Fuel cell system

Abstract

The present invention provides a fuel cell system that can achieve appropriate humidity control during fuel cell startup. [Solution] A fuel cell system comprising: a fuel cell that generates electricity using anode gas supplied to the anode and cathode gas supplied to the cathode; a cathode supply path that supplies the cathode gas to the fuel cell via a humidifier; a cathode supply bypass circuit that supplies the cathode gas to the fuel cell by bypassing the humidifier; a bypass supply valve provided on the cathode supply bypass circuit; a temperature acquisition unit that acquires the ambient temperature of the fuel cell; and a control device that, when the ambient temperature is below a predetermined temperature at startup of the fuel cell, performs warm-up control to put the fuel cell into a power generation state and raise the temperature to above a predetermined temperature, and after the warm-up control is performed, performs humidity control to open the bypass supply valve and supply the cathode gas that has bypassed the humidifier to the fuel cell.

Description

Technical Field

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

Background Art

[0002] In recent years, research and development on fuel cells that contribute to energy efficiency have been conducted in order to enable more people to access affordable, reliable, sustainable, and advanced energy. Conventionally, for example, a fuel cell system that removes moisture inside a fuel cell by heating (warming up) the fuel cell by low-efficiency operation when the fuel cell stops operating is known (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in the technology related to fuel cells, it is an issue to appropriately control the amount of moisture inside the fuel cell at the time of startup. For example, when performing humidity control such as warm-up operation as in the above conventional technology at the time of starting the fuel cell, it is desired to suppress the occurrence of inappropriate states such as insufficient drying or excessive drying regardless of various startup states. For example, when the humidity control is being executed along with the startup of the fuel cell and the execution of the humidity control is stopped due to a temporary stop of the system or the like, the inside of the fuel cell may be in an insufficient drying state. Further, for example, when the humidity control at startup is interrupted and then the same humidity control as in normal startup is executed along with the restart of the fuel cell, the inside of the fuel cell may be in an excessive drying state.

[0005] This invention aims to solve the above-mentioned problems by achieving appropriate humidity control during fuel cell startup, thereby contributing to energy efficiency. [Means for solving the problem]

[0006] In order to solve the above problems and achieve the above objectives, the present invention employs the following embodiments. (1): A fuel cell system according to one aspect of the present invention (for example, a fuel cell system 10 in an embodiment) comprises a fuel cell (for example, a fuel cell stack 14 in an embodiment) that generates electricity using anode gas supplied to the anode and cathode gas supplied to the cathode, a cathode supply path (for example, a cathode supply path 11e in an embodiment) that supplies the cathode gas to the fuel cell via a humidifier, a cathode supply bypass circuit (for example, a cathode supply bypass circuit 11g in an embodiment) that supplies the cathode gas to the fuel cell by bypassing the humidifier, and the cathode supply bypass circuit The system includes a bypass supply valve provided above (for example, a bypass supply valve 12c in the embodiment), a temperature acquisition unit that acquires the ambient temperature of the fuel cell (for example, a first temperature sensor 20 and a second temperature sensor 25 in the embodiment), and a control device (for example, a control device 31 in the embodiment) that, when the ambient temperature is below a predetermined temperature at the start of the fuel cell, performs warm-up control to put the fuel cell into a power generation state and raise the temperature to above a predetermined temperature, and after the warm-up control is performed, opens the bypass supply valve and supplies the cathode gas bypassing the humidifier to the fuel cell.

[0007] (2) In the fuel cell system described in (1) above, the humidity control is performed for a predetermined duration, and the predetermined duration is set to a larger value as the temperature of the fuel cell stack decreases before the warm-up control is performed.

[0008] (3) In the fuel cell system described in (1) above, the humidity control is a control that causes the fuel cell to generate electricity while the cathode gas, which has bypassed the humidifier, is supplied to the fuel cell.

[0009] (4): In any of the fuel cell systems described in (1) to (3) above, the warm-up control is a control that causes the fuel cell to generate power while the stoichiometric value of the cathode gas is set to a value lower than a predetermined reference value for the stoichiometric value of the cathode gas during normal power generation. [Effects of the Invention]

[0010] According to (1) to (4) above, the amount of moisture inside the fuel cell can be appropriately controlled by appropriate humidity control. [Brief explanation of the drawing]

[0011] [Figure 1] A diagram illustrating the configuration of a fuel cell system according to an embodiment of the present invention. [Figure 2] A flowchart illustrating the operation of a fuel cell system according to an embodiment of the present invention. [Figure 3] This figure shows an example of the correspondence between the ON / OFF status of the start command in a fuel cell system according to an embodiment of the present invention, the ON / OFF status of the humidity control determination flag, and the count value of the humidity control determination release counter. [Modes for carrying out the invention]

