Fuel cell system and control method thereof

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 timing and amount of fuel gas supply during soaking in accordance with atmospheric pressure, and a control method thereof. [Background technology]

[0002] In recent years, research and development into fuel cells has been conducted to contribute to energy efficiency, ensuring that more people have access to affordable, reliable, sustainable and advanced energy.

[0003] In fuel cell systems that generate electricity using fuel cells, there are problems with the cathode electrode degradation during soak periods when the fuel cell is shut down due to residual oxygen remaining in the cathode electrode system, or with oxygen permeating the electrolyte membrane and reacting with hydrogen in the anode electrode system to produce hydrogen peroxide, which in turn generates OH radicals that can degrade the electrolyte membrane. Furthermore, when the fuel cell resumes operation, if there is more oxygen than the specified amount remaining in the anode electrode system, the potential can rise excessively, causing electrode degradation.

[0004] To mitigate such problems caused by residual oxygen during soaking, a method has been proposed in which hydrogen gas is supplied periodically for a specified period of time, even during soaking, to maintain the hydrogen partial pressure in the anode electrode system above a specified value (lower limit), thereby causing a reaction between the hydrogen that has permeated the electrolyte membrane and the oxygen in the cathode electrode system and consuming the remaining oxygen.

[0005] Hydrogen is often supplied in fixed amounts at regular intervals during the soak period, but there are also technologies that determine the timing of hydrogen supply based on physical parameters within the fuel cell stack. For example, Patent Document 1 discloses a technology that changes the timing of hydrogen supply based on the pressure and temperature within the fuel cell stack, and a technology that supplies hydrogen based on the hydrogen concentration on the anode side. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent No. 8,722,263 Summary of the Invention [Problem to be solved by the invention]

[0007] In the above-mentioned conventional technology, the external environmental conditions of the fuel cell system are not taken into consideration when determining the timing and amount of hydrogen supply during the fuel cell soak. However, because the behavior of the hydrogen partial pressure inside the fuel cell system can change depending on the atmospheric pressure and outside temperature outside the system, if these external environmental conditions are not taken into consideration, it may be difficult to maintain the hydrogen partial pressure inside the system within an appropriate range during the soak.

[0008] The present invention has been 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 the external environmental conditions change, thereby contributing to improved energy efficiency. [Means for solving the problem]

[0009] To achieve this object, the fuel cell system 1 according to claim 1 of the present invention comprises a fuel cell that generates electricity by reacting hydrogen gas as a fuel gas with an oxidant gas, a hydrogen gas supply device that supplies hydrogen gas to the fuel cell, a supply control unit that determines the supply amount and supply timing of hydrogen gas to be supplied to the fuel cell, and an atmospheric pressure acquisition unit that acquires atmospheric pressure, and 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.

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

[0011] First, looking at the changes in the total pressure in the anode and cathode electrode systems (see the diagram above), after the soak begins, the hydrogen in the anode electrode system permeates the electrolyte membrane and moves to the cathode side, causing the total pressure in the anode electrode system to gradually decrease. In the cathode electrode system, the permeated hydrogen reacts with the oxidant gas remaining in the cathode electrode system and is consumed, causing the total pressure to gradually decrease. Comparing low altitude and high altitude, under high altitude conditions where the atmospheric pressure is low, the total pressure in both the anode electrode system and the cathode electrode system remains at a lower level than under low altitude conditions.

[0012] Next, looking at the change in hydrogen concentration in the cathode electrode system (middle diagram), after the soak begins, the hydrogen concentration temporarily rises due to hydrogen permeating from the anode side, and then gradually decreases as the reaction between hydrogen and oxidant gas progresses. The hydrogen concentration in the cathode electrode system has a large effect on the hydrogen concentration in the exhaust gas, and therefore an upper limit is set from the viewpoint of safety. The tendency of change in the hydrogen concentration in the cathode electrode system does not differ significantly between low and high altitude conditions. However, because the total pressure in the cathode electrode system decreases under high altitude conditions, the absolute amount of oxidant gas in the cathode electrode system also decreases. Therefore, if the same amount of hydrogen is supplied as under low altitude conditions, the increase in the hydrogen concentration in the cathode electrode system will be greater, and there is a risk that it will exceed the upper limit. Therefore, under high altitude conditions, it is necessary to supply a smaller amount of hydrogen at one time than under low altitude conditions.

