Fuel cell system

Abstract

To enable smooth warm-up operation in low-temperature environments in a fuel cell system having multiple fuel cells. [Solution] The fuel cell system 100 comprises a plurality of fuel cells 101 and a control unit 102 that controls the plurality of fuel cells 101. Each of the plurality of fuel cells 101 has a temperature detection unit that detects the temperature of each of the plurality of fuel cells 101, and the control unit 102 controls the plurality of fuel cells 101 so that all of the plurality of fuel cells 101 perform a predetermined warm-up operation when the temperature detected by at least one of the temperature detection units of the plurality of fuel cells 101 is below a predetermined value after the plurality of fuel cells 101 have been started up.

Description

Technical Field

[0001] The present invention relates to a fuel cell system having a plurality of fuel cells.

Background Art

[0002] In recent years, in order to enable more people to access affordable, reliable, sustainable, and advanced energy, technological development related to fuel cells that contribute to energy efficiency has been carried out. As a technology related to this type of fuel cell, a technology for warming up a fuel cell when the temperature of the fuel cell becomes lower than a predetermined temperature is known.

[0003] For example, in Patent Document 1, when the cooling water temperature detected after a predetermined time from the completion of the purge of the fuel cell is equal to or lower than a first predetermined temperature, the fuel cell is started to heat the cooling water, and then, when the cooling water temperature reaches a second predetermined temperature higher than the first predetermined temperature, the operation of the fuel cell is stopped. A control method for a fuel cell is described.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in a fuel cell system having a plurality of fuel cells, there is a possibility that the temperatures of the respective fuel cells may vary, and Patent Document 1 does not describe any preferred mode of warming up for such a fuel cell system.

Means for Solving the Problems

[0006] A fuel cell system according to one aspect of the present invention comprises a plurality of fuel cells and a control unit that controls the plurality of fuel cells. Each of the plurality of fuel cells has a temperature detection unit that detects the temperature of each of the plurality of fuel cells, and the control unit controls the plurality of fuel cells so that all of the plurality of fuel cells perform a predetermined warm-up operation when the temperature detected by at least one of the temperature detection units of the plurality of fuel cells is below a predetermined value after the plurality of fuel cells have been started up. [Effects of the Invention]

[0007] According to the present invention, a fuel cell system having multiple fuel cells can be warmed up effectively. [Brief explanation of the drawing]

[0008] [Figure 1] A diagram showing the schematic configuration of a single unit system constituting a fuel cell system according to an embodiment of the present invention. [Figure 2] A block diagram schematically showing the control configuration of a fuel cell system according to an embodiment of the present invention. [Figure 3] This figure schematically shows an example of the process from the start-up of a fuel cell system according to an embodiment of the present invention until the start of warm-up. [Figure 4] A flowchart showing an example of the process executed by the central controller in Figure 2. [Figure 5] A time chart showing an example of the operation of a fuel cell system according to an embodiment of the present invention. [Figure 6] A diagram schematically showing the changes in the operating modes of multiple unit systems included in a fuel cell system according to an embodiment of the present invention. [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described below with reference to Figures 1 to 6. The fuel cell system according to the embodiment of the present invention has a plurality of fuel cells. This fuel cell system can be installed in a large fuel cell vehicle, such as a fuel cell bus. Hereinafter, each of the plurality of fuel cells may be referred to as a unit system. By having a fuel cell system equipped with a plurality of unit systems, the overall power generation can be increased, and sufficient power can be supplied to the drive motor of a large fuel cell vehicle.

[0010] The configurations of multiple unit systems are identical to each other. Figure 1 shows a schematic configuration of a single unit system (fuel cell) 101. As shown in Figure 1, the unit system 101 includes a fuel cell stack 1, a fuel gas supply unit 2 that supplies fuel gas to the fuel cell stack, an oxidant gas supply unit 3 that supplies oxidant gas to the fuel cell stack 1, and a cooling medium supply unit 4 that supplies a cooling medium to the fuel cell stack 1. The fuel gas is, for example, hydrogen. The oxidant gas is, for example, air containing oxygen. The cooling medium is, for example, water or a coolant liquid containing ethylene glycol or propylene glycol.

