Fuel cell system and its control method

Abstract

To provide a fuel cell system that can maintain the hydrogen partial pressure within a system within an appropriate range even when an external environmental condition has changed.SOLUTION: A fuel cell system 1 includes: a fuel cell 2 that generates electric power by a reaction between hydrogen gas as a fuel gas and an oxidant gas; a hydrogen gas supply device 4 that supplies hydrogen gas to the fuel cell 2; a supply control unit 61 that determines a supply amount and a supply timing of hydrogen gas supplied to the fuel cell 2; and an atmospheric pressure acquisition unit (atmospheric pressure sensor 7) that acquires atmospheric pressure. Therein the supply control unit 61 supplies hydrogen gas to the fuel cell 2 at a supply amount and supply timing determined according to at least the atmospheric pressure during soaking when operation of the fuel cell 2 is stopped.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a fuel cell system capable of adjusting the supply timing and supply amount of fuel gas in a soak according to atmospheric pressure, and a control method therefor.

Background Art

[0002] In recent years, research and development on fuel cells that contribute to energy efficiency have been carried out in order to enable more people to access affordable, reliable, sustainable, and advanced energy.

[0003] In a fuel cell system that generates electricity using a fuel cell, during a soak in which the operation of the fuel cell is stopped, oxygen remaining in the cathode electrode system may cause electrode degradation, or oxygen may permeate through the electrolyte membrane and react with hydrogen in the anode electrode system to generate hydrogen peroxide, and the electrolyte membrane may be degraded by the OH radicals generated therefrom. Further, when the operation of the fuel cell is restarted, if oxygen is present in the anode electrode system in an amount equal to or greater than a specified value, there is a problem that the potential rises excessively and the electrode is degraded.

[0004] In order to suppress the problems caused by residual oxygen during such a soak, even during a soak, hydrogen gas is continuously supplied periodically for a predetermined period, and the hydrogen partial pressure in the anode electrode system is maintained at a specified value (lower limit value) or higher, thereby causing a reaction between hydrogen permeating through the electrolyte membrane and oxygen in the cathode electrode system to consume the residual oxygen. A technique has been proposed.

[0005] Hydrogen supply during a soak is often performed in a fixed amount at fixed time intervals, but there is also a technique for determining the hydrogen supply timing based on physical parameters in the fuel cell stack. For example, Patent Document 1 discloses a technique for changing the hydrogen supply timing based on the pressure and temperature in the fuel cell stack, and a technique for supplying hydrogen based on the hydrogen concentration on the anode side.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] U.S. Patent Publication No. 8,722,263 [Overview of the project] [Problems that the invention aims to solve]

[0007] In the conventional technology described above, external environmental conditions of the fuel cell system are not considered when determining the timing and amount of hydrogen supply during the soaking phase of the fuel cell. However, since the behavior of hydrogen partial pressure inside the fuel cell system can change depending on the atmospheric pressure and ambient temperature outside the system, it may be difficult to maintain the hydrogen partial pressure within the system within an appropriate range during soaking if these external environmental conditions are not considered.

[0008] This invention was made to solve these problems and aims to provide a fuel cell system that can maintain the hydrogen partial pressure within the system within an appropriate range even when external environmental conditions change. Ultimately, this contributes to energy efficiency. [Means for solving the problem]

[0009] To achieve this objective, the fuel cell system 1 according to claim 1 of the present invention comprises a fuel cell that generates electricity by the reaction of hydrogen gas as a fuel gas and an oxidizer gas, a hydrogen gas supply device that supplies hydrogen gas to the fuel cell, a supply control unit that determines the amount and timing of hydrogen gas supplied to the fuel cell, and an atmospheric pressure acquisition unit that acquires atmospheric pressure, wherein the supply control unit supplies hydrogen gas to the fuel cell at least the amount and timing determined according to the atmospheric pressure during a soak when the operation of the fuel cell is stopped. The supply control unit then determines the amount of hydrogen gas supplied during soaking so that the amount of hydrogen gas supplied in a single cycle decreases as the atmospheric pressure decreases. do.

[0010] In this fuel cell system, the supply control unit determines the amount and timing of hydrogen gas supply during the fuel cell soak, at least in accordance with atmospheric pressure. Here, the effect of atmospheric pressure, one of the external environmental conditions, on the hydrogen partial pressure in the fuel cell system will be explained with reference to Figure 5. Figure 5 is a diagram illustrating the gas behavior in the system under low-lying and high-lying conditions, i.e., environmental conditions with high atmospheric pressure and environmental conditions with low atmospheric pressure.

[0011] First, looking at the changes in total pressure within the anode and cathode electrode systems (see figure above), after soaking begins, hydrogen present in the anode electrode system permeates through the electrolyte membrane and moves to the cathode side, causing the total pressure in the anode electrode system to gradually decrease. Similarly, in the cathode electrode system, the permeated hydrogen reacts with the oxidizing gas remaining in the cathode electrode system, consuming it and causing the total pressure to gradually decrease. Comparing low-lying and high-lying conditions, under high-lying conditions where atmospheric pressure is lower, the total pressure in both the anode and cathode electrode systems will remain at a lower level than under low-lying conditions.

