Power system and method for controlling same

Abstract

This power system comprises: a power generation unit that includes a plurality of fuel cell systems; a travel motor and a battery that are connected to the power generation unit; and an ECU that controls output power of the power generation unit. The ECU is configured to execute: processing for acquiring requested load power in the travel motor; processing for acquiring a request for a control mode of the power generation unit; processing for controlling the output power of the power generation unit under a first increase rate limit of a positive value so that, while a durability mode is being requested as the control mode, power corresponding to the requested load power is supplied to the travel motor using output from the power generation unit; and processing for controlling the output power of the power generation unit under a second increase rate limit of a positive value which is determined to be larger than the first increase rate limit, so that, while a charging mode is being requested as the control mode, the battery is charged using the output from the power generation unit and power corresponding to the requested load power is supplied to the travel motor.

Description

Power system and control method therefor

[0001] The present invention relates to a power system and a control method therefor. More specifically, the present invention relates to a power system including a plurality of fuel cell systems and a control method for the power system.

[0002] In recent years, research and development have been conducted on fuel cells that contribute to energy efficiency, in order to enable more people to secure access to affordable, reliable, sustainable and advanced energy.

[0003] Patent Document 1 describes an invention relating to a power generation control system including a plurality of fuel cell systems and a battery, which is assumed to be mounted on large vehicles such as buses and trucks. In the power generation control system described in Patent Document 1, the fuel cell system to be activated and the fuel cell system to be stopped among the plurality of fuel cell systems are determined based on the state of each fuel cell system, the state of charge of the battery, the required power for the plurality of fuel cell systems, and the like, thereby suppressing uneven deterioration of each fuel cell system.

[0004] Japanese Unexamined Patent Application Publication No. 2022-043648

[0005] Incidentally, in a power generation control system including a plurality of fuel cell systems as described in Patent Document 1, various control modes can be defined, such as a control mode in which a motor is driven by power output from the plurality of fuel cell systems and a battery, and a control mode in which the battery is charged while driving the motor with power output from the plurality of fuel cell systems. However, in the invention described in Patent Document 1, sufficient studies have not been conducted on rate limits imposed on output power from a plurality of fuel cell systems. Here, the rate limit refers to an upper limit or a lower limit for an amount of change in output power per unit time.

[0006] An object of the present invention is to achieve a power system capable of controlling output power of a plurality of fuel cell systems under a rate limit suitable for each control mode, and consequently contributes to improvement in energy efficiency.

[0007] (1) The power system according to the present invention (for example, power system 1 described later) comprises a power generation unit (for example, power generation unit 8 described later) including a plurality of fuel cell systems (for example, fuel cell systems 81, 82, 83, 84 described later), a load (for example, a drive motor M described later) and a battery (for example, a battery B described later) connected to the power generation unit, and control means (for example, ECU 6 described later) for controlling the output power of the power generation unit, wherein the control means includes a process for acquiring load request power at the load (for example, the process of step ST1 described later), a process for acquiring a request for the control mode of the power generation unit (for example, the process of step ST2 described later), and a first control mode (for example, the endurance described later) as the control mode. The system is configured to perform the following: a process to control the output power under a positive first rise rate limit so that, while a second control mode (e.g., a charging mode described later) is requested, the output from the power generation unit supplies power to the load according to the load-requested power (for example, the processes in steps ST4 and ST5 described later); and a process to control the output power under a positive second rise rate limit set to be greater than the first rise rate limit so that, while a second control mode (e.g., a charging mode described later) is requested as the control mode, the output from the power generation unit charges the battery and supplies power to the load according to the load-requested power (for example, the processes in steps ST4 and ST5 described later).

[0008] (2) In this case, it is preferable that the control means divides the plurality of fuel cell systems constituting the power generation unit into power generation targets that generate power and power generation targets that stop power generation while the first control mode is requested as the control mode.

[0009] (3) In this case, it is preferable that the control means is configured to further perform a process (for example, the processes of steps ST4 and ST5 described later) to control the output power under a positive third rise rate limit which is less than or equal to the second rise rate limit and greater than the first rise rate limit, so that power corresponding to the load-requested power is supplied to the load by the output from the power generation unit while the third control mode (for example, the performance mode described later) is requested as the control mode.

[0010] (4) In this case, it is preferable that the control means causes all of the fuel cell systems constituting the power generation unit to generate power while the third control mode is requested as the control mode.

[0011] (5) In this case, it is preferable that the control means controls the output power under a negative first descent rate limit while the first control mode is requested as the control mode, controls the output power under a negative second descent rate limit which is greater than the first descent rate limit while the second control mode is requested as the control mode, and controls the output power under a negative third descent rate limit which is smaller than the first and second descent rate limits while the third control mode is requested as the control mode.

[0012] (6) The power system according to the present invention (for example, power system 1 described later) comprises a power generation unit (for example, power generation unit 8 described later) including a plurality of fuel cell systems (for example, fuel cell systems 81, 82, 83, 84 described later), a load (for example, a drive motor M described later) and a battery (for example, a battery B described later) connected to the power generation unit, and a control means (for example, an ECU 6 described later) for controlling the output power of the power generation unit, wherein the control means includes a process for acquiring load request power at the load (for example, the process of step ST1 described later), a process for acquiring a request for the control mode of the power generation unit (for example, the process of step ST2 described later), and a first control mode (for example, the endurance described later) as the control mode. The system is configured to perform the following: a process to control the output power under a negative first decline rate limit (for example, the process in steps ST4 and ST5 described later) so that, while a second control mode (for example, the charging mode described later) is requested as the control mode, the output from the power generation unit supplies power to the load according to the load-requested power; and a process to control the output power under a negative second decline rate limit that is greater than the first decline rate limit (for example, the process in steps ST4 and ST5 described later) so that, while a second control mode (for example, the charging mode described later) is requested as the control mode, the output from the power generation unit charges the battery and supplies power to the load according to the load-requested power.

[0013] (7) In this case, it is preferable that the control means divides the plurality of fuel cell systems constituting the power generation unit into power generation targets that generate power and power generation targets that stop power generation while the first control mode is requested as the control mode.

[0014] (8) In this case, it is preferable that the control means is further configured to perform a process of controlling the output power under a negative third decline rate limit which is smaller than the first decline rate limit and the second decline rate limit, so that while the third control mode is requested as the control mode, power corresponding to the load request power is supplied to the load by the output from the power generation unit.

[0015] (9) In this case, it is preferable that the control means causes all of the fuel cell systems constituting the power generation unit to generate power while the third control mode (for example, the performance mode described later) is required as the control mode.

[0016] (10) In this case, it is preferable that the control means controls the output power under a positive first rise rate limit while the first control mode is requested as the control mode, controls the output power under a positive second rise rate limit which is greater than the first rise rate limit while the second control mode is requested as the control mode, and controls the output power under a positive third rise rate limit which is less than or equal to the second rise rate limit and greater than the first rise rate limit while the third control mode is requested as the control mode.

[0017] (11) In this case, it is preferable that the control means increases the output power of the power generation unit by a predetermined surplus amount compared to the load-requested power while the second control mode is requested as the control mode, and charges the battery with the surplus power.

[0018] (12) In this case, it is preferable that the control means causes all of the fuel cell systems constituting the power generation unit to generate power while the second control mode is requested as the control mode.

[0019] (13) In this case, it is preferable that the control means obtain a request for the control mode based on at least one of the load power request, the battery charge level, and the user's operation on the user interface (for example, the user interface 9 described later).

[0020] (14) A control method according to the present invention is a control method for a power system (e.g., power system 1 described later) comprising a power generation unit (e.g., power system 1 described later) including a plurality of fuel cell systems (e.g., fuel cell systems 81, 82, 83, 84 described later), and a load (e.g., a driving motor M described later) and a battery (e.g., a battery B described later) connected to the power generation unit, the method comprising: a step of obtaining load request power at the load (e.g., step ST1 described later); a step of obtaining a request for a control mode of the power generation unit (e.g., step ST2 described later); and a first control mode (e.g., a durability mode described later) being requested as the control mode. The system is characterized by comprising: a step of controlling the output power under a positive first rise rate limit (for example, steps ST4 and ST5 described later) so that power corresponding to the load's requested power is supplied to the load by the output from the power generation unit while the power generation unit is in operation; and a step of controlling the output power under a positive second rise rate limit set to be greater than the first rise rate limit (for example, steps ST4 and ST5 described later) so that the battery is charged by the output from the power generation unit and power corresponding to the load's requested power is supplied to the load by the output from the power generation unit while the second control mode (for example, the charging mode described later) is requested as the control mode.

