Fuel cell module

Abstract

To prevent a current from flowing from a fuel cell stack to a power storage device.SOLUTION: A fuel cell module includes a fuel cell stack, a DCDC converter and a controller. The DCDC converter includes a diode provided in a high side and a switching element provided in a low side. The fuel cell stack is connected between the diode and the switching element; and the controller turns off a switch provided between the DCDC converter and a power storage device in the situation that the voltage of the fuel cell stack can be higher than that of the power storage device.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to fuel cell modules. [Background technology]

[0002] The fuel cell module disclosed in Patent Document 1 includes a fuel cell stack and a DC-DC converter. The DC-DC converter includes six switching elements, diodes connected in parallel to each of the six switching elements, and a reactor. The six switching elements include three pairs of switching elements connected in series. The fuel cell stack is connected to the midpoint of the two switching elements connected directly to each other via a reactor. The DC-DC converter is connected to a power storage device. The DC-DC converter boosts the output voltage of the fuel cell stack through the switching operation of the switching elements, thereby supplying power to the power storage device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2024-13960 Summary of the Invention [Problem to be solved by the invention]

[0004] When the voltage of the power storage device is lower than the voltage of the fuel cell stack and the switching element is not performing a switching operation, current flows from the fuel cell stack to the power storage device via the diode. There are cases where it is desirable to prevent current from flowing from the fuel cell stack to the power storage device via the diode. [Means for solving the problem]

[0005] A fuel cell module that solves the above problem comprises a fuel cell stack, a DCDC converter that transforms the output voltage of the fuel cell stack and outputs it to a power storage device, the DCDC converter having a diode on the high side and a switching element on the low side, and a control unit, and controls power generation of the fuel cell stack based on commands from a higher-level system, the fuel cell stack being connected between the diode and the switching element, and the control unit turning off a switch provided between the DCDC converter and the power storage device in a situation where the voltage of the fuel cell stack may become higher than the voltage of the power storage device.

[0006] By turning off the switch in a situation where the voltage of the fuel cell stack may become higher than the voltage of the power storage device, the path from the fuel cell stack to the power storage device is blocked, thereby preventing current from flowing from the fuel cell stack to the power storage device.

[0007] In the above fuel cell module, the switch may include a module-side switch provided in the fuel cell module, and the control unit may turn off the module-side switch in a situation where the voltage of the fuel cell stack may become higher than the voltage of the storage device.

[0008] The above fuel cell module may be provided with an air compressor connected between the DC-DC converter and the module side switch, and the situation in which the voltage of the fuel cell stack may become higher than the voltage of the power storage device may include a situation in which scavenging of the fuel cell stack is performed, and the control unit may scavenge the fuel cell stack by supplying the generated power of the fuel cell stack to the air compressor after turning off the module side switch in a situation in which the voltage of the fuel cell stack may become higher than the voltage of the power storage device.

[0009] For the fuel cell module, the switch may include a system-side switch provided in the upper system, and the control unit may turn off the system-side switch by sending a command to the upper system to turn off the system-side switch in a situation where the voltage of the fuel cell stack may become higher than the voltage of the storage device.

[0010] For the fuel cell module, the switch may include a system-side switch provided in the upper system, and the control unit may notify the upper system not to turn off the system-side switch when the module-side switch is turned off in a situation where the voltage of the fuel cell stack may become higher than the voltage of the storage device. [Effects of the Invention]

[0011] According to the present invention, it is possible to prevent current from flowing from the fuel cell stack to the power storage device. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram of a fuel cell system. [Figure 2] Figure 2 is a circuit diagram of a DC-DC converter. [Figure 3] FIG. 3 is a flowchart showing the control performed by the control unit. [Figure 4] FIG. 4 is a schematic diagram showing the fuel cell system in a state where the module-side switch is turned off. [Figure 5] FIG. 5 is a flowchart showing the control performed by the control unit. [Figure 6] FIG. 6 is a schematic diagram showing the fuel cell system when the system-side switch is turned off. DETAILED DESCRIPTION OF THE INVENTION

[0013] [First embodiment] A first embodiment of the fuel cell module will be described. As shown in FIG. 1, the fuel cell system FS includes a host system 90 and a fuel cell module 10.