[0011] The fuel cell stack 1 is composed of multiple power generation cells stacked on top of each other. Each power generation cell has an electrolyte membrane, an anode separator positioned opposite one side of the electrolyte membrane, and a cathode separator positioned opposite the other side of the electrolyte membrane. The electrolyte membrane is, for example, a solid polymer electrolyte membrane. An anode electrode is formed on one side of the electrolyte membrane, and fuel gas is supplied to the anode electrode via the anode separator. A cathode electrode is formed on the other side of the electrolyte membrane, and oxidant gas is supplied to the cathode electrode via the cathode separator. Between a pair of adjacent power generation cells, an anode separator and a cathode separator are arranged as a single unit, and a cooling medium flows between these anode separators and cathode separators.

[0012] At the anode electrode, fuel gas (hydrogen) supplied via the anode separator is ionized by the action of a catalyst and moves to the cathode electrode side through the electrolyte membrane. The electrons generated at this time pass through an external circuit and are extracted as electrical energy. At the cathode electrode, oxidizing gas (oxygen) supplied via the cathode separator reacts with hydrogen ions introduced from the anode electrode and electrons that have moved from the anode electrode to produce water. The generated water provides appropriate humidity to the electrolyte membrane, and excess water is discharged to the outside.

[0013] The fuel gas supply unit 2 includes a fuel gas tank 21 in which fuel gas is stored, and a fuel gas flow path PA1 that guides the fuel gas in the fuel gas tank to the fuel cell stack 1. The fuel gas flow path PA1 includes a fuel gas supply flow path PA11 that runs from the fuel gas tank 21 to the fuel gas inlet 21a of the fuel cell stack 1, and a fuel gas circulation flow path PA12 that runs from the fuel gas outlet 21b of the fuel cell stack 1 to a point along the fuel gas supply flow path PA11. An on / off valve 22, an injector 23, and an ejector 24 are arranged in the fuel gas supply flow path PA11. A gas-liquid separator 25 is arranged in the fuel gas circulation flow path PA12.

[0014] The on-off valve 22 is a solenoid valve that opens and closes by electromagnetic force and is located between the fuel gas tank 21 and the injector 23. The on-off valve 22 opens or closes the flow path between the fuel gas tank 21 and the injector 23. The injector 23 has one or more electromagnetic injectors connected in parallel. When the injector 23 is driven, fuel gas is injected toward the ejector 24. The ejector 24 has a nozzle section, a suction section, a confluence section, and a diffuser section. The fuel gas injected from the injector 23 passes through the small-diameter nozzle section and then flows into the diffuser section via the confluence section. The fuel gas that has passed through the ejector 24 is supplied to the fuel cell stack 1 via the fuel gas inlet 21a.

[0015] The fuel gas (fuel exhaust gas) discharged from the fuel gas outlet 21b is separated into fuel gas and water in the gas-liquid separator 25. The water separated in the gas-liquid separator 25 is discharged to the outside via an electromagnetic on-off valve 26. The fuel gas separated in the gas-liquid separator 25 is drawn into the ejector 24 by the flow of fuel gas injected from the injector 23. The drawn-in fuel gas merges with the fuel gas that has passed through the nozzle section of the ejector 24 at the confluence section of the ejector 24, and after being made into a uniform flow in the diffuser section of the ejector 24, it is supplied to the fuel cell stack 1 via the fuel gas inlet 21a.

[0016] The oxidant gas supply unit 3 includes a compressor 31 that generates high-pressure oxidant gas and an oxidant gas flow path AR2 that guides the oxidant gas to the fuel cell stack 1. The oxidant gas flow path PA2 includes an oxidant gas supply flow path PA21 that runs from the compressor 31 to the oxidant gas inlet 31a of the fuel cell stack 1, an oxidant gas discharge flow path PA22 that discharges oxidant gas (oxidant exhaust gas) from the fuel cell stack 1 via the oxidant gas outlet 31b, and a bypass flow path PA23 that bypasses the fuel cell stack 1 and guides the oxidant gas from the oxidant gas supply flow path PA21 to the oxidant gas discharge flow path PA22.

[0017] The compressor 31 compresses air taken in from the atmosphere and supplies it as an oxidizer gas. Humidifiers 32 are placed in the oxidizer gas supply channel PA21 and the oxidizer gas discharge channel PA22. In the humidifiers 32, the oxidizer gas in the oxidizer gas supply channel PA21 is humidified by the moisture contained in the oxidizer exhaust gas from the oxidizer gas discharge channel PA22. The bypass channel PA23 is connected to the oxidizer gas supply channel PA21 upstream of the humidifiers 32 and to the oxidizer gas discharge channel PA22 downstream of the humidifiers 32. An adjustable electromagnetic control valve 33 is placed in the bypass channel PA23, and the flow rate of oxidizer gas bypassing the fuel cell stack 1 can be adjusted by adjusting the opening of the control valve 33.