[0012] Hereinafter, a fuel cell system according to an embodiment of the present invention will be described with reference to the attached drawings. Figure 1 is a diagram showing the configuration of a fuel cell system 10 according to an embodiment. The fuel cell system 10 according to this embodiment is mounted, for example, in a vehicle. As shown in Figure 1, the fuel cell system 10 of the embodiment includes, for example, an anode supply path 11a, an anode discharge path 11b, an anode circulation path 11c and a discharge confluence path 11d, a cathode supply path 11e, a cathode discharge path 11f and a cathode supply bypass path 11g, a first supply valve 12a, a second supply valve 12b and a bypass supply valve 12c, a first discharge valve 13a and a second discharge valve 13b, a fuel cell stack 14, a fuel supply unit 15, an ejector 16, a gas-liquid separator 17, an air pump 18, a humidifier 19, a first temperature sensor 20, a heat transfer medium supply path 21a and a heat transfer medium discharge path 21b, a heat transfer medium cooling path 21c and a heat transfer medium cooling bypass path 21d, a three-way valve 22, a heater 23, a cooler 24, a second temperature sensor 25, and a control device 31.

[0013] The fuel cell stack 14 is, for example, a polymer electrolyte fuel cell and a solid oxide fuel cell. The fuel cell stack 14 comprises an assembly of multiple fuel cell cells. Each fuel cell comprises an electrolyte electrode structure and a pair of separators that sandwich the electrolyte electrode structure. The electrolyte electrode structure comprises an electrolyte and a fuel electrode (anode) and an oxygen electrode (cathode) that sandwich the electrolyte. Each fuel cell generates electricity through a catalytic reaction between a fuel containing hydrogen supplied to the fuel electrode (anode) and an oxidizer such as air containing oxygen supplied to the oxygen electrode (cathode).

[0014] The fuel supply unit 15 includes, for example, a fuel tank for storing hydrogen-containing fuel. The fuel supply unit 15 is connected to the anode supply passage 11a leading to the anode of the fuel cell stack 14 via a first supply valve 12a. The fuel supply unit 15 supplies fuel gas (anode gas) to the anode supply passage 11a toward the anode of the fuel cell stack 14.

[0015] The ejector 16 is positioned, for example, between the first supply valve 12a and the fuel cell stack 14 in the anode supply passage 11a, and is connected to the anode circulation passage 11c, which will be described later. The ejector 16 mixes at least a portion of the unreacted fuel gas discharged from the fuel cell stack 14 with the fuel gas supplied from the fuel supply unit 15 and supplies it again to the anode of the fuel cell stack 14. The unreacted fuel gas is discharged from the fuel cell stack 14 to the anode discharge passage 11b, and then supplied to the ejector 16 from the anode circulation passage 11c via the gas-liquid separator 17, which will be described later.

[0016] The gas-liquid separator 17 includes, for example, a condenser. The gas-liquid separator 17 is connected to the anode discharge passage 11b leading to the anode of the fuel cell stack 14, and to the anode circulation passage 11c and the discharge confluence passage 11d. The gas-liquid separator 17 separates the fluid discharged from the anode of the fuel cell stack 14 to the anode discharge passage 11b into a gaseous component and a liquid component. The gas-liquid separator 17 discharges the gaseous component, which includes unreacted fuel gas, to the anode circulation passage 11c. The gas-liquid separator 17 discharges the liquid component to the discharge confluence passage 11d. The discharge confluence passage 11d is connected to the cathode discharge passage 11f, described later, via, for example, the first discharge valve 13a.

[0017] The air pump 18 is connected to the cathode supply passage 11e, which leads to the cathode of the fuel cell stack 14, via a second supply valve 12b. The air pump 18 supplies an oxidizing gas (cathode gas), such as oxygen-containing air, to the cathode of the fuel cell stack 14 via the cathode supply passage 11e.

[0018] The humidifier 19 includes, for example, a moisture-permeable membrane such as a hollow fiber membrane. The humidifier 19 is positioned, for example, between the second supply valve 12b in the cathode supply passage 11e and the fuel cell stack 14, and is connected to the cathode discharge passage 11f. The humidifier 19 humidifies the oxidizer gas, such as air supplied from the air pump 18, with the moist oxidizer off-gas discharged from the cathode of the fuel cell stack 14.