[0014] The host system 90 has two system input terminals 91 and 92. The fuel cell module 10 is connected to the system input terminals 91 and 92. Power is supplied to the host system 90 from the fuel cell module 10 via the system input terminals 91 and 92.

[0015] The upper system 90 includes a power storage device 93. System input terminals 91 and 92 are connected to the power storage device 93. Specifically, the upper system 90 includes a positive electrode connection line 95 that connects the system input terminal 91 to the positive electrode of the power storage device 93, and a negative electrode connection line 96 that connects the system input terminal 92 to the negative electrode of the power storage device 93. The system input terminals 91 and 92 are connected to the power storage device 93 by the positive electrode connection line 95 and the negative electrode connection line 96. The rated voltage of the power storage device 93 is a first voltage. The first voltage is, for example, 48 V. The power storage device 93 is a secondary battery or a capacitor.

[0016] The upper system 90 includes a system-side switch 97. The system-side switch 97 is an example of a switch. The system-side switch 97 is, for example, a relay switch. The system-side switch 97 may be any switch, such as a semiconductor switch. The system-side switch 97 is provided between the system input terminal 91 and the power storage device 93. The system-side switch 97 is provided in the positive electrode connection line 95. When the system-side switch 97 is off, power from the fuel cell module 10 is not supplied to the upper system 90. When the system-side switch 97 is on, power from the fuel cell module 10 is supplied to the upper system 90.

[0017] The host system 90 includes a host control unit 98. The host control unit 98 switches the system-side switch 97 on and off. The host control unit 98 sends commands to the fuel cell module 10. The commands include a power generation command that controls the power generation of the fuel cell module 10. The power generation command is a target voltage or a command that instructs the fuel cell module 10 on a target voltage.

[0018] A load 99 is connected to the upper system 90. The load 99 is connected between the system-side switch 97 and the power storage device 93. The load 99 is driven by power supplied from at least one of the fuel cell module 10 and the power storage device 93. When the system-side switch 97 is on, the load 99 is driven by power supplied from the fuel cell module 10. When the power supplied from the fuel cell module 10 is greater than the power consumed by the load 99, the power storage device 93 is charged with the surplus power. When the power supplied from the fuel cell module 10 is less than the power consumed by the load 99, power is also supplied to the load 99 from the power storage device 93.

[0019] The load 99 is an electrical component that is driven by the first voltage. The load 99 may include an electrical component that is driven by a voltage different from the first voltage, and a power conversion device that transforms the first voltage and outputs it to the electrical component.

[0020] <Fuel cell module> The fuel cell module 10 includes a fuel cell stack 11. The fuel cell stack 11 includes a plurality of fuel cell cells. The fuel cell cells are, for example, solid polymer membrane fuel cells. The fuel cell stack 11 generates electricity through a chemical reaction between an anode gas and a cathode gas. The anode gas is, for example, hydrogen. The cathode gas is, for example, oxygen in the air.

[0021] The fuel cell module 10 includes a DC-DC converter 12. The DC-DC converter 12 includes two input terminals 13, 14 and two output terminals 15, 16. The fuel cell stack 11 is connected to the two input terminals 13, 14. The power generated by the fuel cell module 10 is input to the DC-DC converter 12. The DC-DC converter 12 transforms the output voltage of the fuel cell stack 11 input to the input terminals 13, 14 and outputs it to the output terminals 15, 16. The DC-DC converter 12 transforms the output voltage of the fuel cell stack 11 to a first voltage, for example, and outputs it.

