Fuel cell system

Abstract

To provide a fuel cell system which can suppress change of the output voltage of a fuel battery caused when power generation of the fuel cell is stopped or started, thereby preventing generation of degradation of the fuel battery.SOLUTION: In a fuel cell system 1 according to an embodiment of the present disclosure, when the natural power generation of the FC stack 11 is stopped or is started, a control unit 15 adjusts the opening-closing rate of an entrance air valve 62 and an exit air valve 71 and / or the lifting rate of the number of rotations of an air compressor 61 according to an FC eddy voltage, which defines the difference between an FC voltage estimated value corresponding to an FC current measured value measured by a current sensor 16 and an FC voltage measured value measured by a voltage sensor 17.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present disclosure relates to a fuel cell system having a fuel cell that generates electricity by receiving supplies of a fuel gas and an oxidant gas.

Background Art

[0002] Patent Document 1 discloses a fuel cell system having a fuel cell that generates electricity by receiving supplies of a fuel gas and an oxidant gas. In this fuel cell system, an air valve (first valve or second valve) and an air compressor (reaction air supply unit) are controlled to adjust the flow rate of the oxidant gas.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the fuel cell system disclosed in Patent Document 1, when stopping or starting the power generation of the fuel cell, the supply amount of the oxidant gas to the fuel cell fluctuates by opening / closing the air valve or increasing / decreasing the rotational speed of the air compressor, so the output voltage of the fuel cell fluctuates. When the fluctuation of the output voltage of this fuel cell becomes large, the fluctuation of the load applied to the fuel cell becomes large, and there is a risk of deterioration of the fuel cell.

[0005] Therefore, the present disclosure has been made to solve the above - described problems, and an object thereof is to provide a fuel cell system that can suppress fluctuations in the output voltage of a fuel cell and suppress deterioration of the fuel cell when stopping or starting the power generation of the fuel cell.

Means for Solving the Problems

[0006] One aspect of the present disclosure made to solve the above problems is a fuel cell system that receives supplies of fuel gas and oxidant gas and generates electricity, a gas supply unit that supplies the oxidant gas to the fuel cell, and a flow rate control valve that controls the flow rate of the oxidant gas supplied to the fuel cell. The fuel cell system has a current sensor that measures the output current of the fuel cell, a voltage sensor that measures the output voltage of the fuel cell, and a control unit that controls the gas supply unit and the flow rate control valve. When a difference between an optimum value of the output voltage of the fuel cell corresponding to a measured value of the output current of the fuel cell measured by the current sensor and a 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 adjusts an opening / closing speed of the flow rate control valve and / or a rising / falling speed of the rotation speed of the gas supply unit according to the output voltage difference when stopping or starting the power generation of the fuel cell.

[0007] According to this aspect, when stopping or starting the power generation of the fuel cell, the opening / closing speed of the flow rate control valve and / or the rising / falling speed of the rotation speed of the gas supply unit are adjusted according to the state of the fuel cell. Thereby, when stopping or starting the power generation of the fuel cell, fluctuations in the output voltage of the fuel cell can be suppressed, and deterioration of the fuel cell can be suppressed from occurring.

[0008] In the above aspect, when the control unit stops the power generation of the fuel cell, if the output voltage difference is equal to or greater than a determination value, the control unit closes the flow rate control valve at a first speed, and if the output voltage difference is less than the determination value, the control unit closes the flow rate control valve at a second speed, and it is preferable that the first speed is slower than the second speed.

[0009] According to this aspect, when stopping the power generation of the fuel cell, if the difference between the optimum value and the measured value of the output voltage of the fuel cell is large, the closing speed of the flow control valve is slowed down. That is, when the state of the fuel cell is a state where the fuel cell is likely to deteriorate due to the fluctuation of the output voltage of the fuel cell caused by the closing operation of the flow control valve, the flow control valve is slowly closed. Thereby, the fluctuation of the output voltage of the fuel cell can be reduced, and the fluctuation of the load applied to the fuel cell can be reduced, so that the occurrence of deterioration of the fuel cell can be suppressed.

[0010] Also, when stopping the power generation of the fuel cell, if the difference between the optimum value and the measured value of the output voltage of the fuel cell is small, the closing speed of the flow control valve is increased. Thereby, the supply of the oxidant gas to the fuel cell can be stopped quickly, and the power generation of the fuel cell can be stopped quickly.

