Fuel cell system

Abstract

Even if the pressure of the fuel gas supplied to the ejector decreases, the concentration of the fuel gas supplied from the ejector to the fuel cell is adjusted to suppress deterioration of the fuel cell due to oxidation. [Solution] The fuel cell system 1 comprises an FC stack 11, a hydrogen gas supply passage 31, a hydrogen off-gas circulation passage 33, an ejector 54, an exhaust drain valve 57, a hydrogen gas pressure sensor 16, and a control device 20. The control device 20 variably controls the time ratio of the open time and closed time per control cycle of the exhaust drain valve 57, controlling the number of opening and closing operations of the exhaust drain valve 57 per unit time by keeping the open time constant and variably controlling the closed time. The control device 20 controls the number of opening and closing operations of the exhaust drain valve 57 according to the pressure measurement value of the pressure sensor 16 in order to adjust the concentration of hydrogen gas in the hydrogen off-gas circulated to the hydrogen gas supply passage 31 via the hydrogen off-gas circulation passage 33.

Description

Technical Field

[0004] , , , , , ,

[0003] , , , ,

[0001] The technology disclosed in this specification relates to a fuel cell system including a fuel cell that generates electricity by receiving supplies of fuel gas and oxidant gas.

Background Art

[0002] Conventionally, as this type of technology, for example, a "fuel cell system" described in Patent Document 1 below is known. This system includes a fuel cell, a fuel gas supply passage that supplies fuel gas to the fuel cell, an injector provided in the fuel gas supply passage, an ejector provided in the fuel gas supply passage and provided between the injector and the fuel cell, and a fuel off-gas circulation passage that circulates fuel off-gas discharged from the fuel cell to the ejector. The ejector generates a negative pressure by the fuel gas injected from the injector, sucks fuel off-gas from the fuel off-gas circulation passage by the negative pressure, mixes the fuel off-gas with the fuel gas, and discharges and supplies the mixture to the fuel cell.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the fuel cell system described in Patent Document 1, the pressure of the fuel gas supplied to the injector may decrease. In this system, when the fuel in the fuel tank decreases, the pressure of the fuel gas supplied to the injector decreases, and the flow velocity of the fuel gas injected from the injector to the ejector decreases. As a result, the negative pressure generated in the ejector decreases, the amount of fuel off-gas drawn in by the ejector decreases, and the circulation efficiency of fuel off-gas to the ejector decreases. Consequently, there is a concern that the concentration of fuel gas supplied to the fuel cell will decrease, and the power generation performance of the fuel cell will decline.

[0005] On the other hand, when hydrogen is used as fuel, a hydrogen alloy canister is sometimes used instead of a fuel tank, which stores hydrogen in an internal hydrogen alloy. In this case, the pressure of the hydrogen gas released from the canister changes significantly depending on the temperature of the hydrogen alloy canister. In particular, if the temperature of the canister decreases, the pressure of the hydrogen gas supplied to the injector decreases, and the same problems as described above are expected.

[0006] This disclosed technology has been made in view of the above circumstances, and its purpose is to provide a fuel cell system that can adjust the concentration of fuel gas supplied from the ejector to the fuel cell, even when the pressure of the fuel gas supplied to the ejector decreases, thereby suppressing a decrease in the power generation performance of the fuel cell. [Means for solving the problem]

[0007] To achieve the above objective, the technology described in claim 1 is a fuel cell system comprising a fuel cell that generates electricity by receiving a fuel gas and an oxidizer gas, comprising: a fuel gas supply passage for supplying fuel gas to the fuel cell; a fuel off-gas discharge passage for discharging fuel off-gas discharged from the fuel cell to the outside; a fuel off-gas circulation passage for circulating at least a portion of the fuel off-gas from the fuel off-gas discharge passage to the fuel gas supply passage; a fuel gas supply means disposed in the fuel gas supply passage for supplying fuel gas; and an ejector disposed downstream of the fuel gas supply means in the fuel gas supply passage for mixing the fuel gas supplied by the fuel gas supply means and the fuel off-gas circulating in the fuel off-gas circulation passage and discharging it, and The system includes an exhaust drain valve located in the fuel off-gas discharge passage for discharging fuel off-gas to the outside, a pressure sensor located in the fuel gas supply passage for measuring the pressure of the fuel gas upstream of the ejector, and a control device for controlling the exhaust drain valve. The control device variably controls the time ratio of the open time to the closed time per control cycle of the exhaust drain valve, and is configured to control the number of opening and closing operations of the exhaust drain valve per unit time by keeping the open time constant and variably controlling the closed time. The purpose of the control device is to control the number of opening and closing operations of the exhaust drain valve according to the pressure measurement value of the pressure sensor in order to adjust the concentration of fuel gas in the fuel off-gas that is circulated to the fuel gas supply passage via the fuel off-gas circulation passage.