[0013] Finally, looking at the change in hydrogen partial pressure in the anode electrode system (see figure below), after the soak begins, hydrogen permeates the electrolyte membrane and moves to the cathode side, where it is consumed by reaction with the oxidant, causing the hydrogen partial pressure in the anode electrode system to gradually decrease. Here, from the viewpoint of suppressing deterioration of the electrodes and electrolyte membrane by consuming the oxidant gas remaining in the cathode electrode system during the soak by reacting it with hydrogen, the hydrogen partial pressure in the anode electrode system needs to be maintained at or above a predetermined lower limit. As described above, under high altitude conditions, the total pressure in the anode electrode system decreases, and therefore the absolute amount of hydrogen in the anode electrode system also decreases. Therefore, under high altitude conditions, it takes less time for the hydrogen partial pressure in the anode electrode system to reach the lower limit than under low altitude conditions. Therefore, under high altitude conditions, it is necessary to supply hydrogen at shorter intervals than under low altitude conditions so that the hydrogen partial pressure in the anode electrode system does not fall 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 the soak, and can supply hydrogen gas accordingly. Therefore, even if the atmospheric pressure as an external environmental condition changes, the hydrogen partial pressure within the system can be maintained within an appropriate range.

[0015] The invention according to claim 2 of the present invention is characterized in that, in the fuel cell system described in claim 1, it further comprises an outside air temperature acquisition unit that acquires outside air temperature, and the supply control unit supplies hydrogen gas to the fuel cell during the soak at a supply timing determined based on at least the atmospheric pressure and the outside air temperature.

[0016] According to this configuration, the supply control unit determines the timing of supplying hydrogen gas during the fuel cell soak in accordance with at least the atmospheric pressure and the outside temperature. Here, the effect of the outside temperature, which is one of the external environmental conditions, on the hydrogen partial pressure in the fuel cell system will be explained with reference to Fig. 6. Fig. 6 is a diagram for explaining the gas behavior in the system at room temperature and low temperature, i.e., under environmental conditions of high and low outside temperatures.

[0017] First, looking at the changes in the total pressure in the anode electrode system and the cathode electrode system (above), as in Figure 5, after the soak begins, the total pressure in the anode electrode system decreases as hydrogen in the anode electrode system permeates to the cathode side, and the total pressure in the cathode electrode system also decreases as hydrogen and oxidant gas react and are consumed in the cathode electrode system. Here, under low temperature conditions where the outside air temperature is low, the temperature of the gas in the system drops faster than under normal temperature conditions due to the influence of the outside air temperature, causing the gas in each system to condense, resulting in a greater drop in total pressure.

[0018] Next, looking at the change in hydrogen concentration in the cathode electrode system (middle figure), as in Figure 5, the hydrogen concentration temporarily rises after the soak begins due to hydrogen permeating from the anode side, and then gradually decreases as the reaction between hydrogen and oxidant gas progresses. The tendency of change in hydrogen concentration in the cathode electrode system does not show a significant difference between low altitude conditions and high altitude conditions.

[0019] Finally, looking at the change in hydrogen partial pressure in the anode electrode system (see figure below), as in Figure 5, after the soak begins, hydrogen permeates the electrolyte membrane and moves to the cathode side, where it is consumed by reaction with the oxidant, causing the hydrogen partial pressure in the anode electrode system to gradually decrease. As described above, under low temperature conditions, the total pressure in the anode electrode system decreases more significantly, and therefore the partial pressure of hydrogen in the anode electrode system also decreases more significantly. Therefore, under low temperature conditions, it is necessary to supply hydrogen at shorter intervals than under room temperature conditions so that the partial pressure of hydrogen in the anode electrode system does not fall below the lower limit.

