Fuel cell system

Abstract

Provided is a fuel cell system that comprises a plurality of units each including a fuel cell stack, an anode circulation path through which an anode gas flows, and an anode valve that discharges anode off-gas from the anode circulation path to the outside, wherein: the fuel cell system comprises a first unit, a second unit, and a control device that controls the first unit and the second unit; the control device opens the anode valve of the first unit at a first predetermined time and opens the anode valve of the second unit at a second predetermined time different from the first predetermined time, makes the valve opening time of the anode valve of the first unit earlier than the first predetermined time on the basis of a physical quantity that indicates the degree of necessity for opening the anode valve in the first unit, and makes the valve opening time of the anode valve of the second unit earlier than the second predetermined time on the basis of a physical quantity that indicates the degree of necessity for opening the anode valve in the second unit.

Description

Fuel cell system

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

[0002] Use of a fuel cell as driving power for vehicles and the like can contribute to improving energy efficiency. As a technology related to such a fuel cell, there is known a technique of shifting the timing to open purge valves that discharge anode gas from anode circulation paths of a plurality of fuel cell units to the outside according to hydrogen concentration (see Patent Document 1).

[0003] Japanese Patent No. 4735816

[0004] Even when the opening / closing timings of the anode exhaust valves are shifted, it is assumed that opening of the anode exhaust valve may be required depending on the power generation state of the fuel cell. However, conventional technology does not disclose anything about such valve opening.

[0005] One aspect of the present invention is a fuel cell system including a plurality of units each including: a fuel cell stack that generates power with anode gas and cathode gas; an anode circulation path through which the anode gas circulates; and an anode valve that discharges anode off-gas from the anode circulation path to the outside, the fuel cell system including: a first unit; a second unit different from the first unit; and a control device that controls the first unit and the second unit, wherein the control device opens the anode valve of the first unit at a first predetermined timing, opens the anode valve of the second unit at a second predetermined timing different from the first predetermined timing, advances the valve opening timing of the anode valve of the first unit from the first predetermined timing based on a physical quantity indicating the necessity of opening the anode valve in the first unit, and advances the valve opening timing of the anode valve of the second unit from the second predetermined timing based on a physical quantity indicating the necessity of opening the anode valve in the second unit.

[0006] According to the present invention, it becomes possible to maintain the anode gas in the unit in an appropriate state.

[0007] A schematic diagram showing an example of the overall configuration of a fuel cell system. A block diagram explaining the overview of the units. A diagram explaining the time schedule determined for each unit. A diagram explaining examples of starting valve opening earlier or later than the time schedule. A flowchart explaining the flow of the anode valve opening and closing control process executed by the control device based on the program.

[0008] <Overview> Figure 1 is a schematic diagram showing an example of the overall configuration of a fuel cell system 200 according to an embodiment of the invention. In Figure 1, each unit 10 (10-1, 10-2, ...) includes a fuel cell stack 12 and load devices LD (for example, an air pump 68 and a heater 82, etc. (Figure 2)) as auxiliary equipment necessary to generate electricity from the fuel cell stack 12. The fuel cell system 200 includes a group of units 10S comprising n units 10 and an FC control device 100 that controls the group of units 10S.

[0009] The FC control device 100 sets a target power generation amount corresponding to the power generation amount requested by the external device 500 (referred to as the requested power generation amount), causes the units 10 in the unit group 10S to generate power, and outputs the current obtained from the power generation as the system output. The system output is used, for example, as power for driving a vehicle. The system output may also be used for mobile objects other than vehicles, such as aircraft and ships, or for various industrial machines such as robots. By combining multiple units 10 to form the unit group 10S, it is possible to respond to load demands that cannot be covered by the power generation amount of a single unit 10 by using the combined unit output of n units 10 as the system output to meet the demand from the external device 500 (in other words, to adjust the system output to the requested power generation amount). Alternatively, each unit 10 may be provided with an individual control device (for example, a control device 900 (Figure 2)), and the n control devices 900 may cooperate to control each unit 10 in the unit group 10S, either in place of the FC control device 100 or together with the FC control device 100. Alternatively, one of the n control devices 900, each provided in one of the n units 10, may be configured to control all the units 10 in the unit group 10S collectively.

[0010] Incidentally, the anode gas supplied to the fuel cell stack 12 is partially used at the anode electrode and then discharged into the anode discharge channel as anode off-gas (details will be described later). The anode off-gas contains anode gas (hydrogen) that did not react with oxygen, as well as nitrogen in the cathode gas that permeates from the cathode side to the anode side inside the fuel cell stack 12, and water generated by the electrochemical reaction during power generation.

[0011] Generally, during power generation by the fuel cell stack 12, it becomes necessary to temporarily discharge (exhaust) the anode off-gas to the outside for reasons such as power generation efficiency. Such discharge must be performed for each unit 10 within the unit group 10S. However, if gas is discharged simultaneously from multiple units 10, the hydrogen concentration of the discharged gas will temporarily increase, posing a danger. Furthermore, if the rotation speed of the air pump that supplies dilution air is increased in order to increase the amount of air used to dilute the discharged anode off-gas, the noise emitted by the air pump will temporarily increase, potentially impairing the marketability of the fuel cell system 200.

[0012] Therefore, in this embodiment, the timing of gas discharge to the outside is made different among the multiple units 10 so that gas is not discharged simultaneously from multiple units 10. Specifically, a time schedule for each unit 10 in the unit group 10S is determined based on the operating conditions of the fuel cell stack 12, and gas is discharged to the outside from each unit 10 according to its respective time schedule. Details of this unit group 10S will be further explained with reference to Figures 2 to 5.

[0013] <Overview of the Unit> First, an overview of the unit 10 will be described with reference to Figure 2. Figure 2 is a block diagram illustrating the main components of the unit 10 in this embodiment. The unit 10 includes a fuel cell stack 12, an anode system 16, a cathode system 18, a cooling system 20, and a control device 900. The output of the fuel cell stack 12 (unit output) is combined with the unit outputs of the other units 10 to form the system output (Figure 1).

[0014] <Fuel Cell Stack> The fuel cell stack 12 has a power generation cell (not shown). The power generation cell has a membrane electrode assembly (MEA) in which electrodes (electrode catalyst layer and gas diffusion layer, etc.) are provided on both sides of a solid polymer electrolyte membrane. The anode electrode of the power generation cell is supplied with anode gas, which is a fuel gas containing hydrogen (H2), from the anode system 16 through the anode inlet Ain. The cathode electrode of the power generation cell is supplied with cathode gas, such as air containing oxygen, from the cathode system 18 through the cathode inlet Cin. As a result, an electrochemical reaction proceeds at the electrodes of the power generation cell, and power is generated in the fuel cell stack 12.

[0015] The anode gas supplied to the fuel cell stack 12 from the anode inlet Ain is partially used at the anode electrode and then discharged as anode off-gas from the anode outlet Aout to the anode discharge passage 42. The anode off-gas contains anode gas (hydrogen) that did not react with oxygen, as well as nitrogen in the cathode gas that permeates from the cathode side to the anode side through the membrane electrode assembly (permeated nitrogen) and water vapor produced by electrochemical reactions (permeated water vapor). On the other hand, the cathode gas supplied to the fuel cell stack 12 from the cathode inlet Cin is partially used at the cathode electrode and then discharged as cathode off-gas from the cathode outlet Cout to the cathode discharge passage 64.

