Fuel cell system

Abstract

In this fuel cell system, when the difference between an optimum value of an output voltage of a fuel cell corresponding to a measured value of an output current of the fuel cell measured by a current sensor and a measured value of the output voltage of the fuel cell measured by a voltage sensor is defined as an output voltage difference, a control unit: when there is a request to shut down power generation of the fuel cell, reduces a target fuel pressure, which is a target pressure of fuel gas supplied by a fuel supply device, and shuts down power generation of the fuel cell; and, when reducing the target fuel pressure of the fuel supply device, changes a pressure reduction rate of the target fuel pressure of the fuel supply device on the basis of the output voltage difference.

Description

fuel cell system

[0001] The present disclosure relates to a fuel cell system having a fuel cell that generates electricity when supplied with a fuel gas and an oxidant gas.

[0002] Patent Document 1 discloses a fuel cell system having a first valve that controls the flow rate of oxidant gas (reaction air) supplied to the fuel cell, and a second valve that controls the flow rate of oxidant off-gas (reaction air) discharged from the fuel cell.

[0003] Japanese Patent Application Laid-Open No. 2022-185247

[0004] The fuel cell system disclosed in Patent Document 1 has a large number of parts due to the inclusion of the first and second valves, which increases the costs required for manufacturing and maintenance. Furthermore, when power generation by the fuel cell is stopped, if the flow rate of the oxidant gas supplied to the fuel cell fluctuates and the output voltage of the fuel cell changes suddenly, a high load is placed on the fuel cell, which may cause deterioration of the fuel cell depending on the state of the fuel cell.

[0005] Therefore, the present disclosure has been made to solve the above-mentioned problems, and aims to provide a fuel cell system that can stop power generation by a fuel cell while reducing costs and suppressing the occurrence of fuel cell deterioration.

[0006] One aspect of the present disclosure made to solve the above problems is a fuel cell system having a fuel cell that generates electricity by receiving a supply of fuel gas and an oxidant gas, a fuel supply passage that supplies the fuel gas to the fuel cell, a fuel supply device that is provided in the fuel supply passage and is driven to supply the fuel gas to the fuel cell, and an oxidant gas supply passage that supplies the oxidant gas to the fuel cell, wherein the fuel cell system is a system in which an output current of the fuel cell depends on a voltage of a battery that charges with electric power generated by the fuel cell, and the fuel cell system has a current sensor that measures the output current of the fuel cell, a voltage sensor that measures an output voltage of the fuel cell, and a control unit that controls the fuel supply device, and when the difference between the optimal value of the output voltage of the fuel cell corresponding to the measured value of the output current of the fuel cell measured by the current sensor and the measured value of the output voltage of the fuel cell measured by the voltage sensor is defined as the output voltage difference, the control unit, when there is a request to stop power generation of the fuel cell, reduces the target fuel pressure, which is the target pressure of the fuel gas supplied by the fuel supply device, to stop power generation of the fuel cell, and when reducing the target fuel pressure of the fuel supply device, changes the rate at which the target fuel pressure of the fuel supply device is reduced based on the output voltage difference.

[0007] According to this aspect, the target fuel pressure of the fuel supply device is reduced to stop the supply of fuel from the fuel supply device to the fuel cell, thereby stopping (e.g., intermittently stopping) the power generation of the fuel cell. Therefore, the power generation of the fuel cell can be stopped without cutting off the supply of oxidant gas to the fuel cell. Therefore, a device (e.g., a valve) for cutting off the supply of oxidant gas to the fuel cell is not required, which reduces the number of parts in the fuel cell system and reduces the cost of the fuel cell system.

[0008] When the target fuel pressure of the fuel supply device is reduced, the rate at which the target fuel pressure of the fuel supply device is reduced is changed depending on the magnitude of the output voltage difference (i.e., the difference between the optimum value and the measured value of the fuel cell output voltage), which is an indicator of the state of the fuel cell. As a result, the target fuel pressure of the fuel supply device can be reduced while suppressing the occurrence of fuel cell degradation, thereby stopping power generation by the fuel cell.