[0020] Based on the above findings, the fuel cell system of the above configuration can determine the timing of hydrogen gas supply according to the atmospheric pressure and outside temperature during the soak and supply hydrogen gas, so that even if the outside temperature changes in addition to the atmospheric pressure as external environmental conditions, 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 next supply amount and supply timing of hydrogen gas during the soak period based on at least the atmospheric pressure and outside temperature at the time of the previous hydrogen gas supply.

[0022] With this configuration, the amount and timing of the next hydrogen gas supply are determined during the soak period based on the atmospheric pressure and outside temperature at the time of the previous hydrogen gas supply, so that the amount and timing of the hydrogen gas supply can be determined with high responsiveness based on the relatively recent atmospheric pressure and outside temperature, thereby making it possible to maintain the hydrogen partial pressure in the system within an appropriate range in response to changes in atmospheric pressure and outside temperature.

[0023] The invention according to claim 4 of the present invention is characterized in that, in the fuel cell system according to any one of claims 1 to 3, the supply control unit determines the timing of supplying hydrogen gas during the soak so that the interval between the previous supply of hydrogen gas and the next supply of hydrogen gas becomes shorter the lower the atmospheric pressure.

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

[0025] The invention of claim 5 of the present invention is characterized in that, in the fuel cell system of claim 2 or 3, the supply control unit determines the timing of supplying hydrogen gas during the soak so that the interval between the previous supply of hydrogen gas and the next supply of hydrogen gas becomes shorter the lower the outside air temperature.

[0026] As described above, the lower the outside temperature, the greater the drop in hydrogen partial pressure in the anode electrode system due to gas condensation, making it more likely to fall below the lower limit. In the fuel cell system of this configuration, the lower the outside temperature, the more frequently hydrogen gas is supplied, so the system can respond appropriately to changes in outside temperature and maintain the hydrogen partial pressure in the system within an appropriate range.

[0027] The invention of claim 6 of the present invention is characterized in that, in the fuel cell system described in claim 1, the supply control unit determines the amount of hydrogen gas supplied during the soak so that the lower the atmospheric pressure, the smaller the amount of hydrogen gas supplied at one time.

[0028] With this configuration, the supply control unit determines the amount of hydrogen gas supplied during the soak so that the lower the atmospheric pressure, the smaller the amount of hydrogen gas supplied per cycle. 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 at low and high altitudes, i.e., under environmental conditions of high and low atmospheric pressure.

[0029] First, looking at the change in total pressure in the anode electrode system and cathode electrode system immediately after hydrogen gas is supplied during soaking (see the diagram above), the supply of hydrogen gas causes a temporary large increase in total pressure in the anode electrode system. 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 in the anode electrode system when hydrogen gas is supplied is constant regardless of whether the conditions are low or high altitude.

[0030] Next, looking at the change in hydrogen concentration in the cathode electrode system (middle diagram), immediately after hydrogen gas is supplied, hydrogen on the anode side permeates the electrolyte membrane and enters the cathode side, causing a temporary large increase in the hydrogen concentration in the cathode electrode system. Here, under high altitude conditions, the total pressure in both the anode electrode system and the cathode electrode system is low, and the absolute amount of gas is also small. Therefore, if hydrogen gas is supplied based on 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, which may cause the hydrogen concentration in the system to exceed its upper limit. Therefore, under high altitude conditions, it is necessary to supply less hydrogen at one time than under low altitude conditions.

