Fuel cell system

Abstract

A fuel cell system (1) comprises an FC stack (11) that generates electric power upon receiving supply of hydrogen and air, but does not comprise a DC-DC converter. The fuel cell system comprises: a hydrogen system (21) that supplies hydrogen to the FC stack (11); and a control device (20) that controls an injector (53) of the hydrogen system (21). When the FC stack (11) stops intermittently, the control device (20) controls the injector (53) so as to lower the outlet hydrogen pressure at an ejector (54) of the hydrogen system (21) to a level higher than a prescribed cutoff hydrogen pressure. Prior to lowering the outlet hydrogen pressure to a level higher than the cutoff hydrogen pressure, the control device (20) controls the injector (53) so as to temporarily lower the outlet hydrogen pressure to the cutoff hydrogen pressure.

Description

fuel cell system

[0001] The technology disclosed in this specification relates to a fuel cell system that generates electricity when supplied with fuel and oxidant.

[0002] A known example of this type of technology is the "air-cooled fuel cell system" described in Patent Document 1 listed below. This system includes a fuel cell that generates electricity by receiving a supply of fuel gas from a fuel gas system and an oxidant gas from an oxidant gas system. This system is configured as a simple fuel cell system that includes a fuel cell, a battery, an inverter, or a motor, and does not include a DC-DC converter. This system controls the battery's state of charge by either running the power or by intermittently stopping the system by closing the oxidant valve (reducing the FC current). To achieve this, this system includes oxidant valves at the cathode inlet and outlet of the fuel cell that intermittently stop the supply of oxidant gas when the oxidant is insufficient.

[0003] Here, the DCDC converter is a device that converts DC (direct current) to DC (direct current), and converts the voltage used in the system into DC.

[0004] Japanese Patent Application Laid-Open No. 2022-185247

[0005] In the fuel cell system described in Patent Document 1, two oxidizer valves are closed to starve the oxidizer gas in order to intermittently shut down the fuel cell, but the provision of the oxidizer valves increases costs. Also, when the supply of fuel gas is stopped to shut down the fuel cell intermittently, negative pressure is created inside the fuel pipe, causing the oxidizer gas to flow into the fuel cell, which could lead to oxidation degradation of the fuel cell, especially the catalyst installed inside.

[0006] This disclosed technology has been made in consideration of the above circumstances, and its purpose is to provide a fuel cell system that can prevent oxidant from flowing into the fuel cell when fuel supply is stopped, thereby preventing oxidation deterioration inside the fuel cell.

[0007] (1) In order to achieve the above-mentioned object, one aspect of the technology disclosed in the present application is a fuel cell system that includes a fuel cell that generates electricity by receiving a supply of fuel and an oxidizer, but does not include a DCDC converter, and includes a fuel supply device for supplying fuel to the fuel cell, and a control device for controlling the fuel supply device, and the control device controls the fuel supply device so that, when the fuel cell intermittently stops, the fuel pressure at the outlet of the fuel supply device is reduced to a fuel pressure higher than a predetermined stop fuel pressure.

[0008] According to the configuration (1) above, when the fuel cell is stopped intermittently, i.e., when the fuel cell is set to generate small current, the control device controls the fuel supply device to reduce the fuel pressure at the outlet of the fuel supply device to a fuel pressure higher than the predetermined stop fuel pressure. Therefore, when the fuel cell is stopped intermittently, the fuel pressure at the outlet does not become the stop fuel pressure, and negative pressure does not occur inside the fuel pipe.

[0009] (2) In order to achieve the above object, in the configuration of (1) above, it is preferable that the control device controls the fuel supply device so that the fuel pressure at the outlet is first reduced to the stop fuel pressure before being reduced to a fuel pressure higher than the stop fuel pressure.

[0010] According to the configuration (2), in addition to the effects of the configuration (1), the control device controls the fuel supply device to temporarily reduce the fuel pressure at the outlet to the stop fuel pressure before reducing the fuel pressure at the outlet to a fuel pressure higher than the stop fuel pressure. Therefore, since the fuel pressure at the outlet is temporarily reduced to the stop fuel pressure, the fuel pressure at the outlet is quickly adjusted to a fuel pressure higher than the stop fuel pressure.