[0022] 2, the DC-DC converter 12 includes a positive wiring 21, a negative wiring 22, six switching elements Q1, Q2, Q3, Q4, Q5, and Q6, six diodes D1, D2, D3, D4, D5, and D6, three reactors 17, 18, and 19, and a capacitor C. The positive wiring 21 is connected to an output terminal 15. The negative wiring 22 is connected to an output terminal 16.

[0023] The first switching element Q1 and the second switching element Q2 are connected in series. The third switching element Q3 and the fourth switching element Q4 are connected in series. The fifth switching element Q5 and the sixth switching element Q6 are connected in series. The first switching element Q1, the third switching element Q3, and the fifth switching element Q5 are connected to a positive wiring 21. The second switching element Q2, the fourth switching element Q4, and the sixth switching element Q6 are connected to a negative wiring 22. The first switching element Q1, the third switching element Q3, and the fifth switching element Q5 form an upper arm. The second switching element Q2, the fourth switching element Q4, and the sixth switching element Q6 form a lower arm. The six switching elements Q1 to Q6 are, for example, MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). The six switching elements Q1 to Q6 may also be IGBTs (Insulated Gate Bipolar Transistors).

[0024] The diodes D1 to D6 are connected in parallel to the switching elements Q1 to Q6, respectively. The diodes D1 to D6 are parasitic diodes of the switching elements Q1 to Q6. The diodes D1 to D6 may be elements. The cathodes of the diodes D1, D3, and D5 connected in parallel to the switching elements Q1, Q3, and Q5 constituting the upper arm are connected to the positive electrode wiring 21. The anodes of the diodes D1, D3, and D5 connected in parallel to the switching elements Q1, Q3, and Q5 constituting the upper arm are connected to the midpoint of the two switching elements Q1 to Q6 connected in series to each other. The cathodes of the diodes D2, D4, and D6 connected in parallel to the switching elements Q2, Q4, and Q6 constituting the lower arm are connected to the midpoint of the two switching elements Q1 to Q6 connected in series to each other. The anodes of the diodes D2, D4, and D6 connected in parallel to the switching elements Q2, Q4, and Q6 constituting the lower arm are connected to the negative electrode wiring 22.

[0025] The DC-DC converter 12 includes diodes D1, D3, and D5 provided on the high side, and switching elements Q2, Q4, and Q6 provided on the low side. The diodes D1, D3, and D5 provided on the high side are diodes connected to the positive electrode wiring 21, which has a higher potential, of the positive electrode wiring 21 and the negative electrode wiring 22. The switching elements Q2, Q4, and Q6 provided on the low side are switching elements connected to the negative electrode wiring 22, which has a lower potential, of the positive electrode wiring 21 and the negative electrode wiring 22.

[0026] A fuel cell stack 11 is connected between diodes D1, D3, and D5 provided on the high side and switching elements Q2, Q4, and Q6 provided on the low side. More specifically, a positive electrode of the fuel cell stack 11 is connected between the two switching elements Q1 and Q2 via a reactor 17. A connection between the two switching elements Q1 and Q2 is between the diode D1 and switching element Q2. A positive electrode of the fuel cell stack 11 is connected between the two switching elements Q3 and Q4 via a reactor 18. A connection between the two switching elements Q3 and Q4 is between the diode D3 and switching element Q4. A positive electrode of the fuel cell stack 11 is connected between the two switching elements Q5 and Q6 via a reactor 19. A connection between the two switching elements Q5 and Q6 is between the diode D5 and switching element Q6.

[0027] The capacitor C is provided between the positive electrode wiring 21 and the negative electrode wiring 22. In the DC-DC converter 12 described above, the switching operations of the switching elements Q1 to Q6 can boost the output voltage of the fuel cell stack 11 and output it from the output terminals 15 and 16. When the output voltage of the fuel cell stack 11 is higher than the voltage of the power storage device 93, the output voltage of the fuel cell stack 11 can be reduced and output from the output terminals 15 and 16 by flowing current through the diodes D1, D3, and D5.