[0016] <Anode System> The anode system 16 has components for supplying anode gas to the fuel cell stack 12 and components for discharging anode off-gas from the fuel cell stack 12. The anode system 16 includes an anode supply path 40, an anode discharge path 42, a circulation path 44, a drain path 46, and a purge path 48. The anode system 16 also includes an anode gas supply valve 51, an injector 50, an ejector 52, a gas-liquid separator 54, a drain valve 56, and a purge valve 58.

[0017] The anode supply line 40 connects a hydrogen tank (not shown) to the anode inlet Ain of the fuel cell stack 12. The anode supply line 40 is equipped with an anode gas supply valve 51, an injector 50, an ejector 52, and a pressure sensor 93. The anode gas supply valve 51 is located upstream of the injector 50. The ejector 52 is located downstream of the injector 50 (on the anode inlet Ain side). The pressure sensor 93 is located downstream of the ejector 52. The pressure sensor 93 detects the pressure of the anode gas and sends a detection signal to the control device 900.

[0018] The anode discharge channel 42 connects the anode outlet Aout of the fuel cell stack 12 to the intake port of the gas-liquid separator 54. The circulation channel 44 connects the exhaust port of the gas-liquid separator 54 to the ejector 52. The drain channel 46 connects the drain port of the gas-liquid separator 54 to the inlet of the diluent 60, which will be described later. A drain valve 56 is provided in the drain channel 46. The purge channel 48 connects the exhaust port of the gas-liquid separator 54 to the drain channel 46 (on the diluent 60 side of the drain valve 56). A purge valve 58 is provided in the purge channel 48.

[0019] With the above configuration, when the injector 50 is opened while the anode gas supply valve 51 is open, anode gas is injected and supplied to the anode supply passage 40 via the ejector 52. The anode gas flows through the anode supply passage 40 and is supplied to the anode inlet Ain of the fuel cell stack 12. The anode off-gas discharged from the anode outlet Aout to the anode discharge passage 42 is then separated from the water via the gas-liquid separator 54, and as anode recirculation gas, it is drawn in via the ejector 52 and supplied (recirculated) again to the anode supply passage 40. The water separated in the gas-liquid separator 54 (sometimes called generated water) is temporarily stored at the bottom of the gas-liquid separator 54. The drain valve 56 is normally closed. The water meter 94 detects the amount of water (or mass) stored and sends a detection signal to the control device 900. When the amount of water stored reaches a predetermined amount, the drain valve 56 is opened by command from the control device 900. When the drain valve 56 opens, the stored water flows through the drain channel 46 and is discharged to the diluent 60. This suppresses the increase in moisture (water vapor) contained in the anode gas, keeping the anode gas in an appropriate state and preventing a condition in which the cell voltage of the fuel cell stack 12 drops below normal (anode flooding). Also, when the drain valve 56 opens after the stored water has been used up, the anode off-gas from the gas-liquid separator 54 flows through the drain channel 46 and is discharged to the diluent 60. In other words, the drain valve 56 is an example of an anode valve for keeping the anode off-gas in an appropriate state. The purge valve 58, which is provided in the purge channel 48, is normally closed. The control device 900 estimates the hydrogen partial pressure (hydrogen concentration) of the anode gas, which corresponds to the pressure of the anode gas (hydrogen), based on the anode gas pressure (total pressure) detected by the pressure sensor 93. When the nitrogen concentration of the anode gas increases, causing the estimated hydrogen concentration of the anode gas to decrease to a predetermined level, the purge valve 58 is temporarily opened by a command from the control device 900. When the purge valve 58 opens, a portion of the anode reflux gas flowing through the circulation channel 44 is discharged (purged) into the purge channel 48 and discharged to the diluent 60 via the drain channel 46. This suppresses the decrease in the hydrogen concentration of the anode gas (in other words, the increase in nitrogen concentration) and makes it possible to maintain the hydrogen concentration above a certain level.In other words, the purge valve 58 is also an example of an anode valve that maintains the anode off-gas in an appropriate state.

[0020] <Cathode System> The cathode system 18 has components for supplying cathode gas to the fuel cell stack 12 and components for discharging cathode off gas from the fuel cell stack 12. The cathode system 18 includes a cathode supply path 62, a cathode discharge path 64, and a bypass path 66. The cathode system 18 also includes an air pump 68, a humidifier 70, a sealing valve (in) 74, a sealing valve (out) 76, and a bypass valve 78.

[0021] The cathode supply passage 62 connects an air intake (not shown) to the cathode inlet Cin of the fuel cell stack 12. The cathode supply passage 62 is equipped with an air pump 68, a sealing valve (in) 74, and a humidifier 70. The portion of the cathode supply passage 62 upstream of the humidifier 70 is called the cathode supply passage 62A. The portion of the cathode supply passage 62 downstream of the humidifier 70 is called the cathode supply passage 62B. The cathode supply passage 62A is equipped with a pressure sensor 95, an airflow sensor 96, an air pump 68, and a sealing valve (in) 74.

[0022] The sealing valve (in) 74 is positioned closer to the humidifier 70 than the air pump 68. The pressure sensor 95 and airflow sensor 96 are positioned upstream of the air pump 68. The pressure sensor 95 detects the pressure of the intake air (atmosphere) and sends a detection signal to the control device 900. The pressure sensor 95 also functions as an external atmospheric pressure sensor for the unit group 10S. The airflow sensor 96 detects the supply flow rate of the cathode gas and sends a detection signal to the control device 900. An airflow sensor 98 is provided in the cathode supply path 62B. The airflow sensor 98 detects the flow rate of the cathode gas supplied to the fuel cell stack 12 (which may also be called the stack supply flow rate) and sends a detection signal to the control device 900. The stack supply flow rate corresponds to the flow rate obtained by subtracting the flow rate of the cathode gas flowing through the bypass path 66 (which may also be called the bypass flow rate) from the value detected by the airflow sensor 96.

[0023] The cathode discharge channel 64 connects the cathode outlet Cout of the fuel cell stack 12 to the inlet of the diluent 60. The cathode discharge channel 64 is equipped with a humidifier 70 and a sealing valve (out) 76. The portion of the cathode discharge channel 64 upstream of the humidifier 70 is called cathode discharge channel 64A. The portion of the cathode discharge channel 64 downstream of the humidifier 70 is called cathode discharge channel 64B. The sealing valve (out) 76 is provided in cathode discharge channel 64B.

[0024] The bypass passage 66 connects, for example, the portion of the cathode supply passage 62A between the air pump 68 and the sealing valve (in) 74, and the portion of the cathode discharge passage 64B downstream of the sealing valve (out) 76. A bypass valve 78 is provided in the bypass passage 66. When the bypass passage 66 is open, a bypass route for cathode gas is secured when the air pump 68 continues to run with the sealing valve (in) 74 and sealing valve (out) 76 closed (corresponding to the cessation of power generation). Furthermore, a bypass route for cathode gas is secured when it is desired to increase the amount of dilution air sent to the diluter 60 without increasing the stack supply flow rate.

[0025] The humidifier 70 recovers moisture contained in the cathode-off gas circulating within the humidifier 70 as needed, and adds the recovered moisture to the cathode gas circulating within the humidifier 70. The cathode gas is humidified to prevent excessive drying of the electrode structure in the fuel cell stack 12.