[0012] Next, looking at the change in hydrogen concentration within the cathode electrode system (middle figure), the hydrogen concentration temporarily increases after the start of soaking due to hydrogen permeating from the anode side, and then gradually decreases as the reaction between hydrogen and the oxidizing gas proceeds. Since the hydrogen concentration within the cathode electrode system significantly affects the hydrogen concentration in the exhaust gas, an upper limit is set for safety reasons. There is no significant difference in the trend of changes in hydrogen concentration within the cathode electrode system between low-altitude and high-altitude conditions. However, under high-altitude conditions, the total pressure within the cathode electrode system decreases, which in turn reduces the absolute amount of oxidant gas within the system. Therefore, if the same amount of hydrogen is supplied as under low-altitude conditions, the increase in hydrogen concentration within the cathode electrode system will also be larger, potentially exceeding the upper limit. For this reason, under high-altitude conditions, the amount of hydrogen supplied at one time needs to be smaller than under low-altitude conditions.

[0013] Finally, looking at the change in hydrogen partial pressure within the anode electrode system (see figure below), after the start of soaking, hydrogen permeates through the electrolyte membrane and moves to the cathode side, where it is consumed by reaction with the oxidizing agent, causing the hydrogen partial pressure within the anode electrode system to gradually decrease. Here, from the perspective of suppressing the deterioration of the electrode and electrolyte membrane by consuming the oxidizing agent gas remaining in the cathode electrode system during soaking through reaction with hydrogen, the hydrogen partial pressure in the anode electrode system needs to be maintained above a predetermined lower limit. As mentioned above, under high-altitude conditions, the total pressure within the anode electrode system decreases, which in turn reduces the absolute amount of hydrogen within the anode electrode system. Therefore, under high-altitude conditions, the time it takes for the partial pressure of hydrogen within the anode electrode system to reach its lower limit is shorter than under low-altitude conditions. Consequently, under high-altitude conditions, it is necessary to supply hydrogen at shorter intervals than under low-altitude conditions to prevent the partial pressure of hydrogen within the anode electrode system from falling below the lower limit.

[0014] Based on the above findings, the fuel cell system of the present invention can determine the amount and timing of hydrogen gas supply according to the atmospheric pressure during soaking, and supply hydrogen gas accordingly. Therefore, even if the atmospheric pressure, which is an external environmental condition, changes, the hydrogen partial pressure within the system can be maintained within an appropriate range. Furthermore, in the fuel cell system of the present invention, the supply control unit determines the amount of hydrogen gas supplied during soaking such that the amount of hydrogen gas supplied in a single cycle decreases as the atmospheric pressure decreases. Here, the change in hydrogen concentration in the cathode electrode system during hydrogen supply due to differences in atmospheric pressure will be explained with reference to Figure 7. Figure 7 is a diagram illustrating the gas behavior in the system under low-lying and high-lying conditions, i.e., environmental conditions with high atmospheric pressure and environmental conditions with low atmospheric pressure. First, looking at the changes in total pressure within the anode and cathode electrode systems immediately after hydrogen gas supply during soaking (see figure above), the total pressure within the anode electrode system temporarily rises significantly upon hydrogen gas supply. In this example, the amount of hydrogen gas supplied is determined based on gauge pressure, i.e., pressure relative to atmospheric pressure. Therefore, the increase in total pressure within the anode electrode system upon hydrogen gas supply remains constant regardless of whether the conditions are low or high altitude. Next, looking at the change in hydrogen concentration within the cathode electrode system (middle figure), immediately after the supply of hydrogen gas, hydrogen from the anode side permeates through the electrolyte membrane and enters the cathode side, causing a temporary and significant increase in the hydrogen concentration within the cathode electrode system. Under high-altitude conditions, the total pressure is low in both the anode and cathode electrode systems, and the absolute amount of gas is also small. Therefore, if hydrogen gas is supplied using the same gauge pressure range as under low-altitude conditions, the increase in hydrogen concentration in the cathode electrode system will be greater than under low-altitude conditions, potentially exceeding the upper limit of the hydrogen concentration in the system. Therefore, under high-altitude conditions, the amount of hydrogen supplied at one time needs to be smaller than under low-altitude conditions. Finally, looking at the change in hydrogen partial pressure within the anode electrode system (see figure below), the supply of hydrogen gas causes a temporary large increase in hydrogen partial pressure within the anode electrode system. Subsequently, it gradually decreases as hydrogen permeates to the cathode side, eventually reaching equilibrium. The magnitude of the increase in hydrogen partial pressure within the anode electrode system upon hydrogen gas supply remains constant regardless of whether the conditions are low or high altitude. Based on the above findings, the fuel cell system of the present invention determines the amount of hydrogen supplied during soaking so that the amount of hydrogen gas supplied in a single cycle decreases as the atmospheric pressure decreases. Therefore, when the atmospheric pressure, which is an external environmental condition, changes, the hydrogen partial pressure within the system can be maintained more effectively within an appropriate range.