[0011] In the above aspect, when starting the power generation of the fuel cell, if the output voltage difference is equal to or greater than the determination value, the flow control valve is opened at the third speed, and if the output voltage difference is less than the determination value, the flow control valve is opened at the fourth speed, and it is preferable that the third speed is slower than the fourth speed.

[0012] According to this aspect, when starting the power generation of the fuel cell, if the difference between the optimum value and the measured value of the output voltage of the fuel cell is large, the opening speed of the flow control valve is slowed down. That is, when the state of the fuel cell is a state where the fuel cell is likely to deteriorate due to the fluctuation of the output voltage of the fuel cell caused by the opening operation of the flow control valve, the flow control valve is slowly opened. Thereby, the fluctuation of the output voltage of the fuel cell can be reduced, and the fluctuation of the load applied to the fuel cell can be reduced, so that the occurrence of deterioration of the fuel cell can be suppressed.

[0013] Also, when starting the power generation of the fuel cell, if the difference between the optimum value and the measured value of the output voltage of the fuel cell is small, the opening speed of the flow control valve is increased. Thereby, the supply of the oxidant gas to the fuel cell can be started quickly, and the power generation of the fuel cell can be started quickly.

[0014] In the above aspect, when the control unit stops the power generation of the fuel cell, if the output voltage difference is equal to or greater than the determination value, the rotation speed of the gas supply unit is decreased at a fifth speed, and if the output voltage difference is less than the determination value, the rotation speed of the gas supply unit is decreased at a sixth speed. It is preferable that the fifth speed is slower than the sixth speed.

[0015] According to this aspect, when stopping the power generation of the fuel cell, if the difference between the optimum value and the measured value of the output voltage of the fuel cell is large, the speed at which the rotation speed of the gas supply unit is decreased is slowed down. That is, when the state of the fuel cell is a state where there is a high possibility that the fuel cell will deteriorate due to fluctuations in the output voltage of the fuel cell caused by a decrease in the rotation speed of the gas supply unit, the rotation speed of the gas supply unit is slowly decreased. Thereby, fluctuations in the output voltage of the fuel cell can be reduced, and fluctuations in the load applied to the fuel cell can be reduced, so that deterioration of the fuel cell can be suppressed.

[0016] Also, when starting the power generation of the fuel cell, if the output voltage difference is equal to or greater than the determination value, the rotation speed of the gas supply unit is increased at a seventh speed, and if the output voltage difference is less than the determination value, the rotation speed of the gas supply unit is increased at an eighth speed. It is preferable that the seventh speed is slower than the eighth speed.

[0017] In the above aspect, when the control unit starts the power generation of the fuel cell, if the output voltage difference is equal to or greater than the determination value, the rotation speed of the gas supply unit is increased at a seventh speed, and if the output voltage difference is less than the determination value, the rotation speed of the gas supply unit is increased at an eighth speed. It is preferable that the seventh speed is slower than the eighth speed.

[0018] According to this aspect, when starting the power generation of the fuel cell, if the difference between the optimal value and the measured value of the output voltage of the fuel cell is large, the speed of increasing the rotation speed of the gas supply unit is slowed down. That is, when the state of the fuel cell is a state where the fuel cell is likely to deteriorate due to the fluctuation of the output voltage of the fuel cell caused by the increase in the rotation speed of the gas supply unit, the rotation speed of the gas supply unit is slowly increased. Thereby, the fluctuation of the output voltage of the fuel cell can be reduced, and the fluctuation of the load applied to the fuel cell can be reduced, so that the occurrence of deterioration of the fuel cell can be suppressed.

[0019] Also, when starting the power generation of the fuel cell, if the difference between the optimal value and the measured value of the output voltage of the fuel cell is small, the speed of increasing the rotation speed of the gas supply unit is increased. Thereby, the supply of the oxidant gas to the fuel cell can be started quickly, and the power generation of the fuel cell can be started quickly.

Effect of the Invention

[0020] According to the fuel cell system of the present disclosure, when stopping or starting the power generation of the fuel cell, the fluctuation of the output voltage of the fuel cell can be suppressed, and the occurrence of deterioration of the fuel cell can be suppressed.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

[0022] Embodiments of the fuel cell system of the present disclosure will be described.

