fuel cell system

Abstract

To effectively dry a power generating cell.SOLUTION: A control device 24 executes first power generation control with a first refrigerant flow path 120 and a second refrigerant flow path 140 blocked, and causes a refrigerant in the second refrigerant flow path 140 heated by a heater 144 to flow into the first refrigerant flow path 120 when executing the second power generation control.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fuel cell system. [Background technology]

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

[0003] A system equipped with a fuel cell stack is called a fuel cell system. A fuel cell stack comprises multiple power generation cells. The power generation cells generate electricity through an electrochemical reaction between fuel gas (hydrogen-containing gas) and oxidant gas (oxygen-containing gas). When the power generation cells generate electricity, water is produced. Some of the produced water accumulates inside the fuel cell stack. If the operation of the fuel cell system is stopped in a low-temperature environment, there is a risk that the water accumulated inside the fuel cell stack will freeze. If water freezes in a fuel cell system, the flow of gas is obstructed, and the fuel cell stack will no longer be able to generate electricity.

[0004] Patent Document 1 discloses a method for shutting down a fuel cell system that, when the ignition switch is turned off, executes a dry power generation process and then a wastewater power generation process in order to promote drying of the membrane electrode assemblies (MEAs) of the power generation cells. The amount of humidification of the oxidant gas supplied to the fuel cell stack during the dry power generation process is set to be less than the amount of humidification of the oxidant gas supplied to the fuel cell stack during the wastewater power generation process. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-058188 Summary of the Invention [Problem to be solved by the invention]

[0006] A technique for effectively drying power generating cells is desired.

[0007] The present invention aims to solve the above-mentioned problems. [Means for solving the problem]

[0008] An aspect of the present invention is a fuel cell system comprising: a fuel cell stack including a power generation cell that generates power through an electrochemical reaction between a fuel gas and an oxidant gas; a radiator used to cool the fuel cell stack; a first refrigerant flow path that circulates a refrigerant between the fuel cell stack and the radiator; a valve body that can switch between connection and disconnection between a first refrigerant flow path and a second refrigerant flow path different from the first refrigerant flow path; a heater that heats the refrigerant flowing through the second refrigerant flow path; and a control device that controls power generation of the power generation cell, wherein the control device is capable of performing first power generation control and second power generation control that is different from the first power generation control, and the second power generation control is power generation control for drying an electrolyte membrane provided in the power generation cell, and the control device performs the first power generation control with the first refrigerant flow path and the second refrigerant flow path blocked, and when performing the second power generation control, the control device causes the refrigerant in the second refrigerant flow path that has been heated by the heater to flow into the first refrigerant flow path. [Effects of the Invention]

[0009] According to the present invention, the power generating cell can be dried well. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of a fuel cell system. [Figure 2] FIG. 2 is a flowchart showing the procedure of the power generation control process. [Figure 3] FIG. 3 is a flowchart showing the procedure of post-shutdown processing. [Figure 4] FIG. 4 is a time chart showing the behavior of each part of the fuel cell system during post-shutdown processing. DETAILED DESCRIPTION OF THE INVENTION

[0011] [1 Configuration of fuel cell system 10] FIG. 1 is a schematic diagram of a fuel cell system 10. The fuel cell system 10 is mounted on, for example, a vehicle (fuel cell vehicle). The fuel cell system 10 can also be mounted on moving objects such as ships, aircraft, and robots. The fuel cell system 10 can also be used as a stationary power source for facilities, homes, and the like.

[0012] In the fuel cell system 10, a fuel gas and an oxidant gas are used as reactant gases. The fuel gas is a hydrogen-containing gas. The oxidant gas is an oxygen-containing gas such as air. Each of the fuel gas and the oxidant gas is supplied to the fuel cell stack 12 and subjected to an electrochemical reaction. In this specification, the fuel gas discharged from the fuel cell stack 12 without being subjected to the electrochemical reaction is also referred to as fuel off-gas. In this specification, the oxidant gas discharged from the fuel cell stack 12 without being subjected to the electrochemical reaction is also referred to as oxidant off-gas.

[0013] The fuel cell system 10 includes a fuel cell stack 12, a tank 14, an anode system 16, a cathode system 18, a cooling system 20, and an air conditioning system 22. The fuel cell system 10 also includes a control device 24. Electric power generated by the fuel cell stack 12 is supplied to a load 26. The load 26 includes a drive motor, a battery, and a heater 144 of the fuel cell vehicle. The tank 14 is filled with high-pressure fuel gas.

[0014] The fuel cell stack 12 includes a fuel gas supply port 12a that supplies fuel gas to the inside of the fuel cell stack 12 and a fuel gas discharge port 12b that discharges fuel off-gas from the inside of the fuel cell stack 12. The fuel cell stack 12 includes an oxidant gas supply port 12c that supplies oxidant gas to the inside of the fuel cell stack 12 and an oxidant gas discharge port 12d that discharges oxidant off-gas from the inside of the fuel cell stack 12. The fuel cell stack 12 includes a refrigerant supply port 12e that supplies refrigerant to the inside of the fuel cell stack 12 and a refrigerant discharge port 12f that discharges the refrigerant from the inside of the fuel cell stack 12.