[0031] Finally, looking at the change in hydrogen partial pressure in the anode electrode system (see diagram below), the supply of hydrogen gas causes a temporary large increase in the hydrogen partial pressure in the anode electrode system, then gradually decreases as the hydrogen permeates to the cathode side, eventually reaching equilibrium. The increase in hydrogen partial pressure in the anode electrode system when hydrogen gas is supplied is constant regardless of whether the conditions are low or high altitude.

[0032] Based on the above findings, in the fuel cell system of the above configuration, the amount of hydrogen supplied during the soak is determined so that the lower the atmospheric pressure, the smaller the amount of hydrogen gas supplied at one time. Therefore, when the atmospheric pressure as an external environmental condition changes, the hydrogen partial pressure within the system can be more effectively maintained within an appropriate range.

[0033] The control method for a fuel cell system according to claim 7 of the present invention is a control method for a fuel cell system having a fuel cell that generates electricity by reacting hydrogen gas with an oxidant gas, a hydrogen gas supply means that supplies hydrogen gas to the fuel cell, a supply control means that determines the supply amount and supply timing of hydrogen gas to be supplied to the fuel cell, and an atmospheric pressure acquisition means that acquires atmospheric pressure, wherein the supply control means executes control to supply hydrogen gas to the fuel cell at a supply amount and supply timing determined at least in accordance with the atmospheric pressure during a soak when the operation of the fuel cell is stopped.

[0034] The control method for a fuel cell system of the present invention determines the amount and timing of hydrogen gas supply according to the atmospheric pressure during the soak, and can supply hydrogen gas accordingly. Therefore, even if the atmospheric pressure as an external environmental condition changes, the hydrogen partial pressure within the system can be maintained within an appropriate range. [Brief explanation of the drawings]

[0035] [Figure 1] 1 is a schematic diagram of a fuel cell vehicle equipped with a fuel cell system according to an embodiment of the present invention; [Figure 2] 2 is a flowchart showing a control process for hydrogen supply during soak in the fuel cell system of the example of FIG. 1. [Figure 3] 10 is a flowchart showing a control process of a supply interval / supply amount determination subroutine. [Figure 4] FIG. 10 is an explanatory diagram illustrating the transition of the hydrogen partial pressure in the anode system in the hydrogen supply control during soak in the embodiment and the conventional example. [Figure 5] FIG. 2 is an explanatory diagram for explaining the behavior of gas in the system under high altitude conditions. [Figure 6] FIG. 2 is an explanatory diagram for explaining the behavior of gas in the system under low temperature conditions. [Figure 7] FIG. 2 is an explanatory diagram for explaining the behavior of gas in the system under high altitude conditions. DETAILED DESCRIPTION OF THE INVENTION

[0036] A preferred embodiment of the fuel cell system of the present invention will be described in detail below with reference to the drawings. A 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. Note that the configuration described below is an example of the present invention, and the present invention is not limited to this.

[0037] <Configuration of fuel cell system 1> 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, includes the fuel cell system 1, a battery 200, a current controller 300, a motor 400, etc. The battery 200 may include a secondary battery, a capacitor, etc.

[0038] The fuel cell system 1 includes a fuel cell stack (fuel cell) 2, an oxidizing gas supply device 3, a hydrogen gas supply device 4, a coolant supply device 5, and a control device 6. The oxidizing gas supply device 3 supplies an oxidizing gas to the fuel cell stack 2, and the hydrogen gas supply device 4 supplies hydrogen gas to the fuel cell stack 2 as a fuel gas. The coolant supply device 5 cools the fuel cell stack 2 by circulating and supplying a coolant to the fuel cell stack 2 . The control device 6 is configured by an ECU (Electronic Control Unit), and as will be described later, operates as various control units, etc. by the CPU executing programs stored in memory. The control device 6 controls the entire fuel cell system 1 (each component) through a control line (not shown).

