JP7780487B2 - fuel cell system - Google Patents

Description

The present invention relates to a fuel cell system.

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

Regarding fuel cells, there is a fuel cell system that includes a fuel cell stack containing power-generating cells and a battery that stores the electricity generated by the power-generating cells. Fuel cell systems can be mounted on mobile objects such as vehicles. In fuel cell systems mounted on mobile objects, electricity may be generated even when the mobile object is stopped.

Patent Document 1 discloses a method for shutting down a fuel cell system in which, when the ignition switch is turned off, a dry power generation process is performed, followed by a wastewater power generation process, in order to promote drying of the membrane electrode assembly (MEA) of the power generation cell.

JP 2016-058188 A

When the remaining capacity of the battery provided in a fuel cell system is relatively high, the power generated by the power generation cell cannot be supplied to the battery. Therefore, technology that efficiently consumes the power generated by the power generation cell is desired.

The present invention aims to solve the above-mentioned problems.

One aspect of the present invention is a fuel cell system comprising: a fuel cell stack including a power generation cell that generates electricity through an electrochemical reaction between fuel gas and oxidant gas; a battery capable of storing the power generated by the power generation cell; 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 element 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. The control device is capable of executing first power generation control and second power generation control that is performed based on a system shutdown command to shut down the fuel cell system. The second power generation control includes low-efficiency power generation control that causes the power generation cell to generate electricity at a power generation efficiency lower than the power generation efficiency in the first power generation control. When the second power generation control is performed when the remaining capacity of the battery is equal to or greater than a predetermined remaining capacity threshold, the control device causes the heater to consume the power generated by the power generation cell while the first refrigerant flow path and the second refrigerant flow path are connected to each other.

According to the present invention, the temperature of the refrigerant heated by the heater rises more slowly than when the first refrigerant flow path and the second refrigerant flow path are not connected. Therefore, the time during which the power generated by the power generation cell is consumed by the heater can be extended compared to when the first refrigerant flow path and the second refrigerant flow path are not connected. Therefore, even when the remaining battery capacity is high, the second power generation control can be continued for a relatively long period of time. As a result, the power generated by the power generation cell can be consumed efficiently.

FIG. 1 is a schematic diagram of a fuel cell system. FIG. 2 is a flowchart showing the procedure of the power generation control process. FIG. 3 is a flowchart showing the procedure of the heat control process during the second power generation control.

[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.

In the fuel cell system 10, fuel gas and 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 oxidant gas is supplied to the fuel cell stack 12 and subjected to an electrochemical reaction. Note that, in this specification, fuel gas discharged from the fuel cell stack 12 without being subjected to an electrochemical reaction is also referred to as fuel off-gas. Also, in this specification, oxidant gas discharged from the fuel cell stack 12 without being subjected to an electrochemical reaction is also referred to as oxidant off-gas.

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 battery 26A that stores the power generated by the fuel cell stack 12, a vehicle drive motor 26B, and a heater 144. The tank 14 is filled with high-pressure fuel gas.

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

The fuel cell stack 12 has a plurality of power generating cells 28. Each of the 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. Only one of the power generating cells 28 is shown in Figure 1.

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 generation cells 28, the first separator 32 of one power generation cell 28 and the second separator 34 of the other power generation 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 is connected to the refrigerant supply port 12e and the refrigerant discharge port 12f.

The membrane electrode assembly 30 includes an electrolyte membrane 36, an anode electrode 38, and a cathode electrode 40. The electrolyte membrane 36 is located between the anode electrode 38 and the cathode electrode 40. An anode flow path 42 is formed between the first separator 32 and the anode electrode 38. The anode flow path 42 is connected to 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 electrode 40. The cathode flow path 44 is connected to the oxidant gas supply port 12c and the oxidant gas discharge port 12d.

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.

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

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.

The drain 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 on the vehicle. The drain channel 90 is equipped with a drain valve 100.

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 shut-off valve 116, a second shut-off valve 118, and a bypass valve 119.