[0019] The cathode discharge passage 11f is connected to the discharge merging passage 11d through, for example, a second discharge valve 13b on the downstream side of the humidifier 19. The cathode supply passage 11e is connected to, for example, a cathode supply bypass passage 11g that bypasses the second supply valve 12b and the humidifier 19 between the air pump 18 and the fuel cell stack 14. The cathode supply bypass passage 11g branches, for example, from between the air pump 18 and the second supply valve 12b in the cathode supply passage 11e, and merges into the cathode supply passage 11e between the humidifier 19 and the fuel cell stack 14 through a bypass supply valve 12c.

[0020] The first temperature sensor 20 is disposed, for example, on the upstream side of the air pump 18 in the cathode supply passage 11e. The first temperature sensor 20 detects the temperature of air or the like taken in from the outside by the air pump 18, that is, the temperature related to the temperature outside the fuel cell system 10 (outside air temperature).

[0021] The heat medium supply passage 21a and the heat medium discharge passage 21b, and the heat medium cooling passage 21c and the heat medium cooling bypass passage 21d form a circulation passage of the heat medium together with a heat medium flow passage (not shown) provided in the fuel cell stack 14. The heat medium supply passage 21a and the heat medium discharge passage 21b are connected to the heat medium flow passage of the fuel cell stack 14. The heat medium discharge passage 21b is connected to the heat medium cooling passage 21c and the heat medium cooling bypass passage 21d through a three-way valve 22. The heat medium cooling passage 21c is connected to the heat medium supply passage 21a through a cooler 24 described later. The heat medium cooling bypass passage 21d bypasses the cooler 24 and is connected to the heat medium supply passage 21a.

[0022] The heater 23 is disposed, for example, between the fuel cell stack 14 and the three-way valve 22 in the heat medium discharge passage 21b. The heater 23 heats the heat medium discharged from the fuel cell stack 14. The cooler 24 includes, for example, a radiator or the like. The cooler 24 is disposed, for example, in the heat medium cooling passage 21c. The cooler 24 cools the heat medium that flows from the heat medium discharge passage 21b through the three-way valve 22 into the heat medium cooling passage 21c after being discharged from the heater 23.

[0023] The second temperature sensor 25 is positioned, for example, between the fuel cell stack 14 and the heater 23 in the heat transfer medium discharge passage 21b. The second temperature sensor 25 detects, for example, the temperature of the heat transfer medium discharged from the heat transfer medium passage of the fuel cell stack 14.

[0024] The control device 31 comprehensively controls the operation of the fuel cell system 10, for example. For example, the control device 31 is a software function unit that functions when a predetermined program is executed by a processor such as a CPU (Central Processing Unit). The software function unit is an ECU (Electronic Control Unit) equipped with a processor such as a CPU, a ROM (Read Only Memory) for storing programs, a RAM (Random Access Memory) for temporarily storing data, and electronic circuits such as a timer. At least a part of the control device 31 may be an integrated circuit such as an LSI (Large Scale Integration).

[0025] The operation of the fuel cell system 10 of this embodiment will be described below. Figure 2 is a flowchart showing the operation of the fuel cell system 10 of the embodiment. Figure 3 is a diagram showing an example of the correspondence between the ON / OFF status of the start command in the fuel cell system 10 of the embodiment, the ON / OFF status of the humidity control determination flag, and the count value of the humidity control determination release counter.

[0026] As shown in Figures 2 and 3 at time t1, first, when the control device 31 receives a start command, for example from the vehicle's ignition switch or power switch, it starts the fuel cell system 10 (step S01). The control device 31 starts supplying fuel gas from the fuel supply unit 15 to the anode of the fuel cell stack 14 by opening the first supply valve 12a, for example. The control device 31 also starts supplying oxidizer gas from the air pump 18 to the cathode of the fuel cell stack 14 via the humidifier 19 by opening the second supply valve 12b and closing the bypass supply valve 12c, for example.

[0027] Next, the control device 31 acquires the ambient temperature of the fuel cell stack 14 based on the temperature detection value output from at least one of the first temperature sensor 20 and the second temperature sensor 25 (step S02).

[0028] Next, the control device 31 determines whether the ambient temperature of the fuel cell stack 14 is below a predetermined temperature (step S03). The predetermined temperature is, for example, a threshold temperature used to determine whether or not to perform warm-up control to raise the temperature of the fuel cell stack 14 and humidity control to dry the fuel cell stack 14. If the result of this determination is "NO", the control device 31 proceeds to the end of the process. On the other hand, if the result of this determination is "YES", the control device 31 sets the humidity control determination flag to ON, as shown in time t2 in Figure 3, and proceeds to step S04 of the process.

