Fuel cell system and method for controlling fuel cell unit

Abstract

To provide a fuel cell system that effectively refreshes a fuel cell unit.SOLUTION: A fuel cell system includes a fuel cell unit having a fuel cell cell, and a control unit that controls the fuel cell unit, and the control unit executes a first refresh process that controls to vary the output of the fuel cell unit, and a second refresh process that stops the operation of the fuel cell unit and controls to start up the fuel cell unit.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a fuel cell system and a method for controlling a fuel cell unit. [Background technology]

[0002] Patent Document 1 discloses a fuel cell system that performs refresh control of a fuel cell stack by lowering the voltage of the fuel cell stack. Patent Document 2 discloses a fuel cell system that includes multiple fuel cell groups, a power storage unit for charging and storing the power generated by the fuel cell groups, and a control unit that performs a catalyst poisoning reduction process. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-071957 A [Patent Document 2] JP 2009-059610 A Summary of the Invention [Problem to be solved by the invention]

[0004] In a fuel cell device including a fuel cell stack, the power generation performance of the fuel cell may deteriorate due to long-term operation. When the power generation performance of the fuel cell device deteriorates, a refresh operation is performed.

[0005] The present disclosure provides a fuel cell system that effectively refreshes a fuel cell unit. [Means for solving the problem]

[0006] The present disclosure provides a fuel cell system comprising a fuel cell unit having a fuel cell cell, and a control unit that controls the fuel cell unit, wherein the control unit executes a first refresh process that controls to vary the output of the fuel cell unit, and a second refresh process that stops operation of the fuel cell unit and controls to start up the fuel cell unit. Effect of the Invention

[0007] According to the fuel cell system of the present disclosure, the fuel cell unit can be effectively refreshed. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing an outline of the configuration of a fuel cell system according to a first embodiment. [Diagram 2] FIG. 2 is a flow chart illustrating the process in the fuel cell system according to the first embodiment. [Diagram 3] FIG. 3 is a diagram illustrating the processing in the fuel cell system according to the first embodiment. [Figure 4] FIG. 4 is a flow chart illustrating the first refresh process in the fuel cell system according to the first embodiment. [Diagram 5] FIG. 5 is a diagram illustrating the first refresh process in the fuel cell system according to the first embodiment. [Figure 6] FIG. 6 is a flow diagram illustrating the second refresh process in the fuel cell system according to the first embodiment. [Figure 7] FIG. 7 is a diagram illustrating the second refresh process in the fuel cell system according to the first embodiment. [Figure 8] FIG. 8 is a flow chart illustrating a modified example of the first refresh process in the fuel cell system according to the first embodiment. [Figure 9] FIG. 9 is a diagram illustrating a modification of the first refresh process in the fuel cell system according to the first embodiment. [Figure 10] FIG. 10 is a flow chart illustrating a first modified example of the second refresh process in the fuel cell system according to the first embodiment. [Figure 11] FIG. 11 is a diagram illustrating a first modified example of the second refresh process in the fuel cell system according to the first embodiment. [Figure 12] FIG. 12 is a flow chart illustrating a second modification of the second refresh process in the fuel cell system according to the first embodiment. [Figure 13] FIG. 13 is a diagram illustrating a second modified example of the second refresh process in the fuel cell system according to the first embodiment. [Figure 14] FIG. 14 is a flow chart illustrating the process in the fuel cell system according to the second embodiment. [Figure 15] FIG. 15 is a diagram illustrating the process in the fuel cell system according to the second embodiment. [Figure 16] FIG. 16 is a flow chart illustrating the process in the fuel cell system according to the third embodiment. [Figure 17] FIG. 17 is a diagram illustrating the process in the fuel cell system according to the third embodiment. [Figure 18] FIG. 18 is a diagram showing an outline of the configuration of a fuel cell system according to a fourth embodiment. [Figure 19] FIG. 19 is a diagram illustrating the process in the fuel cell system according to the fourth embodiment. [Figure 20] FIG. 20 is a diagram illustrating the process in the fuel cell system according to the fourth embodiment. [Figure 21] FIG. 21 is a diagram illustrating the process in the fuel cell system according to the fifth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments will be described with reference to the accompanying drawings. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0010] In addition, in the description of the specification and drawings of each embodiment, components having substantially the same or corresponding functional configurations may be denoted by the same reference numerals to avoid redundant explanation. In addition, in order to facilitate understanding, the scale of each part in the drawings may differ from the actual scale.

[0011] First Embodiment A fuel cell system according to a first embodiment will be described. The fuel cell system according to the first embodiment includes a fuel cell unit having fuel cells, and a control unit that controls the fuel cell unit. The control unit in the fuel cell system according to the first embodiment executes a first refresh process that controls the output of the fuel cell unit to vary. The control unit in the fuel cell system according to the first embodiment also executes a second refresh process that stops the operation of the fuel cell unit and controls the fuel cell unit to start up.

[0012] FIG. 1 is a diagram showing an outline of the configuration of a fuel cell system 1, which is an example of a fuel cell system according to a first embodiment.

[0013] The fuel cell system 1 is a fuel cell that uses fuel cells. The fuel cell system 1 is a chemical cell that converts chemical energy into electricity by reacting hydrogen with oxygen in the air as fuel. The fuel cell system 1 supplies an output Pout to an external load EX.

[0014] The fuel cell system 1 includes a fuel cell unit 10, a control unit 20, and a power storage unit 30.

[0015] [Fuel cell unit 10] The fuel cell unit 10 generates electricity by causing a chemical reaction between hydrogen and oxygen. The fuel cell unit 10 includes a fuel cell 11, an output regulator 12, a gas regulator 13, and a controller 14.

[0016] The fuel cell 11 generates electricity by chemically reacting the supplied hydrogen SH with oxygen contained in the air SA. The fuel cell 11 is, for example, a polymer electrolyte fuel cell (PEFC). The fuel cell 11, which is a polymer electrolyte fuel cell, has a stack structure in which many single cells are stacked.

[0017] A single cell in the fuel cell 11, which is a polymer electrolyte fuel cell, includes a membrane electrode assembly (MEA) including a polymer electrolyte membrane and a pair of electrodes provided on both sides of the polymer electrolyte membrane. The polymer electrolyte membrane selectively transports hydrogen ions. Each electrode is formed of a porous material. Each of the pair of electrodes includes a catalyst layer mainly composed of carbon powder supporting a platinum-based metal catalyst (electrode catalyst), and a gas diffusion layer having both air permeability and electronic conductivity. Furthermore, the single cell includes a pair of separators that sandwich the membrane electrode assembly (MEA) from both sides.