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

The oxidant gas discharge channel 108 connects the oxidant gas discharge port 12d of the fuel cell stack 12 with the inlet of the diluter 121. The oxidant gas discharge channel 108 is equipped with a humidifier discharge channel 114B of the humidifier 114 and a second shut-off valve 118. The portion of the oxidant gas discharge channel 108 that is located upstream of the humidifier 114 is referred to as the oxidant gas discharge channel 108A. The portion of the oxidant gas discharge channel 108 that is located downstream of the humidifier 114 is referred to as the oxidant gas discharge channel 108B. The oxidant gas discharge channel 108B is equipped with a second shut-off valve 118.

The bypass path 110 is connected to the oxidant gas supply path 106A between the compressor 112 and the first shut-off valve 116, and to the oxidant gas discharge path 108B downstream of the second shut-off valve 118. The bypass path 110 is equipped with a bypass valve 119.

The cooling system 20 includes a refrigerant flow path 120. The cooling system 20 also includes a pump 126, a radiator 128, a first temperature sensor 130, and a flow shunt valve 132.

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 the fluid discharge port of the radiator 128 to the coolant supply port 12e of the fuel cell stack 12. The coolant discharge path 124 connects the coolant discharge port 12f of the fuel cell stack 12 to the 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.

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

The first temperature sensor 130 is a first temperature detection device that detects the temperature of the refrigerant (refrigerant temperature) in the refrigerant flow path 120. The first temperature sensor 130 is provided in the refrigerant discharge path 124. The first temperature sensor 130 may also be provided in the refrigerant supply path 122. The first temperature sensor 130 may also detect the outlet temperature of the reactant gas. In this case, the first temperature sensor 130 is provided, for example, in the fuel gas discharge port 12b. The above refrigerant temperature or the above outlet temperature corresponds to the internal temperature of the fuel cell stack 12 (stack temperature).

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

The air conditioning system 22 includes a refrigerant flow path 140. The air conditioning system 22 also includes a pump 142, a heater 144, a valve body 146, and a second temperature sensor 160.

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. The refrigerant flow path 140 of the air conditioning system 22 and the refrigerant flow path 120 of the cooling system 20 can be connected via a communication path 148. The communication path 148 has a partial flow path 148A and a partial flow path 148B.

The refrigerant material flowing through the refrigerant flow path 140 of the air conditioning system 22 is the same as the refrigerant material 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 cabin. The air that has undergone heat exchange is supplied, for example, to the vehicle cabin.

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, for example, the control device 24.

The valve element 146 can switch 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 between the refrigerant flow path 140 and partial flow path 148A, and at the connection between the refrigerant flow path 140 and partial flow path 148B.

The second temperature sensor 160 is a second temperature detection device that detects the temperature of the refrigerant (refrigerant temperature) in the refrigerant flow path 140. In this embodiment, the temperature of the refrigerant downstream of the heater 144 is detected, but the temperature of the heater 144 may also be detected as the temperature of the refrigerant in the refrigerant flow path 140.

The control device 24 may be configured with an ECU (Electronic Control Unit). The control device 24 includes a calculation unit 136 and a memory 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 with processing circuitry. 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 memory unit 138.

At least one of the acquisition unit 150, power generation control unit 152, and thermal control unit 154 may be implemented by an integrated circuit such as an ASIC (Application Specific Integrated Circuit) or FPGA (Field-Programmable Gate Array). At least one of the acquisition unit 150, power generation control unit 152, and thermal control unit 154 may be implemented by an electronic circuit including discrete devices.

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, compressor 112, pump 126, various valves, etc. The thermal control unit 154 controls the operation of the flow divider valve 132, heater 144, valve element 146, etc.

The memory unit 138 is a computer-readable storage medium. The storage medium is composed of volatile memory (not shown) and non-volatile memory (not shown). Volatile memory is, for example, RAM (Random Access Memory). Non-volatile memory is, for example, ROM (Read Only Memory) or flash memory. Data, etc., is stored in, for example, the volatile memory. Programs, tables, maps, etc., are stored in, for example, the non-volatile memory. At least a portion of the memory unit 138 may be provided in the processor, integrated circuit, etc. described above.

[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 of oxygen and hydrogen.

The fuel off-gas is supplied to the gas-liquid separator 98 via the 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 the ejector 96 via the circulation path 88. The fuel off-gas sucked from the gas-liquid separator 98 and the fuel gas injected from the injector 94 merge in the ejector 96.

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.

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, some of the moisture contained in the oxidant off-gas is used to humidify the oxidant gas flowing through the humidifier supply path 114A.