[0028] As shown in FIG. 1 , the fuel cell module 10 has two module output terminals 31 and 32, a positive electrode line 33, and a negative electrode line 34. The module output terminals 31 and 32 are connected to system input terminals 91 and 92. The output power of the fuel cell module 10 is output from the module output terminals 31 and 32 and input to a higher-level system 90. The positive electrode line 33 connects the output terminal 15 to the module output terminal 31. The negative electrode line 34 connects the output terminal 16 to the module output terminal 32. As a result, the output power of the DC-DC converter 12 is output to the module output terminals 31 and 32. Therefore, the output power of the fuel cell module 10 is the output power of the DC-DC converter 12. The output power of the fuel cell module 10 is supplied to a power storage device 93. Therefore, the DC-DC converter 12 transforms the output voltage of the fuel cell stack 11 and outputs it to the power storage device 93.

[0029] The fuel cell module 10 includes a module-side switch 35. The module-side switch 35 is provided on the positive electrode line 33. The module-side switch 35 is an example of a switch. The module-side switch 35 is, for example, a relay switch. The module-side switch 35 may be any switch, such as a semiconductor switch.

[0030] The module-side switch 35 is provided between the DC-DC converter 12 and the module output terminal 31. The module-side switch 35 and the system-side switch 97 are provided between the DC-DC converter 12 and the power storage device 93. Therefore, by turning off either the module-side switch 35 or the system-side switch 97, the path from the fuel cell stack 11 to the power storage device 93 is cut off.

[0031] The fuel cell module 10 includes a first voltage auxiliary device 40. The first voltage auxiliary device 40 is driven by a first voltage. The first voltage auxiliary device 40 is connected between the DC-DC converter 12 and the module-side switch 35. In detail, a portion of the positive electrode line 33 between the DC-DC converter 12 and the module-side switch 35 and an arbitrary portion of the negative electrode line 34 are electrically connected to the first voltage auxiliary device 40. It can also be said that the first voltage auxiliary device 40 is connected between the fuel cell stack 11 and the module-side switch 35.

[0032] The first voltage auxiliary device 40 is an electrical component for causing the fuel cell stack 11 to generate electricity. The first voltage auxiliary device 40 includes an air compressor 41, a hydrogen pump 42, a cooling pump 43, and inverters 44 to 46 provided corresponding to these. The inverters 44 to 46 convert DC power input from the positive electrode line 33 and the negative electrode line 34 into AC power and output it.

[0033] The air compressor 41 is driven by AC power output from the inverter 44. The air compressor 41 compresses and discharges cathode gas. The cathode gas discharged from the air compressor 41 is supplied to the fuel cell stack 11. The air compressor 41 is connected between the DC-DC converter 12 and the module-side switch 35.

[0034] The hydrogen pump 42 is driven by AC power output from the inverter 45. The hydrogen pump 42 supplies hydrogen to the fuel cell stack 11. More specifically, the hydrogen pump 42 supplies hydrogen to the fuel cell stack 11 by circulating the hydrogen through a circulation path connected to the fuel cell stack 11.

[0035] The cooling pump 43 is driven by AC power output from the inverter 46. The cooling pump 43 circulates a cooling medium through a cooling path. The cooling medium cools the fuel cell stack 11. The cooling medium may also cool the cathode gas discharged from the air compressor 41.

[0036] The fuel cell module 10 includes a conversion unit 51. The conversion unit 51 is connected between the module-side switch 35 and the module output terminal 31. In detail, the conversion unit 51 is electrically connected to a portion of the positive electrode line 33 between the module-side switches 35 and an arbitrary portion of the negative electrode line 34. It can also be said that the conversion unit 51 is connected between the module-side switch 35 and the power storage device 93.

