Fuel cell system and maximum power calculation method

Abstract

Fuel cell system (100), comprising: a fuel cell (40) which is supplied with reaction gas to generate power; a measuring device (140, 150) for measuring an output current and an output voltage of the fuel cell (40); and a controller (80) designed to: sequentially, in predefined calculation cycles, to update a first output characteristic curve map, which displays current and power characteristics of the fuel cell (40), and a second output characteristic curve map, which displays current and voltage characteristics of the fuel cell (40), based on the output current and output voltage measured by the measuring device (140, 150); to calculate an available maximum power of the fuel cell (40) by: determining an output setpoint current from the first output characteristic curve map that corresponds to an output setpoint power of the fuel cell (40); determining an output setpoint voltage from the second output characteristic curve map that corresponds to the determined output setpoint current; and using the determined output setpoint current and the determined output setpoint voltage to calculate the available maximum power of the fuel cell (40); to determine whether the fuel cell (40) is in an assumed state in which a corresponding value for the current of the fuel cell (40) in the second output characteristic curve is assumed to be temporarily reduced when the fuel cell (40) is in a state that is during intermittent operation in which the power generation of the fuel cell (40) is temporarily interrupted and the reaction gas is supplied intermittently; that is in a state during operation in which the supply of oxidizer gas, which is the reaction gas, is deficient; or that is during an anomalous reduced voltage state in which the output voltage is reduced to a value that is not greater than an assumed value; and to control an operating point of the fuel cell (40) such that the amount of electricity generated by the fuel cell (40) matches the target output power, wherein the controller (80) is further configured to calculate the maximum power using the first and second output characteristic fields updated immediately before the transition to the assumed state, while determining that the fuel cell (40) is in the assumed state.

Description

BACKGROUND OF THE INVENTION Area of ​​the invention

[0001] The present invention relates to a fuel cell system and a maximum power calculation method. State of the art

[0002] A fuel cell system comprising a fuel cell supplied with reaction gas (fuel gas and oxidizer gas) to generate power has been proposed in the prior art and is in practical application. In such a fuel cell system, air is supplied as the oxidizer gas to a cathode side of the fuel cell, and hydrogen gas is supplied as the fuel gas to an anode side of the fuel cell to generate power or electricity by means of the electrochemical reaction of air and hydrogen gas.

[0003] In such a fuel cell system, a current-voltage curve (hereinafter also referred to as the IV curve) of the fuel cell is determined in order to perform control in order to determine the output power of the fuel cell based on the IV curve in order to improve the power generation efficiency of the fuel cell (see JP 2003-346849A). For the prior art, reference is also made to US 2007 / 0154756A1. SUMMARY OF THE INVENTION

[0004] Since the IV curve varies depending on the operating state or environment of the fuel cell, an IV characteristic value is periodically updated to mitigate errors caused by this variation. However, if the operating state of a fuel cell system with such an IV curve update function changes to intermittent operation, the power generation state decreases. Therefore, in this case, the fuel cell's IV characteristic value is updated to reflect the reduced power generation state. A decrease in the IV characteristic value means that the voltage-to-current (V-current) ratio is reduced under the same operating conditions.

[0005] Intermittent operation is an operating state that occurs temporarily, for example, during idling, low-speed driving, or regenerative braking, and from which the system frequently returns to normal operation within a short time. If the IV parameter is updated during intermittent operation and normal operation is then resumed, the fuel cell is controlled based on an IV curve when the power generation state is reduced until the IV parameter is next updated. In this case, a power output lower than the actual maximum available power of the fuel cell is calculated and regulated as the fuel cell's maximum power output.

[0006] The present invention was made based on these circumstances and aims to create a fuel cell system and a maximum power calculation method with which an error in calculating the available maximum power of the fuel cell can be reduced.

