Fuel cell system

Abstract

In this fuel cell system, when the difference between an optimal value of an output voltage of a fuel cell corresponding to a measurement value of an output current of the fuel cell measured by a current sensor and a measurement value of an output voltage of the fuel cell measured by a voltage sensor is defined as an output voltage difference, a control unit adjusts, when stopping or starting power generation of the fuel cell and on the basis of the output voltage difference, the opening / closing speed of a flow rate control valve and / or the increasing / decreasing rate of the rotation speed of a gas supply unit.

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 fuel cell that generates electricity by receiving a supply of fuel gas and an oxidant gas, and in this fuel cell system, the flow rate of the oxidant gas is adjusted by controlling air valves (first valve and second valve) and an air compressor (reaction air supply unit).

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

[0004] In the fuel cell system disclosed in Patent Document 1, when power generation by the fuel cell is stopped or started, the amount of oxidant gas supplied to the fuel cell fluctuates by opening and closing the air valve or increasing or decreasing the rotation speed of the air compressor, which causes fluctuations in the output voltage of the fuel cell. If this fluctuation in the output voltage of the fuel cell becomes large, the fluctuation in the load on the fuel cell also becomes large, which may cause deterioration 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 suppress fluctuations in the output voltage of a fuel cell when stopping or starting power generation of the fuel cell, thereby suppressing deterioration of the fuel cell.

[0006] One aspect of the present disclosure made to solve the above problem is a fuel cell system having a fuel cell that generates electricity by receiving a supply of fuel gas and an oxidant gas, a gas supply unit that supplies the oxidant gas to the fuel cell, and a flow control valve that controls the flow rate of the oxidant gas supplied to the fuel cell, the system further comprising 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 control valve, wherein when an output voltage difference is defined as the difference between an 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, the control unit adjusts the opening / closing speed of the flow control valve and / or the speed at which the rotational speed of the gas supply unit is increased or decreased in accordance with the output voltage difference when stopping or starting power generation of the fuel cell.

[0007] According to this aspect, when power generation by the fuel cell is stopped or started, the opening / closing speed of the flow control valve and / or the rate at which the rotational speed of the gas supply unit is increased or decreased is adjusted according to the state of the fuel cell, thereby suppressing fluctuations in the output voltage of the fuel cell and preventing deterioration of the fuel cell when power generation by the fuel cell is stopped or started.

[0008] In the above aspect, when the control unit stops power generation of the fuel cell, if the output voltage difference is equal to or greater than a judgment value, it closes the flow control valve at a first speed, and if the output voltage difference is less than the judgment value, it closes the flow 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 power generation by the fuel cell is stopped, if the difference between the optimum value and the measured value of the fuel cell's output voltage is large, the speed at which the flow control valve is closed is slowed. In other words, if the state of the fuel cell is such that there is a high possibility that the fuel cell will deteriorate due to fluctuations in the fuel cell's output voltage caused by the closing operation of the flow control valve, the flow control valve is closed slowly. This reduces fluctuations in the fuel cell's output voltage and reduces fluctuations in the load on the fuel cell, thereby preventing fuel cell deterioration.

[0010] Furthermore, when stopping power generation by the fuel cell, if the difference between the optimum value and the measured value of the fuel cell output voltage is small, the speed at which the flow control valve is closed is increased, thereby quickly stopping the supply of oxidant gas to the fuel cell and quickly stopping power generation by the fuel cell.

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

[0012] According to this aspect, when starting power generation of the fuel cell, if there is a large difference between the optimum value and the measured value of the fuel cell's output voltage, the speed at which the flow control valve is opened is slowed. In other words, if the state of the fuel cell is such that there is a high possibility that the fuel cell will deteriorate due to fluctuations in the fuel cell's output voltage caused by the opening operation of the flow control valve, the flow control valve is opened slowly. This reduces fluctuations in the fuel cell's output voltage and reduces fluctuations in the load on the fuel cell, thereby preventing fuel cell deterioration.

