Fuel cell system

Abstract

To provide a fuel cell system which can reduce the quantity of air to be supplied to a cell stack while maintaining the power generation performance of the cell stack.SOLUTION: A fuel cell system supplies hydrogen to an anode electrode and supplies air to a cathode electrode, thereby starting power generation of fuel cells. In a case where a temperature of a heat catalyst is lower than a threshold temperature (S43: NO) in a state where the fuel cells are generating power, the fuel cell system supplies a first supply quantity of air to the cathode electrode (S41). In a case where the temperature of the heat catalyst is equal to or higher than the threshold temperature (S43: YES) in the state where the fuel cells are generating power, the fuel cell system reduces air to be supplied to the cathode electrode to a second supply quantity, which is less than the first supply quantity, step by step (S45). In a case where the supply quantity of air to the cathode electrode becomes the second supply quantity, the fuel cell system continuously supplies the second supply quantity of air to the cathode electrode (S49).SELECTED DRAWING: Figure 12

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses a fuel cell system. The fuel cell system includes a cell stack, an air pump, a cell stack temperature sensor, and a CPU. The air pump supplies air to the cell stack. The cell stack temperature sensor detects the temperature of the cell stack. The CPU controls the output of the air pump based on the temperature of the cell stack detected by the cell stack temperature sensor. After starting the power generation of the cell stack, the CPU sets the output of the air pumped air to be larger than the output when the temperature of the cell stack is equal to or higher than a predetermined temperature for at least a part of the period until the temperature of the cell stack reaches the predetermined temperature. Thereby, the fuel cell system shortens the time required for the temperature rise of the fuel cell.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When returning the supply amount of the air supplied to the cell stack to the original state from the state where the supply amount is increased, if the supply amount is rapidly decreased, there is a problem that the voltage of the cell stack may rapidly drop and the power generation may suddenly stop.

[0005] An object of the present invention is to provide a fuel cell system capable of reducing the supply amount of air supplied to the cell stack while maintaining the power generation performance of the cell stack.

Means for Solving the Problems

[0006] The fuel cell system according to the present invention comprises a stack having at least one cell having an anode electrode, a cathode electrode, and a catalyst; a fuel supply unit that supplies fuel to the anode electrode; an air supply unit that supplies air to the cathode electrode; a measuring unit that measures the temperature of a heat transfer medium that adjusts the temperature of the cell; and a control unit that controls the fuel supply unit and the air supply unit, wherein the control unit performs a power generation process that causes the stack to generate electricity by controlling the fuel supply unit to supply the fuel to the anode electrode and controlling the air supply unit to supply the air to the cathode electrode; and when the stack is generating electricity through the power generation process, if the temperature measured by the measuring unit is below a predetermined threshold temperature, the control unit controls the air supply unit. The present invention provides a first supply process that supplies a first supply amount of air to the cathode electrode, and a second supply process that controls the air supply unit to adjust the air supplied to the cathode electrode when the stack is generating power due to the power generation process and the temperature measured by the measuring unit is equal to or greater than the threshold temperature, wherein the second supply process includes a step supply process that, when the amount of air supplied to the cathode electrode is the first supply amount, gradually reduces the amount of air supplied to the cathode electrode to a second supply amount which is also smaller than the first supply amount, and a continuous supply process that, when the amount of air supplied to the cathode electrode is the second supply amount, continues to supply the second supply amount of air to the cathode electrode.

[0007] In this invention, the fuel cell system gradually reduces the amount of air supplied to the cathode electrode down to a second supply amount. This prevents the fuel cell system from experiencing a sharp drop in stack voltage and a halt in power generation in response to a decrease in the amount of air supplied. [Brief explanation of the drawing]

[0008] [Figure 1] This is a diagram illustrating the overview of fuel cell system 1. [Figure 2] This is a block diagram showing the electrical configuration of the control device 6. [Figure 3] This graph shows the changes in stack voltage, stack current, and output power over time. [Figure 4] This graph shows the change in stack voltage over time when a threshold Th is set. [Figure 5] This graph shows the relationship between the stack current and the temperature of the heat transfer medium measured by the temperature measurement unit 52. [Figure 6] This graph shows the change in stack voltage over time when a threshold value Vh1 is set. [Figure 7] This graph shows the relationship between the stack current and the temperature of the heat transfer medium measured by the temperature measurement unit 52. [Figure 8] This graph shows the changes in stack voltage and output power over time when the air supply is rapidly reduced. [Figure 9] This graph shows the changes in stack voltage and output power over time when the air supply is gradually reduced. [Figure 10] This graph shows the change in stack voltage over time before and after the countermeasures were implemented. [Figure 11] This is a flowchart of the main process. [Figure 12] This is a flowchart of the power generation process. [Figure 13] This is a flowchart of the output control process. [Modes for carrying out the invention]

[0009] One embodiment of the fuel cell system 1 according to the present invention will be described with reference to the drawings. The drawings are used to illustrate the technical features that the present invention may adopt, and the configuration of the device etc. described is not intended to limit the invention to that, but is merely an illustrative example.

[0010] <Overview of Fuel Cell System 1> Referring to Figure 1, the fuel cell system 1 will be described in detail. The fuel cell system 1 includes a fuel cell 1A, a plurality of flow paths 20, a plurality of valves 20A, pumps 31, 32, 34, a filter 33, a hydrogen supply source 41, an air supply source 42, a heat exchanger 43, a power adjustment unit 44, a voltage measurement unit 51, a temperature measurement unit 52, and a control device 6. The plurality of flow paths 20 include a hydrogen supply path 21, a hydrogen discharge path 22, an air supply path 23, an air discharge path 24, and a heat transfer medium circulation path 25. The plurality of valves 20A include a hydrogen supply valve 21A, a hydrogen discharge valve 22A, an air supply valve 23A, and an air discharge valve 24A.

[0011] The fuel cell 1A has a stacked structure in which multiple cells 10 are stacked. Adjacent cells 10 are separated by separators (not shown). Multiple cells 10 are connected in series. Each cell 10 has an anode 11, a cathode 12, and an electrolyte (e.g., a solid polymer electrolyte membrane) 13.

