end voltage Vinv as a parameter.

  When the motor power Pm falls below the threshold power Pmth, the load loss Pmloss is such that a loss characteristic 74 near a low load end voltage Vinvlow, for example, 300 [V] is a loss characteristic near a high load end voltage Vinvhigh, for example, 500 [V]. Note that it is less than 76. Note that the horizontal axis in FIG. 8 can be replaced with a motor rotation speed Nm having a threshold rotation speed Nmth corresponding to the threshold power Pmth.

  The motor power Pm and the motor rotation speed Nm have a unique relationship. Therefore, the load 30 is a low load, for example, a low-speed traveling range on a general road where the motor rotation speed Nm is 0 to 4000 [rpm], and the load 30 is a high load, for example, a motor rotation speed. The determination can be made in a high-speed traveling range on a highway or the like where Nm is 4000 to 10,000 [rpm]. In this case, the threshold rotation speed Nmth can be set to approximately 4000 [rpm].

  When the determination in step S4 is negative (step S4: NO, Pmmean ≧ Pmth), the control according to the main part of this embodiment is not performed.

  If the determination in step S4 is affirmative (step S4: YES, Pmmean <Pmth), it is determined that the load 30 is in a low load state. At time t2, the determination in step S4 (Pmmean <Pmth) becomes affirmative (step S4: YES).

  Then, next, in step S5, the magnitude of the FC voltage Vfc and the BAT voltage Vbat is determined.

  If it is determined in step S5 that the FC voltage Vfc is higher than the BAT voltage Vbat (step S5: NO, Vfc ≧ Vbat), in step S6, the FC voltage Vfc is set to a certain FC voltage amount (minute). (FC voltage amount) ΔVfc is reduced (Vfc ← Vfc−ΔVfc: FC voltage Vfc obtained by subtracting the constant FC voltage amount ΔVfc from the current FC voltage Vfc shown on the right side is changed to the FC voltage Vfc shown on the left side).

  In order to reduce the FC voltage Vfc to Vfc1 and Vfc2, as shown in FIG. 4, even if the FC current Ifc is the same, the standard IV characteristic 70 shown in FIG. 4 is changed to the IV characteristic 70p and the IV characteristic 70q. It is necessary to change (decrease).

  In order to reduce the normal IV characteristic 70 to the IV characteristic 70p and the IV characteristic 70q, the target film water content Zmtar is set to a target film water content Zmtarlow that is lower than the normal target film water content Zmtarnorm. By reducing the humidification amount of the oxidant gas by 31c, the actual membrane water content Zmb before the countermeasure may be lowered to the actual membrane water content Zma after the countermeasure corresponding to the target membrane moisture content Zmtarlow.

  Alternatively, in order to reduce the normal IV characteristic 70 to the IV characteristic 70p or the IV characteristic 70q, the amount of hydrogen or the amount of the oxidant gas supplied to the FC 18 is in a low stoichiometric state (the stoichiometric ratio is smaller than the normal stoichiometric ratio. For example, it may be lowered by reducing the flow rate of the air pump 31a so as to be in a state of 1 or more and less than 1.5. Note that the normal IV characteristic 70 is such that the stoichiometric ratio of oxygen and hydrogen (supply flow rate ÷ consumption flow rate) is set to an appropriate value of 1 or more, for example, 1.5 so that the cell voltage is stabilized even when the stoichiometric ratio is lowered. It is a characteristic when doing.

  Next, in step S7, a deviation ΔV (ΔV = | Vfc−Vbat |) between the reduced FC voltage Vfc and the BAT voltage Vbat is calculated, and in step S8, the deviation ΔV = | Vfc−Vbat | It is determined whether or not the deviation ΔV has narrowed to a minute voltage less than ΔVth (ΔV = | Vfc−V | <ΔVth).

  In this way, the process of step S5: NO → step S6 → step S7 → step S8 is repeated until the determination in step S8 becomes affirmative (step S8: YES).

  On the other hand, if it is determined in step S5 that the BAT voltage Vbat is higher than the FC voltage Vfc in the determination of the magnitude of the FC voltage Vfc and the BAT voltage Vbat (step S5: YES, Vfc <Vbat), the process proceeds to step S9. Thus, the BAT voltage Vbat is decreased by a constant BAT voltage amount (a minute BAT voltage amount) ΔVbat (Vbat ← Vbat−ΔVbat: a BAT voltage Vbat obtained by subtracting the constant BAT voltage amount ΔVbat from the current BAT voltage Vbat shown on the right side to the left side. The target SOCtar [%] of the BAT 20 is decreased by a constant ΔSOC [%] (SOCtar ← SOCtar−ΔSOC) in order to execute the process.