2-3 Fluid Flow in 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.

Note that a portion of the refrigerant discharged from the refrigerant discharge port 12f flows into the refrigerant supply path 122 via the shunt path 125, without passing through the radiator 128. The amount of this flow-in is adjusted according to the opening of the shunt valve 132.

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.

When the refrigerant flow path 120 of the cooling system 20 and the refrigerant flow path 140 of the air conditioning system 22 are connected (second state), 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 the partial flow path 148A of the communication path 148 via the valve body 146. The refrigerant that flows 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.

The refrigerant then flows into the fuel cell stack 12 via the refrigerant supply path 122, circulates through the interior of the fuel cell stack 12, and flows back 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 flows into the refrigerant path 140 reaches the pump 142.

In this second state, the refrigerant circulates through the refrigerant flow path 140 of the air conditioning system 22, the refrigerant flow path 120 of the cooling system 20, and the interior of the fuel cell stack 12.

[3 Power generation control]
The power generation control unit 152 is capable of executing a first power generation control for supplying power according to demand to the load 26 and a second power generation control for drying the electrolyte membrane 36 provided in the power generation cell 28.

Figure 2 is a flowchart showing the steps of the power generation control process. The power generation control unit 152 does not execute the power generation control process unless it receives a system startup command, which is a command to start up the fuel cell system 10. When the power generation control unit 152 receives a system startup command, the power generation control process proceeds to step S1.

In step S1, the power generation control unit 152 executes first power generation control to supply the load 26 with power according to the request. 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 it receives the system stop command, the power generation control unit 152 ends the first power generation control. When the first power generation control ends, the power generation control process proceeds to step S2.

In step S2, the power generation control unit 152 compares the temperature (stack temperature) detected by the first temperature sensor 130 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 less than the temperature threshold (YES in step S2), the power generation control process proceeds to step S3.

In step S3, the power generation control unit 152 executes second power generation control. If a predetermined time has elapsed since the start of the second power generation control, or if the impedance of the fuel cell stack 12 reaches the target impedance, or if the temperature of the fuel cell stack 12 reaches a predetermined temperature, the power generation control unit 152 determines that the power generation cells 28 have dried. In this case, the power generation control unit 152 ends the second power generation control. When the second power generation control ends, the power generation control process ends. When the power generation control unit 152 ends the second power generation control, it does not execute the power generation control process until it receives a system startup command again.

A system start command is issued when the switch (start switch) of the fuel cell system 10 is turned on. A system stop command is issued 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.

In the first power generation control, the power generation control unit 152 controls the operation of the injector 94, compressor 112, pump 126, various valves, etc., and causes the power generation cell 28 to perform normal power generation. During execution of the first power generation control, the power generation control unit 152 controls the injector 94 and compressor 112 based on the required power generation so that the power generated by the power generation cell 28 becomes the required power generation. The required power generation is calculated by the power generation control unit 152 based on, for example, the accelerator position, vehicle speed, road gradient, etc.

The second power generation control includes low-efficiency power generation control, which causes the power generation cells 28 to generate power at a power generation efficiency lower than that of the first power generation control, and dry power generation control, which heats and dries the fuel cell stack 12 in order to dry the electrolyte membrane 36 provided in the power generation cells 28.

During low-efficiency power generation control, power is generated at a low-efficiency operating point that results in greater power generation losses than the normal operating point during first power generation control. During low-efficiency power generation control, the power generation control unit 152 controls the injector 94 and compressor 112 so that the stoichiometric ratio of the oxidant gas supplied to the fuel cell stack 12 is relatively small. More specifically, the power generation control unit 152 sets the stoichiometric ratio of the oxidant gas during second power generation control to a value lower than the stoichiometric ratio of the oxidant gas during first power generation control. In other words, the ratio of oxidant gas to fuel gas during second power generation control is set to a value lower than the ratio of oxidant gas to fuel gas during first power generation control.

As a result, the amount of oxidant gas supplied to the fuel cell stack 12 during second power generation control is less than the amount of oxidant gas supplied to the fuel cell stack 12 during first power generation control. As a result, during second power generation control, low-efficiency power generation is performed in the power generation cells 28, with power generation efficiency reduced compared to normal power generation. Because low-efficiency power generation is performed, the amount of heat generated by the power generation cells 28 increases during second power generation control. In other words, the amount of heat generated by the power generation cells 28 during second power generation control is greater than the amount of heat generated by the power generation cells 28 during first power generation control.