[0015] The invention according to claim 2 of the present invention is a fuel cell system according to claim 1, further comprising an ambient temperature acquisition unit for acquiring ambient temperature, wherein the supply control unit supplies hydrogen gas to the fuel cell during soaking at a supply timing determined according to at least atmospheric pressure and ambient temperature.

[0016] According to this configuration, the supply control unit determines the supply timing of hydrogen gas at least according to the atmospheric pressure and the outside air temperature during the soak of the fuel cell. Here, the influence of the outside air temperature, which is one of the external environmental conditions, on the hydrogen partial pressure in the fuel cell system will be described with reference to FIG. 6. FIG. 6 is a diagram for explaining the gas behavior in the system under normal temperature and low temperature, that is, under environmental conditions with a high outside air temperature and environmental conditions with a low outside air temperature, respectively.

[0017] First, looking at the changes in the total pressure in each of the anode electrode system and the cathode electrode system (the above figure), similar to FIG. 5, after the start of the soak, the hydrogen in the anode electrode system permeates to the cathode side, so the total pressure in the anode electrode system decreases. At the same time, in the cathode electrode system, hydrogen and the oxidant gas react and are consumed, so the total pressure in the cathode electrode system also decreases. Here, under low temperature conditions where the outside air temperature is low, due to the influence of the outside air temperature, the temperature of the gas in the system drops faster than under normal temperature conditions, so the gas in each system condenses, and as a result, the total pressure drops more significantly.

[0018] Next, looking at the change in the hydrogen concentration in the cathode electrode system (the middle figure), similar to FIG. 5, after the start of the soak, the hydrogen concentration temporarily increases due to the hydrogen permeating from the anode side, and then gradually decreases as the reaction between hydrogen and the oxidant gas progresses. There is no significant difference in the tendency of the change in the hydrogen concentration in the cathode electrode system between lowland conditions and highland conditions.

[0019] Finally, looking at the change in the hydrogen partial pressure in the anode electrode system (the lower figure), similar to FIG. 5, after the start of the soak, hydrogen permeates through the electrolyte membrane and moves to the cathode side, and is consumed by the reaction with the oxidant, so the hydrogen partial pressure in the anode electrode system gradually decreases. Here, as described above, under low temperature conditions, the total pressure in the anode electrode system drops more significantly, so the decrease in the hydrogen partial pressure in the anode electrode system also becomes greater. Therefore, under low temperature conditions, it is necessary to supply hydrogen at an interval shorter than under normal temperature conditions so that the hydrogen partial pressure in the anode electrode system does not fall below the lower limit value.

[0020] Based on the above findings, the fuel cell system with the above configuration can determine the timing of hydrogen gas supply according to the atmospheric pressure and ambient temperature during soaking, and supply hydrogen gas accordingly. Therefore, even if the ambient temperature changes in addition to the atmospheric pressure, the hydrogen partial pressure within the system can be maintained within an appropriate range.

[0021] The invention according to claim 3 of the present invention is characterized in that, in the fuel cell system described in claim 2, the supply control unit determines the amount and timing of the next hydrogen gas supply during soaking, at least according to the atmospheric pressure and ambient temperature at the time of the previous hydrogen gas supply.

[0022] With this configuration, during the soak, the amount and timing of the next hydrogen gas supply are determined based on the atmospheric pressure and ambient temperature at the time of the previous hydrogen gas supply. Therefore, the amount and timing of hydrogen gas supply can be determined with high responsiveness based on relatively recent atmospheric pressure and ambient temperature. Consequently, the hydrogen partial pressure within the system can be maintained within an appropriate range in response to changes in atmospheric pressure and ambient temperature.

[0023] The invention according to claim 4 of the present invention is a fuel cell system according to any one of claims 1 to 3, characterized in that the supply control unit determines the timing of hydrogen gas supply during soaking such that the interval from the previous hydrogen gas supply to the next hydrogen gas supply becomes shorter as the atmospheric pressure decreases.

[0024] As described above, the lower the atmospheric pressure, the lower the absolute amount of hydrogen in the anode electrode system, and the shorter the time it takes for the partial pressure of hydrogen in the anode electrode system to reach its lower limit. In this fuel cell system configuration, the system is controlled to supply hydrogen gas at shorter time intervals as the atmospheric pressure decreases, so that it can appropriately respond to changes in atmospheric pressure and maintain the partial pressure of hydrogen in the system within an appropriate range.

[0025] The invention according to claim 5 of the present invention is characterized in that, in the fuel cell system described in claim 2 or 3, the supply control unit determines the timing of hydrogen gas supply during soaking such that the interval from the previous hydrogen gas supply to the next hydrogen gas supply becomes shorter as the ambient temperature decreases.

[0026] As mentioned above, the lower the ambient temperature, the greater the decrease in hydrogen partial pressure within the anode electrode system due to gas condensation, making it more likely to fall below the lower limit. In this fuel cell system configuration, the system is controlled to supply hydrogen gas at shorter time intervals as the ambient temperature decreases, thus appropriately responding to changes in ambient temperature and maintaining the hydrogen partial pressure within the system within an appropriate range.