[0011] (3) In order to achieve the above object, it is preferable that the configuration of (2) above further comprises an ammeter for measuring the output current of the fuel cell, and when the control device reduces the outlet fuel pressure to the stop fuel pressure and then adjusts the fuel pressure to a fuel pressure higher than the stop fuel pressure, it controls the fuel supply device to increase the outlet fuel pressure if the ammeter measurement value is below a predetermined optimal current value, and controls the fuel supply device to decrease the outlet fuel pressure if the ammeter measurement value is above the optimal current value.

[0012] According to the configuration (3) above, in addition to the effects of the configuration (2) above, when the control device adjusts the fuel pressure at the outlet to a higher fuel pressure after reducing the fuel pressure to the stop fuel pressure, the control device controls the fuel supply device to increase the fuel pressure at the outlet if the ammeter measurement value is below a predetermined optimal current value, and controls the fuel supply device to decrease the fuel pressure at the outlet if the ammeter measurement value is above the optimal current value. Therefore, the fuel pressure at the outlet is gradually adjusted in accordance with the state of the power generation current of the fuel cell.

[0013] (4) In order to achieve the above object, in the configuration of (2) above, it is preferable that the control device controls the fuel supply device so that the fuel pressure at the outlet is once reduced to the stop fuel pressure for a predetermined period of time, and then the fuel pressure is increased to a fuel pressure slightly higher than atmospheric pressure.

[0014] According to the configuration (4), in contrast to the configuration (2), the control device controls the fuel supply device so that the fuel pressure at the outlet is once lowered to the stop fuel pressure for a predetermined time and then raised to a fuel pressure slightly higher than atmospheric pressure. Therefore, since the fuel pressure at the outlet is once reliably lowered to the stop fuel pressure, it is easy to adjust the fuel pressure at the outlet to a fuel pressure slightly higher than atmospheric pressure.

[0015] (5) In order to achieve the above object, it is preferable that any of the configurations (1) to (4) above further comprises an oxidant supply device for supplying an oxidant to the fuel cell, the oxidant supply device including a compressor for pumping the oxidant to the fuel cell, and the oxidant is directly supplied from the compressor to the fuel cell and directly discharged from the fuel cell.

[0016] According to the configuration (5) above, in addition to the effects of any of the configurations (1) to (4) above, the oxidant supply device includes a compressor, and the oxidant is directly supplied to the fuel cell from the compressor and directly discharged from the fuel cell. Therefore, no valves or the like other than the compressor are provided on the supply side of the oxidant supply device, and no valves or the like are provided on the discharge side of the oxidant supply device.

[0017] (6) To achieve the above object, in the configuration of (5) above, it is preferable that the control device controls the pump to stop in order to stop the supply of oxidant when the fuel cell is stopped intermittently.

[0018] According to the configuration (6) above, in addition to the effect of the configuration (5) above, the control device controls the pump to stop when the fuel cell stops intermittently, so that the supply of oxidant to the fuel cell is quickly stopped.

[0019] According to the above configuration (1), it is possible to prevent the oxidant from flowing into the fuel cell when the supply of fuel is stopped, and it is possible to prevent oxidation deterioration inside the fuel cell.

[0020] According to the configuration (2) above, in addition to the effect of the configuration (1) above, the fuel cell that is generating electricity as it goes can be quickly stopped intermittently.

[0021] According to the configuration (3) above, in addition to the effect of the configuration (2) above, it is possible to suppress abrupt changes in power generation of the fuel cell, and to suppress deterioration of the fuel cell.

[0022] According to the configuration (4) above, in addition to the effect of the configuration (2) above, the fuel cell that is generating electricity as it goes can be quickly stopped intermittently.

[0023] According to the configuration (5) above, in addition to the effect of any one of the configurations (1) to (4) above, the oxidant supply device can be simplified, and the cost of the fuel cell system can be reduced.

[0024] According to the above-mentioned configuration (6), in addition to the effect of the above-mentioned configuration (5), power generation by the fuel cell can be stopped quickly and reliably.