[0018] The cooling medium supply unit 4 includes a cooling device 41 and a cooling medium flow path PA4 that connects the cooling device 41 and the fuel cell stack 1. The cooling medium flow path PA4 includes a cooling medium supply flow path PA41 that supplies the cooling medium from the cooling device 41 to the fuel cell stack 1, and a cooling medium discharge flow path PA42 that recirculates the cooling medium from the fuel cell stack 1 to the cooling device 41. A temperature sensor 42 for detecting the temperature of the cooling medium is connected to the cooling medium discharge flow path PA42. Although illustration is omitted, the cooling device 41 includes a pump that pumps the cooling medium toward the fuel cell stack 1, and a heat exchanger that cools the cooling medium that has been heated after passing through the fuel cell stack 1.

[0019] FIG. 2 is a block diagram schematically showing the control configuration of the fuel cell system 100 according to an embodiment of the present invention. As shown in FIG. 2, the fuel cell system 100 includes a host controller (host ECU) 51, a general controller (general ECU) 52, and a plurality of individual controllers (individual ECUs) 53. Each of the controllers 51 to 53 is configured to include a computer having a CPU, a ROM, a RAM, and peripheral circuits. The general controller 52 and the plurality of individual controllers 53 may be collectively referred to as a control unit 102.

[0020] The host controller 51 and the general controller 52, and the general controller 52 and the individual controllers 53 are connected to be communicable with each other via a communication protocol such as CAN. The plurality of individual controllers 53 are provided in the same number as the unit systems 101 in association with the plurality (for example, four) of unit systems 101. The individual controller 53 controls the power generation operation by the unit system 101, that is, power generation start, power generation stop, power generation amount, and the like. In FIG. 2, an example in which the fuel cell system 100 has four individual controllers 53 (individual ECU_A, individual ECU_B, individual ECU_C, individual ECU_D) is shown, but the number of individual controllers 53 may be other than four as long as it is plural.

[0021] The fuel cell system 100 according to this embodiment is mounted on a vehicle. The upper controller 51 calculates the power generation amount (required power generation amount) required by the vehicle. More specifically, the upper controller 51 calculates the target drive torque of the driving motor based on a signal from an accelerator opening sensor that detects the opening of the accelerator pedal, and calculates the required power generation amount necessary for the driving motor to generate the target drive torque. Alternatively, the upper controller 51 calculates the required power generation amount so that the remaining capacity of the battery becomes a predetermined value based on a signal from a battery sensor that detects the remaining capacity SOC of the battery.

[0022] The overall controller 52 determines the power generation amount (individual required power generation amount) for each unit system according to the required power generation amount. More specifically, the overall controller 52 determines the presence or absence of an abnormality (failure) in the unit system 101 based on a signal from the individual controller 53, and determines the individual required power generation amount based on the determination result. For example, when an abnormality occurs in a single unit system 101 among the four unit systems 101, the individual required power generation amount is determined so that the required power generation amount is shared among the three unit systems 101 without an abnormality. Furthermore, the overall controller 52 estimates the degree of deterioration of the unit system 101 based on a signal from the individual controller 53, and determines the individual required power generation amount based on the estimation result. Specifically, the individual required power generation amount is determined so that the unit system 101 with a small degree of deterioration (high efficiency) generates power preferentially.

[0023] The fuel cell system 100 according to the embodiment of the present invention has an automatic warm-up function that automatically performs a warm-up operation when the temperature of the fuel cell becomes lower than a predetermined temperature when the fuel cell system 100 stops. The stop of the fuel cell system 100 is, for example, a state (sleep state) in which the operation of the fuel cell system 100 stops, such as when the ignition switch is turned off. Thereby, it is possible to prevent the temperature of the fuel cell from becoming lower than the predetermined temperature. As a result, it is possible to prevent the moisture in the fuel cell stack from freezing, and the start-up (low-temperature start-up) of the unit system 101 in a low-temperature environment is easy.