[0021] (15) A control method according to the present invention is a control method for a power system (e.g., power system 1 described later) comprising a power generation unit (e.g., power system 1 described later) including a plurality of fuel cell systems (e.g., fuel cell systems 81, 82, 83, 84 described later), and a load (e.g., a driving motor M described later) and a battery (e.g., a battery B described later) connected to the power generation unit, the method comprising: a step of acquiring load-required power at the load (e.g., step ST1 described later); a step of acquiring a request for a control mode of the power generation unit (e.g., step ST2 described later); and a first control mode (e.g., endurance mode described later) being requested as the control mode. The system is characterized by comprising: a step of controlling the output power under a negative first decline rate limit (for example, steps ST4 and ST5 described later) so that power according to the load's requested power is supplied to the load by the output from the power generation unit while the power generation unit is in operation; and a step of controlling the output power under a negative second decline rate limit (for example, steps ST4 and ST5 described later) which is set to be greater than the first decline rate limit so that the battery is charged by the output from the power generation unit and power according to the load's requested power is supplied to the load by the output from the power generation unit while the second control mode (for example, the charging mode described later) is requested as the control mode.

[0022] (1) While the first control mode is requested as the control mode, the control means controls the output power of the power generation unit, which is composed of multiple fuel cell systems, under a positive first rise rate limit so that power corresponding to the load's power requirement is supplied to the load by the output of the power generation unit. Furthermore, while the second control mode is requested as the control mode, the control means controls the output power under a positive second rise rate limit, which is set to be greater than the first rise rate limit, so that the battery is charged by the output of the power generation unit and power corresponding to the load's power requirement is supplied to the load by the output of the power generation unit. Here, the rise rate limit refers to the upper limit of the amount of increase in the power generation unit's output power per unit time. Thus, in the present invention, when the second control mode is requested, which charges the battery while supplying power to the load according to its requirements, a faster increase in the power generation unit's output power is permitted than when the first control mode is requested, which supplies power to the load according to its requirements. As a result, under the second control mode, power for charging the battery can be secured while improving responsiveness when the load requirement increases. Furthermore, in the present invention, when the first control mode is required, the increase in the output power of the power generation unit is limited more gradually than when the second control mode, which involves battery charging, is required. As a result, under the first control mode, the deterioration of the multiple fuel cell systems constituting the power generation unit can be suppressed. As described above, according to the present invention, the output power of multiple fuel cell systems can be controlled under an increase rate limit suitable for the first and second control modes, and this can contribute to energy efficiency.

[0023] (2) While the first control mode is required as the control mode, the control means divides the multiple fuel cell systems constituting the power generation unit into power generation targets that generate power and power generation targets that stop generating power. Thus, according to the present invention, it is possible to prevent uneven deterioration of each fuel cell system under the first control mode.

[0024] (3) While the third control mode is requested as the control mode, the control means controls the output power under a positive third rise rate limit that is less than or equal to the second rise rate limit and greater than the first rise rate limit, so that the output from the power generation unit supplies power to the load according to the load demand power. This makes it possible to improve the responsiveness when the load demand increases under the third control mode compared to the first control mode.

[0025] (4) The control means causes all of the fuel cell systems constituting the power generation unit to generate power while the third control mode is requested as the control mode. This makes it possible to improve the responsiveness when the load demand increases under the third control mode compared to the first control mode.

[0026] (5) The control means controls the output power under a negative first decline rate limit while the first control mode is requested as the control mode. The control means also controls the output power under a negative second decline rate limit that is greater than the first decline rate limit, i.e., a negative value closer to zero than the negative first decline rate limit, while the second control mode is requested as the control mode. The control means also controls the output power under a negative third decline rate limit that is smaller than the first and second decline rate limits, i.e., a negative value further from zero than the negative first and second decline rate limits, while the third control mode is requested as the control mode. Here, the decline rate limit refers to the lower limit of the amount of decrease in the output power of the power generation unit per unit time. Thus, in the present invention, when the second control mode is requested, the decrease in the output power of the power generation unit is restricted more gradually than when the first or third control mode is requested. As a result, under the second control mode, it is possible to suppress the deterioration of multiple fuel cell systems while securing power to charge the battery when the load demand decreases. Furthermore, in the present invention, when the first control mode is requested, the decrease in the output power of the power generation unit is limited more gradually than when the third control mode is requested. As a result, under the first control mode, the deterioration of multiple fuel cell systems can be suppressed more effectively than in the third control mode. Furthermore, in the present invention, when the first control mode is requested, a faster decrease in the output power of the power generation unit is permitted than when the second control mode is requested. As a result, under the first control mode, responsiveness when the load demand decreases can be improved compared to the second control mode. Furthermore, in the present invention, when the third control mode is requested, a faster decrease in the output power of the power generation unit is permitted than when the first or second control mode is requested. As a result, under the third control mode, responsiveness when the load demand decreases can be improved compared to the first or second control mode.

[0027] (6) While the first control mode is requested as the control mode, the control means controls the output power of the power generation unit under a negative first decline rate limit so that power corresponding to the load demand is supplied to the load by the output of the power generation unit which is composed of multiple fuel cell systems. Furthermore, while the second control mode is requested as the control mode, the control means controls the output power under a negative second decline rate limit which is set to be larger than the first decline rate limit described above, so that the battery is charged by the output of the power generation unit and power corresponding to the load demand is supplied to the load. Thus, in the present invention, when the second control mode is requested, which charges the battery while supplying power to the load according to its demand, the decline in the output power of the power generation unit is restricted more gradually than when the first control mode is requested, which supplies power to the load according to its demand. As a result, under the second control mode, it is possible to suppress the deterioration of the multiple fuel cell systems while securing power to charge the battery when the load demand decreases. Furthermore, in the present invention, when the first control mode is requested, a faster decline in the output power of the power generation unit is permitted than when the second control mode, which involves battery charging, is requested. As a result, under the first control mode, the responsiveness during a decrease in load demand can be improved compared to the second control mode. As described above, according to the present invention, the output power of multiple fuel cell systems can be controlled under a decrease rate limit suitable for the first and second control modes, thereby contributing to energy efficiency.

[0028] (7) While the first control mode is required as the control mode, the control means divides the multiple fuel cell systems constituting the power generation unit into power generation targets that generate power and power generation targets that stop generating power. Thus, according to the present invention, it is possible to prevent uneven deterioration of each fuel cell system under the first control mode.

[0029] (8) While the third control mode is requested as the control mode, the control means controls the output power under a negative third decline rate limit which is smaller than the first and second decline rate limits, so that the output from the power generation unit supplies power to the load in accordance with the load demand power. This makes it possible to improve the responsiveness when the load demand decreases under the third control mode compared to the first or second control mode.

[0030] (9) The control means causes all of the fuel cell systems constituting the power generation unit to generate power while the third control mode is requested as the control mode. This makes it possible to improve the responsiveness when the load demand increases under the third control mode compared to the first control mode.

[0031] (10) The control means controls the output power under a positive first rise rate limit when the first control mode is requested as the control mode, controls the output power under a positive second rise rate limit which is greater than the first rise rate limit when the second control mode is requested as the control mode, and controls the output power under a positive third rise rate limit which is less than or equal to the second rise rate limit and greater than the first rise rate limit when the third control mode is requested as the control mode. Thus, in the present invention, when the second control mode is requested, a faster rise in the output power of the power generation unit is permitted than when the first control mode is requested. As a result, under the second control mode, power for charging the battery can be secured while improving responsiveness when the load demand increases. Furthermore, in the present invention, when the first control mode is requested, the rise in the output power of the power generation unit is restricted more gradually than when the second or third control mode is requested. As a result, under the first control mode, the deterioration of multiple fuel cell systems can be suppressed more than in the second or third control mode. Furthermore, in this invention, when the third control mode is required, a more rapid increase in the output power of the power generation unit is permitted than when the first control mode is required. As a result, under the third control mode, the responsiveness when the load demand increases can be improved compared to the first control mode.

[0032] (11) While the second control mode is requested as the control mode, the control means increases the output power of the power generation unit by a predetermined surplus amount compared to the load-required power, and charges the battery with this surplus power. This ensures that power for charging the battery is available under the second control mode.

[0033] (12) The control means causes all of the fuel cell systems constituting the power generation unit to generate power while the second control mode is requested as the control mode. This makes it possible to secure power for charging the battery while increasing responsiveness to load requests under the second control mode.

[0034] (13) The control means obtains a request for a control mode based on at least one of the load power request, the battery charge level, and the user's operation of the user interface. This allows the output power of the power generation unit to be controlled under a control mode suitable for the user's load usage, battery status, and the user's intentions.

[0035] (14) According to the control method of the present invention, for the same reasons as the invention described in (1) above, the output power of multiple fuel cell systems can be controlled under rise rate limits suitable for the first and second control modes, thereby contributing to energy efficiency.

[0036] (15) According to the control method of the present invention, for the same reasons as the invention described in (6) above, the output power of multiple fuel cell systems can be controlled under a fall rate limit suitable for the first and second control modes, thereby contributing to energy efficiency.

[0037] This is a diagram showing the configuration of a power system according to one embodiment of the present invention. This is a diagram showing the configuration of the first fuel cell system. This is a flowchart showing the specific procedure of the management process. This is a diagram showing an example of setting the instruction load for each fuel cell system in endurance mode. This is a diagram showing an example of setting the instruction load for each fuel cell system in performance mode. This is a time chart showing the change in output power of the power generation unit realized by the management process.

[0038] The following describes a power system and its control method according to one embodiment of the present invention, with reference to the drawings.