[0008] According to the above technology configuration, the control device variably controls the time ratio of the open time to the closed time per control cycle of the exhaust and drain valve. By keeping the open time constant and variably controlling the closed time, the number of times the exhaust and drain valve is opened and closed per unit time is controlled. The reason for keeping the open time constant is to prevent the exhaust and drain valve from opening too much. Here, the longer the closed time, the fewer times the exhaust and drain valve is opened and closed per unit time, and the shorter the total open time of the exhaust and drain valve per unit time. As a result, the circulation flow rate of fuel off-gas circulating to the fuel gas supply passage via the fuel off-gas circulation passage decreases. On the other hand, the shorter the closed time, the more times the exhaust and drain valve is opened and closed, and the longer the total open time of the exhaust and drain valve per unit time. As a result, gases (nitrogen, water, etc.) generated by the fuel cell's power generation are discharged more frequently, and the concentration of fuel gas in the fuel off-gas circulating to the fuel gas supply passage via the fuel off-gas circulation passage increases. The control device also controls the number of times the exhaust and drain valve is opened and closed according to the pressure measurement value of the fuel gas upstream of the ejector. This adjusts the number of opening and closing operations according to the fuel gas concentration, thereby adjusting the fuel gas concentration in the fuel off-gas that is mixed with the fuel gas in the ejector.

[0009] To achieve the above objective, the technology described in claim 2 further comprises an ammeter for measuring the output current of the fuel cell in the technology described in claim 1, and the control device controls the number of times the exhaust drain valve is opened and closed according to the current measurement of the ammeter in order to adjust the concentration of fuel gas in the fuel off-gas, in addition to control according to the pressure measurement value.

[0010] According to the configuration of the above technology, in addition to the operation of the technology described in claim 1, the control device controls the number of times the exhaust and drain valve is opened and closed according to the current measurement of the fuel cell, in addition to the control according to the pressure measurement. Therefore, the number of times the exhaust and drain valve is opened and closed is adjusted according to the generation status of gases (nitrogen, water, etc.) produced by the power generation of the fuel cell, and the concentration of fuel gas in the fuel off-gas mixed with the fuel gas in the ejector is adjusted.

[0011] To achieve the above objective, the technology described in claim 3 is intended to control the control device in the technology described in claim 2 such that the closing time per control cycle of the exhaust drain valve becomes shorter as the current measurement value increases.

[0012] According to the configuration of the above technology, in addition to the effects of the technology described in claim 2, when the current measurement value of the fuel cell increases, the closing time per control cycle of the exhaust and drain valve decreases, the number of opening and closing operations of the exhaust and drain valve increases, and the total opening time of the exhaust and drain valve increases. Therefore, when the output current of the fuel cell increases, the amount of gas (nitrogen, water, etc.) generated by the power generation of the fuel cell increases, and the concentration of fuel gas in the fuel off-gas discharged to the fuel off-gas discharge passage decreases. However, by increasing the number of operations of the exhaust and drain valve, the gas generated during power generation of the fuel cell is discharged at a high frequency, and the decrease in fuel gas concentration is suppressed.

[0013] To achieve the above objective, the technology described in claim 4 is intended to control the closing time of the exhaust drain valve per control cycle to be longer as the pressure measurement value increases, in the technology described in any one of claims 1 to 3.

[0014] According to the configuration of the above technology, in addition to the effects of the technology described in any one of claims 1 to 3, when the pressure measurement value increases, the control device controls the closing time of the exhaust drain valve per control cycle to be longer. This reduces the number of opening and closing operations of the exhaust drain valve and shortens the total open time of the exhaust drain valve. In this case, the pressure of the fuel gas supplied to the ejector is high, and the fuel off-gas contains a sufficient concentration of fuel gas, so the number of opening and closing operations of the exhaust drain valve may be small. On the other hand, when the pressure measurement value decreases, the control device controls the closing time of the exhaust drain valve per control cycle to be shorter. This increases the number of opening and closing operations of the exhaust drain valve and lengthens the total open time of the exhaust drain valve. In this case, the pressure of the fuel gas supplied to the ejector is low, and gases (nitrogen, water, etc.) generated by the power generation of the fuel cell are discharged at a high frequency, resulting in an insufficient concentration of fuel gas in the fuel off-gas. Therefore, increasing the number of opening and closing operations of the exhaust drain valve increases the concentration of fuel gas in the fuel off-gas. [Effects of the Invention]