[0025] 1 is a schematic configuration diagram showing a fuel cell system according to a first embodiment; FIG. 2 is a graph showing an example of the relationship between (A) FC current and FC voltage, and (B) battery current and battery voltage when there is power consumption in the inverter in the fuel cell system according to the first embodiment; FIG. 3 is a graph showing an example of the relationship between (A) FC current and FC voltage, and (B) battery current and battery voltage when there is no power consumption in the inverter in the fuel cell system according to the first embodiment; FIG. 4 is a flowchart showing an example of the control content of the fuel cell system according to the first embodiment; FIG. 5 is a time chart showing changes in various parameters related to the control of the fuel cell system according to the first embodiment; and FIG. 6 is a flowchart showing an example of the control content of the fuel cell system according to a second embodiment.

[0026] Hereinafter, an embodiment of a fuel cell system mounted on an electric vehicle will be described.

[0027] First Embodiment First, a first embodiment will be described in detail with reference to the drawings.

[0028] [Configuration of the Fuel Cell System] Figure 1 is a schematic diagram showing the configuration of a fuel cell system 1 according to this embodiment. As shown in Figure 1, the fuel cell system 1 of this embodiment is configured as a DCDC converter-less system that does not have a DCDC converter. That is, this fuel cell system 1 includes an FC stack 11, a battery 12, and an inverter 13 (or a motor), and these devices 11 to 13 are connected in parallel, making it a simple DCDC converter-less system that does not have a DCDC converter. Here, the DCDC converter is a device that converts DC (direct current) to DC (direct current), and converts the voltage used in the system into DC. In this embodiment, the FC stack 11 corresponds to an example of a "fuel cell" in the disclosed technology.

[0029] This fuel cell system 1 includes a hydrogen system 21 and an air system 22. The FC stack 11 generates power by receiving a supply of fuel and a supply of oxidant. In this embodiment, the fuel is hydrogen gas, and the oxidant is air. The FC stack 11 generates power by receiving a supply of hydrogen gas from the hydrogen system 21 and a supply of air from the air system 22. The power generated by the FC stack 11 is supplied to a battery 12 and an inverter 13.

[0030] The battery 12 is connected to the FC stack 11 via first wiring 14a and 14b and is charged with power generated by the FC stack 11. The battery 12 is connected to the inverter 13 via second wiring 15a and 15b and supplies the charged power to the inverter 13. The inverter 13 is driven by power supplied from the FC stack 11 and / or the battery 12 via the second wiring 15a and 15b. An ammeter 17 for measuring the FC current, which is the "output current" of the FC stack 11, is provided on the first wiring 14a immediately adjacent to the output port of the FC stack 11.

[0031] The hydrogen system 21 is provided on the anode side of the FC stack 11. The hydrogen system 21 includes a hydrogen supply passage 31, a hydrogen discharge passage 32, a filling passage 33, and a circulation passage .

[0032] The hydrogen supply passage 31 is a passage for supplying hydrogen gas from a hydrogen tank 41 in which hydrogen gas is stored to the FC stack 11. The hydrogen discharge passage 32 is a passage for discharging hydrogen gas (i.e., hydrogen off-gas) discharged from the FC stack 11.

[0033] The hydrogen system 21 also includes, in the hydrogen supply passage 31, a hydrogen valve 51, a hydrogen pressure reducing valve 52, an injector 53, and an ejector 54, in this order from the hydrogen tank 41 side.

[0034] The filling passage 33 is a passage for filling hydrogen gas into the hydrogen tank 41 from the filling port 42. The circulation passage 34 is a passage that connects the hydrogen discharge passage 32 (more specifically, the gas-liquid separator 56) and the ejector 54, and is a passage for circulating and supplying hydrogen off-gas to the ejector 54.

[0035] The hydrogen valve 51 is a valve that switches between supplying and blocking hydrogen gas from the hydrogen tank 41 to the hydrogen supply passage 31, and is composed of multiple devices including, for example, a solenoid valve. The hydrogen pressure reducing valve 52 is a pressure adjustment valve that reduces the pressure of hydrogen gas, and is composed of, for example, a solenoid valve. The injector 53 is a device that injects hydrogen gas introduced from the hydrogen tank 41 downstream, and is composed of, for example, a solenoid valve. The injector 53 is configured to adjust the discharge pressure of the hydrogen gas (hydrogen pressure), for example, by adjusting the opening of an injection port by moving a needle valve. The ejector 54 is a device that generates negative pressure using the hydrogen gas injected from the injector 53, sucks in hydrogen off-gas from the circulation passage 34, mixes the hydrogen off-gas with the hydrogen gas, and discharges the mixture downstream from an outlet 54 a.