[0013] Furthermore, when starting power generation in the fuel cell, if the difference between the optimum value and the measured value of the fuel cell output voltage is small, the speed at which the flow control valve is opened is increased, thereby quickly starting the supply of oxidant gas to the fuel cell and quickly starting power generation in the fuel cell.

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

[0015] According to this aspect, when power generation by the fuel cell is stopped, if the difference between the optimum value and the measured value of the fuel cell's output voltage is large, the rate at which the rotation speed of the gas supply unit is reduced is slowed. In other words, if the state of the fuel cell is such that there is a high possibility that the fuel cell will deteriorate due to fluctuations in the fuel cell's output voltage caused by a drop in the rotation speed of the gas supply unit, the rotation speed of the gas supply unit is slowly reduced. This reduces fluctuations in the fuel cell's output voltage and fluctuations in the load on the fuel cell, thereby suppressing fuel cell deterioration.

[0016] Furthermore, when power generation by the fuel cell is stopped, if the difference between the optimum value and the measured value of the fuel cell output voltage is small, the rate at which the rotation speed of the gas supply unit is reduced is increased, thereby quickly stopping the supply of oxidant gas to the fuel cell and quickly stopping power generation by the fuel cell.

[0017] In the above aspect, when the control unit starts generating electricity from the fuel cell, if the output voltage difference is greater than or equal to a judgment value, it increases the rotation speed of the gas supply unit at a seventh speed, and if the output voltage difference is less than the judgment value, it increases the rotation speed of the gas supply unit at an eighth speed, and it is preferable that the seventh speed is slower than the eighth speed.

[0018] According to this aspect, when starting power generation of the fuel cell, if there is a large difference between the optimum value and the measured value of the fuel cell's output voltage, the rate at which the rotation speed of the gas supply unit is increased is slowed. In other words, if the state of the fuel cell is such that there is a high possibility that the fuel cell will deteriorate due to fluctuations in the fuel cell's output voltage caused by an increase in the rotation speed of the gas supply unit, the rotation speed of the gas supply unit is increased slowly. This reduces fluctuations in the fuel cell's output voltage and reduces fluctuations in the load on the fuel cell, thereby suppressing fuel cell deterioration.

[0019] Furthermore, when starting power generation in the fuel cell, if the difference between the optimum value and the measured value of the fuel cell output voltage is small, the rate at which the rotation speed of the gas supply unit is increased is increased, thereby quickly starting the supply of oxidant gas to the fuel cell and quickly starting power generation in the fuel cell.

[0020] According to the fuel cell system of the present disclosure, when power generation by the fuel cell is stopped or started, fluctuations in the output voltage of the fuel cell are suppressed, and deterioration of the fuel cell can be suppressed.

[0021] 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 defining 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 defining the relationship between a measured FC current value and a judgment value. FIG. 5 is a flowchart showing the details of the control of closing the air valve during intermittent stop performed in the first embodiment. FIG. 6 is a flowchart showing the details of the control of opening the air valve at the start of run-of-the-mill power generation performed in the first embodiment. FIG. 7 is a flowchart showing the details of the control of decreasing the rotation speed of the air compressor during intermittent stop performed in the second embodiment. FIG. 8 is a flowchart showing the details of the control of increasing the rotation speed of the air compressor at the start of run-of-the-mill power generation performed in the second embodiment.

[0022] An embodiment of a fuel cell system according to the present disclosure will be described.

[0023] <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).

[0024] 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.

[0025] 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).

[0026] 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").

[0027] 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, 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 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.

[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, is discharged from the FC stack 11. The hydrogen circulation passage 23 is a passage for circulating at least a portion 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 this order from the hydrogen tank 31 side in the hydrogen gas supply passage 21.

