JP2016095911A - Fuel cell system control method and fuel-cell vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system control method and fuel-cell vehicle that appropriately control a first and second voltage converters to make it possible to further improve system efficiency.SOLUTION: Direct connection of a SUC 21 (first voltage converter) and SUDC 22 (second voltage converter) in the case that a voltage difference |Vdif| between a FC voltage Vfc and BAT voltage Vbat is within a predetermined range |Vdif|<Vth and small causes reduction in voltage conversion losses of the SUC 21 and SUDC 22 to make it possible to improve efficiency of the whole system.SELECTED DRAWING: Figure 5

Description

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

  Conventionally, for example, as shown in FIG. 1 of Patent Document 1, between the inverter of a load including a motor and an inverter that drives the motor and the output terminal of the fuel cell, and input / output of the inverter and the power storage device 2. Description of the Related Art There is known a fuel cell vehicle equipped with a fuel cell system in which a boost converter is provided between each end and the load (an inverter and a motor driven by the inverter) is driven.

  In the technique according to Patent Document 1, a motor required voltage that is a voltage of electric power supplied to the load and a fuel cell voltage (power generation voltage, output voltage) of the fuel cell to cause the load to exert a predetermined driving force. Based on the correlation, when the fuel cell voltage is higher than the motor required voltage, the voltage is not directly boosted by the boost converter on the fuel cell side, and the switching loss of the boost converter on the fuel cell side is suppressed. ([0011], [0012] of Patent Document 1).

International Publication No. 2009/084650 Pamphlet

  By the way, in a fuel cell system having two converters (first and second voltage conversion devices) disposed between a fuel cell and an inverter and between a power storage device and the inverter, the system efficiency is always improved. It is hoped that.

  However, Patent Document 1 discloses a technique for suppressing the switching loss of the converter on the fuel cell side, but does not disclose a technique for reducing the switching loss of the converter on the power storage apparatus side. There is room for.

  The present invention has been made in consideration of such problems, and is capable of appropriately controlling the first and second voltage converters and further improving the system efficiency, thereby controlling the fuel cell system. It is an object to provide a method and a fuel cell vehicle.

  A control method of 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 A first voltage conversion device that converts the fuel cell voltage of the battery into a DC terminal side of the inverter as a load terminal voltage, and converts the power storage device voltage of the power storage apparatus into the load terminal voltage as the load terminal voltage. In a control method of a fuel cell system, comprising: a second voltage conversion device applied to a DC terminal side; a voltage difference grasping step for grasping a voltage difference between the fuel cell voltage and the power storage device voltage; and When the voltage conversion operation of the first and second voltage converters is within a predetermined range where the voltage conversion operation can be stopped, the voltage conversion operation of the first and second voltage converters is stopped. Te, having a voltage converter stopping step of directly connecting the fuel cell and the power storage device to the load.

  According to this invention, when the voltage difference between the fuel cell voltage and the power storage device voltage is within a predetermined range and is small, the first and second voltage conversion devices are directly connected. Conversion loss is reduced, and the efficiency of the entire system can be improved.

  In this case, the method further includes a generated power divergence width grasping step for grasping a difference between the generated power command value for the fuel cell and the actual generated power as a generated power divergence width, and after the start of the voltage conversion stop step, When the width is equal to or greater than the predetermined width, it is preferable that the voltage conversion stop process is terminated and at least one voltage conversion operation of the first and second voltage conversion devices is executed.

  According to the present invention, since it is detected that the controllability of the fuel cell is deteriorated and the direct connection is released, it is possible to prevent the target generated power from being obtained and the merchantability from being deteriorated.

  In addition, it is preferable that the predetermined range of the voltage difference for determining the start of the voltage conversion stop process is smaller as the temperature of the power storage device is lower. Further, the predetermined range of the voltage difference for determining the start of the voltage conversion stop process may be made smaller as the allowable charge / discharge power range of the power storage device becomes smaller.

  As described above, since the direct connection determination is performed in consideration of whether or not the power storage device can be assisted, it is possible to prevent the merchantability from being deteriorated without obtaining the target controllability due to the direct connection.

  In addition, when the voltage conversion stop process is ended, it is preferable that the voltage conversion operation of the first voltage conversion device is restarted prior to the voltage conversion operation of the second voltage conversion device. Also in this case, it is possible to suppress deterioration of the controllability of the fuel cell, and it is possible to prevent deterioration of the durability of the fuel cell.

  Furthermore, since the power storage device voltage can be increased by increasing the target SOC of the power storage device after completing the voltage conversion stop step, the boosting state of the first voltage conversion device that boosts the fuel cell voltage may be continued. As a result, the system efficiency can be prevented from deteriorating due to both boosted states, and as a result, the frequency of performing the voltage conversion operation of the first voltage converter that boosts the power storage device voltage can be reduced.