  For example, SOCtar = 50 [%], which is a normal target SOCtar of BAT 20, may be reduced by 1 [%] within a range of reduction to 40 [%]. In this case, in order to forcibly reduce the SOC of the BAT 20, for example, the ratio of the load power that the BAT 20 should bear with respect to the required power of the load 30 managed by the ECU 24 is larger than the ratio that the FC 18 should bear. If the reduction amount is still not sufficient, the air pump 31a constituting the FC auxiliary machine 31 is idled or the fan (not shown) constituting the air conditioning auxiliary machine 32 is idled so that the BAT 20 The stored power may be consumed.

  In this way, the process of step S5: YES → step S9 → step S7 → step S8 is repeated until the determination in step S8 becomes affirmative (step S8: YES).

  When the determination in step S8 becomes affirmative at time t3 (step S8: YES), the duty ratio of SUC21 and SUDC22, which are both voltage converters, is set to 0 [%] in step S10. The switching element 21b is held in the off state, and the FC voltage Vfc is processed to become the load end voltage Vinv, and the switching element 22b is turned off (the switching element 22d is also turned off, but the direction of current flow is BAT20). Since the inverter 16 side is on the side, it may be in the off state or the on state.), And the BAT voltage Vbat is processed to become the load end voltage Vinv.

  That is, in step S10, FC18 and BAT20 are in a low voltage state, and both are controlled to be directly connected to inverter 16 (load 30).

  As described above, in this embodiment, when the moving average motor power Pmmean that is the power of the load 30 including the inverter 16 and the drive motor 14 is continuously lower than the threshold power Pmth regarded as a low load, the FC voltage Vfc is equal to the BAT voltage Vbat. In the case of the above voltage, the FC voltage Vfc is decreased, the deviation ΔV that is a predetermined voltage difference from the BAT voltage Vbat is set to a value less than the threshold deviation ΔVth, and both the SUC21 (FC18) and the SUDC22 (BAT20) are directly connected. Control to the state. As a result, the switching loss of the SUC 21 and SUDC 22 can be completely eliminated, and the efficiency of the fuel cell system 12 and thus the fuel cell vehicle 10 can be improved.

  Alternatively, when the moving average motor power Pmmean that is the power of the load 30 composed of the inverter 16 and the drive motor 14 is continuously lower than the threshold power Pmth regarded as a low load, the BAT voltage Vbat is a voltage equal to or higher than the FC voltage Vfc. In this case, the BAT voltage Vbat is decreased, the deviation ΔV, which is a predetermined voltage difference from the FC voltage Vfc, is set to a value less than the threshold deviation ΔVth, and both the SUC21 (FC18) and the SUDC22 (BAT20) are controlled to be directly connected. As a result, the switching loss of the SUC 21 and SUDC 22 can be completely eliminated, and the efficiency of the fuel cell system 12 and thus the fuel cell vehicle 10 can be improved.

  9A to 9F show application examples and modification examples of this embodiment.

  In the fuel cell vehicle 10A equipped with the fuel cell system 12A having the SUC 21 and the SUDC 22 in FIG. 9A, Vfc> Vbat is set, and when it is determined that the load is not low, the SUC 21 is directly connected and the SUDC 22 is When it is used in the boosted state and determined to be in the low load state, the target remaining capacity SOCtar of the BAT 20 is reduced, and the SUDC 22 (BAT 20) is also used in both directly connected states in which the SUDC 22 (BAT 20) is also in the directly connected state.

  In the fuel cell vehicle 10B equipped with the fuel cell system 12B in which the SUC 21 of FIG. 9B is omitted, Vfc> Vbat is set, and if it is determined that the load is not low, the FC 18 is directly connected and the SUDC 22 is When the boosted state is used and it is determined that the load is low, the target remaining capacity SOCtar of the BAT 20 is decreased, and the SUDC 22 is used in both directly connected states.

  In the fuel cell vehicle 10C equipped with the fuel cell system 12C in which the SUC 21 and the SUDC 22 in FIG. 9C are omitted, when it is determined that the load is low, the target membrane water content Zmtar of the FC 18 is decreased or the low stoichiometric ratio. Used for use.