[0039] Figure 1 shows the configuration of the power system 1 according to this embodiment. The power system 1 comprises a power generation unit 8 comprising a plurality of fuel cell systems 81 to 84, a drive motor M connected to a drive wheel W, a battery B that stores the power output from the power generation unit 8 and the drive motor M, a power circuit 7 that electrically connects the drive motor M and the battery B to the power generation unit 8, an ECU 6 which is a computer that controls the power generation unit 8 and the power circuit 7, and a user interface 9 such as buttons and an operation panel that accepts input operations from the user of the power system 1 (for example, the driver of a vehicle equipped with the power system 1). In the following description, the case in which the drive motor M is used as an electrical load for the power generation unit 8 and the battery B, and the power system 1 is mounted on a fuel cell vehicle (for example, a large fuel cell vehicle such as a bus or truck) that is driven by the drive wheel W described above, is described, but the present invention is not limited to this. The power system according to the present invention may be mounted on mobile bodies such as ships, aircraft and robots in addition to fuel cell vehicles, or it may be a stationary type.

[0040] Figure 2 shows the configuration of the first fuel cell system 81. The first fuel cell system 81 comprises a fuel cell stack 2 that generates electricity when anode gas and cathode gas are supplied, an anode gas supply device 3 that supplies hydrogen as anode gas to the anode flow path 21 of the fuel cell stack 2, a cathode gas supply device 4 that supplies air as cathode gas to the cathode flow path 22 of the fuel cell stack 2, and a cooling system 5 that cools the fuel cell stack 2.

[0041] The fuel cell stack 2 is, for example, a stack structure in which tens to hundreds of fuel cell cells are stacked. Each fuel cell is constructed by sandwiching a membrane electrode structure (MEA) between a pair of separators. The membrane electrode structure consists of two electrodes, an anode electrode (cathode) and a cathode electrode (anode), and a solid polymer electrolyte membrane sandwiched between these electrodes. Typically, both electrodes are formed from a catalyst layer that performs oxidation-reduction reactions in contact with the solid polymer electrolyte membrane, and a gas diffusion layer in contact with this catalyst layer. In this fuel cell stack 2, when hydrogen is supplied to the anode channel 21 formed on the anode electrode side and oxygen-containing air is supplied to the cathode channel 22 formed on the cathode electrode side, electricity is generated by these electrochemical reactions. The electricity generated by the fuel cell stack 2 is supplied to the drive motor M, battery B, etc. via the power circuit 7 (see Figure 1).

[0042] The anode gas supply device 3 includes a hydrogen tank 31 for storing hydrogen gas at high pressure, a hydrogen supply pipe 32 from the hydrogen tank 31 to the inlet side of the anode flow path 21 of the fuel cell stack 2, a hydrogen discharge pipe 33 from the outlet side of the anode flow path 21 to a diluent (not shown) provided in the cathode gas supply device 4, and a hydrogen reflux pipe 34 that branches off from the hydrogen discharge pipe 33 and goes to the hydrogen supply pipe 32.

[0043] The hydrogen supply pipe 32 is a pipe that connects the hydrogen tank 31 to the inlet side of the anode flow path 21, and guides the high-pressure hydrogen gas stored in the hydrogen tank 31 to the anode flow path 21 as anode gas. The hydrogen supply pipe 32 is equipped with a shut-off valve 321, an injector 322, and an ejector 323 in order from the high-pressure side (hydrogen tank 31) to the low-pressure side (fuel cell stack 2).

[0044] The hydrogen tank 31 is connected to a hydrogen supply pipe 32. The shut-off valve 321 is a solenoid valve that opens and closes in response to a command signal from the ECU 6. The injector 322 is a solenoid valve that opens and closes in response to a command signal from the ECU 6. When the injector 322 is opened, high-pressure hydrogen gas supplied via the shut-off valve 321 is injected toward the ejector 323. The injection amount of hydrogen gas from the injector 322 is controlled by PWM control performed by the ECU 6. The ejector 323 mixes the hydrogen gas injected from the injector 322 with anode off-gas discharged from a hydrogen recirculation pipe 34 (that is, hydrogen-containing gas discharged from the outlet side of an anode flow path 21), and injects the mixture into the inlet side of the anode flow path 21. Therefore, in such an anode gas supply device 3, the hydrogen gas stored in the hydrogen tank 31 can be supplied to the fuel cell stack 2 by opening and closing the injector 322 with the shut-off valve 321 opened.

[0045] The hydrogen recirculation pipe 34 is a pipe that connects a hydrogen discharge pipe 33 connected to the outlet side of the anode flow path 21 and the ejector 323 provided on the downstream side of the injector 322 in the hydrogen supply pipe 32, and guides part of the anode off-gas flowing through the hydrogen discharge pipe 33 to the ejector 323. Thereby, the anode off-gas containing hydrogen circulates, together with the anode gas newly injected from the injector 322, in a circulation flow path constituted by the hydrogen supply pipe 32, the anode flow path 21, the hydrogen discharge pipe 33, the hydrogen recirculation pipe 34, and the ejector 323.

[0046] The hydrogen discharge pipe 33 is a pipe connecting the outlet side of the anode flow path 21 and a diluter (not shown) of the cathode gas supply device 4. In the hydrogen discharge pipe 33, a catch tank 331 configured to store water contained in anode off-gas and a purge valve 332 configured to discharge anode off-gas to the cathode gas supply device 4 side are provided in order from the fuel cell stack 2 side toward the cathode gas supply device 4 side. The catch tank 331 is also provided with a drain pipe 35 for discharging accumulated water. The drain pipe 35 extends from the catch tank 331 to a position downstream of the purge valve 332 in the hydrogen discharge pipe 33. A drain valve 351 is provided on the drain pipe 35. When the drain valve 351 is opened, the water accumulated in the catch tank 331 is discharged to a diluter (not shown) via the hydrogen discharge pipe 33. The purge valve 332 and the drain valve 351 are solenoid valves that open and close in response to command signals from the ECU 6.

[0047] The cathode gas supply device 4 includes an air compressor 41, an air supply pipe 42 extending from the air compressor 41 to an introduction portion of the cathode flow path 22, an air discharge pipe 43 extending from a discharge portion of the cathode flow path 22 to a diluter not shown, an air bypass pipe 45 branched from the air discharge pipe 43 and connected to the air supply pipe 42, and a humidifier 46 connecting the air discharge pipe 43 and the air supply pipe 42.

[0048] The air compressor 41 supplies outside air to the cathode flow path 22 of the fuel cell stack 2 via the air supply pipe 42. The air compressor 41 operates in accordance with a command signal from the ECU 6. The humidifier 46 recovers water contained in gas discharged from the cathode flow path 22 (hereinafter also referred to as "cathode off-gas"), and humidifies the air supplied from the air compressor 41 using the recovered water. By the function of the humidifier 46, the MEA of the fuel cell stack 2 during power generation is maintained in a wet state suitable for power generation.

[0049] The air supply pipe 42 is provided with a humidifier bypass pipe 47 that bypasses the humidifier 46. This humidifier bypass pipe 47 is provided with a bypass valve 471. When the bypass valve 471 is opened, most of the air supplied from the air compressor 41 bypasses the humidifier 46 and is supplied to the fuel cell stack 2. The bypass valve 471 is a solenoid valve that opens and closes in response to a command signal from the ECU 6.

[0050] Furthermore, the air supply pipe 42 and the air discharge pipe 43 are each provided with an inlet sealing valve 421 and an outlet sealing valve 431. When these sealing valves 421 and 431 are closed, the inside of the cathode flow path 22 is isolated from the outside air. These sealing valves 421 and 431 are solenoid valves that open and close in response to command signals from the ECU 6.

[0051] The air bypass pipe 45 is a pipe that connects the high-pressure side air supply pipe 42 and the low-pressure side air discharge pipe 43. More specifically, the air bypass pipe 45 connects the air supply pipe 42 upstream of the humidifier 46 and the inlet sealing valve 421, and the air discharge pipe 43 downstream of the humidifier 46 and the outlet sealing valve 431. Therefore, a portion of the air supplied from the air compressor 41 bypasses the humidifier 46 and the cathode flow path 22, and is discharged to the air discharge pipe 43 via the air bypass pipe 45.

[0052] The air bypass pipe 45 is equipped with a back pressure control valve 451 for adjusting the back pressure in the cathode flow path 22 of the fuel cell stack 2. The back pressure control valve 451 is a solenoid valve that opens and closes in response to a command signal from the ECU 6.

[0053] The cooling system 5 includes a refrigerant circulation path 51 that includes the inside of the fuel cell stack 2 as part of the flow path, a cooling pump 52 that circulates refrigerant within the refrigerant circulation path 51, a radiator 53 provided upstream of the cooling pump 52 in the refrigerant circulation path 51, a thermovalve 54 provided downstream of the cooling pump 52 in the refrigerant circulation path 51, and a bypass pipe 55 that connects the thermovalve 54 to the upstream side of the radiator 53 in the refrigerant circulation path 51.

