Fuel cell system

Abstract

In systems with multiple fuel cell stacks, this reduces variations in lifespan. [Solution] The fuel cell system comprises a plurality of fuel cell stacks, at least one supply source that supplies fluid to the plurality of fuel cell stacks, a distribution unit that distributes the fluid supplied from the at least one supply source to each of the plurality of fuel cell stacks according to a commanded distribution ratio, and a control unit, the control unit calculates the remaining life of each fuel cell stack and commands the distribution ratio according to the remaining life.

Description

Technical Field

[0001] The present disclosure relates to a fuel cell system.

Background Art

[0002] Conventionally, a control method suitable for a fuel cell system including a plurality of fuel cell stacks has been studied (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a fuel cell system including a plurality of fuel cell stacks, it is preferable that the variation in the remaining life of the plurality of fuel cell stacks is small. Therefore, it is required to reduce the variation in the remaining life.

Means for Solving the Problems

[0005] The present disclosure can be realized in the following forms.

[0006] (1) According to one aspect of the present disclosure, a fuel cell system is provided. The fuel cell system includes a plurality of fuel cell stacks, at least one supply source that supplies fluid to the plurality of fuel cell stacks, a distribution unit that distributes the fluid supplied from the at least one supply source to each of the plurality of fuel cell stacks according to a commanded distribution ratio, and a control unit. The control unit calculates the remaining life of each fuel cell stack and commands the distribution ratio according to the remaining life. According to this aspect, since the distribution ratio is controlled according to the calculated remaining life, the variation in the remaining life of the plurality of fuel cell stacks is reduced. (2) In the fuel cell system of the above embodiment, the at least one supply source includes an oxidizing gas supply source for supplying oxidizing gas and a fuel gas supply source for supplying fuel gas, the distribution unit is provided corresponding to at least one of the oxidizing gas supply source and the fuel gas supply source, the plurality of fuel cell stacks include a first fuel cell stack and a second fuel cell stack whose remaining lifespan is shorter than that of the first fuel cell stack, the control unit commands the distribution ratio such that the power generation start time of the first fuel cell stack is earlier than the power generation start time of the second fuel cell stack, and the first fuel cell stack may be controlled so that the power generation time is longer than that of the second fuel cell stack. According to this embodiment, the power generation time of the first fuel cell stack is longer than that of the second fuel cell stack. In this power generation, the load on the first fuel cell stack is greater than the load on the second fuel cell stack. Therefore, the difference between the remaining lifespan of the first fuel cell stack and the remaining lifespan of the second fuel cell stack can be reduced. (3) In the fuel cell system of the above configuration, a temperature sensor is provided to detect the temperature of the plurality of fuel cell stacks, and the control unit may, when the temperature detected by the temperature sensor is lower than a predetermined reference temperature, perform a warm-up operation in which each fuel cell stack is operated at a low-efficiency operating point that is less efficient than the reference operating point, prior to normal operation in which each fuel cell stack is operated at a reference operating point, and when performing the warm-up operation, the control unit may instruct the distribution ratio so that the start time of the warm-up operation of the first fuel cell stack is earlier than the start time of the warm-up operation of the second fuel cell stack. In this configuration, the first fuel cell stack finishes the warm-up operation and moves to normal operation before the second fuel cell stack. Therefore, the operating time of the normal operation of the first fuel cell stack is longer than the operating time of the normal operation of the second fuel cell stack. As a result, the difference between the remaining lifespan of the first fuel cell stack and the remaining lifespan of the second fuel cell stack can be reduced. (4) In the fuel cell system of the above configuration, the at least one supply source includes a cooling water supply source for supplying cooling water, the fuel cell system includes a circulation channel for circulating the cooling water, the first fuel cell stack is the fuel cell stack with the longest remaining life among the plurality of fuel cell stacks, and the control unit commands the distribution ratio of the cooling water supply source to supply the cooling water to the first fuel cell stack during the warm-up operation of the first fuel cell stack, and not to supply the cooling water to each of the plurality of fuel cell stacks except the first fuel cell stack, so that the cooling water heated by the first fuel cell stack performing the warm-up operation is circulated only to the first fuel cell stack. According to this configuration, by circulating the cooling water only to the first fuel cell stack, the temperature of the cooling water can be raised quickly, and the first fuel cell stack can be warmed up efficiently. (5) In the fuel cell system of the above embodiment, the at least one supply source includes an oxidizing gas supply source for supplying oxidizing gas and a fuel gas supply source for supplying fuel gas, the distribution unit is provided corresponding to at least one of the oxidizing gas supply source and the fuel gas supply source, each fuel cell stack has a plurality of stacked cells and a plurality of cell voltage sensors for detecting voltage in units of one or more cells among the plurality of cells, the control unit performs normal operation to operate each fuel cell stack at a reference operating point, and in the normal operation, if there is a low-voltage fuel cell stack among the plurality of fuel cell stacks in which the cell voltage indicated by each cell voltage sensor of the plurality of cell voltage sensors is smaller than a predetermined first reference voltage, the control unit may command the distribution ratio such that the flow rate of at least one of the oxidizing gas and the fuel gas supplied to the low-voltage fuel cell stack is greater than the flow rate at the reference operating point. In some cases, water generated during the power generation reaction can accumulate in the fuel gas and oxidizing gas channels within the fuel cell stack. This can lead to insufficient fuel gas and oxidizing gas supply, resulting in insufficient power generation and a decrease in cell voltage. This configuration allows for the supply of excess fuel gas and oxidizing gas to cells with low voltages, which are likely experiencing insufficient supply. This effectively removes the water accumulated in the fuel gas and oxidizing gas channels. This disclosure can be implemented in various forms, and in addition to a fuel cell system, it can be implemented in the form of, for example, a control method for a fuel cell system, a computer program for causing a computer to execute the control method, or a non-temporary tangible recording medium in which the computer program is recorded in a readable manner. [Brief explanation of the drawing]

[0007] [Figure 1] This diagram shows a schematic configuration of a fuel cell system installed in a vehicle. [Figure 2] This diagram shows the mounting locations for various sensors. [Figure 3] This is a block diagram showing the configuration of the control unit and the distribution unit. [Figure 4] This is a diagram illustrating stress information. [Figure 5] This is a flowchart of the process at the start of operation. [Figure 6] This is a flowchart of the processing during normal operation. [Modes for carrying out the invention]

[0008] A. Embodiments: A1. Configuration of the fuel cell system: Figure 1 shows a schematic configuration of a fuel cell system 100 mounted on a vehicle. The fuel cell system 100 comprises a plurality of fuel cell stacks 10, an oxidizing gas system circuit 20, a fuel gas system circuit 40, a cooling system circuit 60, a power control unit 16, a battery 17, a load 18, and a control unit 80. In this embodiment, the plurality of fuel cell stacks 10 include a first fuel cell stack 10A, a second fuel cell stack 10B, and a third fuel cell stack 10C. In this embodiment, the first fuel cell stack 10A, the second fuel cell stack 10B, and the third fuel cell stack 10C are electrically connected in parallel. In the following description, when the first fuel cell stack 10A, the second fuel cell stack 10B, and the third fuel cell stack 10C are not distinguished, they will simply be referred to as "fuel cell stack 10".