  Furthermore, it is preferable to increase the amount of charge to the power storage device after the voltage conversion stop step is completed. Since the power storage device voltage can be increased by forcibly charging the power storage device, the frequency of executing the voltage conversion operation of the second voltage conversion device that boosts the power storage device voltage can be reduced.

  Furthermore, the first and second voltage conversions when the voltage difference between the fuel cell voltage and the power storage device voltage is within a predetermined range in which the voltage conversion operation of the first and second voltage conversion devices can be stopped. In the voltage conversion stop step of stopping the voltage conversion operation of the device and directly connecting the fuel cell and the power storage device to the load, the voltage difference can stop the voltage conversion operation of the first and second voltage conversion devices. When approaching a predetermined range, as a first method, the target SOC of the power storage device is varied to increase or decrease the power storage device voltage, and the voltage difference between the power storage device voltage and the fuel cell voltage is within the predetermined range. As a second method, the fuel cell voltage is increased / decreased by changing the target membrane moisture content of the fuel cell, and the voltage difference between the fuel cell voltage and the power storage device voltage is within the predetermined range, 3 methods and The fuel cell voltage is varied by varying the target stoichiometric ratio of the fuel cell, and the voltage difference between the fuel cell voltage and the power storage device voltage is within the predetermined range. By narrowing the voltage difference between the power storage device voltage and the fuel cell voltage to the predetermined range and stopping the voltage conversion operation of the first and second voltage conversion devices, both are directly connected (simultaneous direct connection). The system efficiency can be further improved by increasing the frequency of

  In this case, the application priority of the first, second, and third methods for narrowing the voltage difference between the power storage device voltage and the fuel cell voltage to the predetermined range is first, second, and third. It is preferable to follow the order of these methods. The variable control of the target SOC of the power storage device is simpler than the target moisture content control and the target stoichiometric ratio variable control of the fuel cell. The target moisture content variable control is the power generation of the fuel cell compared to the target stoichiometric ratio variable control. Little reduction in efficiency.

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

  According to this invention, when the voltage difference between the fuel cell voltage and the power storage device voltage is within a predetermined range and is small, the first and second voltage conversion devices are directly connected. The effect that the conversion loss is reduced and the efficiency of the entire system can be improved is achieved.

1 is a schematic overall configuration diagram of a fuel cell vehicle to which a fuel cell system as a dual power load driving 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 embodiment. It is a flowchart provided for operation | movement description of embodiment. It is a temperature characteristic figure of charge / discharge electric power restriction of an electrical storage device. It is a table | surface figure explaining the method of narrowing the difference of 2 voltage of a modification. It is explanatory drawing explaining the change of IV characteristic with respect to increase / decrease in a film | membrane moisture content and a stoichiometric ratio. It is a timing chart used for operation | movement description of a modification.

  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, in the BAT 20, when the power for driving the drive motor 14 by the FC 18 becomes surplus, the surplus power (surplus power) is passed through the boosted SUC 21 or the directly connected SUC 21. It is supplied through the SUDC 22 in the step-down state or the direct connection state, and the BAT 20 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 includes a BAT voltage (battery voltage) Vbat, a BAT current (battery current) Ib (BAT discharge current Ibd, charging current Ibc), a BAT temperature (battery temperature) Tbat, and an SOC (State Of Charge) that is the remaining capacity of the BAT 20. Is detected or managed by the ECU 24.

  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 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 (not shown) including a membrane moisture meter 31b, a current sensor, a temperature sensor including a temperature sensor 20a of the BAT 20, Detection values of pressure sensors, hydrogen concentration sensors, various rotation speed sensors, accelerator pedal opening sensors, etc.) and on / off information of various switches (air conditioning switches, ignition switches, etc.) 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. Note that the execution subject of the program according to the flowchart shown in FIG. 6 is the CPU of the ECU 24.

  In step S1, the ECU 24 allows the absolute value | Vfc−Vbat | (hereinafter also simply referred to as the voltage difference | Vdif |) of the difference between the FC voltage Vfc and the BAT voltage Vbat to allow the SUC21 and the SUDC22 to be connected directly. It is determined whether or not the threshold voltage (simultaneous direct coupling setting threshold voltage or simultaneous direct coupling allowable threshold voltage) is lower than Vth (| Vfc−Vbat | = | Vdif | <Vth).

  At the time of simultaneous direct connection, the FC voltage Vfc generally sticks to the BAT voltage Vbat. Therefore, when the voltage difference | Vdif | = | Vfc−Vbat | is larger than the threshold voltage Vth (step S1: NO), the FC18 In consideration of the possibility that the controllability may be deteriorated, the simultaneous direct connection state is not set. In step S2, normal control {one of SUC21 and SUDC22 is in a direct connection state or both are in a voltage conversion state such as a boosted state. Control}.