[0012] The electrolyte 13 is sandwiched between the anode 11 and the cathode 12. The anode 11 includes an anode electrode 11A and an anode catalyst 11B. The cathode 12 includes a cathode electrode 12A and a cathode catalyst 12B. The anode electrode 11A and the cathode electrode 12A are electrodes. The anode catalyst 11B and the cathode catalyst 12B are made of, for example, Pt supported on acetylene black. Note that the materials of the anode catalyst 11B and the cathode catalyst 12B are not limited to the materials exemplified and other materials may be used. The separator is plate-shaped and placed between each cell 10, with a fuel channel on one side facing the anode electrode 11A of the cell 10 and an oxidizer channel on the other side facing the cathode electrode 12A of the cell 10. In this embodiment, hydrogen is used as the fuel and air is used as the oxidizer.

[0013] The hydrogen supply source 41 is an intake port for hydrogen and functions as a supply source for the hydrogen consumed in the fuel cell 1A. For example, the hydrogen supply source 41 is connected to a hydrogen tank (not shown), and the hydrogen stored in the hydrogen tank is taken in. The hydrogen supply source 41 may be connected to a water electrolysis device in addition to the hydrogen tank. The air supply source 42 is an intake port for air and functions as a supply source for the air consumed in the fuel cell 1A. For example, the air in the atmosphere is taken into the air supply source 42. Note that the air supply source 42 may be connected to an air tank or may be connected to a water electrolysis device.

[0014] The hydrogen supply path 21 and the hydrogen discharge path 22 are pipes through which hydrogen flows. The hydrogen supply path 21 supplies hydrogen from the hydrogen supply source 41 to the anode electrode 11A of each cell 10. The hydrogen discharge path 22 discharges hydrogen from the anode electrode 11A of each cell 10. The air supply path 23 and the air discharge path 24 are pipes through which air flows. The air supply path 23 supplies air from the air supply source 42 to the cathode electrode 12A of each cell 10. The air discharge path 24 discharges air from the cathode electrode 12A of each cell 10.

[0015] The pump 31 is interposed in the hydrogen supply path 21. The pump 31 causes a flow of hydrogen from the hydrogen supply source 41 toward the anode electrode 11A of each cell 10 to be formed in the hydrogen supply path 21. The pump 32 is interposed in the air supply path 23. The pump 32 causes a flow of air from the air supply source 42 toward the cathode electrode 12A of each cell 10 to be formed in the air supply path 23. The filter 33 is provided in the air supply path 23 between the air supply source 42 and the pump 32. The filter 33 removes impurities from the air flowing through the air supply path 23.

[0016] The hydrogen supply valve 21A is provided in the hydrogen supply passage 21. The hydrogen supply valve 21A is a regulating valve capable of opening and closing the hydrogen supply passage 21. The hydrogen discharge valve 22A is provided in the hydrogen discharge passage 22. The hydrogen discharge valve 22A is a regulating valve capable of opening and closing the hydrogen discharge passage 22. The air supply valve 23A is provided in the air supply passage 23. The air supply valve 23A is a regulating valve capable of opening and closing the air supply passage 23. The air discharge valve 24A is provided in the air discharge passage 24. The air discharge valve 24A is a regulating valve capable of opening and closing the air discharge passage 24.

[0017] The hydrogen supply valve 21A is capable of controlling the flow rate of hydrogen flowing through the hydrogen supply passage 21. The air supply valve 23A is capable of controlling the flow rate of air flowing through the air supply passage 23. The hydrogen supply valve 21A and the air supply valve 23A can each adjust the flow rate stepwise according to an electric signal output from the control device 6.

[0018] The hydrogen supply source 41, the pump 31, the hydrogen supply valve 21A, and the hydrogen supply passage 21 function as a fuel supply unit 1B that supplies hydrogen to the anode electrode 11A of the fuel cell 1A. The fuel supply unit 1B supplies hydrogen to the anode electrode 11A via the hydrogen supply passage 21 by driving the pump 31 and opening the hydrogen supply valve 21A. The fuel supply unit 1B can adjust the supply amount of hydrogen to the anode electrode 11A stepwise by a predetermined step amount r by controlling the flow rate of hydrogen flowing through the hydrogen supply passage 21 with the hydrogen supply valve 21A. Further, the fuel supply unit 1B stops the supply of hydrogen to the anode electrode 11A by stopping the drive of the pump 31 and closing the hydrogen supply valve 21A.

[0019] The air supply source 42, filter 33, pump 32, air supply valve 23A, and air supply passage 23 function as an air supply unit 1C that supplies air to the cathode electrode 12A of the fuel cell 1A. The air supply unit 1C supplies air to the cathode electrode 12A via the air supply passage 23 by driving the pump 32 and opening the air supply valve 23A. The air supply unit 1C can adjust the amount of air supplied to the cathode electrode 12A in predetermined step amounts q by controlling the flow rate of air flowing through the air supply passage 23 with the air supply valve 23A. The air supply unit 1C also stops supplying air to the cathode electrode 12A by stopping the driving of the pump 32 and closing the air supply valve 23A.

[0020] When fuel cell 1A generates electricity, a voltage is applied between the output terminals 18 of fuel cell 1A. The value of this voltage is equal to the sum of the voltages between the anode 11A and cathode 12A of each cell 10. Hereafter, this voltage will be referred to as the "stack voltage". The current output from the output terminals 18 of fuel cell 1A will be referred to as the "stack current".

[0021] The fuel cell system 1 has a connection terminal 19 to which an external load Ld can be connected. The output terminal 18 of the fuel cell 1A is connected to the connection terminal 19 via a power adjustment unit 44. The power adjustment unit 44 is a converter that boosts or lowers the stack voltage between the output terminals 18. The power adjustment unit 44 adjusts the power that can be supplied to the external load Ld connected to the connection terminal 19 by controlling the voltage and current output from the connection terminal 19. Hereinafter, this power will be referred to as "output power".