[0009] In the above aspect, it is preferable that the control unit sets the pressure reduction rate to a first rate when the output voltage difference is less than a predetermined value, and sets the pressure reduction rate to a second rate slower than the first rate when the output voltage difference is equal to or greater than the predetermined value.

[0010] According to this aspect, when the output voltage difference is equal to or greater than a predetermined value, the fuel cell is in a state where it is susceptible to degradation, so when power generation by the fuel cell is stopped, the target fuel pressure of the fuel cell is slowly reduced. Therefore, when the fuel cell is in a state where it is susceptible to degradation, the output voltage of the fuel cell does not change suddenly, so power generation by the fuel cell can be stopped while suppressing the occurrence of fuel cell degradation.

[0011] In the above aspect, it is preferable that the control unit sets the target fuel pressure of the fuel supply device to atmospheric pressure or approximately atmospheric pressure when the measured value of the output current of the fuel cell measured by the current sensor becomes 0 or approximately 0.

[0012] According to this aspect, when power generation by the fuel cell stops and the measured value of the fuel cell's output current becomes zero or approximately zero, the fuel supply passage can be prevented from becoming negative pressure (i.e., pressure lower than atmospheric pressure). This prevents oxidant gas from flowing from the oxidant gas supply passage into the fuel supply passage via the fuel cell. This prevents the catalyst in the fuel cell from being deteriorated by the oxidant gas.

[0013] In the above aspect, it is preferable that the control unit controls the target fuel pressure of the fuel supply device so that the output voltage of the fuel cell becomes a target voltage lower than the voltage of the battery when the measured value of the output current of the fuel cell measured by the current sensor becomes 0 or approximately 0.

[0014] According to this aspect, when power generation by the fuel cell is stopped, a target voltage is set for the output voltage of the fuel cell so that it does not become an overvoltage (voltage drop) or a high voltage, and feedback control of the target fuel pressure of the fuel supply device is performed accordingly. Therefore, the output voltage of the fuel cell can be prevented from becoming an overvoltage (voltage drop) or a high voltage, and deterioration of the fuel cell can be suppressed.

[0015] According to the fuel cell system of the present disclosure, power generation by the fuel cell can be stopped while reducing costs and suppressing the occurrence of fuel cell deterioration.

[0016] Fig. 1 is a diagram showing a schematic configuration of a fuel cell system of this embodiment. Fig. 2 is a diagram showing the IV characteristics of an FC stack. Fig. 3 is a diagram showing an example of a map that defines the relationship between a measured FC current value and an estimated FC voltage value. Fig. 4 is a diagram showing an example of a map that defines the relationship between a measured FC current value and a judgment value. Fig. 5 is a flowchart showing the content of control performed in a first embodiment. Fig. 6 is a flowchart showing the content of control performed in a second embodiment.

[0017] An embodiment of a fuel cell system according to the present disclosure will now be described.

[0018] <Outline of Fuel Cell System> First, an outline of a fuel cell system 1 according to this embodiment will be described. The fuel cell system 1 is a system that is mounted on a fuel cell vehicle and supplies electric power to its drive motor (not shown).

[0019] 1, the fuel cell system 1 includes an FC stack 11, a hydrogen system 12, an air system 13, a cooling system 14, and a control unit 15. The FC stack 11 is an example of the "fuel cell" of the present disclosure.

[0020] The FC stack 11 generates electricity by receiving a supply of fuel gas and an oxidant gas. In this embodiment, the fuel gas is hydrogen gas, and the oxidant gas is air. That is, the FC stack 11 generates electricity by receiving a supply of hydrogen gas from the hydrogen system 12 and a supply of air from the air system 13. The electricity generated by the FC stack 11 is then supplied to the battery 101 and the inverter 102 (or the motor).