[0054] The fuel cell stack 2 is cooled by heat exchange with the refrigerant flowing through its internal passages. The radiator 53 cools the refrigerant by heat exchange with the outside air. The cooling pump 52 operates in response to command signals from the ECU 6. The rotational speed of the cooling pump 52 is controlled by the ECU 6. Increasing the rotational speed of the cooling pump 52 increases the flow rate of the refrigerant circulating in the refrigerant circulation path 51, which includes the fuel cell stack 2 and the radiator 53 in its refrigerant passages, thereby increasing the cooling capacity of the fuel cell stack 2.

[0055] The thermovalve 54 is a three-way valve that opens and closes in response to a command signal from the ECU 6. The opening ratio of the thermovalve 54 (the ratio of the opening on the refrigerant circulation path 51 side (100% to 0%) to the opening on the bypass pipe 55 side (0% to 100%)) is controlled by the ECU 6. When the opening ratio of the thermovalve 54 is set to the maximum (i.e., "1"), all the refrigerant discharged from the cooling pump 52 is supplied to the fuel cell stack 2, thereby increasing the cooling capacity of the fuel cell stack 2. When the opening ratio of the thermovalve 54 is set to the minimum (i.e., "0"), all the refrigerant discharged from the cooling pump 52 is supplied to the bypass pipe 55.

[0056] Returning to Figure 1, the power generation unit 8 comprises a first fuel cell system 81 as described with reference to Figure 2, and a second fuel cell system 82, a third fuel cell system 83, and a fourth fuel cell system 84, each having the same configuration as the first fuel cell system 81. The following description will focus on a case where one power generation unit 8 is composed of four fuel cell systems 81-84, but the present invention is not limited to this. The number of fuel cell systems constituting one power generation unit 8 can be any number of two or more. Furthermore, the following description will focus on a case where each of these four fuel cell systems 81-84 is equipped with an independent anode gas supply device 3, a cathode gas supply device 4, and a cooling system 5, and where the fuel cell stacks 2 of each fuel cell system 81-84 can be independently powered or stopped, but the present invention is not limited to this. Among the multiple devices that make up the anode gas supply device 3, cathode gas supply device 4, and cooling system 5 necessary for generating and stopping the fuel cell stack 2, for example, the hydrogen tank 31 which is the source of anode gas, the air compressor 41 which is the source of cathode gas, the diluent for diluting the anode gas, and the radiator 53 for cooling the refrigerant may be common to multiple fuel cell systems 81 to 84. Even if these hydrogen tank 31, air compressor 41, diluent, and radiator 53 are common to multiple fuel cell systems 81 to 84, the fuel cell stack 2 of each fuel cell system 81 to 84 can be generated and stopped independently.

[0057] Battery B is a secondary battery capable of both discharging, which converts chemical energy into electrical energy, and charging, which converts electrical energy into chemical energy. In the following description, a so-called lithium-ion battery, which charges and discharges by the movement of lithium ions between electrodes, is used as Battery B, but the present invention is not limited to this. Battery B may also be a capacitor, for example.

[0058] Battery B is equipped with a battery sensor unit BS for estimating its internal state. The battery sensor unit BS consists of multiple sensors that detect physical quantities (for example, the terminal voltage of battery B, the current flowing through battery B, and the temperature of battery B, etc.) necessary for the ECU 6 to obtain the charge rate (the so-called SOC, which represents the battery's stored charge as a percentage) corresponding to the remaining charge of battery B, and transmit signals to the ECU 6 according to the detected values.

[0059] The power circuit 7 consists of power lines connecting the fuel cell stacks 2 of each fuel cell system 81 to 84 that constitute the power generation unit 8 to the driving motor M, battery B, etc., a DC-DC converter installed in these power lines to step up or step down the DC power output from the power generation unit 8, and an inverter installed in the power lines to convert the DC power output from the DC-DC converter into three-phase AC power to supply to the driving motor M, or to convert the three-phase AC power supplied from the driving motor M into DC power to supply to the battery B. Multiple switching elements that make up these DC-DC converters and inverters are driven on / off according to gate drive signals generated at predetermined timings from a gate drive circuit (not shown) of the ECU 6. Therefore, the ECU 6 can control the output power from the power generation unit 8 to the power circuit 7, and the flow of power between the power generation unit 8, battery B, and driving motor M in the power circuit 7 by operating the DC-DC converters and inverters using the gate drive circuit.

[0060] ECU6 is a computer equipped with a processor configured to perform management processes, which will be described below with reference to Figure 3.

[0061] Figure 3 is a flowchart showing the specific procedures for a management process that manages the power generation status of the multiple fuel cell systems 81 to 84 that constitute the power generation unit 8, as well as the power flow in the entire power system 1. This management process is repeatedly executed by the ECU 6 at predetermined control cycles in response to the user operating a start switch (not shown) and activating the ECU 6.

[0062] First, in step ST1, the ECU 6 obtains the load request power, which corresponds to the power required by the electrical load, and then proceeds to step ST2. Here, the electrical load corresponds to the drive motor M in the power system 1 described above. Therefore, the ECU 6 calculates the drive torque requested by the user based on the amount of operation of pedals (not shown), such as the accelerator pedal and brake pedal, by the user driving the fuel cell vehicle, and further obtains the load request power for the drive motor M by converting this requested drive torque into power. Consequently, this load request power is a positive value when the vehicle is being driven and a negative value when the vehicle is being regenerated.

[0063] Next, in step ST2, the ECU 6 obtains a request for the control mode of the power generation unit 8 and the power circuit 7, and proceeds to step ST3. The ECU 6 has defined at least three control modes for the power generation unit 8 and the power circuit 7: endurance mode, performance mode, and charging mode. Here, the endurance mode is a control mode that controls the power generation unit 8 and the power circuit 7 so that suppression of degradation of the multiple fuel cell systems 81 to 84 is prioritized, and is the most basic control mode among these three. The performance mode is a control mode that controls the power generation unit 8 and the power circuit 7 so that response performance is prioritized. The charging mode is a control mode that controls the power generation unit 8 and the power circuit 7 so that charging of battery B is prioritized. In step ST2, the ECU 6 obtains the currently requested control mode from among the multiple control modes, including the endurance mode, performance mode, and charging mode. The ECU 6 obtains a request for the control mode based on at least one of the load request power obtained in step ST1, the charge rate of battery B calculated based on the detected value of the battery sensor unit BS, and the user's operation of the user interface 9. In the following, the currently requested control mode will also be referred to as the requested control mode.

[0064] Next, in step ST3, the ECU 6 obtains the output request power corresponding to the request for the output power of the power generation unit 8, and then proceeds to step ST4.

[0065] As described above, in the power system 1, power can be supplied to the drive motor M, which is an electrical load, from both the power generation unit 8 and the battery B. Therefore, when the requested control mode is endurance mode or performance mode, the ECU 6 calculates the output request power by subtracting the battery request power, which corresponds to the power that can be output from battery B, from the load request power, in order to take into account the power supplied from battery B to the drive motor M.

[0066] As described above, the power system 1 is capable of supplying the power generated by the power generation unit 8 to the drive motor M and the battery B. Therefore, when the request control mode is the charging mode, the ECU 6 calculates the output request power by adding the power that can be supplied to the battery B as a surplus to the load request power, taking into account the power supplied from the power generation unit 8 to the battery B. In this way, when the request control mode is the charging mode, the ECU 6 makes the output request power to the power generation unit 8 larger than the load request power by a predetermined surplus. That is, when the request control mode is the charging mode, the ECU 6 makes the output request power to the power generation unit 8 larger by at least a surplus than when the request control mode is the endurance mode or performance mode.

[0067] Next, in step ST4, the ECU 6 performs a power generation state control process that individually controls the power generation state of each of the multiple fuel cell systems 81 to 84 that make up the power generation unit 8 based on the load request power, request control mode, and output request power obtained through the above procedure, and then moves to step ST5. The specific procedure of this power generation state control process will be described below in order for the cases where the request control mode is endurance mode, the request control mode is performance mode, and the request control mode is charging mode.

[0068] <When the requested control mode is endurance mode> First, the procedure for controlling the power generation state when the requested control mode is endurance mode will be explained. While endurance mode is requested as the control mode, the ECU 6 divides the multiple fuel cell systems 81 to 84 that make up the power generation unit 8 into power generation targets and power generation stop targets, and sets the instruction load for each fuel cell system 81 to 84. Here, the instruction load corresponds to the command value for the output power of the target fuel cell system. Therefore, the instruction load for the fuel cell systems determined to be power generation targets will be a positive value greater than 0, and the instruction load for the fuel cell systems determined to be stopped will be 0. Also, since the output power from the power generation unit 8 to the power circuit 7 is the sum of the output power from each fuel cell system 81 to 84, the ECU 6 sets the instruction load for each fuel cell system 81 to 84 so that the sum of the instruction loads for each fuel cell system 81 to 84 is equal to the output requested power obtained in step ST3.

[0069] As described above, under endurance mode, the priority is to suppress the degradation of the multiple fuel cell systems 81 to 84. Also, the fuel cell stack 2 is basically more prone to degradation the longer the power generation time is. Therefore, in order to prevent uneven degradation among the multiple fuel cell systems 81 to 84, the ECU 6 divides these fuel cell systems 81 to 84 into those to be used for power generation and those to be shut down. More specifically, the ECU 6 calculates the cumulative power generation time by the fuel cell stack 2 for each fuel cell system 81 to 84, and while endurance mode is required, it determines which fuel cell systems 81 to 84 are to be used for power generation and which are to be shut down so that the cumulative power generation time of each fuel cell system 81 to 84 is equal.