[0018] The output adjustment unit 12 adjusts the output output from the fuel cell 11 to the outside of the fuel cell unit 10. The output adjustment unit 12 boosts the voltage of electricity p1 (output power p1) generated by the fuel cell 11. Then, the output adjustment unit 12 outputs a predetermined output P1 (output power P1). The output adjustment unit 12 includes, for example, a DC / DC converter.

[0019] The gas adjustment unit 13 adjusts the flow rates of hydrogen SH and air SA supplied from the outside. The gas adjustment unit 13 supplies hydrogen SHs and air SAs after flow rate adjustment to the fuel cell 11. The gas adjustment unit 13 includes a control valve for adjusting the flow rate or pressure of the hydrogen SH, and a control valve and a booster for adjusting the flow rate or pressure of the air SA.

[0020] The control section controls the fuel cell unit under control of the control unit 20. The control section controls the fuel cell 11, the output adjustment section 12, and the gas adjustment section in the fuel cell unit .

[0021] [Control unit 20] The control unit 20 controls the fuel cell unit 10. The control unit 20 is, for example, a computer or a programmable logic controller (PLC).

[0022] The control unit 20 controls the fuel cell unit 10 by sending commands to a control unit 14 included in the fuel cell unit 10. The control unit 20 also obtains operational data of the fuel cell unit 10 from the control unit 14.

[0023] The control unit 20 includes a timer 21 for measuring time. The control unit 20 determines whether a predetermined time has elapsed by using the timer 21. The control unit 20 may measure the time by an interrupt from the timer 21, or may determine whether the time has elapsed by sequentially referring to the count value of the timer 21.

[0024] [Energy storage unit 30] The power storage unit 30 supplies startup power when starting up the fuel cell unit 10. The power storage unit 30 may store electricity supplied from an external power source, or may supply the stored electricity to an external device as necessary. The power storage unit 30 charges when there is excess power from the fuel cell unit 10 to the external load EX. And the power storage unit 30 discharges when there is a shortage of power from the fuel cell unit 10 to the external load EX.

[0025] The power storage unit 30 includes, for example, a lithium ion capacitor, a lithium ion battery, or an electric double layer capacitor.

[0026] The output Pout from the fuel cell system 1 is based on the output P1 supplied from the fuel cell unit 10 and the output Ps input / output to / from the power storage unit 30.

[0027] By providing the fuel cell system 1 with the power storage unit 30, the output Pout from the fuel cell system 1 can be stably output.

[0028] <Processing in the fuel cell system according to the first embodiment> The processing in the fuel cell system according to the first embodiment will be described. Fig. 2 is a flow diagram illustrating the processing in the fuel cell system 1, which is an example of the fuel cell system according to the first embodiment. Fig. 3 is a diagram illustrating the processing in the fuel cell system 1, which is an example of the fuel cell system according to the first embodiment. Fig. 3 is a diagram illustrating the schematic results of the processing in the fuel cell system 1. The horizontal axis of Fig. 3 indicates time, and the vertical axis indicates output.

[0029] An overview of the processing in the fuel cell system 1 will be described with reference to Fig. 3. It is assumed that the fuel cell system 1 starts operating at time 0:00. The fuel cell system 1 performs a first refresh process Proc1 at every period Prd21. It also performs a second refresh process Proc2 at every period Prd22. Note that when the fuel cell system 1 performs the second refresh process Proc2, it does not perform the first refresh process Proc1.

[0030] In the example shown in Fig. 3, the cycle Prd21 in which the fuel cell system 1 performs the first refresh process Proc1 is set to 4 hours. Also, in the example shown in Fig. 3, the cycle Prd22 in which the fuel cell system 1 performs the second refresh process Proc2 is set to 24 hours.

[0031] The set time that defines the period Prd21 is a first set time, and the set time that defines the period Prd22 is a second set time.

[0032] (Step S10) When processing starts, the fuel cell system 1 sets the output setting of the fuel cell unit 10 to a predetermined output setting. Specifically, the control unit 20 commands the fuel cell unit 10 to output a predetermined output. The control unit 14 in the fuel cell unit 10, which has been commanded by the control unit 20 to output a predetermined output, controls the fuel cell 11, the output adjustment unit 12, and the gas adjustment unit 13 to output the predetermined output.

[0033] In Fig. 3, as an example, it is assumed that the output of the fuel cell unit 10 is controlled to be the output Pop. Note that in Fig. 3, the output is constant at the output Pop except for the time when the first refresh process Proc1 and the second refresh process Proc2 are performed, but the output may be changed as appropriate.

[0034] (Step S20) Next, the fuel cell system 1 starts a timer for measuring time. Specifically, the control unit 20 starts the timer 21. The control unit 20 uses the timer 21 to determine whether a predetermined time has elapsed.

[0035] (Step S30) The control unit 20 in the fuel cell system 1 determines whether the second set time has elapsed. If the second set time has not elapsed (NO in step S30), the control unit 20 proceeds to step S40. If the second set time has elapsed (YES in step S30), the control unit 20 proceeds to step S60. The second set time is set to 6 to 24 hours, preferably 10 hours.

[0036] Referring to the example of FIG. 3, the control unit 20 determines whether or not 24 hours, which is an example of the second set time, has elapsed.

[0037] (Step S40) In step S30, if the second set time has not elapsed (NO in step S30), the control unit 20 determines whether the first set time has elapsed. If the first set time has elapsed (YES in step S40), the control unit 20 proceeds to step S50. If the first set time has not elapsed (NO in step S40), the control unit 20 returns to step S30 and repeats the process. The first set time is 30 minutes to 6 hours, preferably 2 hours.

[0038] Referring to the example of FIG. 3, the control unit 20 determines whether or not four hours, which is an example of a first set time, has elapsed.

[0039] (Step S50) In step S40, if the first set time has elapsed (YES in step S40), the control unit 20 performs a first refresh process.

[0040] The first refresh process in the fuel cell system 1 will be described. Fig. 4 is a flow diagram illustrating the first refresh process in the fuel cell system 1, which is an example of the fuel cell system according to the first embodiment. Fig. 5 is a diagram illustrating the first refresh process in the fuel cell system 1, which is an example of the fuel cell system according to the first embodiment. Fig. 5 is a diagram illustrating generally the results of performing the process in the fuel cell system 1. The horizontal axis of Fig. 5 indicates time, and the vertical axis indicates output.