[0033] Claims of the present invention 6 The control method for a fuel cell system relating to the present invention is a control method for a fuel cell system comprising: a fuel cell that generates electricity by the reaction of hydrogen gas and an oxidizing gas; a hydrogen gas supply means for supplying hydrogen gas to the fuel cell; a supply control means for determining the amount and timing of hydrogen gas supplied to the fuel cell; and an atmospheric pressure acquisition means for acquiring atmospheric pressure, wherein the supply control means supplies hydrogen gas to the fuel cell at least the amount and timing determined according to the atmospheric pressure during a soak when the operation of the fuel cell is stopped. Furthermore, the supply control means determines the amount of hydrogen gas supplied during soaking so that the amount of hydrogen gas supplied in a single cycle decreases as the atmospheric pressure decreases. Execute the control.

[0034] In the control method for the fuel cell system of the present invention, the amount and timing of hydrogen gas supply can be determined according to the atmospheric pressure during soaking, and hydrogen gas can be supplied accordingly. Therefore, even if the atmospheric pressure, which is an external environmental condition, changes, the hydrogen partial pressure within the system can be maintained within an appropriate range. [Brief explanation of the drawing]

[0035] [Figure 1] This is a schematic diagram of a fuel cell vehicle equipped with a fuel cell system according to one embodiment of the present invention. [Figure 2]Figure 1 is a flowchart showing the control process for hydrogen supply during soaking in the example fuel cell system. [Figure 3] This is a flowchart showing the control process of the supply interval and supply quantity determination subroutine. [Figure 4] This is an explanatory diagram illustrating the changes in the hydrogen partial pressure within the anode system during hydrogen supply control in an embodiment and a conventional example. [Figure 5] This is an explanatory diagram illustrating the behavior of gases within a system under high-altitude conditions. [Figure 6] This is an explanatory diagram illustrating the behavior of gases within a system under low-temperature conditions. [Figure 7] This is an explanatory diagram illustrating the behavior of gases within a system under high-altitude conditions. [Modes for carrying out the invention]

[0036] Preferred embodiments of the fuel cell system of the present invention will be described in detail below with reference to the drawings. The fuel cell system 1 according to the illustrated embodiment is mounted on a fuel cell vehicle 100 and functions as one of the power sources of the fuel cell vehicle 100. The configuration described below is illustrative of the present invention and is not limited thereto.

[0037] <Configuration of Fuel Cell System 1> Figure 1 is a schematic diagram of a fuel cell vehicle 100 equipped with a fuel cell system 1 according to one embodiment. The fuel cell vehicle 100 is, for example, a fuel cell electric vehicle and, as shown in the figure, comprises a fuel cell system 1, a battery 200, a current controller 300, a motor 400, and the like. The battery 200 may include a secondary battery or a capacitor.

[0038] The fuel cell system 1 comprises a fuel cell stack (fuel cell) 2, an oxidizer gas supply device 3, a hydrogen gas supply device 4, a refrigerant supply device 5, and a control device 6. The oxidizer gas supply device 3 supplies oxidizer gas to the fuel cell stack 2, and the hydrogen gas supply device 4 supplies hydrogen gas as fuel gas to the fuel cell stack 2. The refrigerant supply device 5 cools the fuel cell stack 2 by circulating and supplying refrigerant to the fuel cell stack 2. The control device 6 is composed of an ECU (Electronic Control Unit) and, as will be described later, operates as various control units, etc., by having the CPU execute a program stored in memory. The control device 6 controls the entire fuel cell system 1 (each component) through control lines (not shown).

[0039] The fuel cell stack 2 is a structure formed by stacking multiple power generation cells 21. The fuel cell stack 2 is provided with an oxidizer gas inlet 2a, an oxidizer gas outlet 2b, a hydrogen gas inlet 2c, a hydrogen gas outlet 2d, an output electrode 2e, a refrigerant outlet 2f, and a refrigerant inlet 2g.

[0040] Each power generation cell 21 of the fuel cell stack 2 has a configuration in which a solid polymer electrolyte membrane (hereinafter also simply referred to as an electrolyte membrane) 22, which is, for example, a thin film of perfluorosulfonic acid containing water, is sandwiched between an anode electrode 23 and a cathode electrode 24. In addition to fluorine-based electrolytes, hydrocarbon-based electrolytes and the like can be used as the electrolyte membrane 22. A pressure sensor 23a capable of measuring the total pressure (gauge pressure) inside the anode electrode 23 is provided within the sealing system of the anode electrode 23.

[0041] The fuel cell stack 2 generates electricity through an electrochemical reaction between an oxidant gas (e.g., air) supplied from the oxidant gas inlet 2a by the oxidant gas supply device 3 and hydrogen gas supplied from the hydrogen gas inlet 2c by the hydrogen gas supply device 4. The electricity generated by the fuel cell stack 2 can be used to charge the battery 200 via the output electrode 2e through the current controller 300 or to supply power to the motor 400, under the control of the control device 6.

[0042] The oxidizer gas supply device 3 includes an air pump 31 that compresses and supplies air from the atmosphere, and the air pump 31 is located in the air supply passage 32. The air supply passage 32 is provided with a humidifier 33 and a bypass passage 35 that bypasses the humidifier 33 via a valve 34. The air supply passage 32 is in communication with the oxidizer gas inlet 2a of the fuel cell stack 2. It is also possible to omit the bypass channel 35 and valve 34.

