Fuel cell system

Abstract

To accurately determine the performance degradation of fuel cell cells. [Solution] The fuel cell system comprises a fuel cell stack having multiple fuel cell cells, a voltage detection unit that detects the voltage of each of the multiple fuel cell cells, and a control unit. During intermittent operation of the fuel cell stack, the control unit acquires the lowest cell voltage, which is the lowest voltage among the multiple fuel cell cells. The control unit determines a representative value of the lowest cell voltages collected over a predetermined period. The control unit determines whether the performance of the fuel cell has deteriorated by determining whether the representative value falls below a threshold voltage. The representative value is the median or average value.

Description

Technical Field

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

Background Art

[0002] The fuel cell system of Patent Document 1 includes a fuel cell stack, a temperature sensor, and a control unit. The fuel cell stack includes a plurality of fuel cells. The temperature sensor detects the temperature of the fuel cells. The control unit performs deterioration determination of the fuel cells using the temperature of the fuel cells and the generated power. The correlation between the temperature of the fuel cells and the generated power changes according to the cumulative power generation time of the fuel cells. Therefore, deterioration determination of the fuel cells can be performed using the temperature of the fuel cells and the generated power.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The generated power of the fuel cells also changes depending on the state of the load and measurement noise. Therefore, it may not be possible to accurately determine the performance degradation of the fuel cells.

Means for Solving the Problems

[0005] A fuel cell system that solves the above problems comprises a fuel cell stack having a plurality of fuel cell cells, a voltage detection unit that detects the voltage of each of the plurality of fuel cell cells, and a control unit. The control unit acquires the lowest cell voltage, which is the lowest voltage among the plurality of fuel cell cells, during intermittent operation of the fuel cell stack, determines a representative value of the lowest cell voltages collected over a predetermined period, and determines whether the representative value falls below a threshold voltage to determine if the performance of the fuel cell has deteriorated. The representative value is the median or average value.

[0006] The control unit determines a representative value of the lowest cell voltage collected over a predetermined period and determines whether the representative value falls below a threshold voltage. By making the determination based on the representative value of the lowest cell voltage, the system is less susceptible to the effects of load conditions and measurement noise from the voltage detection unit. Therefore, it is possible to accurately determine the performance degradation of the fuel cell.

[0007] The fuel cell system described above includes a server and a communication device configured to communicate with the server, and the control unit may include a server-side control unit provided by the server.

[0008] With respect to the fuel cell system described above, the control unit may acquire the minimum cell voltage after a predetermined time has elapsed since the start of intermittent operation of the fuel cell stack. With respect to the fuel cell system described above, the control unit may continuously acquire the minimum cell voltage from the time after the predetermined period has elapsed until the end of the intermittent operation.

[0009] The fuel cell system described above comprises a boost converter connected to the fuel cell stack and an energy storage device connected to the boost converter, wherein the boost converter comprises a switching element and a diode connected in parallel to the switching element, and is configured such that when the switching element is off, current flows from the fuel cell stack to the energy storage device via the diode, and the control unit may determine that the fuel cell stack is in intermittent operation if the current flowing from the fuel cell stack is less than a current threshold. [Effects of the Invention]

[0010] According to the present invention, it is possible to accurately determine the performance degradation of a fuel cell. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a schematic diagram of the fuel cell system. [Figure 2] Figure 2 is a circuit diagram of a boost converter. [Figure 3] Figure 3 is a flowchart showing the performance degradation detection control. [Figure 4] Figure 4 is a graph plotting the median of the lowest cell voltage at predetermined intervals. [Figure 5] Figure 5 plots the average value of the minimum cell voltage at predetermined intervals. [Modes for carrying out the invention]

[0012] An embodiment of a fuel cell system will be described. As shown in Figure 1, the vehicle 10 includes a load 11 and a key switch 12. The load 11 is a device driven by electric power. The load 11 is, for example, an electric motor driven by electric power. The vehicle 10 moves by the drive of this electric motor. The vehicle 10 is, for example, an industrial vehicle, agricultural machinery, or a passenger car. An industrial vehicle is, for example, a forklift or a towing tractor.

[0013] The key switch 12 is operated by the user of the vehicle 10. The user switches the key switch 12 on and off. The user turns the key switch 12 on when operating the vehicle 10. The user turns the key switch 12 off when ending the operation of the vehicle 10. In the following description, turning the key switch 12 on may be referred to as "key on," and turning the key switch 12 off may be referred to as "key off."