[0007] To solve this problem, a fuel cell system according to a first aspect of the present invention comprises: a fuel cell supplied with reaction gas to generate power; a measuring device for measuring an output current and output voltage of the fuel cell; and a controller configured to sequentially update, in predetermined calculation cycles, a first output characteristic map, which displays current and power characteristics of the fuel cell, and a second output characteristic map, which displays current and voltage characteristics of the fuel cell, based on the output current and output voltage measured by the measuring device; and to calculate an available maximum power of the fuel cell by: determining a target output current from the first output characteristic map, which corresponds to a target output power of the fuel cell;from the second output characteristic curve, a target output voltage is determined that corresponds to the determined target output current; and the determined target output current and the determined target output voltage are used to calculate the available maximum power of the fuel cell; to determine whether the fuel cell is in a presumed state in which a corresponding value for the fuel cell current in the second output characteristic curve is assumed to be temporarily reduced when the fuel cell is in a state that occurs during intermittent operation in which the power generation of the fuel cell is temporarily interrupted and the reaction gas is supplied intermittently; or that occurs during operation in which the supply of oxidizer gas, which is the reaction gas, is deficient.or which is during an anomalously reduced voltage state in which the output voltage is reduced to a value not greater than an assumed value; and to control an operating point of the fuel cell such that a power generation quantity of the fuel cell corresponds to the output set power, the controller being further configured to calculate the maximum power using the first and second output characteristic fields updated immediately before the transition to the assumed state while determining that the fuel cell is in the assumed state.

[0008] A current-voltage curve determination method according to the present invention is a method for calculating the available maximum power of a fuel cell supplied with reaction gas to generate power, wherein the method comprises: a measurement step for measuring an output current and output voltage of the fuel cell; an output characteristic curve update step for updating an output characteristic curve of the fuel cell based on the output current and output voltage measured in the measurement step; a maximum power calculation step for calculating the available maximum power of the fuel cell using the output characteristic curve;and a determination step to determine whether a value of the output characteristic curve is in an assumed state where the output characteristic curve value is assumed to be temporarily reduced, wherein, while determining in the determination step that the output characteristic curve is in the assumed state, the output characteristic curve updated in the output characteristic curve update step immediately before the transition to the assumed state is used for calculating the maximum power in the maximum power calculation step.

[0009] By using the aforementioned configuration and procedure, the fuel cell output characteristic can be updated as needed based on the output current and output voltage measured by the measuring device in order to calculate the available maximum power of the fuel cell using the updated output characteristic. Furthermore, while it is determined that the output characteristic value is in the assumed state where it is assumed to be temporarily reduced, the output characteristic updated immediately before the transition to the assumed state can be used to calculate the maximum power.

[0010] The fuel cell system may further include a notification device designed to inform a user that the maximum power is limited when an output power limitation process is executed to reduce the fuel cell's output current due to a deterioration of the power generation state.

[0011] Another aspect of the invention relates to a maximum power calculation method for calculating the available maximum power of a fuel cell according to claim 3.

[0012] According to the present invention, a fuel cell system can be created which can reduce an error in the calculation of the available maximum power. BRIEF DESCRIPTION OF THE DRAWING Fig. Figure 1 shows a view of the structure of a fuel cell system according to an embodiment of the present invention; Fig. Figure 2 shows a flowchart to explain a maximum power calculation method for the fuel cell system. Fig. 1; Fig. Figure 3 shows a flowchart to explain the maximum power calculation method of the fuel cell system. Fig. 1; and Fig. Figure 4 shows a flowchart to explain the maximum power calculation method of the fuel cell system. Fig. 1. DETAILED DESCRIPTION OF EXECUTION FORMS

[0013] A fuel cell system according to one embodiment of the present invention is described below with reference to the accompanying drawing. The fuel cell system of this embodiment is a power or electricity generation system that is mounted in a hybrid vehicle (FCHV: fuel cell hybrid vehicle) as a moving vehicle.