[0026] In the above configuration, when power generation is performed in the fuel cell stack 12, the sealing valve (in) 74 and sealing valve (out) 76 are opened by command from the control device 900. When the air pump 68, which acts as a cathode gas supply device, is operated, cathode gas is supplied to the fuel cell stack 12 through the cathode supply passage 62, and cathode-off gas discharged from the fuel cell stack 12 is sent to the diluent 60 through the cathode discharge passage 64. When power generation by the fuel cell stack 12 is stopped, the sealing valve (in) 74 and sealing valve (out) 76 are closed by command from the control device 900.

[0027] The bypass valve 78 is normally closed and is temporarily opened by a command from the control device 900. The bypass valve 78 is opened, for example, to adjust the amount of cathode gas supplied to the fuel cell stack 12 during power generation, to increase the amount of dilution air sent to the diluent 60 without increasing the stack supply flow rate, or to keep the air pump 68 running when power generation is stopped. The air pump 68 is one of the load devices LD.

[0028] The diluent 60 dilutes the combined gas, which is formed by the convergence of cathode-off gas flowing through the cathode discharge passage 64B and anode-off gas flowing through the drain passage 46 and purge passage 48. The combined gas and moisture diluted in the diluent 60 are discharged to the outside (into the atmosphere) via the exhaust pipe P100. The control device 900 controls the rotation speed of the air pump 68 to supply the necessary air to the diluent 60 to dilute the combined gas (which may also be called the mixed gas) to a predetermined concentration or lower.

[0029] <Cooling System> The cooling system 20 has components for supplying refrigerant to the fuel cell stack 12 and components for discharging refrigerant from the fuel cell stack 12. The cooling system 20 includes a refrigerant supply passage 84 and a refrigerant discharge passage 86. The cooling system 20 also includes a refrigerant pump 88, a mixing valve 80, a radiator 90, a heater 82, and a temperature sensor 92.

[0030] A refrigerant flow path (not shown) for cooling the fuel cell stack 12 is formed inside the fuel cell stack 12. The refrigerant supply passage 84 connects the outlet of the radiator 90 to the inlet Rin of the refrigerant flow path. The refrigerant supply passage 84 is equipped with a mixing valve 80 and a refrigerant pump 88. The refrigerant discharge passage 86 connects the outlet Rout of the refrigerant flow path to the inlet of the radiator 90. When the refrigerant pump 88 is running, refrigerant circulates from the refrigerant pump 88 to the refrigerant supply passage 84, the fuel cell stack 12, the refrigerant discharge passage 86, and the radiator 90.

[0031] A temperature sensor 92 and a heater 82 are provided in the refrigerant discharge passage 86. The temperature sensor 92 detects the temperature of the refrigerant discharged from the fuel cell stack 12 and sends a detection signal to the control device 900. The heater 82 heats the refrigerant according to a command from the control device 900. The heater 82 is one of the load devices LD. The heater 82 and the mixing valve 80 are connected by a refrigerant bypass passage 85. The mixing valve 80 adjusts the mixing ratio of the refrigerant cooled by the radiator 90 and the refrigerant heated by the heater 82 according to a command from the control device 900.

[0032] The control device 900 is comprised of a computer with a CPU, RAM, ROM, I / O interface, and other peripheral circuits. Sensors such as pressure sensors 93 and 95, temperature sensor 92, airflow sensor 96 and 98, and water meter 94 are connected to the information acquisition unit 911 of the control device 900, and detected values ​​from each sensor of unit 10 are input to the information acquisition unit 911. In addition, various parts of unit 10 such as the anode gas supply valve 51, injector 50, drain valve 56, purge valve 58, sealing valve (in) 74, sealing valve (out) 76, and bypass valve 78 are connected to the control device 900, and the control device 900 controls the opening and closing of these. Furthermore, the control device 900 receives the requested power generation amount for unit 10 from the FC control device 100 (Figure 1). The control device 900 has a timing unit 912 that timings the discharge of anode off gas from unit 10 according to a time schedule.

[0033] <Time Schedule> Figure 3 is a diagram illustrating the time schedule determined for each unit 10. For clarity, we will illustrate the case where n = 2 is the number of units 10 included in the unit group 10S. That is, the unit group 10S includes unit 10-1 (sometimes called the first unit) and unit 10-2 (sometimes called the second unit).

[0034] In Figure 3, the upper waveform shows the change in the degree to which the anode valve needs to be opened based on the physical quantities acquired in unit 10-1, and the planned opening / closing cycle T1 of the purge valve 58 as the anode valve of unit 10-1. In this embodiment, the control device 900 determines the planned opening / closing cycle T1 of the purge valve 58 of unit 10-1 as a time schedule. In Figure 3, the lower waveform shows the change in the degree to which the anode valve needs to be opened based on the physical quantities acquired in unit 10-2, and the planned opening / closing cycle T2 of the purge valve 58 as the anode valve of unit 10-2. In this embodiment, the control device 900 determines the planned opening / closing cycle T2 of the purge valve 58 of unit 10-2 as a time schedule.

[0035] <Degree of Need for Valve Opening> When the partial pressure of nitrogen in the anode gas (nitrogen concentration), which corresponds to the pressure of nitrogen in the anode gas, increases, the partial pressure of hydrogen in the anode gas (hydrogen concentration), which corresponds to the pressure of hydrogen in the anode gas, relatively decreases, hindering proper power generation in the fuel cell stack 12. To avoid such a nitrogen excess state (in other words, a hydrogen deficiency state), in this embodiment, the partial pressure of nitrogen in the anode gas is used as a physical quantity indicating the degree of need for opening the purge valve 58, and is used as a criterion for determining when to open the purge valve 58. In this embodiment, the higher the partial pressure of nitrogen in the anode gas (in other words, the lower the hydrogen concentration), the higher the need for opening the purge valve 58, and the lower the partial pressure of nitrogen in the anode gas (in other words, the higher the hydrogen concentration), the lower the need for opening the purge valve 58.

[0036] <Scheduled Opening and Closing Cycles> The scheduled opening and closing cycle T1 is the sum of the scheduled valve opening time a1 and the scheduled valve closing time b1. The scheduled opening and closing cycle T2 is the sum of the scheduled valve opening time a2 and the scheduled valve closing time b2. The scheduled valve opening time a1 and scheduled valve opening time a2 each represent the time when the purge valve 58 is open, and the scheduled valve closing time b1 and scheduled valve closing time b2 each represent the time when the purge valve 58 is closed. The scheduled opening and closing cycles T1 and T2 are the same, and are offset by half a cycle. In other words, the control device 900 intentionally staggers the start timing of the scheduled valve opening time a1 and the start timing of the scheduled valve opening time a2 so that the scheduled valve opening time a1 of unit 10-1 and the scheduled valve opening time a2 of unit 10-2 do not completely overlap. The scheduled valve opening time a1 of unit 10-1 and the scheduled valve opening time a2 of unit 10-2 may overlap in some respects. The control device 900 determines the time schedules for unit 10-1 and unit 10-2 such that the valve opening interval from the valve opening time (valve opening start timing) of the purge valve 58 of unit 10-1 to the valve opening time (valve opening start timing) of the purge valve 58 of unit 10-2 is equal to the valve opening interval from the valve opening time (valve opening start timing) of the purge valve 58 of unit 10-2 to the valve opening time (valve opening start timing) of the purge valve 58 of unit 10-1.