  In this embodiment, in the normal control process in step S2, the FC voltage Vfc is higher than the target load end voltage Vinvtar described below, so the target of the load end voltage Vinv applied to the DC input end of the inverter 16 is set. The FC voltage Vfc is directly connected to the target load end voltage Vinvtar which is a voltage (SUC21: direct connection, SUDC22: boost, refer to the period from time t0 to time t1).

  The target load end voltage Vinvtar is set, for example, according to the following procedure.

  First, the ECU 24 inputs values from various switches and various sensors [Vfc, Ifc, Vbat, Ib, Vinv, I2 (input / output current with respect to INV16, secondary current; see FIGS. 1 and 2), Im (drive motor). 14 motor current, normally two phases, see FIG. 2), Nm (rotation speed of the drive motor 14), θp (accelerator pedal operation amount not shown), Tbat {BAT20 battery temperature (BAT temperature) TBAT}, etc. ] Is calculated, and the motor required power Pmreq [kW] for the drive motor 14 is calculated.

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

  Here, the load end voltage Vinv of the inverter 16, which is the minimum voltage for realizing the motor required power Pmreq, uniquely corresponds to the motor required power Pmreq. Therefore, the load end voltage Vinv can be calculated, and the calculated load The end voltage Vinv is set to the target load end voltage Vinvtar.

  In this way, the target load end voltage Vinvtar is calculated and set for each predetermined cycle in which the flowchart of FIG. 6 is executed.

  In FIG. 5 again, the target load end voltage Vinvtar gradually decreases between time t0 and time t1, and the directly connected FC voltage Vfc gradually decreases simultaneously. Since the FC voltage Vfc gradually decreases, the FC current Ifc increases, and the target generated power Pfctar and the generated power Pfc that is the actual generated power gradually increase.

  At time t1, when the voltage difference | Vdif | = | Vfc−Vbat | between the FC voltage Vfc and the BAT voltage Vbat becomes smaller than the threshold voltage Vth, the determination in step S1 is positive (step S1: YES). In step S3, both the SUC 21 and the SUDC 22 are shifted to the direct connection state. That is, in step S3, the switching element 21b of the SUC 21 is kept in the OFF state, and the switching element 22b and the switching element 22d of the SUDC 22 are set to the simultaneous direct connection state that turns off. Note that when the BAT 20 is charged during the simultaneous direct connection, the switching element 22d is switched to the ON state. After the time point t1, the SUC 21 and SUDC 22 are in the directly directly connected state, that is, both are directly connected, so that the switching loss of the SUC 21 and SUDC 22 becomes zero and the system efficiency is improved.

  Here, at the time of the direct connection, the FC voltage Vfc is generally stuck to the BAT voltage Vbat, so that the BAT 20 can absorb (correspond) the fluctuation of the secondary current I2 (see FIG. 2) due to the fluctuation of the power of the load 30. It is necessary to carry out simultaneous direct operation.

  FIG. 7 shows the temperature characteristics of the charge / discharge power limit (discharge power limit and charge power limit) of the BAT 20. A battery discharge limiting characteristic 74 when the BAT discharge current Ibd is output (discharged) from the BAT 20 and a battery charge limiting characteristic 76 when the BAT 20 inputs (charges) the charging current Ibc are from a normal temperature Tnorm = 25 [° C.]. When the temperature is lowered, the output BAT discharge current Ibd and the input charge current Ibc are limited, and at a temperature of several tens of degrees below the freezing point on the left end side in FIG. 7, the BAT 20 is not activated and becomes almost zero. In addition, at temperatures higher than room temperature Tnorm, the output BAT discharge current Ibd and the input charge current Ibc are limited at large values of the allowable discharge power Padmax [kW] and the allowable charge power Pacmax.

  In consideration of the battery discharge restriction characteristic 74 and the battery charge restriction characteristic 76 which are the temperature characteristics of the power restriction of the BAT 20, when the direct connection is made at the same time in step S3, the BAT temperature Tbat is lower than the room temperature Tnorm. As a result, it is preferable to reduce the voltage value of the threshold voltage Vth (voltage width) that permits simultaneous direct connection to make it difficult to shift to the simultaneous direct connection state to ensure controllability.

  Next, in step S4, the ECU 24 determines that the absolute value | Pfctar−Pfc | (hereinafter referred to as power deviation width | Pfcdif | or power difference | Pfcdif |) of the difference between the target FC power Pfctar and the FC power Pfc is the difference between the SUC21 and the SUDC22. It is determined whether or not the power value is lower than the threshold power for canceling the simultaneous direct connection state (simultaneous direct connection cancellation threshold power) Pfcth (| Pfcdif | = | Pfctar−Pfc | <Pfcth).

