Control device, fuel cell system, control method of fuel cell system, and program

Abstract

To provide an excellent control device, a fuel cell system, a control method of the fuel cell system, and a program.SOLUTION: A controller 10 of a fuel cell system 12 includes: a control part 78 which controls a by-pass valve 58; and a determination unit 84 which determines whether the by-pass valve is frozen by generated water generated through electric power generation of the fuel cell or not. When the determination unit determines that the by-pass valve is not frozen by the generated water, the control part configures an opening lower limit of the by-pass valve to be a first opening lower limit. When the determination unit determines that the by-pass valve is frozen by the generated water, the control part configures the opening lower limit of the by-pass valve to be a second opening lower limit that is larger than the first opening lower limit.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a control device, a fuel cell system, a control method for a fuel cell system, and a program. [Background technology]

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

[0003] For example, Patent Document 1 discloses a fuel cell system in which an exhaust valve with an adjustable opening is provided in an oxidant gas exhaust flow path through which oxidant exhaust gas discharged from a fuel cell stack flows. In this fuel cell system, when there is a possibility that the exhaust valve will freeze due to water generated in the fuel cell stack, the opening of the exhaust valve is prohibited from becoming equal to or smaller than a predetermined opening. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2004-311288 A Summary of the Invention [Problem to be solved by the invention]

[0005] There is a need for a better control device, fuel cell system, and control method and program for a fuel cell system.

[0006] The present invention aims to solve the above-mentioned problems. [Means for solving the problem]

[0007] A first aspect of the present invention is a control device for controlling a fuel cell system including a fuel cell that generates electricity by an electrochemical reaction between a fuel gas and an oxidant gas, a bypass flow path that connects an oxidant gas supply flow path that supplies the oxidant gas to the fuel cell and an oxidant gas discharge flow path through which oxidant exhaust gas discharged from the fuel cell flows, and a bypass valve that is provided in the bypass flow path and has an adjustable opening, the control device having a control unit that controls the bypass valve, and a determination unit that determines whether the bypass valve is in a state where it will freeze due to water generated by power generation of the fuel cell, wherein if the determination unit determines that the bypass valve is not in a state where it will freeze due to the generated water, the control unit sets a lower limit value of the opening of the bypass valve to a first lower limit value, and if the determination unit determines that the bypass valve is in a state where it will freeze due to the generated water, the control unit sets the lower limit value of the bypass valve to a second lower limit value that is greater than the first lower limit value.

[0008] A second aspect of the present invention is a fuel cell system including the above-mentioned control device.

[0009] A third aspect of the present invention is a control method for a fuel cell system including a fuel cell that generates electricity by an electrochemical reaction between a fuel gas and an oxidant gas, a bypass flow path that connects an oxidant gas supply flow path that supplies the oxidant gas to the fuel cell and an oxidant gas discharge flow path through which oxidant exhaust gas discharged from the fuel cell flows, and a bypass valve that is provided in the bypass flow path and has an adjustable opening, the control method including a determination step of determining whether the bypass valve is in a state where it will freeze due to water generated by power generation of the fuel cell, and a setting step of setting a lower limit value of opening of the bypass valve, wherein in the setting step, if it is determined in the determination step that the bypass valve is not in a state where it will freeze due to the generated water, a control unit sets the lower limit value of opening of the bypass valve to a first lower limit value, and if it is determined in the determination step that the bypass valve is in a state where it will freeze due to the generated water, the control unit sets the lower limit value of opening of the bypass valve to a second lower limit value that is greater than the first lower limit value.

[0010] A fourth aspect of the present invention is a program for causing a computer to execute the above-mentioned fuel cell system control method. Effect of the Invention

[0011] According to the present invention, it is possible to obtain a better control device, a fuel cell system, a control method for a fuel cell system, and a program. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a fuel cell system according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a flowchart showing a control method for a fuel cell system according to one embodiment of the present invention. [Diagram 3] FIG. 3 is a flowchart showing a control method for a fuel cell system according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The fuel cell system includes a bypass flow path connecting an oxidant gas supply flow path and an oxidant gas discharge flow path, and a bypass valve for opening and closing the bypass flow path. When the bypass valve is opened, the oxidant gas flowing through the oxidant gas supply flow path is guided to the oxidant gas discharge flow path via the bypass flow path. The generated water generated by the power generation of the fuel cell stack is discharged to the oxidant gas discharge flow path together with the oxidant exhaust gas. When the bypass valve is fully closed, the generated water flowing through the oxidant gas discharge flow path may enter the bypass valve. In this case, for example, if the bypass valve is at a low temperature (for example, below the freezing point), the generated water may freeze the bypass valve. When the bypass valve freezes, the bypass valve is not opened and closed smoothly. An object of the present disclosure is to suppress the bypass valve from freezing due to the generated water.

