Fuel cell system and its control method

Abstract

Fuel cell system, characterized in that it has: a fuel cell (20); an oxidation gas supply unit (30) configured to supply an oxidation gas to a cathode electrode of the fuel cell (20); and a gas pressure control unit (60) configured to perform control processing by detecting a ratio of a fluctuation of an output of the fuel cell (20) to a fluctuation of the pressure of the oxidation gas as a gas pressure sensitivity at a predetermined time during operation of the fuel cell (20), specifying a characteristic curve which indicates a correspondence relationship between the pressure of the oxidation gas and the output of the fuel cell (20) based on the detected gas pressure sensitivity, and repeatedly controlling the pressure of the oxidation gas based on the specified characteristic curve.

Description

BACKGROUND OF THE INVENTION 1. Technical Field

[0001] The invention relates to a fuel cell system containing a fuel cell and a control method for the fuel cell system. 2. Description of the state of the art

[0002] A fuel cell system that, in response to a deviation of the power output generated by a fuel cell from a target airflow rate corresponding to a required power output, and that controls the air pressure on the cathode inlet side, is available in the prior art (JP 2002-42839 A). The air pressure on the cathode inlet side is controlled by adjusting a backpressure control valve provided on a cathode outlet side (JP 2002-42839 A and JP 2011-29158 A).

[0003] However, the prior art did not adequately consider a control system that is implemented in a case where the amount of power generated by the fuel cell decreases due to a reduction in the surface area of ​​a platinum that serves as an electrode catalyst during the use of the fuel cell.

[0004] Furthermore, DE 10 2005 038 455 A1 discloses a method for determining and / or adjusting the oxidizer volume flow rate supplied to a cathode device of a fuel cell system, in which the oxidizer is supplied to the cathode device via a driven conveying device, the back pressure is measured, the oxidizer is conveyed against the fuel cell system, and the supplied oxidizer volume flow rate is determined from the measured back pressure and one or more drive parameters of the conveying device.

[0005] DE 10 2007 046 058 B4 discloses a method for managing fuel cell power increases in a fuel cell system using an airflow feedback delay, the method comprising the steps of: a. determining properties affecting a gas flow of an airflow path of the fuel cell system between an air-supplying compressor and a cathode outlet of a fuel cell stack by modeling the length and static volume of a duct connecting the compressor to a cathode inlet of the fuel cell stack and the lengths and static volumes of a plurality of channels formed between the cathode inlet and the cathode outlet; b. determining an air mass flow in the airflow path between the compressor and the cathode outlet; c. determining a gas pressure of the fuel cell system on the cathode side; d.an airflow feedback delay is calculated as a function of the properties of the airflow path, the air mass flow rate, and the gas pressure that affect the gas flow; and e. a withdrawal of current from the fuel cell stack is delayed by an external circuit by the magnitude of the airflow feedback delay.

[0006] JP 2010 - 267 516 A discloses a fuel cell system comprising a storage part that stores a corresponding relationship between a surface area of ​​a catalyst and a gas diffusion resistance in a state where the surface area of ​​the catalyst is smaller than a predetermined threshold, a sensing part that detects a value of the surface area of ​​the catalyst, and a control part that controls at least one of a gas pressure and a gas flow rate based on the corresponding relationship in a case where the detected value of the surface area of ​​the catalyst is smaller than the threshold.

[0007] Furthermore, JP H01-122570A discloses a lifetime prediction method for a fuel cell in which many unit cells are stacked to form a cell stack. Under normal operating conditions, a switching valve is opened, and air drawn from the atmosphere is supplied to the air electrode side of the stack for power generation. Under these conditions, the output voltage is measured continuously. Conversely, the valve is temporarily closed, a valve is opened, oxidizer gas with a high oxygen concentration is supplied, and the output voltage is measured. These processes are repeated as needed to determine the aging change in the output voltage and the voltage difference.The deterioration of the electrode catalyst layer on the air electrode side and the degree of reduction of the initial characteristic caused by excessive humidification by the electrode electrolyte, as well as their future value, are estimated based on the aging change pattern, and the cell lifetime is predicted and assessed. SUMMARY OF THE INVENTION

[0008] The aforementioned problems and the resulting task are solved by the subject matter of the dependent claims. Advantageous embodiments of the invention are the subject matter of the subsequent dependent claims.

[0009] The invention provides a fuel cell system and a control method thereof, with which the fuel cell system can be controlled according to a reduction of a surface area of ​​a platinum serving as an electrode catalyst.

[0010] A first explanatory aspect of the present disclosure is a fuel cell system comprising: a fuel cell; an oxidation gas supply unit configured to supply an oxidation gas to a cathode electrode of the fuel cell; and a gas pressure control unit configured to detect, as a gas pressure sensitivity, a ratio of a fluctuation of a fuel cell output to a fluctuation of the oxidation gas pressure, specify a correspondence relationship between the oxidation gas pressure and the fuel cell output based on the detected gas pressure sensitivity, and control the oxidation gas pressure based on the specified correspondence relationship.