Dry power generation control is initiated after low-efficiency power generation control ends. For example, when the temperature detected by the first temperature sensor 130 reaches the target temperature, low-efficiency power generation control is switched to dry power generation control. In dry power generation control, power generation is performed at the normal operating point in first power generation control, an operating point with smaller power generation losses than the normal operating point, or an operating point equivalent to the normal operating point. That is, the power generation control unit 152 controls the injector 94 and compressor 112 to cause the power generation cell 28 to perform steady operation at the same normal operating point as in first power generation control, or to generate power in a highly stoichiometric state in which the ratio of oxidant gas to fuel gas supplied to the fuel cell stack 12 is increased.

[4. Thermal Control]
During the first power generation control, the thermal control unit 154 drives the pump 126 provided in the coolant flow path 120. Furthermore, during the first power generation control, the thermal control unit 154 sets the opening degree of the shunt valve 132 so that the coolant discharged from the fuel cell stack 12 to the coolant discharge path 124 is supplied to the radiator 128 without being supplied to the coolant supply path 122 via the shunt path 125. Note that the thermal control unit 154 may adjust the opening degree of the shunt valve 132.

Furthermore, while the first power generation control is being performed, the thermal control unit 154 controls the valve element 146 so that the refrigerant flow path 120 of the cooling system 20 and the refrigerant flow path 140 of the air conditioning system 22 are blocked. Therefore, while the first power generation control is being performed, the refrigerant in the refrigerant flow path 140 of the air conditioning system 22 is not supplied to the fuel cell stack 12. While the first power generation control is being performed, only the refrigerant in the refrigerant flow path 120 of the cooling system 20 is supplied to the fuel cell stack 12. Note that while the first power generation control is being performed, the thermal control unit 154 may also control the valve element 146 so that the refrigerant flow path 120 of the cooling system 20 and the refrigerant flow path 140 of the air conditioning system 22 are connected for a desired period of time.

Figure 3 is a flowchart showing the steps of the heat control process during the second power generation control. The heat control unit 154 executes a predetermined heat control process during the second power generation control. The heat control process proceeds to step S11 when the second power generation control is started.

In step S11, the thermal control unit 154 drives the pump 126 provided in the refrigerant flow path 120 and the pump 142 provided in the refrigerant flow path 140. The pump 126 and the pump 142 may be driven using power supplied from the battery 26A, or may be driven using power generated from the power generating cell 28 by second power generation control. The thermal control unit 154 also sets the aperture of the diverter valve 132 so that the refrigerant discharged from the fuel cell stack 12 to the refrigerant discharge path 124 is supplied to the refrigerant supply path 122 without being supplied to the radiator 128. Once the pumps 126 and 142 are driven and the aperture of the diverter valve 132 is set, the thermal control process proceeds to step S12.

In step S12, 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. 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 when a predetermined time has elapsed since the second power generation control was started.

When 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 power generating cells 28 can be heated using the heat generated by the power generation of the power generating cells 28 and the heat of the refrigerant heated by the heater 144. Therefore, the power generating cells 28 can be heated more quickly and sufficiently than when the power generating cells 28 are heated using only the heat generated by the power generation of the power generating cells 28. After 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 heat control process proceeds to step S13.

In step S13, the thermal control unit 154 determines whether the remaining capacity of battery 26A is equal to or greater than a predetermined remaining capacity threshold. The remaining capacity of battery 26A is obtained, for example, from a capacity sensor provided in battery 26A. If the remaining capacity of battery 26A is less than the predetermined remaining capacity threshold (NO in step S13), the thermal control process proceeds to step S14. On the other hand, if the remaining capacity of battery 26A is equal to or greater than the predetermined remaining capacity threshold (YES in step S13), the thermal control process proceeds to step S15.

In step S14, the thermal control unit 154 charges the battery 26A and drives the heater 144 using the power supplied from the battery 26A. That is, the thermal control unit 154 sets a power supply path so that the power generated from the power generation cell 28 by the second power generation control is supplied to the battery 26A. The thermal control unit 154 also sets a power supply path so that power is supplied from the battery 26A to the heater 144. This makes it possible to drive the heater 144 while suppressing the power consumption of the battery 26A. When driving of the heater 144 using the power supplied from the battery 26A begins, the thermal control process proceeds to step S16.