[0014] A control device 10, a fuel cell system 12, a control method for the fuel cell system 12, and a program according to one embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of a fuel cell system 12 according to this embodiment. The fuel cell system 12 is mounted on a vehicle (not shown), such as a fuel cell electric vehicle. Specifically, the fuel cell system 12 is disposed, for example, in a front room located in front of the dashboard of the vehicle. Note that the fuel cell system 12 may also be mounted on equipment other than a vehicle.

[0015] As shown in FIG. 1, a fuel cell system 12 according to this embodiment includes a fuel cell stack (fuel cell) 14, a cathode system device 16, an anode system device 18, and a controller 10. The fuel cell stack (fuel cell) 14 is a fuel cell stack.

[0016] The fuel cell stack 14 generates power through an electrochemical reaction between a fuel gas and an oxidant gas. The fuel gas is, for example, hydrogen gas. The fuel gas is not particularly limited as long as it is a gas containing hydrogen. The oxidant gas is, for example, air. The oxidant gas is not limited to air as long as it is a gas containing oxygen. The fuel cell stack 14 is formed by stacking a plurality of power generation cells 20. Each power generation cell 20 has a membrane electrode assembly (MEA) 22 and a pair of separators 24a, 24b that sandwich the membrane electrode assembly 22.

[0017] The membrane electrode assembly 22 includes an electrolyte membrane 26, a cathode electrode 28, and an anode electrode 30. The electrolyte membrane 26 is sandwiched between the cathode electrode 28 and the anode electrode 30. The electrolyte membrane 26 is, for example, a solid polymer electrolyte membrane. The solid polymer electrolyte membrane is, for example, a thin film of perfluorosulfonic acid containing moisture. Although not shown in detail, each of the cathode electrode 28 and the anode electrode 30 includes an electrode catalyst layer bonded to the electrolyte membrane 26 and a gas diffusion layer laminated on the electrode catalyst layer.

[0018] One of the separators, 24a, has an oxidant gas flow path 32 formed on its surface facing the membrane electrode assembly 22. The oxidant gas flow path 32 communicates with an oxidant gas inlet port 34 and an oxidant gas outlet port 36 of the fuel cell stack 14. The other separator, 24b, has a fuel gas flow path 38 formed on its surface facing the membrane electrode assembly 22. The fuel gas flow path 38 communicates with a fuel gas inlet port 40 and a fuel gas outlet port 42 of the fuel cell stack 14. The fuel cell stack 14 may also have components other than those described above, but descriptions of these will be omitted here.

[0019] The cathode system 16 has an oxidant gas supply passage 44, an oxidant gas discharge passage 46, a bypass passage 48, a pump 50, an intercooler (heat exchanger) 52, a supply valve 54, a discharge valve 56, a bypass valve 58, and a humidifier 60. The cathode system 16 may also be provided with components other than these components, but the description thereof will be omitted here.

[0020] The oxidant gas supply flow path 44 is connected to the oxidant gas inlet portion 34 of the fuel cell stack 14. The oxidant gas supply flow path 44 is provided with a pump 50, an intercooler 52, and a supply valve 54. The pump 50 is, for example, an air compressor that supplies the oxidant gas. The type of the pump 50 is not limited. The pump 50 is capable of adjusting the flow rate of the oxidant gas. The oxidant gas supply flow path 44 supplies the oxidant gas sent from the pump 50 to the fuel cell stack 14.

[0021] The intercooler 52 is located at a position downstream of the pump 50 in the oxidant gas supply passage 44. The intercooler 52 adjusts the temperature of the oxidant gas sent from the pump 50. The intercooler 52 cools the oxidant gas (compressed oxidant gas) sent from the pump 50. For example, a cooling medium that has cooled the fuel cell stack 14 flows through the intercooler 52. When the outside air temperature outside the fuel cell system 12 is below freezing point, the temperature of the cooling medium guided to the intercooler 52 becomes higher than the temperature of the oxidant gas sent from the pump 50 by flowing through the fuel cell stack 14. Therefore, the intercooler 52 can increase the temperature of the oxidant gas sent from the pump 50 when the outside air temperature is below freezing point. Note that the intercooler 52 is not limited to the above-mentioned configuration.