[0037] The conversion unit 51 is a transformer. The conversion unit 51 converts a first voltage input from the positive electrode line 33 and the negative electrode line 34 into a second voltage and outputs the second voltage. The second voltage is lower than the first voltage. The second voltage is, for example, 12 V.

[0038] The fuel cell module 10 includes a second voltage auxiliary device 60. The second voltage auxiliary device 60 is driven by a second voltage. The second voltage auxiliary device 60 is connected to the conversion unit 51. The second voltage auxiliary device 60 is an electrical component for causing the fuel cell stack 11 to generate power. The second voltage auxiliary device 60 includes an injector 61 and a control unit 62. The injector 61 injects hydrogen into the fuel cell stack 11.

[0039] The control unit 62 includes a processor and a memory. The processor may be, for example, a central processing unit (CPU), a graphics processing unit (GPU), or a digital signal processor (DSP). The memory includes a random access memory (RAM) and a read-only memory (ROM). The memory stores program code or instructions configured to cause the processor to execute a process. The memory, i.e., a computer-readable medium, includes any available medium accessible by a general-purpose or special-purpose computer. The control unit 62 may be configured with a hardware circuit such as an application-specific integrated circuit (ASIC) or a field-programmable gate array (FPGA). The control unit 62, which is a processing circuit, may include one or more processors operating according to a computer program, one or more hardware circuits such as an ASIC or FPGA, or a combination thereof. The host control unit 98 may have a hardware configuration similar to that of the control unit 62.

[0040] The control unit 62 switches the module-side switch 35 on and off. The control unit 62 is configured to be able to communicate with the host control unit 98. This allows the control unit 62 to receive commands from the host system 90. The control unit 62 can notify the host system 90 of the status of the fuel cell module 10, etc. The control unit 62 can send commands to the host system 90 to cause the host control unit 98 to switch the system-side switch 97 on and off.

[0041] The fuel cell module 10 controls the power generation of the fuel cell stack 11 based on commands from the host system 90. For example, the control unit 62 controls the amount of anode gas supplied to the fuel cell stack 11 and the amount of cathode gas supplied to the fuel cell stack 11 in response to a power generation command received from the host system 90. In this way, the control unit 62 causes the fuel cell stack 11 to generate power at a target voltage or so as to follow the target voltage.

[0042] <Control performed by the control unit> The control unit 62 controls the on / off switching of the module-side switch 35 and the system-side switch 97. The control performed by the control unit 62 will be described.

[0043] As shown in FIG. 3, in step S1, the control unit 62 determines whether or not scavenging needs to be started. Scavenging is a process of discharging the produced water remaining in the fuel cell stack 11 to the outside of the fuel cell stack 11 when the power to the fuel cell module 10 is turned off. When the power to the fuel cell module 10 is turned off, the fuel cell stack 11 is unable to generate power. If the ambient temperature drops below freezing while produced water remains in the fuel cell stack 11, the produced water will freeze. If the produced water freezes, it may cause blockage of the flow paths within the fuel cell stack 11, malfunction of the valves, or a lack of hydrogen or oxygen in the fuel cell stack 11. For this reason, scavenging must be started when there is a risk of the produced water freezing.

[0044] For example, whether or not scavenging needs to be started may be determined based on weather information for the next day, the outside air temperature detected by an outside air temperature sensor, or whether the date on the calendar corresponds to winter. Whether or not scavenging is needed may be determined by the control unit 62 or the upper control unit 98. In the case where the upper control unit 98 makes the determination, the control unit 62 may set the determination result of step S1 to "Yes" when it receives a scavenging command from the upper control unit 98.