[0021] The fuel cell system 1 is also provided with a current sensor 16 and a voltage sensor 17. The current sensor 16 is a sensor that measures the output current of the FC stack 11 (i.e., the current of the electric power generated by the FC stack 11, hereinafter referred to as "FC current"). The voltage sensor 17 is a sensor that measures the output voltage of the FC stack 11 (i.e., the voltage of the electric power generated by the FC stack 11, hereinafter referred to as "FC voltage").

[0022] The hydrogen system 12 is provided on the anode side of the FC stack 11. The hydrogen system 12 includes a hydrogen filling passage 20, a hydrogen gas supply passage 21, and a hydrogen off-gas discharge passage 22.

[0023] The hydrogen filling passage 20 is a passage for filling hydrogen gas into the hydrogen tank 31 from the filling port 30. The hydrogen gas supply passage 21 is a passage for supplying hydrogen gas from the hydrogen tank 31 to the FC stack 11, and is an example of the "fuel supply passage" of the present disclosure.

[0024] The hydrogen off-gas discharge passage 22 is a passage through which hydrogen off-gas, which is hydrogen gas not used in power generation, is discharged from the FC stack 11 .

[0025] The hydrogen system 12 includes a valve 32, a pressure reducing valve 33, an injector 34, and a pressure sensor 35 in this order from the hydrogen tank 31 side in the hydrogen gas supply passage 21.

[0026] The valve 32 switches between supplying and blocking hydrogen gas from the hydrogen tank 31 to the hydrogen gas supply passage 21, and between supplying and blocking hydrogen gas from the filling port 30 to the hydrogen tank 31. The pressure reducing valve 33 is a pressure regulating valve for reducing the pressure of hydrogen gas.

[0027] The injector 34 is a valve that is driven to supply (i.e., inject) hydrogen gas to the FC stack 11, and is an example of the "fuel supply device" of the present disclosure. The pressure sensor 35 measures the pressure of the hydrogen gas injected from the injector 34 (i.e., fuel pressure or outlet pressure).

[0028] The hydrogen system 12 also includes a gas-liquid separator 41 and an exhaust drain valve 42 in the hydrogen off-gas discharge passage 22 .

[0029] The gas-liquid separator 41 is a device that separates moisture from the hydrogen off-gas. The exhaust drain valve 42 is a valve that controls the discharge of the hydrogen off-gas discharged from the FC stack 11 to the outside.

[0030] The air system 13 is provided on the cathode side of the FC stack 11. The air system 13 includes an air supply passage 51 and an air off-gas discharge passage 52.

[0031] The air supply passage 51 is a passage for supplying air from outside the fuel cell system 1 to the FC stack 11, and is an example of an "oxidant gas supply passage" in the present disclosure. The air off-gas discharge passage 52 is a passage for discharging air off-gas, which is air not used for power generation, from the FC stack 11.

[0032] The air system 13 includes an air compressor 61 in the air supply passage 51. The air compressor 61 is a device that supplies air to the FC stack 11.

[0033] The air system 13 of this embodiment does not have an inlet air valve that controls the flow rate of air supplied from the air supply passage 51 to the FC stack 11, or an outlet air valve that controls the flow rate of air off-gas discharged from the FC stack 11 to the air off-gas discharge passage 52.

[0034] The cooling system 14 is a system that cools the FC stack 11, and includes a cooling water passage 81 and a cooling fan 82. The cooling water passage 81 is a passage through which cooling water flows. The cooling fan 82 is a device that cools the cooling water flowing through the cooling water passage 81.

[0035] The control unit 15 is a device having, for example, an arithmetic processing unit such as a CPU, a storage unit such as a ROM for storing control programs and control data processed by the CPU and a RAM used as various work areas for control processing, and an input / output interface unit. The control unit 15 performs various controls of the fuel cell system 1 in accordance with the control programs stored in the storage unit.

[0036] Specifically, the control unit 15 controls, for example, the driving of the injector 34 and the rotation speed of the air compressor 61. The control unit 15 also controls the valve 32, the pressure reducing valve 33, the exhaust drain valve 42, the cooling fan 82, etc. The control unit 15 also acquires information on the measurement values ​​of the current sensor 16, the voltage sensor 17, and the pressure sensor 35.