[0022] The supply valve 54 is located in the oxidizing gas supply channel 44 at a position downstream of the intercooler 52. The supply valve 54 opens and closes the oxidizing gas supply channel 44. The supply valve 54 is configured so that the opening degree can be adjusted. An example of the supply valve 54 is a butterfly valve.

[0023] The oxidant gas discharge flow path 46 is connected to the oxidant gas outlet portion 36 of the fuel cell stack 14. The oxidant gas discharge flow path 46 discharges water generated by power generation in the fuel cell stack 14 together with the oxidant exhaust gas. The oxidant gas discharge flow path 46 discharges the oxidant exhaust gas containing the generated water to the outside of the fuel cell system 12. The oxidant gas discharge flow path 46 is provided with a discharge valve 56 that opens and closes the oxidant gas discharge flow path 46. The discharge valve 56 is configured so that the opening degree can be adjusted. An example of the discharge valve 56 is a butterfly valve.

[0024] The bypass flow passage 48 connects the oxidant gas supply flow passage 44 and the oxidant gas discharge flow passage 46 to each other. One end of the bypass flow passage 48 is connected to a portion of the oxidant gas supply flow passage 44 between the intercooler 52 and the supply valve 54. The other end of the bypass flow passage 48 is connected to a portion of the oxidant gas discharge flow passage 46 downstream of the discharge valve 56. The bypass flow passage 48 is provided with a bypass valve 58 that opens and closes the bypass flow passage 48. The bypass valve 58 is configured so that the opening degree can be adjusted. An example of the bypass valve 58 is a butterfly valve.

[0025] The humidifier 60 humidifies the oxidant gas flowing through the oxidant gas supply flow passage 44 with the oxidant exhaust gas flowing through the oxidant gas discharge flow passage 46. The oxidant gas flowing through a portion of the oxidant gas supply flow passage 44 downstream of the supply valve 54 flows through the humidifier 60. In addition, the oxidant exhaust gas containing generated water flowing through a portion of the oxidant gas discharge flow passage 46 upstream of the discharge valve 56 flows through the humidifier 60. The oxidant gas sent from the pump 50 is supplied to the fuel cell stack 14 in a humidified state by the humidifier 60.

[0026] The anode system device 18 has a fuel gas supply unit 62, a fuel gas supply passage 64, and a fuel gas discharge passage 66. The anode system device 18 may also be provided with components other than these components, but the description thereof will be omitted here.

[0027] The fuel gas supply unit 62 supplies fuel gas to a fuel gas supply flow path 64. The fuel gas supply unit 62 includes an injector and an ejector, not shown. The fuel gas supply flow path 64 connects the fuel gas supply unit 62 to the fuel gas inlet portion 40 of the fuel cell stack 14. The fuel gas supply flow path 64 supplies fuel gas to the fuel cell stack 14. The fuel gas discharge flow path 66 allows fuel exhaust gas discharged from the fuel cell stack 14 to flow.

[0028] The fuel cell system 12 includes a cooling system (not shown). The cooling system circulates a cooling medium through the fuel cell stack 14. Examples of the cooling medium include pure water, ethylene glycol, and oil. As described above, the cooling medium that has circulated through the fuel cell stack 14 is guided to the intercooler 52.

[0029] An outside air temperature sensor 68 and an intake air temperature sensor 70 are connected to the control device 10. Sensors other than the outside air temperature sensor 68 and the intake air temperature sensor 70 may be connected to the control device 10. The outside air temperature sensor 68 sequentially measures the outside air temperature outside the fuel cell system 12. The outside air temperature sensor 68 is provided, for example, in the front room of the vehicle. The intake air temperature sensor 70 sequentially measures the temperature of the oxidant gas flowing through the oxidant gas flow passage 32. The intake air temperature sensor 70 is provided, for example, in a portion of the oxidant gas flow passage 32 between a branch portion 72 to the bypass flow passage 48 and the intercooler 52.

[0030] The control device 10 includes a calculation unit 74 and a storage unit 76. The calculation unit 74 is configured by a processor such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit). That is, the calculation unit 74 is configured by a processing circuitry.