[0015] The fuel cell stack 12 has a plurality of power generating cells 28. Each of the plurality of power generating cells 28 has the same configuration. Each power generating cell 28 includes a membrane electrode assembly 30, a first separator 32, and a second separator 34. The membrane electrode assembly 30 is sandwiched between the first separator 32 and the second separator 34. One of the plurality of power generating cells 28 is shown in FIG. 1.

[0016] The first separator 32 and the second separator 34 are formed, for example, from a metal sheet having a corrugated cross section. In two adjacent power generating cells 28, the first separator 32 of one power generating cell 28 and the second separator 34 of the other power generating cell 28 are joined to each other. A cell cooling channel (not shown) is formed between the first separator 32 and the second separator 34. The cell cooling channel communicates with the refrigerant supply port 12e and the refrigerant discharge port 12f.

[0017] The membrane electrode assembly 30 includes an electrolyte membrane 36, an anode 38, and a cathode 40. The electrolyte membrane 36 is located between the anode 38 and the cathode 40. An anode flow path 42 is formed between the first separator 32 and the anode 38. The anode flow path 42 communicates with the fuel gas supply port 12a and the fuel gas discharge port 12b. A cathode flow path 44 is formed between the second separator 34 and the cathode 40. The cathode flow path 44 communicates with the oxidant gas supply port 12c and the oxidant gas discharge port 12d.

[0018] The anode system 16 includes a fuel gas supply channel 84, a fuel gas discharge channel 86, a circulation channel 88, and a drain channel 90. The anode system 16 also includes an injector 94, an ejector 96, a gas-liquid separator 98, and a drain valve 100.

[0019] The fuel gas supply path 84 connects the outlet of the tank 14 and the fuel gas supply port 12a of the fuel cell stack 12. The fuel gas supply path 84 is provided with an injector 94 and an ejector 96. The ejector 96 is disposed between the injector 94 and the fuel cell stack 12.

[0020] The fuel gas discharge path 86 connects the fuel gas discharge port 12b of the fuel cell stack 12 to the supply port of the gas-liquid separator 98. The circulation path 88 connects the discharge port of the gas-liquid separator 98 to the ejector 96.

[0021] The drainage channel 90 connects the drain outlet of the gas-liquid separator 98 to the inlet of the diluter 121. The outlet of the diluter 121 is connected to an exhaust port provided in the vehicle. The drainage channel 90 is provided with a drain valve 100.

[0022] The cathode system 18 includes an oxidant gas supply channel 106, an oxidant gas discharge channel 108 (discharge channel), and a bypass channel 110. The cathode system 18 also includes a compressor 112 (oxidant gas supplier), a humidifier 114 (HUM), a first shutoff valve 116, a second shutoff valve 118, and a bypass valve 119.

[0023] The oxidant gas supply channel 106 connects an air intake port (not shown) provided in the vehicle and the oxidant gas supply port 12c of the fuel cell stack 12. The oxidant gas supply channel 106 is provided with a compressor 112, a first shut-off valve 116, and a humidifier supply channel 114A of the humidifier 114. A portion of the oxidant gas supply channel 106 that is arranged upstream of the humidifier 114 is referred to as the oxidant gas supply channel 106A. A portion of the oxidant gas supply channel 106 that is arranged downstream of the humidifier 114 is referred to as the oxidant gas supply channel 106B. The oxidant gas supply channel 106A is provided with the compressor 112 and the first shut-off valve 116. The first shut-off valve 116 is arranged between the compressor 112 and the humidifier 114.

[0024] The oxidant gas discharge channel 108 connects the oxidant gas discharge port 12d of the fuel cell stack 12 and the inlet of the diluter 121. The oxidant gas discharge channel 108 is provided with a humidifier discharge channel 114B of the humidifier 114 and a second shutoff valve 118. A portion of the oxidant gas discharge channel 108 that is arranged upstream of the humidifier 114 is referred to as the oxidant gas discharge channel 108A. A portion of the oxidant gas discharge channel 108 that is arranged downstream of the humidifier 114 is referred to as the oxidant gas discharge channel 108B. The oxidant gas discharge channel 108B is provided with the second shutoff valve 118.

[0025] The bypass passage 110 is connected to the oxidizing gas supply passage 106A between the compressor 112 and the first shutoff valve 116, and to the oxidizing gas discharge passage 108B downstream of the second shutoff valve 118. The bypass passage 110 is provided with a bypass valve 119.

[0026] The cooling system 20 includes a refrigerant flow path 120. The cooling system 20 also includes a pump 126, a radiator 128, a temperature sensor 130, and a flow dividing valve 132.

[0027] The coolant flow path 120 circulates a coolant between the fuel cell stack 12 and the radiator 128. The coolant is, for example, water containing ethylene glycol. The coolant flow path 120 includes a coolant supply path 122, a coolant discharge path 124, and a branch path 125. The coolant supply path 122 connects a fluid outlet of the radiator 128 to a coolant supply port 12e of the fuel cell stack 12. The coolant discharge path 124 connects a coolant discharge port 12f of the fuel cell stack 12 to a fluid supply port of the radiator 128. The branch path 125 branches off from the coolant discharge path 124 and merges with the coolant supply path 122.

[0028] The pump 126 is provided in the coolant supply path 122. The pump 126 is provided, for example, between a portion where a partial flow path 148B (described later) and the coolant supply path 122 are connected and a portion where a partial flow path 148A (described later) and the coolant supply path 122 are connected. The pump 126 may also be provided in the coolant discharge path 124. The radiator 128 is a heat dissipator that dissipates heat from the coolant in the coolant path 120. The radiator 128 may include a fan.