[0011] With this aspect of the fuel cell system, if the surface area of ​​the platinum serving as an electrode catalyst of the cathode electrode decreases during fuel cell operation, leading to a reduction in fuel cell output, the pressure of the oxidation gas can be controlled while taking gas pressure sensitivity into account, thereby ensuring a more reliable required output. This allows the fuel cell system to maintain high-performance generation.

[0012] The gas pressure control unit can be configured to receive a required output requested by the fuel cell (a setpoint gas pressure), calculate the corresponding oxidation gas pressure by comparing the required output with the relevant relationship, and then adjust the oxidation gas pressure to match the setpoint gas pressure. This allows for simple control of the oxidation gas pressure, resulting in even higher power generation performance.

[0013] The fuel cell system can further include a storage unit that stores tabular data in which correspondence relationships between the oxidation gas pressure and the fuel cell output are mapped to individual values ​​of gas pressure sensitivity, and a gas pressure control unit that can be configured to specify the correspondence relationship between the oxidation gas pressure and the fuel cell output by selecting the relationship that corresponds to the gas pressure sensitivity detected in the tabular data. According to this configuration, the correspondence relationship between the oxidation gas pressure and the fuel cell output can be specified quickly.

[0014] The fuel cell system can further include a backpressure control valve configured to regulate the pressure of the oxidation gas discharged from the fuel cell's cathode electrode outlet, and a gas pressure control unit configured to control the oxidation gas pressure by adjusting the opening of the backpressure control valve. According to this configuration, by controlling the pressure (a backpressure) of the oxidation gas discharged from the cathode electrode outlet, the oxidation gas can be controlled with a high degree of responsiveness.

[0015] The gas pressure control unit can be configured to detect the gas pressure sensitivity and specify the correspondence between the oxidation gas pressure and the fuel cell output at a specific time to increase the oxidation gas pressure. According to this configuration, the required output can be obtained with a high degree of responsiveness when a request to increase the fuel cell output is issued.

[0016] The gas pressure control unit can detect the gas pressure sensitivity and specify the correspondence relationship between the oxidation gas pressure and the fuel cell output at a point in time when the fuel cell load begins to shift to an operating point with a predetermined load. According to this configuration, when a high-load or low-load request is issued, an output corresponding to the high-load or low-load request can be obtained with a high degree of responsiveness.

[0017] The fuel cell may contain an electrode catalyst; the correspondence relationship between the pressure of the oxidation gas and the output of the fuel cell may include a first correspondence relationship and a second correspondence relationship, the second correspondence relationship being defined such that a magnitude or size of the pressure of the oxidation gas of the second correspondence relationship corresponds to an identical output of the fuel cell greater than that of a magnitude or size of the second correspondence relationship.The magnitude of the oxidation gas pressure of the first correspondence relationship is determined by the gas pressure control unit. This relationship can be specified by selecting the first correspondence relationship when the fuel cell is not in a predetermined operating state where the utilization rate of the platinum contained in the electrode catalyst decreases, and by selecting the second correspondence relationship when the fuel cell is in the predetermined operating state. According to this configuration, the required output can be obtained more reliably even in an operating state where the utilization rate of the platinum decreases.

[0018] The predetermined operating state can be a flooded state of the fuel cell. According to this configuration, the required output can be ensured more reliably, even when the fuel cell is in a flooded state.

[0019] The predetermined operating state can be an idle state of the fuel cell. According to this configuration, the required output can be reliably ensured even when the fuel cell is in an idle state.

[0020] The fuel cell system can further include a non-volatile memory configured to continue storing the correspondence relationship between the oxidation gas pressure and the fuel cell output, as specified by the gas pressure control unit, after the fuel cell power supply has been switched off. The gas pressure control unit can be configured to control the oxidation gas pressure within a predetermined period based on the correspondence relationship stored in the non-volatile memory. This configuration can enhance processing response.

[0021] The fuel cell system can further include a flood detection unit configured to determine whether flooding has occurred in the fuel cell by comparing a specific gas pressure sensitivity, determined by the correspondence relationship between the oxidation gas pressure and the fuel cell output specified by the gas pressure control unit, with an actual gas pressure sensitivity derived from the actual oxidation gas pressure and the actual fuel cell output, and by comparing a specific output absolute value, which is an absolute value of the output corresponding to the specific gas pressure sensitivity, with an actual output absolute value. According to this configuration, the occurrence of flooding can be detected with a high degree of accuracy.

[0022] If the flood determination unit determines that flooding has occurred, it can be configured to perform flood prevention processing. According to this configuration, flooding can be avoided, thereby further improving power generation performance.