[0023] <Regarding the outline of the fuel cell system> First, the outline of the fuel cell system 1 of the present embodiment will be described. The fuel cell system 1 is a system mounted on a fuel cell vehicle and supplies power to its drive motor (not shown).

[0024] (Regarding the schematic configuration of the fuel cell system) As shown in FIG. 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. Note that the FC stack 11 is an example of the "fuel cell" of the present disclosure.

[0025] The FC stack 11 generates power by receiving supplies of fuel gas and oxidant gas. In the present embodiment, the fuel gas is hydrogen gas and the oxidant gas is air (i.e., atmospheric air). That is, the FC stack 11 generates power by receiving the supply of hydrogen gas from the hydrogen system 12 and the supply of air from the air system 13. Then, the power generated by the FC stack 11 is supplied to the battery 101 and the inverter 102 (or the motor).

[0026] In addition, a current sensor 16 and a voltage sensor 17 are provided in the fuel cell system 1. The current sensor 16 is a sensor that measures the output current of the FC stack 11 (that is, the current of the 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 (that is, the voltage of the power generated by the FC stack 11, hereinafter referred to as "FC voltage").

[0027] The hydrogen system 12 is provided on the anode side of the FC stack 11. This hydrogen system 12 includes a hydrogen filling passage 20, a hydrogen gas supply passage 21, a hydrogen off-gas discharge passage 22, and a hydrogen circulation passage 23.

[0028] The hydrogen filling passage 20 is a passage for filling hydrogen gas from the filling port 30 into the hydrogen tank 31. The hydrogen gas supply passage 21 is a passage for supplying hydrogen gas from the hydrogen tank 31 to the FC stack 11.

[0029] The hydrogen off-gas discharge passage 22 is a passage through which hydrogen off-gas, which is hydrogen gas not used for power generation from the FC stack 11, is discharged. The hydrogen circulation passage 23 is a passage for circulating at least a part of the hydrogen off-gas from the hydrogen off-gas discharge passage 22 to the hydrogen gas supply passage 21.

[0030] The hydrogen system 12 includes a valve 32, a pressure reducing valve 33, an injector 34, and an ejector 35 in the hydrogen gas supply passage 21 in order from the hydrogen tank 31 side.

[0031] The valve 32 is a valve that switches the supply and cutoff of hydrogen gas from the hydrogen tank 31 to the hydrogen gas supply passage 21, or switches the supply and cutoff of 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. The injector 34 is a valve that injects hydrogen gas toward the ejector 35. The ejector 35 is a device that combines the hydrogen gas introduced from the injector 34 with the hydrogen off-gas sucked from the hydrogen off-gas discharge passage 22 and circulates it to the FC stack 11.

[0032] Further, the hydrogen system 12 includes a gas-liquid separator 41 and an exhaust drain valve 42 in the hydrogen off-gas discharge passage 22.

[0033] The gas-liquid separator 41 is a device that separates moisture in the hydrogen off-gas. The gas-liquid separator 41 is connected to the ejector 35 via the hydrogen circulation passage 23. 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.

[0034] The air system 13 is provided on the cathode side of the FC stack 11. This air system 13 includes an air supply passage 51 and an air off-gas discharge passage 52.

[0035] The air supply passage 51 is a passage for supplying air from the outside of the fuel cell system 1 to the FC stack 11. The air off-gas discharge passage 52 is a passage through which the air off-gas, which is the air not used for power generation from the FC stack 11, is discharged.

[0036] The air system 13 includes an air compressor 61 and an inlet air valve 62 in the air supply passage 51. The air compressor 61 is a device that supplies air to the FC stack 11. The inlet air valve 62 is a valve that controls the flow rate of the air supplied to the FC stack 11. Note that the air compressor 61 is an example of the "gas supply unit" of the present disclosure. Also, the inlet air valve 62 is an example of the "flow rate control valve" of the present disclosure.

[0037] Further, the air system 13 includes an outlet air valve 71 in the air off-gas discharge passage 52. The outlet air valve 71 is a valve that controls the flow rate of the air off-gas discharged from the FC stack 11 to the air off-gas discharge passage 52.