[0014] <Fuel cell system> The fuel cell system FS includes a fuel cell module 20 and a server 200. The fuel cell module 20 is mounted on the vehicle 10.

[0015] The fuel cell module 20 includes a fuel cell stack 21, a cathode system 40, an anode system 60, an electrical system 80, a control device 110, and a communication device 120. The fuel cell stack 21 includes a plurality of fuel cells 22. The fuel cells 22 are, for example, solid polymer membrane fuel cells. The fuel cells 22 generate electricity through a chemical reaction between an oxidant gas and a fuel gas. The fuel cells 22 include an anode electrode to which the fuel gas is supplied, a cathode electrode to which the oxidant gas is supplied, and an electrolyte membrane disposed between the anode electrode and the cathode electrode.

[0016] The fuel cell stack 21 includes a cathode flow path 30 and an anode flow path 33. An oxidant gas flows through the cathode flow path 30. A fuel gas flows through the anode flow path 33. The cathode flow path 30 includes an inlet 31 and an outlet 32. The oxidant gas flows into the cathode flow path 30 from the inlet 31 and flows out from the outlet 32. The anode flow path 33 includes an inlet 34 and an outlet 35. The fuel gas flows into the anode flow path 33 from the inlet 34 and flows out from the outlet 35. The oxidant gas is, for example, oxygen in the air. The fuel gas is, for example, hydrogen gas.

[0017] The cathode system 40 includes an inlet 41, an electric compressor 42, an inverter 44, an intercooler 45, a cathode supply path 46, a cathode discharge path 49, a first valve 51, and a second valve 52.

[0018] The inlet 41 sucks an oxidant gas into the fuel cell module 20. The inlet 41 may be open to the atmosphere. The inlet 41 may be connected to a gas cylinder. The electric compressor 42 includes an electric motor 43. The electric compressor 42 is driven by the electric motor 43. The electric compressor 42 supplies oxidant gas to the fuel cell stack 21. Specifically, the electric compressor 42 compresses the oxidant gas supplied from the suction port 41 and supplies it to the fuel cell stack 21. The oxidant gas supplied from the electric compressor 42 to the fuel cell stack 21 flows through the cathode flow path 30.

[0019] The inverter 44 is connected to the electric motor 43. The inverter 44 converts DC power into AC power and supplies it to the electric motor 43. Thereby, the electric motor 43 is driven.

[0020] The intercooler 45 is supplied with the oxidant gas discharged from the electric compressor 42. The intercooler 45 cools the oxidant gas supplied from the electric compressor 42. The oxidant gas supplied to the fuel cell stack 21 is the oxidant gas cooled by the intercooler 45.

[0021] The cathode supply path 46 connects the electric compressor 42 and the cathode flow path 30. Specifically, the cathode supply path 46 connects the electric compressor 42 and the inlet 31 of the cathode flow path 30. The cathode supply path 46 includes a first supply path 47 and a second supply path 48. The first supply path 47 connects the electric compressor 42 and the intercooler 45. The second supply path 48 connects the intercooler 45 and the cathode flow path 30.

[0022] The cathode discharge path 49 is a passage through which the oxidant exhaust gas flows. The oxidant exhaust gas is the oxidant gas discharged from the fuel cell stack 21 and contains generated water. The generated water is water generated by power generation in the fuel cell stack 21.

[0023] The first valve 51 is located in the cathode supply passage 46. In this embodiment, the first valve 51 is located in the second supply passage 48, i.e., between the intercooler 45 and the cathode flow path 30. The first valve 51 may also be located in the first supply passage 47, i.e., between the intercooler 45 and the electric compressor 42.

[0024] The second valve 52 is located in the cathode discharge passage 49. The second valve 52 is a valve whose opening degree can be adjusted. By adjusting the opening degree of the second valve 52, the pressure of the oxidizer exhaust gas can be adjusted.

[0025] The anode system 60 includes a tank 61, a pressure reducing valve 62, a fuel gas supply unit 63, a supply passage 64, a circulation passage 65, a gas-liquid separator 66, a circulation pump 67, and an exhaust drain valve 68.