[0022] The voltage measurement unit 51 includes a voltage divider resistor and an AD converter. The voltage divider resistor is connected to the output terminal 18 and divides the stack voltage. The AD converter is connected to the voltage divider resistor and outputs an electrical signal indicating the voltage across the voltage divider resistor to the control device 6.

[0023] The heat transfer medium circulation path 25 is a pipe through which the heat transfer medium circulates. The heat transfer medium is a fluid used to heat the fuel cell 1A. The heat transfer medium circulation path 25 has an annular shape. A portion of the heat transfer medium circulation path 25 is located inside the fuel cell 1A. Hereinafter, the portion of the heat transfer medium circulation path 25 located inside the fuel cell 1A will be referred to as the "heating section 25A". The heat transfer medium passing through the heating section 25A heats the multiple cells 10 of the fuel cell 1A by supplying heat to them. The heat transfer medium is also cooled by supplying heat to the multiple cells 10 in the heating section 25A.

[0024] A pump 34 and a heat exchanger 43 are interposed in the heat transfer medium circulation path 25. The pump 34 sends the heat transfer medium discharged from the outlet 252 of the heating section 25A toward the heat exchanger 43. The heat exchanger 43 heats the heat transfer medium by supplying heat to the heat transfer medium sent by the pump 34. The heat transfer medium heated by the heat exchanger 43 is sent toward the inlet 251 of the heating section 25A.

[0025] The temperature measuring unit 52 is connected between the outlet 252 of the heating unit 25A and the pump 34 in the heat transfer medium circulation path 25. The temperature measuring unit 52 is a thermocouple. The temperature measuring unit 52 measures the temperature of the heat transfer medium discharged from the outlet 252 of the heating unit 25A and outputs an electrical signal indicating the measurement result to the control device 6.

[0026] The control device 6 is a control board included in the fuel cell system 1 and is responsible for the overall control of the fuel cell system 1.

[0027] <Power generation principle of fuel cell 1A> Hydrogen is supplied to the anode electrode 11A of anode 11 from a hydrogen supply source 41 via a hydrogen supply path 21. The hydrogen is decomposed into hydrogen ions and electrons by the anode catalyst 11B of anode 11. The hydrogen ions flow towards cathode 12 via electrolyte 13. The electrons flow towards cathode electrode 12A of cathode 12 via output terminal 18, connection terminal 19, and external load Ld. This supplies power to the external load Ld.

[0028] Air is supplied to the cathode electrode 12A of cathode 12 from the air supply source 42 via the air supply passage 23. In the cathode catalyst 12B of cathode 12, hydrogen ions flowing from the anode 11 via the electrolyte 13, electrons flowing via the output terminal 18, connection terminal 19, and external load Ld combine with oxygen molecules from the air to generate water.

[0029] <Electrical configuration of control device 6> Referring to Figure 2, the electrical configuration of the control device 6 will be described. The control device 6 includes a CPU 61, a memory device 62, an input unit 63, and an output unit 64. The CPU 61 is electrically connected to the memory device 62, the input unit 63, the output unit 64, a plurality of valves 20A, pumps 31, 32, and 34, a power adjustment unit 44, a voltage measurement unit 51, and a temperature measurement unit 52.

[0030] The CPU 61 controls the entire fuel cell system 1, including the control device 6. The memory device 62 stores programs for the CPU 61 to perform the main processing (see Figure 11), power generation processing (see Figure 12), and output control processing (see Figure 13), which will be described later.

[0031] The input unit 63 is a push button and accepts input operations for the fuel cell system 1. The output unit 64 is a display and outputs the status of the fuel cell system 1, etc.

[0032] The CPU 61 can control the pump 31 to cause hydrogen to flow from the hydrogen supply source 41 to the anode electrode 11A of each cell 10 via the hydrogen supply passage 21. The CPU 61 can control the pump 32 to cause air to flow from the air supply source 42 to the cathode electrode 12A of each cell 10 via the air supply passage 23. The CPU 61 can circulate the heat transfer medium via the heat transfer medium circulation passage 25 by controlling the pump 34. As a result, the heat transfer medium heated in the heat exchanger 43 is sent to the heating section 25A of the heat transfer medium circulation passage 25. The CPU 61 can open and close multiple flow paths 20 by controlling multiple valves 20A.

[0033] The CPU 61 can adjust the output power of the fuel cell system 1 by outputting an electrical signal to the power adjustment unit 44 for control.

[0034] The CPU 61 can acquire the stack voltage of the fuel cell 1A based on the electrical signal output from the voltage measurement unit 51. The CPU 61 can acquire the temperature of the heat transfer medium discharged from the outlet 252 of the heating unit 25A of the heat transfer medium circulation path 25 based on the signal output from the temperature measurement unit 52.

[0035] <Performance degradation due to flooding> Flooding refers to the phenomenon where water generated during the power generation process of fuel cell 1A adheres to the cathode electrode 12A. When flooding occurs, the water adhering to the cathode electrode 12A blocks the air passage, reducing the power generation performance of fuel cell 1A. Figure 3 is a graph showing the time-dependent changes in the stack voltage, stack current, and output power of fuel cell system 1 of fuel cell 1A. The stack voltage and stack current decrease sharply after time t11 from the start of power generation, indicating that flooding is occurring at this time.

[0036] In this embodiment, the fuel cell system 1 takes the following measures to suppress flooding: (1) heating of the fuel cell 1A, (2) controlling the output power, (3) adjusting the amount of air supplied at the start of power generation, and (4) adjusting the amount of air supplied after the temperature of the heat transfer medium has risen.

[0037] (1) Countermeasures by heating fuel cell 1A Flooding is more likely to occur when the temperature of the fuel cell 1A during power generation is low. This is because, at lower temperatures, water condenses and adheres more easily to the cathode electrode 12A. For this reason, when the temperature of the heat transfer medium measured by the temperature measurement unit 52 falls below a predetermined threshold Tk, the CPU 61 drives the pump 34 interposed in the heat transfer medium circulation path 25 to supply heat transfer medium to the heating unit 25A and heat the multiple cells 10.