[0045] The situation in which scavenging of the fuel cell stack 11 is performed is an example of a situation in which the voltage of the fuel cell stack 11 may become higher than the voltage of the power storage device 93. When controlling the power generation of the fuel cell stack 11 based on a command from the higher-level system 90, the control unit 62 cannot adjust the voltage of the fuel cell stack 11. As a result, the voltage of the fuel cell stack 11 may unintentionally become higher than the voltage of the power storage device 93. When the voltage of the fuel cell stack 11 is higher than the voltage of the power storage device 93, current flows from the fuel cell stack 11 to the power storage device 93 via diodes D1, D3, and D5. Although scavenging of the fuel cell stack 11 is performed for the purpose of discharging generated water remaining in the fuel cell stack 11, when current flows from the fuel cell stack 11 to the power storage device 93, new generated water is produced. The situation in which scavenging of the fuel cell stack 11 is performed is a situation in which, if the voltage of the fuel cell stack 11 becomes higher than the voltage of the power storage device 93 and water is produced in the fuel cell stack 11, the generated water may hinder the power generation of the fuel cell stack 11.

[0046] If the determination result of step S1 is positive, the control unit 62 proceeds to step S2. If the determination result of step S1 is negative, the control unit 62 repeats step S1. In step S2, the control unit 62 compares the voltage of the fuel cell stack 11 with the voltage of the power storage device 93. For example, the control unit 62 determines whether the voltage of the fuel cell stack 11 is higher than the voltage of the power storage device 93. If the determination result in step S2 is positive, the control unit 62 proceeds to step S6. If the determination result in step S2 is negative, the control unit 62 proceeds to step S3.

[0047] In step S3, the control unit 62 turns on the system-side switch 97 and turns on the module-side switch 35. The module-side switch 35 may be off when the fuel cell stack 11 is not generating power. If the module-side switch 35 is off, the control unit 62 simply turns on the module-side switch 35.

[0048] 1, when the module-side switch 35 and the system-side switch 97 are turned on, power can be supplied from the power storage device 93 to the first voltage auxiliary device 40. The control unit 62 drives the air compressor 41 to supply cathode gas to the fuel cell stack 11. The control unit 62 drives the hydrogen pump 42 to supply anode gas to the fuel cell stack 11.

[0049] Next, in step S4, the control unit 62 starts scavenging. Next, in step S5, the control unit 62 compares the voltage of the fuel cell stack 11 with the voltage of the power storage device 93. For example, the control unit 62 determines whether the voltage of the fuel cell stack 11 is higher than the voltage of the power storage device 93. The output voltage of the fuel cell stack 11 may be measured, for example, by a voltage sensor that measures the voltage between the positive and negative electrodes of the fuel cell stack 11. If the determination result in step S5 is positive, that is, if the voltage of the fuel cell stack 11 is higher than the voltage of the power storage device 93, the control unit 62 proceeds to step S6. If the determination result in step S5 is negative, that is, if the voltage of the fuel cell stack 11 is lower than the voltage of the power storage device 93, the control unit 62 repeats step S5.

[0050] In step S6, the control unit 62 turns on the system-side switch 97 and turns off the module-side switch 35. When the processing of step S6 is performed, both the system-side switch 97 and the module-side switch 35 are on. Therefore, the control unit 62 simply turns off the module-side switch 35. By turning off the module-side switch 35, no current flows from the fuel cell stack 11 to the power storage device 93 even if the voltage of the fuel cell stack 11 is higher than the voltage of the power storage device 93. Therefore, water is less likely to be produced in the fuel cell stack 11. In this way, the control unit 62 turns off the module-side switch 35 in a situation where the voltage of the fuel cell stack 11 may be higher than the voltage of the power storage device 93.

[0051] 4, power is supplied to the first voltage auxiliary device 40 from the fuel cell stack 11. This allows scavenging of the fuel cell stack 11 to continue. After the module-side switch 35 is turned off, the power generated by the fuel cell stack 11 is supplied to the air compressor 41, thereby scavenging the fuel cell stack 11.

[0052] The current flowing from the fuel cell stack 11 to the first voltage auxiliary device 40 is smaller than the current flowing to the power storage device 93. Therefore, although water is generated by the current flowing to the first voltage auxiliary device 40 to scavenge the fuel cell stack 11, it can be discharged by scavenging.