[0037] In this embodiment, as an example, the change in hydrogen partial pressure (hydrogen concentration) is estimated based on the change in nitrogen partial pressure (nitrogen concentration) of the anode gas. The control device 900 determines a time schedule for controlling the opening and closing of the purge valve 58 so that it opens the purge valve 58 when the estimated hydrogen concentration falls below the lower limit of a predetermined allowable range of hydrogen concentration, and closes the purge valve 58 when the estimated hydrogen concentration recovers to the upper limit of the allowable range. When the purge valve 58 opens, as described above, a portion of the anode reflux gas, whose nitrogen partial pressure has increased (in other words, whose hydrogen partial pressure has decreased), flows through the drain channel 46 and is discharged to the diluent 60, causing the nitrogen concentration of the anode gas to decrease (in other words, the hydrogen concentration to increase relatively). When the purge valve 58 closes, the nitrogen concentration of the anode gas increases again (in other words, the hydrogen concentration to decrease relatively again).

[0038] <Scheduled valve opening time> The control device 900 determines the scheduled valve opening time a1 for unit 10-1 and the scheduled valve opening time a2 for unit 10-2 based on the time required for the nitrogen partial pressure of the anode gas to decrease (in other words, for the hydrogen partial pressure of the anode gas to increase). Specifically, based on the pressure difference (called differential pressure) between the upstream and downstream of the purge valve 58, the control device 900 calculates the scheduled discharge time of the anode gas with increased nitrogen partial pressure by referring to a pre-prepared characteristic map, etc. The calculated scheduled discharge time is then set as the scheduled valve opening time a1 and scheduled valve opening time a2. Here, the pressure upstream of the purge valve 58 can be estimated based on the pressure of the anode gas (value detected by the pressure sensor 93). The pressure downstream of the purge valve 58 can be estimated based on atmospheric pressure (value detected by the pressure sensor 95).

[0039] <Scheduled valve closing time> The control device 900 also determines the scheduled valve closing time b1 for unit 10-1 and the scheduled valve closing time b2 for unit 10-2 based on the time required for the nitrogen partial pressure to rise from the lower limit to the upper limit of the allowable range (in other words, for the hydrogen partial pressure to fall from the upper limit to the lower limit of the allowable range). Specifically, the rate of increase in nitrogen concentration is determined by referring to a pre-prepared characteristic map based on the power generation amount (current density) of the fuel cell stack 12, and the scheduled required time is calculated using this rate of increase. The scheduled required time is then set as the scheduled valve closing time b1 and the scheduled valve closing time b2. Here, the increase in nitrogen concentration depends on the permeated nitrogen that permeates from the cathode side to the anode side. The permeated nitrogen can be calculated based on the power generation state, such as the current density of the fuel cell stack 12 and the temperature of the fuel cell stack 12 (for example, the temperature of the refrigerant detected by the temperature sensor 92). The current density of the fuel cell stack 12 is determined by the target power generation amount set by the control device 900. In other words, there is a correlation between the rate of increase in nitrogen partial pressure and the target amount of power generated.

[0040] To explain the estimation of hydrogen partial pressure (hydrogen concentration) in more detail, the control device 900 calculates the hydrogen partial pressure of the anode gas, which corresponds to the pressure P of the anode gas (hydrogen), based on the total pressure of the anode gas detected by the pressure sensor 93, and the partial pressure of nitrogen and water vapor of the anode gas. The partial pressure of nitrogen and water vapor of the anode gas are calculated based on the flow rate (permeation rate) of permeated nitrogen and permeated water vapor, and the discharge rate of the anode reflux gas. The permeation rate can be calculated based on the power generation status of the fuel cell stack 12, such as the power generation amount (current value) and the temperature of the fuel cell stack 12 (for example, the temperature of the refrigerant detected by the temperature sensor 92). The amount of nitrogen discharged through the drain channel 46 can be calculated based on the pressure of the anode gas (value detected by the pressure sensor 93), atmospheric pressure (value detected by the pressure sensor 95), and the gas density of the anode supply channel 40. The gas density of the anode supply channel 40 can be calculated based on the pressure of the anode gas, the internal temperature of the fuel cell stack 12, and the average molecular weight. The average molecular weight is calculated from the pressure of the anode gas and the partial pressure of nitrogen in the anode gas.

[0041] The rate of increase of nitrogen in the anode gas depends on the cathode gas pressure, the refrigerant temperature of the cooling system 20, the humidity of the electrolyte membrane in the fuel cell stack 12, etc. These are determined based on the power generation current of the fuel cell stack 12. The power generation current of the fuel cell stack 12 is determined by the target power generation amount set for unit 10. In other words, there is a correlation between the rate of increase of nitrogen partial pressure in the anode gas (in other words, the rate of decrease of hydrogen partial pressure) and the target power generation amount. Because there is a correlation between the target power generation amount and the rate of increase of nitrogen partial pressure (the rate of decrease of hydrogen partial pressure), the time schedule for controlling the opening and closing of the purge valve 58 changes when the required power generation amount for unit 10 changes. The control device 900 successively determines a time schedule based on the latest information and controls the opening and closing of the purge valve 58 in unit 10 according to the determined time schedule (in other words, it discharges a portion of the anode reflux gas from unit 10 according to the time schedule).

[0042] <Valve Opening Timing> The control device 900 of unit 10-1 will, in principle, open the purge valve 58 at the start of the scheduled valve opening time a1 in the time schedule. In other words, the start of valve opening may, exceptionally, be earlier or later than the time schedule. Details will be described later. Similarly, the control device 900 of unit 10-1 will, in principle, close the purge valve 58 at the start of the scheduled valve closing time b1 in the time schedule. In other words, the start of valve closing may, exceptionally, be earlier or later than the time schedule. Details will be described later. Likewise, the control device 900 of unit 10-2 will, in principle, open the purge valve 58 at the start of the scheduled valve opening time a2 in the time schedule. In other words, the start of valve opening may, exceptionally, be earlier or later than the time schedule. Details will be described later. Furthermore, the control device 900 of unit 10-2 will, in principle, close the purge valve 58 at the start of the scheduled valve closing time b2 in the time schedule. In other words, the start of valve closing may, exceptionally, be earlier or later than the scheduled time. Details will be provided later.

[0043] <Changing the valve opening and closing timing> Referring to Figure 4, an example of starting the valve opening earlier or later than the time schedule will be explained. In Figure 4, the case where the number of units 10 included in the unit group 10S is n=4 is shown as an example. That is, the unit group 10S has unit 10-1, unit 10-2, unit 10-3, and unit 10-4. In Figure 4, the upper waveform shows the change in the degree to which the anode valve needs to be opened based on the physical quantity obtained in unit 10-1 of the four units 10, and the planned opening and closing period T1 of the purge valve 58 as the anode valve of unit 10-1. In Figure 4, the lower waveform shows the change in the degree to which the anode valve needs to be opened based on the physical quantity obtained in unit 10-2 of the four units 10, and the planned opening and closing period T2 of the purge valve 58 as the anode valve of unit 10-2. The planned opening / closing cycles T1 and T2 are the same, and are shifted by 1 / 4 cycle. In other words, the control device 900 intentionally shifts the start timing of each planned opening time by 1 / 4 cycle so that the planned opening times a1 to a4 of units 10-1 to 10-4 do not completely overlap. The control device 900 determines the time schedules for units 10-1 to 10-4 so that the opening interval from the opening time (opening start timing) of the purge valve 58 of each unit 10 to the opening time (opening start timing) of the next unit 10 to open is the same.