[0070] Furthermore, there is an upper limit to the power that can be output from each fuel cell system 81 to 84. For example, if the power output request for the entire power generation unit 8 exceeds the upper limit of power that can be output from one fuel cell system, it is necessary to select at least two of the multiple fuel cell systems 81 to 84 as targets for power generation. Also, for example, if the power output request exceeds the sum of the upper limits of power that can be output from two fuel cell systems, it is necessary to select at least three of the multiple fuel cell systems 81 to 84 as targets for power generation. Also, for example, if the power output request exceeds the sum of the upper limits of power that can be output from three fuel cell systems, it is necessary to select all fuel cell systems 81 to 84 as targets for power generation. Therefore, the ECU 6 determines the number of fuel cell systems to be targeted for power generation (hereinafter also referred to as the "set number") by comparing the upper limit of power that can be output from each fuel cell system 81 to 84 with the power output request obtained in step ST3. After determining the set number of targets for power generation according to the above procedure, the ECU 6 extracts the set number of fuel cell systems from the multiple fuel systems 81 to 84 in order from those with the shortest cumulative power generation time, and determines these extracted fuel cell systems as targets for power generation, and the remaining ones as targets for shutdown.

[0071] Figure 4 shows an example of setting the command load for each fuel cell system 81 to 84 in endurance mode. Figure 4 shows the case where the cumulative power generation time is longest for the first fuel cell system 81, the second fuel cell system 82, the third fuel cell system 83, and the fourth fuel cell system 84. Furthermore, the following explanation will describe the case where the upper limit of power that can be output from each fuel cell system 81 to 84 is A [kW].

[0072] When the requested power output is between 0 and A [kW], the ECU 6 determines that the first fuel cell system 81, which has the shortest cumulative power generation time, will be the target for power generation, and the other fuel cell systems 82 to 84 will be the target for shutdown. In this case, the ECU 6 sets the instructed load for the fuel cell systems 82 to 84, which have been determined to be shut down, to 0 [kW], and changes the instructed load for the first fuel cell system 81, which has been determined to be the target for power generation, between 0 and A [kW] according to the requested power output.

[0073] Next, when the requested power output is between A and 2A [kW], the ECU 6 determines two fuel cell systems 81 and 82, in order of shortest cumulative power generation time, to be used for power generation, and determines the other fuel cell systems 83 and 84 to be used for shutdown. In this case, the ECU 6 sets the instruction load for the fuel cell systems 83 and 84, which have been determined to be used for shutdown, to 0 [kW], and determines the instruction load for the fuel cell systems 81 and 82, which have been determined to be used for power generation, such that their sum equals the requested power output. Here, in order to improve the response performance of the power generation unit 8 and suppress degradation, it is preferable to minimize fluctuations in the instruction load for each fuel cell system. For this reason, as shown in Figure 4, it is preferable for the ECU 6 to fix the instruction load for the first fuel cell system 81, which has already been determined to be used for power generation, at its upper limit of A [kW], and to vary the instruction load for the second fuel cell system 82, which has been newly determined to be used for power generation, between 0 and A [kW] according to the requested power output.

[0074] Next, when the requested power output is 2A to 3A [kW], the ECU 6 determines the three fuel cell systems 81 to 83, in order of shortest cumulative power generation time, as targets for power generation, and determines the other fuel cell system 84 as a target for shutdown. In this case, the ECU 6 sets the instructed load for the fuel cell system 84, which has been determined to be shut down, to 0 [kW], and determines the instructed loads for the fuel cell systems 81 to 83, which have been determined to be targets for power generation, such that their sum equals the requested power output. Furthermore, in order to minimize fluctuations in the instructed load for each fuel cell system, it is preferable for the ECU 6 to fix the instructed loads for the two fuel cell systems 81 and 82, which have already been determined to be targets for power generation, at their upper limit of A [kW], and to vary the instructed load for the newly determined third fuel cell system 83 between 0 and A [kW] according to the requested power output.

[0075] Next, if the power output request is 3A to 4A [kW], the ECU 6 determines all fuel cell systems 81 to 84 as targets for power generation. In this case, the ECU 6 determines the instruction loads for all fuel cell systems 81 to 84 that have been determined as targets for power generation, such that their sum equals the power output request. Furthermore, in order to minimize fluctuations in the instruction loads for each fuel cell system, it is preferable for the ECU 6 to fix the instruction loads for the three fuel cell systems 81 to 83 that have already been determined as targets for power generation at their upper limit of A [kW], and to vary the instruction load for the newly determined fourth fuel cell system 84 between 0 and A [kW] according to the power output request.

[0076] Returning to Figure 3, while the endurance mode is required as the control mode, the ECU 6 divides the multiple fuel cell systems 81 to 84 into those to be used for power generation and those to be used for shutdown using the procedure described above, and then determines the instruction load for each fuel cell system 81 to 84. Based on the determined instruction load, the ECU 6 individually controls the power generation state of each fuel cell system 81 to 84. More specifically, the ECU 6 stops power generation by the fuel cell systems determined to be used for shutdown and operates the anode gas supply device 3, cathode gas supply device 4, etc., so that the fuel cell systems determined to be used for power generation generate power according to the instruction load.

[0077] <When the requested control mode is performance mode> Next, the procedure for controlling the power generation state when the requested control mode is performance mode will be explained. As mentioned above, under performance mode, response performance takes precedence. For this reason, while performance mode is requested as the control mode, the ECU 6 determines all of the multiple fuel cell systems 81 to 84 that constitute the power generation unit 8 to be powered, and sets the instruction load for each fuel cell system 81 to 84. More specifically, the ECU 6 sets the instruction load for each fuel cell system 81 to 84 so that the sum of the instruction loads for each fuel cell system 81 to 84 is equal to the output requested power obtained in step ST3. Furthermore, it is preferable for the ECU 6 to distribute the instruction load to each fuel cell system 81 to 84 evenly, as will be explained below.

[0078] Figure 5 shows an example of setting the instructed load for each fuel cell system 81 to 84 in performance mode.

[0079] When the output power request is between 0 and A [kW], the ECU 6 determines all fuel cell systems 81 to 84 to be used for power generation and distributes the instructed load evenly to each fuel cell system 81 to 84. Therefore, the ECU 6 changes the instructed load for all fuel cell systems 81 to 84 between 0 and A / 4 [kW] according to the output power request.

[0080] Next, when the output power is between A and 2A [kW], the ECU 6 determines that all fuel cell systems 81 to 84 are to be used for power generation and distributes the instructed load evenly to each fuel cell system 81 to 84. Therefore, the ECU 6 changes the instructed load for all fuel cell systems 81 to 84 between A / 4 and A / 2 [kW] according to the output power request.

[0081] Next, when the output power is 2A to 3A [kW], the ECU 6 determines that all fuel cell systems 81 to 84 are to be used for power generation and distributes the instructed load evenly to each fuel cell system 81 to 84. Accordingly, the ECU 6 changes the instructed load for all fuel cell systems 81 to 84 between A / 2 and 3A / 4 [kW] according to the output power request.

[0082] Next, when the output power is 3A to 4A [kW], the ECU 6 determines that all fuel cell systems 81 to 84 are to be used for power generation and distributes the instruction load evenly to each fuel cell system 81 to 84. Therefore, the ECU 6 changes the instruction load for all fuel cell systems 81 to 84 between 3A / 4A [kW] according to the output power request.

[0083] Returning to Figure 3, while the performance mode is requested as the control mode, the ECU 6 determines all of the multiple fuel cell systems 81 to 84 as targets for power generation using the procedure described above, and then determines the instructed load for each fuel cell system 81 to 84. Based on the determined instructed load, the ECU 6 individually controls the power generation state of each fuel cell system 81 to 84. More specifically, the ECU 6 controls the anode gas supply device 3, cathode gas supply device 4, etc., so that all fuel cell systems determined as targets for power generation generate electricity according to the instructed load.

[0084] <When the requested control mode is the charging mode> Next, the procedure for controlling the power generation state when the requested control mode is the charging mode will be explained. As mentioned above, under the charging mode, battery charging takes priority. Also, as mentioned above, when the requested control mode is the charging mode, the output power requested to the power generation unit 8 is set to a value that is at least larger than when the requested control mode is the endurance mode or performance mode, by an amount that is sufficient to charge the battery B (see step ST3 above). For this reason, while the charging mode is requested as the control mode, the ECU 6 sets the power generation target and the instruction load for each fuel cell system 81 to 84 using the same procedure as when the requested control mode is the performance mode. That is, while the charging mode is requested as the control mode, the ECU 6 determines all of the fuel cell systems 81 to 84 that make up the power generation unit 8 as the power generation target in order to have all of them generate power, and sets the instruction load for each fuel cell system 81 to 84 so that the sum of the instruction loads for each fuel cell system 81 to 84 is equal to the output requested power obtained in step ST3. Furthermore, it is preferable that the ECU 6 evenly distributes the instruction load to each fuel cell system 81-84, similar to the performance mode described above. The specific example of setting the instruction load for each fuel cell system 81-84 in the charging mode is the same as in Figure 5, so its explanation is omitted.