[0015] According to the technology described in claim 1, even if the pressure of the fuel gas supplied to the ejector decreases, the concentration of the fuel gas supplied from the ejector to the fuel cell can be adjusted, thereby suppressing a decrease in the power generation performance of the fuel cell.

[0016] According to the technology described in claim 2, similar to the technology described in claim 1, even if the flow rate of the fuel gas supplied to the ejector decreases, the concentration of the fuel gas supplied from the ejector to the fuel cell can be adjusted, thereby suppressing a decrease in the power generation performance of the fuel cell.

[0017] According to the technology described in claim 3, in addition to the effects of the technology described in claim 2, the concentration of fuel gas supplied from the ejector to the fuel cell can be increased, thereby suppressing a decrease in the power generation performance of the fuel cell.

[0018] According to the technology described in claim 4, in addition to the effects of the technology described in any one of claims 1 to 3, the number of times the exhaust drain valve operates can be controlled according to the difference in the concentration of fuel gas in the fuel off-gas, thereby suppressing a decrease in the power generation performance of the fuel cell. [Brief explanation of the drawing]

[0019] [Figure 1] A schematic diagram illustrating a fuel cell system according to one embodiment. [Figure 2] A time chart showing the opening and closing operation of an exhaust drain valve according to one embodiment. [Figure 3] A time chart showing the opening and closing operation of an exhaust drain valve according to one embodiment. [Figure 4] A graph showing the relationship between the hydrogen concentration and hydrogen pressure of hydrogen absorbed into and released from a hydrogen alloy canister, and the canister temperature, according to one embodiment. [Figure 5] A flowchart illustrating the details of hydrogen off-gas circulation amount control according to one embodiment. [Figure 6]A closing time map showing the relationship between the inlet gas pressure and the closing time with respect to the FC current. [Embodiments for Carrying out the Invention]

[0020] Hereinafter, an embodiment in which a fuel cell system is embodied as a fuel cell system mounted on an electric vehicle will be described in detail with reference to the drawings.

[0021] [Regarding the Configuration of the Fuel Cell System] FIG. 1 schematically shows a fuel cell system 1 according to this embodiment. As shown in FIG. 1, the fuel cell system 1 of this embodiment includes an FC stack 11, a battery 12, and an inverter 13 (or a motor).

[0022] Further, the fuel cell system 1 of this embodiment is a simple DCDC converterless system in which the above devices 11 to 13 are connected in parallel and do not have a DCDC converter. Here, the DCDC converter is a device that converts DC (direct current) to DC (direct current), and is a device that converts the voltage used in the system to DC.

[0023] This fuel cell system 1 further includes a hydrogen system 21 and an air system 22. In this embodiment, the fuel gas is hydrogen gas and the oxidant gas is air (atmospheric air). The FC stack 11 generates electricity by receiving the supply of hydrogen gas from the hydrogen system 21 and the supply of air from the air system 22. The FC stack 11 corresponds to an example of the "fuel cell" of this disclosed technology. The electric power generated by the FC stack 11 is supplied to the battery 12 and the inverter 13.

[0024] Battery 12 is connected to the FC stack 11 via first wirings 14a and 14b. Power generated by the FC stack 11 charges battery 12 via first wirings 14a and 14b. Battery 12 is connected to the inverter 13 via first wirings 14a and 14b and second wirings 15a and 15b. Second wiring 15a is connected to first wiring 14a. Second wiring 15b is connected to first wiring 14b. Power charged to battery 12 is supplied to the inverter 13 via first wirings 14a and 14b and second wirings 15a and 15b. The inverter 13 is powered by power supplied from the FC stack 11 and / or battery 12 via first wirings 14a and 14b and second wirings 15a and 15b. An ammeter 17 is provided on first wiring 14a near the output port of the FC stack 11 to measure the FC current IFC, which is the "output current" of the FC stack 11.