[0039] The fuel cell stack 2 is a structure in which a plurality of power generation cells 21 are stacked. The fuel cell stack 2 is provided with an oxidant gas inlet 2a, an oxidant 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 the 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. As the electrolyte membrane 22, a fluorine-based electrolyte, a hydrocarbon-based electrolyte, etc. can be used. Within the sealing system of the anode electrode 23, a pressure sensor 23a capable of measuring the total pressure (gauge pressure) within the anode electrode 23 is provided.

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

[0042] The oxidizing gas supply device 3 includes an air pump 31 that compresses and supplies air from the atmosphere, and the air pump 31 is disposed in an air supply flow path 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 communicates with an oxidizing gas inlet 2a of the fuel cell stack 2. It is also possible to omit the bypass flow path 35 and the valve 34.

[0043] The oxidizing gas outlet 2b is connected to an air discharge passage 36 that passes through a humidifier 33. An EGR (Exhaust Gas Recirculation) pump 37 is provided between the air discharge passage 36 and the air supply passage 32. The EGR pump 37 returns a portion of the gas discharged from the oxidizing gas outlet 2b to the oxidizing gas inlet 2a side. It is also possible to omit the EGR pump 37.

[0044] A supply-side seal valve 32a is provided downstream of the air pump 31 in the air supply flow path 32, and the supply of air to the fuel cell stack 2 is switched on and off by opening and closing the supply-side seal valve 32a. A discharge-side seal valve 36a is provided in the air discharge flow path 36, and a diluter 38 (described later) is connected downstream of the discharge-side seal valve 36a via a back pressure control valve 36b. It is also possible to provide only a single seal valve instead of providing the discharge side seal valve 36a and the back pressure control valve 36b separately.

[0045] The hydrogen gas supply device 4 has a hydrogen tank 41 that stores 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 passage . The hydrogen supply channel 42 is provided with a shutoff valve 42a, an injector 43, and an ejector 44 in series, in this order from the upstream side. As will be described later, the opening of the injector 43 is controlled by the control device 6, thereby determining the flow rate and timing of the hydrogen gas supplied to the fuel cell stack 2. The ejector 44 creates a negative pressure inside, thereby sucking in hydrogen gas from a circulation path 45, which will be described later.

[0046] An off-gas passage 46 communicates with the hydrogen gas outlet 2d of the fuel cell stack 2. A gas-liquid separator 47 is connected to the off-gas passage 46. The gas-liquid separator 47 is provided with a drain passage 48 for discharging the liquid component, a circulation passage 45 for causing the gas component to flow into the ejector 44, and a purge passage 49 for purging the gas component to the outside. The drain passage 48 communicates with the diluter 38 via a valve 48a. The purge passage 49 is connected to the diluter 38 and is opened or closed by the operation of a purge valve 49a.

[0047] The diluter 38 mixes the fuel off-gas discharged from the hydrogen gas outlet 2d of the fuel cell stack 2 and separated via the gas-liquid separator 47 with the oxidant off-gas discharged from the oxidant gas outlet 2b of the fuel cell stack 2, diluting the hydrogen concentration to a specified value or less, and then discharging the mixture to the outside.

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

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

[0050] In addition, 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 outside air temperature sensor 8 that detects the outside air temperature, which is the air temperature near the fuel cell vehicle 100, and the detection signals from these sensors are input sequentially. The control device 6 realizes the functions of the supply control unit 61 described below by reading and executing a program stored in the ROM or RAM, and the supply control unit 61 uses the acquired atmospheric pressure and outside temperature values to perform the hydrogen supply control during soak described below.

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

[0052] The oxidizing gas supply device 3 supplies air as an oxidizing gas to an air supply passage 32 via an air pump 31. This air is humidified by passing through a humidifier 33, or passes through a bypass passage 35 to bypass the humidifier 33, and then is supplied to the fuel cell stack 2 from an oxidizing gas inlet 2a.