[0085] While the charging mode is requested as the control mode, the ECU 6 determines all of the multiple fuel cell systems 81 to 84 as targets for power generation using the procedure described above, and then determines the instructed load for each fuel cell system 81 to 84. Based on the determined instructed load, the ECU 6 individually controls the power generation state of each fuel cell system 81 to 84. More specifically, the ECU 6 controls the anode gas supply device 3, cathode gas supply device 4, etc., so that all fuel cell systems determined as targets for power generation generate electricity according to the instructed load.

[0086] As described above, in the power generation state control process in step ST4, the ECU 6 controls the power generation state of each of the multiple fuel cell systems 81 to 84 that constitute the power generation unit 8 according to the above procedure based on the load power request, the requested control mode, and the output power request.

[0087] Next, in step ST5, the ECU 6 executes output power control processing to control the output power of the power generation unit 8 and the power flow in the power circuit 7 based on the load request power, request control mode, output request power, and instructed load for each fuel cell system 81-84 obtained through the above procedure, and then terminates the management processing shown in Figure 3. Below, the specific procedure of this output power control processing will be explained in order for the cases where the request control mode is endurance mode, the request control mode is performance mode, and the request control mode is charging mode.

[0088] <When the requested control mode is endurance mode> First, the procedure for output power control processing when the requested control mode is endurance mode will be explained. While endurance mode is requested as the control mode, the ECU 6 controls the output power of the power generation unit 8 and the flow of power in the power circuit 7 so that power according to the load request power is supplied to the drive motor M by the output from the power generation unit 8 and battery B. Also, while endurance mode is requested as the control mode, the ECU 6 controls the output power of the power generation unit 8 while limiting its rise rate and fall rate under predetermined positive first rise rate limit [kW / sec] and negative first fall rate limit [kW / sec]. Here, the rise rate limit refers to the upper limit of the amount of increase in the output power of the power generation unit 8 per unit time, and the fall rate limit refers to the lower limit of the amount of decrease in the output power of the power generation unit 8 per unit time. More specifically, the ECU 6 operates the power circuit 7 so that power is output from the power generation unit 8 to the power circuit 7 according to the output request power, power is output from the battery B to the power circuit 7 according to the battery request power, and power is supplied from the power circuit 7 to the drive motor 7 according to the load request power. In this case, it is preferable that the ECU 6 causes each of the fuel cell systems 81 to 84 constituting the power generation unit 8 to output power to the power circuit 7 according to the instructed load determined for each in step ST4. Furthermore, in the case of regenerative operation where the load request power is a negative value, or during deceleration when the output request power to the power generation unit 8 temporarily exceeds the load request power, it is preferable that the ECU 6 supplies the surplus of the output request power relative to the load request power to the battery B and charges the battery B.

[0089] <When the requested control mode is performance mode> Next, the procedure for output power control processing when the requested control mode is performance mode will be explained. While performance mode is requested as the control mode, the ECU 6 controls the output power of the power generation unit 8 and the power flow in the power circuit 7 so that power corresponding to the load request power is supplied to the drive motor M by the output from the power generation unit 8 and battery B. Also, while performance mode is requested as the control mode, the ECU 6 controls the output power of the power generation unit 8 while limiting its rise and fall rates under predetermined positive third rise rate limit [kW / sec] and negative third fall rate limit [kW / sec]. More specifically, the ECU 6 operates the power circuit 7 so that power corresponding to the output request power is output from the power generation unit 8 to the power circuit 7, power corresponding to the battery request power is output from battery B to the power circuit 7, and power corresponding to the load request power is supplied from the power circuit 7 to the drive motor 7. In this case, it is preferable that the ECU 6 causes each of the fuel cell systems 81 to 84 constituting the power generation unit 8 to output power to the power circuit 7 according to the instructed load determined for each in step ST4. Furthermore, in the case of regenerative operation where the load-required power is a negative value, or during deceleration when the output-required power to the power generation unit 8 temporarily exceeds the load-required power, it is preferable that the ECU 6 supplies the surplus of the output-required power relative to the load-required power to the battery B and charges the battery B.

[0090] Furthermore, as mentioned above, under performance mode, response performance takes precedence. For this reason, the positive third rise rate limit is set to a value greater than the positive first rise rate limit in endurance mode (third rise rate limit > first rise rate limit > 0). Also, the negative third fall rate limit is set to a value smaller than the negative first fall rate limit in endurance mode (0 > first fall rate limit > third fall rate limit). As a result, when the request control mode is performance mode, a faster rise and fall in the output power of the power generation unit 8 is permitted than when the request control mode is endurance mode.

[0091] <When the requested control mode is charging mode> Next, the procedure for output power control processing when the requested control mode is charging mode will be explained. While charging mode is requested as the control mode, the ECU 6 controls the output power of the power generation unit 8 and the flow of power in the power circuit 7 so that the battery B is charged by the output from the power generation unit 8 and power according to the load request power is supplied to the drive motor M. Also, while charging mode is requested as the control mode, the ECU 6 controls the output power of the power generation unit 8 while limiting its rising and falling speeds under predetermined positive second rising rate limit [kW / sec] and negative second falling rate limit [kW / sec]. More specifically, the ECU 6 operates the power circuit 7 so that power according to the output request power is output from the power generation unit 8 to the power circuit 7, power according to the load request power is supplied from the power circuit 7 to the drive motor M, and the surplus of the output request power relative to the load request power is supplied from the power circuit 7 to the battery B. In this case, it is preferable that the ECU 6 causes each of the fuel cell systems 81 to 84 constituting the power generation unit 8 to output power to the power circuit 7 according to the instructed load determined for each in step ST4. As explained in step ST3, when the request control mode is the charging mode, the ECU 6 increases the output power requested from the power generation unit 8 by a predetermined surplus amount compared to the load requested power. Therefore, when the request control mode is the charging mode, a portion of the output power of the power generation unit 8 can be supplied to the battery B and charged not only during regenerative driving and deceleration, but also during power driving and acceleration.

[0092] As mentioned above, under charging mode, charging of battery B takes priority. For this reason, the positive second rise rate limit is set to a value greater than the positive first rise rate limit in endurance mode and greater than or equal to the positive third rise rate limit in performance mode (second rise rate limit ≥ third rise rate limit > first rise rate limit > 0). The negative second fall rate limit is set to a value greater than the negative first fall rate limit in endurance mode and the negative third fall rate limit in performance mode (0 > second fall rate limit > first fall rate limit > third fall rate limit). As a result, when the required performance mode is charging mode, a faster increase in the output power of the power generation unit 8 is permitted than when the required control mode is endurance mode. Also, when the required performance mode is charging mode, the decrease in the output power of the power generation unit 8 is restricted more gradually than when the required control mode is endurance mode or performance mode.

[0093] Figure 6 is a time chart showing the change in output power of the power generation unit 8 achieved by the management process described above. In Figure 6, the load-required power is shown by a thick solid line, the output power of the power generation unit 8 in endurance mode is shown by a dashed line, the output power of the power generation unit 8 in performance mode is shown by a broken line, the output power of the power generation unit 8 in charging mode is shown by a solid line, and the upper limit of output of the power generation unit 8 (i.e., 4 × A [kW] in the examples shown in Figures 4 and 5) is shown by a thin dashed line. Figure 6 also shows the case where the output power of battery B is 0 for ease of understanding. In the example shown in Figure 6, the load-required power becomes a predetermined value B which is less than the upper limit of output of the power generation unit 8 between times t0 and t1, the load-required power becomes a predetermined value C which is equal to the upper limit of output of the power generation unit 8 between times t2 and t3, and the load-required power becomes 0 at other times. Figure 6 also shows the case where the second rise rate limit in charging mode and the third rise rate limit in performance mode are equal.

[0094] First, we will explain the change in output power of the power generation unit 8 when the request control mode is endurance mode (see the dashed line in Figure 6). While the request control mode is endurance mode, the ECU 6 calculates the output power required for the power generation unit 8 by subtracting the power that can be output from battery B (0 in the example in Figure 6) from the load request power (see step ST3 in Figure 3). Therefore, while the request control mode is endurance mode, the output power required for the power generation unit 8 is set to a value equal to the load request power. Therefore, in response to the load request power rising to value B at time t0, the ECU 6 increases the output power of the power generation unit 8 toward value B while limiting it under the first rise rate limit. Then, in response to the load request power falling to 0 at time t1, the ECU 6 decreases the output power of the power generation unit 8 toward value 0 while limiting it under the first fall rate limit. Subsequently, at time t2, as the load-required power increases towards value C, which is equal to the upper limit of the output of the power generation unit 8, the ECU 6 increases the output power of the power generation unit 8 towards value C while limiting it under the first increase rate limit. Then, at time t3, as the load-required power decreases to 0, the ECU 6 decreases the output power of the power generation unit 8 towards value 0 while limiting it under the first decrease rate limit. Furthermore, at times t1 and t3 and beyond, during periods when the output power of the power generation unit 8 temporarily exceeds the load-required power, the ECU 6 supplies the surplus of the output power of the power generation unit 8 relative to the load-required power to the battery B and charges the battery B.