[0043] An air discharge channel 36, which passes through a humidifier 33, is connected to the oxidizer gas outlet 2b. An EGR (Exhaust Gas Recirculation) pump 37 is installed between the air discharge channel 36 and the air supply channel 32. The EGR pump 37 recirculates a portion of the gas discharged from the oxidizer gas outlet 2b back to the oxidizer gas inlet 2a. It is also possible to omit the EGR pump 37.

[0044] A supply-side sealing valve 32a is provided downstream of the air pump 31 in the air supply passage 32, and the supply of air to the fuel cell stack 2 can be switched on or off by opening and closing the supply-side sealing valve 32a. Furthermore, an air discharge passage 36 is provided with a discharge-side sealing valve 36a, and a diluent 38, which will be described later, is connected to the downstream side of the discharge-side sealing valve 36a via a back pressure control valve 36b. It is also possible to configure the system by providing only a single sealing valve, rather than separately providing the discharge side sealing valve 36a and the back pressure control valve 36b.

[0045] The hydrogen gas supply device 4 has a hydrogen tank 41 for storing high-pressure hydrogen gas. The hydrogen tank 41 communicates with the hydrogen gas inlet 2c of the fuel cell stack 2 via a hydrogen supply channel 42. In the hydrogen supply channel 42, a shut-off valve 42a, an injector 43, and an ejector 44 are provided in series from the upstream side. As will be described later, the injector 43's opening is controlled by the control device 6, thereby defining the flow rate and timing of hydrogen gas supplied to the fuel cell stack 2. The ejector 44 draws hydrogen gas from the circulation path 45, which will be described later, by creating a negative pressure inside it.

[0046] An off-gas channel 46 is connected to the hydrogen gas outlet 2d of the fuel cell stack 2. A gas-liquid separator 47 is connected to the off-gas channel 46. The gas-liquid separator 47 is provided with a drain channel 48 for discharging the liquid component, a circulation channel 45 for introducing the gaseous component into the ejector 44, and a purge channel 49 for purging the gaseous component to the outside. The drain channel 48 is connected to the diluent 38 via a valve 48a. The purge channel 49 is also connected to the diluent 38, and its opening and closing are switched by the operation of the purge valve 49a.

[0047] The diluent 38 mixes the fuel off-gas, which is discharged from the hydrogen gas outlet 2d of the fuel cell stack 2 and separated via the gas-liquid separator 47, with the oxidizer off-gas, which is discharged from the oxidizer gas outlet 2b of the fuel cell stack 2, to dilute the hydrogen concentration to below a specified value before discharging it to the outside.

[0048] The refrigerant supply device 5 communicates with the refrigerant outlet 2f and refrigerant inlet 2g of the fuel cell stack 2 and has a refrigerant flow path 51 that circulates and supplies refrigerants such as pure water and ethylene glycol. A cooling water pump 52 is provided on the refrigerant inlet 2g side of the refrigerant flow path 51, and a radiator 53 is provided on the refrigerant outlet 2f side.

[0049] The control unit 6 is an ECU composed of a microcomputer consisting of a CPU, RAM, ROM, and I / O interfaces (none of which are shown). The control unit 6 controls the opening and closing of various valves in the fuel cell system 1, the driving of various auxiliary equipment (air pump 31, cooling water pump 52, etc.), and the power generation amount of the fuel cell stack 2, which is controlled via the current controller 300. The control unit 6 also controls the amount and timing of hydrogen gas supplied to the fuel cell stack 2 by controlling the opening degree of the injector 43 while referring to the value of the pressure sensor 23a provided on the anode electrode 23. The control device 6 may also perform charge and discharge control for the battery 200 and power and regenerative drive control for the motor 400.

[0050] Furthermore, the control device 6 is connected to an atmospheric pressure sensor 7 that detects the atmospheric pressure near the fuel cell vehicle 100, and an ambient temperature sensor 8 that detects the ambient temperature near the fuel cell vehicle 100, and the detection signals from these sensors are input sequentially. The control device 6 reads and executes a program stored in ROM or RAM to realize the functions of the supply control unit 61, which will be described later. The supply control unit 61 uses the acquired atmospheric pressure and ambient temperature values ​​to perform the hydrogen supply control during soaking, which will be described later.

[0051] <Power generation operation of fuel cell system 1> The power generation operation of the fuel cell system 1 configured in this way (power generation operation in the fuel cell stack 2) will be described below.

[0052] The oxidizer gas supply device 3 supplies air as an oxidizer gas to the air supply channel 32 via the air pump 31. This air is humidified by passing through the humidifier 33, or bypassed by passing through the bypass channel 35, before being supplied to the fuel cell stack 2 from the oxidizer gas inlet 2a.

[0053] Meanwhile, the hydrogen gas supply device 4 supplies hydrogen gas from the hydrogen tank 41 to the hydrogen supply channel 42 based on the opening degree control of the injector 43 by the control device 6. This hydrogen gas passes through the ejector 44 and is then supplied to the fuel cell stack 2 from the hydrogen gas inlet 2c.