[0036] The hydrogen system 21 further includes, in the hydrogen discharge passage 32, a gas-liquid separator 56 and an exhaust / drain valve 57, in this 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 blocking the hydrogen off-gas and moisture from the gas-liquid separator 56, and is configured by, for example, a solenoid valve.

[0037] In this embodiment, the hydrogen system 21 corresponds to an example of the "fuel supply device" of the disclosed technology. Also, the outlet 54a of the ejector 54 corresponds to an example of the "outlet of the fuel supply device" of the disclosed technology.

[0038] In the hydrogen system 21, a pressure sensor 16 is provided in the hydrogen supply passage 31 between the ejector 54 and the FC stack 11 to measure the pressure of the hydrogen gas discharged from the outlet 54a of the ejector 54 (outlet hydrogen pressure). This outlet hydrogen pressure corresponds to an example of the "fuel pressure at the outlet of the fuel supply device" in the disclosed technology.

[0039] 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.

[0040] The air system 22 also includes an air compressor 71 in the air supply passage 61. The air compressor 71 is an electrically driven 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 and the air discharge passage 62 between the air compressor 71 and the FC stack 11. In other words, in this embodiment, air is directly supplied from the air compressor 71 to the FC stack 11, and air off-gas is directly discharged from the FC stack 11 to the outside.

[0041] In this embodiment, the air system 22 corresponds to an example of the "oxidant supply device" of the disclosed technology for supplying an oxidant to the FC stack 11. The air compressor 71 corresponds to an example of the "compressor" of the disclosed technology.

[0042] In addition, the fuel cell system 1 of this embodiment further includes a cooling system 23 that cools the FC stack 11. The cooling system 23 includes a cooling water passage 81 that circulates cooling water, and an electric cooling fan 82 that cools the cooling water flowing through the passage 81.

[0043] The fuel cell system 1 further includes 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 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 device 20 executes various controls of the fuel cell system 1 in accordance with the control programs stored in the storage unit. In particular, in this embodiment, the control device 20 controls a hydrogen system 21.

[0044] In this embodiment, the control device 20 uses as measurement values ​​the outlet hydrogen pressure measured by the pressure sensor 16 and the FC current measured by the ammeter 17. Based on these measurement values, the control device 20 controls the inverter 13, hydrogen valve 51, hydrogen pressure reducing valve 52, injector 53, gas-liquid separator 56, exhaust drain valve 57, air compressor 71, cooling fan 82, etc., in order to control the fuel cell system 1.

[0045] [Operation of the fuel cell system] In the fuel cell system 1 configured as described above, hydrogen gas supplied from the hydrogen supply passage 31 to the FC stack 11 is used for power generation in the FC stack 11, and then discharged from the FC stack 11 as hydrogen off-gas via the hydrogen discharge passage 32 to the outside of the fuel cell system 1. In addition, air supplied from the air supply passage 61 to the FC stack 11 is used for power generation in the FC stack 11, and then discharged from the FC stack 11 as air off-gas via the air discharge passage 62 to the outside of the fuel cell system 1.

[0046] The electric power generated by the FC stack 11 is supplied to the battery 12 to charge the battery 12, or is supplied to the inverter 13 to drive the inverter 13. The inverter 13 is also supplied with electric power from the battery 12.

[0047] [Regarding the DCDC converter-less system] As described above, the fuel cell system 1 of this embodiment is configured as a DCDC converter-less system. Therefore, in the fuel cell system 1, the voltage of the FC stack 11 (FC voltage) is equal to (or approximately equal to) the voltage of the battery 12 (battery voltage), and the FC current depends on the battery voltage. In other words, this fuel cell system 1 supplies the power generated by the FC stack 11 to the battery 12 and the inverter 13 without converting the FC voltage. Note that the FC current corresponds to an example of the "fuel cell output current" in this disclosed technology, and is the current of the power generated by the FC stack 11. Furthermore, the battery voltage is the voltage of the battery 12.