[0009] The fuel cell stack 10 generates electricity through a power generation reaction using a fuel gas and an oxidizing gas. The fuel cell stack 10 is a polymer electrolyte fuel cell and has a stack structure in which a plurality of cells 90 are stacked. Each cell 90 has a structure in which a MEGA (Membrane Electrode and Gas Diffusion Layer Assembly) (not shown) is sandwiched between separators (not shown). The MEGA comprises an MEA (Membrane Electrode Assembly) and gas diffusion layers arranged on both sides of the MEA. The MEA comprises an electrolyte membrane, an electrode catalyst layer that functions as an anode formed on one side of the electrolyte membrane, and an electrode catalyst layer that functions as a cathode formed on the other side of the electrolyte membrane. In this embodiment, hydrogen is used as the fuel gas and oxygen from the air is used as the oxidizing gas. In the following description, the fuel gas and the oxidizing gas may be collectively referred to as the reaction gas.

[0010] The electricity generated by the fuel cell stack 10 is supplied to the power control unit 16 and the battery 17. The electricity output from the fuel cell stack 10 may be boosted by a DC / DC converter (not shown). The battery 17 is a secondary battery charged by the supplied DC power. The power control unit 16 controls the distribution of the electricity generated by the fuel cell stack 10 to the load 18 and to the battery 17. The load 18 is, for example, a vehicle drive motor.

[0011] The oxidizing gas system circuit 20 is a circuit for supplying air as a fluid to the cathode of the fuel cell stack 10. The oxidizing gas system circuit 20 includes an air compressor 21 as an oxidizing gas supply source, an oxidizing gas distribution unit 22, an oxidizing gas supply main pipe 23, a first oxidizing gas branch pipe 24, a second oxidizing gas branch pipe 25, a third oxidizing gas branch pipe 26, a first oxidizing off-gas discharge pipe 27, a second oxidizing off-gas discharge pipe 28, a third oxidizing off-gas discharge pipe 29, and an oxidizing off-gas discharge main pipe 30.

[0012] The air compressor 21 sends compressed air to the main oxidizing gas supply pipe 23. The main oxidizing gas supply pipe 23 branches into a first oxidizing gas branch pipe 24, a second oxidizing gas branch pipe 25, and a third oxidizing gas branch pipe 26. The first oxidizing gas branch pipe 24 is connected to an oxidizing gas inlet (not shown) of the first fuel cell stack 10A. The second oxidizing gas branch pipe 25 is connected to an oxidizing gas inlet (not shown) of the second fuel cell stack 10B. The third oxidizing gas branch pipe 26 is connected to an oxidizing gas inlet (not shown) of the third fuel cell stack 10C.

[0013] In this embodiment, the oxidizing gas distribution unit 22 includes a first oxidizing gas valve 221, a second oxidizing gas valve 222, and a third oxidizing gas valve 223. The first oxidizing gas valve 221 is located in the first oxidizing gas branch pipe 24. The second oxidizing gas valve 222 is located in the second oxidizing gas branch pipe 25. The third oxidizing gas valve 223 is located in the third oxidizing gas branch pipe 26. The oxidizing gas distribution unit 22 adjusts the flow rate of oxidizing gas supplied to the first fuel cell stack 10A, the second fuel cell stack 10B, and the third fuel cell stack 10C, respectively, by adjusting the opening degrees of the first oxidizing gas valve 221, the second oxidizing gas valve 222, and the third oxidizing gas valve 223.

[0014] The first oxidation-off gas exhaust pipe 27 is connected to an oxidation-off gas outlet (not shown) of the first fuel cell stack 10A. The second oxidation-off gas exhaust pipe 28 is connected to an oxidation-off gas outlet (not shown) of the second fuel cell stack 10B. The third oxidation-off gas exhaust pipe 29 is connected to an oxidation-off gas outlet (not shown) of the third fuel cell stack 10C. The first oxidation-off gas exhaust pipe 27, the second oxidation-off gas exhaust pipe 28, and the third oxidation-off gas exhaust pipe 29 merge into the oxidation-off gas main exhaust pipe 30. The oxidation-off gas main exhaust pipe 30 is in communication with the atmosphere and discharges the oxidation-off gas emitted from the three fuel cell stacks 10 into the atmosphere.

[0015] The fuel gas system circuit 40 is a circuit for supplying fuel gas as a fluid to the anode of the fuel cell stack 10. The fuel gas system circuit 40 includes a fuel gas tank 41, a hydrogen circulation device 42, a fuel gas distribution unit 43, a gas-liquid separator 44, an exhaust drain valve 45, a main fuel gas supply pipe 46, a first fuel gas branch pipe 47, a second fuel gas branch pipe 48, a third fuel gas branch pipe 49, a first fuel exhaust gas pipe 52, a second fuel exhaust gas pipe 53, a third fuel exhaust gas pipe 54, and a main fuel exhaust gas pipe 55.

[0016] The fuel gas tank 41 stores high-pressure hydrogen gas. The fuel gas stored in the fuel gas tank 41 is sent to the main fuel gas supply pipe 46. A hydrogen circulation device 42 is arranged in the main fuel gas supply pipe 46. The hydrogen circulation device 42 incorporates a circulation pump 42a as a fuel gas supply source. The main fuel gas supply pipe 46 branches into a first fuel gas branch pipe 47, a second fuel gas branch pipe 48, and a third fuel gas branch pipe 49. The first fuel gas branch pipe 47 is connected to a fuel gas inlet (not shown) of the first fuel cell stack 10A. The second fuel gas branch pipe 48 is connected to a fuel gas inlet (not shown) of the second fuel cell stack 10B. The third fuel gas branch pipe 49 is connected to a fuel gas inlet (not shown) of the third fuel cell stack 10C.

[0017] In the present embodiment, the fuel gas distribution unit 43 includes a first fuel gas valve 431, a second fuel gas valve 432, and a third fuel gas valve 433. The first fuel gas valve 431 is arranged in the first fuel gas branch pipe 47. The second fuel gas valve 432 is arranged in the second fuel gas branch pipe 48. The third fuel gas valve 433 is arranged in the third fuel gas branch pipe 49. The fuel gas distribution unit 43 adjusts the flow rate of the fuel gas supplied to each of the first fuel cell stack 10A, the second fuel cell stack 10B, and the third fuel cell stack 10C by adjusting the opening degree of each of the first fuel gas valve 431, the second fuel gas valve 432, and the third fuel gas valve 433.

[0018] The first fuel exhaust gas pipe 52 is connected to a fuel off-gas outlet (not shown) of the first fuel cell stack 10A. The second fuel exhaust gas pipe 53 is connected to a fuel off-gas outlet (not shown) of the second fuel cell stack 10B. The third fuel exhaust gas pipe 54 is connected to a fuel off-gas outlet (not shown) of the third fuel cell stack 10C. The first fuel exhaust gas pipe 52, the second fuel exhaust gas pipe 53, and the third fuel exhaust gas pipe 54 merge into the main fuel exhaust gas pipe 55.

[0019] The main fuel exhaust gas pipe 55 is connected to the gas-liquid separator 44. The reflux pipe 51 connects the gas-liquid separator 44 and the hydrogen circulation device 42. The exhaust gas pipe 56 is connected to the gas-liquid separator 44. The exhaust drain valve 45 is disposed in the exhaust gas pipe 56.