[0041] In the first refresh process, the fuel cell system 1 changes the output of the fuel cell unit 10 in the following order: high output, low output, high output. In other words, in the first refresh process, the fuel cell system 1 changes the load on the fuel cell unit 10 in the following order: high load, low load, high load. Meanwhile, in the first refresh process, the fuel cell system 1 continues to supply hydrogen and air to the fuel cell unit 10 without stopping.

[0042] (Step S51) The control unit 20 sets the output power setting of the fuel cell unit 10 to a high output power setting. The control unit 20 then maintains the output power setting of the fuel cell unit 10 at the high output power setting for a certain period of time.

[0043] Explaining using the example of FIG. 5, at time t1, the control unit 20 sets the output of the fuel cell unit 10 to an output Pu, which is a high output setting. For example, assuming that the maximum output of the fuel cell unit 10 is 100%, the high output setting is an output between 80% and 100%. The control unit 20 maintains the output setting of the fuel cell unit 10 at the high output setting for a time Prd1. The time Prd1 is, for example, between 10 seconds and 3 minutes, and preferably 1 minute.

[0044] In the fuel cell system 1, by temporarily performing high output operation (high load operation), the amount of moisture inside the fuel cell 11 is increased by water produced by power generation.

[0045] 5, the output of the fuel cell unit 10 changes from output Pop to output Pu from time t1 to time t2. For example, assuming that the maximum output of the fuel cell unit 10 is 100%, the output conversion speed is anywhere between 1% per second and 100% per second, and preferably 10% per second.

[0046] (Step S52) Next, the control unit 20 sets the output power setting of the fuel cell unit 10 to a low output power setting. Then, the control unit 20 maintains the output power setting of the fuel cell unit 10 at the low output power setting for a certain period of time.

[0047] Explaining using the example of Fig. 5, at time t3, the control unit 20 sets the output of the fuel cell unit 10 to an output Pd, which is a low output setting. For example, assuming that the maximum output of the fuel cell unit 10 is 100%, the low output setting is an output between 0% and 20%. The control unit 20 maintains the output setting of the fuel cell unit 10 at the low output setting for a time Prd2. The time Prd2 is, for example, between 10 seconds and 3 minutes, and preferably 1 minute.

[0048] In the fuel cell system 1, by performing a high-output operation (high-load operation) and then a low-output operation (low-load operation), the water generated by power generation is made uniform on the surface of the fuel cell 11.

[0049] 5, the output of the fuel cell unit 10 changes from output Pu to output Pd from time t3 to time t4. For example, assuming that the maximum output of the fuel cell unit 10 is 100%, the output conversion speed is anywhere between 1% per second and 100% per second, and preferably 10% per second.

[0050] (Step S53) Next, the control unit 20 sets the output power setting of the fuel cell unit 10 to the high output power setting. Then, the control unit 20 maintains the output power setting of the fuel cell unit 10 at the high output power setting for a certain period of time.

[0051] Explaining using the example of FIG. 5, at time t5, the control unit 20 sets the output of the fuel cell unit 10 to output Pu, which is a high output setting. For example, assuming that the maximum output of the fuel cell unit 10 is 100%, the high output setting is an output between 80% and 100%. The control unit 20 maintains the output setting of the fuel cell unit 10 at the high output setting for a time Prd3. The time Prd3 is, for example, between 10 seconds and 3 minutes, and preferably 1 minute.

[0052] In the fuel cell system 1, high power operation (high load operation), low power operation (low load operation), and high power operation (high load operation) are performed in sequence, thereby again increasing the amount of moisture in the fuel cell 11. By increasing the amount of moisture in the fuel cell 11, it is possible to moisten dry parts within the surface of the fuel cell 11 that have been dried by performing continuous operation. By moistening the dry parts within the surface of the fuel cell 11, it is possible to suppress deterioration of the battery characteristics of the fuel cell 11.

[0053] 5, the output of the fuel cell unit 10 changes from output Pd to output Pu from time t5 to time t6. For example, assuming that the maximum output of the fuel cell unit 10 is 100%, the output conversion speed is anywhere between 1% per second and 100% per second, and preferably 10% per second.

[0054] (Step S54) The control unit 20 then sets the power output setting in the fuel cell unit 10 to a predetermined power output setting.

[0055] To explain using the example of FIG. 5, at time t7, the control unit 20 sets the output of the fuel cell unit 10 to a predetermined setting, that is, output Pop.

[0056] 5, the output of the fuel cell unit 10 changes from output Pu to output Pop from time t7 to time t8. For example, assuming that the maximum output of the fuel cell unit 10 is 100%, the output conversion speed is anywhere between 1% per second and 100% per second, and preferably 10% per second.

[0057] When the process in step S54 ends, the fuel cell system 1 ends the first refresh process.

[0058] In the first refresh process in the fuel cell system 1, hydrogen and oxygen are continuously supplied to the fuel cell unit 10. By continuing the supply of hydrogen and oxygen to the fuel cell unit 10, deterioration of the fuel cell cells 11 due to a lack of oxygen can be suppressed.

[0059] (Step S60) In step S30, if the second set time has elapsed (YES in step S30), the control unit 20 performs a second refresh process.

[0060] The second refresh process in the fuel cell system 1 will now be described. Fig. 6 is a flow diagram illustrating the second refresh process in the fuel cell system 1, which is an example of the fuel cell system according to the first embodiment. Fig. 7 is a diagram illustrating the second refresh process in the fuel cell system 1, which is an example of the fuel cell system according to the first embodiment. Fig. 7 is a diagram illustrating in outline the results of processing in the fuel cell system 1. The horizontal axis of Fig. 7 indicates time, and the vertical axis indicates output.

[0061] In the second refresh process, the fuel cell system 1 causes the fuel cell unit 10 to output high power, then stops the fuel cell system 1 once and restarts it. Then, after restarting, the fuel cell system 1 causes the fuel cell unit 10 to output high power, and then performs normal operation. In other words, in the second refresh process, the fuel cell system 1 operates the fuel cell unit 10 under high load, stops it, restarts it, and then performs high load operation. In the second refresh process, the fuel cell system 1 stops the supply of hydrogen and air to the fuel cell unit 10 while the fuel cell unit 10 is stopped.