[0029] Next, the control device 31 performs warm-up control to raise the temperature of the fuel cell stack 14 to a predetermined temperature or higher over an appropriate period of time (step S04). The control device 31 performs low-oxygen power generation, for example, by reducing the output of the air pump 18 while supplying fuel gas by the fuel supply unit 15 and continuing to generate power with the fuel cell stack 14. Low-oxygen power generation is power generation performed with the stoichiometric value of the oxygen in the oxidizer gas (= oxygen supply amount / theoretical oxygen consumption corresponding to the power generation current) set to a value lower than the standard value for normal power generation (for example, 1). Low-oxygen power generation promotes heat generation of the fuel cell stack 14 by lowering the power generation efficiency and cell voltage compared to normal power generation. Note that for warm-up control, it is sufficient if the fuel cell stack 14 can promote warm-up through self-heating associated with power generation, and low-oxygen power generation is not required.

[0030] Next, the control device 31 starts executing humidity control for a predetermined duration (step S05). The control device 31 starts supplying oxidant gas from the air pump 18 to the cathode of the fuel cell stack 14, bypassing the humidifier 19, for example, by closing the second supply valve 12b and opening the bypass supply valve 12c. The control device 31 generates electricity while drying the cell surface of the fuel cell stack 14 by supplying unhumidified oxidant gas to the cathode of the fuel cell stack 14. The control device 31 sets a predetermined duration prior to the start of humidity control. For example, as the ambient temperature of the fuel cell stack 14 decreases before the warm-up control is performed, the control device 31 tends to increase the predetermined duration. The control device 31 starts measuring the execution time of the humidity control control when the humidity control control is initiated. For example, as shown from time t3 onwards in Figure 3, the control device 31 accumulates the count value of the humidity control control release counter as the execution time of the humidity control control by accumulating the accumulation timer or the like.

[0031] Next, as shown in Figure 2, the control device 31 determines whether the execution time of the humidity control is less than a predetermined duration (step S06). If the result of this determination is "NO", the control device 31 proceeds to step S07. On the other hand, if the result of this determination is "YES", the control device 31 proceeds to step S08.

[0032] Next, the control device 31 terminates the execution of humidity control (step S07). The control device 31 is initialized by erasing the information on the execution time and predetermined duration of the humidity control that it has held at this point. Then, the control device 31 proceeds to the end of the process.

[0033] Furthermore, the control device 31 determines whether or not there is a command to stop the fuel cell system 10, for example, from the vehicle's ignition switch or power switch (step S08). If the result of this determination is "NO", the control device 31 returns to step S06. On the other hand, if the result of this determination is "YES", the control device 31 proceeds to step S09.

[0034] Next, as shown from time t4 onwards in Figures 2 and 3, the control device 31 interrupts the execution of humidity control when the fuel cell system 10 stops, and retains the execution time of the humidity control that has been executed up to this point (step S09). For example, as shown from time t4 onwards in Figure 3, the control device 31 stops accumulating the count value of the decision release counter and retains the count value Ca of the decision release counter at time t4.

[0035] Next, as shown in Figure 2, the control device 31 determines whether a predetermined waiting time has elapsed since the fuel cell system 10 stopped (step S10). If the result of this determination is "NO", the control device 31 proceeds to step S12. On the other hand, if the result of this determination is "YES", the control device 31 determines that the fuel cell system 10 has entered a soak state and proceeds to step S11. Next, the control device 31 initializes the information on the execution time and predetermined duration of the humidity control that it holds at this point (step S11). Then, the control device 31 proceeds to the end of the process. In other words, if there is a start instruction for the fuel cell system 10 after the information on the execution time and predetermined duration of the humidity control has been initialized, the measurement of the execution time and predetermined duration of the humidity control will start from the initial values ​​at startup.

[0036] Furthermore, the control device 31 determines whether or not there is an instruction to start the fuel cell system 10, for example, from the vehicle's ignition switch or power switch (step S12). If the result of this determination is "NO", the control device 31 returns to step S10. On the other hand, as shown at time t5 in Figure 3, if the result of this determination is "YES", the control device 31 proceeds to step S13.

[0037] Next, the control device 31 determines whether it is necessary to continue executing the humidity control (step S13). For example, in step S13, it is determined whether the execution time of the humidity control is less than a predetermined duration. If this execution time is equal to or greater than the predetermined duration, the control device 31 determines the result to be "NO" and proceeds to the end of the process. On the other hand, if the result of this determination is "YES", the control device 31 proceeds to step S14.