[0031] The calculation unit 74 has a control unit 78, a pump control unit 80, an acquisition unit 82, and a determination unit 84. The control unit 78, the pump control unit 80, the acquisition unit 82, and the determination unit 84 can be realized by the calculation unit 74 executing a program stored in the storage unit 76.

[0032] At least a part of the control unit 78, the pump control unit 80, the acquisition unit 82, and the determination unit 84 may be realized by an integrated circuit such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field-Programmable Gate Array). At least a part of the control unit 78, the pump control unit 80, the acquisition unit 82, and the determination unit 84 may be configured by an electronic circuit including a discrete device.

[0033] The storage unit 76 is composed of a volatile memory (not shown) and a non-volatile memory (not shown). An example of the volatile memory is a random access memory (RAM). The volatile memory is used as a working memory of the processor, and temporarily stores data and the like required for processing or calculation. An example of the non-volatile memory is a read only memory (ROM) or a flash memory. The non-volatile memory is used as a storage memory, and stores programs, tables, maps, and the like. At least a part of the storage unit 76 may be provided in the processor, integrated circuit, and the like described above.

[0034] The control unit 78 is responsible for overall control of the fuel cell system 12. The control unit 78 controls the fuel gas supply unit 62, the supply valve 54, the exhaust valve 56, and the bypass valve 58. The pump control unit 80 controls the pump 50. The acquisition unit 82 can grasp the outside air temperature around the fuel cell system 12 based on a signal supplied from the outside air temperature sensor 68. The acquisition unit 82 can grasp the temperature of the oxidant gas flowing through the oxidant gas supply passage 44 (intake air temperature) based on a signal supplied from the intake air temperature sensor 70.

[0035] Next, an example of a control method for the fuel cell system 12 according to this embodiment will be described. Figures 2 and 3 are flowcharts for explaining the control method for the fuel cell system 12. The flowcharts in Figures 2 and 3 are executed at a predetermined cycle while the fuel cell system 12 is in operation.

[0036] When the fuel cell system 12 is operated, an oxidant gas is supplied from the cathode device 16 to the oxidant gas flow path 32 of the fuel cell stack 14, and a fuel gas is supplied from the anode device 18 to the fuel gas flow path 38 of the fuel cell stack 14. Each power generation cell 20 then generates power through an electrochemical reaction between the oxidant gas and the fuel gas. In the power generation cell 20, water is generated by power generation. The water present in the oxidant gas flow path 32 is discharged into the oxidant gas discharge flow path 46 together with the oxidant exhaust gas. The water present in the fuel gas flow path 38 is discharged into the fuel gas discharge flow path 66 together with the fuel exhaust gas.

[0037] However, if the bypass valve 58 is fully closed while the fuel cell stack 14 is generating electricity, the produced water flowing through the oxidant gas discharge passage 46 may be guided to the bypass valve 58 via the bypass passage 48 together with the oxidant exhaust gas. If this happens, when the fuel cell system 12 is in a low-temperature environment (e.g., an environment below the freezing point), the produced water may freeze the bypass valve 58, which may prevent the bypass valve 58 from opening and closing smoothly. As described below, the control method for the fuel cell system 12 according to this embodiment can prevent the produced water from freezing the bypass valve 58.

[0038] In step S1, the determination unit 84 determines whether the bypass valve 58 is in a state where it will freeze due to the generated water. Specifically, in step S2 of Fig. 3, the determination unit 84 determines whether the fuel cell stack 14 is undergoing a startup process. The startup process of the fuel cell stack 14 is started, for example, when the control device 10 receives a startup signal from a power switch or the like (not shown). The fuel cell stack 14 generates power after the startup process is completed. If the determination unit 84 determines that the fuel cell stack 14 is undergoing a startup process (YES in step S2), the process proceeds to step S3. If the determination unit 84 determines that the fuel cell stack 14 is not undergoing a startup process (NO in step S2), the process proceeds to step S7.

[0039] When the fuel cell system 12 is installed in a front room, the temperature inside the front room is higher than the temperature outside the front room for a while after the operation of the fuel cell system 12 is stopped. In other words, even if the temperature outside the front room is below the freezing point, the temperature inside the front room may be higher than the freezing point. If the temperature inside the front room is higher than the freezing point, the bypass valve 58 will not freeze due to the generated water.