[0053] Meanwhile, the hydrogen gas supply device 4 supplies hydrogen gas from the hydrogen tank 41 to the hydrogen supply flow path 42 based on the control of the opening degree of the injector 43 by the control device 6. After passing through the ejector 44, this hydrogen gas is supplied to the fuel cell stack 2 from the hydrogen gas inlet 2c.

[0054] Air supplied to the fuel cell stack 2 from the oxidant 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, generating electricity. The generated electric power is supplied to the battery 200 or the motor 400 through the current controller 300 under the control of the control device 6.

[0055] The air (including the post-reaction gas and the off-gas) after the reaction at the cathode electrode 24 of each power generation cell 21 is discharged from the oxidant gas outlet 2b to the air discharge passage 36. The discharged air passes through the humidifier 33, where moisture is recovered, and then the air is introduced into the diluter 38. The moisture recovered by the humidifier 33 is used to humidify the air passing through the air supply passage 32, thereby maintaining the electrolyte membrane 22 in each power generation cell 21 of the fuel cell stack 2 at a humidity suitable for power generation.

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

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

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

[0059] First, in step 1 (shown as "S1"; the same applies below), control is executed to determine the supply interval and supply amount of hydrogen during the soak period.

[0060] 3 shows the subroutine for controlling the supply interval and supply amount determination. First, in step 11, the atmospheric pressure detected by the atmospheric pressure sensor 7 during the previous hydrogen gas supply is acquired as the atmospheric pressure during the previous supply Pprev. Here, the time of the previous hydrogen gas supply refers to the time of the previous hydrogen gas supply after the current soak started, and does not refer to the time of the hydrogen gas supply during the previous soak. Also, if there is no previous hydrogen gas supply time point, i.e., if this is the first time that the supply interval and supply amount determination control has been executed since the current soak started, then exceptionally, the atmospheric pressure value at the start of the soak is obtained as the previous supply atmospheric pressure Pprev.

[0061] In the following step 12, the value of the outside air temperature detected by the outside air temperature sensor 8 at the time of the previous supply of hydrogen gas is acquired as the outside air temperature at the time of the previous supply Tprev. Here again, the previous hydrogen gas supply time refers to the time of the previous hydrogen gas supply after the current soak started. If there is no previous hydrogen gas supply time, then exceptionally, the value of the outside air temperature at the start of the soak is obtained as the outside air temperature at the previous supply time Tprev.

[0062] In the following step 13, the next timing for supplying hydrogen gas is determined based on the acquired atmospheric pressure Pprev at the time of the previous supply and the outside air temperature Tprev at the time of the previous supply. This determination may be made by substituting the acquired values of the atmospheric pressure Pprev at the time of the previous supply and the outside air temperature Tprev at the time of the previous supply into a pre-prepared function or the like to derive the next timing for supplying hydrogen gas through calculation. Alternatively, the next timing for supplying hydrogen gas may be determined by reading a map or table that defines the corresponding hydrogen gas supply timing based on the atmospheric pressure Pprev at the time of the previous supply and the outside air temperature Tprev at the time of the previous supply and other parameters, and searching the map or table.

[0063] Although not shown, such a map or table can be designed to have a tendency to determine the timing of hydrogen gas supply so that the interval between the previous supply of hydrogen gas and the next supply of hydrogen gas becomes shorter the lower the atmospheric pressure and the outside temperature. Furthermore, the timing of hydrogen gas supply can be determined taking into consideration the pressure and temperature within the fuel cell stack 2, the hydrogen partial pressure and hydrogen concentration in each power generation cell 21 of the fuel cell stack 2, and the like, in addition to the atmospheric pressure and the outside temperature.

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

[0065] In the next step 15, a gauge pressure target value is determined as a reference for the amount of hydrogen to be supplied the next time based on the acquired atmospheric pressure Pprev at the time of the previous supply, and the process ends. The gauge pressure target value is set as the gauge pressure value that the total pressure in the anode electrode 23 system should reach as a result of the supply of hydrogen gas. The target gauge pressure value can be determined, for example, by reading a map or table that predetermines 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 or other parameters, and searching the map or table to obtain the target gauge pressure value.