[0020] The fuel off-gas discharged from each fuel off-gas outlet of the three fuel cell stacks 10 is separated into a gas component and a liquid component by the gas-liquid separator 44. The exhaust drain valve 45 switches the exhaust gas pipe 56 between communication and non-communication. The gas component of the fuel exhaust gas separated by the gas-liquid separator 44 is refluxed to the main fuel gas supply pipe 46 by the hydrogen circulation device 42. Thereby, the unreacted hydrogen contained in the fuel off-gas is reused. When the concentration of gas components other than hydrogen gas in the fuel off-gas becomes high, the exhaust drain valve 45 is opened, and the liquid component and the fuel off-gas are discharged to the outside.

[0021] The cooling system circuit 60 is a circuit for adjusting the temperature of the fuel cell stack 10 by circulating cooling water as a fluid. The cooling system circuit 60 includes a radiator 61, a circulation pump 62 as a cooling water supply source, a main cooling water supply channel 66, a main cooling water discharge channel 67, a bypass channel 68, a first valve 64, a second valve 65, a first cooling water branch channel 69, a second cooling water branch channel 70, a third cooling water branch channel 71, a first cooling water discharge channel 72, a second cooling water discharge channel 73, and a third cooling water discharge channel 74.

[0022] Inside the fuel cell stack 10, a cooling water manifold 75 for circulating cooling water is formed. In the present embodiment, the cooling water manifold 75 has a structure in which a supply cooling water manifold and a discharge cooling water manifold are connected via a cooling water flow path in the cell 90. In FIG. 1, the cooling water manifold 75 is schematically represented by a broken line. The main cooling water supply channel 66 is connected to the outlet of the radiator 61.

[0023] The main cooling water supply channel 66 branches into a first cooling water branch channel 69, a second cooling water branch channel 70, and a third cooling water branch channel 71. The first cooling water branch channel 69 is connected to a cooling water manifold (not shown) for supplying cooling water to the first fuel cell stack 10A. The second cooling water branch channel 70 is connected to a cooling water manifold (not shown) for supplying cooling water to the second fuel cell stack 10B. The third cooling water branch channel 71 is connected to a cooling water manifold (not shown) for supplying cooling water to the third fuel cell stack 10C.

[0024] In this embodiment, the cooling water distribution unit 63 includes a first cooling water valve 631, a second cooling water valve 632, and a third cooling water valve 633. The first cooling water valve 631 is located in the first cooling water branch passage 69. The second cooling water valve 632 is located in the second cooling water branch passage 70. The third cooling water valve 633 is located in the third cooling water branch passage 71. The cooling water distribution unit 63 adjusts the flow rate of cooling water supplied to the first fuel cell stack 10A, the second fuel cell stack 10B, and the third fuel cell stack 10C by adjusting the opening degrees of the first cooling water valve 631, the second cooling water valve 632, and the third cooling water valve 633, respectively.

[0025] The first cooling water drainage channel 72 is connected to a cooling water manifold (not shown) for the discharge of the first fuel cell stack 10A. The second cooling water drainage channel 73 is connected to a cooling water manifold (not shown) for the discharge of the second fuel cell stack 10B. The third cooling water drainage channel 74 is connected to a cooling water manifold (not shown) for the discharge of the third fuel cell stack 10C. The first cooling water drainage channel 72, the second cooling water drainage channel 73, and the third cooling water drainage channel 74 merge into the main cooling water discharge channel 67.

[0026] A circulation pump 62 is located in the main cooling water supply channel 66. The radiator 61 cools the cooling water that flows in from the main cooling water discharge channel 67 through the inlet using airflow from an electric fan (not shown), and discharges it into the main cooling water supply channel 66 through the outlet.

[0027] The bypass passage 68 is a passage that branches off from the main coolant discharge passage 67 and merges with the main coolant supply passage 66. A second valve 65 is located in the bypass passage 68. A first valve 64 is located in the main coolant discharge passage 67. The passage through which the coolant circulates, passing through the bypass passage 68 without going through the radiator 61, is called the circulation passage CF.

[0028] By adjusting the opening degrees of the first valve 64 and the second valve 65, the flow rate of coolant passing through the radiator 61 and the flow rate of coolant passing through the circulation passage CF are adjusted. For example, during the warm-up operation described later, the second valve 65 is fully open and the first valve 64 is fully closed, so that the coolant flowing from the coolant manifold of the fuel cell stack 10 into the main coolant discharge passage 67 does not go to the radiator 61 but instead goes to the bypass passage 68. As a result, the coolant circulates through the circulation passage CF without being cooled by the radiator 61.

[0029] In the following description, the oxidizing gas, fuel gas, and cooling water are collectively referred to as the fluid. The air compressor 21, circulation pump 42a, and circulation pump 62 are collectively referred to as the supply source DA. The oxidizing gas distribution unit 22, fuel gas distribution unit 43, and cooling water distribution unit 63 are collectively referred to as the distribution unit DB. In this disclosure, the supply source DA refers to the device that delivers the fluid to the fuel cell stack 10.

[0030] The fuel cell system 100 of this embodiment is configured to have one air compressor 21, one circulation pump 42a, and one circulation pump 62 for each of the multiple fuel cell stacks 10, and the fluid is supplied to each fuel cell stack 10 by distribution. Compared to a configuration that has multiple air compressors 21, circulation pumps 42a, and circulation pumps 62, this configuration of the fuel cell system 100 is expected to be lower in cost, save space, and have lower fuel consumption.

[0031] Figure 2 shows the mounting positions of various sensors. The mounting positions of the various sensors in the fuel cell stack 10 are common to the first fuel cell stack 10A, the second fuel cell stack 10B, and the third fuel cell stack 10C. Therefore, the mounting positions of the various sensors will be explained using the first fuel cell stack 10A as a representative example.

[0032] As shown in Figure 2, the fuel cell stack 10, in addition to the above configuration, includes a temperature sensor 12, a voltage sensor 13, and a plurality of cell voltage sensors 14. The temperature sensor 12 of the first fuel cell stack 10A is provided in the first cooling water drainage channel 72. The voltage sensor 13 is provided between both electrodes of the fuel cell stack 10 and detects the total voltage of the first fuel cell stack 10A. In this embodiment, each of the plurality of cell voltage sensors 14 detects the cell voltage, which is the voltage of a single cell 90. The detected value of each sensor is transmitted to the control unit 80. The cell voltage sensors 14 may be configured to detect voltage in units of two or more cells 90. In this disclosure, cell voltage refers to the voltage per cell 90. When the cell voltage sensors 14 are configured to detect voltage in units of two or more cells 90, the average value of the detected voltages is used as the cell voltage.

[0033] Figure 3 is a block diagram showing the configuration of the control unit 80. Figure 4 is a diagram illustrating stress information 88. As shown in Figure 3, the control unit 80 is configured as a computer having a processor 81, a storage device 82, and a bus 83. The storage device 82 is configured to include, for example, ROM and RAM. The processor 81 has a stress counter 86. The stress counter 86 is a functional unit realized by the processor 81 executing a program 87 stored in the storage device 82. The control unit 80 performs startup processing and normal operation processing, which will be described later, by having the processor 81 execute the program 87. As will be described in detail later, the control unit 80 determines the operating point of the fuel cell stack 10 and commands the oxidizing gas distribution unit 22, the fuel gas distribution unit 43, and the cooling water distribution unit 63 to set the distribution ratio.