[0062] (Step S61) The control unit 20 sets the output power setting of the fuel cell unit 10 to a high output power setting. The control unit 20 then maintains the output power setting of the fuel cell unit 10 at the high output power setting for a certain period of time.

[0063] Explaining using the example of FIG. 7, at time t11, the control unit 20 sets the output of the fuel cell unit 10 to output Pu, which is a high output setting. For example, assuming that the maximum output of the fuel cell unit 10 is 100%, the high output setting is an output between 80% and 100%, for example 100%. The control unit 20 maintains the output setting of the fuel cell unit 10 at the high output setting for a time Prd11. The time Prd11 is, for example, any time between 10 seconds and 3 minutes, preferably 1 minute.

[0064] In the fuel cell system 1, by temporarily performing high output operation (high load operation), the amount of moisture inside the fuel cell 11 is increased by water produced by power generation.

[0065] 7, the output of the fuel cell unit 10 changes from output Pop to output Pu from time t11 to time t12. For example, assuming that the maximum output of the fuel cell unit 10 is 100%, the output conversion speed is anywhere from 1% per second to 100% per second, and preferably 10% per second.

[0066] (Step S62) Next, the control unit 20 controls the fuel cell unit 10 so that the operation is stopped continuously for a predetermined minimum time or longer.

[0067] 7, at time t13, the control unit 20 commands the fuel cell unit 10 to stop operation. The control unit 20 stops the operation of the fuel cell unit 10 for a period of time Prd12. The period of time Prd12 is, for example, any period between 10 seconds and 1 hour, and preferably 1 minute.

[0068] In the fuel cell system 1, stopping the operation of the fuel cell unit 10 reduces the cell voltage in the fuel cell 11. By reducing the cell voltage in the fuel cell 11, impurities such as decomposition products adhering to the catalyst of the fuel cell 11 can be released from the catalyst of the fuel cell 11.

[0069] 7, the output of the fuel cell unit 10 changes from output Pu to zero from time t13 to time t14. For example, assuming that the maximum output of the fuel cell unit 10 is 100%, the output conversion speed is anywhere from 1% per second to 100% per second, and preferably 10% per second.

[0070] (Step S63) Next, the control unit 20 controls the fuel cell unit 10 to restart.

[0071] Explaining this using the example of Figure 7, at time t15, the control unit 20 commands the fuel cell unit 10 to restart. Time Prd13 is the time required for the fuel cell unit 10 to start up.

[0072] (Step S64) Next, the control unit 20 sets the output power setting of the fuel cell unit 10 to the high output power setting. Then, the control unit 20 maintains the output power setting of the fuel cell unit 10 at the high output power setting for a certain period of time.

[0073] Explaining using the example of FIG. 7, at time t16, the control unit 20 sets the output of the fuel cell unit 10 to output Pu, which is a high output setting. For example, assuming that the maximum output of the fuel cell unit 10 is 100%, the high output setting is an output between 80% and 100%, for example 100%. The control unit 20 maintains the output setting of the fuel cell unit 10 at the high output setting for a time Prd14. The time Prd14 is, for example, any time between 10 seconds and 3 minutes, preferably 1 minute.

[0074] In the fuel cell system 1, impurities desorbed from the catalyst of the fuel cell 11 can be washed away by performing high-output operation (high-load operation) after restarting.

[0075] 7, the output of the fuel cell unit 10 changes from 0 to Pu from time t16 to time t17. For example, assuming that the maximum output of the fuel cell unit 10 is 100%, the output conversion speed is anywhere from 1% per second to 100% per second, and preferably 10% per second.

[0076] (Step S65) The control unit 20 then sets the power output setting in the fuel cell unit 10 to a predetermined power output setting.

[0077] To explain using the example of FIG. 7, at time t18, the control unit 20 sets the output of the fuel cell unit 10 to a predetermined setting, that is, output Pop.

[0078] 7, the output of the fuel cell unit 10 changes from output Pu to output Pop from time t18 to time t19. For example, assuming that the maximum output of the fuel cell unit 10 is 100%, the output conversion speed is anywhere from 1% per second to 100% per second, and preferably 10% per second.

[0079] When the process in step S65 ends, the fuel cell system 1 ends the second refresh process.

[0080] (Step S70) The control unit 20 initializes the timer 21 .

[0081] (Step S80) The control unit 20 judges whether to continue the process. If the control unit 20 decides to continue the process (YES in step S80), the control unit 20 returns to step S30 and repeats the process. If the control unit 20 decides not to continue the process (NO in step S80), the control unit 20 advances the process to step S90.

[0082] (Step S90) Next, the fuel cell system 1 stops the timer for measuring time. Specifically, the control unit 20 stops the timer 21. Then, the process ends.

[0083] According to the fuel cell system of the first embodiment, the first refresh process and the second refresh process are performed, thereby making it possible to effectively refresh the fuel cell unit.

[0084] <Modification> In the fuel cell system according to the first embodiment, the first refresh process and the second refresh process are not limited to the above examples. Using the fuel cell system 1, modified examples of the first refresh process and the second refresh process in the fuel cell system according to the first embodiment will be described.

[0085] [Modification of the first refresh process] A modified example of the first refresh process in the fuel cell system according to the first embodiment will be described. FIG. 8 is a flow diagram illustrating a modified example of the first refresh process in the fuel cell system 1, which is an example of the fuel cell system according to the first embodiment. FIG. 9 is a diagram illustrating a modified example of the first refresh process in the fuel cell system 1, which is an example of the fuel cell system according to the first embodiment. FIG. 9 is a diagram illustrating a schematic result of performing processing in the fuel cell system 1. The horizontal axis of FIG. 9 indicates time, and the vertical axis indicates output.

[0086] In the modified first refresh process, the fuel cell system 1 changes the output of the fuel cell unit 10 in the following order: low output, high output, low output. In other words, in the modified first refresh process, the fuel cell system 1 changes the load on the fuel cell unit 10 in the following order: low load, high load, low load. Meanwhile, even in the modified first refresh process, the fuel cell system 1 continues to supply hydrogen and air to the fuel cell unit 10 without stopping.

[0087] (Step S51a) The control unit 20 sets the output power setting of the fuel cell unit 10 to a low output power setting. The control unit 20 then maintains the output power setting of the fuel cell unit 10 at the low output power setting for a certain period of time.