[0048] In this fuel cell system 1, since the FC voltage is equal to the battery voltage as described above, the FC stack 11 performs "run-of-the-run power generation" according to the battery voltage when generating power. When the charging rate of the battery 12 becomes high, the air compressor 71 is stopped, causing the FC voltage to drop below the battery voltage, thereby intermittently stopping power generation by the FC stack 11 and performing "small current power generation." This improves fuel efficiency. In this embodiment, the state in which the FC stack 11 performs "run-of-the-run power generation" is referred to as the "run-of-the-run power generation mode," and the state in which it performs "small current power generation" is referred to as the "small current power generation mode."

[0049] FIG. 2 is a graph showing an example of the relationship between (A) FC current and FC voltage and (B) battery current and battery voltage in this fuel cell system 1 when power is consumed by the inverter 13. As shown in FIG. 2, when power is consumed by the inverter 13 and the battery voltage is 47 V, the FC voltage is equal to the battery voltage, also 47 V. This results in an FC current of 50 A. Therefore, "FC output = 47 V × 50 A = 2.3 kW," and "battery output = 47 V × 100 A = 4.7 kW." By adding these FC output and battery output together, the inverter 13 can obtain "power consumption = 47 V × 150 A = 7.0 kW." The FC output is the power generated by the FC stack 11 and output from the FC stack 11. The battery output is the power output from the battery 12.

[0050] Figure 3 shows an example of the relationship between (A) the FC current and FC voltage, and (B) the relationship between the battery current and battery voltage in this fuel cell system 1 when there is no power consumption in the inverter 13. As shown in Figure 3, when there is no power consumption in the inverter 13, if the battery voltage is "49 V", the FC voltage will be equal to the battery voltage, i.e., "49 V". As a result, the FC current will be "30 A". Therefore, "FC output = 49 V x 30 A = 1.5 kW", and "battery output = 49 V x -30 A = -1.5 kW".

[0051] [Control of the fuel cell system] Next, a description will be given of the control of the fuel cell system 1 executed by the control device 20. Fig. 4 is a flowchart showing an example of the control content of the fuel cell system 1 according to this embodiment. The control program according to this flowchart is stored in the storage unit of the control device 20.

[0052] 4, the control device 20 determines whether the request has changed from the "run-around power generation mode" to the "small current power generation mode" in step 100. If the result of this determination is positive, the control device 20 proceeds to step 110, and if the result of this determination is negative, the control device 20 temporarily terminates the subsequent processing.

[0053] In step 110, the control device 20 controls the injector 53 so that the outlet hydrogen pressure of the ejector 54 becomes a predetermined "stop hydrogen pressure" for shutting down the FC stack 11. Here, the "stop hydrogen pressure" may be, for example, "0 (kPaG)" or "-5 (kPaG)." The "stop hydrogen pressure" corresponds to an example of the "stop fuel pressure" in the disclosed technology.

[0054] Next, in step 120, the control device 20 controls the air compressor 71 to stop.

[0055] Next, in step 130 , the control device 20 acquires the FC current measured by the ammeter 17 .

[0056] Next, in step 140, the control device 20 determines whether the FC current taken in is smaller than a predetermined optimal current value. If the result of this determination is positive, the control device 20 proceeds to step 150, and if the result of this determination is negative, the control device 20 proceeds to step 160. Here, the "optimal current value" is the current value obtained when hydrogen gas is supplied to the FC stack 11 at a hydrogen pressure higher than the shutdown hydrogen pressure. For example, "5 (A)" can be used as the "optimal current value."

[0057] Then, in step 150, the control device 20 controls the injector 53 to increase the outlet hydrogen pressure of the ejector 54 by a predetermined value. Here, the "predetermined value" to be increased may be, for example, "1 (kPa)." The control device 20 controls the injector 53 by feeding back the measurement value of the pressure sensor 16.

[0058] On the other hand, in step 160, the control device 20 controls the injector 53 to reduce the outlet hydrogen pressure of the ejector 54 by a predetermined value. Here, the "predetermined value" to be reduced may be, for example, "1 (kPa)." The control device 20 controls the injector 53 by feeding back the measurement value of the pressure sensor 16.