[0038] Figure 4 is a graph showing the change in stack voltage over time when the threshold Tk is set to 13-15°C, 15-17°C, 17-19°C, and 21-23°C. When the threshold Tk was set to 13-15°C, the stack voltage dropped sharply after time t21 from the start of power generation. Similarly, when the threshold Tk was set to 15-17°C, the stack voltage dropped sharply after time t22 from the start of power generation. In both cases, flooding occurred at this timing. On the other hand, when the threshold Tk was set to 17-19°C and 21-23°C, no sharp drop in stack voltage due to flooding was observed. For this reason, in this embodiment, the threshold Tk was set to 17°C. The CPU 61 controlled the heating of the fuel cell 1A based on the set threshold Tk.

[0039] Figure 5 is a graph showing the relationship between the stack current and the temperature of the heat transfer medium measured by the temperature measurement unit 52, at thresholds Tk (17-19°C (ambient temperature 9°C / 14°C), 20-22°C, 21-23°C, 22-24°C, 24-26°C). Note that the temperature of the heat transfer medium increases as the elapsed time since the start of power generation of fuel cell 1A increases, so the horizontal axis of the graph (heat transfer medium temperature) can be considered synonymous with the elapsed time since the start of power generation of fuel cell 1A.

[0040] These results show that setting the threshold Tk to a larger value delays the timing at which the stack current begins to flow, and suppresses a rapid increase in the stack current (arrow Y11). This means that setting the threshold Tk to a larger value suppresses the large stack current that occurs when fuel cell 1A generates electricity at low temperatures. Therefore, it was found that setting the threshold Tk to a larger value allows fuel cell 1A to generate electricity in an environment where flooding is less likely to occur.

[0041] (2) Countermeasures by controlling output power One example of a method to suppress flooding is to control the power output from the fuel cell system 1. When the voltage of one of the multiple cells 10 of the fuel cell 1A falls below a predetermined threshold Vh1, the CPU 61 controls the power adjustment unit 44 to reduce the output power. On the other hand, when the voltage of each of the multiple cells 10 of the fuel cell 1A rises to or above a predetermined threshold Vh2, which is greater than the threshold Vh1, the CPU 61 controls the power adjustment unit 44 to increase the output power. In this way, the CPU 61 controls the voltage of each cell 10 so that it does not fall below the threshold Vh1, thereby suppressing flooding.

[0042] Figure 6 is a graph showing the change in stack voltage over time when the threshold Vh1 is set to 0.60V / cell, 0.63V / cell, 0.64V / cell, and 0.66V / cell. When the threshold Vh1 was set to 0.60V / cell, the stack voltage dropped sharply after time t41 from the start of power generation. When the threshold Vh1 was set to 0.63V / cell, the stack voltage dropped sharply after time t42 from the start of power generation. When the threshold Vh1 was set to 0.64V / cell, the stack voltage dropped sharply after time t43 from the start of power generation. Note that in Figure 6, the sharp drop in stack voltage is not shown due to the sampling period. In all of these cases, flooding occurs at this timing. On the other hand, when the threshold Vh1 was set to 0.66V / cell, no sharp drop in stack voltage based on the occurrence of flooding was observed. Therefore, in this embodiment, the threshold Vh1 was set to 0.66V / cell, and the threshold Vh2 was set to 0.68V / cell, which is greater than the threshold Vh1. The CPU 61 controlled the output power based on the set thresholds Vh1 and Vh2.

[0043] Furthermore, if the output power is increased to a large extent when the voltage of each cell 10 exceeds the threshold Vh2, flooding is likely to occur due to a rapid increase in stack current. Hereinafter, the extent to which the output power is increased will be referred to as the "increase Wu".

[0044] Figure 7 is a graph showing the relationship between the stack current and the temperature of the heat transfer medium measured by the temperature measurement unit 52, for each increase in output power Wu (1W / 2sec, 2W / 2sec, 5W / 2sec). As with Figure 5, the horizontal axis of the graph (heat transfer medium temperature) can be considered synonymous with the elapsed time since the start of power generation by fuel cell 1A.

[0045] From these results, it was found that setting the increase amount Wu to a smaller value delays the timing at which the stack current begins to flow, and suppresses a rapid increase in the stack current (arrow Y12). This means that setting the increase amount Wu to a smaller value suppresses the generation of a large stack current by the fuel cell 1A at low temperatures. Therefore, it was found that setting the increase amount Wu to a smaller value allows the fuel cell 1A to generate power in an environment where flooding is less likely to occur. In this embodiment, the increase amount Wu was set to 1W.

[0046] (3) Measures by adjusting the amount of air supplied at the start of power generation When the fuel cell 1A starts generating power, the fuel cell system 1 supplies a large amount of air to the cathode electrode 12A of each cell 10 via the air supply unit 1C, removing water from the cathode electrode 12A by blowing away any water adhering to it. More specifically, the CPU 61, from just before starting to generate power from the fuel cell 1A until the temperature of the heat transfer medium measured by the temperature measurement unit 52 reaches a predetermined threshold Th or higher, supplies twice the amount of air normally required for power generation. Hereinafter, the amount of air normally required for power generation will be referred to as the "second supply amount Q2," and twice the second supply amount will be referred to as the "first supply amount Q1." In this embodiment, the threshold Th is set to 37.5°C.

[0047] Figure 8 is a graph showing the changes in stack voltage and output power over time when the amount of air supplied is adjusted as described above. Furthermore, after time t61 has elapsed from the start of power generation, the power adjustment unit 44 switches to a state where power can be supplied from the connection terminal 19. After time t61 has elapsed and from the start of power generation until time t62 has elapsed, the stack voltage and output power are stabilized with the supply of the first supply amount Q1 of air, and flooding is suppressed.

[0048] (4) Measures by adjusting the amount of air supplied after the temperature of the heat transfer medium has risen. As shown in Figure 8, from the start of power generation until time t62 has elapsed, the temperature of the heat transfer medium measured by the temperature measurement unit 52 gradually rises from 32.9°C. Then, at the end of time t62, the temperature of the heat transfer medium measured by the temperature measurement unit 52 reaches a threshold Th. At this time, the CPU 61 controls the amount of air supplied to the cathode electrode 12A of each cell 10 by the air supply unit 1C to rapidly decrease from the first supply amount Q1 to the second supply amount Q2. In this case, the stack voltage temporarily drops to 9.55V due to the rapid decrease in the amount of air supplied (see Sample P1). A temporary drop in the stack voltage to 9.55V is undesirable because it makes the output power from the fuel cell system 1 unstable.