[0044] In Figure 4, the control device 900 sets the upper limit of the above-mentioned allowable range of nitrogen partial pressure as the second threshold, and the lower limit of the above-mentioned allowable range as the third threshold. Furthermore, the control device 900 sets a design limit value greater than the second threshold as the first threshold, and designates the range from the second threshold to the first threshold as a range requiring attention. The control device 900 further closes the purge valve 58 when the nitrogen partial pressure falls to the third threshold. The first threshold indicates the highest degree of need for opening the purge valve 58. The third threshold indicates the lowest degree of need for opening the purge valve 58. The second threshold indicates that the degree of need for opening the purge valve 58 is lower than the first threshold and higher than the third threshold.

[0045] Since the time schedule is only a planned opening and closing cycle, it may not match the actual change in nitrogen concentration in the anode gas (in other words, the change in hydrogen concentration) depending on operating conditions of the fuel cell stack 12 and other factors. Therefore, the start timing of valve opening and valve closing is advanced or delayed from the time schedule. (First modification example) For example, attention is focused on the time region enclosed by the broken line R41 in FIG. 4 in the unit 10-1. The time region enclosed by the broken line R41 exemplifies a case where the actual change in nitrogen partial pressure during the closing period of the purge valve 58 (shown by the one-dot chain line) becomes much faster than the change in nitrogen partial pressure on which the time schedule is based (shown by the broken line) due to some factor such as the power generation environment. When the nitrogen partial pressure in the anode gas exceeds a first threshold that is even higher than a caution range while the purge valve 58 is closed, the control device 900 advances the end timing of the valve closing period by Δt1 earlier than the end timing of the planned valve closing period b1 so as to immediately open the purge valve 58. In other words, when the nitrogen partial pressure in the anode gas exceeds the first threshold, the purge valve 58 is opened promptly. In the case of FIG. 4, the valve is opened at time t11 which is Δt1 earlier than the valve opening timing of the time schedule.

[0046] (Second example of modification) For example, in unit 10-1, let's focus on the time region enclosed by the dashed line R42 in Figure 4. The time region enclosed by the dashed line R42 exemplifies a case where the actual change in nitrogen partial pressure during the closing time of the purge valve 58 (shown by the dashed line) is slightly faster than the change in nitrogen partial pressure that formed the basis of the time schedule (shown by the dashed line) due to some factor such as the power generation environment. The control device 900 determines whether or not to open the purge valve 58 when the actual nitrogen partial pressure in the anode gas reaches the caution range earlier than the opening time in the time schedule. If the control device 900 satisfies a predetermined number of possible openings, it opens the purge valve 58 earlier than in the time schedule. The number of possible openings is the number of units 10 in the unit group 10S in which the opening times of the purge valve 58 are allowed to overlap with each other. For example, if the number of units 10 included in the unit group 10S is n=4, this number is set to 3. The number of valves that can be opened is determined based on the rotational speed of the air pump 68 in each unit 10 when supplying dilution air, taking into consideration the sound and vibration generated. If the number of valves that can be opened is not met, the control device 900 waits for the purge valve 58 that is open in another unit 10-2 to close before opening the purge valve 58 in unit 10-1. The time region enclosed by the dashed line R42 illustrates the latter case. In other words, the control device 900 waits until time t12 when the purge valve 58 in unit 10-2, which is the first of the other units 10-2 to 10-4 to close, closes, before opening the purge valve 58 in unit 10-1. In other words, the start timing of the opening time of the purge valve 58 is delayed by time Δt2' from the start time of the scheduled opening time a1. Time Δt2' corresponds to time Δt2 in the third modification example described later.

[0047] (Third Modification Example) For example, focus on the time region enclosed by the broken line R44 in FIG. 4 in the unit 10-2. The time region enclosed by the broken line R44 illustrates a case where an actual change in nitrogen partial pressure (indicated by the alternate long and short dash line) deviates from the change in nitrogen partial pressure (indicated by the broken line) that serves as the basis of the time schedule. Assuming that the actual nitrogen partial pressure at the opening timing of the purge valve 58 is high, and further that the decrease rate of the nitrogen partial pressure after opening the purge valve 58 is substantially the same as the decrease rate of the nitrogen partial pressure that serves as the basis of the time schedule, the nitrogen partial pressure decreases to the third threshold at time t21, which is delayed by time Δt2 compared to the time schedule. In this case, the control device 900 sets the valve opening time to be longer than the scheduled valve opening time a2 so as to close the purge valve 58 at time t21. In other words, the end timing of the valve opening time is delayed by time Δt2 (or it can also be expressed as that the start timing of the valve closing time is delayed by time Δt2).

[0048] (Fourth Modification Example) For example, focus on the time region enclosed by the broken line R43 in FIG. 4 in the unit 10-1. In the time region enclosed by the broken line R43, in the above-described second modification example, the valve opening timing of the purge valve 58 of the unit 10-1 is extended by time Δt2' to time t12 corresponding to time t21 at which the purge valve 58 of another unit 10-2 is closed. Based on the amount of change in nitrogen partial pressure during the generated time Δt2', the control device 900 sets the valve opening time of the purge valve 58 of the unit 10-1 to be longer than the scheduled valve opening time a2. In other words, the purge valve 58 is opened at time t13 when the end timing of the valve opening time of the purge valve 58 is delayed by time Δt3 (or it can also be expressed as that the start timing of the valve closing time is delayed by time Δt3).

[0049] (Fifth example of modification) For example, in unit 10-2, let's focus on the time region enclosed by the dashed line R45 in Figure 4. The time region enclosed by the dashed line R45 illustrates the case where the actual change in nitrogen partial pressure (shown by the dashed line) deviates from the change in nitrogen partial pressure that formed the basis of the time schedule (shown by the dashed line). Assuming that the actual nitrogen partial pressure at the time the purge valve 58 is opened is low, and that the rate of decrease of the actual nitrogen partial pressure is approximately the same as the rate of decrease of the nitrogen partial pressure that formed the basis of the time schedule, the actual nitrogen partial pressure will fall to the third threshold at time t22, which is time Δt4 later than the change in nitrogen partial pressure that formed the basis of the time schedule. In this case, the control device 900 makes the opening time longer than the scheduled opening time a2 so that the purge valve 58 is closed at time t22. In other words, the end timing of the opening time is advanced by time Δt4 (or, it can be said that the start timing of the closing time is advanced by time Δt4).

[0050] <Explanation of the flowchart> Figure 5 is a flowchart illustrating the flow of the anode valve opening and closing control process executed by the control device 900 (Figure 2) of each unit 10 based on the program. For example, each time the FC control device 100 (Figure 1) receives a command for the amount of power to be generated from an external device 500 to the unit group 10S, it sends a command for the amount of power to be generated for each unit 10 to the control device 900 of each unit 10 in the unit group 10S, and also causes the control device 900 to determine the scheduled opening and closing cycle of the anode valve of each unit 10 as a time schedule. The control device 900 of each unit 10 starts the process shown in Figure 5 to open and close the anode valve in accordance with its respective time schedule in order to discharge gas to the outside. As mentioned above, the control device 900 works in cooperation with the FC control device 100. The FC control device 100 acquires information indicating the open / closed state of the anode valve and information indicating the time schedule from each control device 900 of each unit 10 that constitutes the unit group 10S, and makes this information shareable with each unit 10 in the unit group 10S. With this configuration, each control device 900 in each unit 10 can understand the open / closed state and time schedule of the anode valves of the other units 10.