[0095] Next, we will explain the change in output power of the power generation unit 8 when the request control mode is performance mode (see dashed line in Figure 6). While the request control mode is performance mode, the ECU 6 calculates the output request power for the power generation unit 8 using the same procedure as in the endurance mode described above (see step ST3 in Figure 3). Therefore, the change in output power of the power generation unit 8 while the request control mode is performance mode is qualitatively the same as in the endurance mode described above, except for the rate of increase and rate of decrease. As described above, while the request control mode is performance mode, the ECU 6 limits the rate of increase of the output power of the power generation unit 8 to a third rate of increase limit that is larger than the first rate of increase limit in endurance mode. Therefore, from time t0 and t2 onward, a faster increase in output power than in endurance mode is permitted. Also, while the request control mode is performance mode, the ECU 6 limits the rate of decrease of the output power of the power generation unit 8 to a third rate of decrease limit that is smaller than the first rate of decrease limit in endurance mode. Therefore, from time t1 and t3 onward, a faster decrease in output power than in endurance mode is permitted. Furthermore, during times t1 and t3 and beyond, if the output power of the power generation unit 8 temporarily exceeds the load-required power, the ECU 6 supplies the surplus of the output power of the power generation unit 8 relative to the load-required power to the battery B and charges the battery B.

[0096] Next, we will explain the change in output power of the power generation unit 8 when the request control mode is the charging mode (see the thin solid line in Figure 6). While the request control mode is the charging mode, the ECU 6 sets the output power request to the power generation unit 8 to a value that is a predetermined surplus larger than the load request power (see step ST3 in Figure 3). For this reason, even when the load request power is 0 before time t0, the ECU 6 causes the power generation unit 8 to output power corresponding to the surplus. Then, at time t0, in response to the load request power rising to value B, the ECU 6 increases the output power of the power generation unit 8 towards the output request power set to be a surplus larger than value B, while limiting it under the second rise rate limit. Then, at time t1, in response to the load request power falling to 0, the ECU 6 decreases the output power of the power generation unit 8 towards the output request power set to be a surplus larger than value 0, while limiting it under the second fall rate limit. Subsequently, at time t2, in response to the load power request rising towards a value C equal to the output upper limit of the power generation unit 8, the ECU 6 increases the output power of the power generation unit 8 towards the output upper limit while limiting it under the second increase rate limit. Then, at time t3, in response to the load power request falling to 0, the ECU 6 decreases the output power of the power generation unit 8 towards an output power request set to be slightly greater than 0 while limiting it under the second decrease rate limit. Furthermore, except for the period when the load power request reaches the output upper limit of the power generation unit 8 (times t2 to t3), during the period when the output power of the power generation unit 8 exceeds the load power request (before time t2 and after time t3), the ECU 6 supplies the surplus of the output power of the power generation unit 8 relative to the load power request to the battery B, thereby charging the battery B. In this way, under charging mode, a longer period can be secured during which the output power of the power generation unit 8 exceeds the load power request compared to endurance mode or performance mode, so that the battery B can be charged quickly.

[0097] Furthermore, while the request control mode is in charging mode, the ECU 6 limits the rate at which the output power of the power generation unit 8 increases under a second rate at which it is set to be equal to the third rate at which it increases under the third rate at which it increases under the third rate at which it increases under the third rate at which it increases under the third rate at which it increases under the third rate at which it increases under the third rate at which it increases under the third rate at which it increases under the third rate at which it decreases increases under the third rate at which it decreases under the third rate at which it increases under the third rate at which it decreases under the third rate at which it increases under the third rate at which it increases under the third rate at which it increases under the third rate at which it increases under the third rate at which it increases under the third rate at which it increases under the third rate at which it increases under the third rate at which it increases under the third rate at which it increases under the third rate at which it increases under the third rate at which it increases under the third rate at which it increases under the third rate at which it increases under the

[0098] The power system 1 and its control method according to this embodiment provide the following effects: (1) While the endurance mode is requested as the control mode, the ECU 6 controls the output power of the power generation unit 8 under a positive first rise rate limit so that power corresponding to the load demand power is supplied to the driving motor M by the output of the power generation unit 8, which is composed of a plurality of fuel cell systems 81 to 84. Also, while the charging mode is requested as the control mode, the ECU 6 controls the output power under a positive second rise rate limit, which is set to be greater than the first rise rate limit, so that the battery B is charged by the output of the power generation unit 8 and power corresponding to the load demand power is supplied to the driving motor M. In this way, the power system 1 allows a faster rise in the output power of the power generation unit 8 when the charging mode is requested, which supplies power to the driving motor M according to its demands while charging the battery B, than when the endurance mode is requested, which supplies power to the driving motor M according to its demands. As a result, under the charging mode, power can be secured to charge the battery B while improving responsiveness when the load demand increases. Furthermore, in power system 1, when endurance mode is required, the increase in output power of power generation unit 8 is limited more gradually than when a charging mode involving charging of battery B is required. This makes it possible to suppress the deterioration of the multiple fuel cell systems 81 to 84 that constitute power generation unit 8 under endurance mode. As described above, power system 1 allows for the control of the output power of the multiple fuel cell systems 81 to 84 under an increase rate limit suitable for endurance mode and charging mode, and ultimately contributes to energy efficiency.

[0099] (2) While the endurance mode is required as the control mode, the ECU 6 divides the multiple fuel cell systems 81 to 84 that make up the power generation unit 8 into those that generate power and those that stop generating power. Thus, the power system 1 can prevent uneven deterioration of each fuel cell system 81 to 84 under the endurance mode.

[0100] (3) While the performance mode is requested as the control mode, the ECU 6 controls the output power under a positive third rise rate limit that is less than or equal to the second rise rate limit and greater than the first rise rate limit, so that power corresponding to the load demand power is supplied to the drive motor M by the output from the power generation unit 8. This makes it possible to improve the responsiveness when the load demand increases under the performance mode compared to the endurance mode.

[0101] (4) While the performance mode is required as the control mode, the ECU 6 causes all of the fuel cell systems 81 to 84 that make up the power generation unit 8 to generate power. This makes it possible to improve the responsiveness when the load demand increases in the performance mode compared to the endurance mode.

[0102] (5) The ECU 6 controls the output power under a negative first decline rate limit when endurance mode is required as the control mode, controls the output power under a negative second decline rate limit set to be greater than the first decline rate limit when charging mode is required as the control mode, and controls the output power under a negative third decline rate limit set to be smaller than the first and second decline rate limits when performance mode is required as the control mode. In this way, when charging mode is required in the power system 1, the decline in output power of the power generation unit 8 is restricted more gradually than when endurance mode or performance mode is required. This makes it possible to suppress the deterioration of the multiple fuel cell systems 81 to 84 while securing power to charge battery B when the load requirement decreases in charging mode. Furthermore, in power system 1, when endurance mode is required, a faster decrease in the output power of the power generation unit 8 is permitted than when charge mode is required. This allows for improved responsiveness to decreases in load demand under endurance mode compared to charge mode. Also, in power system 1, when performance mode is required, a faster decrease in the output power of the power generation unit 8 is permitted than when endurance mode or charge mode is required. This allows for improved responsiveness to decreases in load demand under performance mode compared to endurance mode or charge mode.

[0103] (6) While the endurance mode is requested as the control mode, the ECU 6 controls the output power of the power generation unit 8 under a negative first decline rate limit so that power according to the load demand is supplied to the drive motor M by the output of the power generation unit 8 which is composed of multiple fuel cell systems 81 to 84. Also, while the charging mode is requested as the control mode, the ECU 6 controls the output power under a negative second decline rate limit which is set to be larger than the first decline rate limit described above so that the battery B is charged by the output of the power generation unit 8 and power according to the load demand is supplied to the drive motor M. In this way, the power system 1 limits the decline in the output power of the power generation unit 8 more gradually when the charging mode is requested than when the endurance mode is requested. As a result, under the charging mode, power for charging the battery B when the load demand decreases can be secured while suppressing the deterioration of the multiple fuel cell systems 81 to 84. Also, the power system 1 allows a faster decline in the output power of the power generation unit 8 when the endurance mode is requested than when the charging mode is requested. As a result, under endurance mode, responsiveness during decreases in load demand can be improved compared to charging mode. As described above, the power system 1 can control the output power of multiple fuel cell systems 81-84 under a decrease rate limit suitable for endurance mode and charging mode, thereby contributing to energy efficiency.

[0104] (7) While the performance mode is requested as the control mode, the ECU 6 controls the output power under a third negative value set smaller than the first and second decline rate limits, so that power corresponding to the load demand power is supplied to the drive motor M by the output from the power generation unit 8. This makes it possible to improve the responsiveness when the load demand decreases in the performance mode compared to the endurance mode or charging mode.