[0053] 3, next, in step S7, the control unit 62 starts scavenging if scavenging is not being performed, or continues scavenging if scavenging is already being performed. Next, in step S8, the control unit 62 notifies the upper system 90 not to turn off the system-side switch 97. The second voltage auxiliary machine 60 is supplied with power from the power storage device 93. For this reason, the system-side switch 97 needs to be kept on while the fuel cell stack 11 is being scavenged. For example, the control unit 62 may notify that the fuel cell stack 11 is being scavenged. The upper control unit 98 may not turn off the system-side switch 97 while the fuel cell stack 11 is being scavenged.

[0054] By controlling the module-side switch 35 and the system-side switch 97 as described above, it is possible to scavenge the fuel cell stack 11 while preventing current from flowing from the fuel cell stack 11 to the power storage device 93 .

[0055] [Effects of the first embodiment] The effects of the first embodiment will be described. (1-1) In a situation where the voltage of the fuel cell stack 11 may become higher than the voltage of the power storage device 93, the control unit 62 turns off the module-side switch 35 to block the path from the fuel cell stack 11 to the power storage device 93. This prevents current from flowing from the fuel cell stack 11 to the power storage device 93.

[0056] (1-2) The control unit 62 turns off the module-side switch 35 in a situation where the voltage of the fuel cell stack 11 may become higher than the voltage of the power storage device 93. By issuing a command to the upper control unit 98, the processing can be made faster than when the system-side switch 97 is turned off.

[0057] (1-3) After turning off the module-side switch 35, the control unit 62 supplies the power generated by the fuel cell stack 11 to the air compressor 41 to scavenge the fuel cell stack 11. This allows scavenging to be performed using the power generated by the fuel cell stack 11. Although water is generated when a current flows through the air compressor 41, the amount of water generated is less than when a current flows through the electricity storage device 93. Therefore, it is possible to discharge the generated water by scavenging.

[0058] (1-4) When the control unit 62 turns off the module-side switch 35, it notifies the upper system 90 not to turn off the system-side switch 97. This prevents the power supply from the power storage device 93 to the second-voltage auxiliary machine 60 from being interrupted.

[0059] (1-5) The first voltage auxiliary device 40 is connected between the fuel cell stack 11 and the module-side switch 35. By turning off the module-side switch 35, it is possible to prevent current from flowing from the power storage device 93 to the first voltage auxiliary device 40. Therefore, by turning off the module-side switch 35 when the first voltage auxiliary device 40 is not being driven, it is possible to prevent dark current from flowing from the power storage device 93 to the first voltage auxiliary device 40.

[0060] (1-6) The conversion unit 51 that supplies power to the second-voltage auxiliary device 60 is connected between the module-side switch 35 and the power storage device 93. By turning on the system-side switch 97, power can be supplied from the power storage device 93 to the second-voltage auxiliary device 60. Therefore, the fuel cell module 10 does not need to be equipped with a power storage device for supplying power to the second-voltage auxiliary device 60.

[0061] [Second embodiment] A second embodiment of the fuel cell module will be described. The second embodiment differs from the first embodiment in the control performed by the control unit. The control performed by the control unit of the second embodiment will be described.

[0062] As shown in FIG. 5, in the second embodiment, if the determination result in step S2 is positive or the determination result in step S5 is positive, the control unit 62 proceeds to step S11. In step S11, the control unit 62 turns off the system-side switch 97 and turns on the module-side switch 35. When step S11 is performed, both the system-side switch 97 and the module-side switch 35 are on. Therefore, the control unit 62 simply turns off the system-side switch 97. The control unit 62 turns off the system-side switch 97 by sending a command to the higher-level system 90. By turning off the system-side switch 97, no current flows from the fuel cell stack 11 to the power storage device 93, even if the voltage of the fuel cell stack 11 is higher than the voltage of the power storage device 93. Therefore, water is less likely to be generated in the fuel cell stack 11.