[0051] In step S10 of Figure 5, the control device 900 determines whether or not it is the scheduled valve opening time. If the time measured by the timing unit 912 matches the scheduled valve opening time (valve opening start timing) in the time schedule, the control device 900 affirms step S10 and proceeds to step S20. If they do not match, it negates step S10 and waits for the scheduled valve opening time to arrive.

[0052] In step S20, the control device 900 opens the drain valve 56, which acts as an anode valve, and proceeds to step S30.

[0053] In step S30, the control device 900 determines whether or not it is the scheduled valve closing time. If the time measured by the timing unit 912 matches the scheduled valve closing time (valve closing start timing) of the time schedule, the control device 900 affirms step S30 and proceeds to step S40; otherwise, it negates step S30 and proceeds to step S50.

[0054] In step S40, the control device 900 determines whether the partial pressure of nitrogen in the anode gas is less than the third threshold. If it is less than the third threshold, the control device 900 affirms step S40 and proceeds to step S60. If it is not less than the third threshold, it denies step S40 and repeats the determination process. As a result, if the partial pressure of nitrogen in the anode gas is less than the third threshold at the scheduled valve closing time, the purge valve 58 is closed according to the time schedule. On the other hand, if the partial pressure of nitrogen in the anode gas is not less than the third threshold at the scheduled valve closing time, step S40 is denied and the device waits for the nitrogen partial pressure to decrease. In this case, the valve closing start timing is delayed compared to the time schedule (in other words, the valve opening time is extended).

[0055] In step S50, which proceeds after a negative determination of step S30, the control device 900 determines whether the partial pressure of nitrogen in the anode gas is less than the third threshold. If it is less than the third threshold, the control device 900 affirms step S50 and proceeds to step S60; otherwise, it negates step S50 and returns to step S30, repeating the process described above. As a result, if the partial pressure of nitrogen in the anode gas is less than the third threshold before the scheduled valve closing time, the purge valve 58 is closed earlier than the time schedule. On the other hand, if the partial pressure of nitrogen in the anode gas is not less than the third threshold before the scheduled valve closing time, the control device 900 negates step S50 and waits for the scheduled valve opening time.

[0056] In step S60, the control device 900 closes the purge valve 58, which acts as the anode valve, and returns to step S10. Upon returning to step S10, the control device 900 repeats the process described above.

[0057] In step S70, which proceeds after a negative determination of step S10, the control device 900 determines whether the nitrogen partial pressure of the anode gas has exceeded a first threshold. If it has exceeded the first threshold, the control device 900 affirms step S70 and proceeds to step S20; if it has not exceeded the first threshold, it negates step S70 and proceeds to step S80. As a result, when the nitrogen partial pressure of the anode gas exceeds the first threshold, the purge valve 58 is opened promptly in step S20.

[0058] In step S80, which proceeds after a negative determination of step S70, the control device 900 determines whether the nitrogen partial pressure of the anode gas is equal to or greater than the second threshold. If it is equal to or greater than the second threshold, the control device 900 affirms step S80 and proceeds to step S90; otherwise, it negates step S80 and returns to step S10. As a result, if it is less than the second threshold, the purge valve 58 is opened and closed according to the time schedule.

[0059] In step S90, the control device 900 determines whether the number of units that can be opened is met. If the predetermined number of units that can be opened (as described above, 3 in this example) is met, the control device 900 affirms step S90 and proceeds to step S20. If the number of units that can be opened is not met, the control device 900 denies step S90 and proceeds to step S100. When the number of units that can be opened is set to 3, the control device 900 affirms step S90 if the number of units 10 that are open is 1 or 2, and denies step S90 if the number is 3 or more. As a result, if the number of units that can be opened is met, the purge valve 58 is opened promptly in step S20. On the other hand, if the number of units that can be opened is not met, the control device proceeds to step S100 and waits for the valve to open.

[0060] In step S100, the control device 900 determines whether the purge valve 58 in another unit 10 has changed from an open state to a closed state. If the purge valve 58 that was open in another unit 10 constituting the unit group 10S is closed, the control device 900 affirms step S100 and proceeds to step S20. If the purge valve 58 is not closed in another unit 10, the control device 900 denies step S100 and repeats the determination process. As a result, the control device waits for the purge valve 58 that was open in another unit 10 to be closed before proceeding to step S20, and the purge valve 58 is opened. Alternatively, the control device 900 may be configured to return to step S10 if step S100 is denied. If the control device 900 returns to step S10, it becomes possible to open the purge valve 58 at the earlier of the closing time of the first purge valve 58 to be closed among the purge valves 58 that were open in the other unit 10, or the opening time indicated in the time schedule of its own unit 10.

[0061] The embodiments described above provide the following effects: (1) The fuel cell system 200 comprises a plurality of units 10, each including a fuel cell stack 12 that generates electricity using anode gas and cathode gas, an anode supply path 40, an anode discharge path 42 and a circulation path 44 as an anode circulation path through which anode gas flows, and a purge valve 58 as an anode valve that discharges anode off-gas to the outside from the anode circulation path. In other words, the unit group 10S comprises a unit 10-1 as the first unit, a unit 10-2 as the second unit of the unit group 10S, and a control device 900 that controls units 10-1 and 10-2. The control device 900 opens the purge valve 58 of unit 10-1 at a first predetermined time, and opens the purge valve 58 of unit 10-2 at a second predetermined time different from the first predetermined time. Based on the partial pressure of nitrogen of the anode gas, which is a physical quantity indicating the degree to which the purge valve 58 in unit 10-1 needs to be opened, the control device 900 opens the purge valve 58 of unit 10-1 earlier than the first predetermined time, and based on the partial pressure of nitrogen of the anode gas, which indicates the degree to which the purge valve 58 in unit 10-2 needs to be opened, the control device 900 opens the purge valve 58 of unit 10-2 earlier than the second predetermined time. With this configuration, the purge valve 58 is opened earlier than the first predetermined time and the second predetermined time depending on the degree to which opening is necessary, so that the anode reflux gas with increased nitrogen partial pressure (in other words, with relatively lower hydrogen concentration) is discharged into the purge channel 48. As a result, it becomes possible to maintain the anode gas in an appropriate state.

[0062] (2) In the fuel cell system 200 described in (1) above, the control device 900 controls the opening and closing of the purge valve 58 in unit 10-1 according to a first schedule (time schedule) in which opening and closing are repeated in a planned opening and closing cycle T1 as the first cycle, and controls the opening and closing of the purge valve 58 in unit 10-2 according to a second schedule (time schedule) in which opening and closing are repeated in a planned opening and closing cycle T2 as the second cycle, so that the opening timings differ between the first schedule and the second schedule, the start timing of the planned opening time a1 as the first predetermined time is shown in the first schedule, and the start timing of the planned opening time a2 as the second predetermined time is shown in the second schedule. With this configuration, the control device 900 can appropriately control the opening and closing so that the opening timings of the purge valve 58 of unit 10-1 and the purge valve 58 of unit 10-2 do not overlap.