[0025] An FC relay 18 is provided in the first wiring 14a between the FC stack 11 and the inverter 13 to switch the connection and disconnection of the wiring 14a. A battery relay 19 is provided in the first wiring 14a between the battery 12 and the inverter 13 to switch the connection and disconnection of the wiring 14a. The FC relay 18 is positioned in the first wiring 14a between the connection point C1 between the first wiring 14a and the second wiring 15a and the ammeter 17. The battery relay 19 is positioned in the first wiring 14a between the connection point C1 between the first wiring 14a and the second wiring 15a and the battery 12. Here, each relay 18, 19 is a component that receives an electrical signal from an external source and switches the electrical circuit on / off or on / off, and has a well-known configuration.

[0026] The hydrogen system 21 is installed on the anode side of the FC stack 11. This hydrogen system 21 includes a hydrogen gas supply passage 31, an exhaust drainage passage 32, a hydrogen off-gas circulation passage 33, and a hydrogen alloy canister 41.

[0027] The hydrogen gas supply passage 31 is a passage for supplying hydrogen from the hydrogen alloy canister 41, in which hydrogen is absorbed, to the FC stack 11. The hydrogen gas supply passage 31 corresponds to an example of a "fuel gas supply passage" in this disclosed technology. The hydrogen alloy canister 41 contains a hydrogen alloy that enables the absorption and release of hydrogen. The hydrogen alloy canister 41 corresponds to an example of a "fuel gas supply means" in this disclosed technology. The exhaust and drainage passage 32 is a passage for discharging hydrogen off-gas and wastewater discharged from the FC stack 11. The exhaust and drainage passage 32 corresponds to an example of a "fuel off-gas discharge passage" in this disclosed technology.

[0028] Furthermore, the hydrogen system 21 includes an injector 53 and an ejector 54 downstream of the hydrogen alloy canister 41 in the hydrogen gas supply passage 31.

[0029] The hydrogen off-gas circulation passage 33 is a passage connecting the exhaust drainage passage 32 (specifically, the gas-liquid separator 56) and the ejector 54, and is a passage for circulating hydrogen off-gas to the hydrogen gas supply passage 31 via the ejector 54. The hydrogen off-gas circulation passage 33 corresponds to an example of a "fuel off-gas circulation passage" in this disclosed technology.

[0030] The injector 53 is a device that injects hydrogen gas, which is discharged from the hydrogen alloy canister 41, toward the ejector 54. The injector 53 is composed of, for example, a solenoid valve. The injector 53 is configured to adjust the discharge pressure of hydrogen gas (hydrogen gas pressure) by adjusting the opening of the injection port by moving a needle valve, for example. The injector 53 is an example of a "fuel gas supply means" in this disclosed technology.

[0031] The ejector 54 generates negative pressure using hydrogen gas injected from the injector 53, and uses this negative pressure to draw in hydrogen off-gas flowing through the hydrogen off-gas circulation passage 33. The hydrogen off-gas is then mixed with hydrogen gas and discharged from the outlet 54a toward the FC stack 11.

[0032] The hydrogen system 21 further includes a gas-liquid separator 56 and an exhaust-drain valve 57 in the exhaust-drain passage 32, in order from the FC stack 11 side. The gas-liquid separator 56 is an electrically operated device that separates moisture from the hydrogen off-gas. The exhaust-drain valve 57 is a valve that switches between discharging and shutting off the hydrogen off-gas and moisture from the gas-liquid separator 56. This valve 57 is configured, for example, as a solenoid valve. In this embodiment, the exhaust-drain valve 57 is configured so that the number of opening and closing operations of the valve body per unit time relative to the valve seat can be changed by controlling the amount of supplied current.

[0033] In the hydrogen system 21, a pressure sensor 16 is provided in the hydrogen gas supply passage 31 between the hydrogen alloy canister 41 and the injector 53. This pressure sensor 16 is a sensor for measuring the pressure (inlet gas pressure) PH1 of the hydrogen gas supplied to the injector 53.

[0034] On the other hand, the air system 22 is provided on the cathode side of the FC stack 11. This air system 22 includes an air supply passage 61 and an air discharge passage 62. The air supply passage 61 is a passage for supplying air from outside the fuel cell system 1 to the FC stack 11. The air discharge passage 62 is a passage for discharging air (i.e., air-off gas) discharged from the FC stack 11.