[0049] Therefore, the CPU 61 gradually reduces the amount of air supplied from the first supply amount Q1 to the second supply amount Q2. In Figure 9, at time t71 elapsed from the start of power generation, the temperature of the heat transfer medium measured by the temperature measurement unit 52 has reached the threshold Th. Also, the amount of air supplied to the cathode electrode 12A of each cell 10 gradually decreases from the first supply amount Q1 to the second supply amount Q2 between the start of power generation and time t72 elapsed.

[0050] In this case, the stack voltage temporarily drops to 10.2V as the air supply decreases (see Sample P2). This value is higher than that in the case of Figure 8 (Sample P1, 9.55V). Therefore, it was found that by gradually reducing the air supply, the output power of the fuel cell system 1 can be stabilized compared to the case of Figure 8.

[0051] Effects of (1) to (4) Figure 10 is a graph showing the change in stack voltage over time before and after implementing the above measures (1) to (4). Before the measures were implemented, the stack voltage dropped sharply after time t81 from the start of power generation, indicating that flooding occurred at this time. On the other hand, after the measures were implemented, no sharp drop in stack voltage was observed, and the stack voltage remained stable. Therefore, it was found that flooding can be suppressed by implementing measures (1) to (4).

[0052] <Main Processing> The main process will be explained with reference to Figures 11 to 13. When the power supply to the control device 6 is turned on, the CPU 61 starts the main process by reading and executing the program stored in the storage device 62. At the start of the main process, the supply of hydrogen to the anode 11A is stopped, and the supply of air to the cathode 12A is also stopped. In addition, the power adjustment unit 44 sets the output power of the fuel cell system 1 to 0W. An external load Ld is connected to the connection terminal 19 of the fuel cell system 1.

[0053] As shown in Figure 11, the CPU 61 determines whether it has detected an input operation to start power generation of the fuel cell 1A via the input unit 63 (S11). If the CPU 61 does not detect an input operation (S11: NO), it returns to S11 and continues to wait for an input operation. If the CPU 61 detects an input operation to start power generation of the fuel cell 1A via the input unit 63 (S11: YES), it proceeds to S13.

[0054] The CPU 61 controls the pump 31 and hydrogen supply valve 21A of the fuel supply unit 1B to start supplying hydrogen to the anode electrode 11A. The CPU 61 controls the hydrogen supply valve 21A so that the amount of hydrogen supplied is equal to the initial supply amount Ri. The initial supply amount Ri is the amount of hydrogen required to start generating power from the fuel cell 1A in accordance with the process of S15 described later, and is the amount required to fill the fuel cell 1A with hydrogen. Furthermore, the initial supply amount Ri is the amount of water that can be blown off and removed from the anode electrode 11A using hydrogen. Specifically, the initial supply amount Ri is 1 normal liter (1 NL / purge) per purge.

[0055] The CPU 61 controls the pump 32 and air supply valve 23A of the air supply unit 1C to start supplying air to the cathode electrode 12A (S13). The CPU 61 controls the air supply valve 23A so that the amount of air supplied is equal to the initial supply amount Qi. The initial supply amount Qi is the amount of air necessary to start generating power from the fuel cell 1A in accordance with the process described in S15, and is the amount necessary to fill the fuel cell 1A with air. Furthermore, the initial supply amount Qi is the amount that can be used to blow away and remove any water adhering to the cathode electrode 12A with air.

[0056] As a result, any water adhering to the cathode electrode 12A is blown away and removed from the cathode electrode 12A before the fuel cell system 1 begins supplying power to the external load Ld. The fuel cell 1A starts generating power when hydrogen is supplied to the anode electrode 11A by the fuel supply unit 1B and air is supplied to the cathode electrode 12A by the air supply unit 1C. A stack voltage is applied between the output terminals 18 of the fuel cell 1A.

[0057] The CPU 61 controls the power adjustment unit 44 to switch the output power of the fuel cell system 1 from 0W to the initial power Wi (S15). This initiates the supply of power to the external load Ld connected to the connection terminal 19 of the fuel cell system 1.

[0058] The CPU 61 starts the power generation process (see Figure 12) (S17), and then starts the output control process (S19). The power generation process and the output control process are executed in parallel with the main process.

[0059] The CPU 61 determines whether it has detected an input operation to terminate the power generation of the fuel cell 1A via the input unit 63 (S21). If the CPU 61 does not detect an input operation (S21: NO), it returns to processing S21. During this time, the power generation process and output control process continue.

[0060] Referring to Figure 12, the power generation process will be explained. When the fuel cell 1A is generating power, the CPU 61 controls the hydrogen supply valve 21A so that the amount of hydrogen supplied to the anode electrode 11A is equal to the power generation supply amount Rv (S41). The power generation supply amount Rv is the amount of hydrogen supplied that is normally required for power generation. The power generation supply amount Rv is greater than or equal to the initial supply amount Ri (Rv≧Ri). Also, the CPU 61 controls the air supply valve 23A so that the amount of air supplied to the cathode electrode 12A is equal to the first supply amount Q1 (S41). The first supply amount Q1 is approximately the same as the initial supply amount Qi.

[0061] The CPU 61 acquires the temperature of the heat transfer medium measured by the temperature measurement unit 52. The CPU 61 determines whether the acquired temperature of the heat transfer medium is equal to or greater than the threshold Th (S43). If the CPU 61 determines that the temperature of the heat transfer medium is less than the threshold Th (S43: NO), it returns to processing S41. The CPU 61 continues to control the hydrogen supply valve 21A so that the amount of hydrogen supplied to the anode electrode 11A is equal to the power generation supply amount Rv (S41). The CPU 61 also continues to control the air supply valve 23A so that the amount of air supplied to the cathode electrode 12A is equal to the first supply amount Q1 (S41).