  In the fuel cell vehicle 10D equipped with the fuel cell system 12D having the SUC 21 and the SUDC 22 in FIG. 9D, Vbat> Vfc is set, and when it is determined that the load is not low, the SUDC 22 is directly connected and the SUC 21 is set. When used in a boosted state and determined to be in a low load state, the target membrane moisture content Zmtar of FC18 is reduced or the stoichiometric ratio is reduced, and SUC21 (FC18) is also in a directly connected state. Provide.

  In the fuel cell vehicle 10E equipped with the fuel cell system 12E in which the SUDC 22 of FIG. 9E is omitted, Vbat> Vfc is set, and when the SUDC 22 is omitted and it is determined that the load is not low, the BAT 20 is set. Directly connected state, when SUC21 is used in a boosted state and it is determined that the load is low, FC18 target membrane water content Zmtar or stoichiometric ratio is reduced, and SUC21 (FC18) is also directly connected state. Used for use.

  In the range extender type electric vehicle 11 of FIG. 9F, the generator (GEN) 15 is generated by the engine (ENG) 13 and the generated voltage Vgen is supplied to the primary side of the SUC 21, and the SUDC 22 is used in a boosted state, thereby reducing the load. When it is determined that the state is in the state, the target remaining capacity SOCtar of the BAT 20 is decreased, and the SUDC 22 (BAT 20) is used in a directly connected state.

[Summary of embodiments and further modifications]
As described above, the FC system 12 according to the above-described embodiment includes a load including the FC 18 that outputs the FC voltage Vfc, the BAT 20 that outputs the BAT voltage Vbat, and the drive motor 14 driven through the inverter 16 and the inverter 16. 30, SUC 21 as a first voltage converter that converts the FC voltage Vfc of the FC 18 to a DC terminal side of the inverter 16 as a load terminal voltage Vinv, and a voltage converter (boosts) the BAT voltage Vbat of the BAT 20. In the control method of the FC system 12 including the SUDC 22 as the second voltage converter that is applied to the DC terminal side of the inverter 16 as the load terminal voltage Vinv, the request of the load 30 of the FC system 12 (motor required power Pmreq) Based on the motor rotation speed Nm of the drive motor 14 Is a motor control setting step (step S1) for setting the motor power Pm, and the set motor speed Nm or the motor power Pm is a threshold value (for example, the threshold power Pmth set corresponding to the moving average motor power Pmean). A low load determination step (step S4) for determining whether or not the load is lower, and when it is determined that the load is low (step S4: YES), the higher one of the BAT voltage Vbat and the FC voltage Vfc Voltage lowering step (step S6 or step S9).

  According to this embodiment, when it is determined that the load 30, for example, the motor power Pm, is a low load (step S4: YES), the voltage lowering step of lowering the higher one of the BAT voltage Vbat and the FC voltage Vfc. Since (Step S6 or Step S9) is provided, a low voltage can be supplied to the load 30 as the load end voltage Vinv, and the load loss can be reduced. As a result, the efficiency of the FC system 12 can be improved.

  In this case, it is preferable to have a voltage conversion stop step (step S10) in which the voltage conversion operation of the SUC 21 and SUDC 22 is stopped and the FC 18 and the BAT 20 are directly connected to the load 30 after the voltage reduction step (step S6 or step S9).

  It is determined that the load 30 is a low load (step S4: YES), and the voltage conversion of the SUC 21 and the SUDC 22 is stopped in a region where a loss can be reduced by supplying a low voltage (a region below the threshold power Pmth in FIG. 8). . As a result, a low voltage can be supplied to the load 30 and the load loss can be reduced. Further, since the switching loss due to the voltage conversion of the SUC 21 and SUDC 22 can be eliminated, the efficiency of the fuel cell system 12 can be reliably improved. it can.

  In this case, a deviation ΔV (ΔV = | Vfc−Vbat |) which is a voltage difference between the FC voltage Vfc and the BAT voltage Vbat after the voltage reduction process (step S6 or step S9) and before the voltage conversion stop process (step S10). ) And the difference ΔV (ΔV = | Vfc−Vbat |) ascertained is within a predetermined value that allows the simultaneous stop of the SUC 21 and SUDC 22 (a minute voltage less than the threshold deviation ΔVth). The voltage difference control process (step S8: ΔV = | Vfc−Vbat | <ΔVth) is performed so that the voltage difference between the FC voltage Vfc and the BAT voltage Vbat is reduced, and then directly connected. Therefore, the direct connection can be made smoothly without impairing the controllability of the FC 18 and the BAT 20. The threshold deviation ΔVth can be determined for each fuel cell system 12 in advance.