[0034] The oxidizing gas distribution unit 22 has, in addition to the above configuration, a distribution control unit 224. The distribution control unit 224 controls the opening degrees of the first oxidizing gas valve 221, the second oxidizing gas valve 222, and the third oxidizing gas valve 223 according to the commanded distribution ratio. The fuel gas distribution unit 43 has, in addition to the above configuration, a distribution control unit 434. The distribution control unit 434 controls the opening degrees of the first fuel gas valve 431, the second fuel gas valve 432, and the third fuel gas valve 433 according to the commanded distribution. The cooling water distribution unit 63 has, in addition to the above configuration, a distribution control unit 634. The distribution control unit 634 controls the opening degrees of the first cooling water valve 631, the second cooling water valve 632, and the third cooling water valve 633 according to the commanded distribution.

[0035] The stress counter 86 records the cumulative power generation time [h] in a high-load environment for each of the three fuel cell stacks 10. A high-load environment refers to an environment where the load is greater than that of a predetermined reference environment. In this embodiment, the reference environment is defined by temperature. Specifically, the reference environment refers to the range in which the temperature of the fuel cell stack 10 is between 0°C and 70°C. In this embodiment, the cumulative power generation time during normal operation under conditions where the temperature of the fuel cell stack 10 is greater than 70°C is set as the cumulative power generation time in a high-load environment. In this embodiment, the temperature detected by the temperature sensor 12 is used as the temperature of the fuel cell stack 10.

[0036] Specifically, the stress counter 86 records stress information 88. As shown in Figure 4, the stress information 88 is information recorded for each fuel cell stack 10, showing the cumulative power generation time of the fuel cell stack 10 at temperatures of 100°C, 90°C, and 80°C, respectively. More specifically, a temperature of 100°C refers to a temperature range higher than 90°C and 100°C or less. More specifically, a temperature of 90°C refers to a temperature range higher than 80°C and 90°C or less. More specifically, a temperature of 80°C refers to a temperature range higher than 70°C and 80°C or less.

[0037] In power generation after calculating the remaining lifespan, the control unit 80 commands the distribution ratio so that the power generation load of the first fuel cell stack 10 is greater than the power generation load of the second fuel cell stack 10, which has a shorter remaining lifespan than the first fuel cell stack 10. In this embodiment, the control unit 80 commands the distribution ratio so that the power generation load of the fuel cell stack 10 with the longest remaining lifespan among the multiple fuel cell stacks 10 is greater than the power generation load of the fuel cell stack 10 with the shortest remaining lifespan. As a result, the distribution ratio is controlled so that the power generation load of the fuel cell stack 10 with the longest remaining lifespan is greater than the power generation load of the fuel cell stack 10 with the shortest remaining lifespan, thereby reducing the variation in the remaining lifespans of the multiple fuel cell stacks.

[0038] The power generation load specifically includes power generation time and power generation amount. In this embodiment, the fuel cell stacks 10 are controlled so that the power generation time of the fuel cell stack 10 with the longest remaining life is longer than the power generation time of the fuel cell stack 10 with the shortest remaining life, in order to increase the power generation load. Specifically, when the fuel cell system 100 starts power generation, the fuel cell system 100 is controlled so that the start of warm-up operation of the fuel cell stack 10 with the longest remaining life is earlier than the start of warm-up operation of the fuel cell stack 10 with the shortest remaining life. When the fuel cell system 100 finishes power generation, the fuel cell system 100 is controlled so that the multiple fuel cell stacks 10 finish power generation at the same time.

[0039] The memory device 82 pre-stores the lifetime under a standard environment (not shown) and the lifetime converted to 100°C. The control unit 80 also records the integrated power generation time under a standard environment and the integrated power generation time converted to 100°C (not shown) in the memory device 82. The lifetime under a standard environment and the lifetime converted to 100°C are predetermined times and are commonly set for multiple fuel cell stacks 10. Furthermore, the lifetime under a standard environment and the lifetime converted to 100°C are convertible to each other using predetermined coefficients. The lifetime converted to 100°C is shorter than the lifetime under a standard environment. Similarly, the integrated power generation time under a standard environment and the integrated power generation time converted to 100°C are convertible to each other using predetermined coefficients. The integrated power generation time under a standard environment and the integrated power generation time converted to 100°C represent the total power generation time from the time of shipment of the fuel cell system 100 to the present. The integrated power generation time under a standard environment and the integrated power generation time converted to 100°C are recorded for each of the multiple fuel cell stacks 10.

[0040] A2. Normal operation and warm-up: The normal operation and warm-up operation of the fuel cell stack 10 will be described below. In normal operation, power is generated by supplying more air than the theoretical amount of air required to generate the target output power. Specifically, the control unit 80 determines the operating point of the fuel cell stack 10, which indicates the output voltage and output current required to meet the required power. The control unit 80 determines the amount of oxidizing gas and fuel gas to be supplied to satisfy the determined operating point. As described above, in normal operation, the control unit 80 determines that the amount of oxidizing gas supplied is greater than or equal to the theoretical amount of air.

[0041] In normal operation, unless otherwise specified, the control unit 80 determines the operating point so that the power generation of the three fuel cell stacks 10 is equally divided, that is, so that the three fuel cell stacks 10 have the same operating point. Therefore, the control unit 80 determines the distribution ratio so that the flow rates of the fluid supplied from the supply source DA to the first fuel cell stack 10A, the second fuel cell stack 10B, and the third fuel cell stack 10C are the same. In other words, if the flow rate supplied to the first fuel cell stack 10A is represented as "FA1", the flow rate supplied to the second fuel cell stack 10B as "FA2", and the flow rate supplied to the third fuel cell stack 10C as "FA3", then the distribution ratio FA1:FA2:FA3 is set to 1:1:1.

[0042] During warm-up operation, power generation is performed with a lower amount of air than that supplied during normal operation in order to reduce operating efficiency. During warm-up operation, the air-stoichiometric ratio is set to, for example, about 1.0. The air-stoichiometric ratio is the ratio of the amount of air actually supplied to the theoretical amount of air required to generate the target output power. During warm-up operation, the fuel cell stack 10 is operated at the low-efficiency operating point, which increases the concentration overvoltage, and the fuel cell stack 10 is warmed up by self-heating.

[0043] Warm-up is mainly performed when the outside temperature is below freezing. Below freezing, moisture generated during the previous run that remains in the fuel cell stack 10 may freeze, potentially partially blocking the fuel gas flow path in the fuel cell stack 10. Therefore, warm-up is performed prior to normal operation to thaw the ice.

[0044] The fuel cell system 100 of this embodiment comprises multiple fuel cell stacks 10. By starting the warm-up operation with the fuel cell stack 10 with the longest remaining life, the fuel cell stack 10 with the longest remaining life transitions to normal operation before the fuel cell stack 10 with the shortest remaining life. Therefore, the operating time of the fuel cell stack 10 with the longest remaining life becomes longer than the operating time of the fuel cell stack 10 with the shortest remaining life. Thus, the variation in the remaining life of the multiple fuel cell stacks 10 can be reduced.

[0045] Furthermore, the inventors have confirmed that warming up one fuel cell stack 10 sequentially results in a shorter time to reach maximum output and better fuel efficiency compared to warming up multiple fuel cell stacks 10 simultaneously. Therefore, in this embodiment, when warming up, the warm-up periods of multiple fuel cell stacks 10 are controlled to be staggered. This shortens the time required for the fuel cell system 100 to reach maximum output compared to when all fuel cell stacks 10 are warmed up simultaneously, thereby improving fuel efficiency.