[0038] The cooling system 14 is a system for cooling 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 for cooling the cooling water flowing through the cooling water passage 81.

[0039] 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 that stores a control program and control data processed by the CPU, and a RAM used as various work areas for control processing, and an input / output interface unit. Then, the control unit 15 performs various controls of the fuel cell system 1 according to the control program stored in the storage unit.

[0040] Specifically, the control unit 15 performs, for example, rotation speed control of the air compressor 61 and opening / closing control of the opening degrees of the inlet air valve 62 and the outlet air valve 71. In addition, the control unit 15 also performs controls of other valves such as the valve 32, the pressure reducing valve 33, the injector 34, the exhaust and drainage valve 42, and the cooling fan 82.

[0041] (Regarding the operation of the fuel cell system) In the fuel cell system 1 configured as described above, in the hydrogen system 12, the 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, as hydrogen off-gas, is discharged to the outside through the hydrogen off-gas discharge passage 22, or is sucked into the ejector 35 through the hydrogen off-gas discharge passage 22 and the hydrogen circulation passage 23. Also, in the air system 13, the 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, as air off-gas, is discharged to the outside through the air off-gas discharge passage 52.

[0042] (Regarding the system without a DCDC converter) As shown in FIG. 1, in the fuel cell system 1 of the present embodiment, the FC stack 11, the battery 101, and the inverter 102 (or motor) are connected in parallel, forming a simple system configuration without a DCDC converter. That is, the fuel cell system 1 is a system without a DCDC converter. Note that the DCDC converter is a device that converts the FC voltage.

[0043] Thus, the fuel cell system 1 of the present embodiment is a system without a DCDC converter, and since the FC voltage becomes equal to (or approximately equal to) the voltage of the battery 101, the FC current depends on the voltage of the battery 101. In other words, for the power generated by the FC stack 11 in the fuel cell system 1, the FC voltage is not converted and is supplied to the battery 101 and the inverter 102.

[0044] And in the fuel cell system 1, since the FC voltage becomes equal to the voltage of the battery 101 in this way, the FC stack 11 performs natural power generation according to the voltage of the battery 101 during power generation. When the SOC (i.e., charge rate) of the battery 101 increases, the inlet air valve 62 and the outlet air valve 71 are closed to lower the FC voltage below the voltage of the battery 101, and the natural power generation of the FC stack 11 is intermittently stopped.

[0045] <Regarding the First Embodiment (Opening and Closing Control of Air Valve)> When intermittently stopping or starting the natural power generation of the FC stack 11, by closing or opening the inlet air valve 62 and the outlet air valve 71, the amount of air supplied to the FC stack 11 fluctuates, so the FC voltage fluctuates. And when this fluctuation of the FC voltage becomes large, the fluctuation of the load applied to the FC stack 11 becomes large, and there is a possibility of deterioration of the FC stack 11.

[0046] Therefore, in this embodiment, when intermittently stopping or starting the natural power generation of the FC stack 11, the control unit 15 adjusts the opening and closing speeds of the inlet air valve 62 and the outlet air valve 71 according to the state of the FC stack 11.

[0047] Specifically, when intermittently stopping or starting the natural power generation of the FC stack 11, the control unit 15 adjusts the opening and closing speeds of the inlet air valve 62 and the outlet air valve 71 according to the magnitude of the FC overvoltage.

[0048] Here, the "FC overvoltage" is the difference between the estimated value of the FC voltage (hereinafter referred to as the "FC voltage estimated value") corresponding to the measured value of the FC current measured by the current sensor 16 (hereinafter referred to as the "FC current measured value") and the measured value of the FC voltage measured by the voltage sensor 17 (hereinafter referred to as the "FC voltage measured value"), and is an example of the "output voltage difference" of the present disclosure. The FC voltage estimated value is an example of the "optimal value of the output voltage of the fuel cell" of the present disclosure.

[0049] For example, in the I-V characteristics of the FC stack 11, the FC current measured value, the FC voltage estimated value, and the FC voltage measured value are respectively represented as shown in FIG. 2. And at this time, as shown in FIG. 2, the FC overvoltage is represented as the FC voltage difference, which is the difference between the FC voltage estimated value and the FC voltage measured value. The FC voltage estimated value is estimated from the FC current measured value using, for example, the map of FIG. 3.