In step S15, the thermal control unit 154 drives the heater 144 using the power generated from the power generation cell 28 through the second power generation control. That is, the thermal control unit 154 sets a power supply path so that the power generated from the power generation cell 28 is supplied to the heater 144, and causes the heater 144 to consume that power. This makes it possible to drive the heater 144 while suppressing excessive power accumulation in the battery 26A. When driving of the heater 144 using the power generated by the power generation cell 28 begins, the thermal control process proceeds to step S16.

In step S16, the heat control unit 154 compares the refrigerant temperature detected by the first temperature sensor 130 with the target temperature. If the refrigerant temperature is equal to or higher than the target temperature (YES in step S16), the heat control process proceeds to step S17. On the other hand, if the refrigerant temperature is lower than the target temperature (NO in step S16), the heat control process proceeds to step S18.

In step S17, the thermal control unit 154 adjusts the opening of the diverter valve 132 according to the refrigerant temperature detected by the first temperature sensor 130. The opening of the diverter valve 132 is adjusted so that the amount of refrigerant supplied to the radiator 128 increases as the temperature detected by the first temperature sensor 130 increases. This allows the temperature of the fuel cell stack 12 to be maintained at the target temperature. Once the opening of the diverter valve 132 has been adjusted, the thermal control process proceeds to step S18.

In step S18, the heat control unit 154 compares the refrigerant temperature detected by the second temperature sensor 160 with a predetermined temperature threshold. The temperature threshold is set higher than the target temperature. If the temperature of the refrigerant flowing through the refrigerant flow path 140 is equal to or higher than the temperature threshold (YES in step S18), the heat control process proceeds to step S19. On the other hand, if the temperature of the refrigerant flowing through the refrigerant flow path 140 is lower than the temperature threshold (NO in step S18), the heat control process returns to step S17.

In step S19, the heat control unit 154 cuts off the supply of power to the heater 144 to stop the heater 144. Once the heater 144 has been stopped, the heat control process returns to step S17.

The above heat control process is performed while the second power generation control is being performed. When the second power generation control ends, the heat control unit 154 stops the pump 126 and the pump 142. Furthermore, if the heater 144 was not stopped in step S19 described above, the heat control unit 154 stops the heater 144 when the second power generation control ends.

[5. Effects of the above embodiment]
In the above embodiment, after the first power generation control ends based on a system stop command, if the stack temperature is below the temperature threshold, the control device 24 starts the second power generation control. First, the control device 24 executes low-efficiency power generation control by setting the stoichiometric ratio of the oxidant gas in the second power generation control to be lower than the stoichiometric ratio of the oxidant gas in the first power generation control. Then, the control device 24 executes dry power generation control by setting the stoichiometric ratio of the oxidant gas to be equal to or higher than the stoichiometric ratio of the oxidant gas in the first power generation control. This allows the electrolyte membrane 36 to be satisfactorily dried. As a result, the power generation cell 28 can be started up satisfactorily at low temperatures. Furthermore, deterioration of the electrolyte membrane 36 due to freezing of water is suppressed.

When the second power generation control is performed when the remaining capacity of the battery 26A is equal to or greater than a predetermined remaining capacity threshold, the control device 24 causes the heater 144 to consume the power generated by the power generation cell 28 while the refrigerant flow path 120 of the cooling system 20 and the refrigerant flow path 140 of the air conditioning system 22 are connected to each other.

As a result, the temperature of the refrigerant heated by the heater 144 rises more slowly than when the refrigerant flow path 120 and the refrigerant flow path 140 are not connected. Therefore, the time during which the power generated by the power generating cell 28 is consumed by the heater 144 can be extended compared to when the refrigerant flow path 120 and the refrigerant flow path 140 are not connected. Therefore, even when the remaining capacity of the battery 26A is high, the second power generation control can be continued for a relatively long period of time. In this way, according to this embodiment, the power generated by the power generating cell 28 can be consumed efficiently.