[0054] Air supplied to the fuel cell stack 2 from the oxidizer gas inlet 2a is supplied to the cathode electrode 24 of each power generation cell 21, and hydrogen gas supplied to the fuel cell stack 2 from the hydrogen gas inlet 2c is supplied to the anode electrode 23 of each power generation cell 21. As a result, in each power generation cell 21, hydrogen and oxygen in the air are consumed by an electrochemical reaction, and power is generated. The electricity generated is supplied to the battery 200 or motor 400 via the current controller 300, based on the control of the control device 6.

[0055] The air (including post-reaction gas and off-gas) remaining after the reaction at the cathode electrode 24 of each power generation cell 21 is discharged from the oxidizer gas outlet 2b into the air discharge channel 36. After the discharged air has had its moisture recovered as it passes through the humidifier 33, it is introduced into the diluent 38. Furthermore, the moisture recovered by the humidifier 33 is used to humidify the air passing through the air supply channel 32, thereby maintaining the electrolyte membrane 22 in each power generation cell 21 of the fuel cell stack 2 at a humidity level suitable for power generation.

[0056] Furthermore, the hydrogen gas produced after the reaction at the anode electrode 23 of each power generation cell 21 is discharged as fuel off-gas (fuel gas that has been partially consumed) from the hydrogen gas outlet 2d into the off-gas flow path 46. The discharged fuel off-gas is then introduced from the off-gas flow path 46 into the gas-liquid separator 47 to separate the liquid water, and then drawn into the ejector 44 via the circulation path 45.

[0057] Furthermore, during the execution of the series of power generation operations described above, the refrigerant supply device 5, based on control by the control device 6, drives the cooling water pump 52 to supply refrigerant to the fuel cell stack 2 from the refrigerant inlet 2g, and cools each power generation cell 21 through heat exchange between the refrigerant and each power generation cell 21. After cooling each power generation cell 21, the refrigerant is discharged from the refrigerant outlet 2f, cooled by the radiator 53, and then supplied back to the fuel cell stack 2.

[0058] <Hydrogen supply control during soak> Next, the hydrogen supply control during soaking in the fuel cell system 1 of this embodiment, and the supply interval and supply amount determination control as a subroutine thereof, will be described with reference to Figures 2 and 3. Figure 2 is a flowchart showing the hydrogen supply control process during soaking in this embodiment. This process is repeatedly executed at predetermined intervals during soaking when the power generation operation (power generation operation in the fuel cell stack 2) in the fuel cell system 1 is stopped. In addition, soaking in the fuel cell system 1 may be started when the ignition switch of the fuel cell vehicle 100 is turned off, or it may be started automatically depending on the charge state of the battery 200 or the operating state of the fuel cell vehicle 100.

[0059] First, in Step 1 (illustrated as "S1"; the same applies hereafter), supply interval and supply amount determination control is performed to determine the hydrogen supply timing and supply amount during the soak.

[0060] Figure 3 shows the subroutine for determining the supply interval and supply amount. First, in step 11, the atmospheric pressure value detected by the atmospheric pressure sensor 7 during the previous hydrogen gas supply is obtained as the previous supply atmospheric pressure Pprev. Here, "the previous hydrogen gas supply" refers to the time of the last hydrogen gas supply after the current soak began, and not the time of the hydrogen gas supply during the previous soak. Furthermore, if there is no previous hydrogen gas supply point, that is, if the current supply interval / supply amount determination control is being executed for the first time since the current soak started, the atmospheric pressure value at the start of the soak will be exceptionally obtained as the atmospheric pressure Pprev at the time of the previous supply.

[0061] In the following step 12, the ambient temperature value detected by the ambient temperature sensor 8 during the previous hydrogen gas supply is obtained as the ambient temperature Tprev at the time of the previous supply. Here, "the previous hydrogen gas supply time" refers to the time of the last hydrogen gas supply after the current soak has started. If there is no previous hydrogen gas supply time, the ambient temperature value at the start of the soak is exceptionally obtained as the previous supply ambient temperature Tprev.

[0062] In the following step 13, the timing of the next hydrogen gas supply is determined based on the acquired atmospheric pressure Pprev and ambient temperature Tprev at the time of the previous supply. This determination may be performed by substituting the acquired values ​​of atmospheric pressure Pprev and ambient temperature Tprev at the time of the previous supply into a pre-prepared function or the like to calculate and derive the timing of the next hydrogen gas supply. Alternatively, the timing may be obtained by reading a map or table that has been pre-defined based on the atmospheric pressure Pprev and ambient temperature Tprev at the time of the previous supply and other parameters, and searching the map or table.

[0063] Although not shown in the diagram, such maps and tables can be designed to determine the hydrogen gas supply timing in such a way that the interval between the last hydrogen gas supply and the next hydrogen gas supply becomes shorter as atmospheric pressure and ambient temperature decrease. In addition to atmospheric pressure and ambient temperature, the system may also be configured to determine the hydrogen gas supply timing by considering factors such as the pressure and temperature inside the fuel cell stack 2, and the hydrogen partial pressure and hydrogen concentration in each power generation cell 21 of the fuel cell stack 2.