[0026] Tank 61 stores fuel gas. Fuel gas is supplied to the pressure reducing valve 62 from the tank 61. The pressure reducing valve 62 reduces the pressure of the fuel gas supplied from the tank 61. The reduced pressure fuel gas is then supplied to the fuel gas supply unit 63.

[0027] The fuel gas supply unit 63 is a component for adjusting the amount of fuel gas supplied to the fuel cell stack 21. The amount of fuel gas supplied to the fuel cell stack 21 can be adjusted by controlling the fuel gas supply unit 63. For example, a solenoid valve such as an injector can be used as the fuel gas supply unit 63.

[0028] The supply channel 64 connects the fuel gas supply unit 63 and the anode flow path 33. More specifically, the supply channel 64 connects the fuel gas supply unit 63 and the inlet 34 of the anode flow path 33. The fuel gas injected from the fuel gas supply unit 63 is supplied to the fuel cell stack 21 through the supply channel 64.

[0029] The circulation path 65 connects the anode flow path 33 and the supply path 64. More specifically, the circulation path 65 connects the outlet 35 of the anode flow path 33 and the supply path 64. Fuel exhaust gas flows through the circulation path 65. The fuel exhaust gas contains unreacted fuel gas and generated water. The circulation path 65 is a passage for returning the unreacted fuel gas contained in the fuel exhaust gas back to the supply path 64.

[0030] The gas-liquid separator 66 is installed in the circulation path 65. The gas-liquid separator 66 separates the fuel exhaust gas into fuel gas and generated water. The generated water separated from the fuel exhaust gas is stored in the gas-liquid separator 66.

[0031] The circulation pump 67 is located in the circulation path 65. The circulation pump 67 supplies the fuel gas separated from the fuel exhaust gas by the gas-liquid separator 66 to the supply path 64. This circulates the fuel gas to the fuel cell stack 21.

[0032] The exhaust and drain valve 68 is connected to the gas-liquid separator 66. The exhaust and drain valve 68 can be switched between an open state and a closed state. When the exhaust and drain valve 68 is open, the generated water is discharged from the gas-liquid separator 66. Also, exhaust is carried out from the circulation path 65. When the exhaust and drain valve 68 is closed, the generated water can no longer be discharged from the gas-liquid separator 66. That is, when the exhaust and drain valve 68 is closed, the generated water is stored in the gas-liquid separator 66. The exhaust and drain valve 68 is switched from the closed state to the open state at predetermined valve opening intervals.

[0033] The electrical system 80 includes a boost converter 81, a voltage detection unit 85, a current detection unit 86, a power conversion device 95, a first energy storage device 96, a charge state detection unit 98, and a second energy storage device 99.

[0034] The boost converter 81 is connected to the fuel cell stack 21. The boost converter 81 boosts the output voltage of the fuel cell stack 21 and outputs it. For example, the boost converter 81 transforms the output voltage of the fuel cell stack 21 to 48[V] and outputs it. The output power from the boost converter 81 is supplied to the load 11.

[0035] As shown in Figure 2, the boost converter 81 comprises a positive terminal wiring Lp, a negative terminal wiring Ln, six switching elements Q1, Q2, Q3, Q4, Q5, Q6, six diodes D1, D2, D3, D4, D5, D6, three reactors 82, 83, 84, and a capacitor C.

[0036] The first switching element Q1 and the second switching element Q2 are connected in series with each other. The third switching element Q3 and the fourth switching element Q4 are connected in series with each other. The fifth switching element Q5 and the sixth switching element Q6 are connected in series with each other. The first switching element Q1, the third switching element Q3, and the fifth switching element Q5 are connected to the positive terminal wiring Lp. The second switching element Q2, the fourth switching element Q4, and the sixth switching element Q6 are connected to the negative terminal wiring Ln. The first switching element Q1, the third switching element Q3, and the fifth switching element Q5 constitute the upper arm. The second switching element Q2, the fourth switching element Q4, and the sixth switching element Q6 constitute the 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).