[0063] (3) In the fuel cell system 200 described in (2) above, the physical quantity is the partial pressure of nitrogen corresponding to the hydrogen concentration of the anode gas. The control device 900 promptly opens the purge valve 58 of unit 10 where the partial pressure of nitrogen while the purge valve 58 is closed has reached a first threshold indicating the highest need for opening the purge valve 58. It also opens the purge valve 58 of unit 10 where the partial pressure of nitrogen while the purge valve 58 is closed has reached a second threshold indicating a lower need than the first threshold, after the purge valve 58 that is open in other units 10 different from unit 10 has closed. By monitoring the partial pressure of nitrogen as a physical quantity indicating the need for opening the purge valve 58, it becomes possible to open the purge valve 58 ahead of schedule as needed. This makes it possible to discharge the anode reflux gas, in which the nitrogen partial pressure has increased (in other words, the hydrogen concentration has decreased relatively), at the appropriate time, and maintain the anode gas in an optimal state.

[0064] (4) In the fuel cell system 200 described in (3) above, the control device 900 opens the purge valve 58 of unit 10 whose nitrogen partial pressure while the purge valve 58 is closed is below the second threshold, according to a first predetermined time or a second predetermined time. With this configuration, if the nitrogen partial pressure while the purge valve 58 is closed is also below the second threshold, which is lower in necessity than the first threshold, the purge valve 58 is opened and closed according to the time schedule. This makes it possible to appropriately control the opening and closing of the purge valve 58 of unit 10-1 and the purge valve 58 of unit 10-2 so that their opening times do not overlap.

[0065] (5) In the fuel cell system 200 described in (4) above, there are at least three units 10, and the control device 900 controls the opening and closing of the purge valve 58 for each unit 10 in accordance with a time schedule that repeats opening and closing at a predetermined period, so that the opening timing differs among the units 10. For a unit 10 in which the nitrogen partial pressure while the purge valve 58 is closed has reached a second threshold, if the number of units 10 with the purge valve 58 open among the three or more units 10 is less than a predetermined number of units that can be opened, the purge valve 58 is opened immediately. If the number of units 10 with the purge valve 58 open is equal to or greater than the number of units that can be opened, the purge valve 58 in the unit 10 is opened after the purge valve 58 that is open in another unit 10 different from unit 10 has been closed. With this configuration, it becomes possible to appropriately adjust the timing of opening the purge valves 58 between units 10 so that the opening times of more units 10 than the number of units that can be opened do not overlap, in other words, so that the anode reflux gas is not discharged simultaneously at the same time. Furthermore, since the discharge timing of the anode reflux gas from multiple units 10 does not overlap, the range of fluctuation in the concentration of the discharged gas is suppressed compared to when they are discharged simultaneously at the same time.

[0066] (6) In the fuel cell system 200 described in (5) above, each of the three or more units 10 further has an air pump 68 that supplies cathode gas to the fuel cell stack 12, and the control device 900 sets a predetermined number based on a predetermined allowable value based on the rotational speed of each air pump 68 of the unit 10. With this configuration, it is possible to suppress noise, vibration, etc. caused by the air pumps 68 as a whole fuel cell system 200.

[0067] (7) In the fuel cell system 200 described in (5) or (6) above, the control device 900 opens the purge valve 58 of a unit 10 in which the nitrogen partial pressure while the purge valve 58 is closed has reached the second threshold, at the earlier of the closing time of the first purge valve 58 to be closed among the purge valves 58 that are open in other units 10 different from unit 10, or the opening time shown in the time schedule corresponding to the unit 10. With this configuration, it becomes possible to appropriately adjust the timing of opening the purge valves 58 between units 10 so that the opening times of more units 10 than the number of units 10 that can be opened do not overlap, in other words, so that the anode reflux gas is not discharged all at the same time. In addition, since the discharge timing of the anode reflux gas from multiple units 10 does not overlap, the range of fluctuation in the concentration of the discharged gas is suppressed compared to the case in which it is discharged all at the same time.

[0068] (8) In the fuel cell system 200 described in (7) above, the control device 900 closes the purge valve 58 of unit 10 when the nitrogen partial pressure while the purge valve 58 is open has decreased to a third threshold indicating the lowest degree to which the purge valve 58 needs to be opened. With this configuration, it becomes possible to appropriately change the opening time of the purge valve 58 so that the anode reflux gas is not discharged more than necessary.

[0069] (9) In the fuel cell system 200 described in (7) above, the control device 900 waits for the purge valve 58 of a unit 10 in which the nitrogen partial pressure has reached a second threshold while the purge valve 58 is closed until the purge valve 58 that is open in another unit 10 different from the unit 10 in which the nitrogen partial pressure has reached the second threshold is closed, and extends the opening time of the purge valve 58 after waiting based on the amount of change in nitrogen partial pressure during waiting. With this configuration, if the nitrogen partial pressure increases further by waiting until the purge valve 58 that is open in another unit 10 is closed, the opening time of the purge valve 58 after waiting is extended, making it possible to appropriately discharge the anode reflux gas in which the nitrogen partial pressure has increased during waiting.

[0070] (10) In the fuel cell system 200 described in (2) above, the control device 900 sets a first schedule and a second schedule such that the opening interval from the opening of the purge valve 58 of unit 10-1 to the opening of the purge valve 58 of unit 10-2 is equal to the opening interval from the opening of the purge valve 58 of unit 10-2 to the opening of the purge valve 58 of unit 10-1. With this configuration, it becomes possible to appropriately control the opening and closing of the purge valves so that the opening times of the purge valve 58 of unit 10-1 and the purge valve 58 of unit 10-2 do not overlap.

[0071] (11) In the fuel cell system 200 described in (10) above, each of the multiple units 10 has a cathode supply path 62 that supplies cathode gas to the fuel cell stack 12, a cathode discharge path 64 that discharges cathode off gas from the fuel cell stack 12, an air pump 68 that sends cathode gas to the cathode supply path 62, and a bypass path 66 that bypasses the fuel cell stack 12 and connects the cathode supply path 62 and the cathode discharge path 64. The anode off gas discharged from the anode circulation path merges with the cathode discharge path 64 to form a mixed gas, and the control device 900 drives the air pumps 68 of the multiple units 10 so that the concentration of the mixed gas is below a predetermined concentration. The opening times of the purge valves 58 of the multiple units 10 are staggered so that their opening times do not overlap, and the timing of when the air pumps 68 of the multiple units 10 are operated for dilution is also staggered. Therefore, compared to operating the air pumps 68 of multiple units 10 simultaneously, it is possible to suppress the generation of noise and vibration, as well as the temporary increase in power consumption. In addition, since the discharge timing of the anode reflux gas from multiple units 10 does not overlap, the range of fluctuation in the concentration of the discharged gas is suppressed compared to when they are discharged simultaneously at the same time.

[0072] The above embodiment can be modified into various forms. Modifications are described below. (Modification 1) Instead of the purge valve 58 described above, or in parallel with the opening and closing control of the purge valve 58, the opening and closing control of the drain valve 56 as an anode valve can also be performed in the same way as in the case of the purge valve 58.

[0073] As described above, if the anode gas contains excess moisture as water vapor, an anode flooding state occurs in which the cell voltage of the fuel cell stack 12 decreases below normal levels. To avoid such anode flooding, in Modification 1, the cell voltage of the fuel cell stack 12 is used as a physical quantity indicating the degree to which the drain valve 56 needs to be opened, and is used as a criterion for determining when to open the drain valve 56. In Modification 1, the lower the cell voltage (in other words, the higher the amount of generated water stored in the gas-liquid separator 54), the greater the need to open the drain valve 56, and the higher the cell voltage (in other words, the lower the amount of generated water stored), the less the need to open the drain valve 56.