[0035] Furthermore, the air system 22 includes an air compressor 71 in the air supply passage 61. The air compressor 71 is an electrically powered device that supplies air to the FC stack 11. In this embodiment, no devices such as air valves are provided in the air supply passage 61 or the air discharge passage 62 between the air compressor 71 and the FC stack 11. In other words, in this embodiment, air is supplied directly to the FC stack 11 from the air compressor 71, and the air-off gas is discharged directly from the FC stack 11 to the outside.

[0036] In addition, the fuel cell system 1 of this embodiment further includes a cooling system 23 for cooling the FC stack 11. This cooling system 23 includes an air passage 81 for circulating air and an electrically operated cooling fan 82 for cooling the air flowing through the passage 81. In other words, in this embodiment, the cooling system 23 and the air system 22 are configured as a "closed cathode system" in which they are separate.

[0037] The fuel cell system 1 further comprises a control device 20 for controlling the system 1. The control device 20 includes, for example, an arithmetic processing unit such as a CPU, a storage unit including a ROM that stores control programs and control data processed by the CPU, a RAM used as various work areas for control processing, and an input / output interface unit. The control device 20 performs various controls on the fuel cell system 1 according to the control programs stored in the storage unit.

[0038] Figures 2 and 3 show the opening and closing operation of the exhaust and drain valve 57 using a time chart. In this embodiment, as shown in Figures 2 and 3, the control device 20 is configured to control the number of opening and closing operations of the exhaust and drain valve 57 per unit time TU by variably controlling (duty cycle control) the time ratio between the opening time TOP and the closing time TCL per control cycle P1 of the exhaust and drain valve 57, and by keeping the opening time TOP constant and variably controlling the closing time TCL. Figure 2 shows the case where the closing time TCL is long. Figure 3 shows the case where the closing time TCL is short. From Figures 2 and 3, it can be seen that when the closing time TCL is short, the number of opening and closing operations of the exhaust and drain valve 57 per unit time TU is greater than when the closing time TCL is long, and the total opening time per unit time TU is longer.

[0039] [Regarding the operation of the fuel cell system] In the fuel cell system 1 configured as described above, the hydrogen gas supplied to the FC stack 11 from the hydrogen gas supply passage 31 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 of the fuel cell system 1 via the exhaust drainage passage 32, and also circulates back to the hydrogen gas supply passage 31 via the hydrogen off-gas circulation passage 33 and ejector 54. In addition, the air supplied to the FC stack 11 from the air supply passage 61 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 of the fuel cell system 1 via the air discharge passage 62.

[0040] The electricity generated by the FC stack 11 is used to charge the battery 12 or to power the inverter 13. The inverter 13 is also powered by the battery 12.

[0041] In this embodiment, the fuel cell system 1 is electrically configured such that the voltage of the FC stack 11 (FC voltage) is equal to (or approximately equal to) the voltage of the battery 12 (battery voltage). Therefore, the current of the FC stack 11 (FC current) IFC depends on the battery voltage. In other words, the power generated by the FC stack 11 is supplied to the battery 12 and inverter 13 without converting the FC voltage. The FC current IFC is the current of the power generated by the FC stack 11. The battery voltage is the voltage of the battery 12.

[0042] In this fuel cell system 1, the FC voltage becomes equal to the battery voltage, so the FC stack 11 performs "progressive power generation" according to the battery voltage during power generation. Furthermore, in this fuel cell system 1, when the battery 12's charge level becomes high, the hydrogen injection pressure of the injector 53 is controlled to a stopping pressure, and the air compressor 71 is stopped, thereby lowering the FC voltage below the battery voltage and intermittently stopping power generation by the FC stack 11, performing "low-current power generation." This improves the fuel efficiency of the fuel cell system 1.

[0043] In this embodiment, since a hydrogen alloy canister 41 is used in the hydrogen system 21, the pressure of the hydrogen gas released from the hydrogen alloy canister 41 changes significantly depending on the temperature of the canister 41. Figure 4 shows a graph of the relationship between the "hydrogen concentration" and "hydrogen pressure" of hydrogen absorbed and released from the hydrogen alloy canister and the "canister temperature THC". As shown in Figure 4, the relationship between hydrogen concentration and hydrogen pressure decreases as the canister temperature THC decreases in the range of "0 to 60 (°C)". In Figure 4, at each canister temperature THC, the hydrogen pressure is higher during absorption than during release.