[0088] Explaining using the example of Fig. 9, at time t1, the control unit 20 sets the output of the fuel cell unit 10 to an output Pd, which is a low output setting. For example, assuming that the maximum output of the fuel cell unit 10 is 100%, the low output setting is an output between 0% and 20%. The control unit 20 maintains the output setting of the fuel cell unit 10 at the low output setting for a time Prd1a. The time Prd1a is, for example, between 10 seconds and 3 minutes, and preferably 1 minute.

[0089] In the fuel cell system 1, by temporarily performing low output operation (low load operation), the water generated by power generation is made uniform on the surface of the fuel cell 11.

[0090] In addition, since the output conversion speed is the same in the modified example, the above explanation is to be referred to and the explanation will be omitted. The same applies to the following explanation.

[0091] (Step S52a) Next, the control unit 20 sets the output power setting of the fuel cell unit 10 to the high output power setting. Then, the control unit 20 maintains the output power setting of the fuel cell unit 10 at the high output power setting for a certain period of time.

[0092] Explaining using the example of FIG. 9, at time t3, the control unit 20 sets the output of the fuel cell unit 10 to output Pu, which is a high output setting. For example, assuming that the maximum output of the fuel cell unit 10 is 100%, the high output setting is an output between 80% and 100%. The control unit 20 maintains the output setting of the fuel cell unit 10 at the high output setting for a time Prd2a. The time Prd2a is, for example, between 10 seconds and 3 minutes, and preferably 1 minute.

[0093] In the fuel cell system 1, by temporarily performing high output operation (high load operation), the amount of moisture inside the fuel cell 11 is increased by water produced by power generation.

[0094] (Step S53a) Next, the control unit 20 sets the output power setting of the fuel cell unit 10 to a low output power setting. Then, the control unit 20 maintains the output power setting of the fuel cell unit 10 at the low output power setting for a certain period of time.

[0095] Explaining using the example of Fig. 9, at time t5, the control unit 20 sets the output of the fuel cell unit 10 to an output Pd, which is a low output setting. For example, the low output setting is an output between 0% and 20% of the maximum output of the fuel cell unit 10, which is taken as 100%. The control unit 20 maintains the output setting of the fuel cell unit 10 at the high output setting for a time Prd3a. The time Prd3a is, for example, between 10 seconds and 3 minutes, and preferably 1 minute.

[0096] In the fuel cell system 1, high-power operation (high-load operation) is followed by low-power operation (low-load operation), thereby making the water generated by power generation uniform on the surface of the fuel cell 11. By making the water generated by power generation uniform on the surface of the fuel cell 11, it is possible to moisten dry parts within the surface of the fuel cell 11 that have been dried by performing continuous operation. By moistening the dry parts within the surface of the fuel cell 11, it is possible to suppress deterioration of the battery characteristics of the fuel cell 11.

[0097] (Step S54) The control unit 20 then sets the power output setting in the fuel cell unit 10 to a predetermined power output setting.

[0098] To explain using the example of FIG. 9, at time t7, the control unit 20 sets the output of the fuel cell unit 10 to a predetermined setting, that is, output Pop.

[0099] When the process in step S54 ends, the fuel cell system 1 ends the modified first refresh process.

[0100] [First modified example of the second refresh process] A first modified example of the second refresh process in the fuel cell system according to the first embodiment will be described. FIG. 10 is a flow diagram illustrating a first modified example of the second refresh process in the fuel cell system 1, which is an example of the fuel cell system according to the first embodiment. FIG. 11 is a ... schematic result of performing processing in the fuel cell system 1. The horizontal axis of FIG. 11 indicates time, and the vertical axis indicates output.

[0101] In a first modified example of the second refresh process in the fuel cell system according to the first embodiment, the high output operation (high load operation) in step S61 is not performed, and the fuel cell unit is stopped in step S62.

[0102] 11, the control unit 20 sets the output setting of the fuel cell unit 10 to the output Pop until time t13. Then, at time t13, the control unit 20 commands the fuel cell unit 10 to stop operation. For operations after time t13, refer to the above description and a detailed description will be omitted here.

[0103] In a first modified example of the second refresh process in the fuel cell system according to the first embodiment, the operation of the fuel cell unit 10 is stopped, thereby decreasing the cell voltage in the fuel cell 11. As a result of the decrease in the cell voltage in the fuel cell 11, the fuel cell system according to the first embodiment can remove impurities such as decomposition products adhering to the catalyst of the fuel cell 11 from the catalyst of the fuel cell 11. Furthermore, the fuel cell system according to the first embodiment can wash away the impurities and the like that have been removed from the catalyst of the fuel cell 11 by performing high-output operation (high-load operation) after restarting the system according to the first modified example of the second refresh process.

[0104] [Second modified example of the second refresh process] A second modified example of the second refresh process in the fuel cell system according to the first embodiment will be described. FIG. 12 is a flow diagram illustrating a second modified example of the second refresh process in the fuel cell system 1, which is an example of the fuel cell system according to the first embodiment. FIG. 13 is a ... schematic result of performing processing in the fuel cell system 1. The horizontal axis of FIG. 13 indicates time, and the vertical axis indicates output.

[0105] In a second modification of the second refresh process in the fuel cell system according to the first embodiment, the high output operation (high load operation) in step S64 is not performed, and a predetermined output setting is performed in step S65.

[0106] Explaining the example of Figure 13, the operation before time t16 is similar to the example of Figure 7. And, in explaining the example of Figure 13, at time t16, the control unit 20 sets the output setting of the fuel cell unit 10 to the output Pop. After time t16, the fuel cell unit 10 is started up with the output setting set to the output Pop.

[0107] In a second modified example of the second refresh process in the fuel cell system according to the first embodiment, the operation of the fuel cell unit 10 is stopped, thereby decreasing the cell voltage in the fuel cell 11. As a result of the decrease in the cell voltage in the fuel cell 11, the fuel cell system according to the first embodiment can remove impurities such as decomposition products adhering to the catalyst of the fuel cell 11 from the catalyst of the fuel cell 11. Furthermore, in the second modified example of the second refresh process, the fuel cell system according to the first embodiment can wash away the impurities and the like that have been removed from the catalyst of the fuel cell 11 by operating the system after restarting.