[0024] The automatic warm-up function of the fuel cell system 100 is described below. The temperature of each fuel cell (fuel cell stack 1) is detected by the temperature sensor 42 in Figure 1. Of the four individual controllers 53, one designated individual controller 53 (for example, individual ECU_A) is a master individual controller 531 that is actively started when the fuel cell system 100 is stopped, without being commanded by the other controllers, while the remaining individual controllers 53 (individual ECU_B, individual ECU_C, individual ECU_D) are slave individual controllers 532 that are passively started by being commanded by the other controllers.

[0025] Figure 3 is a schematic diagram illustrating an example of the process from the start-up of the fuel cell system 100 until the start of warm-up. In Figure 3, for convenience, only the master individual controller 531 (individual ECU_A) and a single slave individual controller 532 (individual ECU_B) are shown as individual controllers 53. The remaining slave individual controllers 532 (individual ECU_C, individual ECU_D) operate similarly to individual ECU_B.

[0026] As shown in Figure 3, the operation of the fuel cell system 100 from a shutdown starts when the master individual controller 531 is activated (step S11). The master individual controller 531 is set with a target start time (master target start time) for automatically performing a warm-up operation before the master individual controller 531 is shut down (before the power is turned off) during the previous operation. The master individual controller 531 is activated when the timer measures the master target start time.

[0027] The master target startup time is set by the central controller 52. Figure 4 is a flowchart showing an example of the process in the central controller 52 for setting the master target startup time. The process shown in this flowchart is started, for example, when the ignition switch is turned off and the central controller 52 is instructed by the higher-level controller 51 to stop the fuel cell system 100.

[0028] As shown in Figure 4, first, in step S1, the main controller 52 sends a stop command to all individual controllers 53. Upon receiving the stop command, the individual controllers 53 start the stop process and stop (power off) after the stop process is completed. During the stop process, the individual controllers 53 control the valves for fuel gas, oxidizer gas, and cooling medium at predetermined timings, consume the remaining fuel gas in the fuel cell stack, and then stop power generation in the fuel cell stack 1. In addition, the individual controllers 53 perform a scavenging process as part of the stop process. During the scavenging process, the compressor 31 is driven to forcibly flow oxidizer gas into the fuel cell stack and remove any remaining moisture in the fuel cell stack.

[0029] Furthermore, each of the individual controllers 53 calculates a target start-up time for warm-up operation based on the fuel cell temperature detected by the temperature sensor 42. The target start-up time is calculated based on a predetermined relationship between the fuel cell temperature and the target start-up time, so that the lower the temperature of the fuel cell (fuel cell stack k1), the shorter the time. There is usually variation in the temperatures of the multiple fuel cells. Temperature variations also occur due to errors in the temperature sensor 42, etc. Therefore, there is also variation in the target start-up times of the multiple individual controllers 53. Once each of the multiple individual controllers 53 has calculated its target start-up time, it transmits the target start-up time information to the central controller 52.

[0030] In step S2, the master controller 52 determines whether it has received target start-up time information from all individual controllers 53. Step S2 is repeated until affirmed, and if affirmed in step S2, the process proceeds to step S3. In step S3, the master controller 52 determines the shortest target start-up time among the received target start-up times as the master target start-up time. Then, in step S4, the master controller 52 transmits the master target start-up time to the master individual controller 531 (individual ECU_A) and terminates the process. At this time, the master individual controller 531 stores the master target start-up time in memory. In step S4, the master controller 52 may also transmit a predetermined target start-up time longer than the master target start-up time to the remaining individual controllers 53, i.e., all slave individual controllers 532. This makes it possible to set the shortest target start-up time based on the lowest temperature among the multiple fuel cells as the master target start-up time, reducing the processing load for determining the master target start-up time while preventing the water in the fuel cell stack from freezing.

[0031] The master individual controller 531 starts its timer from the moment it stops. Then, as shown in step S11 of Figure 3, when the timer of the master individual controller 531 has measured the master target startup time, the master individual controller 531 powers on and starts the startup process. When the master individual controller 531 starts the startup process, it sends a startup notification to the central controller 52. When the central controller 52 receives the startup notification, in step S21 it sends a startup command to all slave individual controllers 532 (individual ECU_B in Figure 3). As a result, the slave individual controllers 532 power on and start the startup process.