[0062] As power generation from fuel cell 1A continues, the temperature of fuel cell 1A rises, and the temperature of the heat transfer medium also rises. If CPU 61 determines that the temperature of the heat transfer medium is above a threshold Th (S43: YES), it proceeds to S45. CPU 61 controls the air supply valve 23A and gradually reduces the amount of air supplied to the cathode electrode 12A from the first supply amount Q1 to the second supply amount Q2 by a step amount q every second (S45). The second supply amount Q2 is half the value of the first supply amount Q1. In other words, the amount of air supplied to the cathode electrode 12A gradually decreases and eventually becomes half of the first supply amount Q1.

[0063] After the amount of air supplied to the cathode electrode 12A decreases to the second supply amount Q2, the CPU 61 acquires the temperature of the heat transfer medium measured by the temperature measurement unit 52. The CPU 61 determines whether the acquired temperature of the heat transfer medium is above the threshold Th (S47). If the CPU 61 determines that the temperature of the heat transfer medium is above the threshold Th (S47: YES), it continues to control the hydrogen supply valve 21A so that the amount of hydrogen supplied to the anode electrode 11A becomes the power generation supply amount Rv (S49). The CPU 61 also continues to control the air supply valve 23A so that the amount of air supplied to the cathode electrode 12A becomes the second supply amount Q2 (S49).

[0064] If the CPU 61 determines that the temperature of the heat transfer medium is below the threshold Th after the amount of air supplied to the cathode electrode 12A has decreased to the second supply amount Q2 (S47: NO), it returns to processing S41. The CPU 61 continues to control the hydrogen supply valve 21A so that the amount of hydrogen supplied to the anode electrode 11A becomes the power generation supply amount Rv (S41). The CPU 61 also controls the air supply valve 23A so that the amount of air supplied to the cathode electrode 12A becomes the first supply amount Q1 (S41). As a result, the amount of air supplied to the cathode electrode 12A increases to twice the second supply amount Q2.

[0065] Referring to Figure 13, the output control process will be explained. The CPU 61 acquires the stack voltage measured by the voltage measurement unit 51. Based on the acquired stack voltage, the CPU 61 identifies the voltage of each of the multiple cells 10 (hereinafter referred to as "cell voltage"). The CPU 61 determines whether the identified cell voltage is less than the threshold Vh1 (S61). If the CPU 61 determines that the cell voltage is less than the threshold Vh1 (S61: YES), it controls the power adjustment unit 44 so that the output power becomes a value obtained by subtracting a predetermined power (hereinafter referred to as "reduction amount Wd") from the current output power (S63). In this embodiment, the reduction amount Wd is 10W. The CPU 61 proceeds to process S69.

[0066] If the CPU 61 determines that the identified cell voltage is greater than or equal to the threshold Vh1 (S61: NO), it determines whether the identified cell voltage is greater than or equal to the threshold Vh2 (S65). If the CPU 61 determines that the identified cell voltage is greater than or equal to the threshold Vh2 (S65: YES), it controls the power adjustment unit 44 so that the output power becomes the current output power plus an increase amount Wu (S67). In this embodiment, the increase amount Wu is set to 1W, so the increase amount Wu is 1 / 10 of the decrease amount Wd (10W). The CPU 61 proceeds to process S69.

[0067] If CPU61 determines that the identified cell voltage is less than the threshold Vh2 (S65:NO), it proceeds to S69 without changing the current output power.

[0068] CPU 61 determines (S69) whether 2 seconds have passed since the completion of processing S61 to S67. If CPU 61 determines that 2 seconds have not passed since the completion of processing S61 to S67 (S69: NO), it returns to processing S69. If CPU 61 determines that 2 seconds have passed since the completion of processing S61 to S67 (S69: YES), it returns to processing S61.

[0069] As shown in Figure 11, when the CPU 61 detects an input operation to terminate the power generation of the fuel cell 1A (S21: YES), it terminates the power generation process started by the process in S17 (S23) and terminates the output control process started by the process in S19 (S25).

[0070] The CPU 61 controls the power adjustment unit 44 to switch the output power of the fuel cell system 1 to 0W (S27). This stops the power supply to the external load Ld connected to the connection terminal 19 of the fuel cell system 1. The CPU 61 controls the pump 31 and hydrogen supply valve 21A of the fuel supply unit 1B to stop the supply of hydrogen to the anode electrode 11A (S29). The CPU 61 controls the pump 32 and air supply valve 23A of the air supply unit 1C to stop the supply of air to the cathode electrode 12A (S29). This stops the power generation of the fuel cell 1A. The CPU 61 terminates the main processing.

[0071] <Operation and effects of this embodiment> In the fuel cell system 1, after the start of power generation by the fuel cell 1A, if the temperature of the heat transfer medium that heats the fuel cell 1A is below the threshold Th (S43:NO), the amount of air supplied to the cathode electrode 12A is set to a first supply amount Q1 (S41). The first supply amount Q1 is twice the value of the second supply amount Q2. By supplying a large amount of air to the cathode electrode 12A, water adhering to the cathode electrode 12A is blown away and removed from the cathode electrode 12A. Therefore, in low-temperature environments where flooding is likely to occur, the fuel cell system 1 can suppress the occurrence of flooding by supplying a large amount of air.

[0072] On the other hand, when the fuel cell system 1 is supplying air to the cathode electrode 12A at a first supply amount Q1 and the temperature of the heat transfer medium exceeds a threshold Th (S43: YES), it gradually reduces the amount of air supplied to the cathode electrode 12A from the first supply amount Q1 to the second supply amount Q2 (S45). The second supply amount Q2 is half the value of the first supply amount Q1. In this way, the fuel cell system 1 can suppress the sharp drop in voltage of the fuel cell 1A and the resulting cessation of power generation in the process of changing the amount of air supply to the second supply amount Q2 required for normal power generation.