[0037] (Operation of the fuel cell system) In the fuel cell system 1 configured as described above, in the hydrogen system 12, hydrogen gas supplied from the hydrogen gas supply passage 21 to the FC stack 11 is used for power generation in the FC stack 11, and then discharged from the FC stack 11 as hydrogen off-gas to the outside via the hydrogen off-gas discharge passage 22. In addition, in the air system 13, air supplied from the air supply passage 51 to the FC stack 11 is used for power generation in the FC stack 11, and then discharged from the FC stack 11 as air off-gas to the outside via the air off-gas discharge passage 52.

[0038] (Regarding a DCDC converter-less system) As shown in FIG. 1, in a fuel cell system 1 of this embodiment, an FC stack 11, a battery 101, and an inverter 102 (or a motor) are connected in parallel, forming a simple system configuration that does not have a DCDC converter. In other words, the fuel cell system 1 is a DCDC converter-less system. The DCDC converter is a device that converts FC voltage. The battery 101 is also connected to the FC stack 11 and charges with power generated by the FC stack 11. The battery 101 is also connected to the inverter 102 and supplies the charged power to the inverter 102.

[0039] As described above, the fuel cell system 1 of this embodiment is a DCDC converter-less system, and since the FC voltage is equal to (or nearly equal to) the voltage of the battery 101, the FC current depends on the voltage of the battery 101. In other words, the fuel cell system 1 supplies the power generated in the FC stack 11 to the battery 101 and the inverter 102 without converting the FC voltage.

[0040] In the fuel cell system 1, the FC voltage is thus equal to the voltage of the battery 101, so that the FC stack 11 generates electricity in a non-stop manner according to the voltage of the battery 101. When the SOC (i.e., the charging rate) of the battery 101 becomes high, the FC voltage is reduced below the voltage of the battery 101, and the non-stop power generation of the FC stack 11 is stopped intermittently.

[0041] <Regarding control performed when intermittently stopping power generation of FC stack> When intermittently stopping power generation of FC stack 11, it is possible to use an air valve (not shown) to block the supply of air to FC stack 11 and the discharge of air off-gas from FC stack 11, but having an air valve increases the number of parts, which increases the cost of fuel cell system 1 (i.e., the cost required for manufacturing and maintenance).

[0042] Therefore, in this embodiment, when power generation by the FC stack 11 is to be stopped intermittently, the supply of hydrogen gas from the injector 34 to the FC stack 11 is stopped, thereby causing power generation by the FC stack 11 to be stopped intermittently.

[0043] Specifically, when there is a request to intermittently stop power generation by the FC stack 11, the control unit 15 reduces the target fuel pressure (hereinafter referred to as the "target fuel pressure of the injector 34"), which is the target pressure of the hydrogen gas supplied (i.e., injected) by the injector 34, thereby intermittently stopping power generation by the FC stack 11.

[0044] In this way, the target fuel pressure of the injector 34 is reduced to intermittently stop power generation in the FC stack 11. However, if the flow rate of hydrogen gas supplied from the injector 34 to the FC stack 11 fluctuates and the FC voltage changes suddenly, a high load is placed on the FC stack 11, which may cause deterioration of the FC stack 11 depending on the condition of the FC stack 11.

[0045] Therefore, when reducing the target fuel pressure of the injector 34 , the control unit 15 changes the speed at which the target fuel pressure of the injector 34 is reduced based on the FC overvoltage, which is an index of the state of the FC stack 11 .

[0046] Here, "FC overvoltage" refers to the difference between the estimated value of FC voltage (hereinafter referred to as "estimated FC voltage value") corresponding to the measured value of FC current measured by current sensor 16 (hereinafter referred to as "measured FC current value") and the measured value of FC voltage (hereinafter referred to as "measured FC voltage value") measured by voltage sensor 17, and is an example of the "output voltage difference" of the present disclosure. Note that the estimated FC voltage value is the optimal FC voltage value for improving the power generation efficiency of FC stack 11 relative to the measured FC current, and is an example of the "optimum value of fuel cell output voltage" of the present disclosure.