[0032] Each of the multiple individual controllers 53 sends a startup completion notification to the main controller 52 in step S12 once it has completed its startup process. There may be variations in the startup completion times of the multiple individual controllers 53. When the main controller 52 receives startup completion notifications from all of the individual controllers 53, in step S22 it sends a warm-up determination command to the multiple individual controllers 53 to determine whether or not warm-up is necessary. Alternatively, instead of sending a warm-up determination command to all of the individual controllers 53, the system may send a warm-up determination command to each individual controller 53 each time it receives a startup completion notification from that controller.

[0033] When multiple individual controllers 53 receive a warm-up determination command, they determine in step S13 whether warm-up is necessary. Specifically, the individual controllers 53 determine whether the temperature of the fuel cell detected by the temperature sensor 42 is below a predetermined temperature (warm-up start temperature). The predetermined temperature is, for example, the temperature at which the cooling medium begins to freeze or the temperature at which it is likely to begin freezing. If the fuel cell temperature is below the predetermined temperature, the individual controllers 53 determine that warm-up is necessary, and if it is above the predetermined temperature, they determine that warm-up is unnecessary. They then transmit the determination result to the main controller 52. For example, if they determine that warm-up is necessary, the individual controllers 53 output a warm-up request and transmit the warm-up request to the main controller 52.

[0034] When the central controller 52 receives determination results from all individual controllers 53, it determines in step S23 whether or not a warm-up operation is necessary. Specifically, if it receives a warm-up request from at least one of the multiple individual controllers 53, it determines that a warm-up operation is necessary. In this case, the central controller 52 sends a warm-up preparation command to the multiple individual controllers 53 in step S24.

[0035] When the individual controller 53 receives a warm-up preparation command, in step S14 it performs a mode transition for warm-up operation and then sends a warm-up operation preparation trigger to the main controller 52. As a result, instead of being in a state where warm-up is unnecessary, it enters a state where it is waiting for permission to perform warm-up operation.

[0036] When the main controller 52 receives notifications from all individual controllers 53 that the warm-up preparation is complete, it sends a warm-up request to the higher-level controller 51 in step S25. When the higher-level controller 51 receives the warm-up request, it starts the warm-up preparation in step S31. The warm-up preparation includes processes such as commanding the opening of the fuel gas tank 21 and preparing the high voltage to be applied to the fuel cell. When the warm-up preparation is complete, the higher-level controller 51 sends a warm-up permission command to the main controller 52 in step S32.

[0037] When the central controller 52 receives a warm-up permission command, it simultaneously sends warm-up commands to multiple individual controllers 53 in step S26. As a result, after preparing for warm-up in step S15, such as setting the voltage command value of the fuel cell stack 1 to an initial value, the multiple unit systems 101 each perform warm-up operations based on commands from the multiple individual controllers 53. In this case, low-efficiency power generation is performed, which is less efficient than usual. Specifically, the individual controllers 53 control the supply amount of oxidizer gas so that the supply amount of oxidizer gas is lower than the supply amount of fuel gas to the fuel cell stack 1. This lowers the air-stoichiometric ratio, increasing the thermal energy, which is the power loss after deducting the power generation energy from the energy extracted by the reaction of hydrogen and oxygen, and allowing the fuel cell (fuel cell stack 1) to warm up quickly.

[0038] Figure 5 is a time chart showing an example of the operation of the fuel cell system 100. Figure 5 shows the state of a pair of unit systems 101,101 (FC_A, FC_B) out of four unit systems 101 (Figure 2), the temperature of the cooling medium of the pair of unit systems 101,101 (Ta, Tb), and the warm-up requirement (Ra, Rb) for the pair of unit systems 101,101, as they change over time. In the figure, temperature Tα is a predetermined warm-up start temperature, and temperature Tβ is a predetermined warm-up end temperature.

[0039] As shown in Figure 5, at time t0, the shutdown process for the pair of unit systems 101,101 begins when the ignition switch is turned off. When the shutdown process is completed at time t1, the pair of unit systems 101,101 enter a sleep state. Figure 5 is a time chart of a vehicle equipped with the fuel cell system 100 when placed in a low-temperature environment. Therefore, after the fuel cell system 100 is shut down and before warm-up operation is performed, the fuel cell temperatures Ta,Tb gradually decrease. Initially, the fuel cell temperatures Ta,Tb are above the warm-up start temperature Tα, and the warm-up request (Ra,Rb) is not output and is off.