[0037] Diodes D1 to D6 are connected in parallel to each switching element Q1 to Q6. Diodes D1 to D6 may be parasitic diodes or elements of switching elements Q1 to Q6. The cathodes of diodes D1, D3, and D5, which are connected in parallel to the switching elements Q1, Q3, and Q5 that make up the upper arm, are connected to the positive terminal wiring Lp. The anodes of diodes D1, D3, and D5, which are connected in parallel to the switching elements Q1, Q3, and Q5 that make up the upper arm, are connected to the midpoint of two switching elements Q1 to Q6 that are connected in series with each other. The cathodes of diodes D2, D4, and D6, which are connected in parallel to the switching elements Q2, Q4, and Q6 that make up the lower arm, are connected to the midpoint of two switching elements Q1 to Q6 that are connected in series with each other. The anodes of diodes D2, D4, and D6, which are connected in parallel to the switching elements Q2, Q4, and Q6 that make up the lower arm, are connected to the negative terminal wiring Ln.

[0038] One reactor each, 82, 83, and 84, is connected to the midpoint between the switching elements Q1, Q3, and Q5 that make up the upper arm and the switching elements Q2, Q4, and Q6 that make up the lower arm. Reactors 82, 83, and 84 are connected to the fuel cell stack 21.

[0039] Capacitor C is connected to the positive terminal wire Lp and the negative terminal wire Ln. In the boost converter 81 described above, the voltage is boosted by the switching operation of switching elements Q1 to Q6. If the switching elements Q1 to Q6 are not switching, and the output voltage of the fuel cell stack 21 is higher than the voltage downstream of the boost converter 81, current flows from the fuel cell stack 21 through diodes D1, D3, and D5.

[0040] As shown in Figure 1, the voltage detection unit 85 detects the voltage of each of the multiple fuel cell cells 22. The voltage detection unit 85 is, for example, equipped with multiple ports, to which the positive and negative electrodes of the fuel cell cells 22 are connected. This allows the voltage detection unit 85 to measure the voltage of each fuel cell cell 22 individually.

[0041] The current detection unit 86 measures the output current [A] of the fuel cell stack 21. The power converter 95 is connected to the boost converter 81. The power converter 95 transforms the output voltage of the boost converter 81 and outputs it. For example, the power converter 95 transforms the output voltage of the boost converter 81 to 12[V] and outputs it.

[0042] The first energy storage device 96 is connected to the boost converter 81. The first energy storage device 96 is connected in parallel to the boost converter 81 with the 48V auxiliary equipment 97. When the output power from the boost converter 81 exceeds the power consumption of the load 11 and the 48V auxiliary equipment 97, the first energy storage device 96 is charged with the surplus power. When the output power from the boost converter 81 is less than the power consumption of the load 11 and the 48V auxiliary equipment 97, the first energy storage device 96 discharges. The first energy storage device 96 can be anything as long as it is rechargeable and dischargeable. The first energy storage device 96 is, for example, a secondary battery and a capacitor. The 48V auxiliary equipment 97 includes an electric compressor 42 and a circulation pump 67. The first energy storage device 96 is an example of an energy storage device connected to the boost converter 81.

[0043] The charge state detection unit 98 detects the charge state of the first energy storage device 96. The charge state detection unit 98 is, for example, a battery management system. The charge state detection unit 98 includes a sensor and a derivation unit that derives the state of the first energy storage device 96 from the sensor's detection result. The sensor is, for example, a current sensor and a voltage sensor. The derivation unit can derive the charge rate of the first energy storage device 96 from the sensor's detection result. Methods for deriving the charge rate include, for example, a method using the open-circuit voltage of the first energy storage device 96, a current integration method, or a combination thereof.

[0044] The second energy storage device 99 is connected to the power converter 95. The second energy storage device 99 is connected in parallel with the 12V auxiliary equipment 100 to the power converter 95. When the output power from the power converter 95 exceeds the power consumption of the 12V auxiliary equipment 100, the second energy storage device 99 is charged with the surplus power. When the output power from the power converter 95 is less than the power consumption of the 12V auxiliary equipment 100, the second energy storage device 99 discharges. The second energy storage device 99 can be anything as long as it is rechargeable and dischargeable. The second energy storage device 99 is, for example, a secondary battery and a capacitor. The 12V auxiliary equipment 100 includes a first valve 51 and a second valve 52.

[0045] The control device 110 comprises a processor 111 and a storage unit 112. The storage unit 112 includes RAM (Random Access Memory) and ROM (Read Only Memory). The storage unit 112 stores program code or instructions configured to cause the processor 111 to execute processing. The storage unit 112, i.e., the computer-readable medium, includes any available medium accessible by a general-purpose or dedicated computer. The control device 110 may be composed of hardware circuits such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array). The control device 110, which is a processing circuit, may include one or more processors that operate according to a computer program, one or more hardware circuits such as an ASIC or FPGA, or a combination thereof.