[0044] As can be seen from Figure 4, in this embodiment, when the canister temperature THC decreases, the pressure of the hydrogen gas supplied to the injector 53 decreases, the negative pressure generated in the ejector 54 decreases, and the circulation efficiency of hydrogen off-gas to the ejector 54 decreases. As a result, the pressure of the hydrogen off-gas mixed with the hydrogen gas in the ejector 54 decreases, and the pressure of the hydrogen gas supplied from the ejector 54 to the FC stack 11 decreases. Consequently, the concentration of hydrogen gas supplied to the FC stack 11 does not increase, and the power generation efficiency of the FC stack 11 decreases. Therefore, in this embodiment, in order to address the above problem, the control device 20 performs the following control of the amount of hydrogen off-gas circulated to the ejector 54. In this control, the control device 20 controls the exhaust drain valve 57 based on the measured values ​​of the pressure sensor 16 and the ammeter 17.

[0045] [Regarding hydrogen off-gas circulation volume control] Next, the "hydrogen off-gas circulation amount control" performed by the control device 20 will be described. Figure 5 shows an example of the contents of this control in a flowchart. The control program related to this flowchart is stored in the memory unit of the control device 20. In this embodiment, the control device 20 is configured to perform this "hydrogen off-gas circulation amount control" when performing "spontaneous power generation" according to the battery voltage and when performing "low-current power generation" which intermittently stops power generation by the FC stack 11.

[0046] When the process transitions to the routine shown in Figure 5, the control device 20 acquires the inlet gas pressure PH1 and FC current IFC of the injector 53 in step 100. The inlet gas pressure PH1 is obtained from the measurement value of the pressure sensor 16. The FC current IFC is obtained from the measurement value of the ammeter 17.

[0047] Next, in step 110, the control device 20 calculates the closing time TCL of the exhaust drain valve 57 in one control cycle P1 based on the intake inlet gas pressure PH1 and the FC current IFC.

[0048] The control device 20 can determine the closing time TCL by, for example, referring to the closing time map shown in Figure 6. This closing time map sets the relationship between the closing time TCL and the inlet gas pressure PH1 and the FC current IFC. The map in Figure 6 is set so that as the inlet gas pressure PH1 increases in the range of "50 to 600 (kPaG)", the closing time TCL increases in the range of "10 to 50 (ms)". Also, as the FC current IFC increases in the range of "0 to 150 (A)", the closing time TCL decreases in the range of "25 to 10 (ms)". In this embodiment, by controlling the closing time TCL per control cycle P1 in duty cycle control, the number of opening and closing operations of the exhaust drain valve 57 per unit time TU, and consequently the total open time per unit time, is controlled.

[0049] Next, in step 120, the control device 20 controls the number of opening and closing operations of the exhaust drain valve 57 per unit time TU by combining the calculated closing time TCL with a constant opening time TOP (for example, "200 ms"). The control device 20 then terminates the subsequent processing.

[0050] According to the above control, the control device 20 controls the number of times the exhaust drain valve 57 is opened and closed according to the measurement value of the pressure sensor 16 in order to adjust the circulation flow rate of hydrogen off-gas circulated to the hydrogen gas supply passage 31 via the hydrogen off-gas circulation passage 33. In addition to the control according to the pressure measurement value of the pressure sensor 16, the control device 20 also controls the number of times the exhaust drain valve 57 is opened and closed according to the current measurement value of the ammeter 17 in order to adjust the circulation flow rate of hydrogen off-gas.

[0051] According to the above control, the control device 20 controls the closing time TCL of the exhaust and drain valve 57 to be shorter per control cycle P1 as the current measurement value of the ammeter 17 increases. Also, the control device 20 controls the closing time TCL of the exhaust and drain valve 57 to be longer as the pressure measurement value of the pressure sensor 16 increases.