[0029] The temperature sensor 130 is provided in the coolant discharge path 124. The temperature sensor 130 may also be provided in the coolant supply path 122. The temperature sensor 130 detects the temperature of the coolant in the coolant flow path 120 (coolant temperature). The temperature sensor 130 may also detect the outlet temperature of the reactant gas. In this case, the temperature sensor 130 is provided, for example, in the fuel gas discharge port 12b. The coolant temperature or the outlet temperature corresponds to the internal temperature of the fuel cell stack 12 (stack temperature).

[0030] The flow dividing valve 132 is provided at a junction where the branch path 125 joins the refrigerant supply path 122. The flow dividing valve 132 may also be provided at a branch point where the branch path 125 branches off from the refrigerant discharge path 124. The opening degree of the flow dividing valve 132 is adjustable. The amount of refrigerant supplied to the radiator 128 is adjusted depending on the opening degree of the flow dividing valve 132. The opening degree of the flow dividing valve 132 is controlled by the control device 24.

[0031] The air conditioning system 22 includes a refrigerant flow path 140. The air conditioning system 22 also includes a pump 142, a heater 144, and a valve body 146.

[0032] The refrigerant flow path 140 is provided separately from the refrigerant flow path 120 of the cooling system 20. That is, the refrigerant flow path 140 is different from the refrigerant flow path 120. 140 A temperature sensor 160 is provided in the cooling system 20. The refrigerant flow path 140 of the air conditioning system 22 and the refrigerant flow path 120 of the cooling system 20 are connected via a communication path 148. The communication path 148 has a partial flow path 148A and a partial flow path 148B.

[0033] The material of the refrigerant flowing through the refrigerant flow path 140 of the air conditioning system 22 is the same as the material of the refrigerant flowing through the refrigerant flow path 120 of the cooling system 20. The refrigerant flowing through the refrigerant flow path 140 exchanges heat with air taken in from, for example, the vehicle interior. The air after heat exchange is supplied to, for example, the vehicle interior.

[0034] The pump 142 is provided in the refrigerant flow path 140 of the air conditioning system 22. The heater 144 is a heater that heats the refrigerant in the refrigerant flow path 140 of the air conditioning system 22. The heating of the refrigerant by the heater 144 is controlled by the control device 24, for example.

[0035] The valve element 146 switches between connection and disconnection between the refrigerant flow path 120 of the cooling system 20 and the refrigerant flow path 140 of the air conditioning system 22. This switching is performed by the control device 24. The valve element 146 may be a three-way valve. In this case, the valve element 146 is provided at the connection portion between the refrigerant flow path 140 and the partial flow path 148A, and at the connection portion between the refrigerant flow path 140 and the partial flow path 148B, respectively.

[0036] The control device 24 may be configured by an ECU (Electronic Control Unit). The control device 24 includes a calculation unit 136 and a storage unit 138. The calculation unit 136 is, for example, a processor such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit). In other words, the calculation unit 136 may be configured by processing circuitry.

[0037] The calculation unit 136 includes an acquisition unit 150, a power generation control unit 152, and a thermal control unit 154. The acquisition unit 150, the power generation control unit 152, and the thermal control unit 154 may be realized by the calculation unit 136 executing a program stored in the storage unit 138. At least a portion of the acquisition unit 150, the power generation control unit 152, and the thermal control unit 154 may be realized by an integrated circuit such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field-Programmable Gate Array). Furthermore, at least a portion of the acquisition unit 150, the power generation control unit 152, and the thermal control unit 154 may be realized by an electronic circuit including a discrete device. The acquisition unit 150 acquires information from electronic components (sensors, ECUs, etc.) other than the control device 24. The power generation control unit 152 controls the operation of the injector 94, the compressor 112, the pump 126, each valve, etc. The thermal control unit 154 controls the operations of the flow dividing valve 132, the heater 144, the valve element 146, and the like.

[0038] The storage unit 138 is a computer-readable storage medium. The storage medium is composed of a volatile memory (not shown) and a non-volatile memory (not shown). The volatile memory is, for example, a random access memory (RAM). The non-volatile memory is, for example, a read-only memory (ROM), a flash memory, etc. Data, etc. are stored in, for example, the volatile memory. Programs, tables, maps, etc. are stored in, for example, the non-volatile memory. At least a part of the storage unit 138 may be provided in the above-mentioned processor, integrated circuit, etc.

[0039] [2. Fluid flow in fuel cell system 10] 2-1 Fluid flow in the anode system 16 The injector 94 injects fuel gas supplied from the tank 14 downstream of the fuel gas supply path 84. The fuel gas injected from the injector 94 is supplied to the fuel gas supply port 12a of the fuel cell stack 12 via the fuel gas supply path 84. The fuel gas that does not react inside the fuel cell stack 12 is discharged as fuel off-gas from the fuel gas discharge port 12b of the fuel cell stack 12. The fuel off-gas contains hydrogen that did not react with oxygen, nitrogen in the oxidant gas that has permeated the electrolyte membrane 36, and moisture produced by the reaction between oxygen and hydrogen.