[0031] The valve 32 switches between supplying and cutting off hydrogen gas from the hydrogen tank 31 to the hydrogen gas supply passage 21, and between supplying and cutting off 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 the combined hydrogen gas to the FC stack 11.

[0032] 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 .

[0033] The gas-liquid separator 41 is a device that separates moisture from the hydrogen off-gas and 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. The 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 to the FC stack 11 from outside the fuel cell system 1. 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.

[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 air supplied to the FC stack 11. The air compressor 61 is an example of the "gas supply unit" in the present disclosure. The inlet air valve 62 is an example of the "flow rate control valve" in the present disclosure.

[0037] The air system 13 also 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 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 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.

[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 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.

[0040] Specifically, the control unit 15 controls, for example, the rotation speed of the air compressor 61 and the opening and closing of the inlet air valve 62 and the outlet air valve 71. The control unit 15 also controls the valve 32, the pressure reducing valve 33, the injector 34, the exhaust drain valve 42, the cooling fan 82, and the like.

[0041] (Operation of 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 as hydrogen off-gas from the FC stack 11 to the outside via the hydrogen off-gas discharge passage 22, or is sucked into the ejector 35 via the hydrogen off-gas discharge passage 22 and the hydrogen circulation passage 23. 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 as air off-gas from the FC stack 11 to the outside via the air off-gas discharge passage 52.

[0042] (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 the FC voltage.

[0043] 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.

[0044] In the fuel cell system 1, the FC voltage becomes equal to the voltage of the battery 101 in this way, and so the FC stack 11 generates electricity in a spontaneous manner according to the voltage of the battery 101. When the SOC (i.e., the charging rate) of the battery 101 becomes high, the inlet air valve 62 and outlet air valve 71 are closed to reduce the FC voltage below the voltage of the battery 101, and the spontaneous power generation of the FC stack 11 is stopped intermittently.

[0045] <First Example (Air Valve Opening / Closing Control)> When intermittently stopping or starting the natural power generation of the FC stack 11, the amount of air supplied to the FC stack 11 fluctuates by opening and closing the inlet air valve 62 and the outlet air valve 71, which causes fluctuations in the FC voltage. If this fluctuation in FC voltage becomes large, the fluctuation in the load on the FC stack 11 also becomes large, which may cause 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 depending on 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 speed of the inlet air valve 62 and the outlet air valve 71 according to the magnitude of the FC overvoltage.

[0048] 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" in the present disclosure. The estimated FC voltage value is an example of the "optimum value of fuel cell output voltage" in the present disclosure.

[0049] 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 estimated from the measured FC current value using, for example, the map in Fig. 3.

[0050] In this embodiment, when the control unit 15 intermittently stops the natural power generation of the FC stack 11, it performs control according to the contents shown in the flowchart of FIG.

[0051] 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 stop (FC current=0) (step S1).

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

[0053] The judgment value is calculated from the measured FC current value using, for example, the map in Fig. 4. In the map in Fig. 4, the judgment value changes in proportion to the measured FC current value; for example, when the measured FC current value is 10 A, the judgment value is 3 V, and when the measured FC current value is 30 A, the judgment value is 5 V.

[0054] Returning to the explanation of Figure 5, if the FC overvoltage is less than the judgment 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 Figure 5) (step S3).

[0055] In this way, when intermittently stopping the natural power generation 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 that is faster than the first speed, which will be described later. In other words, when intermittently stopping the natural power generation of the FC stack 11, if the state of the FC stack 11 is such that there is little possibility that the FC stack 11 will deteriorate due to fluctuations in FC voltage caused by the closing operation 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. The second speed is, for example, a speed that reduces the opening angle by 5° per second.

[0056] This allows the supply of air to the FC stack 11 to be stopped quickly, and the natural power generation of the FC stack 11 to be stopped intermittently quickly.