[0023] The fuel cell system can further include a battery and a gas flow rate control unit configured to control the flow rate of the oxidation gas such that, when the gas pressure control unit controls the pressure of the oxidation gas while the battery is in a predetermined state, the fuel cell output reaches the required output earlier than when the pressure of the oxidation gas reaches the set gas pressure. According to this configuration, a power increase generated when the fuel cell output reaches the required output earlier than when the pressure of the oxidation gas reaches the set gas pressure can be allocated to an amount of power required to improve the battery's state of health, and therefore a balance between demand and output can be achieved.The power demand and supply are maintained consistently throughout the entire fuel cell system.

[0024] The fuel cell system can further include a state-of-charge (SOC) sensing unit configured to detect the battery's state of charge (SOC). It can determine that the battery is in a predetermined state when the detected SOC deviates from a predefined range. According to this configuration, a balance between power demand and supply can be maintained throughout the entire fuel cell system even when the battery's SOC deviates from the appropriate range.

[0025] The fuel cell system can further include a gas flow rate control unit configured to control the flow rate of the oxidation gas such that, when the gas pressure control unit controls the pressure of the oxidation gas while the fuel cell is in a predetermined state, the fuel cell output reaches the required output earlier than the point at which the oxidation gas pressure reaches the set gas pressure. According to this configuration, a power increase generated when the fuel cell output reaches the required output earlier can be allocated to the amount of power needed to improve the state of the fuel cell, and therefore a balance between power demand and supply can be maintained throughout the entire fuel cell system.

[0026] It can be determined that the fuel cell is in the predetermined state when flooding occurs. According to this configuration, a balance between power demand and supply can be maintained throughout the entire fuel cell system when the fuel cell is in the flooded state.

[0027] A second explanatory aspect of the present disclosure is a fuel cell system comprising: a fuel cell; an oxidation gas supply unit configured to supply an oxidation gas to a cathode electrode of the fuel cell; a gas pressure control unit configured to control the pressure of the oxidation gas; and a platinum surface area estimation unit configured to detect a ratio of a fluctuation in a fuel cell output to a fluctuation in the pressure of the oxidation gas as a gas pressure sensitivity, and to estimate a platinum surface area of ​​the cathode electrode based on the detected gas pressure sensitivity. With the fuel cell system according to this aspect, the platinum surface area of ​​the cathode electrode can be estimated with a high degree of accuracy.

[0028] A third explanatory aspect of the present disclosure is a control method for a fuel cell system comprising a fuel cell and an oxidation gas supply unit configured to supply an oxidation gas to a cathode electrode of the fuel cell, comprising: detecting a ratio of a fluctuation of a fuel cell output to a fluctuation of an oxidation gas pressure as a gas pressure sensitivity; specifying a correspondence relationship between the pressure of the oxidation gas and the fuel cell output based on the detected gas pressure sensitivity; and controlling the pressure of the oxidation gas based on the specified correspondence relationship.The control method for a fuel cell system according to this aspect, similar to the fuel cell system according to the first aspect, can ensure the required output more reliably, and thereby achieve higher power generation performance.

[0029] A fourth explanatory aspect of the present disclosure is a control method for a fuel cell system comprising a fuel cell and an oxidation gas supply unit configured to supply oxidation gas to a cathode electrode of the fuel cell. This method includes: controlling the pressure of the oxidation gas; detecting the ratio of a fluctuation in the fuel cell output to a fluctuation in the pressure of the oxidation gas as the gas pressure sensitivity; and estimating a platinum surface area of ​​the cathode electrode based on the detected gas pressure sensitivity. Using the control method for a fuel cell system according to this aspect, similar to the fuel cell system according to the second aspect, the platinum surface area of ​​the cathode electrode can be estimated with a high degree of accuracy. BRIEF DESCRIPTION OF THE FIGURES