  Between time t1 and time t2, the determination in step S4 is negative (step S4: NO), so the simultaneous direct connection state is continued in step S5 (step S1: YES → step S3 → step S4: NO → Step S5).

  At time t2, the target generated power Pfctar starts increasing, and the difference between the target generated power Pfctar and the generated power Pfc is started. At time t3, the power divergence width | Pfcdif between the target generated power Pfctar and the generated power Pfc When | = | Pfctar−Pfc | becomes larger than the threshold power (predetermined width) Pfcth (| Pfctar−Pfc |> Pfcth), the determination in step S4 becomes affirmative (step S4: YES). In step S6, the simultaneous direct connection state is canceled by shifting the SUC 21 to the boosting state while maintaining the SUDC 22 in the direct connection state.

  The threshold power Pfcth for canceling the simultaneous direct connection state is also set to a smaller power value (power deviation width) as the BAT temperature Tbat is lower than the normal temperature Tnorm, so that the simultaneous direct connection state can be easily released. It is preferable to ensure controllability.

  In order to determine whether or not the power divergence width | Pfcdif | = | Pfctar−Pfc | continues to exceed the threshold power Pfcth after time t3, in step S7, the power divergence width | Pfcdif | = | Pfctar It is determined whether or not -Pfc | is greater than the threshold power Pfcth and the SUC 21 was in the boosted state during the previous control process (when the previous program was executed). At the time of the previous control process (at the time of the previous program execution), since the SUC 21 was in the direct connection state, the determination in step S7 becomes negative (step S7: NO), and in step S8, the direct connection state of the SUDC 22 and the SUC 21 The boosted state is maintained.

  When the power deviation width | Pfcdif | = | Pfctar−Pfc | is greater than the threshold power Pfcth at time t4 when the next control process is performed, the SUC 21 was in the boosted state during the previous control process. Therefore, the determination in step S7 becomes affirmative (step S7: YES), and in step S9 corresponding to this time point t4, the simultaneous boosting state in which the SUDC 22 is boosted in addition to the SUC 21 is set.

  In this case, in step S9, when the motor required power Pmreq is calculated, the load end voltage Vinv is set to the target load end voltage Vinvtar as shown in FIG. When the motor required power Pmreq is not calculated, such as during stoppage while waiting for a signal, the load end voltage Vinvtar is set to an appropriate voltage value higher than the FC voltage Vfc and the BAT voltage Vbat. In this case, the setting value of the load end voltage Vinvtar is desirably higher than a value obtained by adding a margin to the FC voltage Vfc so that the controllability of the FC 18 can be maintained.

[Modification]
Next, a modified example of the control process by the ECU 24 of the fuel cell system 12 according to the above embodiment will be described.

  In the embodiment described above, the voltage difference | Vdif | = | Vfc−Vbat |, which is the absolute value of the difference between the FC voltage Vfc and the BAT voltage Vbat, is smaller than the threshold voltage Vth (| Vfc−Vbat | <Vth). When (step S1: YES), in step S3, both the SUC 21 and SUDC 22 are directly connected (switching elements 21b, 22b, 22d: off. When charging the BAT 20, the switching element 22d: on). In the simultaneous direct connection state, the switching loss of the SUC 21 and the SUDC 22 becomes zero, and the system efficiency is improved.

  Therefore, in this modification, in order to further improve the system efficiency, in order to increase the frequency of the simultaneous direct connection state and / or the cumulative time of the simultaneous direct connection state, a voltage difference that is an absolute value of the difference between the FC voltage Vfc and the BAT voltage Vbat | When the time change of Vdif | = | Vfc−Vbat | tends to be small (between time point t10 and time point t11 in FIG. 10 described later, or between time point t14 and time point t16), FC is determined under a predetermined condition. A method of actively narrowing the voltage difference | Vdif | between the voltage Vfc and the BAT voltage Vbat will be described.

  The process of this modification is executed as a pre-process of the determination process in step S1. That is, when the voltage difference | Vdif | = | Vfc−Vbat | between the FC voltage Vfc and the BAT voltage Vbat is gradually decreased with time, for example, the voltage difference | Vdif | becomes the threshold voltage Vth (positive When the voltage is higher (larger) by a predetermined voltage ΔVth (takes a positive value) (| Vdif | = Vth + ΔVth) than the BAT voltage Vbat and / or the FC voltage Vfc ( In this process, the voltage difference | Vdif | is forcibly set to a voltage smaller than the threshold voltage Vth (step S1: YES). When either the BAT voltage Vbat or the FC voltage Vfc is brought closer to the other, the voltage at the time of the direct connection is higher than the voltage necessary for driving the motor 14 (motor drive request voltage). It is a necessary condition to make it.