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

[0058] In this way, when intermittently stopping the natural power generation of the FC stack 11, if the FC overvoltage is high, the control unit 15 closes the inlet air valve 62 and the outlet air valve 71 at a first speed that is slower than the second speed described above. Here, if the FC overvoltage is high, the FC voltage decreases while the FC current increases, and fluctuations in the FC voltage cause large fluctuations in the FC current, which is likely to cause deterioration of the FC stack 11. Therefore, when intermittently stopping the natural power generation of the FC stack 11, if the state of the FC stack 11 is such that fluctuations in the FC voltage caused by the closing operation of the inlet air valve 62 and the outlet air valve 71 are likely to cause deterioration of the FC stack 11, the control unit 15 slowly closes the inlet air valve 62 and the outlet air valve 71. Note that the first speed is, for example, a speed that reduces the opening angle by 1° per second.

[0059] As a result, even if the FC overvoltage is large when intermittently stopping the natural power generation of the FC stack 11, the inlet air valve 62 and the outlet air valve 71 can be closed slowly to reduce fluctuations in the FC voltage. This reduces fluctuations in the load on the FC stack 11, thereby preventing deterioration of the FC stack 11.

[0060] In particular, the fuel cell system 1 of this embodiment is a DCDC converter-less system, and the FC current depends on the voltage of the battery 101. Therefore, even if, for example, the battery 101 deteriorates and the voltage of the battery 101 decreases, causing the FC voltage to decrease and the FC overvoltage to increase, the inlet air valve 62 and the outlet air valve 71 can be slowly closed to reduce fluctuations in the FC voltage. Therefore, even if the fuel cell system 1 is a DCDC converter-less system, fluctuations in the load on the FC stack 11 can be reduced, and deterioration of the FC stack 11 can be suppressed.

[0061] Furthermore, when the FC stack 11 starts power generation as it goes, the control unit 15 performs control as shown in the flowchart of FIG.

[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 flow-through power generation (step S11).

[0063] Then, if there is a request to switch from intermittent stop to uninterrupted power generation (step S11: YES) (i.e., when uninterrupted power generation starts), the control unit 15 determines whether the FC overvoltage is less than the determination value (step S12).

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

[0065] In this way, when starting 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 that is faster than the third speed described below. In other words, when starting natural power generation of the FC stack 11, if the state of the FC stack 11 is such that there is little possibility that the FC stack 11 will be deteriorated due to fluctuations in FC voltage caused by the opening operations of the inlet air valve 62 and the outlet air valve 71, the control unit 15 quickly opens the inlet air valve 62 and the outlet air valve 71. Note that the fourth speed is, for example, a speed that increases the opening angle by 5° per second.

[0066] This allows air to be supplied to the FC stack 11 quickly, and the FC stack 11 can start generating electricity as it goes along quickly.

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

[0068] In this way, when starting natural power generation of the FC stack 11, if the FC overvoltage is high, the control unit 15 opens the inlet air valve 62 and the outlet air valve 71 at a third speed, which is slower than the fourth speed described above. In other words, when starting 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 will deteriorate due to fluctuations in FC voltage caused by the opening operations of the inlet air valve 62 and the outlet air valve 71, the control unit 15 slowly opens the inlet air valve 62 and the outlet air valve 71. Note that the third speed is, for example, a speed at which the opening degree increases by 1° per second.

[0069] As a result, even if the FC overvoltage is large when the FC stack 11 starts generating electricity naturally, the inlet air valve 62 and the outlet air valve 71 can be opened slowly to reduce fluctuations in the FC voltage and reduce fluctuations in the load on the FC stack 11, thereby preventing deterioration of the FC stack 11.

[0070] In particular, the fuel cell system 1 of this embodiment is a DCDC converter-less system, and the FC current depends on the voltage of the battery 101. Therefore, even if, for example, the battery 101 deteriorates and the voltage of the battery 101 decreases, causing the FC voltage to decrease and the FC overvoltage to increase, the inlet air valve 62 and the outlet air valve 71 can be slowly opened to reduce fluctuations in the FC voltage. Therefore, even if the fuel cell system 1 is a DCDC converter-less system, fluctuations in the load on the FC stack 11 can be reduced, and deterioration of the FC stack 11 can be suppressed.