[0073] Immediately after the start of the power generation process (see Figure 12), the process in S41 supplies air at a first supply amount Q1 to the cathode electrode 12A. In other words, immediately after the start of power generation by the fuel cell 1A, regardless of the temperature of the heat transfer medium, air at a first supply amount Q1 is supplied to the cathode electrode 12A. As a result, the fuel cell system 1 can blow away any water adhering to the cathode electrode 12A with air at the start of power generation by the fuel cell 1A, thereby removing water from the cathode electrode 12A. Therefore, the fuel cell system 1 can suppress flooding, which occurs when water adheres to the cathode electrode 12A and reduces power generation efficiency, from the start of power generation by the fuel cell 1A.

[0074] The air supply valve 23A of the air supply unit 1C gradually reduces the amount of air supplied to the cathode electrode 12A by a step amount q every second down to a second supply amount Q2. By using the air supply valve 23A to change the amount of air supplied in steps of q, the fuel cell system 1 can control the amount of air supplied with precision using a simple configuration. Furthermore, by gradually reducing the amount of air supplied every second, the fuel cell system 1 can keep the time change of the amount of air supplied to the cathode electrode 12A constant. As a result, the fuel cell system 1 can appropriately suppress the sharp drop in the voltage of the fuel cell 1A and the resulting cessation of power generation in response to a decrease in the amount of air supplied.

[0075] When the stack voltage of the fuel cell system 1 is less than the threshold Vh1 (S61: YES), the fuel cell system 1 reduces the output power by a reduction amount Wd (S63). This prevents flooding from occurring when a large amount of power is supplied to the external load Ld while the stack voltage of the fuel cell 1A is low. Furthermore, when the stack voltage of the fuel cell system 1 is greater than the threshold Vh2, the fuel cell system 1 increases the output power by an increase amount Wu (S67). This allows the fuel cell system 1 to efficiently utilize the power generation capacity of the fuel cell 1A to supply power to the external load Ld.

[0076] Furthermore, the fuel cell system 1 can stabilize the output power when the stack voltage is above threshold Vh1 and below threshold Vh2 by determining whether or not to increase or decrease the output power based on two thresholds (thresholds Vh1 and Vh2). In addition, by making the increase amount Wu smaller than the decrease amount Wd, the fuel cell system 1 can suppress flooding caused by a rapid increase in output power. Moreover, by making the decrease amount Wd 10 times the increase amount Wu, the fuel cell system 1 rapidly decreases the output power when the stack voltage is below threshold Vh1. Therefore, the fuel cell system 1 can quickly resolve conditions in which flooding is likely to occur.

[0077] <Variation> The present invention is not limited to the above embodiments, and various modifications are possible. The fuel cell 1A may generate electricity when a substance other than hydrogen is supplied by the fuel supply unit 1B. For example, the fuel supply unit 1B may supply methanol to the fuel cell 1A to generate electricity. The temperature measuring unit 52 may measure the temperature of the heat transfer medium flowing through the heating unit 25A.

[0078] The fuel cell system 1 may also be provided with a circulation path connecting the hydrogen supply path 21 and the hydrogen discharge path 22. The circulation path may circulate hydrogen by directing a portion of the hydrogen discharged through the hydrogen discharge path 22 towards the hydrogen supply path 21. If the initial pressure of the hydrogen supplied from the hydrogen supply source 41 is sufficiently high, the pump 31 may not be provided.

[0079] The fuel cell system 1 may remove deposits (dust, dirt, etc.) attached to the cathode electrode 12A, excluding deposits that are chemically bonded to the cathode electrode 12A (organic gases, NOx, SOx, etc.), by supplying air from the air supply unit 1C.

[0080] The specific examples of threshold values ​​Tk, Th, Vh1, and Vh2 in the above embodiment are merely examples, and other values ​​may be set as appropriate.

[0081] When the fuel cell system 1 starts supplying air to the cathode electrode 12A and begins generating power from the fuel cell 1A (S13), the amount of air supplied may be controlled to be a first supply amount Q1.

[0082] If the temperature of the heat transfer medium is above a threshold Th immediately after power generation by the fuel cell 1A, the fuel cell system 1 may gradually reduce the amount of air supplied by the air supply unit 1C from the initial supply amount Qi to the second supply amount Q2. In other words, the fuel cell system 1 does not necessarily have to always supply the first supply amount Q1 of air from the air supply unit 1C immediately after power generation by the fuel cell 1A.

[0083] When performing the process in S45, the fuel cell system 1 may gradually reduce the amount of air supplied to the cathode electrode 12A by a predetermined percentage of the first supply amount Q1 up to the second supply amount Q2. For example, the percentage may be set to 0.4%. In this case, the result of calculating Q1 × 0.004 may be calculated as the percentage amount U. When performing the process in S45, the fuel cell system 1 may gradually reduce the amount of air supplied by the air supply unit 1C from the first supply amount Q1 by a percentage amount U. As a result, the fuel cell system 1 can gradually reduce the amount of air supplied to the cathode electrode 12A at a constant percentage, thereby appropriately suppressing the sharp drop in stack voltage and the resulting cessation of power generation in response to the decrease in the amount of air supplied.

[0084] When performing the process in S45, the fuel cell system 1 may vary the step amount q when gradually reducing the amount of air supplied to the cathode electrode 12A from a first supply amount Q1 to a second supply amount Q2. In other words, the fuel cell system 1 may gradually reduce the amount of air supplied by different step amounts. The period for gradually reducing the amount of air supplied by step amount q in the fuel cell system 1 may be other than 1 second. For example, this period may be 2 seconds. Furthermore, the fuel cell system 1 may linearly change the amount of air supplied to the cathode electrode 12A from a first supply amount Q1 to a second supply amount Q2. In other words, the change in the amount of air supplied to the cathode electrode 12A does not have to be stepwise.

[0085] The fuel cell system 1 may not supply hydrogen to the anode electrode 11A before the fuel cell 1A starts generating power through the process in S13, and may only supply air to the cathode electrode 12A. That is, the fuel cell system 1 may supply air to the cathode electrode 12A via the air supply unit 1C before the fuel cell 1A starts generating power, thereby removing water adhering to the cathode electrode 12A. In this way, the fuel cell system 1 can remove water adhering to the cathode electrode 12A before the fuel cell 1A starts generating power. Therefore, the fuel cell system 1 can suppress the decrease in power generation efficiency caused by flooding due to water adhering to the cathode electrode 12A before the fuel cell 1A starts generating power.