The control device 24 also controls the diverter valve 132 provided in the refrigerant flow path 120 in accordance with the refrigerant temperature detected by the first temperature sensor 130, adjusting the flow rate of the refrigerant whose heat is dissipated by the radiator 128. This allows the heater 144 to consume the power generated by the power generating cell 28 while maintaining the temperature of the fuel cell stack 12 at a target temperature.

More specifically, when the temperature of the fuel cell stack is below the target temperature, the control device 24 closes the diverter valve 132. This prevents the temperatures of the refrigerant flow path 140 and the refrigerant flow path 120 from rising too easily. Furthermore, when the temperature of the fuel cell stack is equal to or higher than the target temperature, the control device 24 opens the diverter valve 132. This allows the radiator 128 to lower the temperature of the refrigerant flowing into the heater 144, thereby further extending the time during which the power generated by the power generating cell 28 is consumed by the heater 144.

Furthermore, if the temperature of the refrigerant flowing through the refrigerant flow path 140 exceeds a predetermined temperature threshold, the control device 24 stops the heater 144 from consuming power. This prevents the refrigerant from heating excessively. In particular, even if the heater 144 fails, the refrigerant can be prevented from heating excessively.

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

(Variation 1)
When the remaining capacity of the battery 26A is less than a predetermined remaining capacity threshold, the thermal control unit 154 may drive the heater 144 using both the power supplied from the battery 26A and the power generated by the power generating cell 28 through the second power generation control. In this modification, when the remaining capacity of the battery 26A is equal to or greater than the predetermined remaining capacity threshold, the thermal control unit 154 drives the heater 144 using only the power generated by the power generating cell 28 through the second power generation control.

(Variation 2)
If the radiator 128 has a fan 128F, the control device 24 may perform fan control as follows.

That is, when performing first power generation control, the control device 24 drives the fan 128F. The fan 128F may be driven using power supplied from the battery 26A, or may be driven using power generated by the power generation cell 28 through the first power generation control. Furthermore, while the first power generation control is being performed, the control device 24 may adjust the rotation speed of the fan 128F depending on the temperature detected by the first temperature sensor 130.

On the other hand, when the second power generation control is performed when the remaining capacity of the battery 26A is equal to or greater than the remaining capacity threshold, the control device 24 stops the fan 128F. This allows the temperature of the fuel cell stack 12 to be increased compared to when the fan 128F is not stopped, and as a result, the electrolyte membrane 36 can be dried more efficiently. Furthermore, the noise level can be reduced during the second power generation control, which is performed when the start switch is off.

[7. Supplementary Note]
In addition to the above disclosure, the following additional notes are also disclosed.

(Appendix 1)
The present disclosure relates to a fuel cell stack (12) including a power generation cell (28) that generates power through an electrochemical reaction between a fuel gas and an oxidant gas, a battery (26A) capable of storing the power generated by the power generation cell, 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, and a second refrigerant flow path (140) different from the first refrigerant flow path, a valve body (146) that can switch between connection and disconnection between the first refrigerant flow path and a second refrigerant flow path (140), a heater (144) that heats the refrigerant flowing through the second refrigerant flow path, and a control device ( 24), wherein the control device is capable of executing first power generation control and second power generation control that is performed based on a system stop command for stopping the fuel cell system, and the second power generation control includes low-efficiency power generation control that causes the power generation cell to generate power at a power generation efficiency that is lower than the power generation efficiency in the first power generation control, and when the second power generation control is performed in a state where the remaining capacity of the battery is equal to or greater than a predetermined remaining capacity threshold, the control device causes the heater to consume the power generated from the power generation cell in a state where the first refrigerant flow path and the second refrigerant flow path are connected to each other.

As a result of the above, the temperature of the refrigerant heated by the heater rises more slowly than when the first refrigerant flow path and the second refrigerant flow path are not connected. Therefore, the time during which the power generated by the power generation cell is consumed by the heater can be extended compared to when the first refrigerant flow path and the second refrigerant flow path are not connected. Therefore, even when the remaining battery capacity is high, the second power generation control can be continued for a relatively long period of time. As a result, the power generated by the power generation cell can be consumed efficiently.