[0040] Therefore, in step S3, the determination unit 84 determines whether the soak time is equal to or longer than a predetermined time. Here, the soak time refers to the time from when the previous operation of the fuel cell system 12 is stopped to when the current operation is started. The predetermined time is set to the time from when the operation of the fuel cell system 12 is stopped to when the temperature inside the front room becomes the same as the temperature outside the front room. The predetermined time is stored in the memory unit 76 in advance. The predetermined time is set, for example, to a range of 1 hour to 10 hours.

[0041] If the determination unit 84 determines that the soak time is shorter than the predetermined time (NO in step S3), the process proceeds to step S4. If the determination unit 84 determines that the soak time is equal to or longer than the predetermined time (YES in step S3), the process proceeds to step S5.

[0042] In step S4, the determination unit 84 determines that the bypass valve 58 is not in a state where it will freeze due to the generated water. This is because the soak time is shorter than the predetermined time and the temperature in the front room is relatively high. In this case (NO in step S1), the process proceeds to step S12 in FIG. 2.

[0043] In step S5, the determination unit 84 determines whether the outside air temperature acquired by the outside air temperature sensor 68 or the intake air temperature acquired by the intake air temperature sensor 70 is equal to or lower than a first temperature threshold. The first temperature threshold is set to, for example, a temperature slightly higher than the freezing point, taking into account the measurement error of the outside air temperature sensor 68 or the intake air temperature sensor 70. The first temperature threshold may also be set to the freezing point. The first temperature threshold is stored in advance in the storage unit 76.

[0044] If the determination unit 84 determines that the outside air temperature acquired by the outside air temperature sensor 68 or the intake air temperature acquired by the intake air temperature sensor 70 is equal to or lower than the first temperature threshold (YES in step S5), the process proceeds to step S6. If the determination unit 84 determines that the outside air temperature acquired by the outside air temperature sensor 68 and the intake air temperature acquired by the intake air temperature sensor 70 are higher than the first temperature threshold (NO in step S5), the process proceeds to step S4.

[0045] In step S6, the determination unit 84 determines that the generated water is in a state in which the bypass valve 58 will freeze. In this case (YES in step S1), the process proceeds to step S14 in FIG.

[0046] In step S7, the determination unit 84 determines that power is being generated in the fuel cell stack 14. Then, the process proceeds to step S8.

[0047] In step S8, the determination unit 84 determines whether the vehicle speed (vehicle speed) is equal to or greater than a predetermined speed. The acquisition unit 82 can grasp the vehicle speed, for example, based on a signal supplied from a vehicle speed sensor (not shown). The predetermined speed can be set appropriately, for example, within a range of 10 km / h to 30 km / h. The predetermined speed is stored in the storage unit 76 in advance.

[0048] If the determination unit 84 determines that the vehicle speed is lower than the predetermined speed (NO in step S8), the process proceeds to step S5. If the determination unit 84 determines that the vehicle speed is equal to or higher than the predetermined speed (YES in step S8), the process proceeds to step S9.

[0049] Incidentally, as the vehicle speed increases, the amount of heat generated by heat-generating devices, such as a motor for driving the vehicle, provided in the front compartment also increases. When the vehicle speed exceeds a predetermined speed, the outside air temperature sensor 68 and the intake air temperature sensor 70 are more susceptible to the heat from the heat-generating devices. As a result, the outside air temperature sensor 68 may detect a temperature higher than the actual outside air temperature outside the fuel cell system 12. Also, the intake air temperature sensor 70 may detect a temperature higher than the actual intake temperature of the oxidant gas in the oxidant gas supply passage 44.

[0050] Therefore, in step S9, the determination unit 84 determines whether the outside air temperature acquired by the outside air temperature sensor 68 or the intake air temperature acquired by the intake air temperature sensor 70 is equal to or lower than a second temperature threshold determined in advance. The second temperature threshold is set to a temperature higher than the first temperature threshold, taking into consideration the influence of heat from the heat generating device. Note that, when the outside air temperature sensor 68 and the intake air temperature sensor 70 are disposed in a position where they are subjected to wind while traveling, the second temperature threshold may be set taking into consideration the influence of the wind while traveling. The second temperature threshold is stored in the storage unit 76 in advance.

[0051] If the determination unit 84 determines that the outside air temperature acquired by the outside air temperature sensor 68 or the intake air temperature acquired by the intake air temperature sensor 70 is equal to or lower than the second temperature threshold (YES in step S9), the process proceeds to step S10. If the determination unit 84 determines that the outside air temperature acquired by the outside air temperature sensor 68 and the intake air temperature acquired by the intake air temperature sensor 70 are higher than the second temperature threshold (NO in step S9), the process proceeds to step S11.