[0030] Features, advantages and technical and industrial significance of exemplary embodiments of the invention are described below with reference to the accompanying figures, in which the same reference numerals denote the same components, and wherein: Fig. 1 is a descriptive view that represents a configuration of a fuel cell system as a first embodiment of the invention; Fig. 2 is a flowchart that represents a cathode backpressure control process to be performed by the control unit; Fig. 3 is a diagram that represents a cathode backpressure output characteristic curve; Fig. 4 is a flowchart that represents a cathode backpressure control process according to a second embodiment; Fig. 5 is a diagram that represents a cathode backpressure output characteristic curve according to the second embodiment; Fig. 6 is a diagram that represents a cathode backpressure output characteristic curve according to a modified example of the second embodiment; Fig. 7 is a flowchart that represents a characteristic curve estimation processing according to a third embodiment; Fig. 8 is a diagram that represents a cathode backpressure output characteristic curve according to the third embodiment; Fig. 9 is a flowchart representing a characteristic curve estimation processing according to a fourth embodiment; Fig. 10 is a flowchart that represents a characteristic curve estimation processing according to a second modified example of the fourth embodiment; Fig. 11 is a flowchart representing a characteristic curve estimation processing according to a sixth embodiment; Fig. 12 is a flowchart representing a humidity control processing according to a seventh embodiment; Fig. Figures 13A to 13D depict views that show a fluctuation of a cathode backpressure output characteristic curve depending on the presence or absence of flooding under the corresponding conditions; Fig. 14 is a flowchart that represents an overall control processing according to an eighth embodiment; Fig. 15 is a diagram that shows a correspondence relationship between the cathode back pressure and a cathode flow rate during the execution of the cathode back pressure control processing; Fig. 16 is a time diagram that represents a fluctuation in the cathode back pressure, the cathode flow rate and an output of a fuel cell; Fig. 17 is a flowchart representing an overall tax processing according to a ninth embodiment; and Fig. 18 is a flowchart that represents an overall tax processing according to a tenth embodiment. DETAILED DESCRIPTION OF THE EXECUTION FORMS

[0031] As previously considered in the prior art, no adequate consideration has been given to a control system that would be implemented in a case where the amount of power generated by a fuel cell decreases due to a reduction in the surface area of ​​the platinum that serves as an electrode catalyst, which is used in conjunction with the fuel cell. It may therefore be impossible to obtain high power generation performance by implementing a control system such as that described in JP 2002-42839 A. It is also difficult to ensure a required amount of power generation. Furthermore, the response time of an air pressure control system is low.Furthermore, there is a requirement to improve driving performance when a fuel cell system is installed in a vehicle, to reduce the size and cost of the fuel cell system, to reduce the amount of natural resources consumed, to simplify a manufacturing process, to improve user-friendliness, etc.

[0032] The invention can solve at least some of the problems described above by enabling it to control a fuel cell system according to a reduction of a surface area of ​​platinum serving as an electrode catalyst.

[0033] Next, the embodiments of the invention will be described. First embodiment

[0034] Fig. Figure 1 is an illustrative view showing a configuration of a fuel cell system 10, which serves as a first embodiment of the invention. In this embodiment, the invention is applied to a vehicle-side vehicle generation system for a fuel cell vehicle. As shown in Fig. As shown in Figure 1, the fuel cell system 10 includes a fuel cell (FC) 20, which performs power generation upon receiving a supply of an oxidation gas and a fuel gas, and generates electrical power through power generation; an oxidation gas piping system 30, which supplies air serving as the oxidation gas to the fuel cell 2; a fuel gas piping system 40, which supplies hydrogen gas serving as the fuel gas to the fuel cell 20; an electrical power system 50, which charges or discharges electrical power to and from the system; a control unit 60, which performs overall control of the entire system; etc.

[0035] Fuel cell 20 is a solid polymer electrolyte fuel cell and comprises a stacked structure in which a large number of individual cells are stacked. Each individual cell of fuel cell 20 includes a cathode electrode (an air electrode) and an anode electrode (fuel electrode) on corresponding surfaces of an electrolyte formed by an ion-exchange membrane. A porous carbon material, for example, is used as the base for the electrodes containing the cathode and anode electrodes, and platinum (Pt) is used as a catalyst for the electrodes (an electrode catalyst). Furthermore, a pair of separators is provided to sandwich the cathode and anode electrodes together on both sides.Fuel gas is fed into one of the separators via a fuel gas flow path, and oxidation gas is fed into the other separator via an oxidation gas flow path. As a result of this gas supply, the fuel cell 20 generates electrical power.

[0036] A current sensor 2a, which detects a current (an output current) during power generation, a voltage sensor 2b, which detects a voltage, and a temperature sensor 2c, which detects a temperature of the fuel cell 20, are attached to the fuel cell 20.

[0037] The oxidation gas piping system 30 includes an air compressor 31, an oxidation gas supply passage 32, a humidification module 33, a cathode exhaust gas flow passage 34, a motor M1 that drives the air compressor 31, etc.

[0038] The air compressor 31 is driven by a motive force from the motor M1, which is actuated by a control command from the control unit 60, to supply oxygen (oxidation gas), which is drawn from ambient air via an air filter (not shown in the figure), and the compressed oxygen to the cathode electrode of the fuel cell 20. A speed sensor 3a, which detects the rotational speed (one rotation per predetermined time; similar to what follows) of the motor M1, is attached to the motor M1. The oxidation gas supply passage 32 is a gas flow passage for guiding the oxygen supplied by the air compressor 31 to the cathode electrode of the fuel cell 20. Cathode exhaust gas is discharged from the cathode electrode of the fuel cell through the cathode exhaust flow passage 34. The cathode exhaust gas contains the exhaust gas of the oxygen after contributing to a fuel cell reaction in the fuel cell 20.The cathode exhaust contains moisture generated by the cell reaction in the fuel cell 20 and is therefore in a state of high humidity.