[0071] <Second embodiment (control of air compressor rotation speed)> Furthermore, when intermittently stopping or starting the natural power generation of the FC stack 11, increasing or decreasing the rotation speed of the air compressor 61 changes the amount of air supplied to the FC stack 11, which in turn changes the FC voltage. If this FC voltage fluctuation becomes large, the fluctuation in the load on the FC stack 11 also becomes large, which may cause deterioration of the FC stack 11.

[0072] Therefore, in this embodiment, the control unit 15 adjusts the speed at which the rotational speed of the air compressor 61 increases or decreases depending on the state of the FC stack 11 when intermittently stopping or starting the natural power generation 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 speed at which the rotational speed of the air compressor 61 increases or decreases depending on the magnitude of the FC overvoltage.

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

[0075] As shown in Figure 7, the difference from Figure 5 is that in step S22, if the FC overvoltage is less than the judgment value (step S22: YES), the control unit 15 increases the rate at which the rotation speed of the air compressor 61 decreases (step S23).

[0076] In this way, when intermittently stopping the natural power generation of the FC stack 11, if the FC overvoltage is small, the control unit 15 reduces the rotation speed of the air compressor 61 at a sixth speed that is faster than the fifth speed described below. In other words, when intermittently stopping the natural power generation of the FC stack 11, if the state of the FC stack 11 is such that there is little possibility that the FC stack 11 will deteriorate due to fluctuations in FC voltage caused by a drop in the rotation speed of the air compressor 61, the control unit 15 quickly reduces the rotation speed of the air compressor 61. Note that the sixth speed is, for example, a speed at which the rotation speed is reduced by 1000 rpm per second.

[0077] As a result, when the natural power generation of the FC stack 11 is to be stopped intermittently, the supply of air to the FC stack 11 can be stopped quickly, and the natural power generation of the FC stack 11 can be stopped quickly.

[0078] On the other hand, if 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 rate at which the rotation speed of the air compressor 61 is reduced (step S24).

[0079] In this way, when intermittently stopping the natural power generation of the FC stack 11, if the FC overvoltage is large, the control unit 15 reduces the rotation speed of the air compressor 61 at a fifth speed, which is slower than the sixth speed described above. In other words, when intermittently stopping 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 will deteriorate due to fluctuations in FC voltage caused by a drop in the rotation speed of the air compressor 61, the control unit 15 slowly reduces the rotation speed of the air compressor 61. Note that the fifth speed is, for example, a speed at which the rotation speed is reduced by 100 rpm per second.

[0080] As a result, when the natural power generation of the FC stack 11 is stopped intermittently, even if the FC overvoltage is large, the rotation speed of the air compressor 61 can be slowly reduced to reduce fluctuations in the FC voltage and fluctuations in the load on the FC stack 11, thereby preventing deterioration of the FC stack 11.

[0081] Furthermore, as in the first embodiment, even if the fuel cell system 1 is a DCDC converter-less system, the fluctuations in the load on the FC stack 11 can be reduced, thereby suppressing deterioration of the FC stack 11.

[0082] Furthermore, when the FC stack 11 starts power generation as it goes, the control unit 15 performs control as shown in the flowchart of FIG.

[0083] As shown in Figure 8, the difference from Figure 6 is that in step S32, if the FC overvoltage is less than the judgment value (step S32: YES), the control unit 15 increases the rate of increase in the rotation speed of the air compressor 61 (step S33).