[0046] A3. Startup procedures: Figure 5 is a flowchart of the startup process. In Figure 5 and Figure 6 described later, "fuel cell stack" is abbreviated as "fuel cell". After startup, the control unit 80 performs the startup process. In step S10, the control unit 80 acquires the temperatures of the multiple fuel cell stacks 10. In this embodiment, the control unit 80 acquires the average of the temperatures detected by the temperature sensors 12 of the three fuel cell stacks 10 as the temperature of the multiple fuel cell stacks 10. In this embodiment, the three fuel cell stacks 10 are located close to each other, and it is assumed that the temperatures of the three fuel cell stacks 10 are approximately the same.

[0047] In step S12, the control unit 80 determines whether or not to perform a warm-up operation. Specifically, the control unit 80 determines to perform a warm-up operation if the acquired temperature of the fuel cell stack 10 is below a predetermined reference temperature. Conversely, the control unit 80 determines not to perform a warm-up operation if the acquired temperature of the fuel cell stack 10 is higher than the reference temperature. The reference temperature is, for example, around -10°C. If the control unit 80 determines not to perform a warm-up operation in step S12, it terminates this processing routine.

[0048] If it is determined in step S12 to perform a warm-up operation, in step S14 the control unit 80 acquires stress information 88 stored in the memory device 82 in order to calculate the remaining lifespan. Also in step S12, the control unit 80 acquires the lifespan converted to 100°C stored in the memory device 82.

[0049] In step S16, the control unit 80 uses the acquired stress information 88 to calculate the remaining lifespan of each of the three fuel cell stacks 10. Specifically, the control unit 80 uses the following equation (1) to determine the cumulative power generation time ATs at 100°C. ATs=PT(80)×a+PT(90)×b+PT(100) (1) In equation (1), PT(80) is the cumulative power generation time at 80°C. PT(90) is the cumulative power generation time at 90°C. PT(100) is the cumulative power generation time at 100°C. Coefficient a is a predetermined number for converting the cumulative power generation time at 80°C to the cumulative power generation time at 100°C. Coefficient b is a predetermined coefficient for converting the cumulative power generation time at 90°C to the cumulative power generation time at 100°C. Coefficients a and b are less than 1. Also, coefficient b is greater than coefficient a. Next, the control unit 80 calculates the remaining life by subtracting the cumulative power generation time ATs converted to 100°C from the life time converted to 100°C. In other words, the remaining life in this embodiment indicates the cumulative power generation time that can be generated in the future under a high-load environment.

[0050] In this embodiment, the calculation of remaining life does not use the cumulative power generation time in the reference environment, the cumulative power generation time in a temperature environment below 0°C, or the cumulative operation time during warm-up. In another embodiment, for example, the cumulative power generation time in the reference environment may be converted to the cumulative power generation time at 100°C, and the remaining life may be used as the time obtained by subtracting the 100°C converted cumulative power generation time and the converted value of the cumulative power generation time in the reference environment from the life time at 100°C. This allows for a more accurate determination of the remaining life. Alternatively, the cumulative power generation time in a temperature environment below 0°C and the cumulative operation time during warm-up may be recorded in the storage device 82, and the remaining life may be calculated using the cumulative power generation time in a temperature environment below 0°C and the cumulative operation time during warm-up, similar to the calculation method using the cumulative power generation time in the reference environment.

[0051] In step S18, the control unit 80 assigns numbers to the fuel cell stacks 10 in ascending order of remaining lifespan. Specifically, for example, if the first fuel cell stack 10A has the longest remaining lifespan and the third fuel cell stack 10C has the shortest remaining lifespan, the control unit 80 assigns numbers such that the first fuel cell stack 10A is number 1, the second fuel cell stack 10B is number 2, and the third fuel cell stack 10C is number 3. The control unit 80 also sets the variable n used in this processing routine to its initial value of 1.

[0052] In step S20, the control unit 80 determines whether the variable n is greater than 3. Note that in step S20, which is the first step performed after the start-up process begins, it is determined that the variable n is not greater than 3. If it is determined in step S20 that the variable n is not greater than 3, in step S22, the control unit 80 warms up the nth fuel cell stack 10. Specifically, the control unit 80 commands the oxidizing gas distribution unit 22, the fuel gas distribution unit 43, and the cooling water distribution unit 63 to set the distribution ratios so that oxidizing gas, fuel gas, and cooling water are supplied to the nth fuel cell stack 10. Note that during the warm-up of the first fuel cell stack 10, the other fuel cell stacks 10 are controlled so that oxidizing gas, fuel gas, and cooling water are not supplied. In other words, the control unit 80 sets the ratio of oxidizing gas supplied to the first fuel cell stack 10 to "1" and the ratio of oxidizing gas supplied to the other two fuel cell stacks 10 to "0". The control unit 80 sets the ratios of fuel gas and cooling water in the same way. As a result, the cooling water heated by the first fuel cell stack 10 during warm-up is circulated only to the first fuel cell stack 10. Therefore, the first fuel cell stack 10 can be warmed up efficiently.

[0053] In step S24, the control unit 80 switches the operation of the first fuel cell stack 10 from warm-up operation to normal operation. In this embodiment, the control unit 80 performs step S24 when the detected temperature of the nth fuel cell stack 10 becomes equal to or above a predetermined switching temperature.

[0054] In step S26, the control unit 80 determines whether the battery voltage, which is the voltage detected by the voltage sensor 13 of the nth fuel cell stack 10, is greater than a predetermined switching voltage. If, in step S26, the control unit 80 determines that the battery voltage is not greater than the switching voltage, the control unit 80 returns to step S26 after a predetermined time has elapsed. If, in step S26, the control unit 80 determines that the battery voltage is greater than the switching voltage, the nth fuel cell stack 10 is in a state of stable power generation, so in step S28, the control unit 80 increments the variable n and returns to step S20. The switching voltage is, for example, 80% of the theoretical power generation voltage of the fuel cell stack 10. The predetermined time is, for example, a few milliseconds.

[0055] When warming up the second or subsequent fuel cell stacks 10, the control unit 80 starts the warm-up operation with the fuel cell stack 10 that is already in normal operation running normally. If the control unit 80 determines in step S20 that the variable n is greater than 3, it terminates this processing routine.

[0056] A4. Processing during normal operation: Figure 6 is a flowchart of the processing during normal operation. During normal operation, water generated by the power generation reaction may accumulate in the fuel gas flow path and oxidizing gas flow path inside the fuel cell stack 10. In such cases, the pressure loss of the reaction gas increases, and the actual amount of reaction gas supplied becomes less than the target amount of reaction gas supplied, resulting in cells 90 where the power generation reaction does not occur. In cells 90 where the power generation reaction does not occur, the actual cell voltage drops below the target cell voltage and is typically negative. Therefore, during normal operation processing, excess fuel gas and oxidizing gas are supplied to the fuel cell stack 10 where the cell voltage has dropped in order to remove the accumulated water generated. Note that in Figure 6, the "low-voltage fuel cell stack" described later is abbreviated as "low-voltage fuel cell".