[0039] The humidity module 33 humidifies the oxidation gas supplied to the fuel cell 20 by facilitating a moisture exchange between the low-humidity oxidation gas flowing through the oxidation gas supply passage 32 and the high-humidity cathode exhaust flowing through the cathode exhaust flow passage 34. The cathode exhaust flow passage 34 is a gas flow passage for discharged to the outside of the system, and a backpressure control valve A1 is located near a cathode electrode outlet of the gas flow passage. The pressure (hereinafter referred to as the "cathode backpressure") of the oxidation gas discharged by the fuel cell 20 is regulated by the backpressure control valve A1. A pressure sensor 3b, which detects the cathode backpressure, is mounted on the cathode exhaust flow passage 34 between the fuel cell 20 and the backpressure control valve A1.

[0040] The fuel gas piping system 40 includes a fuel gas supply source 41, a fuel gas supply source 42, a fuel gas recirculation passage 43, an anode exhaust gas flow passage 44, a hydrogen circulation pump 45, a check valve 46, a motor M2 for driving the hydrogen circulation pump 45, etc.

[0041] The fuel gas supply source 41 supplies the fuel gas, such as hydrogen gas, to the fuel cell 20 and is formed, for example, by a high-pressure hydrogen tank, a hydrogen storage tank, or the like. The fuel gas supply passage 42 is a gas flow passage for guiding the fuel gas released by the fuel gas supply source 41 to the anode electrode of the fuel cell 20, and valves, such as a tank valve H1, a hydrogen supply valve H2, and a fuel cell inlet valve H3, are arranged in the gas flow passage in sequence from an upstream side to a downstream side. The tank valve H1, the hydrogen supply valve H2, and the fuel cell inlet valve H3 are shut-off valves for supplying (or interrupting the supply of) the fuel gas to the fuel cell 20 and are, for example, designed as solenoid valves.

[0042] The fuel gas recirculation passage 43 is a control gas flow passage for recirculating unreacted fuel gas to the fuel cell 20. A fuel cell outlet valve H4, the hydrogen circulation pump 45, and the check valve 46 are arranged in the gas flow passage in sequence from upstream to downstream. Low-pressure unreacted fuel gas supplied by the fuel cell 20 is pressurized by the hydrogen circulation pump 45, which is driven by the motor M2 actuated by a control command from the control unit 60, and fed to the fuel gas supply passage 42. Backflow of fuel cell gas from the fuel gas supply passage 42 to the fuel gas recirculation passage 43 is suppressed by the check valve 46.The anode exhaust gas flow passage 44 is a gas flow passage for releasing an anode exhaust gas containing hydrogen exhaust gas, which is released from the fuel cell 20 to the outside of the system, and a drain valve H5 is arranged in the gas flow passage.

[0043] The electrical power system 50 includes a high-pressure direct current / direct current (DC / DC) converter 51, a battery 52, a traction inverter 53, an auxiliary inverter 54, a traction motor M3, an auxiliary motor M4, etc.

[0044] The high-pressure DC / DC converter 51 is a DC / DC converter with a function for regulating a DC voltage input from the battery 52 and outputting the regulated DC voltage to the traction inverter 53, and a function for regulating a DC voltage input from the fuel cell 20 or the traction motor M3 and outputting the regulated DC voltage to the battery 52. ​​Charging and discharging of the battery 52 is achieved by these functions of the high-pressure DC / DC converter 51. Furthermore, the output voltage of the fuel cell 20 is controlled by the high-pressure DC / DC converter 51.

[0045] Battery 52 is a rechargeable / dischargeable secondary battery. Various types of secondary batteries, such as a nickel-hydrogen battery or the like, can be used. Battery 52 can be charged with an overvoltage under the control of a battery computer (not shown in the figure) and can also supply additional power. A portion of the DC power generated by the fuel cell 20 is boosted or attenuated by the high-pressure DC / DC converter 51 and used to charge battery 52. ​​A state-of-charge (SOC) sensor 5a, which detects the state of charge (SOC) of battery 52, is attached to battery 52. ​​It should be noted that a rechargeable / dischargeable storage device other than a secondary battery, such as a capacitor, can be used instead of battery 52.

[0046] A traction inverter 53 and the auxiliary inverter 54 are pulse-width modulation (PWM) inverters with a pulse-width modulation system that converts the DC power output of the fuel cell 20 or the battery 52 into the three-phase AC voltage in response to a given control command and supplies the three-phase AC voltage to the traction motor M3 and the auxiliary motor M4. The traction motor M3, which is an example of a load power source, is a motor (a vehicle drive motor) for driving vehicle wheels 71, 72. A speed sensing sensor 5b, which detects the rotational speed of the traction motor M3, is attached to the traction motor M3. The auxiliary motor M4 is a motor for driving various accessories. The motor M1, which drives the air compressor 31, the motor M2, which drives the hydrogen circulation pump 45, etc. are collectively referred to as auxiliary motor M4.