[0059] Then, in step 170, which is the step proceeding from step 150 or step 160, the control device 20 determines whether or not the request has changed from the "small current power generation mode" to the "run-around power generation mode." If the result of this determination is negative, the control device 20 proceeds to step 130, and if the result of this determination is positive, the control device 20 temporarily terminates the subsequent processing.

[0060] In the above control, when the FC stack 11 is stopped intermittently, i.e., in "low current power generation mode," the control device 20 controls the injector 53 to reduce the outlet hydrogen pressure of the ejector 54 to a hydrogen pressure higher than the predetermined stop hydrogen pressure.

[0061] In addition, in the above control, the control device 20 controls the injector 53 so that the outlet hydrogen pressure of the ejector 54 is first reduced to the stop hydrogen pressure before being reduced to a hydrogen pressure higher than the stop hydrogen pressure.

[0062] Furthermore, in the above control, the control device 20 reduces the outlet hydrogen pressure to the stop hydrogen pressure and then adjusts the hydrogen pressure to a hydrogen pressure higher than the stop hydrogen pressure. At this time, the control device 20 controls the injector 53 to increase the outlet hydrogen pressure by a predetermined value when the measurement value of the ammeter 17 is below a predetermined optimal current value, and controls the injector 53 to decrease the outlet hydrogen pressure by a predetermined value when the measurement value of the ammeter 17 is above the optimal current value.

[0063] Additionally, in the above control, when the FC stack 11 is put into the "small current power generation mode", the control device 20 controls the air compressor 71 to stop in order to stop the supply of air.

[0064] Figure 5 shows a time chart of the changes in various parameters (a) to (d) related to the control of the fuel cell system, where (a) shows the FC voltage (FC) and battery voltage (BT), (b) shows the battery current (FC current), (c) shows the outlet hydrogen pressure, and (d) shows the operating frequency (DYTY) of the air compressor 71.

[0065] As shown in Figure 5, when the outlet hydrogen pressure is increased by the injector 53 to a predetermined value for spontaneous power generation at time t1 during operation of the air compressor 71, the battery current (FC current) increases, and the FC voltage and battery voltage also increase.

[0066] Then, at time t2, due to intermittent shutdown of the fuel cell system 1, the outlet hydrogen pressure is reduced from a predetermined increased value by the injector 53, and when the air compressor 71 is stopped, the battery current (FC current) decreases toward 0 (A), and the FC voltage and battery voltage decrease. At this time, at time t3, immediately after time t2, the outlet hydrogen pressure temporarily drops to 0 (kPaG), which is the shutdown hydrogen pressure, and then, from time t3 onwards, the fuel pressure is adjusted to a fuel pressure slightly higher than the shutdown hydrogen pressure. Furthermore, from time t3 onwards, the battery current (FC current) periodically changes between 0 (A) and a predetermined small current.

[0067] Then, at time t4, in order to resume natural power generation in the FC stack 11, the outlet hydrogen pressure is increased by the injector 53, and when the air compressor 71 operates, the battery current (FC current) increases again, and the FC voltage and battery voltage also increase. At this time, the outlet hydrogen pressure temporarily drops to the stop hydrogen pressure of "0 (kPaG)" at time t3, immediately after time t2, and then from time t3 onwards, it is adjusted to a fuel pressure slightly higher than the stop hydrogen pressure. Furthermore, from time t3 onwards, the battery current (FC current) changes periodically between "0 (A)" and a predetermined small current.

[0068] Furthermore, the behavior of each of the parameters (a) to (d) when intermittent stopping is performed again at time t5 to t6 is the same as that at time t2 to t3.

[0069] [Regarding the function and effect of the fuel cell system] According to the configuration of the fuel cell system 1 of this embodiment described above, since it is a DCDC converter-less system and the FC current depends on the battery voltage, the fuel cell system 1 can be configured more simply.

[0070] According to the configuration of this embodiment, when the FC stack 11 is stopped intermittently, that is, when the FC stack 11 is set to generate small current, the control device 20 controls the injector 53 to reduce the outlet hydrogen pressure of the ejector 54 that constitutes the hydrogen system 21 to a fuel pressure higher than a predetermined stop hydrogen pressure. Therefore, when the FC stack 11 is stopped intermittently, the outlet hydrogen pressure does not become equal to the stop hydrogen pressure, and therefore negative pressure does not occur inside the hydrogen supply passage 31. This makes it possible to prevent air from flowing into the FC stack 11 when the supply of hydrogen is stopped, and to suppress oxidation deterioration inside the FC stack 11.