[0064] In the following step 14, a timer is set and the countdown starts based on the timing of the next hydrogen gas supply determined in step 13.

[0065] In the following step 15, based on the previously obtained atmospheric pressure Pprev, the gauge pressure target value to be used as the basis for the hydrogen supply amount during the next hydrogen supply is determined, and this process is terminated. The gauge pressure target value is set as the gauge pressure value that the total pressure in the anode electrode 23 system should reach when hydrogen gas is supplied. The determination of the target gauge pressure can be configured, for example, by reading a map or table that pre-defines the corresponding gauge pressure value (or a correction coefficient for the reference gauge pressure) based on the atmospheric pressure Pprev at the time of the previous supply and other parameters, and then obtaining the target gauge pressure value by searching the said map or table.

[0066] Although not shown in the diagram, such maps and tables can be designed to have a tendency to determine the gauge pressure target value such that the next hydrogen gas supply amount decreases as the atmospheric pressure decreases. In addition to atmospheric pressure, the hydrogen gas supply amount may also be determined by considering the pressure and temperature inside the fuel cell stack 2, the hydrogen partial pressure and hydrogen concentration in each power generation cell 21 of the fuel cell stack 2, etc.

[0067] Returning to Figure 2, after determining the timing and amount of hydrogen gas supply (gauge pressure target value) in Step 1, in the following Step 2, the timer set and started counting in Step 14 of Figure 3 is referenced to determine whether the set time has elapsed. If the result of this check is YES and the time set by the timer has elapsed, proceed to step 3. On the other hand, if the result of this judgment is NO and the time set by the timer has not yet elapsed, the judgment in step 2 is repeated until the set time has elapsed.

[0068] In the subsequent step 3, hydrogen gas is supplied based on the gauge pressure target value for the next hydrogen gas supply determined in step 1. At this time, the detected value of the pressure sensor 23a provided on the anode electrode 23 is referenced, and hydrogen gas is supplied until this detected value reaches the gauge pressure target value.

[0069] In the following steps 4-5, it is determined whether or not the termination conditions for hydrogen supply control during soaking have been met. First, in step 4, the elapsed time since the start of the current soak is referenced to determine whether a predetermined time has elapsed. This predetermined time is set as a sufficient elapsed time to determine that it is no longer necessary to supply hydrogen during the soak. For example, it can be set as a time at which it can be determined that the oxidizing gas remaining in the cathode electrode 24 has been sufficiently consumed by the reaction with hydrogen through repeated hydrogen supply during the soak (steps 1 to 3). Alternatively, instead of a predetermined time, the system may count the number of times hydrogen supply (steps 1 to 3) is performed during the soak, and determine the termination of the hydrogen supply control during the soak when the predetermined number of hydrogen supply operations are confirmed.

[0070] If the result of Step 4 is YES, and it is determined that the execution of hydrogen supply control during soaking is no longer necessary after the predetermined time has elapsed, proceed to Step 6. In step 6, the timer and gauge pressure target value set in step 1 (Supply timing and supply amount determination control, Figure 3) are reset, and then this control process is terminated. On the other hand, if the result of step 4 is NO, and it is determined that the predetermined time has not yet elapsed since the start of the soak, proceed to step 5.

[0071] Step 5 determines whether the soak of fuel cell system 1 has finished. If the result of this determination is YES and the completion of the soak of fuel cell system 1 is confirmed, the process proceeds to step 6, where the timer and gauge pressure target value are reset, and then this control process ends. On the other hand, if the result of step 5 is NO and fuel cell system 1 is still soaking, the process returns to step 1 and repeats from step 1 until the termination conditions of step 4 or step 5 are met.

[0072] As explained above, in the hydrogen supply control during soaking of fuel cell system 1, the timing (interval) and supply amount (gauge pressure target value) of hydrogen gas during soaking are changed based on recently acquired atmospheric pressure and ambient temperature values. Figure 4 is an explanatory diagram for comparing the change in hydrogen partial pressure within the anode electrode system in a conventional example of hydrogen supply control during soaking with the change in hydrogen partial pressure within the anode electrode system in this embodiment of hydrogen supply control during soaking.

[0073] As is clear from the figure, in conventional cases where a fixed amount of hydrogen gas is supplied at regular intervals (fixed hydrogen supply amount and interval), it is not possible to respond to changes in external environmental conditions. For example, in environments where atmospheric pressure is low and the outside temperature is also low, the supply of hydrogen gas may not keep up with the decrease in hydrogen partial pressure, and the hydrogen partial pressure may fall below the lower limit. In this case, the oxidizing agent gas remaining in the cathode electrode system during soaking cannot be consumed by reaction with hydrogen, and the degradation of the electrodes and electrolyte membrane cannot be suppressed.

[0074] On the other hand, in this embodiment, in which the timing and amount of hydrogen gas supply can be changed according to external environmental conditions (atmospheric pressure and ambient temperature), even when external environmental conditions change, hydrogen gas can be supplied at the appropriate timing and amount, thereby maintaining the hydrogen partial pressure within an appropriate range. This effectively suppresses the deterioration of electrodes and electrolyte membranes.