[0040] The fuel off-gas is supplied to a gas-liquid separator 98 via a fuel gas discharge path 86. The gas-liquid separator 98 separates the fuel off-gas into a gas component (fuel off-gas) and a liquid component (water). The fuel off-gas discharged from the gas-liquid separator 98 is supplied to an ejector 96 via a circulation path 88. The fuel off-gas sucked from the gas-liquid separator 98 and the fuel gas injected from the injector 94 join together in the ejector 96.

[0041] [2-2 Fluid flow in the cathode system 18] The compressor 112 discharges oxidant gas (air) taken in from outside the vehicle downstream of the oxidant gas supply channel 106. The oxidant gas discharged from the compressor 112 is supplied to the oxidant gas supply port 12c of the fuel cell stack 12 via the oxidant gas supply channel 106. The oxidant gas that has not reacted inside the fuel cell stack 12 is discharged as oxidant off-gas from the oxidant gas discharge port 12d of the fuel cell stack 12. The oxidant off-gas contains each component contained in the oxidant gas and moisture produced by the reaction of oxygen and hydrogen.

[0042] The oxidant off-gas is discharged to the diluter 121 via the oxidant gas discharge path 108. The oxidant off-gas contains moisture. In the humidifier 114, a portion of the moisture contained in the oxidant off-gas is used to humidify the oxidant gas flowing through the humidifier supply path 114A.

[0043] 2-3 Fluid flow in the cooling system 20 The pump 126 discharges the coolant toward the coolant supply port 12e of the fuel cell stack 12. The coolant discharged from the pump 126 is supplied to the coolant supply port 12e of the fuel cell stack 12 via the coolant supply path 122. The coolant that has circulated inside the fuel cell stack 12 is discharged from the coolant discharge port 12f of the fuel cell stack 12. The coolant discharged from the coolant discharge port 12f is supplied to the radiator 128 via the coolant discharge path 124. The coolant that has dissipated heat in the radiator 128 reaches the pump 126.

[0044] A part of the refrigerant discharged from the refrigerant discharge port 12f flows into the refrigerant supply path 122 via the branch path 125 without passing through the radiator 128. The amount of this flow-in is adjusted according to the opening of the branch valve 132.

[0045] [2-4 Fluid flow in air conditioning system 22] The heater 144 heats the refrigerant in the refrigerant flow path 140. In a state (first state) in which the refrigerant flow path 120 of the cooling system 20 and the refrigerant flow path 140 of the air conditioning system 22 are blocked, the refrigerant heated by the heater 144 is circulated through the refrigerant flow path 140 by the pump 142.

[0046] In a state (second state) in which the refrigerant flow path 120 of the cooling system 20 and the refrigerant flow path 140 of the air conditioning system 22 are connected, the refrigerant heated by the heater 144 flows into the refrigerant flow path 120. That is, in the second state, the refrigerant heated by the heater 144 flows into a partial flow path 148A of the communication path 148 via the valve body 146. The refrigerant that has flowed into the partial flow path 148A flows into the refrigerant flow path 120 of the cooling system 20 and merges with the refrigerant in the refrigerant flow path 120.

[0047] The refrigerant then flows into the fuel cell stack 12 via the refrigerant supply path 122, circulates inside the fuel cell stack 12, and flows into the refrigerant supply path 122 via the refrigerant discharge path 124 or the branch path 125. A portion of the refrigerant flowing into the refrigerant supply path 122 flows into the refrigerant path 140 of the air conditioning system 22 via the partial path 148B of the communication path 148. The refrigerant that has flowed into the refrigerant path 140 reaches the pump 142.

[0048] Thus, in the second state, the coolant circulates through the coolant flow path 140 of the air conditioning system 22, the coolant flow path 120 of the cooling system 20, and the inside of the fuel cell stack 12.

[0049] [3 Power generation control] The power generation control unit 152 is capable of executing first power generation control and second power generation control. Fig. 2 is a flowchart showing the procedure of the power generation control process. The power generation control unit 152 does not execute the power generation control process unless it has received a system startup command, which is a command to start up the fuel cell system 10. When the power generation control unit 152 receives the system startup command, the power generation control process proceeds to step S1.

[0050] In step S1, the power generation control unit 152 executes the first power generation control. The power generation control unit 152 continues the first power generation control until it receives a system stop command, which is a command to stop the fuel cell system 10. When the system stop command is received, the power generation control unit 152 ends the first power generation control. When the first power generation control ends, the fuel cell system 10 is shut down. After that, the power generation control process proceeds to step S2.

[0051] In step S2, the power generation control unit 152 monitors the temperature (stack temperature) detected by the temperature sensor 130 while the system is stopped. The power generation control unit 152 compares the stack temperature with a predetermined temperature threshold. This temperature threshold is selected, for example, from a range of 0°C to 5°C. If the stack temperature is equal to or higher than the temperature threshold (NO in step S2), the power generation control unit 152 compares the stack temperature with the temperature threshold again after a predetermined time has elapsed. If the stack temperature is lower than the temperature threshold (YES in step S2), the power generation control process executes step S3.

[0052] In step S3, the power generation control unit 152 executes the second power generation control. When the second power generation control ends, the power generation control process ends. After the power generation control process ends, the power generation control unit 152 does not execute the power generation control process until it receives a system startup command again.

[0053] The system start command is supplied when the switch (start switch) of the fuel cell system 10 is turned on. The system stop command is supplied when the switch of the fuel cell system 10 is turned off. The switch of the fuel cell system 10 corresponds to, for example, the ignition switch of a vehicle.