[0105] (8) When the endurance mode is required as the control mode, the ECU 6 controls the output power under a positive first rise rate limit; when the charge mode is required as the control mode, it controls the output power under a positive second rise rate limit which is greater than the first rise rate limit; and when the performance mode is required as the control mode, it controls the output power under a positive third rise rate limit which is less than or equal to the second rise rate limit and greater than the first rise rate limit. In this way, when the charge mode is required, the power system 1 allows a faster rise in the output power of the power generation unit 8 than when the endurance mode is required. This makes it possible to secure power to charge the battery B while improving responsiveness when the load demand increases in the charge mode. Also, when the power system 1 is required, it limits the rise in the output power of the power generation unit 8 more gradually than when the charge mode or performance mode is required. This makes it possible to suppress the deterioration of the multiple fuel cell systems 81 to 84 more in the endurance mode than in the charge mode or performance mode. Furthermore, in power system 1, when performance mode is required, a more rapid increase in the output power of the power generation unit 8 is permitted than when endurance mode is required. This allows for improved responsiveness to increased load demands in performance mode compared to endurance mode.

[0106] (9) While the charging mode is requested as the control mode, the ECU 6 increases the output power of the power generation unit 8 by a predetermined surplus amount compared to the load-required power, and charges the battery B with this surplus power. This ensures that power for charging the battery B is available under the charging mode.

[0107] (10) While the charging mode is requested as the control mode, the ECU 6 causes all of the fuel cell systems 81 to 84 that make up the power generation unit 8 to generate power. This ensures that under the charging mode, power is secured to charge the battery B while increasing responsiveness to load requests.

[0108] (11) The ECU 6 acquires a requested control mode based on at least one of the load power request, the charge level of the battery B, and the user's operation of the user interface 9. This allows the output power of the power generation unit 8 to be controlled under a control mode suitable for the user's load usage, the state of the battery B, and the user's intentions.

[0109] (12) According to the control method of the power system 1 according to this embodiment, the output power of the multiple fuel cell systems 81 to 84 can be controlled under rise rate limits suitable for endurance mode, performance mode, and charging mode, thereby contributing to energy efficiency.

[0110] (15) According to the control method of the power system 1 according to this embodiment, the output power of the multiple fuel cell systems 81 to 84 can be controlled under a decline rate limit suitable for the endurance mode, performance mode, and charging mode, thereby contributing to energy efficiency.

[0111] Although one embodiment of the present invention has been described above, the present invention is not limited thereto. Within the scope of the spirit of the present invention, the details of the configuration may be modified as appropriate.

[0112] For example, in the above embodiment, while the charging mode is requested as the control mode, the ECU 6 determines all of the fuel cell systems 81 to 84 constituting the power generation unit 8 to be powered, in the same way as in the performance mode (see step ST4 in Figure 3), but the present invention is not limited to this. While the charging mode is requested as the control mode, the ECU 6 may divide the multiple fuel cell systems 81 to 84 constituting the power generation unit 8 into power generation targets and stop targets for which power generation is stopped, using the same procedure as in the endurance mode.

[0113] Furthermore, in the above embodiment, for example, while the ECU 6 is required to be in performance mode or charging mode as the control mode, it is described as causing all of the multiple fuel cell systems 81 to 84 constituting the power generation unit 8 to generate power and distributing the instruction load to each fuel cell system 81 to 84 evenly. However, the present invention is not limited to this. While the ECU 6 is required to be in performance mode or charging mode as the control mode, it is also possible to cause all of the multiple fuel cell systems 81 to 84 constituting the power generation unit 8 to generate power and set the instruction load to each fuel cell system 81 to 84 to a different value according to the state of each fuel cell system 81 to 84.

[0114] 1...Power system 2...Fuel cell stack 3...Anode gas supply device 4...Cathode gas supply device 5...Cooling system 6...ECU (control unit) 7...Power circuit 8...Power generation unit 81...First fuel cell system 82...Second fuel cell system 83...Third fuel cell system 84...Fourth fuel cell system 9...User interface B...Battery BS...Battery sensor unit M...Train motor (load) W...Drive wheel

Claims

1. A power system comprising: a power generation unit including a plurality of fuel cell systems; loads and batteries connected to the power generation unit; and control means for controlling the output power of the power generation unit, wherein the control means is configured to perform: a process for acquiring load-requested power at the load; a process for acquiring a request for a control mode of the power generation unit; a process for controlling the output power under a positive first rise rate limit so that, while a first control mode is requested as the control mode, power corresponding to the load-requested power is supplied to the load by the output from the power generation unit; and a process for controlling the output power under a positive second rise rate limit set to be greater than the first rise rate limit so that, while a second control mode is requested as the control mode, the battery is charged by the output from the power generation unit and power corresponding to the load-requested power is supplied to the load.

2. The power system according to claim 1, characterized in that the control means divides the plurality of fuel cell systems constituting the power generation unit into power generation targets that generate power and power generation targets that stop power generation while the first control mode is requested as the control mode.

3. The power system according to claim 2, characterized in that the control means is configured to further perform a process to control the output power under a positive third rise rate limit which is less than or equal to the second rise rate limit and greater than the first rise rate limit, so that power corresponding to the load-requested power is supplied to the load by the output from the power generation unit while the third control mode is requested as the control mode.

4. The power system according to claim 3, characterized in that the control means causes all of the fuel cell systems constituting the power generation unit to generate power while the third control mode is requested as the control mode.

5. The power system according to claim 4, characterized in that the control means controls the output power under a negative first decline rate limit while the first control mode is requested as the control mode, controls the output power under a negative second decline rate limit set to be greater than the first decline rate limit while the second control mode is requested as the control mode, and controls the output power under a negative third decline rate limit set to be smaller than the first decline rate limit and the second decline rate limit while the third control mode is requested as the control mode.

6. A power system comprising: a power generation unit including a plurality of fuel cell systems; loads and batteries connected to the power generation unit; and control means for controlling the output power of the power generation unit, wherein the control means is configured to perform: a process for acquiring load-requested power at the load; a process for acquiring a request for a control mode of the power generation unit; a process for controlling the output power under a negative first decline rate limit so that, while a first control mode is requested as the control mode, power corresponding to the load-requested power is supplied to the load by the output from the power generation unit; and a process for controlling the output power under a negative second decline rate limit set to be greater than the first decline rate limit so that, while a second control mode is requested as the control mode, the battery is charged by the output from the power generation unit and power corresponding to the load-requested power is supplied to the load.

7. The power system according to claim 6, characterized in that the control means divides the plurality of fuel cell systems constituting the power generation unit into power generation targets that generate power and power generation targets that stop power generation while the first control mode is required as the control mode.

8. The power system according to claim 7, characterized in that the control means is configured to further perform a process of controlling the output power under a third negative rate limit which is smaller than the first rate limit and the second rate limit, so that while a third control mode is requested as the control mode, the output from the power generation unit supplies power to the load according to the load request power.

9. The power system according to claim 8, characterized in that the control means causes all of the fuel cell systems constituting the power generation unit to generate power while the third control mode is requested as the control mode.

10. The power system according to claim 9, characterized in that the control means controls the output power under a positive first rise rate limit while the first control mode is requested as the control mode, controls the output power under a positive second rise rate limit which is greater than the first rise rate limit while the second control mode is requested as the control mode, and controls the output power under a positive third rise rate limit which is less than or equal to the second rise rate limit and greater than the first rise rate limit while the third control mode is requested as the control mode.

11. The power system according to any one of claims 3 to 5 and 8 to 10, characterized in that the control means increases the output power of the power generation unit by a predetermined surplus amount compared to the load-requested power while the second control mode is requested as the control mode, and charges the battery with the surplus power.

12. The power system according to claim 11, characterized in that the control means causes all of the fuel cell systems constituting the power generation unit to generate power while the second control mode is requested as the control mode.

13. The power system according to 12, characterized in that the control means obtains a request for the control mode based on at least one of the load power request, the battery charge level, and the user's operation of the user interface.

14. A control method for a power system comprising a power generation unit including a plurality of fuel cell systems, and loads and batteries connected to the power generation unit, the method comprising: acquiring load-requested power at the loads; acquiring a request for a control mode of the power generation unit; controlling the output power under a positive first rise rate limit so that, while a first control mode is requested as the control mode, power corresponding to the load-requested power is supplied to the loads by the output from the power generation unit; and controlling the output power under a positive second rise rate limit, which is greater than the first rise rate limit, so that, while a second control mode is requested as the control mode, the battery is charged by the output from the power generation unit and power corresponding to the load-requested power is supplied to the loads.

15. A control method for a power system comprising a power generation unit including a plurality of fuel cell systems, and loads and batteries connected to the power generation unit, the method comprising: a step of acquiring load-requested power at the loads; a step of acquiring a request for a control mode of the power generation unit; a step of controlling the output power under a negative first decline rate limit so that, while a first control mode is requested as the control mode, power corresponding to the load-requested power is supplied to the loads by the output from the power generation unit; and a step of controlling the output power under a negative second decline rate limit, which is greater than the first decline rate limit, so that, while a second control mode is requested as the control mode, the batteries are charged by the output from the power generation unit and power corresponding to the load-requested power is supplied to the loads.

Images