[0108] Second Embodiment A fuel cell system according to a second embodiment will be described. The fuel cell system according to the second embodiment differs in processing from the fuel cell system according to the first embodiment. For the configuration of the fuel cell system according to the second embodiment, please refer to the description of the configuration of the fuel cell system according to the first embodiment, and the description will be omitted here.

[0109] <Processing in the fuel cell system according to the second embodiment> The processing in the fuel cell system according to the second embodiment will be described. FIG. 14 is a flow diagram illustrating the processing in the fuel cell system according to the second embodiment. FIG. 15 is a diagram illustrating the processing in the fuel cell system according to the second embodiment. FIG. 15 is a diagram illustrating the schematic results of the processing in the fuel cell system according to the second embodiment. The horizontal axis of FIG. 15 indicates time, and the vertical axis indicates cell voltage.

[0110] An overview of the process in the fuel cell system according to the second embodiment will be described with reference to FIG. 15. The process in the fuel cell system according to the second embodiment will be described below with reference to the fuel cell system 1. It is assumed that the fuel cell system 1 starts operating from time 0. The fuel cell system 1 first sets a reference voltage V1 based on the cell voltage between time t21 and time t22. The fuel cell system 1 then calculates a first reference (V1×α1) and a second reference (V1×β1) (where 0<β1<α1<1) from the reference voltage V1. The fuel cell system 1 then performs a second refresh process Proc2 when the cell voltage becomes lower than the first reference during the reference time T1 and further becomes lower than the second reference. The fuel cell system 1 also performs a first refresh process Proc1 when the cell voltage is higher than the first reference during the reference time T1 and becomes lower than the first reference. The time t21 is set to be 5 minutes to 1 hour, preferably 20 minutes, after the time 0. The time t22 is set to be between 5 minutes and 2 hours, preferably 1 hour, after the time t21.

[0111] (Step S110) When the process starts, the fuel cell system 1 sets a predetermined output setting in the fuel cell unit 10. For specific processing, refer to the description of step S10 and a description thereof will be omitted here.

[0112] (Step S120) Next, the fuel cell system 1 starts a timer for measuring time. For specific processing, refer to the description of step S20 and a description thereof will be omitted here.

[0113] (Step S130) The fuel cell system 1 sets a reference voltage V1 for the cell voltage of the fuel cell 11. The fuel cell system 1 sets the reference voltage V1 from the cell voltage after a predetermined time has elapsed since the start-up of the fuel cell unit 10. The predetermined time is set to 5 minutes to 1 hour, and preferably 20 minutes.

[0114] 15, the control unit 20 sets a reference voltage V1 from the cell voltage of the fuel cell 11 during a predetermined period from time t21 to time t22 after startup. The reference voltage V1 is, for example, the average of the cell voltage during the period from time t21 to time t22.

[0115] The control unit 20 calculates a first reference (V1×α1) and a second reference (V1×β1) from the reference voltage V1, where 0<β1<α1<1. α1 is, for example, 0.98, and β1 is, for example, 0.96.

[0116] (Step S140) Next, the control unit 20 determines whether the stack voltage (cell voltage of the fuel cell 11) is lower than the first reference. If the stack voltage is lower than the first reference (YES in step S140), the control unit 20 proceeds to step S150. If the stack voltage is higher than the first reference (NO in step S140), the control unit 20 returns to step S140 and repeats the process.

[0117] (Step S150) Next, the control unit 20 determines whether the set time has elapsed. If the set time has elapsed (YES in step S150), the control unit 20 proceeds to step S160. If the set time has not elapsed (NO in step S150), the control unit 20 proceeds to step S170.

[0118] (Step S160) In step S150, if the set time has elapsed (YES in step S150), the control unit 20 performs a first refresh process. For details of the first refresh process, refer to the description of the fuel cell system according to the first embodiment, and the description will be omitted here.

[0119] (Step S170) In step S150, if the set time has not elapsed (NO in step S150), the control unit 20 determines whether the stack voltage is lower than the second reference. If the stack voltage is lower than the second reference (YES in step S170), the control unit 20 proceeds to step S180. If the stack voltage is higher than the second reference (NO in step S170), the control unit 20 returns to step S140 and repeats the process.

[0120] (Step S180) In step S170, if the stack voltage is lower than the second reference (YES in step S170), the control unit 20 performs a second refresh process. For details of the second refresh process, refer to the description of the fuel cell system according to the first embodiment, and the description will be omitted here.

[0121] (Step S190) The control unit 20 initializes the timer 21 .

[0122] (Step S200) The control unit 20 determines whether to continue the process. If the process is to be continued (YES in step S200), the control unit 20 returns to step S140 and repeats the process. If the process is not to be continued (NO in step S200), the control unit 20 advances the process to step S210.

[0123] (Step S210) Next, the fuel cell system 1 stops the timer for measuring time. Specifically, the control unit 20 stops the timer 21. Then, the process ends.

[0124] 15, the cell voltage is higher than the first standard (V1×α1) until the reference time T1 has elapsed, so the fuel cell system 1 executes the first refresh process at times t23, t24, t25, and t26. On the other hand, after time t27, the cell voltage falls below the first standard (V1×α1) before the reference time T1 has elapsed, and then falls below the second standard (V1×β1), so the fuel cell system 1 executes the second refresh process.

[0125] According to the fuel cell system of the second embodiment, the first refresh process and the second refresh process are performed, thereby making it possible to effectively refresh the fuel cell unit.

[0126] Third Embodiment A fuel cell system according to a third embodiment will be described. The fuel cell system according to the third embodiment differs in processing from the fuel cell system according to the first embodiment. For the configuration of the fuel cell system according to the third embodiment, please refer to the description of the configuration of the fuel cell system according to the first embodiment, and the description will be omitted here.

[0127] <Processing in the fuel cell system according to the third embodiment> The processing in the fuel cell system according to the third embodiment will be described. FIG. 16 is a flow diagram illustrating the processing in the fuel cell system according to the third embodiment. FIG. 17 is a diagram illustrating the processing in the fuel cell system according to the third embodiment. FIG. 17 is a diagram illustrating the schematic results of the processing in the fuel cell system according to the third embodiment. The horizontal axis of FIG. 17 indicates time, and the vertical axis indicates cell voltage.