[0047] For example, in the I-V characteristics of the FC stack 11, the measured FC current value, estimated FC voltage value, and measured FC voltage value are each expressed as shown in Fig. 2. At this time, the FC overvoltage is expressed as an FC voltage difference, which is the difference between the estimated FC voltage value and the measured FC voltage value, as shown in Fig. 2. The estimated FC voltage value is the value of the FC voltage estimated with respect to the measured FC current value when the FC stack 11 is new, and is estimated from the measured FC current value using, for example, the map in Fig. 3.

[0048] First Embodiment A first embodiment will now be described with respect to the control performed during the intermittent shutdown of power generation by the FC stack 11. In this embodiment, the control unit 15 performs the control shown in the flowchart of FIG.

[0049] As shown in FIG. 5, the control unit 15 determines whether or not there is a request to switch from continuous power generation to intermittent shutdown (step S1).

[0050] Then, when there is a request to switch from continuous power generation to intermittent stop (that is, during intermittent stop) (step S1: YES), the control unit 15 stops the air compressor 61 (step S2).

[0051] Next, the control unit 15 determines whether the FC overvoltage is less than the determination value (step S3).

[0052] The judgment value is calculated from the measured FC current value using, for example, the map of Fig. 4. In the map of Fig. 4, the judgment value changes in proportion to the measured FC current value, and for example, the judgment value is 3 V when the measured FC current value is 10 A, and the judgment value is 5 V when the measured FC current value is 30 A. The judgment value is an example of the "predetermined value" of the present disclosure.

[0053] Returning to the explanation of FIG. 5, if the FC overvoltage is less than the determination value (step S3: YES), the control unit 15 greatly (that is, quickly) reduces the target fuel pressure of the injector 34 (step S4).

[0054] In this way, the control unit 15 determines that when the FC overvoltage is small, the FC stack 11 is unlikely to deteriorate even if the flow rate of hydrogen gas supplied from the injector 34 to the FC stack 11 fluctuates and the FC voltage changes suddenly, and therefore sets the reduction rate of the target fuel pressure of the injector 34 to a first rate SP1 (for example, a rate at which the pressure is reduced by 5 kPa per second) which is faster than the second rate SP2 described below.

[0055] On the other hand, if the FC overvoltage is equal to or greater than the determination value (step S3: NO), the control unit 15 reduces the target fuel pressure of the injector 34 slowly (step S5).

[0056] In this way, the control unit 15 determines that when the FC overvoltage is large, the FC stack 11 is likely to deteriorate if the flow rate of hydrogen gas supplied from the injector 34 to the FC stack 11 fluctuates and the FC voltage changes suddenly, and therefore sets the reduction rate of the target fuel pressure of the injector 34 to a second rate SP2 (for example, a rate at which the pressure is reduced by 1 kPa per second) which is slower than the first rate SP1.

[0057] Next, the control unit 15 determines whether the measured FC current value is approximately equal to 0 A, that is, whether the measured FC current value is 0 A or approximately 0 A (step S6).

[0058] If the FC current measurement value is ≈0 A (step S6: YES), that is, if the FC current measurement value is 0 A or approximately 0 A, it is considered that power generation by the FC stack 11 has been intermittently stopped, and the control unit 15 sets the target fuel pressure of the injector 34 to atmospheric pressure (0 kPaG) or a slight negative pressure (e.g., -5 kPaG) (step S7).

[0059] In this way, when the measured FC current value becomes 0 A or approximately 0 A, the control unit 15 sets the target fuel pressure of the injector 34 to atmospheric pressure or approximately atmospheric pressure (specifically, a slight negative pressure).

[0060] On the other hand, if the FC current measurement value is not approximately 0 A (step S5: NO), that is, if the FC current measurement value is not 0 A or approximately 0 A, it is considered that power generation by the FC stack 11 is not intermittently stopped, and the control unit 15 performs the processing of step S3.