[0063] 6, when the system-side switch 97 is turned off in a situation where the voltage of the fuel cell stack 11 may become higher than the voltage of the power storage device 93, power is supplied from the fuel cell stack 11 to the second-voltage auxiliary device 60. Therefore, while the fuel cell stack 11 is being scavenged, the first-voltage auxiliary device 40 and the second-voltage auxiliary device 60 are driven by the power generated by the fuel cell stack 11.

[0064] [Effects of the second embodiment] The following describes the effects of the second embodiment: According to the second embodiment, in addition to the effects (1-1), (1-3), (1-5), and (1-6) of the first embodiment, the following effects can be obtained.

[0065] (2-1) The control unit 62 prevents current from flowing from the fuel cell stack 11 to the power storage device 93 by turning off the system-side switch 97. If the system-side switch 97 is turned off in a situation where the voltage of the fuel cell stack 11 may be higher than the voltage of the power storage device 93, power is supplied to the second voltage auxiliary device 60 from the fuel cell stack 11. This makes it possible to prevent the charge rate of the power storage device 93 from decreasing due to the driving of the second voltage auxiliary device 60.

[0066] [Example of change] Each embodiment can be modified as follows: Each embodiment and the following modifications can be combined with each other to the extent that no technical contradiction occurs.

[0067] In each embodiment, the first voltage auxiliary machine 40 may be connected between the module-side switch 35 and the power storage device 93. In each embodiment, the second voltage auxiliary device 60 may be connected between the DC-DC converter 12 and the module-side switch 35. In this case, the fuel cell module 10 may include a power storage device that supplies power to the second voltage auxiliary device 60.

[0068] In the first embodiment, step S8 may be omitted. [Explanation of symbols]

[0069] D1, D3, D5...diodes, Q2, Q4, Q6...switching elements, 10...fuel cell module, 11...fuel cell stack, 12...DC-DC converter, 35...module side switch which is an example of a switch, 41...air compressor, 62...control unit, 90...higher system, 97...system side switch which is an example of a switch.

Claims

1. a fuel cell stack; a DC-DC converter that transforms the output voltage of the fuel cell stack and outputs the transformed voltage to a power storage device, the DC-DC converter having a diode provided on a high side and a switching element provided on a low side; a control unit that controls power generation by the fuel cell stack based on a command from a host system, the fuel cell stack is connected between the diode and the switching element, The control unit turns off a switch provided between the DC-DC converter and the power storage device in a situation where the voltage of the fuel cell stack may become higher than the voltage of the power storage device.

2. the switch includes a module-side switch provided in the fuel cell module, 2. The fuel cell module according to claim 1, wherein the control unit turns off the module-side switch in a situation where the voltage of the fuel cell stack may become higher than the voltage of the power storage device.

3. an air compressor connected between the DC-DC converter and the module-side switch; the situation in which the voltage of the fuel cell stack may be higher than the voltage of the power storage device includes a situation in which scavenging of the fuel cell stack is performed; 3. The fuel cell module according to claim 2, wherein, in a situation where the voltage of the fuel cell stack may be higher than the voltage of the power storage device, the control unit scavenges the fuel cell stack by supplying the generated power of the fuel cell stack to the air compressor after turning off the module-side switch.

4. the switch includes a system-side switch provided in the higher-level system, 2. The fuel cell module according to claim 1, wherein the control unit turns off the system-side switch by sending a command to the host system to turn off the system-side switch in a situation where the voltage of the fuel cell stack may become higher than the voltage of the power storage device.

5. the switch includes a system-side switch provided in the higher-level system, 3. The fuel cell module according to claim 2, wherein, when the control unit turns off the module-side switch in a situation where the voltage of the fuel cell stack may become higher than the voltage of the power storage device, the control unit notifies the higher-level system not to turn off the system-side switch.

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