[0052] [Regarding the operation and effects of fuel cell systems] According to the configuration of the fuel cell system 1 of this embodiment described above, the control device 20 controls the time ratio of the opening time TOP to the closing time TCL of the exhaust and drain valve 57 per control cycle P1 in a variable manner. By keeping the opening time TOP constant and controlling the closing time TCL in a variable manner, the number of opening and closing operations of the exhaust and drain valve 57 per unit time TU is controlled. The reason for keeping the opening time TOP constant is to prevent the exhaust and drain valve 57 from opening too much. Here, the longer the closing time TCL, the fewer the number of opening and closing operations of the exhaust and drain valve 57 per unit time TU, and the shorter the total opening time of the exhaust and drain valve 57 per unit time TU. As a result, the circulation flow rate of hydrogen off-gas circulating to the hydrogen gas supply passage 31 via the hydrogen off-gas circulation passage 33 decreases. On the other hand, the shorter the closing time TCL, the more opening and closing operations there are, and the longer the total opening time of the exhaust and drain valve 57 per unit time TU. As a result, gases (nitrogen, water, etc.) generated by the power generation of the FC stack 11 are frequently discharged, increasing the concentration of hydrogen gas in the hydrogen off-gas circulating to the hydrogen gas supply passage 31 via the hydrogen off-gas circulation passage 33. In addition, the control device 20 controls the number of times the exhaust drain valve 57 is opened and closed according to the hydrogen gas inlet gas pressure PH1 (pressure measurement value) upstream of the ejector 54. This adjusts the number of opening and closing operations according to the hydrogen gas concentration, thereby adjusting the concentration of hydrogen gas in the hydrogen off-gas mixed with the hydrogen gas at the ejector 54. Therefore, even if the pressure of the hydrogen gas supplied to the ejector 54 decreases, the concentration of hydrogen gas supplied from the ejector 54 to the FC stack 11 can be adjusted, suppressing a decrease in the power generation performance of the FC stack 11.

[0053] According to the configuration of this embodiment, the control device 20 controls the number of times the exhaust drain valve 57 is opened and closed according to the FC current IFC (current measurement value), which is the output current of the FC stack 11, in addition to controlling according to the inlet gas pressure PH1 (pressure measurement value).Therefore, the number of times the exhaust drain valve 57 is opened and closed is adjusted according to the generation status of gases (nitrogen, water, etc.) produced by the power generation of the FC stack 11, and the concentration pressure of hydrogen gas in the hydrogen off gas mixed with hydrogen gas in the ejector 54 is adjusted.As a result, even if the flow velocity of hydrogen gas supplied to the ejector 54 decreases, the concentration of hydrogen gas supplied from the ejector 54 to the FC stack 11 can be adjusted, and a decrease in the power generation performance of the FC stack 11 can be suppressed.

[0054] According to the configuration of this embodiment, when the FC current IFC increases, the closing time of the exhaust drain valve 57 per control cycle P1 decreases, the number of opening and closing operations of the exhaust drain valve 57 increases, and the total opening time of the exhaust drain valve 57 increases. Therefore, when the output current of the FC stack 11 increases, the amount of gas (nitrogen, water, etc.) generated by the power generation of the FC stack 11 increases, and the concentration of hydrogen gas in the hydrogen off-gas discharged to the exhaust drain passage 32 decreases. However, by increasing the number of operations of the exhaust drain valve 57, the gas generated during power generation by the FC stack 11 is discharged at a high frequency, and the decrease in hydrogen gas concentration is suppressed. As a result, the concentration of hydrogen gas supplied from the ejector 54 to the FC stack 11 can be increased, and the decrease in the power generation performance of the FC stack 11 can be suppressed.

[0055] According to the configuration of this embodiment, when the hydrogen gas inlet gas pressure PH1 increases, the control device 20 controls the closing time TCL per control cycle P1 of the exhaust drain valve 57 to be longer. As a result, the number of times the exhaust drain valve 57 is opened and closed decreases, and the total open time of the exhaust drain valve 57 decreases. In this case, the pressure of the hydrogen gas supplied to the ejector 54 is high, and the hydrogen off-gas contains a sufficient concentration of hydrogen gas, so the number of times the exhaust drain valve 57 is opened and closed may be small. On the other hand, when the hydrogen gas inlet gas pressure PH1 decreases, the control device 20 controls the closing time TCL per control cycle P1 of the exhaust drain valve 57 to be shorter. As a result, the number of times the exhaust drain valve 57 is opened and closed increases, and the total open time of the exhaust drain valve 57 increases. In this case, the pressure of the hydrogen gas supplied to the ejector 54 is low, and gases (nitrogen, water, etc.) generated by the power generation of the FC stack 11 are discharged at a high frequency, resulting in an insufficient concentration of hydrogen gas in the hydrogen off-gas. Therefore, by increasing the number of times the exhaust drain valve 57 is opened and closed, the concentration of hydrogen gas in the hydrogen off-gas can be increased. As a result, the number of times the exhaust drain valve 57 is opened can be controlled in accordance with the difference in the concentration of hydrogen gas in the hydrogen off-gas, thereby suppressing a decrease in the power generation performance of the FC stack 11.