[0061] In step S1, if there is no request to switch from run-of-the-mill power generation to intermittent stop (i.e., run-of-the-mill power generation) (step S1: NO), the control unit 15 performs the process of step S6.

[0062] As described above, according to this embodiment, when there is a request to intermittently stop power generation by the FC stack 11, the control unit 15 reduces the target fuel pressure of the injector 34 to intermittently stop power generation by the FC stack 11. When reducing the target fuel pressure of the injector 34, the control unit 15 changes the rate at which the target fuel pressure of the injector 34 is reduced based on the FC overvoltage.

[0063] In this way, in this embodiment, the target fuel pressure of the injector 34 is reduced to stop the supply of hydrogen gas from the injector 34 to the FC stack 11, thereby intermittently stopping the power generation of the FC stack 11. Therefore, the power generation of the FC stack 11 can be intermittently stopped without cutting off the supply of air to the FC stack 11. Therefore, there is no need for a device (for example, a valve) to cut off the supply of air to the FC stack 11, so the number of parts in the fuel cell system 1 can be reduced, and the cost of the fuel cell system 1 can be reduced.

[0064] When the target fuel pressure of the injector 34 is reduced, the rate at which the target fuel pressure of the injector 34 is reduced is changed depending on the magnitude of the FC overvoltage, which is an indicator of the state of the FC stack 11. Therefore, the target fuel pressure of the injector 34 can be reduced while suppressing the occurrence of deterioration of the FC stack 11, thereby intermittently stopping power generation by the FC stack 11.

[0065] Specifically, when the FC overvoltage is less than the determination value, the control unit 15 sets the target fuel pressure reduction rate of the injector 34 to a first speed SP1 that is faster than the second speed SP2. On the other hand, when the FC overvoltage is equal to or greater than the determination value, the control unit 15 sets the target fuel pressure reduction rate of the injector 34 to a second speed SP2 that is slower than the first speed SP1.

[0066] In this way, when the FC overvoltage is equal to or greater than the judgment value, that is, when the FC stack 11 is in a state where it is susceptible to degradation, the target fuel pressure of the injector 34 is slowly reduced when intermittently stopping power generation in the FC stack 11. Therefore, when the FC stack 11 is in a state where it is susceptible to degradation, the FC voltage does not change suddenly, so it is possible to intermittently stop power generation in the FC stack 11 while suppressing the occurrence of degradation in the FC stack 11.

[0067] Furthermore, when the measured FC current value becomes 0 A or approximately 0 A, the control unit 15 sets the target fuel pressure of the injector 34 to atmospheric pressure or a slight negative pressure.

[0068] This prevents the hydrogen gas supply passage 21 from becoming negative pressure (i.e., a pressure lower than atmospheric pressure) when power generation in the FC stack 11 is stopped intermittently and the measured FC current value becomes 0 A or approximately 0 A. This prevents air from flowing from the air supply passage 51 into the hydrogen gas supply passage 21 via the FC stack 11. This prevents the catalyst (not shown) in the FC stack 11 from being deteriorated by air, and more specifically, prevents the catalyst in the FC stack 11 from being oxidized and deteriorated by air, resulting in a decrease in the power generation performance of the FC stack 11.

[0069] Second Example Next, a second example will be described regarding the control performed during intermittent shutdown of power generation by the FC stack 11. In this example, differences from the first example will be described, and explanations of commonalities with the first example will be omitted.

[0070] In this embodiment, the control unit 15 performs control as shown in the flowchart of FIG.

[0071] 6, different from FIG. 5, when the measured FC current value is approximately 0 A (step S16: YES), the control unit 15 feeds back the target fuel pressure of the injector 34 so that the FC voltage becomes a target voltage lower than the battery voltage (i.e., the voltage of the battery 101) (step S17). Note that the target FC voltage is set, for example, to (target FC voltage) = (battery voltage) - 10 V, and when the battery voltage is 40 V, the target FC voltage is set to 30 V.