  When it is determined that the BAT voltage Vbat is higher than the FC voltage Vfc in the voltage difference determination step (step S5) (step S5: YES), the target SOC of the BAT 20 is determined in the voltage difference control step (step S9). By controlling so as to reduce the deviation, the deviation ΔV (ΔV = | Vfc−Vbat |), which is the voltage difference between the FC voltage Vfc and the BAT voltage Vbat, can be reduced by a simple method.

  Further, when the voltage difference grasping step (step S5) finds that the FC voltage Vfc is higher than the BAT voltage Vbat (step S5: NO), the voltage difference controlling step (step S6) includes the membrane water content of FC18. By reducing the rate Zm and / or the stoichiometric ratio, the deviation ΔV (ΔV = | Vfc−Vbat |), which is the voltage difference between the FC voltage Vfc and the BAT voltage Vbat, can be similarly reduced by a simple method.

  The threshold power Pmth, which is the determination value in the low load determination step (step S4), is determined based on the load loss Pmloss, which is the total loss of the inverter 16 and the drive motor 14, so that the efficiency of the entire FC system 12 is generally considered. As a result, the efficiency of the FC system 12 can be improved.

  Further, as shown in FIG. 9B, the FC system 12B according to the above-described embodiment supplies the load 30 including the inverter 16 and the drive motor 14 driven through the inverter 16 and the FC voltage Vfc to the DC end side of the inverter 16. FC18 that is directly applied as the load end voltage Vinv, BAT20 that outputs the BAT voltage Vbat, and a voltage converter that converts (boosts) the BAT voltage Vbat of the BAT20 and applies it to the DC end side of the inverter 16 as the load end voltage Vinv. In the control method of the FC system 12B including the SUDC 22 as a motor control setting step (step S1) for setting the motor rotation speed Nm or the motor power Pm of the drive motor 14 based on the load request of the load 30 of the FC system 12B. ) And the set motor speed Nm A low load determination step (step S4) for determining whether or not the motor power Pm is a low load lower than a threshold value (for example, a threshold power Pmth set corresponding to the moving average motor power Pmmean); When the determination is made (step S4: YES), a voltage reduction step (step S6) for reducing the FC voltage Vfc is provided, so that a low voltage can be supplied to the load 30 as the load end voltage Vinv, thereby reducing load loss. can do. As a result, the efficiency of the FC system 12B can be improved.

[Modification A]
Furthermore, for any one of connection examples of the FC system 12B (FIG. 9B) and the FC system 12E (FIG. 9E) according to the above-described embodiment, the FC 18 that outputs the FC voltage Vfc and the BAT 20 that outputs the BAT voltage Vbat. Then, the load 30 composed of the inverter 16 and the drive motor 14 driven through the inverter 16 and the FC voltage Vfc of the FC 18 or the BAT voltage Vbat of the BAT 20 are voltage-converted and applied to the DC end side of the inverter 16 as the load end voltage Vinv. In the control method of the fuel cell systems 12B and 12E including one voltage converter (SUDC22 in FIG. 9B or SUC21 in FIG. 9E), based on the request (motor required power Pmreq) of the load 30 of the fuel cell systems 12B and 12E The motor rotation speed of the drive motor 14 The motor control setting step for setting m or motor power Pm, and the set motor rotation speed Nm or motor power Pm is a threshold value (threshold rotation speed Nmth, for example, the upper limit motor rotation speed Nm of the low-speed traveling range). A low load determination step (analogue) for determining whether the load is lower than 4000 [rpm] or threshold power Pmth, for example, a value determined from the threshold rotational speed Nmth and the required torque of the drive motor 14. Step S4), and when it is determined that the load is low, the FC 18 and the BAT 20 are connected to the DC terminal side of the inverter 16 without passing through the voltage converter (SUDC 22 in FIG. 9B or SUC 21 in FIG. 9E). A voltage lowering step for lowering the voltage of FC18 (FIG. 9B) or BAT20 (FIG. 9E).

  As described above, in the modified example A targeting either one of the FC system 12B in FIG. 9B and the FC system 12E in FIG. 9E, when the load 30 is determined to be a low load, the voltage converter (in the FC 18 and the BAT 20) ( Since a voltage lowering step for lowering the voltage of the FC 18 or BAT 20 directly connected to the DC terminal side of the inverter 16 without going through the SUC 21 or SUDC 22) is provided, a low voltage can be supplied to the load 30 to reduce load loss. be able to. As a result, the efficiency of the FC systems 12B and 12E can be improved.