[0057] The control unit 80 repeatedly performs normal operation processing while normal operation is in progress. In step S30, the control unit 80 obtains the minimum cell voltage VL of each fuel cell stack 10. In step S32, the control unit 80 determines whether there is a fuel cell stack 10 in which the minimum cell voltage VL is less than the first reference voltage Vth1. A fuel cell stack 10 in which the minimum cell voltage VL is less than the first reference voltage Vth1 is also called a low-voltage fuel cell stack. In step S32, if the control unit 80 determines that there is no fuel cell stack 10 in which the minimum cell voltage VL is less than the first reference voltage Vth1, the control unit 80 terminates this processing routine.

[0058] In step S32, if it is determined that there is a fuel cell stack 10 in which the minimum cell voltage VL is less than the first reference voltage Vth1, in step S34, the control unit 80 increases the flow rate of the oxidizing gas and fuel gas in the low-voltage fuel cell stack. Step S34 is a processing step aimed at blowing away and removing any remaining generated water in the cell 90 with the reaction gas. Step S32 is also called the scavenging process. However, even after performing the scavenging process, it may not be possible to completely remove the remaining generated water in the cell 90.

[0059] In this embodiment, in step S34, the flow rate of the reaction gas is increased by a predetermined percentage relative to the flow rate of the reaction gas at the reference operating point. In this embodiment, the flow rate of the reaction gas sent from the supply source DA to the fuel cell stack 10 is increased, and the flow rate of the supply gas to the low-voltage fuel cell stack is increased, while the flow rate of the supply gas to the fuel cell stacks 10 other than the low-voltage fuel cell stack remains unchanged, and the distribution ratio is adjusted accordingly.

[0060] In step S36, the control unit 80 obtains the minimum cell voltage VL of each fuel cell stack 10. In step S38, the control unit 80 determines whether there is a fuel cell stack 10 in which the minimum cell voltage VL is less than the second reference voltage Vth2. In this embodiment, the second reference voltage Vth2 is set to a value smaller than the first reference voltage Vth1. If the generated water remaining in the cell 90 cannot be sufficiently removed even after scavenging, the low-voltage fuel cell stack cannot generate electricity. The second reference voltage Vth2 is a threshold value for determining whether the fuel cell stack 10 can generate electricity. For example, the first reference voltage Vth1 is about 0.2V, and the second reference voltage Vth2 is about 0.0V. By setting the first reference voltage Vth1 to a value greater than the second reference voltage Vth2, scavenging can be performed in advance before generated water accumulates in the cell 90 to the point where the cell 90 cannot generate electricity.

[0061] In step S38, if it is determined that there is a fuel cell stack 10 in which the minimum cell voltage VL is less than the second reference voltage Vth2, in step S40, the control unit 80 determines whether the fuel cell stack 10 in which the minimum cell voltage VL is equal to or greater than the second reference voltage Vth2 is capable of generating the required power.

[0062] In step S40, if the control unit 80 determines that the fuel cell stack 10 with a minimum cell voltage VL equal to or greater than the second reference voltage Vth2 cannot generate the required power, in step S42, the control unit 80 sets the target power generation amount to the maximum power that can be generated by the fuel cell stack 10 with a minimum cell voltage VL equal to or greater than the second reference voltage Vth2. In this case, the target power generation amount is less than the required power. In step S44, the control unit 80 operates the fuel cell stacks 10, excluding the low-voltage fuel cell stack, in a normal manner so that the power generated is equal to the target power generation amount. Specifically, the control unit 80 adjusts the flow rates of the fuel gas and oxidizing gas so that the flow rates of the fuel gas, oxidizing gas, and cooling water supplied to the low-voltage fuel cell stack become zero, and fuel gas, oxidizing gas, and cooling water are supplied to the other fuel cell stacks 10. In detail, the control unit 80 determines the flow rate of the fluid to be sent to the fuel cell stack 10 and the distribution ratio of the distribution unit DB for each supply source DA. After performing step S44, the control unit 80 terminates this processing routine.

[0063] In step S40, if the control unit 80 determines that the fuel cell stack 10 can generate the required power when the minimum cell voltage VL is equal to or greater than the second reference voltage Vth2, in step S46, the control unit 80 sets the required power to the target power generation amount. In step S48, the control unit 80 operates all fuel cell stacks 10 normally so that the power generated reaches the target power generation amount. After performing step S48, the control unit 80 terminates this processing routine.

[0064] According to the embodiment described above, the fuel cell system 100 comprises a plurality of fuel cell stacks 10, a supply source DA, a distribution unit DB, and a control unit 80. The control unit 80 calculates the remaining lifespan of each fuel cell stack 10 and commands the distribution ratio of the distribution unit DB using the calculated remaining lifespan. In this embodiment, the distribution ratio is commanded so that the power generation load of the fuel cell stack 10 with the longest remaining lifespan is greater than the power generation load of the fuel cell stack 10 with the shortest remaining lifespan. Specifically, the control unit 80 commands the distribution ratio so that the power generation start time of the fuel cell stack 10 with the longest remaining lifespan is earlier than the power generation start time of the fuel cell stack 10 with the shortest remaining lifespan. In this embodiment, the control unit 80 supplies fuel gas and oxidizing gas to the first fuel cell stack 10, which has the longest remaining lifespan, in order to start the warm-up operation. The fuel cell stacks 10 undergoing warm-up operation transition to normal operation as the temperature of the fuel cell stack 10 rises. Therefore, the power generation time of a fuel cell stack 10 with a long remaining lifespan will be longer than that of a fuel cell stack 10 with a short remaining lifespan. As a result, the difference between the remaining lifespan of a fuel cell stack 10 with a long remaining lifespan and a fuel cell stack 10 with a short remaining lifespan can be reduced, thereby reducing variations in remaining lifespan.

[0065] Furthermore, when the control unit 80 starts the warm-up operation of the first fuel cell stack 10, which has the longest remaining lifespan, it controls the system so that the cooling water heated by the first fuel cell stack 10, which is undergoing warm-up operation, is circulated only to the first fuel cell stack 10, without warming up the second and subsequent fuel cell stacks 10. This allows the first fuel cell stack 10 to be warmed up efficiently.

[0066] Furthermore, during normal operation, if there is a low-voltage fuel cell stack where the cell voltage is lower than the first reference voltage, the control unit 80 commands the distribution ratio so that the flow rates of oxidizing gas and fuel gas supplied to the low-voltage fuel cell stack become greater than the flow rates at the reference operating point. This makes it possible to remove generated water accumulated in the fuel gas flow path and the oxidizing gas flow path within the fuel cell stack 10.

[0067] B. Other embodiments: (B1) In the above embodiment, the power generation time is adjusted so that a large power load is applied to the fuel cell stack 10 with a long remaining life. In other embodiments, the amount of power as the power load may be adjusted. For example, if the required power is less than the maximum output of the fuel cell system 100, the target power of the fuel cell stack 10 with a long remaining life may be controlled to be greater than the target power of the fuel cell stack 10 with a short remaining life. In this embodiment, the stress counter 86 may record the power generation cumulative time for each fuel cell stack 10 for each predetermined range of output power.

[0068] (B2) In the above embodiment, the warm-up operation of the first fuel cell stack 10 is started first, so that the operating time of the first fuel cell stack 10 is controlled to be longer than the operating time of the second fuel cell stack 10. In another embodiment, when normal operation is started without a warm-up operation, the control may be made so that normal operation starts from the fuel cell stack 10 with the longest remaining life. In other words, the control to stagger the start times of operation for multiple fuel cell stacks 10 may be performed in either normal operation or warm-up operation, or in both normal operation and warm-up operation.