[0074] The control device 900 determines a time schedule for controlling the opening and closing of the drain valve 56 so that it opens the drain valve 56 when the cell voltage falls below a predetermined lower limit of the allowable range, and closes the drain valve 56 when the cell voltage recovers to the upper limit of the allowable range.

[0075] When the drain valve 56 is closed, the cell voltage decreases as the fuel cell stack 12 generates power (in other words, the need to open the valve increases). When the drain valve 56 is opened, the cell voltage increases as the generated water stored in the gas-liquid separator 54 is discharged (in other words, the need to open the valve decreases). According to Modification 1, it becomes possible to maintain the anode gas in the unit 10 in an appropriate state, similar to when the purge valve 58 is controlled to open and close in the embodiment described above.

[0076] (Modification 2) In this embodiment, in Figure 4, the number of units 10 included in the unit group 10S is set to n=4, and the planned opening / closing cycles T1, T2, T3, and T4 are made the same. Then, the planned opening / closing cycles T1 and T2 are shifted by 1 / 4 cycle, the planned opening / closing cycles T2 and T3 are shifted by 1 / 4 cycle, and the planned opening / closing cycles T3 and T4 are shifted by 1 / 4 cycle. With this configuration, it becomes possible to shift the start timing of the planned valve opening time a1 of unit 10-1, the planned valve opening time a2 of unit 10-2, the planned valve opening time a3 of unit 10-3, and the planned valve opening time a4 of unit 10-4. The number of units 10 included in the unit group 10S is not limited to n=4, but may be increased further. In this case, it is advisable to use, for example, a quiet type air pump 68, a low-vibration type air pump 68, or a power-saving type air pump 68. This makes it possible to increase the number of valves that can be opened and to increase the number of units 10 that can discharge gas at the same time. On the other hand, it is possible to suppress the increase in noise, vibration, and power consumption of the fuel cell system 200.

[0077] The above description is merely an example, and the present invention is not limited by the embodiments and modifications described above, as long as the features of the present invention are not impaired. It is also possible to arbitrarily combine one or more of the above embodiments and modifications, and to combine modifications with each other.

[0078] 10 Unit, 10-1 First unit, 10-2 Second unit, 10S Unit group, 12 Fuel cell stack, 40 Anode supply path, 42 Anode discharge path, 44 Circulation path, 56 Drain valve, 58 Purge valve, 62 Cathode supply path, 64 Cathode discharge path, 66 Bypass path, 68 Air pump, 78 Bypass valve, 100 FC control device, 200 Fuel cell system, 500 External device, 900 Control device, 911 Information acquisition unit, 912 Timing unit, a1, a2 Scheduled valve opening time, b1, b2 Scheduled valve closing time, T1, T2 Scheduled opening / closing cycle

Claims

1. A fuel cell system comprising a plurality of units, each unit including a fuel cell stack that generates electricity using anode gas and cathode gas, an anode circulation path through which the anode gas flows, and an anode valve that discharges anode off-gas to the outside from the anode circulation path, wherein the system comprises: a first unit; a second unit different from the first unit; and a control device that controls the first unit and the second unit, wherein the control device opens the anode valve of the first unit at a first predetermined time, opens the anode valve of the second unit at a second predetermined time different from the first predetermined time, advances the opening time of the anode valve of the first unit compared to the first predetermined time based on a physical quantity indicating the degree of necessity for opening the anode valve of the first unit, and advances the opening time of the anode valve of the second unit compared to the second predetermined time based on the physical quantity indicating the degree of necessity for opening the anode valve of the second unit.

2. A fuel cell system according to claim 1, wherein the control device controls the opening and closing of the anode valve of the first unit in accordance with a first schedule which repeats opening and closing in a first cycle, controls the opening and closing of the anode valve of the second unit in accordance with a second schedule which repeats opening and closing in a second cycle, the opening timings of the valves differ between the first schedule and the second schedule, the first predetermined timing is shown in the first schedule, and the second predetermined timing is shown in the second schedule.

3. A fuel cell system according to claim 2, wherein the physical quantity is the hydrogen concentration of the anode gas or the cell voltage of the fuel cell stack, and the control device promptly opens the anode valve of the first unit and the second unit when the physical quantity while the anode valve is closed reaches a first threshold indicating the highest degree of necessity, and opens the anode valve of the unit where the physical quantity while the anode valve is closed reaches a second threshold indicating the degree of necessity is lower than the first threshold, after the anode valve that is open in another unit different from the first unit has closed.

4. A fuel cell system according to claim 3, wherein the control device opens the anode valve of a unit in which the physical quantity is less than the second threshold while the anode valve is closed, according to the first predetermined time or the second predetermined time.

5. A fuel cell system according to claim 4, wherein at least three of the units are provided, the control device controls the opening and closing of the anode valve for each of the units in accordance with a schedule that repeats opening and closing at a predetermined period, such that the opening timing differs among the units, and for a unit in which the physical amount while the anode valve is closed reaches the second threshold, if the number of the three or more units with the anode valve open is less than a predetermined number, the control device quickly opens the anode valve, and if the number of the units with the anode valve open is the predetermined number or more, the control device opens the anode valve after the anode valve that is open in another unit different from the unit has been closed.

6. A fuel cell system according to claim 5, wherein each of the three or more units further has an air pump that supplies the cathode gas to the fuel cell stack, and the control device sets the predetermined number based on a predetermined allowable value based on the rotational speed of each of the air pumps of the unit.

7. A fuel cell system according to claim 5 or 6, wherein the control device opens the anode valve of the unit in which the physical quantity of the anode valve that is closed has reached the second threshold at the earlier of the closing time of the anode valve that is closed first among the anode valves that are open in other units different from the unit in which the physical quantity of the anode valve that has reached the second threshold, or the opening time shown in the schedule corresponding to the unit.

8. A fuel cell system according to claim 7, wherein the control device closes the anode valve of a unit in which the physical quantity while the anode valve is open has decreased to a third threshold indicating the lowest degree of necessity.

9. A fuel cell system according to claim 7, wherein the control device waits for the anode valve of a unit in which the physical quantity of which the anode valve is closed has reached the second threshold until the anode valve of another unit different from the unit in which the physical quantity of which has reached the second threshold has closed, and extends the opening time of the anode valve after the waiting period based on the amount of change of the physical quantity during the waiting period.

10. A fuel cell system according to claim 2, characterized in that the control device sets the first schedule and the second schedule such that the valve opening interval from the opening of the anode valve of the first unit to the opening of the anode valve of the second unit is equal to the valve opening interval from the opening of the anode valve of the second unit to the opening of the anode valve of the first unit.

11. A fuel cell system according to claim 10, wherein each of the plurality of units has a cathode supply path that supplies the cathode gas to the fuel cell stack, a cathode discharge path that discharges cathode off gas from the fuel cell stack, an air pump that sends the cathode gas to the cathode supply path, and a bypass path that bypasses the fuel cell stack and connects the cathode supply path and the cathode discharge path, wherein the anode off gas discharged from the anode circulation path merges with the cathode discharge path to form a mixed gas, and the control device drives the air pump to the plurality of units so that the concentration of the mixed gas is below a predetermined concentration.

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