[0052] In step S10, the determination unit 84 determines that the generated water is in a state in which the bypass valve 58 will freeze. In this case (YES in step S1), the process proceeds to step S14 in FIG.

[0053] In step S11, the determination unit 84 determines that the generated water is not in a state in which the bypass valve 58 will freeze. In this case (NO in step S1), the process proceeds to step S12 in FIG.

[0054] In step S12, the control unit 78 sets the opening degree lower limit of the bypass valve 58 to a first opening degree lower limit. The first opening degree lower limit is set to, for example, the minimum opening degree of the bypass valve 58. In this case, when the bypass valve 58 is set to the first opening degree lower limit, the oxidant gas sent from the pump 50 can be efficiently supplied to the fuel cell stack 14. Note that the first opening degree lower limit may be larger than the minimum opening degree of the bypass valve 58. The first opening degree lower limit can be set as appropriate. The first opening degree lower limit is stored in advance in the storage unit 76. Then, the process proceeds to step S13.

[0055] In step S13, when the opening of the bypass valve 58 is at the first lower limit, the control unit 78 controls the pump 50 to supply the oxidant gas at a target flow rate to the fuel cell stack 14. The target flow rate of the oxidant gas is determined according to the amount of power generation required for the fuel cell stack 14. Then, the process shown in FIG. 2 is completed.

[0056] In step S14, the control unit 78 sets the opening degree lower limit of the bypass valve 58 to a second opening degree lower limit. The second opening degree lower limit is greater than the first opening degree lower limit. The bypass valve 58 may be configured to be in a fully closed state at an opening degree of 0% and in a fully open state at an opening degree of 100%. In this case, the second opening degree lower limit is set to an opening degree of 5% or less, for example. The second opening degree lower limit may also be set to an opening degree of 1% or less.

[0057] When the opening degree of the bypass valve 58 is at the second lower limit, the oxidant gas that flows from the pump 50 into the bypass flow path 48 via the oxidant gas supply flow path 44 flows through the bypass valve 58 and into the oxidant gas discharge flow path 46. This makes it possible to prevent the generated water discharged from the fuel cell stack 14 to the oxidant gas discharge flow path 46 from entering the bypass valve 58. In other words, when the bypass valve 58 is in a state where it would freeze due to the generated water, the oxidant gas constantly flows through the bypass valve 58, making it possible to prevent the bypass valve 58 from freezing due to the generated water.

[0058] Furthermore, in a low-temperature environment (for example, an environment below the freezing point), the oxidant gas flowing through the bypass valve 58 is heated by the intercooler 52, and therefore the bypass valve 58 can be warmed by the oxidant gas having a relatively high temperature. This makes it possible to further prevent the bypass valve 58 from freezing due to the generated water.

[0059] After step S14, the process proceeds to step S15. In step S15, when the opening of the bypass valve 58 is at the second lower limit, the control unit 78 controls the pump 50 taking into account the flow rate of the oxidant gas flowing through the bypass valve 58, thereby supplying the oxidant gas at a target flow rate to the fuel cell stack 14. That is, the control unit 78 increases the flow rate of the oxidant gas sent from the pump 50 by the flow rate of the oxidant gas flowing through the bypass valve 58. This makes it possible to prevent the flow rate of the oxidant gas supplied to the fuel cell stack 14 from becoming less than the target flow rate. After step S15, the process shown in FIG. 2 is completed.

[0060] According to this embodiment, when the bypass valve 58 is in a state where it would freeze due to water generated by power generation in the fuel cell stack 14, the oxidant gas sent from the pump 50 can be circulated from the oxidant gas supply flow path 44 to the oxidant gas discharge flow path 46 via the bypass valve 58. This makes it possible to prevent the generated water discharged from the fuel cell stack 14 to the oxidant gas discharge flow path 46 from entering the bypass valve 58 by the oxidant gas flowing from the bypass flow path 48 to the oxidant gas discharge flow path 46. In other words, when the bypass valve 58 is in a state where it would freeze due to the generated water, the oxidant gas constantly flows through the bypass valve 58, so that it is possible to prevent the bypass valve 58 from being frozen by the generated water.

[0061] In addition to the above disclosure, the following notes are also disclosed.