[0050] In this embodiment, when intermittently stopping the natural power generation of the FC stack 11, the control unit 15 performs the control shown in the flowchart in FIG. 5.

[0051] As shown in FIG. 5, the control unit 15 determines whether there is a switching request from natural power generation to intermittent stop (FC current = 0) (step S1).

[0052] When there is a request to switch from power generation in the natural course to intermittent stop (i.e., during intermittent stop) (step S1: YES), the control unit 15 determines whether the FC overvoltage is less than the determination value (step S2).

[0053] Note that the determination value is calculated from the measured FC current value using, for example, the map in FIG. 4. Also, in the map of FIG. 4, the determination value changes in proportion to the measured FC current value. For example, when the measured FC current value is 10 A, the determination value is 3 V, and when the measured FC current value is 30 A, the determination value is 5 V.

[0054] Then, returning to the description of FIG. 5, when the FC overvoltage is less than the determination value (step S2: YES), the control unit 15 increases the closing speed of the inlet air valve 62 and the outlet air valve 71 (denoted as "air valve" in FIG. 5) (step S3).

[0055] In this way, when the control unit 15 intermittently stops the power generation in the natural course of the FC stack 11, if the FC overvoltage is less than the determination value, the control unit 15 closes the inlet air valve 62 and the outlet air valve 71 at a second speed faster than the first speed described later. That is, when the control unit 15 intermittently stops the power generation in the natural course of the FC stack 11, if the state of the FC stack 11 is such that there is a low possibility of deterioration of the FC stack 11 due to fluctuations in the FC voltage caused by the closing operations of the inlet air valve 62 and the outlet air valve 71, the control unit 15 quickly closes the inlet air valve 62 and the outlet air valve 71. Note that the second speed is, for example, a speed at which the opening degree is decreased by 5° per second.

[0056] As a result, the supply of air to the FC stack 11 can be quickly stopped, and the power generation in the natural course of the FC stack 11 can be quickly intermittently stopped.

[0057] On the other hand, when the FC overvoltage is equal to or greater than the determination value in step S2 (step S2: NO), the control unit 15 decreases the closing speed of the inlet air valve 62 and the outlet air valve 71 (step S4).

[0058] In this way, when the control unit 15 intermittently stops the natural power generation of the FC stack 11, if the FC overvoltage is large, the inlet air valve 62 and the outlet air valve 71 are closed at a first speed slower than the above-described second speed. Here, when the FC overvoltage is large, while the FC voltage is decreasing, the FC current is increasing, and due to the fluctuation of the FC voltage, the FC current fluctuates greatly, and there is a high possibility that the FC stack 11 deteriorates. Therefore, when the control unit 15 intermittently stops the natural power generation of the FC stack 11, if the state of the FC stack 11 is such that there is a high possibility that the FC stack 11 deteriorates due to the fluctuation of the FC voltage caused by the closing operation of the inlet air valve 62 and the outlet air valve 71, the inlet air valve 62 and the outlet air valve 71 are slowly closed. Note that the first speed is, for example, a speed at which the opening degree is decreased by 1° per second.

[0059] Thereby, when intermittently stopping the natural power generation of the FC stack 11, even if the FC overvoltage is large, the inlet air valve 62 and the outlet air valve 71 can be slowly closed to reduce the fluctuation of the FC voltage. Therefore, the fluctuation of the load applied to the FC stack 11 can be reduced, and thus the occurrence of deterioration of the FC stack 11 can be suppressed.

[0060] In particular, the fuel cell system 1 of the present embodiment is a system without a DCDC converter, and the FC current depends on the voltage of the battery 101. Therefore, for example, when the battery 101 deteriorates and the voltage of the battery 101 decreases, even if the FC voltage decreases and the FC overvoltage increases, the inlet air valve 62 and the outlet air valve 71 can be slowly closed to reduce the fluctuation of the FC voltage. Therefore, even if the fuel cell system 1 is a system without a DCDC converter, the fluctuation of the load applied to the FC stack 11 can be reduced, and thus the occurrence of deterioration of the FC stack 11 can be suppressed.