[Modification B]
Furthermore, for a connection example of the FC system 12C (FIG. 9C) according to the above-described embodiment, a load 30 including the FC 18 that outputs the FC voltage Vfc, the inverter 16 and the drive motor 14 that is driven through the inverter 16, In the control method of the fuel cell system 12C comprising: a motor control setting step of setting the motor rotation speed Nm or the motor power Pm of the drive motor 14 based on a request (motor required power Pmreq) of the load 30 of the fuel cell system 12C. The set motor rotation speed Nm or motor power Pm is a threshold value (threshold rotation speed Nmth, for example, 4000 [rpm] described above, which is the upper limit motor rotation speed Nm of the low-speed traveling range), or threshold power Pmth, for example, Determined from the threshold rotational speed Nmth and the required torque of the drive motor 14 A low load determination step (analogue step S4) for determining whether or not the load is lower, and if it is determined that the load is low, the drive request voltage (drive request load end voltage Vinvd) of the drive motor 14 Or a voltage lowering step for reducing the FC voltage Vfc to a lower limit voltage at which stable power generation of the FC18 can be performed.

  As described above, in Modification B targeting the FC system 12C of FIG. 9C, when the load 30 is determined to be low, the FC voltage Vfc is set to the drive request voltage (drive request load end voltage Vinvd) of the drive motor 14 or Since the voltage lowering step for lowering to the lower limit voltage of FC18 is provided, a low voltage can be supplied to the load 30 and load loss can be reduced. As a result, the efficiency of the FC system 12C can be improved. The lower limit voltage of FC18 refers to, for example, the lower limit voltage of a so-called platinum reduction stable region, in which the reduction reaction of platinum (platinum oxide) contained in the FC cell proceeds stably.

  In addition, the present invention is not limited to the above-described embodiment, and it is needless to say that various configurations can be adopted based on the contents described in this specification.

10, 10A-10E ... Fuel cell vehicle (FC vehicle)
12, 12A-12E ... Fuel cell system (FC system)
14 ... Drive motor 16 ... Inverter (INV)
18 ... Fuel cell (FC) 20 ... Power storage device, High voltage battery (BAT)
21 ... Boost converter (booster, voltage converter, SUC)
22 ... Buck-boost converter (buck-boost, voltage converter, SUDC)
24 ... ECU

Claims (5)

A fuel cell that outputs a fuel cell voltage;
A power storage device that outputs a power storage device voltage;
A load comprising an inverter and a motor driven through the inverter;
A first voltage converter for converting the fuel cell voltage of the fuel cell and applying the voltage to the DC terminal side of the inverter as a load terminal voltage;
A second voltage converter that converts the voltage of the power storage device of the power storage device and applies the voltage to the DC terminal side of the inverter as the load terminal voltage;
In a control method of a fuel cell system comprising:
A motor control setting step for setting the motor rotation speed or motor power of the motor based on the load requirement of the fuel cell system;
A low load determination step for determining whether the set motor rotation speed or the motor power is a low load lower than a threshold;
When it is determined that the load is low, a voltage lowering step of lowering the higher voltage among the power storage device voltage and the fuel cell voltage;
A voltage difference grasping step for grasping a voltage difference between the fuel cell voltage and the power storage device voltage;
A voltage difference control step for controlling the grasped voltage difference to be within a predetermined value that allows the stop of the first and second voltage converters;
A voltage conversion stop step of stopping the voltage conversion operation of the first and second voltage conversion devices and directly connecting the fuel cell and the power storage device to the load when the voltage difference is within the predetermined value;
A control method for a fuel cell system, comprising: In the control method of the fuel cell system according to claim 1 ,
In the voltage difference grasping step, when it is grasped that the power storage device voltage is higher than the fuel cell voltage,
In the voltage difference control step, the SOC of the power storage device is reduced. A control method for a fuel cell system. In the control method of the fuel cell system according to claim 1 or 2 ,
In the voltage difference grasping step, when it is grasped that the fuel cell voltage is higher than the power storage device voltage,
In the voltage difference control step, the membrane water content and / or stoichiometric ratio of the fuel cell is reduced. A control method for a fuel cell system. In the control method of the fuel cell system according to any one of claims 1 to 3 ,
The control method of a fuel cell system, wherein the threshold value that is a determination value of the low load determination step is determined based on a total loss of the inverter and the motor. A fuel cell vehicle that implements the control method for a fuel cell system according to any one of claims 1 to 4 .

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