  FIG. 8 shows a method of narrowing the difference between the two voltages (each voltage) of the FC voltage Vfc and the BAT voltage Vbat and the two voltages in each state, that is, forcing the voltage difference | Vdif | = Vth + ΔVth from the threshold voltage Vth. It is a table | surface explaining the 1st method, 2nd method, and 3rd method of a process (step S1: YES) which makes it a small voltage (| Vdif | <Vth).

  Regarding the variation of the BAT voltage Vbat in the first method, it is known that the BAT voltage Vbat increases (decreases) if the SOC is increased (decreased) by increasing (decreasing) the target SOC and the SOC increases (decreases). is there.

  Regarding the variation of the membrane water content Zm of the electrolyte membrane of FC18 in the second method, the characteristic diagram on the upper left side in FIG. 9 shows the IV characteristic 70im when the membrane water content Zm of FC18 is increased (increased), and the membrane The water content Zm shows the relationship with the normal IV characteristic 70. By increasing the membrane water content Zm, a large amount of water molecules that can easily conduct electricity can be formed in the vicinity of the electrolyte membrane that is a reaction membrane, thereby facilitating electricity conduction. As a result, an excessive resistance value is reduced and the FC voltage Vfc is increased. In addition, the characteristic diagram on the lower left side in FIG. 9 shows the relationship between the IV characteristic 70 dm when the membrane moisture content Zm of FC18 is reduced (lowered) and the IV property 70 when the membrane moisture content Zm is normal. ing.

  From these relationships, as a second method, if the membrane water content Zm increases (decreases) by increasing (decreasing) the target membrane water content Zmtar, the FC voltage Vfc becomes equal on the same FC current (generated current) Ifc. It is understood that it rises (falls).

  Regarding the variable of the target stoichiometric ratio of FC18 of the third method, the upper and lower characteristic diagrams on the right side in FIG. 9 are obtained when the stoichiometric ratio (supply amount / consumption amount) of hydrogen or oxidant gas is increased (increased). This shows the relationship between the IV characteristic 70is or the IV characteristic 70ds when it is reduced (decreased) and the IV characteristic 70 when the stoichiometric ratio is normal. For example, by increasing the stoichiometric ratio, the reaction gas is sufficiently distributed to every corner of the electrolyte membrane, so that a sufficient chemical reaction between hydrogen and oxygen is possible, and as a result, no excessive voltage drop occurs during power generation, and the same FC The FC voltage Vfc increases on the current (generated current) Ifc.

  From these relationships, as a third method, if the stoichiometric ratio decreases (increases) by decreasing (increasing) the target stoichiometric ratio, the FC voltage Vfc decreases (increases) on the same FC current (generated current) Ifc. To be understood.

  Here, the variable control of the target SOC of the BAT 20 by the ECU 24 only needs to perform a control process to increase or decrease the share of the BAT 20 in response to the load request. For the target film moisture content Zmtar control and the target stoichiometric ratio variable control of the FC18. Note that the target membrane water content Zmtar variable control is less in comparison with the target stoichiometric ratio variable control, and the amount of decrease in the power generation efficiency of the FC 18 is small.

  Based on this consideration, regarding the priority of which one of the first to third methods is adopted, the first priority is the target SOC variable control, the second priority is the target membrane water content variable control, 3. Set priority to target stoichiometric ratio control.

  Next, the operation of a modification of the control process performed by the ECU 24 of the fuel cell system 12 according to the above embodiment will be described with reference to the timing chart of FIG.

  In the timing chart of FIG. 10, the third method (variable target stoichiometric ratio) is taken as an example for convenience of understanding. Further, when at least one of the SUC 21 and SUDC 22 is in a direct connection state, and when both are in a direct connection state (simultaneous direct connection state), the BAT voltage Vbat and the FC voltage Vfc at the time of direct connection are both the target load terminals. It is assumed that the voltage is higher than the voltage Vinvtar.

  As shown in FIG. 10, the target SOC [%] is increased from time t10 to time t13, is constant from time t13 to time t14, is decreased from time t14 to time t18, and time t18. The following description is based on the transition state that is constant. Actually, the actual SOC [%] follows the target SOC [%].

  Between time t10 and time t13, since the BAT voltage Vbat increases and the target SOC also increases, the BAT power Pbat (BAT charging power Pac) increases.