[0061] Further, when starting the natural power generation of the FC stack 11, the control unit 15 performs control of the content shown in the flowchart in FIG. 6.

[0062] As shown in FIG. 6, the control unit 15 determines whether there is a request to switch from intermittent stop (FC current = 0) to natural power generation (step S11).

[0063] And when there is a request to switch from intermittent stop to natural power generation (step S11: YES) (that is, at the start of natural power generation), the control unit 15 determines whether the FC overvoltage is less than the determination value (step S12).

[0064] And when the FC overvoltage is less than the determination value (step S12: YES), the control unit 15 increases the valve opening speed of the inlet air valve 62 and the outlet air valve 71 (step S13).

[0065] In this way, when starting the natural power generation of the FC stack 11, if the FC overvoltage is small, the control unit 15 opens the inlet air valve 62 and the outlet air valve 71 at a fourth speed faster than the third speed described later. That is, when starting the natural power generation of the FC stack 11, if the state of the FC stack 11 is a state where the possibility of deterioration of the FC stack 11 due to the fluctuation of the FC voltage caused by the valve opening operation of the inlet air valve 62 and the outlet air valve 71 is low, the inlet air valve 62 and the outlet air valve 71 are quickly opened. The fourth speed is, for example, a speed at which the opening degree is increased by 5° per second.

[0066] Thereby, the supply of air to the FC stack 11 can be started quickly, and the natural power generation of the FC stack 11 can be started quickly.

[0067] On the other hand, when the FC overvoltage is greater than or equal to the determination value in step S12 (step S12: NO), the control unit 15 decreases the valve opening speed of the inlet air valve 62 and the outlet air valve 71 (step S14).

[0068] In this way, when the control unit 15 starts the natural power generation of the FC stack 11, if the FC overvoltage is large, the inlet air valve 62 and the outlet air valve 71 are opened at the third speed slower than the fourth speed described above. That is, when the control unit 15 starts the natural power generation of the FC stack 11, if the state of the FC stack 11 is such that the FC stack 11 is likely to deteriorate due to the fluctuation of the FC voltage caused by the opening operation of the inlet air valve 62 and the outlet air valve 71, the inlet air valve 62 and the outlet air valve 71 are slowly opened. The third speed is, for example, a speed at which the opening degree is increased by 1° per second.

[0069] Thereby, when starting the natural power generation of the FC stack 11, even if the FC overvoltage is large, the inlet air valve 62 and the outlet air valve 71 can be slowly opened, the fluctuation of the FC voltage can be reduced, and the fluctuation of the load applied to the FC stack 11 can be reduced, so that the deterioration of the FC stack 11 can be suppressed.

[0070] In particular, the fuel cell system 1 of the present embodiment is a system without a DCDC converter, and the FC current depends on the voltage of the battery 101. Therefore, for example, when the battery 101 deteriorates and the voltage of the battery 101 decreases, even if the FC voltage decreases and the FC overvoltage increases, the inlet air valve 62 and the outlet air valve 71 can be slowly opened to reduce the fluctuation of the FC voltage. Therefore, even if the fuel cell system 1 is a system without a DCDC converter, the fluctuation of the load applied to the FC stack 11 can be reduced, so that the deterioration of the FC stack 11 can be suppressed.

[0071] <Regarding the Second Embodiment (Rotation Speed Control of the Air Compressor)> In addition, when intermittently stopping or starting the natural power generation of the FC stack 11, the rotation speed of the air compressor 61 is increased or decreased, so the amount of air supplied to the FC stack 11 fluctuates, and the FC voltage fluctuates. When this fluctuation of the FC voltage becomes large, the fluctuation of the load applied to the FC stack 11 becomes large, and there is a risk of deterioration of the FC stack 11.

[0072] Therefore, in this embodiment, when intermittently stopping or starting the natural power generation of the FC stack 11, the control unit 15 adjusts the rising and falling speed of the rotation speed of the air compressor 61 according to the state of the FC stack 11.

[0073] Specifically, when intermittently stopping or starting the natural power generation of the FC stack 11, the control unit 15 adjusts the rising and falling speed of the rotation speed of the air compressor 61 according to the magnitude of the FC overvoltage.

[0074] More specifically, when intermittently stopping the natural power generation of the FC stack 11, the control unit 15 performs control of the content shown in the flowchart in FIG. 7.