[0128] An overview of the processing in the fuel cell system according to the third embodiment will be described with reference to FIG. 17. The processing in the fuel cell system according to the third embodiment will be described below with reference to the fuel cell system 1. It is assumed that the fuel cell system 1 starts operating from time 0. The fuel cell system 1 first sets a reference voltage V2 based on the cell voltage between time t31 and time t32. The fuel cell system 1 then calculates a first reference (V2×α2) and a second reference (V2×β2) (where 0<β2<α2<1) from the reference voltage V2. The fuel cell system 1 then performs the first refresh process Proc1 a predetermined number of times N1. The fuel cell system 1 then performs the second refresh process Proc2 after performing the first refresh process Proc1 the predetermined number of times N1.

[0129] (Step S310) When the process starts, the fuel cell system 1 sets a predetermined output setting in the fuel cell unit 10. For specific processing, refer to the description of step S10 and a description thereof will be omitted here.

[0130] (Step S320) The fuel cell system 1 sets a reference voltage V2 for the cell voltage of the fuel cell 11. The fuel cell system 1 sets the reference voltage V2 from the cell voltage after a predetermined time has elapsed since the fuel cell unit 10 was started up.

[0131] For the process of setting the reference voltage, refer to the explanation of step S130 and a detailed explanation will be omitted. α2 is, for example, 0.98, and β2 is, for example, 0.96.

[0132] (Step S330) Next, the control unit 20 determines whether the stack voltage is lower than the first reference. If the stack voltage is lower than the first reference (YES in step S330), the control unit 20 proceeds to step S340. If the stack voltage is higher than the first reference (NO in step S330), the control unit 20 returns to step S330 and repeats the process.

[0133] (Step S340) In step S330, if the stack voltage is lower than the first reference (YES in step S330), the control unit 20 performs a first refresh process. For details of the first refresh process, refer to the description of the fuel cell system according to the first embodiment, and the description will be omitted here.

[0134] (Step S350) Next, the control unit 20 determines whether the first refresh process has been performed a predetermined number of times. If the first refresh process has been performed a predetermined number of times (YES in step S350), the control unit 20 proceeds to step S360. If the first refresh process has not been performed a predetermined number of times (NO in step S350), the control unit 20 returns to step S330 and repeats the process.

[0135] (Step S360) Next, in step S350, if the first refresh process has been performed a predetermined number of times (YES in step S350), the control unit 20 determines whether the stack voltage is lower than the second reference. If the stack voltage is lower than the second reference (YES in step S360), the control unit 20 proceeds to step S370. If the stack voltage is higher than the second reference (NO in step S360), the control unit 20 returns to step S360 and repeats the process.

[0136] (Step S370) In step S360, if the stack voltage is lower than the second reference (YES in step S360), the control unit 20 performs a second refresh process. For details of the second refresh process, refer to the description of the fuel cell system according to the first embodiment, and the description will be omitted here.

[0137] (Step S380) The control unit 20 determines whether to continue the process. If the process is to be continued (YES in step S380), the control unit 20 returns to step S330 and repeats the process. Note that, when returning to step S330, the number of times the first refresh process has been performed is initialized to 0. If the process is not to be continued (NO in step S380), the control unit 20 ends the process.

[0138] 17, the fuel cell system 1 executes a first refresh process at times t33, t34, t35, and t36. Then, after executing the first refresh process a predetermined number of times N1 (here, N1=4), at time t37, the fuel cell system 1 executes a second refresh process.

[0139] According to the fuel cell system of the third embodiment, the first refresh process and the second refresh process are performed, thereby making it possible to effectively refresh the fuel cell unit.

[0140] Fourth Embodiment The following describes a fuel cell system according to embodiment 4. The fuel cell system according to embodiment 4 includes a plurality of fuel cell units.

[0141] FIG. 18 is a diagram showing an outline of the configuration of a fuel cell system 2, which is an example of a fuel cell system according to a fourth embodiment.

[0142] The fuel cell system 2 includes a plurality of fuel cell units, a control unit 120, and a power storage unit 30. In an example of the fuel cell system 2, the fuel cell system 2 includes four fuel cell units: a fuel cell unit 10a, a fuel cell unit 10b, a fuel cell unit 10c, and a fuel cell unit 10d. The number of fuel cell units is not limited to the above example, and may be two or more.

[0143] In the fuel cell system 2, the output P1a of the fuel cell unit 10a, the output P1b of the fuel cell unit 10b, the output P1c of the fuel cell unit 10c, and the output P1d of the fuel cell unit 10d are combined into an output P1f. Then, the output P1f and the output Ps of the power storage unit 30 are used to supply the output Pout of the fuel cell system 2 to the external load EX.

[0144] Each of the fuel cell unit 10a, the fuel cell unit 10b, the fuel cell unit 10c, and the fuel cell unit 10d has the same configuration as the fuel cell unit 10 in the fuel cell system 1, which is an example of a fuel cell system according to the first embodiment. For each of the fuel cell unit 10a, the fuel cell unit 10b, the fuel cell unit 10c, and the fuel cell unit 10d, the description of the fuel cell unit 10 is to be referred to and will not be repeated here.

[0145] [Control unit 120] The control unit 120 controls each of the fuel cell units 10a, 10b, 10c, and 10d. The control unit 120 includes the functions of the control unit 20.

[0146] <Processing in the fuel cell system according to the fourth embodiment> The following describes the processing in the fuel cell system according to the fourth embodiment. Figures 19 and 20 are diagrams for explaining the processing in a fuel cell system 2, which is an example of a fuel cell system according to the fourth embodiment.

[0147] 19, the horizontal axis represents time, and the vertical axis represents the output of each of fuel cell unit 10a, fuel cell unit 10b, fuel cell unit 10c, and fuel cell unit 10d. In FIG.

[0148] During the refresh period Prsh1, the control unit 120 performs the refresh process on the fuel cell unit 10a, the fuel cell unit 10b, the fuel cell unit 10c, and the fuel cell unit 10d in that order. The refresh operation is either the first refresh process or the second refresh process described in the fuel cell system according to the first embodiment. In Fig. 19, the refresh process is indicated by an arrowed line Proc.

[0149] When a fuel cell unit undergoes a refresh process, the output temporarily fluctuates significantly, whereas a fuel cell system is required to maintain a constant output.

[0150] Therefore, as shown in Figure 19, the fuel cell system 2 performs the refresh process by switching between fuel cell unit 10a, fuel cell unit 10b, fuel cell unit 10c, and fuel cell unit 10d in that order, thereby maintaining the output Pa state as shown in Figure 20. The control unit 120 distributes the power generated by the fuel cell unit undergoing the refresh process to other fuel cell units not undergoing the refresh process, thereby allowing the fuel cell system 2 to maintain a constant output.