[0062] (Appendix 1) The control device (10) controls a fuel cell system (12) including a fuel cell (14) that generates electricity by an electrochemical reaction between a fuel gas and an oxidant gas, a bypass flow path (48) that connects an oxidant gas supply flow path (44) that supplies the oxidant gas to the fuel cell and an oxidant gas discharge flow path (46) through which oxidant exhaust gas discharged from the fuel cell flows, and a bypass valve (58) that is provided in the bypass flow path and has an adjustable opening degree, and includes a control unit (78) that controls the bypass valve, and a determination unit (84) that determines whether or not the bypass valve is in a state where it will freeze due to generated water generated by power generation, and when the determination unit determines that the bypass valve is not in a state where it will freeze due to the generated water, the control unit sets the opening lower limit value of the bypass valve to a first opening lower limit value, and when the determination unit determines that the bypass valve is in a state where it will freeze due to the generated water, the control unit sets the opening lower limit value of the bypass valve to a second opening lower limit value that is larger than the first opening lower limit value.

[0063] According to this configuration, when the bypass valve is in a state where it would freeze due to the generated water caused by the power generation of the fuel cell, the oxidant gas can be circulated from the oxidant gas supply flow path through the bypass valve to the oxidant gas discharge flow path. This makes it possible to prevent the generated water discharged from the fuel cell to the oxidant gas discharge flow path from entering the bypass valve by the oxidant gas flowing from the bypass flow path to the oxidant gas discharge flow path. In other words, when the bypass valve is in a state where it would freeze due to the generated water, the oxidant gas constantly flows through the bypass valve, so that it is possible to prevent the bypass valve from being frozen by the generated water.

[0064] (Appendix 2) The control device described in Appendix 1 may further include a pump control unit (80) that controls a pump (50) provided in a portion of the oxidant gas supply flow path upstream of a branch portion (72) to the bypass flow path, and when the opening of the bypass valve is at the first lower limit, the pump control unit controls the pump to supply the oxidant gas at a predetermined target flow rate to the fuel cell, and when the opening of the bypass valve is at the second lower limit, the pump control unit controls the pump taking into account a flow rate of the oxidant gas flowing through the bypass valve, to supply the oxidant gas at the target flow rate to the fuel cell.

[0065] With this configuration, the flow rate of the oxidant gas sent from the pump can be increased by the flow rate of the oxidant gas flowing through the bypass valve, so that when the opening of the bypass valve is at its lower limit (second lower limit), the flow rate of the oxidant gas supplied to the fuel cell stack can be prevented from becoming less than the target flow rate. This makes it possible to prevent liquid water from freezing in the bypass valve and to prevent the amount of power generated by the fuel cell from falling below the required amount of power generation.

[0066] (Appendix 3) In the control device described in Supplementary Note 1 or 2, the fuel cell system may further include a heat exchanger (52) that is provided in a portion of the oxidant gas supply passage upstream of a branch point to the bypass passage and that is capable of raising the temperature of the oxidant gas.

[0067] According to this configuration, the oxidant gas heated by the heat exchanger flows through the bypass valve, so that the bypass valve can be further warmed by the oxidant gas.

[0068] (Appendix 4) In the control device described in any one of Supplementary Notes 1 to 3, the determination unit may determine whether or not the generated water can freeze at the bypass valve, based on a temperature detected by a temperature sensor (68, 70) capable of grasping a temperature of the bypass valve.

[0069] With this configuration, it is possible to easily determine whether or not the generated water can freeze in the bypass valve.

[0070] (Appendix 5) In the control device described in Supplementary Note 4, the temperature sensor may include an outside air temperature sensor (68) that detects an outside air temperature outside the fuel cell system.

[0071] According to this configuration, the temperature of the bypass valve can be determined based on the outside air temperature.

[0072] (Appendix 6) In the control device according to Supplementary Note 4 or 5, the temperature sensor may include an intake air temperature sensor (70) that detects an intake temperature of the oxidant gas.

[0073] According to this configuration, the temperature of the bypass valve can be determined from the intake air temperature.

[0074] (Appendix 7) The fuel cell system includes the control device according to any one of claims 1 to 6.