(Appendix 2)
The fuel cell system described in Appendix 1 includes a first temperature detection device (130) capable of detecting the temperature of the fuel cell stack, and 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, 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 a branch path (125) connecting the refrigerant supply path and the refrigerant discharge path, and a branch valve (132) whose opening degree can be adjusted is provided at the connection between the branch path and the refrigerant supply path or at the connection between the branch path and the refrigerant discharge path, and the control device controls the branch valve in accordance with the temperature of the fuel cell stack to adjust the flow rate of the refrigerant radiated by the radiator.

As described above, the temperature of the fuel cell stack can be maintained at a target temperature while the heater consumes the power generated by the power generation cells. Furthermore, if the 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 diverter valve is open when the temperature of the fuel cell stack is above the target temperature, the radiator reduces the temperature of the refrigerant flowing into the heater, thereby further extending the time during which the heater consumes the power generated by the power generation cells.

(Appendix 3)
In the fuel cell system described in Appendix 1, the radiator is equipped with a fan (128F), and when the second power generation control is performed when the remaining capacity of the battery is equal to or greater than the remaining capacity threshold, the control device may stop the fan and have the heater consume the power generated from the power generation cell.

As a result of the above, the amount of heat generated by the power generation cell can be increased compared to when the fan is not stopped, and as a result, the electrolyte membrane can be dried more efficiently. Furthermore, the noise level can be reduced compared to when the fan is driven during execution of the second power generation control.

(Appendix 4)
The fuel cell system described in Appendix 1 may be provided with a second temperature detection device (160) capable of detecting the temperature of the second refrigerant flow path, and when the temperature of the second refrigerant flow path becomes equal to or higher than a predetermined temperature threshold, the control device may stop the consumption of power by the heater.

The above prevents the refrigerant from heating excessively. In particular, it prevents the refrigerant from heating excessively even if the heater fails.

(Appendix 5)
In the fuel cell system according to Supplementary Note 1, the stoichiometric ratio of the oxidant gas in the low-efficiency power generation control may be lower than the stoichiometric ratio of the oxidant gas in the first power generation control.

As a result of the above, the amount of heat generated by the power generation cell increases compared to the first power generation control, allowing the electrolyte membrane to be dried effectively. As a result, deterioration of the electrolyte membrane due to freezing of water is suppressed.

The present invention is not limited to the above disclosure, and various configurations may be adopted without departing from the spirit of the present invention.

REFERENCE SIGNS LIST 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 (4)

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 battery capable of storing the power generated by the power generation cell;
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;
A fuel cell system having:
the control device is capable of executing a first power generation control and a second power generation control that is performed based on a system stop command for stopping the fuel cell system,
the second power generation control includes low-efficiency power generation control in which the power generation cell is caused to generate power at a power generation efficiency lower than the power generation efficiency in the first power generation control,
When the second power generation control is performed in a state where the remaining capacity of the battery is equal to or greater than a predetermined remaining capacity threshold, the control device causes the heater to consume the electric power generated from the power generation cell in a state where the first refrigerant flow path and the second refrigerant flow path are connected to each other ,
a first temperature detection device capable of detecting the temperature of the fuel cell stack;
a second temperature detection device capable of detecting the temperature of the heater;
Equipped with
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, a coolant discharge path connecting a coolant discharge port of the fuel cell stack and a fluid supply port of the radiator, and a branch path connecting the coolant supply path and the coolant discharge path;
a branch valve whose opening degree is adjustable is provided at a connection portion between the branch flow path and the refrigerant supply path or at a connection portion between the branch flow path and the refrigerant discharge path,
The control device controls the diverter valve in accordance with the temperature of the fuel cell stack, adjusts the flow rate of the refrigerant whose heat is dissipated by the radiator, and stops the consumption of power by the heater when the temperature detected by the second temperature detection device becomes equal to or higher than a predetermined temperature threshold . 2. The fuel cell system according to claim 1,
A fuel cell system , wherein the temperature threshold is set higher than a target temperature detected by the first temperature detection device . 2. The fuel cell system according to claim 1,
the heat sink comprises a fan;
When the second power generation control is performed while the remaining capacity of the battery is equal to or greater than the remaining capacity threshold, the control device stops the fan and causes the heater to consume the power generated from the power generation cell. The fuel cell system according to any one of claims 1 to 3 ,
A fuel cell system, wherein the stoichiometric ratio of the oxidant gas in the low-efficiency power generation control is lower than the stoichiometric ratio of the oxidant gas in the first power generation control.