[0084] In this way, when natural power generation of the FC stack 11 is started, if the FC overvoltage is small, the control unit 15 increases the rotation speed of the air compressor 61 at an eighth speed that is faster than the seventh speed described below. In other words, when natural power generation of the FC stack 11 is started, if the state of the FC stack 11 is such that there is little possibility that the FC stack 11 will deteriorate due to fluctuations in FC voltage caused by an increase in the rotation speed of the air compressor 61, the control unit 15 quickly increases the rotation speed of the air compressor 61. Note that the eighth speed is, for example, a speed that increases the rotation speed by 1000 rpm per second.

[0085] This allows air to be supplied to the FC stack 11 quickly, and the FC stack 11 can start generating electricity as it goes along quickly.

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

[0087] In this way, when starting 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 the seventh speed, which is slower than the above-mentioned eighth speed. In other words, when starting 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 will deteriorate due to fluctuations in FC voltage caused by an increase in the rotation speed of the air compressor 61, the control unit 15 slowly increases the rotation speed of the air compressor 61. Note that the seventh speed is, for example, a speed at which the rotation speed is increased by 100 rpm per second.

[0088] As a result, even if the FC overvoltage is large when the FC stack 11 starts generating electricity naturally, the rotation speed of the air compressor 61 can be slowly increased, reducing fluctuations in the FC voltage and fluctuations in the load on the FC stack 11, thereby preventing deterioration of the FC stack 11.

[0089] Furthermore, as in the first embodiment, even if the fuel cell system 1 is a DCDC converter-less system, the fluctuations in the load on the FC stack 11 can be reduced, thereby suppressing deterioration of the FC stack 11.

[0090] 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.

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

[0092] Furthermore, in the above description, the fuel cell system 1 is described as a DCDC converter-less system, but is not limited to this and may be a system that includes a DCDC converter. In this case, as shown in Figures 5 to 8, the control unit 15 may adjust the opening and closing speed of the inlet air valve 62 and the outlet air valve 71 and / or the speed at which the rotational speed of the air compressor 61 is increased or decreased depending on the magnitude of the FC overvoltage when stopping or starting power generation in the FC stack 11.

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

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

[0095] 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 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 system having a fuel cell that generates electricity by receiving a supply of fuel gas and an oxidant gas, a gas supply unit that supplies the oxidant gas to the fuel cell, and a flow control valve that controls the flow rate of the oxidant gas supplied to the fuel cell, comprising: a current sensor that measures an 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 gas supply unit and the flow control valve, wherein an output voltage difference is defined as the difference between an 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, and the control unit adjusts the opening and closing speed of the flow control valve and / or the speed at which the rotational speed of the gas supply unit is increased or decreased in accordance with the output voltage difference when power generation of the fuel cell is stopped or started.

2. A fuel cell system according to claim 1, wherein, when power generation by the fuel cell is stopped, the control unit closes the flow control valve at a first speed if the output voltage difference is equal to or greater than a determination value, and closes the flow control valve at a second speed if the output voltage difference is less than the determination value, and the first speed is slower than the second speed.

3. A fuel cell system according to claim 1, wherein, when power generation by the fuel cell is started, the control unit opens the flow control valve at a third speed if the output voltage difference is equal to or greater than a determination value, and opens the flow control valve at a fourth speed if the output voltage difference is less than the determination value, and the third speed is slower than the fourth speed.

4. A fuel cell system according to claim 1, wherein, when power generation by the fuel cell is stopped, the control unit reduces the rotation speed of the gas supply unit to a fifth speed if the output voltage difference is equal to or greater than a determination value, and reduces the rotation speed of the gas supply unit to a sixth speed if the output voltage difference is less than the determination value, the fifth speed being slower than the sixth speed.

5. A fuel cell system according to claim 1, wherein, when power generation of the fuel cell is started, the control unit increases the rotation speed of the gas supply unit at a seventh speed if the output voltage difference is equal to or greater than a determination value, and increases the rotation speed of the gas supply unit at an eighth speed if the output voltage difference is less than the determination value, the seventh speed being slower than the eighth speed.

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