  At time t11, the voltage difference | Vdif | = | Vfc−Vbat | between the FC voltage Vfc and the BAT voltage Vbat becomes a voltage Vth + ΔVth (this is referred to as a predetermined voltage Vp) that is higher (larger) by a predetermined voltage ΔVth than the threshold voltage Vth. When it is detected that (| Vdif | = Vth + ΔVth = Vp), considering that Vfc> Vbat, the target stoichiometric ratio change flag Fstar is switched from normal power generation to low stoichiometric power generation. As a result, the FC voltage Vfc suddenly decreases from time t11 and approaches the BAT voltage Vbat.

  Then, at the time t12 when the determination in step S1 described above (| Vdif | = | Vfc−Vbat | <Vth) becomes affirmative, the simultaneous direct connection determination is changed from the OFF state (non-established state) to the ON state (established state). Then, at the time t12, the switching operation of the SUDC 22 is stopped and the simultaneous direct connection state (SUC21: direct connection, SUDC22: direct connection) is set.

  Then, at the time t12 when the simultaneous direct connection state is established, the target stoichiometric ratio change flag Fstar is switched from the low stoichiometric power generation to the normal stoichiometric power generation (agreement with normal power generation).

  Between time t13 and time t14, a simultaneous direct connection state is established. During this period, the target SOC is constant and the BAT voltage Vbat sticking to the FC voltage Vfc is decreasing, so the BAT power Pbat (BAT discharge power Pbatd) increases.

  At the time point t14, the simultaneous direct connection determination is changed from the ON state to the OFF state, and the simultaneous direct connection state is released. The simultaneous direct connection state release determination condition is, for example, the allowable fulfillment of the BAT 20 described with reference to FIG. When it is determined that the discharge power range (allowable discharge power Padmax or allowable charge power Pacmax) is within the predetermined power range (predetermined discharge power smaller than the allowable discharge power Padmax or predetermined charge power smaller than the allowable charge power Pacmax) You only have to set it.

  Alternatively, the simultaneous direct connection state release determination condition is that the load end voltage Vinv which is a supply voltage from the FC 18 or BAT 20 to the inverter 16, in this case, the FC voltage Vfc or the BAT voltage Vbat is the required voltage of the inverter 16 (load 30). It may be determined that it is determined that the voltage is less than (or is likely to fall below) (the load drive request voltage).

  At time t14, the FC power Pfc starts decreasing, the target SOC starts decreasing, and the power difference | Pfcdif | = | Pfctar−Pfc | which is the absolute value of the difference between the target FC power Pfctar and the FC power Pfc is SUC21. When the power value exceeds the threshold power (simultaneous direct connection cancellation threshold power) Pfcth for canceling the simultaneous direct connection state of SUDC22 (step S4: YES), the direct connection state of SUC21 is canceled and the boosted state is set (step S6), and time t15 Thus, the SUDC 22 is also in a boosted state (both boosted state (step S9)).

  Therefore, at time t14, the BAT voltage Vbat increases stepwise, and thereafter, between time t14 and time t18, the target SOC decreases and the BAT voltage Vbat is a constant voltage. As a result of the decrease in Ibd, the BAT power Pbat (BAT discharge power Pad) decreases.

  At time t16, the voltage difference | Vdif | = | Vfc−Vbat | between the FC voltage Vfc and the BAT voltage Vbat has become a voltage that is higher (larger) by a predetermined voltage ΔVth than the threshold voltage Vth (Vdif = Vth + ΔVth = Vp). When detected, considering that Vfc <Vbat, the target stoichiometric ratio change flag Fstar is switched from normal power generation to high stoichiometric power generation. As a result, the rising speed of the FC voltage Vfc increases from time t16, the FC voltage Vfc approaches the BAT voltage Vbat, and the voltage difference | Vdif | = | Vfc−Vbat |

  Then, at the time t17 when the determination in step S1 described above (| Vdif | = | Vfc−Vbat | <Vth) becomes affirmative, the simultaneous direct connection determination is changed from the OFF state (non-established state) to the ON state (established state). Then, at the time t17, the switching operation of the SUC 21 and the SUDC 22 is stopped, and the simultaneous direct connection state (SUC 21: direct connection, SUDC 22: direct connection) is set.

  Further, at time t17, the high stoichiometric ratio power generation started from time t16 is terminated, and the target stoichiometric ratio change flag Fstar is switched from the high stoichiometric power generation to the normal stoichiometric power generation (agreement with normal power generation).

  In this modification, the length of the period in which the simultaneous direct connection determination is ON is longer after the countermeasure than before the countermeasure, in other words, the frequency of performing the voltage conversion operation of the SUDC 22 that boosts the BAT voltage Vbat. (Refer to the waveform of the FC voltage Vfcb before the countermeasure in FIG. 10), the system efficiency is improved accordingly.