[0040] The sleep state duration ΔT1 corresponds to the master target startup time. This duration ΔT is set based on the lower temperature Tb of the fuel cell temperatures Ta and Tb when the pair of unit systems 101,101 were shut down between time t0 and time t1. After the duration ΔT1 has elapsed, the pair of unit systems 101,101 are started at time t2. More precisely, one unit system 101 (master individual controller 531) starts first, followed by the other unit system 101 (slave individual controller 532). After the unit system 101 is started, the fuel cell temperatures Ta and Tb are detected by the temperature sensor 42.

[0041] Between time points t2 and t3, the temperatures of the pair of unit systems 101, 101 are both above the predetermined warm-up start temperature Tα. Therefore, no warm-up operation is performed on unit system 101, and at time point t3, the pair of unit systems 101, 101 return to sleep mode. At this time, the target start-up time (sleep state duration ΔT2) for the next unit system 101 (master individual controller 531) is set based on the temperature Tb of the lower-temperature fuel cell. Note that the fuel cell temperature Tb at time point t2 is lower than the fuel cell temperature Tb at time point t1. Therefore, ΔT2 is shorter than ΔT1.

[0042] When the sleep state continues for a predetermined duration ΔT2, at time t4, the pair of unit systems 101, 101 are activated and the fuel cell temperatures Ta, Tb are detected. At this point, the fuel cell temperatures Ta, Tb are above the warm-up start temperature Tα, and thereafter, the sleep state and activation process of the pair of unit systems 101, 101 are repeated alternately until the temperatures Ta, Tb fall below the warm-up start temperature Tα.

[0043] Between time point t5 and time point t6, during the startup process, if the temperature Tb of one fuel cell falls below the warm-up start temperature Tα, a warm-up request (Rb) is output at time point t6 and the unit is turned on. As a result, as described above, warm-up commands are simultaneously sent from the main controller 52 to multiple individual controllers 53, and warm-up operation is started simultaneously in the pair of unit systems 101,101 (Figure 3).

[0044] When warm-up operation (low-efficiency power generation) begins at time t6, the fuel cell temperatures Ta and Tb gradually rise. At time T7, when the fuel cell temperature Ta of one unit system 101 reaches the warm-up completion temperature Tβ, the warm-up operation of that unit system 101 ends. At this time, the warm-up request (Rb) is turned off. Alternatively, the warm-up request may be turned off when the temperature Tb reaches or exceeds the warm-up start temperature Tα due to the warm-up operation. At time t8, when the fuel cell temperature Tb of the other unit system 101 reaches the warm-up completion temperature Tβ, the warm-up operation of the other unit system 101 ends. Once the warm-up operation ends, the fuel cell temperatures Ta and Tb gradually decrease due to the influence of the external environment.

[0045] After the warm-up period ends, the pair of unit systems 101,101 perform separate shutdown processes at time t9. These shutdown processes include scavenging. The scavenging process for one unit system 101 (FC_B) starts earlier than that of the other unit system 101 (FC_A), and consequently, the scavenging process for one unit system 101 (FC_B) finishes earlier. At time t9, once the shutdown processes are complete, the pair of unit systems 101,101 enter a sleep state.

[0046] Subsequently, the pair of unit systems 101,101 repeatedly cycle between startup and sleep states until the fuel cell temperatures Ta,Tb fall below the warm-up start temperature Tα. During the startup process from time t12 to time t13, when the fuel cell temperature Ta of one of the unit systems 101 (FC_A) falls below the warm-up start temperature Tα, the warm-up operation of the pair of unit systems 101,101 is restarted at time t13. This causes the fuel cell temperatures Ta,Tb to rise. From then on, warm-up operation is automatically started each time the fuel cell temperatures Ta,Tb fall below the warm-up start temperature Tα. After one warm-up operation is completed, no further warm-up operations may be performed until the next startup control based on turning on the ignition switch is performed. In other words, at least one warm-up operation is sufficient during the sleep state.

[0047] Figure 6 schematically shows the changes in the operating modes of the four unit systems 101 (FC_A, FC_B, FC_C, FC_D) included in the fuel cell system 100 according to this embodiment. In the example in Figure 6, at time t20, all unit systems 101 (more specifically, individual controllers 53) start up simultaneously. Then, at time t21, once the startup process is complete, warm-up operation starts simultaneously in all unit systems 101. The timing at which warm-up operation is completed, that is, the timing at which the fuel cell rises to the warm-up completion temperature Tβ, differs for each unit system 101, with unit system 101 (FC_A) completing warm-up operation the earliest.