[0047] The control unit 60 comprises a central processing unit (CPU), a read-only memory (ROM), a working memory (RAM), etc., and provides overall control of the corresponding parts of the system based on input sensor signals. In particular, the control unit 60 calculates a required amount of power generation (hereinafter referred to as a "required output") required by the fuel cell 20, based on the corresponding sensor signals transmitted by an accelerator pedal sensor 81, which detects the rotation of an accelerator pedal 80, the SOC sensor 5a, the speed sensors 3a, 5b, etc.

[0048] The control unit 60 then controls an output voltage and an output current of the fuel cell 20 such that the fuel cell 20 generates the required output. Furthermore, the control unit 60 controls the traction motor M3 and the auxiliary motor M4 to control output pulses and the like of the traction inverter 53 and the auxiliary inverter 54.

[0049] In fuel cell 20, a platinum surface area decreases as the operating time of fuel cell 20 increases over time, and this reduces the output voltage. In other words, if the platinum surface area on the cathode catalyst layer decreases as the operating time of fuel cell 20 increases, it becomes impossible to obtain the required output power from fuel cell 20. Therefore, the control unit 60 ensures that the required output power can be obtained by estimating the platinum surface area and controlling the backpressure control valve A1 according to this estimate.This control processing (cathode backpressure control processing) is implemented by the operation of a required output acquisition unit 61, a gas pressure sensitivity sensing unit 62, a correspondence relationship calculation unit 63, a target gas pressure calculation unit 64, and a gas pressure modification unit 65. The corresponding units 61 to 65 are described in detail below. The cathode backpressure control processing is described in detail below.

[0050] Fig. Figure 2 is a flowchart illustrating cathode backpressure control processing performed by the control unit 60. This processing is executed repeatedly at predetermined time intervals (e.g., every 10 ms). When processing begins, the control unit 60 first determines whether an instantaneous time (a time at which the cathode backpressure control processing is executed) corresponds to a time to start increasing the cathode backpressure (a cathode backpressure increase time) (step S110). When a driver creates a load request by depressing the accelerator pedal 80, the amount of oxidizing gas supplied by the air compressor 31 is increased by control processing (not shown in the figures), resulting in an increase in cathode backpressure. This leads to a determination at step S110 as to whether an instantaneous time corresponds to the cathode backpressure increase time.

[0051] If, at step S110, it is determined that the current time corresponds to the cathode backpressure increase time, the control unit 60 advances the processing to step S120, in which the processing is carried out to obtain a cathode backpressure P from the pressure sensor 3p. Next, the control unit 60 calculates a fluctuation ΔP of the cathode backpressure from a cathode backpressure obtained during the previous execution of the cathode backpressure control processing by subtracting the previous cathode backpressure from the cathode backpressure P obtained in step S110 (step S130).

[0052] Next, the control unit 60 receives an output W from the fuel cell 20 (step S140). Specifically, the control unit 60 determines an output power as output W by obtaining the current from the current sensor 2a and the voltage from the voltage sensor 2b, and multiplying the current by the voltage. Next, the control unit 60 calculates a fluctuation ΔW of the output from an output obtained during the previous execution of the cathode backpressure control processing by subtracting the previous output from the received output W (step S150).

[0053] Next, the control unit 60 divides the output fluctuation ΔW by the cathode backpressure fluctuation ΔP and stores the resulting quotient as a cathode backpressure sensitivity S (step S160). In other words, the cathode backpressure sensitivity S is stored in RAM as a ratio of ΔW to ΔP. The control unit 60 then performs the processing to estimate a cathode backpressure output characteristic curve based on the cathode backpressure sensitivity S (step S170).

[0054] Fig. Figure 3 is a diagram representing a cathode backpressure output characteristic curve. As shown by the diagram, when the cathode backpressure P is plotted on the abscissa, an output W of the fuel cell 20 is plotted on the ordinate, and the output W corresponding to the cathode backpressure P is plotted, resulting in a cathode backpressure output characteristic curve indicated by curve C1, for example. Curve C1 and curves C2 and C3, to be described below, can be determined beforehand by experiment or simulation. According to curve C1, the output W increases as the cathode backpressure P increases, and after reaching a peak value, the output W decreases as the cathode backpressure P increases.