[0151] According to the fuel cell system of the fourth embodiment, the first refresh process and the second refresh process are performed, thereby effectively refreshing the fuel cell unit. Moreover, according to the fuel cell system of the fourth embodiment, the final output can be maintained at a desired output even during the refresh process.

[0152] Fifth embodiment A fuel cell system according to a fifth embodiment will be described. The fuel cell system according to the fifth embodiment differs in processing from the fuel cell system according to the fourth embodiment. For the configuration of the fuel cell system according to the fifth embodiment, please refer to the description of the configuration of the fuel cell system according to the fourth embodiment, and the description will be omitted here.

[0153] <Processing in the fuel cell system according to the fifth embodiment> The following describes the processing in the fuel cell system according to the fifth embodiment. Fig. 21 is a diagram illustrating the processing in the fuel cell system according to the fifth embodiment.

[0154] In FIG. 21, the horizontal axis represents time, and the vertical axis represents the output of each of fuel cell unit 10a, fuel cell unit 10b, fuel cell unit 10c, and fuel cell unit 10d.

[0155] The control unit 120 performs a refresh process on any one of the fuel cell units 10a, 10b, 10c, and 10d during the refresh period Prsh2. The refresh operation is either the first refresh process or the second refresh process described in the fuel cell system according to the first embodiment. In Fig. 21, the refresh process is indicated by an arrowed line Proc.

[0156] The fuel cell system according to the fifth embodiment can maintain output by performing a refresh process in any of fuel cell unit 10a, fuel cell unit 10b, fuel cell unit 10c, and fuel cell unit 10d, as shown in Fig. 21. The output in the fuel cell system according to the fifth embodiment is the same as the output shown in Fig. 20.

[0157] According to the fuel cell system of the fifth embodiment, the first refresh process and the second refresh process are performed, thereby effectively refreshing the fuel cell unit. Also, according to the fuel cell system of the fifth embodiment, the final output can be maintained at a desired output even during the refresh process.

[0158] The embodiments disclosed herein should be considered as illustrative and not restrictive in all respects. The above-described embodiments may be omitted, substituted, or modified in various forms without departing from the scope and spirit of the appended claims. [Explanation of symbols]

[0159] 1, 2 Fuel cell system 10, 10a, 10b, 10c, 10d Fuel cell unit 11 Fuel cell 12 Output adjustment section 13 Gas adjustment section 14 Control section 20, 120 Control unit 21 Timer 30 Energy Storage Unit

Claims

1. a fuel cell unit including a fuel cell; a control unit for controlling the fuel cell unit; Equipped with The control unit a first refresh process for controlling the output of the fuel cell unit to vary; a second refresh process for stopping the operation of the fuel cell unit and controlling the fuel cell unit to start up; Execute Fuel cell system.

2. The control unit, in the first refresh process, (a) controlling the fuel cell unit to operate at a first output; (b) controlling the fuel cell unit to operate at a second output lower than the first output; (c) controlling the fuel cell unit to operate at a third output power, the third output power being higher than the second output power; Execute the following in order. The fuel cell system according to claim 1 .

3. The control unit In the process (a), a control is performed so as to maintain the first output for a certain period of time; In the process (b), the second output is controlled to be maintained for a certain period of time; In the process (c), control is performed so as to maintain the third output for a certain period of time. The fuel cell system according to claim 2 .

4. each of the first output and the third output is equal to or greater than 80% and equal to or less than 100% of a maximum output of the fuel cell system; The second output is an output that is equal to or greater than 0% and equal to or less than 20% of a maximum output of the fuel cell system. The fuel cell system according to claim 2 .

5. The control unit, in the first refresh process, (d) controlling the fuel cell unit to operate at a fourth output; and (e) controlling the fuel cell unit to operate at a fifth output power, the fifth output power being higher than the fourth output power; (f) controlling the fuel cell unit to operate at a sixth output lower than the fifth output; Execute the following in order. The fuel cell system according to claim 1 .

6. The control unit In the process (d), the fourth output is controlled to be maintained for a certain period of time; In the process (e), the fifth output is controlled to be maintained for a certain period of time; In the process (f), the sixth output is controlled to be maintained for a certain period of time. The fuel cell system according to claim 5 .

7. the fifth output is an output that is equal to or greater than 80% and equal to or less than 100% of a maximum output of the fuel cell system, Each of the fourth output and the sixth output is an output that is equal to or greater than 0% and equal to or less than 20% of a maximum output of the fuel cell system. The fuel cell system according to claim 5 .

8. When performing the first refresh process, the supply of hydrogen and air to the fuel cell unit is continued. The fuel cell system according to any one of claims 1 to 7.

9. The control unit, in the second refresh process, (g) controlling the fuel cell unit to shut down; (h) controlling the fuel cell unit to start up; (i) controlling the fuel cell unit to operate at a seventh output; Execute the following in order. The fuel cell system according to any one of claims 1 to 7.

10. the control unit controls the fuel cell unit to be continuously stopped for a minimum time or more in the process (g); The fuel cell system according to claim 9.

11. The seventh output is any output between 80% and 100% of a maximum output of the fuel cell system. The fuel cell system according to claim 9.

12. When performing the first refresh process, the supply of hydrogen and air to the fuel cell unit is continued. The fuel cell system according to claim 9.

13. The control unit, in the second refresh process, (j) controlling the fuel cell unit to operate at an eighth output; (k) controlling the fuel cell unit to stop operating; (l) controlling the fuel cell unit to start up; (m) controlling the fuel cell unit to operate at a ninth output; Execute the following in order. The fuel cell system according to any one of claims 1 to 7.

14. the control unit controls the fuel cell unit to be continuously stopped for a minimum time or more in the process (k); 14. The fuel cell system of claim 13.

15. Each of the eighth output and the ninth output is an output that is 80% or more and 100% or less of a maximum output in the fuel cell system.

14. The fuel cell system of claim 13.

16. When performing the first refresh process, the supply of hydrogen and air to the fuel cell unit is continued.

14. The fuel cell system of claim 13.

17. A method for controlling a fuel cell unit including fuel cells, comprising the steps of: controlling the output of the fuel cell unit to vary; stopping the operation of the fuel cell unit and controlling the fuel cell unit to start up; Including, A method for controlling a fuel cell unit.

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