[0054] The first power generation control is a power generation control for supplying power according to demand to the load 26. In other words, the first power generation control is a control for executing normal power generation. The power generation control unit 152 controls the operations of the injector 94, compressor 112, pump 126, each valve, etc. based on predetermined normal power generation conditions, and causes the power generation cell 28 to perform normal power generation.

[0055] The second power generation control is a power generation control for drying the electrolyte membrane 36 provided in the power generation cell 28. Before executing the second power generation control, the power generation control unit 152 controls the operation of the injector 94, the compressor 112, the pump 126, each valve, etc. to perform warm-up. When performing warm-up, the power generation control unit 152 controls the compressor 112 so that the stoichiometric ratio of the oxidant gas supplied to the fuel cell stack 12 is relatively small. That is, the power generation control unit 152 sets the stoichiometric ratio of the oxidant gas during warm-up to be smaller than the stoichiometric ratio of the oxidant gas during the first power generation control. As a result, during warm-up, low-efficiency power generation is performed in the power generation cell 28, in which the power generation efficiency is lower than that of normal power generation. Because low-efficiency power generation is performed, the amount of heat generated by the power generation cell 28 increases during warm-up. That is, the amount of heat generated by the power generation cell 28 during warm-up is greater than the amount of heat generated by the power generation cell 28 during the first power generation control.

[0056] When the temperature detected by the temperature sensor 130 reaches a target temperature (described later), the power generation control unit 152 ends the warm-up and starts the second power generation control. In this case, the power generation control unit 152 controls the operations of the injector 94, compressor 112, pump 126, valves, etc. based on predetermined dry power generation conditions, and causes the power generation cell 28 to perform dry power generation.

[0057] The stoichiometric ratio of the oxidant gas supplied to the fuel cell stack 12 in dry power generation is set to be higher than the stoichiometric ratio of the oxidant gas supplied to the fuel cell stack 12 in normal power generation. The power generation control unit 152 controls the compressor 112 so that the stoichiometric ratio of the oxidant gas supplied to the fuel cell stack 12 in dry power generation is higher than the stoichiometric ratio of the oxidant gas supplied to the fuel cell stack 12 in normal power generation. Therefore, in dry power generation, the efficiency of discharging water remaining inside the fuel cell stack 12 to the outside is increased. In other words, the efficiency of discharging water in dry power generation is higher than the efficiency of discharging water in normal power generation. This reduces the accumulation of water inside the fuel cell stack 12.

[0058] The humidification amount of the oxidant gas supplied to the fuel cell stack 12 in the second power generation control may be less than the humidification amount of the oxidant gas supplied to the fuel cell stack 12 in the first power generation control. For example, in the second power generation control, the oxidant gas may be supplied to the fuel cell stack 12 via a humidifier bypass flow path (not shown) that branches off from the oxidant gas supply channel 106A and merges with the oxidant gas supply channel 106B without passing through the humidifier 114. On the other hand, in the first power generation control, the oxidant gas supplied to the oxidant gas supply channel 106A is supplied to the fuel cell stack 12 via the humidifier 114 and the oxidant gas supply channel 106B.

[0059] [4 Thermal Control] During the first power generation control, the thermal control unit 154 drives the pump 126 and closes the diverter valve 132. Note that the thermal control unit 154 may adjust the opening degree of the diverter valve 132. During the first power generation control, the thermal control unit 154 also blocks the refrigerant flow path 120 of the cooling system 20 and the refrigerant flow path 140 of the air conditioning system 22 using the valve body 146. Therefore, during the first power generation control, the refrigerant in the refrigerant flow path 140 of the air conditioning system 22 is not supplied to the fuel cell stack 12. During the first power generation control, only the refrigerant in the refrigerant flow path 120 of the cooling system 20 is supplied to the fuel cell stack 12.

[0060] As will be described later, in this embodiment, in order to maintain a sufficiently high temperature of the power generating cell 28 when the second power generation control is performed, the refrigerant heated by the heater 144 is caused to flow into the refrigerant flow path 120. Therefore, when the second power generation control is started, it is preferable that the refrigerant in the refrigerant flow path 140 has been sufficiently heated by the heater 144. Therefore, when warm-up is started, the thermal control unit 154 turns on the heater 144 in advance to raise the temperature of the refrigerant in the refrigerant flow path 140 to a predetermined temperature.

[0061] When heating is performed by the heater 144, the power output from the power generation cell 28 during warm-up may be supplied to the heater 144, or the power stored in the battery may be supplied to the heater 144. When the control device 24 receives a power consumption command requesting consumption of the power stored in the battery, the thermal control unit 154 sets a power supply path so that the power stored in the battery is supplied to the heater 144. In this case, the power stored in the battery is consumed by the heater 144.

[0062] The power consumption command is issued when the remaining battery capacity is equal to or greater than a predetermined remaining capacity threshold. The predetermined temperature is set to be higher than the refrigerant temperature detected by the temperature sensor 130 during warm-up.