[0066] Although not shown, such a map or table can be designed to have a tendency to determine the gauge pressure target value so that the lower the atmospheric pressure, the smaller the next hydrogen gas supply amount. Furthermore, the hydrogen gas supply amount may be determined taking into consideration factors other than atmospheric pressure, such as the pressure and temperature within 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.

[0067] Returning to FIG. 2, after the next hydrogen gas supply timing and supply amount (gauge pressure target value) are determined in step 1, the timer that was set and started in step 14 of FIG. 3 is referenced in the following step 2 to determine whether the set time has elapsed. If the result of this determination is YES and the time set by the timer has elapsed, the process proceeds to step 3. On the other hand, if the result of this determination is NO and the time set by the timer has not yet elapsed, the determination in step 2 is repeatedly executed until the set time has elapsed.

[0068] In the following 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 detection value of the pressure sensor 23a provided on the anode electrode 23 is referenced, and hydrogen gas is supplied until this detection value reaches the gauge pressure target value.

[0069] In the following steps 4 and 5, it is determined whether or not the conditions for ending the soak hydrogen supply control are satisfied. First, in step 4, the time elapsed 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 there is no longer a need to supply hydrogen during the soak, and can be set, for example, as a time to determine that the oxidant gas remaining in the cathode electrode 24 has been sufficiently consumed by reaction with hydrogen through repeated execution of hydrogen supply during the soak (steps 1 to 3). Instead of a predetermined time, the number of times hydrogen is supplied during the soak (steps 1 to 3) may be counted, and when it is confirmed that hydrogen has been supplied a predetermined number of times, the end of hydrogen supply control during the soak may be determined.

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

[0071] In step 5, it is determined whether the soak of the fuel cell system 1 has ended. If the result of this determination is YES, and it is confirmed that the soak of the fuel cell system 1 has ended, the process proceeds to step 6, where the timer and the target gauge pressure value are reset, and then this control process ends. On the other hand, if the determination result in step 5 is NO and the fuel cell system 1 is still soaking, the process returns to step 1, and the process from step 1 onwards is repeated until the termination condition of step 4 or step 5 is met.

[0072] As described above, the hydrogen supply control during soak in the fuel cell system 1 changes the supply timing (interval) and supply amount (gauge pressure target value) of hydrogen gas during soak based on the recently acquired atmospheric pressure and outside temperature values. FIG. 4 is an explanatory diagram for comparing the transition of hydrogen partial pressure in the anode electrode system in the soak hydrogen supply control of the conventional example with the transition of hydrogen partial pressure in the anode electrode system in the soak hydrogen supply control of this embodiment.

[0073] As is clear from the figure, the conventional method of supplying a fixed amount of hydrogen gas at fixed intervals (fixed hydrogen supply amount and interval) cannot respond to changes in external environmental conditions. For example, in an environment where the atmospheric pressure and outside temperature are low, the supply of hydrogen gas cannot keep up with the decrease in hydrogen partial pressure, and the hydrogen partial pressure may fall below the lower limit. In this case, the oxidant gas remaining in the cathode electrode system during the soak cannot be consumed by reaction with hydrogen, and deterioration of the electrodes and electrolyte membrane cannot be suppressed.

[0074] On the other hand, in this embodiment, the timing and amount of hydrogen gas supply can be changed according to the external environmental conditions (atmospheric pressure and outside temperature), so even if the external environmental conditions change, hydrogen gas can be supplied at an appropriate timing and amount, and the hydrogen partial pressure can be maintained within an appropriate range, thereby effectively suppressing deterioration of the electrodes and electrolyte membrane.