[0014] Firstly, referring to Fig. 1 The structure of the fuel cell system according to the embodiment is described. Fig. Figure 1 schematically shows the structure of a vehicle in which a fuel cell system 100 is mounted according to the embodiment.

[0015] A fuel cell (abbreviated as FC) 40 is a device for generating power from supplied reaction gases (fuel gas and oxidizer gas), and various types of fuel cells can be used, for example, a solid polymer fuel cell, a phosphoric acid fuel cell, and a molten carbonate fuel cell. The fuel cell 40 has a stacked configuration in which several individual cells with a MEA and the like are stacked in series. An output current and output voltage of this fuel cell 40 at a current operating point are detected by a current sensor 140 and a voltage sensor 150. Fuel gas, for example, hydrogen gas, is supplied from a fuel gas supply source 10 to a fuel electrode (anode) of the fuel cell 40, and oxidizer gas, for example, air, is supplied from an oxidizer gas supply source 70 to an oxygen electrode (cathode).

[0016] The fuel gas supply source 10 consists, for example, of a hydrogen tank, various valves, and the like, and the valve opening, the opening / closing time, and the like are adjusted to regulate the amount of fuel gas supplied to the fuel cell 40. The oxidation gas supply source 70 consists, for example, of an air compressor, a motor for driving the air compressor, an inverter, and the like, and the speed of this motor and the like is adjusted to regulate the amount of oxidation gas to be supplied to the fuel cell 40.

[0017] A battery 60 is a secondary battery or accumulator that can be charged and discharged, and consists, for example, of a nickel-metal hydride battery or the like. Instead of the battery 60, a capacitor that can be charged and discharged can be used. The battery 60 and the fuel cell 40 are connected in parallel with an inverter 110 for a drive motor, and a DC / DC converter 130 is arranged between the battery 60 and the inverter 110.

[0018] The inverter 110, for example, is a pulse-width modulation inverter (PWM inverter) that converts the direct current power output from the fuel cell 40 or the battery 60 into three-phase alternating current power in response to a command from a controller 80 and supplies this to the drive motor 115. The drive motor 115 is a motor for driving wheels 116L, 116R, and the speed of this motor is controlled by the inverter 110.

[0019] The DC-DC converter 130 has a function for stepping up or stepping down a DC voltage input from the battery 60 to output it to the fuel cell 40, as well as a function for stepping up or stepping down a DC voltage input from the fuel cell 40 or the like to output it to the battery 60. The charging and discharging of the battery 60 is achieved through the functions of the DC-DC converter 130. For example, a full-bridge converter consisting of four power transistors and a dedicated control circuit can be used as the DC-DC converter 130.

[0020] Auxiliary units 120, such as vehicle auxiliary units and FC auxiliary units, are connected to the battery 60 and the DC converter 130. The battery 60 serves as the power source for these auxiliary units 120. Vehicle auxiliary units refer to various devices (lighting, air conditioning, hydraulic pump, etc.) used for driving the vehicle, and FC auxiliary units refer to various devices (pumps for supplying fuel gas and oxidizer gas, etc.) used for operating the fuel cell 40.

[0021] The controller 80 consists of a CPU as a processor, as well as a ROM and a RAM as memory and the like, to control each unit of the fuel cell system 100 integrally based on corresponding sensor signal inputs from the voltage sensor 150 (measuring device) for detecting the FC voltage, the current sensor 140 (measuring device) for detecting the FC current, a temperature sensor 50 for detecting the temperature of the fuel cell 40, a SOC sensor (not shown; SOC = state of charge) for detecting the state of charge of the battery 60, an accelerator pedal sensor (not shown) for detecting the position of the accelerator pedal or the like.