[0063] Before the second power generation control is started, the thermal control unit 154 controls the valve element 146 to connect the refrigerant flow path 120 of the cooling system 20 to the refrigerant flow path 140 of the air conditioning system 22. More specifically, the thermal control unit 154 connects the refrigerant flow path 120 of the cooling system 20 to the refrigerant flow path 140 of the air conditioning system 22 before the warm-up is completed. The timing for connecting the refrigerant flow path 120 of the cooling system 20 to the refrigerant flow path 140 of the air conditioning system 22 may be a timing when a predetermined time has elapsed since the warm-up was started. When the refrigerant flow path 120 of the cooling system 20 is connected to the refrigerant flow path 140 of the air conditioning system 22, the power generation cell 28 is warmed by the heat generated by the power generation of the power generation cell 28 and the heat of the refrigerant heated by the heater 144. Therefore, the power generation cell 28 can be dried more quickly and sufficiently than when the power generation cell 28 is dried using only the heat generated by the power generation of the power generation cell 28.

[0064] During the second power generation control, the thermal control unit 154 successively compares the refrigerant temperature detected by the temperature sensor 130 with the target temperature at predetermined time intervals. The thermal control unit 154 adjusts the opening of the diverter valve 132 according to the temperature detected by the temperature sensor 130. In this case, the thermal control unit 154 reduces the opening of the diverter valve 132 as the temperature detected by the temperature sensor 130 increases. This makes it possible to maintain the temperature of the fuel cell stack 12 at the target temperature.

[0065] [5. Post-shutdown processing] Fig. 3 is a flowchart showing the procedure of the post-shutdown process. Fig. 4 is a time chart showing the behavior of each part of the fuel cell system 10 during the post-shutdown process.

[0066] In FIG. 4, "refrigerant temperature" refers to the temperature detected by the temperature sensor 130. That is, "refrigerant temperature" refers to the temperature of the refrigerant in the refrigerant flow path 120. Also, in FIG. 4, "impedance (HFR)" refers to the impedance of the fuel cell stack 12, i.e., the high frequency resistance of the fuel cell stack 12. This impedance may be detected by an impedance sensor that detects the AC impedance of the entire plurality of power generation cells 28. Also, the "flow dividing valve (CMV)" shown in FIG. 4 corresponds to the flow dividing valve 132, the "valve element" shown in FIG. 4 corresponds to the valve element 146, and the "heater" shown in FIG. 4 corresponds to the heater 144.

[0067] The post-shutdown process is started when the stack temperature becomes lower than the temperature threshold value after the first power generation control ends, and the process proceeds to step S11.

[0068] In step S11, the control device 24 starts warming up. At this time, the control device 24 controls the pump 126 to circulate the refrigerant in the cooling system 20. The control device 24 also controls the diverter valve 132 to reduce the amount of refrigerant supplied to the radiator 128. The thermal control unit 154 also turns on the pump 142 and the heater 144 to raise the temperature of the refrigerant in the air conditioning system 22 to a predetermined temperature. After this, the post-shutdown process proceeds to step S12. Note that the heater 144 may already be on. With the start of warming up, low-efficiency power generation begins in the power generating cell 28, and the refrigerant temperature in the refrigerant flow path 120 gradually increases over time (see FIG. 4). As the refrigerant temperature increases, the amount of water in the power generating cell 28 decreases, causing the impedance of the fuel cell stack 12 to increase (see FIG. 4).

[0069] In step S12, the control device 24 controls the valve element 146 to connect the refrigerant flow path 120 of the cooling system 20 to the refrigerant flow path 140 of the air conditioning system 22. At this time of connection, the refrigerant temperature in the refrigerant flow path 140 of the air conditioning system 22 is higher than the refrigerant temperature in the refrigerant flow path 120 of the cooling system 20. Therefore, the refrigerant in the refrigerant flow path 120 of the cooling system 20 is warmed by the refrigerant in the refrigerant flow path 140 of the air conditioning system 22.

[0070] In step S13, controller 24 compares the refrigerant temperature detected by temperature sensor 130 with the target temperature. If the refrigerant temperature is lower than the target temperature (NO in step S13), step S13 is repeated. On the other hand, if the refrigerant temperature is equal to or higher than the target temperature (YES in step S13), the post-shutdown process proceeds to step S14.

[0071] In step S14, the control device 24 ends the warm-up and starts the second power generation control. This switches the power generation in the power generation cell 28 from low-efficiency power generation to dry power generation (high-efficiency power generation). This switch causes the refrigerant temperature to temporarily drop, but the refrigerant is heated by the heater 144, causing the temperature to rise again (see FIG. 4). Once the second power generation control is started, the post-shutdown process proceeds to step S15.

[0072] In step S15, controller 24 starts a process of adjusting the opening of flow diverter valve 132 in accordance with the refrigerant temperature. For example, when the refrigerant temperature exceeds a target temperature, controller 24 starts a process of adjusting the opening of flow diverter valve 132 in accordance with the refrigerant temperature. This adjusts the refrigerant temperature to approach the target temperature (see FIG. 4). When adjustment of the opening of flow diverter valve 132 starts, the post-shutdown process proceeds to step S16.

[0073] In step S16, the control device 24 determines whether the power generating cells 28 are dry. For example, the control device 24 acquires the impedance of the fuel cell stack 12 at predetermined time intervals. If the acquired impedance of the fuel cell stack 12 does not reach the target impedance, the control device 24 determines that the power generating cells 28 are not dry. On the other hand, if the acquired impedance of the fuel cell stack 12 reaches the target impedance, the control device 24 determines that the power generating cells 28 are dry. If it is determined that the power generating cells 28 are not dry (NO in step S16), the processing of step S16 is repeated. On the other hand, if it is determined that the power generating cells 28 are dry (YES in step S16), the post-shutdown processing proceeds to step S17.