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

[0076] Furthermore, in this embodiment, the timing of hydrogen gas supply can be determined and hydrogen gas can be supplied based on the outside temperature in addition to the atmospheric pressure in the soak hydrogen supply control of the fuel cell system 1. This makes it possible to maintain the hydrogen partial pressure in the fuel cell stack 2 within an appropriate range even if the outside temperature, which is an external environment that can affect the gas behavior in the system of each power generation cell 21 of the fuel cell stack 2, changes.

[0077] Furthermore, the atmospheric pressure and outside temperature referenced in the hydrogen supply control during the soak are the atmospheric pressure and outside temperature at the time of the previous hydrogen gas supply (or the atmospheric pressure and outside temperature at the start of the soak), so the supply amount and supply timing of hydrogen gas can be determined with high responsiveness based on the relatively recent atmospheric pressure and outside temperature.

[0078] Furthermore, in the soak hydrogen supply control (supply timing and supply amount determination control subroutine), the lower the atmospheric pressure and the lower the outside temperature, the shorter the time interval at which hydrogen gas is supplied, making it possible to maintain the hydrogen partial pressure in the system within a more appropriate range in response to changes in atmospheric pressure and outside temperature.

[0079] Furthermore, in the soak hydrogen supply control (supply timing and supply amount determination control subroutine), the lower the atmospheric pressure, the smaller the supply amount for each hydrogen gas supply is set, so that the hydrogen partial pressure in the system can be more effectively maintained within an appropriate range in response to changes in atmospheric pressure.

[0080] The present invention is not limited to the embodiments described above, and can be implemented in various forms. In addition, the detailed configuration can be appropriately changed 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 generation cell 22...Solid polymer electrolyte membrane 23...Anode electrode 24...Cathode electrode 3...Oxidant 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...Outside temperature sensor (outside temperature acquisition unit, outside temperature acquisition means)

Claims

1. a fuel cell that generates electricity by reacting hydrogen gas as fuel gas with an oxidant gas; a hydrogen gas supply device that supplies the hydrogen gas to the fuel cell; a supply control unit that determines the supply amount and supply timing of the hydrogen gas to be supplied to the fuel cell; an atmospheric pressure acquisition unit that acquires atmospheric pressure, the supply control unit supplies the hydrogen gas to the fuel cell at the supply amount and the supply timing determined in accordance with at least the atmospheric pressure during a soak period in which the operation of the fuel cell is stopped. Fuel cell system.

2. Further provided is an outside air temperature acquisition unit that acquires an outside air temperature, The supply control unit supplies the hydrogen gas to the fuel cell during the soak period at the supply timing determined based on at least the atmospheric pressure and the outside air temperature.

2. The fuel cell system according to claim 1, wherein:

3. 3. The fuel cell system according to claim 2, wherein the supply control unit determines the amount and timing of the next supply of hydrogen gas during the soak period based on at least the atmospheric pressure and the outside air temperature at the time of the previous supply of hydrogen gas.

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

5. 4. The fuel cell system according to claim 2, wherein the supply control unit determines the timing of supplying the hydrogen gas during the soak so that the interval between the previous supply of hydrogen gas and the next supply of hydrogen gas becomes shorter the lower the outside air temperature.

6. 4. The fuel cell system according to claim 1, wherein the supply control unit determines the supply amount of the hydrogen gas during the soak so that the lower the atmospheric pressure, the smaller the amount of hydrogen gas supplied at one time.

7. a fuel cell that generates electricity by reacting hydrogen gas with an oxidizing gas; a hydrogen gas supply means for supplying the hydrogen gas to the fuel cell; a supply control means for determining the supply amount and supply timing of the hydrogen gas to be supplied to the fuel cell; and an atmospheric pressure acquisition means for acquiring atmospheric pressure, the supply control means executes control to supply the hydrogen gas to the fuel cell at the supply amount and the supply timing determined in accordance with at least the atmospheric pressure during a soak period in which the operation of the fuel cell is stopped. A method for controlling a fuel cell system.

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