[0022] The controller 80 has a function (output characteristic curve update device) for starting the operation of the fuel cell 40 when a start signal is received from an ignition switch, for determining the output voltage and output current of the fuel cell 40 via the voltage sensor 150 and the current sensor 140 for each predefined calculation cycle, and for sequentially updating an IV curve characteristic map of the fuel cell 40. Specifically, the controller 80 assumes that the voltage of the fuel cell 40 can be expressed as a function of the current (linear function or function with a predefined dimension) in order to determine the IV curve characteristic map using a least squares method or the like. The controller 80 updates a current-power curve characteristic map (hereinafter also referred to as the IP curve characteristic map) based on the IV curve characteristic map.It is known that the IP curve characteristic is uniquely defined based on the IV curve characteristic. In this description, either the IV curve characteristic, the IP curve characteristic, or both together are referred to as the output characteristic of the fuel cell 40. The IV curve characteristic and the IP curve characteristic are stored in memory.

[0023] The controller 80 determines the distribution of the output power of the fuel cell 40 and the battery 60, each based on the output characteristic curve, controls the oxidation gas supply system and the fuel gas supply system in such a way that the amount of power generated by the fuel cell 40 corresponds to a target power, and controls the DC converter 130 to regulate the output voltage of the fuel cell 40 in order to control the operating point (output voltage, output current) of the fuel cell 40.

[0024] The Controller 80 has a function (determination device) for determining whether the value of the output characteristic curve is in a state that is assumed to be temporarily reduced (hereinafter referred to as the "assumed state"). Examples of assumed states include cases during intermittent operation, operation under a lack of air, an anomalous reduced voltage, and the like.

[0025] Intermittent operation is a mode for temporarily stopping the power generation of fuel cell 40 in order to intermittently supply reaction gas. Operation under an air-deficient condition is operation in a state where the supply of oxidizer gas is insufficient, corresponding, for example, to a rapid warm-up operation. The anomalous reduced voltage state refers to a state in which the cell voltage or stack voltage of fuel cell 40 is lower than or equal to an assumed voltage. The voltage lower than or equal to the assumed voltage applies in a range where it is assumed that the fuel cell 40 has degraded.

[0026] The controller 80 has a function (maximum power calculation unit) for calculating the available maximum power of the fuel cell 40 using the output characteristic curve. During the assumed state, the controller 80 calculates the maximum power in this function using the output characteristic curve that was updated immediately before the transition to the assumed state. In other words, the controller 80 stops updating the output characteristic curve during the assumed state.

[0027] It should be noted that the number of output characteristic curves is not limited to one. For example, an output characteristic curve that is continuously updated as needed, as well as an output characteristic curve whose update is stopped in the assumed state, can be prepared so that, for the calculation of maximum power, the output characteristic curve can be switched depending on whether the assumed state exists or not.

[0028] If the calculated maximum power is more severely limited than the maximum power available in the given situation, the controller 80 has a function (notification device) to inform a driver that the maximum power is limited. For example, a situation in which an output power limitation process is executed to reduce the output current of the fuel cell 40 due to a deterioration in the power generation state corresponds to a situation in which the maximum power is limited. Conditions in which the output power limitation process is executed include, for example, a situation in which the temperature of the fuel cell 40 is higher than a stable range, a situation in which the residual value of the fuel gas has dropped to a level requiring attention, and a situation in which the moisture content of the fuel cell 40 stack is excessively dry.

[0029] The driver can be notified by displaying a message indicating that maximum power is limited, or by emitting a voice message or sound through a speaker to indicate that maximum power is limited.

[0030] Referring to the Fig. Sections 2 to 4 below describe the maximum power calculation function of the Controller 80. Fig. Figure 2 is a flowchart depicting a process flow when the assumed state is intermittent operation. The process flow is executed repeatedly from the start of operation of fuel cell 40 until the end of operation.

[0031] First, the controller 80 determines whether intermittent operation is being performed (step S101). If this determination is YES, the controller 80 uses the output characteristic curve map, which was updated immediately before the intermittent operation was performed, to calculate the maximum available power of the fuel cell 40 (step S102).