[0055] Curve C1 shows a case where the platinum surface area of ​​the cathode electrode is at a maximum, or in other words, an initial operating state where there is no change in the state of the electrode catalyst. As the usable operating time of the fuel cell increases such that the platinum surface area decreases, the cathode backpressure output characteristic curve varies from curve C1 to curve C2. On curve C2, the output W is smaller than on curve C1 in all regions, and the difference in output W relative to curve C1 increases as the cathode backpressure P decreases. In other words, a slope k2 (= ΔW2 / ΔP1) during an increasing period of curve C2 is greater than a slope k1 (= ΔW1 / ΔP1) during the increasing period of curve C1.

[0056] Curve C3 shows a case where the platinum surface area is further reduced by curve C2. A slope k3 (= ΔW3 / ΔP1) in the increasing period of curve C3 is greater than the slope k2 in the increasing period of curve C2. The "increasing period" is a period in which the output W reaches a predetermined proportion (90%, for example) of the peak value, and the slope of the period takes on essentially constant values ​​k1, k2, k3 on the corresponding curves C1, C2, C3. It is evident from the above that the cathode backpressure output characteristic curve varies in shape according to a magnitude (an approximate magnitude) of the platinum surface area, and that the shape is determined according to the slopes k1, k2, k3.The slope k1, k2, k3 takes on a value obtained by dividing the fluctuation ΔW of the output over the increasing period of the characteristic curve (the curve) by the fluctuation ΔP of the cathode back pressure, and corresponds to the cathode back pressure sensitivity S, which is determined in step S160.

[0057] In this embodiment, the cathode backpressure increase time point is detected in step S110, and it is then assumed that the cathode backpressure increase time point is contained within the rising period. The processing to determine the cathode backpressure sensitivity S is performed in step S160 at the cathode backpressure increase time point. Next, the processing to estimate the cathode backpressure output characteristic curve based on the cathode backpressure sensitivity S is performed in step S170.In particular, the table data, in which the cathode backpressure output characteristic curves are assigned according to a plurality of slope values, are pre-stored in the ROM of memory unit 60, and the CPU of control unit 60 determines the cathode backpressure output characteristic curve by selecting a slope value corresponding to the cathode backpressure sensitivity S determined in step S160 from the table data and by extracting the cathode backpressure output characteristic curve assigned to the slope value from the table data. It should be noted that the number of cathode backpressure output characteristic curves contained in the table data is not necessarily limited to three curves, as in the example of . Fig. Figure 3 shows that a larger number of curves can be provided. Furthermore, the number of cathode backpressure output characteristic curves contained in the table data can be set to a specific value, and characteristic curves can be obtained between adjacent characteristic curves through interpolation.

[0058] Returning to Fig. After step S170 is executed, control unit 60 receives a required output TW, which is required by fuel cell 20 (step S180). The required output TW corresponds to a previously mentioned required power generation amount and, as described above, is calculated based on the corresponding sensor signals transmitted by the accelerator pedal sensor 81, the SOC sensor 5a, the speed sensing sensors 3a, 5b, etc.

[0059] Next, control unit 60 refers to the cathode backpressure output characteristic curve obtained in step S170 to calculate a target cathode backpressure TP according to the required output TW obtained in step S140 (step S190). For example, if the platinum surface area decreases slightly such that the cathode backpressure output characteristic curve obtained in step S170 matches curve C2 in Fig. If the value is 3, the cathode backpressure P is determined according to the required output TW obtained in step S140 on curve C2 as the target cathode backpressure TP (TP1 in the drawing). For example, if the platinum surface area decreases so significantly that the cathode backpressure output characteristic curve obtained in step S170 exceeds curve C3 in Fig. 3, the cathode back pressure P3 is determined according to the required output TW obtained in step S140 on curve C3 as the target cathode back pressure TP (TP2 in the drawing).

[0060] After executing step S190, the control unit 60 adjusts the cathode back pressure P to the target cathode back pressure TP determined in step S190 by adjusting the opening of the back pressure control valve A1 (step S192). After executing step S192, the control unit 60 temporarily terminates the cathode back pressure control processing.

[0061] If, in step S110, it is determined that the instantaneous time does not correspond to the cathode backpressure increase time, the control unit 60, on the other hand, determines whether the cathode backpressure output characteristic curve has been obtained (step S194). If it is subsequently determined that the cathode backpressure output characteristic curve has been obtained, the control unit 60 proceeds to step S180, in which the control unit 60 calculates the target cathode backpressure TP in the manner described above, using the cathode backpressure output characteristic curve obtained during the preceding cathode backpressure control processing and the required output TW obtained during the execution of the instantaneous cathode backpressure control processing, and controls the cathode backpressure P to the target cathode backpressure TP.

[0062] If step S194 determines that the cathode backpressure output characteristic curve was not obtained, the cathode backpressure control processing is temporarily terminated.