[Summary of embodiments and further modifications]
As described above, the FC system 12 according to the above-described embodiment includes 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. Voltage conversion (step-up) is performed on the load 30, the SUC 21 as a first voltage conversion device that converts the FC voltage Vfc of the FC 18 to the DC terminal side of the inverter 16 as a load terminal voltage Vinv, and 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 voltage difference | Vdif | of the FC voltage Vfc and the BAT voltage Vbat Voltage difference grasping process (step S1) for grasping and voltage difference When Vdif | is within a predetermined range (| Vdif | = | Vfc−Vbat | <Vth) in which the voltage conversion operation of SUC11 and SUDC22 can be stopped, the voltage conversion operation of SUC21 and SUDC22 is stopped, and FC18 and BAT20 And a voltage conversion stop step (step S3) for directly connecting to the load 30.

  According to the above-described embodiment, when the voltage difference | Vdif | between the FC voltage Vfc and the BAT voltage Vbat is within a predetermined range | Vdif | <Vth and is small, the SUC21 and the SUDC22 are directly coupled (simultaneous direct coupling). And the voltage conversion loss of SUDC22 is reduced, and the efficiency of the whole system can be improved.

  In this case, the method further includes a generated power divergence width grasping step (step S4) for grasping a difference | Pfctar−Pfc | between the generated power command value Pfctar for FC 18 and the actual generated power Pfc as a generated power divergence width (step S4). After the start of (Step S3), when the generated power deviation width | Pfctar-Pfc | becomes larger than the predetermined width Pfcth as shown at time t3 in FIG. 5, the voltage conversion stop step (Step S3) is ended. Then, the voltage conversion operation of at least one of the SUC 21 and the SUDC 22 is executed (step S6).

  Thus, since it detects that the controllability of FC18 is deteriorating and the direct connection is released, it is possible to prevent the target generated power Pfc from being obtained and the merchantability from deteriorating.

  The difference voltage threshold voltage Vth as a predetermined range of the voltage difference | Vdif | for determining the start of the voltage conversion stop process (step S3) of the SUC 21 and SUDC 22 is referred to the temperature characteristic diagram of charge / discharge power in FIG. As described above, it is preferable that the temperature is decreased as the temperature of the BAT 20 is lower, or is decreased as the allowable charging / discharging power range (allowable discharging power Padmax or allowable charging power Pacmax) of the BAT 20 is decreased. Thus, the direct connection determination is made in consideration of whether or not the assistance of the BAT 20 is possible, so that it is possible to prevent the merchantability from being deteriorated without obtaining the target controllability due to the direct connection.

  Further, when the voltage conversion stop process (step S3) of the SUC 21 and SUDC 22 is terminated, it is preferable to restart the voltage conversion operation of the SUC 21 prior to the voltage conversion operation of the SUDC 22 (step S6, step S8). It can suppress that the controllability of FC18 deteriorates, and can prevent that durability of FC18 falls.

  As a further modification, the BAT voltage Vbat can be increased by increasing the target SOC of the BAT 20 after the voltage conversion stop process (step S3) of the SUC 21 and the SUDC 22 is finished, so that the boost state of the SUC 21 that boosts the FC voltage Vfc can be changed. It is possible to continue, the SUDC 22 is also in a boosted state, and it is possible to prevent the system efficiency from being deteriorated, and as a result, the frequency of performing the voltage conversion operation of the SUDC 22 that boosts the BAT voltage Vbat is reduced. can do.

  Similarly, after completing the voltage conversion stop step (step S3), the amount of charge to the BAT 20 may be forcibly increased, and the BAT voltage Vbat can be increased by forcibly charging the BAT 20, The frequency of performing the voltage conversion operation of the SUDC 22 that boosts the BAT voltage Vbat can be reduced.

  Further, the voltage difference (| Vdif | = | Vfc−Vbat |) between the FC voltage Vfc and the BAT voltage Vbat is within a predetermined range (| Vdif | = | Vfc−Vbat | <Vth) in which the voltage conversion operation of the SUC21 and SUDC22 can be stopped. ), The voltage conversion operation of the SUC 21 and SUDC 22 is stopped, and in the voltage conversion stop step (step S3) in which the FC 18 and the BAT 20 are directly connected to the load 30, the voltage difference (| Vdif | = | Vfc−Vbat |) Is approaching a predetermined range (| Vdif | = | Vfc−Vbat | = Vth + ΔVth) in which the voltage conversion operation of the SUC 21 and SUDC 22 can be stopped (time t11, time t16 in FIG. 10), By changing the SOC, the BAT voltage Vbat is increased or decreased, and the BAT voltage Vbat and the FC voltage Vfc. As a second method of setting the voltage difference | Vdif | within a predetermined range (| Vdif | <Vth), the FC film Vfc is increased or decreased by changing the FC18 target membrane water content Zmtar, and the FC voltage Vfc and the BAT voltage Vbat. As a third method of setting the voltage difference | Vdif | within a predetermined range (| Vdif | <Vth), the FC stoichiometric ratio of FC18 is varied to increase or decrease the FC voltage Vfc, and the voltage difference | Vdif | The voltage difference | Vdif | between the BAT voltage Vbat and the FC voltage Vfc is narrowed to a predetermined range (| Vdif | <Vth) by at least one method. The voltage conversion operation of the SUDC 22 may be stopped. In this case, the system efficiency can be further improved by increasing the frequency of direct connection of both.