[0075] As shown in FIG. 7, different from FIG. 5, in step S22, when the FC overvoltage is less than the determination value (step S22: YES), the control unit 15 increases the falling speed of the rotation speed of the air compressor 61 (step S23).

[0076] In this way, when intermittently stopping the natural power generation of the FC stack 11, when the FC overvoltage is small, the control unit 15 decreases the rotation speed of the air compressor 61 at a sixth speed faster than the fifth speed described later. That is, when intermittently stopping the natural power generation of the FC stack 11, when the state of the FC stack 11 is a state where the FC stack 11 is less likely to deteriorate due to the fluctuation of the FC voltage caused by the decrease in the rotation speed of the air compressor 61, the control unit 15 quickly decreases the rotation speed of the air compressor 61. The sixth speed is, for example, a speed at which the rotation speed is decreased by 1000 rpm per second.

[0077] Accordingly, when intermittently stopping the natural power generation of the FC stack 11, the supply of air to the FC stack 11 can be quickly stopped, and the natural power generation of the FC stack 11 can be quickly intermittently stopped.

[0078] On the other hand, when the FC overvoltage is equal to or greater than the determination value in step S22 (step S22: NO), the control unit 15 slows down the falling speed of the rotation speed of the air compressor 61 (step S24).

[0079] In this way, when intermittently stopping the natural power generation of the FC stack 11, when the FC overvoltage is large, the control unit 15 lowers the rotation speed of the air compressor 61 at a fifth speed slower than the sixth speed described above. That is, when intermittently stopping the natural power generation of the FC stack 11, when the state of the FC stack 11 is a state in which the FC stack 11 is likely to deteriorate due to fluctuations in the FC voltage caused by the decrease in the rotation speed of the air compressor 61, the control unit 15 slowly decreases the rotation speed of the air compressor 61. The fifth speed is, for example, a speed at which the rotation speed is decreased by 100 rpm per second.

[0080] Accordingly, when intermittently stopping the natural power generation of the FC stack 11, even when the FC overvoltage is large, the rotation speed of the air compressor 61 can be slowly decreased, the fluctuations in the FC voltage can be reduced, and the fluctuations in the load applied to the FC stack 11 can be reduced. Therefore, deterioration of the FC stack 11 can be suppressed.

[0081] Also, similar to the first embodiment, even if the fuel cell system 1 is a system without a DCDC converter, fluctuations in the load applied to the FC stack 11 can be reduced, so that deterioration of the FC stack 11 can be suppressed.

[0082] Also, when starting the natural power generation of the FC stack 11, the control unit 15 performs control of the content shown in the flowchart in FIG. 8.

[0083] As shown in FIG. 8, different from FIG. 6, in step S32, when the FC overvoltage is less than the determination value (step S32: YES), the control unit 15 increases the rising speed of the rotation speed of the air compressor 61 (step S33).

[0084] In this way, when the control unit 15 starts the natural power generation of the FC stack 11, if the FC overvoltage is small, the control unit 15 increases the rotation speed of the air compressor 61 at an eighth speed faster than the seventh speed described later. That is, when the control unit 15 starts the natural power generation of the FC stack 11, if the state of the FC stack 11 is a state where the FC stack 11 is less likely to deteriorate due to the change in the FC voltage caused by the increase in the rotation speed of the air compressor 61, the control unit 15 quickly increases the rotation speed of the air compressor 61. The eighth speed is, for example, a speed at which the rotation speed increases by 1000 rpm per second.

[0085] Thereby, the supply of air to the FC stack 11 can be started quickly, and the natural power generation of the FC stack 11 can be started quickly.

[0086] On the other hand, in step S32, when the FC overvoltage is equal to or greater than the determination value (step S32: NO), the control unit 15 slows down the rising speed of the rotation speed of the air compressor 61 (step S34).

[0087] In this way, when the control unit 15 starts the natural power generation of the FC stack 11, if the FC overvoltage is large, the control unit 15 increases the rotation speed of the air compressor 61 at a seventh speed slower than the eighth speed described above. That is, when the control unit 15 starts the natural power generation of the FC stack 11, if the state of the FC stack 11 is a state where the FC stack 11 is likely to deteriorate due to the change in the FC voltage caused by the increase in the rotation speed of the air compressor 61, the control unit 15 slowly increases the rotation speed of the air compressor 61. The seventh speed is, for example, a speed at which the rotation speed increases by 100 rpm per second.