[0071] According to the configuration of this embodiment, the control device 20 controls the injector 53 to temporarily reduce the outlet hydrogen pressure of the ejector 54 to the stop hydrogen pressure before reducing it to a hydrogen pressure higher than the stop hydrogen pressure. Therefore, since the outlet hydrogen pressure is temporarily reduced to the stop hydrogen pressure, the outlet hydrogen pressure is quickly adjusted to a hydrogen pressure higher than the stop hydrogen pressure. As a result, the FC stack 11 that is generating power can be quickly intermittently shut down.

[0072] According to the configuration of this embodiment, the control device 20 reduces the outlet hydrogen pressure to the stop hydrogen pressure and then adjusts the hydrogen pressure to a level higher than the stop hydrogen pressure. At this time, the control device 20 controls the injector 53 to increase the outlet hydrogen pressure when the measurement value of the ammeter 17 is below a predetermined optimal current value, and controls the injector 53 to decrease the outlet hydrogen pressure when the measurement value of the ammeter 17 is above the optimal current value. Therefore, the outlet hydrogen pressure is gradually adjusted in accordance with the state of the power generation current of the FC stack 11. This makes it possible to suppress sudden changes in power generation of the FC stack 11 and suppress deterioration of the FC stack 11.

[0073] Furthermore, according to the configuration of this embodiment, the air system 22 includes an air compressor 71, and 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 other than the air compressor 71 are provided on the supply side of the air system 22, and no air valves or the like are provided on the discharge side of the air system 22. This allows for simplification of the air system 22, and allows for cost reduction of the fuel cell system 1.

[0074] Furthermore, according to the configuration of this embodiment, the control device 20 controls the air compressor 71 to stop when the FC stack 11 stops intermittently, thereby quickly stopping the supply of air to the FC stack 11. Therefore, power generation by the FC stack 11 can be stopped quickly and reliably.

[0075] Second Embodiment Next, a second embodiment will be described in detail with reference to the drawings. In the following description, components equivalent to those in the first embodiment will be denoted by the same reference numerals, and differences will be mainly described. [Regarding the control of the fuel cell system] This embodiment differs from the first embodiment in the content of the control of the fuel cell system 1. Figure 6 shows an example of the control content of this embodiment in the form of a flowchart.

[0076] 6, the control device 20 determines whether the request has changed from the "run-around power generation mode" to the "small current power generation mode" in step 200. If the result of this determination is positive, the control device 20 proceeds to step 210, and if the result of this determination is negative, the control device 20 temporarily terminates the subsequent processing.

[0077] In step 210, the control device 20 controls the injector 53 so that the outlet hydrogen pressure of the ejector 54 becomes a predetermined "stop hydrogen pressure" for stopping the FC stack 11 for a predetermined time. Here again, "0 (kPaG)" can be used as the "stop hydrogen pressure", for example. "3 (seconds)" can be used as the "predetermined time".

[0078] In step 220, the control device 20 controls the air compressor 71 to stop.

[0079] Next, in step 230, the control device 20 controls the injector 53 so that the outlet hydrogen pressure of the ejector 54 becomes a pressure slightly higher than atmospheric pressure (for example, 5 (kPaG)).

[0080] Then, in step 240, the control device 20 determines whether the request has changed from the "small current power generation mode" to the "run-around power generation mode." If the result of this determination is negative, the control device 20 proceeds to step 230, and if the result of this determination is positive, the control device 20 temporarily terminates the subsequent processing.

[0081] According to the above control, the control device 20 controls the injector 53 so that the outlet hydrogen pressure is first reduced to the stop hydrogen pressure for a predetermined period of time, and then changed to a fuel pressure slightly higher than atmospheric pressure (higher than the stop hydrogen pressure).