[0086] The relationship between the first supply quantity Q1 and the second supply quantity Q2 is not limited to the above embodiment. The first supply quantity Q1 may be appropriately changed as long as the condition that it is greater than the second supply quantity Q2 is met. For example, the first supply quantity Q1 may be 1.5 times, 3 times, or the like of the second supply quantity Q2.

[0087] In the output control process, the fuel cell system 1 may perform a process to increase the output power regardless of the relationship between the cell voltage and the threshold Vh2 if the cell voltage is greater than or equal to the threshold Vh1 (S61:NO). The values ​​of the decrease Wd and increase Wu of the output voltage are not limited to the above embodiment. Each value may be changed as appropriate within the range that satisfies the condition that the decrease Wd is greater than the increase Wu. For example, the decrease Wd may be greater than 10 times the increase Wu. Also, for example, the decrease Wd may be set to 10W and the increase Wu may be set to 5W. Furthermore, the decrease Wd may be less than the increase Wu. The fuel cell system 1 does not have to perform output control processing.

[0088] <Other> The CPU 61 that performs the processing in S17 is an example of the "power generation processing" of the present invention. The CPU 61 that performs the processing in S41 is an example of the "first supply processing" and "start-up supply processing" of the present invention. The CPU 61 that performs the processing in S45 and S49 is an example of the "second supply processing" of the present invention. The CPU 61 that performs the processing in S45 is an example of the "stage supply processing" of the present invention. The CPU 61 that performs the processing in S49 is an example of the "continuous supply processing" of the present invention. The CPU 61 that performs the processing in S13 is an example of the "pre-power generation supply processing" of the present invention. The CPU 61 that performs the processing in S63 is an example of the "power reduction processing" of the present invention. The CPU 61 that performs the processing in S67 is an example of the "power increase processing" of the present invention. Threshold Th is an example of the "threshold temperature" of the present invention. Threshold Vh1 is an example of the "first threshold voltage" of the present invention. Threshold Vh2 is an example of the "second threshold voltage" of the present invention. [Explanation of Symbols]

[0089] 1: Fuel cell system 1A: Fuel cell 1B:Fuel supply section 1C: Air supply unit 5: Temperature measurement unit 6: Control device 10: Cell 11A: Anode 12A: Cathode pole 52: Temperature measurement unit

Claims

1. A stack having at least one cell having an anode, a cathode, and a catalyst, A fuel supply unit that supplies fuel to the anode electrode, An air supply unit that supplies air to the cathode electrode, A measuring unit for measuring the temperature of the heat transfer medium that regulates the temperature of the cell, A control unit that controls the fuel supply unit and the air supply unit, Equipped with, The control unit, A power generation process is performed by controlling the fuel supply unit to supply the fuel to the anode electrode and controlling the air supply unit to supply the air to the cathode electrode, thereby generating power in the stack. When the stack is generating power through the power generation process, and the temperature measured by the measurement unit is below a predetermined threshold temperature, the air supply unit is controlled to supply a first amount of air to the cathode electrode in a first supply process. In the state in which the stack is generating power due to the power generation process, if the temperature measured by the measuring unit is equal to or greater than the threshold temperature, a second supply process is performed to control the air supply unit and adjust the air supplied to the cathode electrode, When the amount of air supplied to the cathode electrode is the first supply amount, a step-by-step supply process is performed to gradually reduce the amount of air supplied to the cathode electrode to a second supply amount that is smaller than the first supply amount. When the amount of air supplied to the cathode electrode is the second supply amount, a continuous supply process is performed to continuously supply the second supply amount of air to the cathode electrode. The second supply process, which includes the above, A fuel cell system characterized by performing the following actions.

2. The control unit, At the start of power generation by the stack due to the power generation process, regardless of the temperature measured by the measuring unit, a start supply process is performed to supply the first supply amount of air to the cathode electrode. The fuel cell system according to claim 1, further characterized by performing the following:

3. The aforementioned air supply unit is The amount of air supplied to the cathode electrode can be adjusted in predetermined step amounts. The aforementioned step-by-step supply process is The fuel cell system according to claim 1, characterized in that the air supplied to the cathode electrode is gradually reduced by the step amount down to the second supply amount.

4. The aforementioned step-by-step supply process is The fuel cell system according to claim 1, characterized in that the amount of air supplied to the cathode electrode is gradually reduced to the second supply amount per unit time.

5. The aforementioned step-by-step supply process is The fuel cell system according to claim 1, characterized in that the amount of air supplied to the cathode electrode is gradually reduced to a second supply amount by a predetermined percentage of the first supply amount.

6. The control unit, A pre-power generation supply process is performed to control the air supply unit and supply air to the cathode electrode before power generation of the stack by the power generation process described above begins. The fuel cell system according to claim 1, further characterized by performing the following:

7. The fuel cell system according to any one of claims 1 to 6, characterized in that the first supply amount is at least twice the value of the second supply amount.

8. The control unit, If the voltage of the stack is less than a predetermined first threshold voltage, a power reduction process is performed to reduce the power that can be output from the stack. If the voltage of the stack is greater than the first threshold voltage, a power increase process is performed to increase the power that can be output from the stack. The fuel cell system according to claim 1, further characterized by performing the following:

9. The aforementioned power increase process is, When the voltage of the stack is greater than or equal to a second threshold voltage which is greater than the first threshold voltage, the power that can be output from the stack is increased. The fuel cell system according to claim 8.

10. The fuel cell system according to claim 8, characterized in that the amount of power reduction due to the power reduction process is greater than the amount of power increase due to the power increase process.

11. The fuel cell system according to claim 10, characterized in that the amount of decrease is 10 times or more the amount of increase.

12. A separate component from the stack, further comprising a heat transfer medium circulation path through which the heat transfer medium circulates, The heat transfer medium circulation path has a heating section located within the stack, The fuel cell system according to claim 1, characterized in that the measuring unit measures the temperature of the heat transfer medium discharged from the outlet of the heating unit.

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