[0032] If, on the other hand, it is determined in step S101 described above that intermittent operation is not carried out (NO in step S101), the controller 80 uses the output characteristic curve map last updated as required for each specified calculation cycle to calculate the available maximum power of the fuel cell 40 (step S103).

[0033] A known technology can be used in a suitable manner as a method for calculating the available maximum power, as described below.

[0034] First, based on driving inputs such as the driver's accelerator pedal press, the controller 80 determines a target output power for the fuel cell 40 according to the required output power. Based on the IP curve map, the controller 80 then determines the target output current corresponding to the target output power. Next, based on the IV curve map, the controller 80 determines the target output voltage corresponding to the target output current. This allows the controller 80 to calculate the maximum power based on the target output current and voltage.

[0035] For example, when the output limiting process is executed, the available maximum power is calculated as follows: based on the IV curve characteristic, the controller 80 determines the output setpoint voltage according to the output-limited setpoint current. This allows the controller 80 to calculate the maximum power based on the output-limited setpoint current and the output setpoint voltage.

[0036] Fig. Figure 3 is a flowchart depicting a process sequence when the assumed operating condition is one of air deficiency. This process sequence is executed repeatedly from the start of operation of fuel cell 40 until the end of operation.

[0037] First, the controller 80 determines whether a state of low air exists during operation (step S201). If this determination is YES, the controller 80 uses the output characteristic curve map updated immediately before the transition to the low air condition to calculate the maximum available power of the fuel cell 40 (step S202).

[0038] If, on the other hand, it is determined in the aforementioned step S201 that no condition exists during operation in an air shortage state (NO in step S201), the controller 80 uses the output characteristic curve map last updated as required for each specified calculation cycle to calculate the available maximum power of the fuel cell 40 (step S203).

[0039] Fig.Figure 4 is a flowchart showing the process sequence when the assumed state corresponds to an anomalous reduced voltage state. This process sequence is executed repeatedly from the start of operation of fuel cell 40 until the end of operation.

[0040] First, the controller 80 determines whether a state corresponding to the anomalous reduced voltage state exists (step S301). If the determination is YES, the controller 80 uses the output characteristic curve map that was updated immediately before the transition to the anomalous reduced voltage state to calculate the maximum available power of the fuel cell 40 (step S302).

[0041] If, on the other hand, it is determined in the aforementioned step S301 that no state corresponding to the anomalously reduced voltage state exists (NO in step S301), the controller 80 uses the output characteristic curve map last updated as required for each specified calculation cycle to calculate the available maximum power of the fuel cell 40 (step S303).

[0042] According to the fuel cell system 100 of the embodiment described above, the output characteristic curve of the fuel cell 40 is updated as needed based on the output current and output voltage measured by the current sensor 140 and the voltage sensor 150, so that the available maximum power of the fuel cell 40 can be calculated using the updated output characteristic curve. Conversely, while the output characteristic curve value is assumed to be in a state where it is assumed that the output characteristic curve value is temporarily reduced, the output characteristic curve updated immediately before the transition to the assumed state is used to calculate the maximum power.

[0043] According to the fuel cell system 100 of the embodiment, an error in the calculation of the available maximum power of the fuel cell 40 can therefore be reduced.

[0044] Although an example of a fuel cell system according to the invention mounted on a fuel cell vehicle is shown in connection with the embodiment described above, the fuel cell system of the present invention can also be mounted on various other mobile vehicles (such as robots, boats, ships, aircraft, etc.) besides the fuel cell vehicle. The fuel cell system of the present invention can also be used as a stationary power generation system, which is used in power generation facilities for buildings (houses, structures, etc.). Furthermore, it can also be applied to portable fuel cell systems. LIST OF REFERENCE SYMBOLS 10 Fuel gas supply source; 40 Fuel cell; 50 Temperature sensor; 60 battery; 70 Oxidation gas supply source; 80 controllers; 100 fuel cell systems; 110 Inverter; 115 Drive motor; 120 auxiliary units; 130 DC / DC converters; 140 Current sensor; 150 voltage sensor;