[0046] The communication device 120 is a network device equipped with a communication control unit, ports, etc., and capable of sending and receiving information through a communication network. The communication device 120 is configured to communicate with the server 200 by being connected to the server 200 via the communication network.

[0047] The server 200 comprises a server-side control device 201 and a server-side communication device 204. The hardware configuration of the server-side control device 201 is, for example, the same as that of the control device 110. The server-side control device 201 comprises, for example, a processor 202 and a storage unit 203.

[0048] The server-side communication device 204 is similar to, for example, the communication device 120. The server-side communication device 204 is connected to the fuel cell module 20 via a communication network. This allows the server 200 and the fuel cell module 20 to send and receive information from each other.

[0049] The server 200 may be managed by the user of the fuel cell module 20, or it may be managed by the manufacturer of the fuel cell module 20. <Control of the boost converter by the control unit> The control device 110 controls the boost converter 81. When the output voltage of the fuel cell stack 21 is lower than the voltage of the first energy storage device 96, the control device 110 boosts the output voltage of the fuel cell stack 21 using the boost converter 81. When the output voltage of the fuel cell stack 21 is higher than the voltage of the first energy storage device 96, the control device 110 does not perform the switching operation of the switching elements Q1 to Q6. In this case, current flows from the diodes D1, D3, and D5 connected in parallel to the switching elements Q1, Q3, and Q5 that constitute the upper arm. That is, even when the switching elements Q1 to Q6 are off, current flows from the fuel cell stack 21 via the diodes D1, D3, and D5. This current flows to the first energy storage device 96. The output voltage of the fuel cell stack 21 can be reduced by the diodes D1, D3, and D5.

[0050] <Control of power generation performed by the control device> The control device 110 controls the output power [kW] of the fuel cell stack 21. The output power of the fuel cell stack 21 varies depending on the amount of cathode gas supplied to the fuel cell stack 21 and the amount of anode gas supplied to the fuel cell stack 21. The output power of the fuel cell stack 21 is the power generated by the fuel cell stack 21. The control device 110 controls the amount of anode gas supplied to the fuel cell stack 21 by controlling the fuel gas supply unit 63. The control device 110 controls the amount of cathode gas supplied to the fuel cell stack 21 by controlling the electric compressor 42.

[0051] The control device 110 sets a target power for the fuel cell stack 21 according to the charge state of the first energy storage device 96, for example. The control device 110 controls the fuel cell stack 21 so that its output power follows the target power.

[0052] <Performance degradation detection control> The performance degradation determination control performed by the control device 110 and the server-side control device 201 will now be described. The performance degradation determination control is performed continuously, for example, while the vehicle 10 is ignitioned. In this embodiment, the control device 110 and the server-side control device 201 are control units.

[0053] As shown in Figure 3, in step S1, the control device 110 determines whether the fuel cell stack 21 is in intermittent operation. Intermittent operation is a state in which the output current of the fuel cell stack 21 is below a current threshold. The current threshold is set so that performance degradation can be determined from the voltage of the fuel cell 22. If the output current of the fuel cell stack 21 is large, it may not be possible to determine the performance degradation of the fuel cell 22 due to the voltage drop caused by the internal resistance of the fuel cell 22. For this reason, intermittent operation is defined as when the output current of the fuel cell stack 21 is below the current threshold, and performance degradation is determined when the fuel cell stack 21 is in intermittent operation.

[0054] Whether or not the fuel cell stack 21 is operating intermittently can also be determined from the target power of the fuel cell stack 21. For example, the control device 110 may determine that the fuel cell stack 21 is operating intermittently when the target power of the fuel cell stack 21 is 0 [kW]. When the target power of the fuel cell stack 21 is 0 [kW], anode gas and cathode gas are not supplied to the fuel cell stack 21, but the fuel cell stack 21 generates electricity using the anode gas and cathode gas remaining in the fuel cell stack 21. This generates a voltage in the fuel cell cell 22. When the target power of the fuel cell stack 21 is 0 [kW], the load 11 is driven by the power of the first energy storage device 96.