[0075] <Effects of this embodiment> The effects of this embodiment will be described below. According to this embodiment, in the hydrogen supply control during soaking of the fuel cell system 1, the timing and amount of hydrogen gas supply can be determined based on atmospheric pressure, and hydrogen gas can be supplied. As a result, even if the atmospheric pressure, which is an external environment that can affect the gas behavior within each power generation cell 21 of the fuel cell stack 2, changes, the hydrogen partial pressure within the fuel cell stack 2 can be maintained within an appropriate range.

[0076] Furthermore, in this embodiment, in the hydrogen supply control during soaking of the fuel cell system 1, the timing of hydrogen gas supply can be determined and supplied based on ambient temperature in addition to atmospheric pressure. As a result, even if the ambient temperature, which is an external environment that can affect the gas behavior within each power generation cell 21 of the fuel cell stack 2, changes, the hydrogen partial pressure within the fuel cell stack 2 can be maintained within an appropriate range.

[0077] Furthermore, since the atmospheric pressure and ambient temperature referenced in hydrogen supply control during soaking are those from the previous hydrogen gas supply (or the atmospheric pressure and ambient temperature at the start of soaking), the amount and timing of hydrogen gas supply can be determined with high responsiveness based on relatively recent atmospheric pressure and ambient temperature data.

[0078] Furthermore, in the hydrogen supply control during soaking (supply timing and supply amount determination control subroutine), hydrogen gas is supplied at shorter time intervals when atmospheric pressure and ambient temperature are low, thus enabling the hydrogen partial pressure within the system to be maintained within a more appropriate range in response to changes in atmospheric pressure and ambient temperature.

[0079] Furthermore, in the hydrogen supply control during soaking (supply timing and supply amount determination control subroutine), the lower the atmospheric pressure, the smaller the amount of hydrogen gas supplied in a single supply is set. This allows the hydrogen partial pressure within the system to be maintained within an appropriate range more effectively in response to changes in atmospheric pressure.

[0080] Furthermore, the present invention is not limited to the embodiments described and can be implemented in various forms. In addition, the details of the configuration can be appropriately modified within the scope of the spirit of the present invention. [Explanation of symbols]

[0081] 1…Fuel cell system 2…Fuel cell stack (fuel cell) 21…Each power cell 22...Solid polymer electrolyte membrane 23... Anode electrode 24... Cathode electrode 3. Oxidizer gas supply device 4. Hydrogen gas supply device (hydrogen gas supply means) 5…Refrigerant supply device 6…Control Unit (ECU) 61... Supply control unit (supply control means) 7. Atmospheric pressure sensor (atmospheric pressure acquisition unit, atmospheric pressure acquisition means) 8. Outdoor temperature sensor (outdoor temperature acquisition unit, outdoor temperature acquisition means)

Claims

1. A fuel cell that generates electricity through the reaction of hydrogen gas as a fuel gas and an oxidizing gas, A hydrogen gas supply device that supplies the hydrogen gas to the fuel cell, A supply control unit that determines the amount and timing of hydrogen gas supplied to the fuel cell, It includes an atmospheric pressure acquisition unit that acquires atmospheric pressure, The supply control unit supplies hydrogen gas to the fuel cell at a supply amount and supply timing determined at least according to the atmospheric pressure during a soak when the operation of the fuel cell is stopped. The supply control unit determines the amount of hydrogen gas supplied in the soak so that the amount of hydrogen gas supplied in a single cycle decreases as the atmospheric pressure decreases. Fuel cell system.

2. It is further equipped with an ambient temperature acquisition unit that acquires the ambient temperature. The supply control unit supplies the hydrogen gas to the fuel cell during the soak at the supply timing determined at least according to the atmospheric pressure and ambient temperature. The fuel cell system according to claim 1, characterized in that

3. The fuel cell system according to claim 2, characterized in that the supply control unit determines the amount and timing of the next hydrogen gas supply during the soak, at least according to the atmospheric pressure and ambient temperature at the time of the previous hydrogen gas supply.

4. The fuel cell system according to any one of claims 1 to 3, characterized in that the supply control unit determines the timing of supplying the hydrogen gas during the soak so that the interval between the previous hydrogen gas supply and the next hydrogen gas supply becomes shorter as the atmospheric pressure decreases.

5. The fuel cell system according to claim 2 or 3, characterized in that the supply control unit determines the timing of the hydrogen gas supply during the soak so that the interval between the previous hydrogen gas supply and the next hydrogen gas supply becomes shorter as the ambient temperature decreases.

6. A fuel cell that generates electricity through the reaction of hydrogen gas and an oxidizing gas, A hydrogen gas supply means for supplying the hydrogen gas to the fuel cell, A supply control means for determining the amount and timing of hydrogen gas supplied to the fuel cell, A control method for a fuel cell system having means for obtaining atmospheric pressure, The supply control means supplies hydrogen gas to the fuel cell at a supply amount and supply timing determined at least according to the atmospheric pressure during a soak when the operation of the fuel cell is stopped. The supply control means performs control to determine the amount of hydrogen gas supplied in the soak, such that the amount of hydrogen gas supplied in a single cycle decreases as the atmospheric pressure decreases. A method for controlling a fuel cell system.

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