[0048] When unit system 101 (FC_A) finishes its warm-up operation at time t22, scavenging operation begins. Subsequently, when scavenging operation ends at time t23, a stop process (stop process after scavenging operation) is executed from time t24. Similarly, for the other unit systems 101 (FC_B, FC_C, FC_D), scavenging operation begins when warm-up operation ends, and a stop process is executed when scavenging operation ends.

[0049] This embodiment can provide the following effects and advantages. (1) The fuel cell system 100 comprises a plurality of fuel cells (unit systems 101), a control unit 102 which is a general controller 52 and a plurality of individual controllers 53 which control the plurality of unit systems 101 (Figure 2). Each of the plurality of unit systems 101 has a temperature sensor 42 which detects the temperature of each of the fuel cell stacks 1 included in the plurality of unit systems 101 (Figure 1). After the plurality of unit systems 101 are started up, the control unit 102 controls the plurality of unit systems 101 so that all of the plurality of unit systems 101 perform a predetermined warm-up operation when the temperature detected by at least one temperature sensor 42 of the plurality of unit systems 101 is less than or equal to the warm-up start temperature Tα.

[0050] Although there is variation in the temperatures of the multiple unit systems 101 used in the fuel cell system 100, the temperature decrease trend of the multiple unit systems 101 is the same when used in a low-temperature environment. Taking this into consideration, in this embodiment, when the temperature of at least one of the multiple unit systems 101 falls below the warm-up start temperature, all unit systems 101 are warmed up. This allows the warm-up of the multiple unit systems 101 to be performed simultaneously and early, enabling efficient warm-up of the fuel cell system 100. Since the multiple unit systems 101 are warmed up simultaneously, the multiple unit systems 101 can be controlled efficiently.

[0051] (2) When the control unit 102 defines a unit system 101 (FC_A, FC_B in Figure 5) whose temperature detected by the temperature sensor 42 after a predetermined warm-up operation is equal to or greater than the warm-up completion temperature (target temperature) Tβ as a post-warm-up fuel cell, if any of the unit systems 101 becomes a post-warm-up fuel cell after the start of the predetermined warm-up operation, the control unit 102 controls each post-warm-up fuel cell to stop the predetermined warm-up operation and perform a predetermined scavenging operation (Figures 5 and 6). As a result, the start of the scavenging operation is determined for each unit system 101, so that the scavenging operation can be realized quickly after the warm-up operation is completed, and moisture generated in the fuel cell stack during the warm-up operation can be immediately discharged.

[0052] (3) The control unit 102 controls each post-warm fuel cell to stop the operation of the post-warm fuel cell (for example, by turning off the power) when the post-warm fuel cell has completed a predetermined scavenging operation (Figure 6). As a result, the completion of the scavenging operation is determined for each unit system 101, so that the inside of the fuel cell stack 1 (especially the electrolyte membrane) does not become too dry.

[0053] (4) The control unit 102 includes a master controller 52 that determines the required power generation amount for each of the multiple unit systems 101, and multiple individual controllers 53 that individually control each of the multiple unit systems 101 to generate power according to the required power generation amount determined by the master controller 52 (Figure 2). The multiple individual controllers 53 determine whether a warm-up is necessary after the start-up of the unit system 101 controlled by each of the multiple individual controllers 53, based on the temperature detected by the temperature sensor 42 (Figure 3). If the master controller 52 determines that a warm-up is necessary by at least one of the multiple individual controllers 53, it outputs a warm-up command to all of the multiple individual controllers 53 so that the multiple unit systems 101 perform a predetermined warm-up operation (Figure 3). This eliminates the need for the multiple individual controllers 53 to communicate with each other and synchronize, thereby reducing the processing load on the individual controllers 53.

[0054] (5) The multiple individual controllers 53 include a single master individual controller 531 that starts up at a predetermined timing after the multiple unit systems 101 have stopped, and slave individual controllers 532 that are other than the master individual controller 531. When the central controller 52 receives a signal from the master individual controller 531 after the master individual controller 531 has started up, it outputs a start command to the slave individual controller 532 to start up (Figure 3). This makes it easy to start up the fuel cell system 100.