[0055] When using a boost converter 81 as in this embodiment, current may flow from the fuel cell stack 21 via diodes D1, D3, and D5 even when the target power of the fuel cell stack 21 is 0 [kW]. For this reason, when using a boost converter 81, it may be determined that the fuel cell stack 21 is operating intermittently when the target power of the fuel cell stack 21 is 0 [kW] and the current detected by the current detection unit 86 is less than the current threshold.

[0056] If the result of step S1 is positive, the control device 110 proceeds to step S2. If the result of step S1 is negative, the control device 110 proceeds to step S4. In step S2, the control device 110 determines whether a predetermined time has elapsed since the start of intermittent operation. The predetermined time can be set to any time. Until the predetermined time has elapsed since the start of intermittent operation, it may not be possible to detect the appropriate minimum cell voltage due to the voltage drop when current was flowing from the fuel cell stack 21. The predetermined time is set so as to suppress the effect of the voltage drop when current was flowing from the fuel cell stack 21. The predetermined time may be set appropriately in the range of, for example, 1 second to 3 seconds. If the determination in step S1 is affirmative, the control device 110 starts counting the elapsed time. When the elapsed time reaches the predetermined time, the control device 110 determines that a predetermined time has elapsed since the start of intermittent operation. If the determination result in step S1 is negative, the control device 110 resets the elapsed time count. As a result, the elapsed time from the start of intermittent operation is counted each time intermittent operation is started. The control device 110 repeatedly performs the determination in step S2 until the determination result in step S2 is affirmative. If the determination result of step S2 is positive, the control device 110 proceeds to step S3.

[0057] In step S3, the control device 110 acquires the minimum cell voltage. The minimum cell voltage is the lowest voltage among the voltages of the multiple fuel cell cells 22. The control device 110 acquires the voltage of each fuel cell cell 22 from the voltage detection unit 85. Then, the control device 110 sets the lowest voltage among the voltages acquired from the voltage detection unit 85 as the minimum cell voltage.

[0058] Next, in step S4, the control device 110 determines whether a predetermined period has elapsed. The predetermined period can be set to any period. For example, the predetermined period is one day. If the predetermined period is one day, the control device 110 only needs to determine whether the predetermined period has elapsed based on whether the current time is 0:00. If the determination result in step S4 is negative, the control device 110 returns to step S1. As a result, the control device 110 acquires the minimum cell voltage during the intermittent operation of the fuel cell stack 21 for the predetermined period. During the intermittent operation of the fuel cell stack 21, the determination in step S1 is maintained as positive, and the process in step S3 is repeated. Therefore, the control device 110 continuously acquires the minimum cell voltage from the predetermined time elapsed since the start of intermittent operation of the fuel cell stack 21 until the end of intermittent operation. If the determination result in step S4 is positive, the process proceeds to step S5.

[0059] In step S5, the server-side control device 201 obtains a representative value of the lowest cell voltage collected during a predetermined period. For example, if the determination result in step S4 is positive, the control device 110 transmits the lowest cell voltage collected during the predetermined period from the communication device 120 to the server-side control device 201. The server-side control device 201 obtains the lowest cell voltage collected during the predetermined period from the server-side communication device 204. The server-side control device 201 sorts the lowest cell voltages during the predetermined period in ascending order and determines the median value of the lowest cell voltages as a representative value. In this way, the server-side control device 201 obtains the median value of the lowest cell voltages.

[0060] Next, in step S6, the server-side control device 201 performs a performance degradation determination. The performance degradation determination determines whether the performance degradation of the fuel cell 22 is within an acceptable range. Performance degradation of the fuel cell 22 includes performance degradation due to deterioration of the fuel cell 22 and performance degradation due to power generation failure caused by foreign matter. When these performance degradations occur, the voltage of the fuel cell 22 decreases. The server-side control device 201 determines whether the median value of the minimum cell voltages obtained in step S5 falls below the threshold voltage. If the median value of the minimum cell voltages falls below the threshold voltage, the server-side control device 201 determines that the performance degradation of the fuel cell 22 is outside an acceptable range. The threshold voltage is set so that it can determine whether the performance degradation of the fuel cell 22 is within an acceptable range. The threshold voltage can be arbitrarily set, for example, in the range of 0.1[V] to 0.3[V].

[0061] If it is determined in step S6 that the performance degradation of the fuel cell 22 is outside the acceptable range, the user may be prompted to replace the fuel cell stack 21 or change the vehicle 10 during maintenance of the vehicle 10. If it is determined in step S6 that the performance degradation of the fuel cell 22 is outside the acceptable range, the user may be notified. The notification may be made by providing a notification unit in the vehicle 10, or by sending a text message to the user's computer.