  Note that the application priority of the first, second, and third methods for narrowing the voltage difference | Vdif | between the BAT voltage Vbat and the FC voltage Vfc to a predetermined range (| Vdif | <Vth) is first, The order is the second and third methods. The variable control of the target SOC of the BAT 20 is simpler than the target moisture content control and the target stoichiometric ratio variable control of the FC18, and the target moisture content variable control is lower in the power generation efficiency of the FC18 than the target stoichiometric ratio variable control. The amount is small.

  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. Fuel cell vehicle (FC vehicle)
12 ... 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 (10)

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 conversion device that converts the fuel cell voltage of the fuel cell and applies it to a DC terminal side of the inverter as a load terminal voltage;
A second voltage conversion device 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 voltage difference grasping step for grasping a voltage difference between the fuel cell voltage and the power storage device voltage;
When the voltage difference is within a predetermined range in which the voltage conversion operation of the first and second voltage conversion devices can be stopped, the voltage conversion operation of the first and second voltage conversion devices is stopped, and the fuel cell And a voltage conversion stop step for directly connecting the power storage device to the load;
A control method for a fuel cell system, comprising: In the control method of the fuel cell system according to claim 1,
Further comprising a generated power deviation width grasping step for grasping a difference between the generated power command value for the fuel cell and the actual generated power as a generated power deviation width;
After the start of the voltage conversion stop step, if the generated power deviation width is equal to or greater than a predetermined width, the voltage conversion stop step is ended, and at least one voltage conversion operation of the first and second voltage conversion devices A control method for a fuel cell system, comprising: In the control method of the fuel cell system according to claim 1 or 2,
The fuel cell system control method, wherein the predetermined range of the voltage difference for determining the start of the voltage conversion stop step is made smaller as the temperature of the power storage device is lower. In the control method of the fuel cell system according to any one of claims 1 to 3,
A control method for a fuel cell system, characterized in that a predetermined range of a voltage difference for determining the start of the voltage conversion stop step is made smaller as an allowable charge / discharge power range of the power storage device becomes smaller. In the control method of the fuel cell system according to any one of claims 2 to 4,
The fuel cell system control method, comprising: resuming the voltage conversion operation of the first voltage conversion device prior to the voltage conversion operation of the second voltage conversion device when ending the voltage conversion stop step. In the control method of the fuel cell system according to any one of claims 1 to 5,
A fuel cell system control method, comprising: increasing the target SOC of the power storage device after finishing the voltage conversion stop step. In the control method of the fuel cell system according to any one of claims 1 to 6,
A control method for a fuel cell system, comprising: increasing a charge amount of the power storage device after the voltage conversion stop step is completed. In the control method of the fuel cell system according to any one of claims 1 to 7,
The voltage of the first and second voltage converters when the voltage difference between the fuel cell voltage and the power storage device voltage is within a predetermined range in which the voltage conversion operation of the first and second voltage converters can be stopped. In the voltage conversion stop step of stopping the conversion operation and directly connecting the fuel cell and the power storage device to the load,
When the voltage difference approaches a predetermined range in which the voltage conversion operation of the first and second voltage converters can be stopped,
As a first method, the target SOC of the power storage device is varied to increase or decrease the power storage device voltage, and the voltage difference between the power storage device voltage and the fuel cell voltage is within the predetermined range.
As a second method, the fuel cell voltage is varied by varying the target membrane water content of the fuel cell, and the voltage difference between the fuel cell voltage and the power storage device voltage is within the predetermined range.
As a third method, the target stoichiometric ratio of the fuel cell is varied to increase or decrease the fuel cell voltage, and the voltage difference between the fuel cell voltage and the power storage device voltage is within the predetermined range.
The voltage conversion operation of the first and second voltage conversion devices is stopped by narrowing the voltage difference between the power storage device voltage and the fuel cell voltage to the predetermined range by at least one method. A control method for a fuel cell system. The control method of a fuel cell system according to claim 8,
The application priority of the first, second, and third methods for narrowing the voltage difference between the power storage device voltage and the fuel cell voltage to the predetermined range is that of the first, second, and third methods. A control method for a fuel cell system, characterized by:   The fuel cell vehicle which implements the control method of the fuel cell system according to any one of claims 1 to 9.

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