[0072] As described above, according to this embodiment, when the FC current measurement value becomes 0 A or approximately 0 A, the control unit 15 controls the target fuel pressure of the injector 34 so that the FC voltage becomes a target voltage lower than the battery voltage.

[0073] In this way, in this embodiment, when power generation by the FC stack 11 is stopped intermittently, a target voltage is set for the FC voltage that prevents it from becoming an overvoltage (voltage drop) or a high voltage, and feedback control of the target fuel pressure of the injector 34 is performed accordingly. This makes it possible to avoid overvoltage (voltage drop) and high voltage for the FC voltage, thereby suppressing deterioration of the FC stack 11.

[0074] It should be noted that the above-described embodiments are merely examples and do not limit the present disclosure in any way. It goes without saying that various improvements and modifications are possible within the scope of the gist of the present disclosure.

[0075] For example, an ejector may be provided in the hydrogen gas supply passage 21 at a position downstream of the injector 34, i.e., at a position between the injector 34 and the FC stack 11 (more specifically, the pressure sensor 35). In this case, the ejector is an example of the "fuel supply device" of the present disclosure. The control unit 15 then reduces the target fuel pressure of the ejector to intermittently stop power generation of the FC stack 11. When reducing the target fuel pressure of the ejector, the control unit 15 changes the rate at which the target fuel pressure of the ejector is reduced based on the FC overvoltage.

[0076] Furthermore, although the above description has been given of a closed cathode system in which the cooling system 14 and the air system 13 are separate, the present disclosure can also be applied to an open cathode system in which the cooling system 14 and the air system 13 are shared.

[0077] REFERENCE SIGNS LIST 1 fuel cell system 11 FC stack 12 hydrogen system 13 air system 14 cooling system 15 control unit 16 current sensor 17 voltage sensor 21 hydrogen gas supply passage 34 injector 35 pressure sensor 51 air supply passage 61 air compressor 101 battery 102 inverter (or motor) SP1 first speed SP2 second speed

Claims

1. A fuel cell system having a fuel cell which generates electricity by receiving a supply of fuel gas and an oxidant gas, a fuel supply passage which supplies the fuel gas to the fuel cell, a fuel supply device which is provided in the fuel supply passage and which is driven to supply the fuel gas to the fuel cell, and an oxidant gas supply passage which supplies the oxidant gas to the fuel cell, wherein the fuel cell system is a system in which an output current of the fuel cell depends on the voltage of a battery which is charged with electric power generated by the fuel cell, and the system has a current sensor which measures the output current of the fuel cell, a voltage sensor which measures the output voltage of the fuel cell, and a control unit which controls the fuel supply device, wherein the difference between an optimal value of the output voltage of the fuel cell which corresponds to the measured value of the output current of the fuel cell measured by the current sensor and the measured value of the output voltage of the fuel cell measured by the voltage sensor is defined as an output voltage difference, the control unit: when there is a request to stop power generation of the fuel cell, reduces a target fuel pressure which is a target pressure of the fuel gas supplied by the fuel supply device to stop power generation of the fuel cell, and when reducing the target fuel pressure of the fuel supply device, changes the rate at which the target fuel pressure of the fuel supply device is reduced based on the output voltage difference, A fuel cell system comprising:

2. A fuel cell system according to claim 1, wherein the control unit sets the pressure reduction speed to a first speed when the output voltage difference is less than a predetermined value, and sets the pressure reduction speed to a second speed slower than the first speed when the output voltage difference is equal to or greater than the predetermined value.

3. A fuel cell system according to claim 1 or 2, characterized in that the control unit sets the target fuel pressure of the fuel supply device to atmospheric pressure or approximately atmospheric pressure when the measured value of the output current of the fuel cell measured by the current sensor becomes zero or approximately zero.

4. A fuel cell system according to claim 1 or 2, characterized in that the control unit controls the target fuel pressure of the fuel supply device so that the output voltage of the fuel cell becomes a target voltage lower than the voltage of the battery when the measured value of the output current of the fuel cell measured by the current sensor becomes zero or approximately zero.

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