[0062] [Operation of this embodiment] Figure 4 shows a plot of the median minimum cell voltage obtained over a predetermined period, plotted for each predetermined period. As can be seen from Figure 4, the median minimum cell voltage tends to decrease as the usage time of the fuel cell stack 21 increases. Therefore, it is possible to determine that the degradation of the fuel cell cell 22 has fallen outside the acceptable range by the performance degradation judgment.

[0063] Figure 5 shows a plot of the average minimum cell voltage obtained over a predetermined period, plotted for each predetermined period. As can be seen from Figure 5, the average minimum cell voltage tends to decrease as the usage time of the fuel cell stack 21 increases. Therefore, the performance degradation judgment can determine when the degradation of the fuel cell cell 22 has fallen outside the acceptable range.

[0064] As can be seen from Figures 4 and 5, the average value of the minimum cell voltage decreases smoothly in accordance with the usage time of the fuel cell stack 21. In contrast, the median value of the minimum cell voltage decreases smoothly until the usage time of the fuel cell stack 21 reaches a certain value, and then decreases more sharply after that value is reached. Thus, it is easier to understand the change in the minimum cell voltage when using the median value as a representative value of the minimum cell voltage than when using the average value.

[0065] [Effects of this embodiment] (1) The server-side control device 201 determines a representative value of the lowest cell voltage collected over a predetermined period and determines whether the representative value falls below the threshold voltage. By making the determination based on the representative value of the lowest cell voltage, the device is less susceptible to the effects of the load 11 condition and the measurement noise of the voltage detection unit 85. Therefore, the performance degradation of the fuel cell cell 22 can be determined with high accuracy.

[0066] (2) The representative value of the minimum cell voltage is the median value of the minimum cell voltage. Experiments conducted by the inventors showed that the median value of the minimum cell voltage makes it easier to grasp the change in the minimum cell voltage than the average value of the minimum cell voltage. Therefore, by using the median value of the minimum cell voltage as the representative value of the minimum cell voltage, it is possible to accurately determine the performance degradation of the fuel cell cell 22.

[0067] (3) Some of the processing for performance degradation determination control is performed by the server-side control device 201. Therefore, the processing load on the control device 110 can be reduced. Also, if the operation of the vehicle 10 is managed by the server-side control device 201, it is easier to coordinate with the operation management. For example, operation management may be performed in such a way that the load is lighter for vehicles 10 in which the performance degradation of the fuel cell cells 22 is significant.

[0068] (4) The control device 110 acquires the minimum cell voltage after a predetermined time has elapsed since the start of intermittent operation of the fuel cell stack 21. Until a predetermined time has elapsed since the start of intermittent operation, it may not be possible to detect an appropriate minimum cell voltage due to the voltage drop when current was flowing from the fuel cell stack 21. By acquiring the minimum cell voltage after a predetermined time has elapsed since the start of intermittent operation of the fuel cell stack 21, it is possible to accurately determine the performance degradation of the fuel cell 22.

[0069] (5) The control device 110 continuously acquires the minimum cell voltage from the time after a predetermined period of time has elapsed until the end of intermittent operation. This increases the number of times the minimum cell voltage is acquired, and makes it possible to set a representative value of the minimum cell voltage to an appropriate value.

[0070] (6) The control device 110 determines that the fuel cell stack 21 is operating intermittently if the current flowing through the boost converter 81 is less than the current threshold. When using a boost converter 81 as in the embodiment, even when the target power of the fuel cell stack 21 is set to 0 [kW], current flows from the fuel cell stack 21 via diodes D1, D3, and D5. Therefore, the current flowing from the fuel cell stack 21 may prevent proper detection of the minimum cell voltage. By determining that the fuel cell stack 21 is operating intermittently when the current flowing through the boost converter 81 is less than the current threshold, an appropriate minimum cell voltage can be obtained.

[0071] [Example of changes] The embodiment can be implemented with the following modifications. The embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0072] ○The boost converter 81 may be configured so that no current flows during the intermittent operation of the fuel cell stack 21. Alternatively, a buck converter may be used instead of a boost converter. ○The predetermined period may be the period from key-on to key-off. In this case, step S4 only needs to determine whether or not the key has been turned off. Also, if the period from key-on to key-off is short, the minimum cell voltage obtained during this period does not need to be used in calculating the representative value.