[0055] The above embodiment can be modified into various forms. Several modifications are described below. In the above embodiment, one of the multiple individual controllers 53 (individual ECU_A) is set in advance as the master individual controller 531 (master individual control unit), and the remaining individual controllers 53 (individual ECU_B, etc.) are set as slave individual controllers 532 (slave individual control units). However, the individual controller 53 with the shortest target startup time calculated by each individual controller 53 may be set as the master individual controller 531. That is, the master individual controller 531 may be changed each time the fuel cell system 100 is started up, depending on the temperature of the fuel cell.

[0056] In the above embodiment, the temperature of the cooling medium detected by the temperature sensor 42 is treated as the temperature of the fuel cell, but the temperature of other parts that have a correlation with the temperature of the fuel cell may be detected instead, and the configuration of the temperature detection unit is not limited to that described above. In the above embodiment, the control unit 102 is configured by a master controller 52 (master control unit) and individual controllers 53 (individual control units), but the configuration of the control unit can be anything as long as it controls the multiple fuel cells so that all of the multiple fuel cells perform a predetermined warm-up operation when the temperature of at least one of the multiple fuel cells is below a predetermined value after the multiple fuel cells have been started up.

[0057] In the above embodiment, an example of applying the fuel cell system 100 to a fuel cell vehicle was described, but the fuel cell system of the present invention can be applied to various mobile devices having multiple fuel cells, and can also be applied to devices other than mobile devices.

[0058] The above description is merely an example, and the present invention is not limited by the embodiments and modifications described above, as long as the features of the present invention are not impaired. It is also possible to arbitrarily combine one or more of the above embodiments and modifications, and to combine modifications with each other. [Explanation of symbols]

[0059] 42 Temperature sensor, 52 Main controller, 53 Individual controllers, 100 Fuel cell system, 101 Unit system, 102 Control unit, 531 Master individual controller, 532 Slave individual controller, Tα Warm-up start temperature, Tβ Warm-up end temperature

Claims

1. Multiple fuel cells, A fuel cell system comprising a control unit for controlling the plurality of fuel cells, Each of the plurality of fuel cells has a temperature detection unit that detects the temperature of each of the plurality of fuel cells, A fuel cell system characterized in that, after the multiple fuel cells are started up, the control unit controls the multiple fuel cells so that all of the multiple fuel cells perform a predetermined warm-up operation when the temperature detected by at least one of the multiple fuel cells by the temperature detection unit is below a predetermined value.

2. In the fuel cell system according to claim 1, The fuel cell system is characterized in that, when the control unit defines a fuel cell among the plurality of fuel cells whose temperature detected by the temperature detection unit after a predetermined warm-up operation is equal to or greater than the target temperature as a post-warm-up fuel cell, if any of the plurality of fuel cells becomes a post-warm-up fuel cell after the start of the predetermined warm-up operation, the control unit controls each post-warm-up fuel cell to stop the predetermined warm-up operation for the post-warm-up fuel cell and perform a predetermined scavenging operation.

3. In the fuel cell system according to claim 2, The fuel cell system is characterized in that the control unit controls each post-warm fuel cell to stop operating when the post-warm fuel cell completes the predetermined scavenging operation.

4. In the fuel cell system according to any one of claims 1 to 3, The control unit comprises a central control unit that determines the required power generation amount for each of the plurality of fuel cells, and a plurality of individual control units that individually control each of the plurality of fuel cells to generate power according to the required power generation amount determined by the central control unit. The plurality of individual control units determine, based on the temperature detected by the temperature detection unit, whether or not a warm-up is necessary after the start-up of the fuel cell controlled by each of the plurality of individual control units. A fuel cell system characterized in that, when the central control unit determines that warming up is necessary based on at least one of the plurality of individual control units, it outputs a warming-up command to all of the plurality of individual control units so that the plurality of fuel cells perform the predetermined warming-up operation.

5. In the fuel cell system according to claim 4, The plurality of individual control units include a single master individual control unit that starts up at a predetermined timing after the plurality of fuel cells are shut down, and slave individual control units other than the master individual control unit. A fuel cell system characterized in that, when the central control unit receives a signal from the master individual control unit after the master individual control unit has been started, it outputs a start command to the slave individual control unit to start the slave individual control unit.

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