[0074] In step S17, the control device 24 ends the second power generation control. In this case, the supply of fuel gas and oxidant gas to the fuel cell stack 12 is stopped, and power generation by the power generation cell 28 is stopped. The control device 24 also ends control of the pump 126 and the diverter valve 132 of the cooling system 20, and ends control of the pump 142 and the heater 144 of the air conditioning system 22. When each control is completed, the post-shutdown process proceeds to step S18.

[0075] In step S18, the control device 24 controls the valve element 146 to block the refrigerant flow path 120 of the cooling system 20 and the refrigerant flow path 140 of the air conditioning system 22. When the refrigerant flow path 120 of the cooling system 20 and the refrigerant flow path 140 of the air conditioning system 22 are blocked, the post-shutdown processing ends.

[0076] [6. Effects of the above embodiment] In the above embodiment, the control device 24 periodically measures the stack temperature during a soak period, which is a period when the start switch is off. When the stack temperature falls below a predetermined temperature threshold, the control device 24 executes a warm-up (low-efficiency power generation control) and then executes second power generation control (dry power generation control). In the second power generation control, the control device 24 causes the refrigerant in the refrigerant flow path 140 of the air conditioning system 22, heated by the heater 144, to flow into the refrigerant flow path 120 of the cooling system 20. This allows the power generation cells 28 to be warmed by the heat generated by the power generation of the power generation cells 28 and the heat of the heated refrigerant. Therefore, even if the amount of heat generated by the power generation cells 28 is suppressed, the temperature of the fuel cell stack 12 can be increased to a target temperature. As a result, the power generation cells 28 can be appropriately dried.

[0077] [7 Modifications of the above embodiment] The above embodiment may be modified as follows.

[0078] For example, the power generation control unit 152 may perform power generation control for charging the battery during the period from when the first power generation control is stopped until when the second power generation control is started.

[0079] [8 Notes] In addition to the above disclosure, the following additional notes are also disclosed.

[0080] (Appendix 1) The present disclosure relates to a fuel cell system (10) including a fuel cell stack (12) including power generation cells (28) that generate electricity through an electrochemical reaction between a fuel gas and an oxidant gas, a radiator (128) used to cool the fuel cell stack, a first refrigerant flow path (120) that circulates a refrigerant between the fuel cell stack and the radiator, a valve element (146) that can switch between connection and disconnection between a first refrigerant flow path (120) and a second refrigerant flow path (140) that is different from the first refrigerant flow path, a heater (144) that heats the refrigerant flowing through the second refrigerant flow path, and a power generation cell (28) that generates electricity through an electrochemical reaction between a fuel gas and an oxidant gas. and a control device (24) that controls power generation of the cell, wherein the control device is capable of executing first power generation control and second power generation control different from the first power generation control, the second power generation control being power generation control for drying an electrolyte membrane (36) provided in the power generation cell, and the control device executes the first power generation control with the first refrigerant flow path and the second refrigerant flow path blocked, and when executing the second power generation control, the control device causes the refrigerant in the second refrigerant flow path that has been heated by the heater to flow into the first refrigerant flow path.

[0081] According to the above, the power generation cells can be warmed by the heat generated by the power generation cells and the heat of the heated refrigerant. Therefore, even if the heat generation amount of the power generation cells is reduced to suppress deterioration of the power generation cells, the temperature of the fuel cell stack can be raised to the target temperature. As a result, the power generation cells can be dried appropriately.

[0082] (Appendix 2) In the fuel cell system according to Supplementary Note 1, the heater and the second refrigerant flow path may be included in an air conditioning system (22).

[0083] (Appendix 3) In the fuel cell system described in Appendix 1, the control device may perform the second power generation control when the temperature of the fuel cell stack falls below a predetermined temperature threshold after receiving a system shutdown command to shut down the fuel cell system.

[0084] Based on the above, even if the fuel cell system is stopped in a low-temperature environment, freezing of water can be suppressed.

[0085] (Appendix 4) In the fuel cell system described in Appendix 1, the control device may execute the second power generation control after warming up the fuel cell stack, and the stoichiometric ratio of the oxidant gas supplied to the fuel cell stack may be different between the warming up and the second power generation control.

[0086] According to the above, compared to the first power generation control, it is possible to increase the amount of heat generated by the power generation cells, or to increase the efficiency of discharging water remaining inside the fuel cell stack to the outside.

[0087] (Appendix 5) In the fuel cell system described in Appendix 4, the stoichiometric ratio during the warm-up may be smaller than the stoichiometric ratio during the first power generation control, and the stoichiometric ratio during the second power generation control may be larger than the stoichiometric ratio during the first power generation control.

[0088] According to the above, compared to the first power generation control, after the heat generation amount of the power generation cell is increased, it is possible to prevent water generated by the power generation from remaining inside the fuel cell stack.

[0089] (Appendix 6) In the fuel cell system described in Appendix 1, the first refrigerant flow path has a refrigerant supply path (122) connecting a refrigerant supply port (12e) of the fuel cell stack and a fluid discharge port of the radiator, and a refrigerant discharge path (124) connecting a refrigerant discharge port (12f) of the fuel cell stack and a fluid supply port of the radiator, and when performing the second power generation control, the control device may cause the refrigerant in the second refrigerant flow path heated by the heater to flow into the refrigerant supply path.