[0069] (B3) In the above embodiment, during the startup process, warm-up and normal operation are started in order of the longest remaining lifespan. In another embodiment, if there are four or more fuel cell stacks 10, for example, the first fuel cell stack 10 may start warm-up earlier than the second fuel cell stack 10, in order of the longest remaining lifespan, and the third and subsequent fuel cell stacks 10 may start warm-up simultaneously with each other. Alternatively, the first fuel cell stack 10 may start warm-up earlier than the fuel cell stack 10 with the shortest remaining lifespan, and the other fuel cell stacks 10 may start warm-up simultaneously with each other. At least for two of the multiple fuel cell stacks 10, the fuel cell stacks 10 with the longest remaining lifespans start warm-up first, thereby reducing variations in remaining lifespan.

[0070] (B4) In the above embodiment, when the first fuel cell stack 10 is warmed up, the flow rate of the fluid supplied to the fuel cell stacks 10 other than the first fuel cell stack 10 is adjusted to zero. In another embodiment, the fuel cell stacks 10 other than the first fuel cell stack 10 may be supplied with a fluid flow rate that is less than the flow rate of the fluid supplied to the first fuel cell stack 10.

[0071] (B5) In the above embodiment, it was explained that during normal operation, generated water accumulates in the internal flow path of the fuel cell stack 10, causing a decrease in cell voltage. Another cause of a decrease in cell voltage is insufficient fuel gas supply. In this case as well, the cell voltage can be restored by performing the above-described normal operation process. This is because the fuel gas shortage is detected as a decrease in cell voltage, and the amount of fuel gas supplied is increased. Furthermore, insufficient fuel gas leads to deterioration of the electrode catalyst layer. Therefore, by performing the normal operation process, deterioration of the electrode catalyst layer can be suppressed.

[0072] (B6) In the above embodiment, in step S34 of the normal operation process, the flow rate of the reaction gas sent from the supply source DA to the fuel cell stack 10 is controlled to increase. In another embodiment, the flow rate of the reaction gas sent from the supply source DA to the fuel cell stack 10 may not be changed, but only the distribution ratio may be changed to increase the flow rate of the reaction gas supplied to the low-voltage fuel cell stack and decrease the flow rate to the other fuel cell stacks 10.

[0073] (B7) In the above embodiment, the oxidizing gas distribution unit 22 comprises a first oxidizing gas valve 221, a second oxidizing gas valve 222, and a third oxidizing gas valve 223. The configuration of the oxidizing gas distribution unit 22 is not limited to the above. For example, a three-way valve may be placed at the branching point between the oxidizing gas supply main pipe 23 and the first oxidizing gas valve 221, the second oxidizing gas valve 222, and the third oxidizing gas valve 223. Also, a thermostat capable of adjusting temperature in addition to flow rate may be placed at the branching point. Furthermore, an ejector may be provided in the first oxidizing off-gas discharge pipe 27 to adjust the back pressure and thereby adjust the flow rate. The oxidizing gas distribution unit 22 may further include a pump for pressurizing the oxidizing gas. The same applies to the fuel gas distribution unit 43 in the other embodiments described above. The fuel gas distribution unit 43 may also include injectors in the first fuel exhaust gas pipe 52, the second fuel exhaust gas pipe 53, and the third fuel exhaust gas pipe 54 to adjust the flow rate. The same applies to the oxidizing gas distribution section 22. Furthermore, the oxidizing gas system circuit 20 may be equipped with a flow pipe that bypasses the main oxidizing gas supply pipe 23 and the main oxidizing off-gas discharge pipe 30.

[0074] (B8) In the above embodiment, the fuel cell system 100 includes one air compressor 21, one circulation pump 42a, and one circulation pump 62. In another embodiment, the fuel cell system 100 may be configured to include one supply source DA for at least one of the oxidizing gas system circuit 20, the fuel gas system circuit 40, and the cooling system circuit 60. Alternatively, for example, the oxidizing gas system circuit 20 may be configured to include multiple air compressors 21 and at least one oxidizing gas distribution unit 22. In other words, the fuel cell system 100 may be configured to include a mixture of multiple fuel cell stacks 10 that share one air compressor 21 and fuel cell stacks 10 that occupy one air compressor 21. Regardless of the type of fluid, by including a distribution unit DB in the fuel cell system 100, the number of supply sources DA can be reduced, resulting in benefits such as space saving.

[0075] (B9) In the normal operation process of the above embodiment, scavenging is performed on fuel cell stacks 10 whose cell voltage is lower than the first reference voltage Vth1. In another embodiment, if there are multiple fuel cell stacks 10 whose cell voltage is lower than the first reference voltage Vth1, scavenging may be performed only on the fuel cell stack 10 with the lowest cell voltage. This limits the total flow rate of reaction gas for scavenging and prioritizes power generation in fuel cell stacks 10 whose cell voltage is equal to or greater than the first reference voltage Vth1. Furthermore, if it is necessary to allow a normal fuel cell stack 10 whose cell voltage is equal to or greater than the first reference voltage Vth1 to generate power at maximum output in order to meet the required power, scavenging may be withheld. In other words, if there is no time to perform scavenging, scavenging may be performed when the required power is low enough to allow for scavenging. In addition, during scavenging, the flow rate of either the oxidizing gas or the fuel gas may be increased.

[0076] (B10) In the normal operation process of the above embodiment, if NO is determined in step S32, the processing routine is terminated. In another embodiment, if NO is determined in step S32, the processing step may return to step S30 after a predetermined first waiting time has elapsed. Similarly, in another embodiment, if NO is determined in step S38, the processing step may return to step S30 after a predetermined second waiting time has elapsed. The first and second waiting times are, for example, several seconds. The first and second waiting times may be the same or different.

[0077] (B11) In the startup process of the above embodiment, it is determined whether or not to perform a warm-up operation for the entire set of three fuel cell stacks 10. In another embodiment, it may be determined whether or not to perform a warm-up operation individually using the temperature sensors 12 of each of the three fuel cell stacks 10. In this case, if there is a mix of fuel cell stacks 10 that require a warm-up operation and fuel cell stacks 10 that do not require a warm-up operation, control may be performed to start normal operation of the fuel cell stacks 10 that do not require a warm-up operation. This allows the fuel cell system 100 to start generating power earlier. Furthermore, if there are multiple fuel cell stacks 10 that require a warm-up operation, the variation in remaining lifespan can be reduced by starting the warm-up operation in order of the longest remaining lifespan.

[0078] (B12) In the above embodiment, the reference environment is defined by temperature. Instead of temperature, the sweep current drawn from the fuel cell stack 10 may be used as the reference environment. Specifically, the reference environment may be set to normal operation in which a current of 80% or less of the maximum output current of the fuel cell stack 10 is swept. In this case, the power generation cumulative time in normal operation in which a current greater than 80% of the maximum output current is swept is set to the power generation cumulative time in the high-load environment. Furthermore, the reference environment may be defined using both temperature and sweep current.

[0079] (B13) In the above embodiment, the stress counter 86 records the cumulative power generation time in a high-load environment. In another embodiment, the stress counter 86 may record the number of times the fuel cell stack 10 has started below freezing. If the reference temperature for warm-up is set to -10°C, and the system is set to perform warm-up when the temperature of the fuel cell stack 10 is -10°C or lower, then if the temperature of the fuel cell stack 10 is greater than -10°C, normal operation will be performed without warm-up. The start of normal operation when the temperature of the fuel cell stack 10 is greater than -10°C and less than 0°C is called a sub-freezing start. When sub-freezing starts occur, the deterioration of the fuel cell stack 10 progresses. For this reason, it can be estimated that the more times a fuel cell stack 10 has been started below freezing, the shorter its remaining lifespan is. This method of calculating remaining lifespan is useful, for example, when the fuel cell stacks 10 are located far apart from each other and their temperatures differ significantly.