Claims

[1] Fuel cell system (100), comprising: a fuel cell (40) supplied with reaction gas to generate power; a measuring device (140, 150) for measuring an output current and an output voltage of the fuel cell (40); and a controller (80) configured to: sequentially, in predetermined calculation cycles, update a first output characteristic map indicating current and power characteristics of the fuel cell (40) and a second output characteristic map indicating current and voltage characteristics of the fuel cell (40) based on the output current and output voltage measured by the measuring device (140, 150); to calculate an available maximum power of the fuel cell (40) by: determining a target output current from the first output characteristic map that corresponds to a target output power of the fuel cell (40); determining a target output voltage from the second output characteristic map that corresponds to the determined target output current; and using the determined target output current and the determined target output voltage to calculate the available maximum power of the fuel cell (40); to determine whether the fuel cell (40) is in an assumed state in which a corresponding value for the current of the fuel cell (40) in the second output characteristic map is assumed to be temporarily reduced when the fuel cell (40) is in a state that is during intermittent operation in which the power generation of the fuel cell (40) is temporarily interrupted and the reaction gas is intermittently supplied; that is during operation in a state in which the supply of oxidizing gas, which is the reaction gas, is deficient; or that is during an abnormally reduced voltage state in which the output voltage is lowered to a value not greater than an assumed value; and to control an operating point of the fuel cell (40) so that a power generation amount of the fuel cell (40) matches the target output power, wherein the controller (80) is further configured to, while determining that the fuel cell (40) is in the assumed state, calculate the maximum power using the first and second output maps updated immediately before the transition to the assumed state. [2] The fuel cell system (100) according to claim 1, further comprising a notification device configured to, when an output power limiting process is executed to reduce the output current of the fuel cell (40) due to deterioration of the power generation state, inform a user that the maximum power is limited. [3] A maximum power calculation method for calculating the available maximum power of a fuel cell (40) supplied with reaction gas to generate power, comprising: a measuring step for measuring an output current and an output voltage of the fuel cell (40); an output characteristic updating step for sequentially updating, in predetermined calculation cycles, a first output characteristic map indicating current and power characteristics of the fuel cell (40) and a second output characteristic map indicating current and voltage characteristics of the fuel cell (40) based on the output current and output voltage measured in the measuring step; a maximum power calculation step for calculating the available maximum power of the fuel cell (40) by: determining a target output current corresponding to a target output power of the fuel cell (40) from the first output characteristic map; determining a target output voltage corresponding to the determined target output current from the second output characteristic map; and using the determined target output current and the determined target output voltage to calculate the available maximum power of the fuel cell (40); a determination step for determining whether the fuel cell (40) is in an assumed state in which a corresponding value for the current of the fuel cell (40) in the second output characteristic map is assumed to be temporarily reduced when the fuel cell (40) is in a state that is during intermittent operation in which the power generation of the fuel cell (40) is temporarily interrupted and the reaction gas is intermittently supplied; that is during operation in a state in which the supply of oxidizing gas, which is the reaction gas, is deficient; or that is during an abnormally reduced voltage state in which the output voltage is lowered to a value not greater than an assumed value; and a control step for controlling an operating point of the fuel cell (40) such that a power generation amount of the fuel cell (40) matches the target output power, wherein, while it is determined in the determining step that the fuel cell (40) is in the assumed state, the first and second output characteristic maps updated in the output characteristic updating step immediately before the transition to the assumed state are used for calculating the maximum power in the maximum power calculating step. [4] The maximum power calculation method according to claim 3, further comprising a notifying step of, when an output power limiting process is executed to reduce the output current of the fuel cell (40) due to deterioration of the power generation state, notifying a user that the maximum power is limited.

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