[0088] Thus, when starting the natural power generation of the FC stack 11, even if the FC overvoltage is large, the rotation speed of the air compressor 61 can be slowly increased to reduce the fluctuation of the FC voltage and the fluctuation of the load applied to the FC stack 11, so that the deterioration of the FC stack 11 can be suppressed.

[0089] Also, similar to the first embodiment, even if the fuel cell system 1 is a system without a DCDC converter, the fluctuation of the load applied to the FC stack 11 can be reduced, so that the deterioration of the FC stack 11 can be suppressed.

[0090] Note 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 without departing from the gist thereof.

[0091] For example, the control unit 15 may perform the controls of the first embodiment and the second embodiment simultaneously.

[0092] Also, in the above description, the fuel cell system 1 is assumed to be a system without a DCDC converter, but it is not limited thereto and may be a system having a DCDC converter. And at this time, as shown in FIGS. 5 to 8, when stopping or starting the power generation of the FC stack 11, the control unit 15 may adjust the opening / closing speed of the inlet air valve 62 and / or the outlet air valve 71 and / or the rising / falling speed of the rotation speed of the air compressor 61 according to the magnitude of the FC overvoltage.

[0093] Also, in the control of the first embodiment, the control unit 15 may perform only the opening / closing control of the inlet air valve 62. Also, the air system 13 may not include the outlet air valve 71 and may include only the inlet air valve 62.

[0094] Also, the determination values in FIGS. 5, 6, 7, and 8 may be different values, such as the first determination value, the second determination value, the third determination value, and the fourth determination value, respectively.

Description of Reference Numerals

[0095] 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 51 Air supply passage 52 Air off-gas discharge passage 61 Air compressor 62 Inlet air valve 71 Outlet air valve 101 Battery 102 Inverter (or motor)

Claims

1. A fuel cell that generates electricity upon receiving a supply of fuel gas and oxidant gas, a gas supply unit that supplies the oxidant gas to the fuel cell, a flow control valve that controls the flow rate of the oxidant gas supplied to the fuel cell, In a fuel cell system having: a current sensor that measures the output current of the fuel cell, a voltage sensor that measures the output voltage of the fuel cell, a control unit that controls the gas supply unit and the flow control valve, When defining the difference between the optimum 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 as the output voltage difference, When stopping or starting the power generation of the fuel cell, the control unit adjusts the opening / closing speed of the flow control valve and / or the rising / falling speed of the rotation speed of the gas supply unit according to the output voltage difference. A fuel cell system characterized by the above.

2. In the fuel cell system according to Claim 1, the control unit: When stopping the power generation of the fuel cell, If the output voltage difference is equal to or greater than the determination value, the flow control valve is closed at the first speed, If the output voltage difference is less than the determination value, the flow control valve is closed at the second speed, The first speed is slower than the second speed. A fuel cell system characterized by the above.

3. In the fuel cell system according to Claim 1, the control unit: When starting the power generation of the fuel cell, If the output voltage difference is equal to or greater than the determination value, the flow control valve is opened at the third speed, If the output voltage difference is less than the determination value, the flow control valve is opened at the fourth speed, The third speed is slower than the fourth speed. A fuel cell system characterized by the above.

4. In the fuel cell system according to Claim 1, the control unit: When stopping the power generation of the fuel cell, If the output voltage difference is equal to or greater than the determination value, the rotation speed of the gas supply unit is decreased at the fifth speed, If the output voltage difference is less than the determination value, the rotation speed of the gas supply unit is decreased at the sixth speed, The fifth speed is slower than the sixth speed. A fuel cell system characterized by the above.

5. In the fuel cell system according to Claim 1, the control unit: When starting the power generation of the fuel cell, If the output voltage difference is equal to or greater than the determination value, the rotation speed of the gas supply unit is increased at the seventh speed, When the output voltage difference is less than the determination value, increase the rotation speed of the gas supply unit at the eighth speed, wherein the seventh speed is slower than the eighth speed, A fuel cell system characterized by the above.

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