[0080] (B14) In the above embodiment, in step S26 of the startup process, it is determined whether the battery voltage is greater than the switching voltage. In another embodiment, it may be determined whether the sweep current drawn from the fuel cell stack 10 is greater than a predetermined switching current. In other words, it may be determined by current instead of voltage whether the fuel cell stack 10 is generating power stably. Alternatively, both voltage and current may be determined.

[0081] (B15) In the above embodiment, the multiple fuel cell stacks 10 are electrically connected in parallel, but the multiple fuel cell stacks 10 may also be electrically connected in series. In the above embodiment, the average temperature of the three temperature sensors 12 is obtained as the temperature of the multiple fuel cell stacks 10. In another embodiment, the fuel cell system 100 may include, for example, a temperature sensor that detects the ambient temperature, and the temperature of this temperature sensor may be obtained as the temperature of the multiple fuel cell stacks 10.

[0082] This disclosure is not limited to the embodiments described above, and can be implemented in various configurations without departing from its spirit. For example, the technical features of the embodiments corresponding to the technical features in each form described in the summary of the invention can be replaced or combined as appropriate in order to solve some or all of the above-described problems, or to achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be deleted as appropriate. [Explanation of Symbols]

[0083] 10...Fuel cell stack, 10A...First fuel cell stack, 10B...Second fuel cell stack, 10C...Third fuel cell stack, 12...Temperature sensor, 13...Voltage sensor, 14...Cell voltage sensor, 16...Power control unit, 17...Battery, 18...Load, 20...Oxidizing gas system circuit, 21...Air compressor, 22...Oxidizing gas distribution section, 23...Oxidizing gas supply main pipe, 24...First oxidizing gas branch pipe, 25...Second oxidizing gas branch pipe, 26...Third oxidizing gas branch pipe, 27...First oxidizing off-gas discharge pipe, 28...No 2. Oxidation-off gas discharge pipe, 29...3rd oxidation-off gas discharge pipe, 30...Oxidation-off gas main discharge pipe, 40...Fuel gas system circuit, 41...Fuel gas tank, 42...Hydrogen circulation device, 42a...Circulation pump, 43...Fuel gas distribution section, 44...Gas-liquid separator, 45...Exhaust drain valve, 46...Fuel gas supply main pipe, 47...1st fuel gas branch pipe, 48...2nd fuel gas branch pipe, 49...3rd fuel gas branch pipe, 51...Recirculation pipe, 52...1st fuel exhaust gas pipe, 53...2nd fuel exhaust gas pipe, 54...3rd fuel exhaust gas pipe, 55...Fuel exhaust gas main pipe, 5 6... Exhaust pipe, 60... Cooling system circuit, 61... Radiator, 62... Circulation pump, 63... Coolant distribution section, 64... First valve, 65... Second valve, 66... ​​Main coolant supply channel, 67... Main coolant discharge channel, 68... Bypass channel, 69... First coolant branch channel, 70... Second coolant branch channel, 71... Third coolant branch channel, 72... First coolant drain channel, 73... Second coolant drain channel, 74... Third coolant drain channel, 75... Coolant manifold, 80... Control unit, 81... Processor, 82... Memory device, 83... Bus, 84 …Remaining life calculation unit, 86…Stress counter, 87…Program, 88…Stress information, 90…Cell, 100…Fuel cell system, 162…Cooling water discharge channel, 221…First oxide gas valve, 222…Second oxide gas valve, 223…Third oxide gas valve, 224, 434, 634…Distribution control unit, 431…First fuel gas valve, 432…Second fuel gas valve, 433…Third fuel gas valve, 631…First cooling water valve, 632…Second cooling water valve, 633…Third cooling water valve, CF…Circulation channel

Claims

1. A fuel cell system, Multiple fuel cell stacks, A supply source that supplies fluid to the plurality of fuel cell stacks, A distribution unit that distributes the fluid supplied from the at least one supply source to each of the plurality of fuel cell stacks according to a commanded distribution ratio, It comprises a control unit and, A fuel cell system comprising a control unit that calculates the remaining lifespan of each fuel cell stack and commands the distribution ratio according to the remaining lifespan.

2. A fuel cell system according to claim 1, The at least one supply source includes an oxidizing gas supply source that supplies oxidizing gas and a fuel gas supply source that supplies fuel gas. The distribution unit is provided in correspondence with at least one of the oxidizing gas supply source and the fuel gas supply source, The plurality of fuel cell stacks include a first fuel cell stack and a second fuel cell stack whose remaining lifespan is shorter than that of the first fuel cell stack. A fuel cell system in which the control unit commands the distribution ratio such that the power generation start time of the first fuel cell stack is earlier than the power generation start time of the second fuel cell stack, and the power generation time of the first fuel cell stack is controlled to be longer than the power generation time of the second fuel cell stack.

3. A fuel cell system according to claim 2, The system includes a temperature sensor that detects the temperature of the plurality of fuel cell stacks, The control unit, If the temperature detected by the temperature sensor is lower than a predetermined reference temperature, a warm-up operation is performed in which each fuel cell stack is operated at a low-efficiency operating point, which is less efficient than the reference operating point, prior to normal operation in which each fuel cell stack is operated at a reference operating point. A fuel cell system that, when performing the warm-up operation, commands the distribution ratio such that the start time of the warm-up operation of the first fuel cell stack is earlier than the start time of the warm-up operation of the second fuel cell stack.

4. A fuel cell system according to claim 3, The at least one supply source includes a cooling water supply source that supplies cooling water, The fuel cell system includes a circulation channel for circulating the cooling water, The first fuel cell stack is the fuel cell stack with the longest remaining lifespan among the plurality of fuel cell stacks. The control unit, during the warm-up operation of the first fuel cell stack, supplies the cooling water to the first fuel cell stack and commands the distribution ratio of the cooling water supply source so as not to supply the cooling water to any of the plurality of fuel cell stacks except the first fuel cell stack, so that the cooling water heated by the first fuel cell stack performing the warm-up operation is circulated only to the first fuel cell stack.

5. A fuel cell system according to claim 1, The at least one supply source includes an oxidizing gas supply source that supplies oxidizing gas and a fuel gas supply source that supplies fuel gas. The distribution unit is provided in correspondence with at least one of the oxidizing gas supply source and the fuel gas supply source, Each of the aforementioned fuel cell stacks is Multiple stacked cells, The system includes a plurality of cell voltage sensors that detect voltage in units of one or more cells among the plurality of cells, The control unit, Normal operation is performed to operate each fuel cell stack at the reference operating point. In the normal operation described above, if there is a low-voltage fuel cell stack among the plurality of fuel cell stacks in which the cell voltage indicated by each of the plurality of cell voltage sensors is smaller than a predetermined first reference voltage, the fuel cell system commands the distribution ratio such that the flow rate of at least one of the oxidizing gas and the fuel gas supplied to the low-voltage fuel cell stack is greater than the flow rate at the reference operating point.

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