[0073] ○The control device 110 may acquire the minimum cell voltage only once after a predetermined time has elapsed since the start of intermittent operation. ○The control device 110 may acquire the minimum cell voltage before a predetermined time has elapsed after the start of intermittent operation of the fuel cell stack 21.

[0074] ○Performance degradation determination control may be performed solely by the control device 110. In this case, the fuel cell system FS does not need to be equipped with a server 200. The control device 110 may transmit the minimum cell voltage to the server 200 each time it acquires the minimum cell voltage.

[0075] [Note] The technical concepts that can be understood from the above embodiments and modified examples are described below. <Note 1> A fuel cell stack comprising multiple fuel cell cells, A voltage detection unit for detecting the voltage of each of the aforementioned multiple fuel cell cells, It comprises a control unit and, The control unit, during intermittent operation of the fuel cell stack, acquires the lowest cell voltage, which is the lowest voltage among the voltages of the plurality of fuel cell cells, A representative value of the minimum cell voltage collected over a predetermined period is determined. The performance degradation of the fuel cell is determined by determining whether the aforementioned representative value falls below the threshold voltage. The aforementioned representative value is the median or mean in a fuel cell system.

[0076] <Note 2> Server and The system includes a communication device configured to communicate with the aforementioned server, The fuel cell system according to Appendix 1, wherein the control unit includes a server-side control device provided by the server.

[0077] <Note 3> The fuel cell system according to Appendix 1 or 2, wherein the control unit acquires the minimum cell voltage after a predetermined time has elapsed since the start of intermittent operation of the fuel cell stack.

[0078] <Note 4> The fuel cell system as described in Appendix 3, wherein the control unit continuously acquires the minimum cell voltage from the time after the predetermined period has elapsed until the end of intermittent operation.

[0079] <Note 5> A boost converter connected to the fuel cell stack, The system comprises a power storage device connected to the aforementioned boost converter, The aforementioned boost converter is Switching element and The switching element comprises a diode connected in parallel with the switching element, When the switching element is turned off, the system is configured to allow current to flow from the fuel cell stack to the energy storage device via the diode. The fuel cell system according to any one of the appendices 1 to 4, wherein the control unit determines that the fuel cell stack is in intermittent operation when the current flowing from the fuel cell stack is less than a current threshold. [Explanation of Symbols]

[0080] D1, D3, D5... Diodes, Q1~Q6... Switching elements, 21... Fuel cell stack, 22... Fuel cell cell, 81... Boost converter, 85... Voltage detection unit, 110... Control device, 120... Communication device, 200... Server, 201... Server-side control device.

Claims

1. A fuel cell stack comprising multiple fuel cell cells, A voltage detection unit for detecting the voltage of each of the aforementioned multiple fuel cell cells, It comprises a control unit and, The control unit, during intermittent operation of the fuel cell stack, acquires the lowest cell voltage, which is the lowest voltage among the voltages of the plurality of fuel cell cells, A representative value of the minimum cell voltage collected over a predetermined period is determined. The performance degradation of the fuel cell is determined by determining whether the aforementioned representative value falls below the threshold voltage. The aforementioned representative value is the median or mean in a fuel cell system.

2. Server and The system includes a communication device configured to communicate with the aforementioned server, The fuel cell system according to claim 1, wherein the control unit includes a server-side control device provided by the server.

3. The fuel cell system according to claim 1, wherein the control unit acquires the minimum cell voltage after a predetermined time has elapsed since the start of intermittent operation of the fuel cell stack.

4. The fuel cell system according to claim 3, wherein the control unit continuously acquires the minimum cell voltage from the time after the predetermined time has elapsed until the end of intermittent operation.

5. A boost converter connected to the fuel cell stack, The system comprises a power storage device connected to the aforementioned boost converter, The aforementioned boost converter is Switching element and The switching element comprises a diode connected in parallel with the switching element, When the switching element is turned off, the system is configured to allow current to flow from the fuel cell stack to the energy storage device via the diode. The fuel cell system according to claim 1, wherein the control unit determines that the fuel cell stack is in intermittent operation when the current flowing from the fuel cell stack is less than a current threshold.

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