[0075] (Appendix 8) A control method for a fuel cell system includes a fuel cell that generates electricity by an electrochemical reaction between a fuel gas and an oxidant gas, a bypass flow path that connects an oxidant gas supply flow path that supplies the oxidant gas to the fuel cell and an oxidant gas discharge flow path through which oxidant exhaust gas discharged from the fuel cell flows, and a bypass valve provided in the bypass flow path and whose opening can be adjusted, the control method including a determination step of determining whether the bypass valve is in a state where it will freeze due to water generated by power generation of the fuel cell, and a setting step of setting a lower limit value of opening of the bypass valve, in which, if it is determined in the determination step that the bypass valve is not in a state where it will freeze due to the generated water, a control unit sets the lower limit value of the bypass valve to a first lower limit value, and if it is determined in the determination step that the bypass valve is in a state where it will freeze due to the generated water, the control unit sets the lower limit value of the bypass valve to a second lower limit value that is greater than the first lower limit value.

[0076] (Appendix 9) The program causes a computer to execute the control method for a fuel cell system described in Supplementary Note 8.

[0077] 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]

[0078] 10...Control device 12...Fuel cell system 44...oxidant gas supply passage 46...oxidant gas discharge passage 48...Bypass flow passage 50...Pump 52...Intercooler (heat exchanger) 54...Supply valve 56...Discharge valve 58...Bypass valve 68...Outside air temperature sensor 70...Intake air temperature sensor 78...Control unit 80...Pump control unit 84…Judgment section

Claims

1. a fuel cell that generates electricity through an electrochemical reaction between a fuel gas and an oxidant gas; a bypass flow path connecting an oxidant gas supply flow path for supplying the oxidant gas to the fuel cell and an oxidant gas discharge flow path through which an oxidant exhaust gas discharged from the fuel cell flows; a bypass valve provided in the bypass flow path and having an adjustable opening degree; A control device for controlling a fuel cell system comprising: A control unit that controls the bypass valve; a determination unit that determines whether or not the bypass valve is in a state where it may freeze due to water generated by power generation of the fuel cell; having When the determination unit determines that the bypass valve is not in a state where it will be frozen by the generated water, the control unit sets a lower limit value of the opening degree of the bypass valve to a first lower limit value of the opening degree, When the determination unit determines that the bypass valve is in a state where it will freeze due to the generated water, the control unit sets the opening lower limit value of the bypass valve to a second opening lower limit value that is greater than the first opening lower limit value.

2. The control device according to claim 1 , a pump control unit that controls a pump provided in a portion of the oxidant gas supply flow path upstream of a branch portion to the bypass flow path, when the opening degree of the bypass valve is the first lower limit value, the pump control unit controls the pump to supply the oxidant gas to the fuel cell at a predetermined target flow rate; A control device, when the opening degree of the bypass valve is the second opening degree lower limit value, wherein the pump control unit controls the pump taking into account the flow rate of the oxidant gas flowing through the bypass valve, thereby supplying the oxidant gas at the target flow rate to the fuel cell.

3. The control device according to claim 1 , The fuel cell system includes a heat exchanger that is provided in the oxidizing gas supply passage upstream of a branch point to the bypass passage and that is capable of increasing the temperature of the oxidizing gas.

4. The control device according to claim 1 , The determination unit determines whether or not the generated water can freeze at the bypass valve based on a temperature detected by a temperature sensor capable of grasping a temperature of the bypass valve.

5. The control device according to claim 4, The temperature sensor includes an outside air temperature sensor that detects the outside air temperature outside the fuel cell system.

6. The control device according to claim 4, The temperature sensor includes an intake air temperature sensor that detects the intake temperature of the oxidant gas.

7. A fuel cell system comprising the control device according to any one of claims 1 to 6.

8. a fuel cell that generates electricity through an electrochemical reaction between a fuel gas and an oxidant gas; a bypass flow path connecting an oxidant gas supply flow path for supplying the oxidant gas to the fuel cell and an oxidant gas discharge flow path through which an oxidant exhaust gas discharged from the fuel cell flows; a bypass valve provided in the bypass flow path and capable of adjusting an opening degree; A control method for a fuel cell system comprising: a determination step of determining whether or not the bypass valve is in a state where it may freeze due to water generated by power generation of the fuel cell; a setting step of setting a lower limit value of the opening degree of the bypass valve; having In the setting step, When it is determined in the determination step that the bypass valve is not in a state in which it is frozen by the generated water, the control unit sets the opening degree lower limit value of the bypass valve to a first opening degree lower limit value, a control unit for setting the lower limit value of the bypass valve to a second lower limit value that is greater than the first lower limit value when the determination step determines that the generated water will cause the bypass valve to freeze.

9. A program for causing a computer to execute the method for controlling a fuel cell system according to claim 8.

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