[0038] Next, the control device 31 resumes the execution of humidity control for a predetermined duration (step S14). In other words, if the control device 31 restarts the fuel cell system 10 within a predetermined waiting time after receiving a request to stop humidity control, without going through a predetermined normal power generation process, it resumes the execution of humidity control from the interrupted state. The control device 31 resumes measuring the execution time of humidity control in conjunction with the resumption of humidity control execution. For example, as shown from time t6 onwards in Figure 3, the control device 31 accumulates the count value of the humidity control determination release counter from the count value Ca held at this point. The control device 31 executes the humidity control after restart for a time obtained by subtracting the execution time held at the time of the humidity control interruption from the predetermined duration.

[0039] Next, as shown in Figure 2, the control device 31 determines whether the execution time of the humidity control is less than a predetermined duration (step S15). If the result of this determination is "NO", the control device 31 returns to step S07. On the other hand, if the result of this determination is "YES", the control device 31 returns to step S08. For example, as shown in Figure 3 from time t7 onwards, when the count value of the humidity control release counter reaches a predetermined threshold count value Cth corresponding to a predetermined duration, the control device 31 sets the humidity control determination flag to off and initializes the count value of the release counter to zero. After the humidity control is completed, for example, the control device 31 performs a predetermined normal power generation.

[0040] As described above, the fuel cell system 10 of the embodiment includes a control device 31 that resumes the execution of humidity control from a state where it was interrupted during restart, thereby enabling appropriate control of the amount of moisture inside the fuel cell stack 14 through appropriate humidity control during startup. When restarting the fuel cell system 10, the control device 31 performs humidity control for a time obtained by subtracting the execution time from a predetermined duration. This prevents the inside of the fuel cell stack 14 from becoming excessively dry by performing humidity control for a period exceeding the predetermined duration.

[0041] The control device 31 can perform humidity control over an appropriate period of time (predetermined duration) in response to the increase in humidity within the stack surface accompanying the warm-up control, by increasing the predetermined duration as the ambient temperature of the fuel cell stack 14 decreases before the warm-up control is performed.

[0042] When the fuel cell system 10 transitions to a soak state due to the elapsed time exceeding a predetermined waiting period from the stop instruction, the control device 31 can suppress unintended interference with other humidity control or drying control performed during soaking by erasing the memory of a predetermined duration and execution time.

[0043] The embodiments of the present invention are presented as examples and are not intended to limit the scope of the invention. These embodiments can be carried out in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of Symbols]

[0044] 10...Fuel cell system, 11a...Anode supply path, 11b...Anode discharge path, 11c...Anode circulation path, 11d...Discharge confluence path, 11e...Cathode supply path, 11f...Cathode discharge path, 11g...Cathode supply bypass path, 12a...First supply valve, 12b...Second supply valve, 12c...Bypass supply valve, 13a...First discharge valve, 13b...Second discharge valve, 14...Fuel cell stack (fuel cell), 15...Fuel supply unit, 16...Ejector, 17...Gas-liquid separator, 18...Air pump, 19...Humidifier, 20...First temperature sensor, 21a...Heat transfer medium supply path, 21b...Heat transfer medium discharge path, 21c...Heat transfer medium cooling path, 21d...Heat transfer medium cooling bypass path, 22...Three-way valve, 23...Heater, 24...Cooler, 25...Second temperature sensor, 31...Control device.

Claims

1. A fuel cell that generates electricity using anode gas supplied to the anode and cathode gas supplied to the cathode, A cathode supply path that supplies the cathode gas to the fuel cell via a humidifier, A cathode supply bypass circuit that bypasses the humidifier and supplies the cathode gas to the fuel cell, A bypass supply valve provided on the cathode supply bypass circuit, A temperature acquisition unit that acquires the ambient temperature of the fuel cell, If the ambient temperature is below a predetermined temperature when the fuel cell is started, warm-up control is performed to put the fuel cell into a power generation state and raise its temperature to above the predetermined temperature. A control device that, after performing the warm-up control, performs humidity control by opening the bypass supply valve and supplying the cathode gas, bypassing the humidifier, to the fuel cell. A fuel cell system equipped with the following features.

2. The humidity control described above is performed for a predetermined duration. The predetermined duration is set to a larger value as the temperature of the fuel cell stack decreases before the warm-up control is executed. The fuel cell system according to claim 1.

3. The humidity control described above is a control that causes the fuel cell to generate electricity while supplying the cathode gas, which has bypassed the humidifier, to the fuel cell. The fuel cell system according to claim 1.

4. The aforementioned warm-up control is a control that causes the fuel cell to generate electricity while the stoichiometric value of the cathode gas is set to a value lower than a predetermined reference value for the stoichiometric value of the cathode gas during normal power generation. A fuel cell system according to any one of claims 1 to 3.

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