[0090] According to the above, the heated coolant flowing into the first coolant flow path can be supplied to the fuel cell stack without passing through a radiator.

[0091] (Appendix 7) In the fuel cell system described in Appendix 6, the first refrigerant flow path may have a branch path (125) connecting the refrigerant supply path and the refrigerant discharge path, and the control device may adjust the flow rate of the refrigerant whose heat is radiated by the radiator according to the temperature of the refrigerant detected by a temperature sensor (130) provided in the first refrigerant flow path.

[0092] (Appendix 8) In the fuel cell system described in Appendix 1, the control device may perform the second power generation control after warming up the fuel cell stack, and during the warming up and before performing the second power generation control, the control device may cause the refrigerant in the second refrigerant flow path heated by the heater to flow into the first refrigerant flow path.

[0093] According to the above, the temperature of the fuel cell stack can be maintained at a target temperature. If the flow diverter valve is closed when the temperature of the fuel cell stack is below the target temperature, it is possible to prevent the temperatures of the first refrigerant flow path and the second refrigerant flow path from becoming difficult to increase. Furthermore, if the flow diverter valve is opened when the temperature of the fuel cell stack is higher than the target temperature, the radiator reduces the temperature of the refrigerant flowing into the heater, thereby further extending the time during which the power generated by the power generation cells is consumed by the heater.

[0094] The present invention is not limited to the above disclosure, and various configurations can be adopted without departing from the gist of the present invention. [Explanation of symbols]

[0095] 10...Fuel cell system 12...Fuel cell stack 20...Cooling system 22...Air conditioning system 24...Control device 28...Power generation cell 36...electrolyte membrane 120, 140...refrigerant flow path 128...Radiator 144...Heater

Claims

1. a fuel cell stack including a power generation cell that generates electricity through an electrochemical reaction between a fuel gas and an oxidant gas; a radiator used to cool the fuel cell stack; a valve body that can switch between connection and disconnection between a first refrigerant flow path that circulates a refrigerant between the fuel cell stack and the radiator and a second refrigerant flow path that is different from the first refrigerant flow path; a heater that heats the refrigerant flowing through the second refrigerant flow path; a control device that controls power generation of the power generating cell; Equipped with the control device is capable of executing a first power generation control and a second power generation control different from the first power generation control, the second power generation control is power generation control for drying an electrolyte membrane provided in the power generation cell, the control device executes the first power generation control in a state in which the first refrigerant flow path and the second refrigerant flow path are blocked, When the second power generation control is performed, the control device causes the refrigerant in the second refrigerant flow path, which has been heated by the heater, to flow into the first refrigerant flow path; the control device executes the second power generation control after warming up the fuel cell stack, A fuel cell system, wherein the stoichiometric ratio of the oxidant gas supplied to the fuel cell stack is different between the warm-up and the second power generation control.

2. 2. The fuel cell system according to claim 1, The heater and the second refrigerant flow path are included in an air conditioning system.

3. 2. The fuel cell system according to claim 1, A fuel cell system, wherein the control device performs the second power generation control when the temperature of the fuel cell stack falls below a predetermined temperature threshold after receiving a system shutdown command to shut down the fuel cell system.

4. 2. The fuel cell system according to claim 1, A fuel cell system, wherein the stoichiometric ratio during the warm-up is smaller than the stoichiometric ratio during the first power generation control, and the stoichiometric ratio during the second power generation control is larger than the stoichiometric ratio during the first power generation control.

5. 2. The fuel cell system according to claim 1, the first coolant flow path includes a coolant supply path connecting a coolant supply port of the fuel cell stack and a fluid discharge port of the radiator, and a coolant discharge path connecting a coolant discharge port of the fuel cell stack and a fluid supply port of the radiator, When the second power generation control is performed, the control device causes the refrigerant in the second refrigerant flow path, which has been heated by the heater, to flow into the refrigerant supply path.

6. 6. The fuel cell system according to claim 5, the first refrigerant flow path has a branch flow path connecting the refrigerant supply path and the refrigerant discharge path, The control device adjusts the flow rate of the coolant whose heat is radiated by the radiator in accordance with the temperature of the coolant detected by a temperature sensor provided in the first coolant flow path.

7. A fuel cell stack including a power generation cell that generates electricity by an electrochemical reaction between a fuel gas and an oxidant gas; a radiator used to cool the fuel cell stack; a valve body that can switch between connection and disconnection between a first refrigerant flow path that circulates a refrigerant between the fuel cell stack and the radiator and a second refrigerant flow path that is different from the first refrigerant flow path; a heater that heats the refrigerant flowing through the second refrigerant flow path; a control device that controls power generation of the power generating cell; Equipped with the control device is capable of executing a first power generation control and a second power generation control different from the first power generation control, the second power generation control is power generation control for drying an electrolyte membrane provided in the power generation cell, the control device executes the first power generation control in a state in which the first refrigerant flow path and the second refrigerant flow path are blocked, When the second power generation control is performed, the control device causes the refrigerant in the second refrigerant flow path, which has been heated by the heater, to flow into the first refrigerant flow path; the control device executes the second power generation control after warming up the fuel cell stack, During the warm-up period and before the second power generation control is executed, the control device causes the refrigerant in the second refrigerant flow path, which has been heated by the heater, to flow into the first refrigerant flow path.

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