[0056] Furthermore, according to the configuration of this embodiment, the air system 22 includes an air compressor 71, air is directly supplied to the FC stack 11 from the air compressor 71, and air-off gas is directly discharged from the FC stack 11. Therefore, no air valves or the like are provided on the supply side of the air system 22 other than the air compressor 71, nor are any air valves or the like provided on the discharge side of the air system 22. This simplifies the air system 22 and reduces the cost of the fuel cell system 1.

[0057] <Another embodiment> Furthermore, this disclosed technology is not limited to the embodiments described above, and it can be implemented by appropriately modifying a part of the configuration without departing from the spirit of the disclosed technology.

[0058] (1) In the above embodiment, the control device 20 used both the pressure measurement value from the pressure sensor 16 and the current measurement value from the ammeter 17 to control the exhaust drain valve 57, but it is also possible to use only the pressure measurement value from the pressure sensor 16.

[0059] (2) In the above embodiment, a hydrogen alloy canister 41 was provided as a fuel gas supply means, but a hydrogen tank filled with hydrogen can also be provided.

[0060] (3) In the above embodiment, the fuel cell system 1 was provided in an electric vehicle, but it can also be provided in a vehicle other than an electric vehicle.

[0061] (4) In the above embodiment, air valves and the like were not provided on the supply side and discharge side of the air system 22, but air valves and the like may be provided.

[0062] (5) In the above embodiment, the fuel cell system 1 is a closed cathode system in which the cooling system 23 and the air system 22 are separate. In contrast, the fuel cell system can also be an open cathode system in which the cooling system is shared with the air system. [Industrial applicability]

[0063] This disclosed technology can be used, for example, in fuel cell systems installed in electric vehicles. [Explanation of symbols]

[0064] 1. Fuel cell system 11 FC Stack (Fuel Cell) 16. Pressure Sensor 17 Ammeter 20 Control device 31. Hydrogen gas supply passage (fuel gas supply passage) 32 Exhaust drainage passage (fuel off-gas discharge passage) 33. Hydrogen off-gas circulation passage (fuel off-gas circulation passage) 41. Hydrogen alloy canister (fuel gas supply means) 53 Injector (fuel gas supply means) 54 Ejectors 57 Exhaust drain valve

Claims

1. In a fuel cell system equipped with a fuel cell that generates electricity by receiving fuel gas and oxidizer gas, A fuel gas supply passage for supplying the fuel gas to the fuel cell, A fuel off-gas discharge passage for discharging fuel off-gas from the fuel cell to the outside, A fuel off-gas circulation passage that circulates at least a portion of the fuel off-gas from the fuel off-gas discharge passage to the fuel gas supply passage, A fuel gas supply means is arranged in the fuel gas supply passage and for supplying the fuel gas, An ejector is located downstream of the fuel gas supply means in the fuel gas supply passage and mixes the fuel gas supplied by the fuel gas supply means with the fuel off gas circulating in the fuel off gas circulation passage and discharges it; An exhaust drain valve is provided in the fuel off-gas discharge passage for discharging the fuel off-gas to the outside, A pressure sensor is provided in the fuel gas supply passage for measuring the pressure of the fuel gas upstream of the ejector. A control device for controlling the exhaust and drain valve Equipped with, The control device controls the time ratio of the open time to the closed time per control cycle of the exhaust and drain valve in a variable manner, and is configured to control the number of opening and closing operations of the exhaust and drain valve per unit time by keeping the open time constant and controlling the closed time in a variable manner. The control device controls the number of times the exhaust drain valve is opened and closed according to the pressure measurement value of the pressure sensor in order to adjust the concentration of the fuel gas in the fuel off-gas that is circulated to the fuel gas supply passage via the fuel off-gas circulation passage. A fuel cell system characterized by the following features.

2. In the fuel cell system according to claim 1, The fuel cell further comprises an ammeter for measuring the output current, In addition to controlling according to the pressure measurement, the control device controls the number of times the exhaust drain valve is opened and closed according to the current measurement of the ammeter in order to adjust the concentration of the fuel gas in the fuel off-gas. A fuel cell system characterized by the following features.

3. In the fuel cell system according to claim 2, The control device controls the closing time of the exhaust and drain valve per control cycle to be shorter as the current measurement value increases. A fuel cell system characterized by the following features.

4. In the fuel cell system according to any one of claims 1 to 3, The control device controls the closing time of the exhaust drain valve per control cycle to be longer as the pressure measurement value increases. A fuel cell system characterized by the following features.

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