[0082] [Regarding the Functions and Effects of the Fuel Cell System] The configuration of the fuel cell system 1 of this embodiment described above provides functions and effects equivalent to those of the first embodiment. In addition, in this embodiment, the control device 20 controls the injector 53 to temporarily lower the outlet hydrogen pressure to the stop hydrogen pressure for a predetermined period of time, and then raise the hydrogen pressure to a pressure slightly higher than atmospheric pressure. Therefore, because the outlet hydrogen pressure is temporarily and reliably lowered to the stop hydrogen pressure, it becomes easier to adjust the outlet hydrogen pressure to a hydrogen pressure slightly higher than atmospheric pressure. This allows the FC stack 11, which is generating electricity as it goes, to be promptly and intermittently shut down.

[0083] <Other Embodiments> The disclosed technology is not limited to the above-described embodiments, and can be implemented by appropriately modifying part of the configuration within the scope of the disclosed technology.

[0084] (1) In the above embodiments, the fuel cell system 1 is assumed to be mounted on an electric vehicle. However, the fuel cell system can also be embodied in a device other than an electric vehicle.

[0085] (2) In the above-described embodiments, no air valves or the like are provided on the supply side and discharge side of the air system 22, but air valves or the like may be provided.

[0086] (3) In each of the above embodiments, when the request is changed from the “run-around power generation mode” to the “low-current power generation mode” in the control of the fuel cell system 1, the injector 53 is controlled so that the outlet hydrogen pressure of the ejector 54 becomes the “stop hydrogen pressure” for stopping the FC stack 11, and then subsequent processing is performed. However, when the request is changed to the “low-current power generation mode”, the control of the injector 53 to make the outlet hydrogen pressure of the ejector 54 become the “stop hydrogen pressure” can also be omitted.

[0087] (4) In each of the above embodiments, a closed cathode system in which the cooling system and the air system are separate has been described. However, the present invention can also be applied to an open cathode system in which the cooling system and the air system are common.

[0088] The disclosed technology can be used, for example, in a fuel cell system mounted on an electric vehicle.

[0089] REFERENCE SIGNS LIST 1 fuel cell system 11 FC stack (fuel cell) 17 ammeter 20 control device 21 hydrogen system (fuel supply device) 22 air system (oxidizer supply device) 53 injector (fuel supply device) 54 ejector (fuel supply device) 54a outlet (outlet of fuel supply device) 71 air compressor (pressure feeder)

Claims

1. A fuel cell system that receives supplies of fuel and an oxidant and generates electricity, and does not include a DC-DC converter, comprising: a fuel supply device for supplying fuel to the fuel cell; and a control device for controlling the fuel supply device, wherein the control device controls the fuel supply device so that when the fuel cell intermittently stops, the fuel pressure at the outlet of the fuel supply device is reduced to a fuel pressure higher than a predetermined stop fuel pressure.

2. The fuel cell system according to claim 1, wherein the control device controls the fuel supply device so that, before reducing the fuel pressure at the outlet to a fuel pressure higher than the stop fuel pressure, the fuel pressure is once reduced to the stop fuel pressure.

3. The fuel cell system according to claim 2, further comprising an ammeter for measuring the output current of the fuel cell, wherein when the control device adjusts the fuel pressure at the outlet from the stop fuel pressure to a fuel pressure higher than the stop fuel pressure, if the measured value of the ammeter is lower than a predetermined optimum current value, the control device controls the fuel supply device to increase the fuel pressure at the outlet, and if the measured value of the ammeter is higher than the optimum current value, the control device controls the fuel supply device to decrease the fuel pressure at the outlet.

4. The fuel cell system according to claim 2, wherein the control device controls the fuel supply device so that after reducing the fuel pressure at the outlet to the stop fuel pressure for a predetermined time, the fuel pressure is changed to a fuel pressure slightly higher than atmospheric pressure.

5. The fuel cell system according to any one of claims 1 to 4, further comprising an oxidant supply device for supplying the oxidant to the fuel cell, wherein the oxidant supply device includes a pump for pumping the oxidant to the fuel cell, and the fuel cell is configured such that the oxidant is directly supplied from the pump and directly discharged from the fuel cell.

6. The fuel cell system according to claim 5, wherein the control device controls the pump to stop in order to stop the supply of the oxidant when the fuel cell intermittently stops.

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