[0063] The processing of step S180 in the cathode backpressure control processing is considered to be the required output acquisition unit 61, as described above. Fig. 1) configured. Furthermore, the processing of steps S120 to S160 functions as the gas pressure sensitivity maintenance unit 62 ( Fig. 1) The processing of step S170 functions as the correspondence relationship calculation unit 63 ( Fig. 1) The processing of step S190 functions as the target gas pressure calculation unit 64 and the processing of step S192 functions as the gas pressure modification unit 65.

[0064] In the fuel cell system 10 according to the first embodiment, configured as described above, the cathode backpressure sensitivity S is determined at startup to increase the cathode backpressure, whereupon the cathode backpressure output characteristic curve is determined based on the cathode backpressure sensitivity S. Subsequently, the required output TW is obtained during each operation, whereupon the cathode backpressure is calculated as the target cathode backpressure TP according to the required output TW by comparing the required output TW with the determined cathode backpressure output characteristic curve, and the cathode backpressure P is controlled to the target cathode backpressure TP. As described above, the cathode backpressure output characteristic curve is determined according to the magnitude of the platinum surface area of ​​the cathode electrode.Therefore, the cathode backpressure output characteristic curve shows the cathode backpressure required to ensure the required output TW, not only when the platinum surface area decreases, but also when the output of the fuel cell 20 decreases due to a reduction in the platinum surface area resulting from the fuel cell's operation. Thus, the required output TW can be reliably ensured with the fuel cell system 10 according to the first embodiment, and the power generation performance can be improved. Furthermore, according to the fuel cell system 10, the cathode backpressure is controlled as the pressure of the oxidation gas, and therefore the oxidation gas control can be implemented with a favorable response. Second embodiment

[0065] Fig. Figure 4 is a flowchart illustrating cathode backpressure control processing according to a second embodiment. A fuel cell system according to the second embodiment differs from the fuel cell system 10 according to the first embodiment only in the cathode backpressure control processing performed by the control unit. A hardware configuration of the second embodiment is identical to that of the first embodiment, and therefore, in the following embodiment, the identical reference numerals are assigned to the corresponding components.

[0066] The in Fig. The cathode backpressure control process shown in Figure 4 differs from the cathode backpressure control process according to the first embodiment, which is described in Figure 4. Fig. 2 is shown in that the processing of step S110 in Fig. 2 with the processing of step S210 in Fig. 4 is replaced. The processing of the remaining steps S120 to S194 is identical. When processing begins, the control unit 60 determines whether the current time (the time at which the cathode backpressure control processing is executed) corresponds to a time at which a load of the fuel cell 20 begins to shift to a high-load operating point (a high-load shift time) (step S210). In particular, for example, if the driver forcefully releases a high-load request by depressing the accelerator pedal 80, the load of the fuel cell 20 shifts to the high-load operating point. Hereinafter, the “high-load operating point” denotes a high-load operating condition in which a current density of the fuel cell is, for example, at least 1 [A / cm²]. 2] is. If step S210 determines that the current time corresponds to the peak load shift time, processing proceeds to step S220, and if it determines that the current time does not correspond to the peak load shift time, processing proceeds to step S194.

[0067] Fig. Figure 5 is a diagram illustrating the cathode backpressure output characteristic curve according to the second embodiment. In the fuel cell system according to the second embodiment, as shown in the figures, when a high-load request, i.e., a request to shift to a high-load operating point X2, is received at a specific time X1, the cathode backpressure sensitivity S, i.e., the slope k2 of the curve, is determined at the high-load shift time at which the shift to the high-load operating point X2 begins. The cathode backpressure output characteristic curve is then determined based on the cathode backpressure sensitivity S. The cathode backpressure corresponding to the required output TW is then calculated as the target cathode backpressure TP using the cathode backpressure output characteristic curve, after which the cathode backpressure P is controlled to the target cathode backpressure TP.

[0068] This allows the fuel cell system according to the second embodiment to ensure the required output TW more reliably, similar to the fuel cell system 10 according to the first embodiment, thereby improving power generation performance. Furthermore, the following effect is achieved. Normally, when the load on the fuel cell 20 is small, the increasing slope of the cathode backpressure output characteristic curve does not change dramatically according to the magnitude of the platinum surface area. However, in the fuel cell system according to the second embodiment, the cathode backpressure sensitivity S is calculated at the time when the load on the fuel cell 20 begins to shift towards the high-load operating point. Therefore, the increasing slope of the cathode backpressure output characteristic curve varies dramatically, making it easier to determine the cathode backpressure sensitivity S.This increases the accuracy of the cathode backpressure sensitivity, thereby enabling a further improvement in power generation performance.

[0069] It should be noted that in the second embodiment, the cathode backpressure sensitivity S is determined at the time when the load of the fuel cell 20 begins to shift towards the high-load operating point. However, as a modified example of the second embodiment, the cathode backpressure sensitivity S can be determined at a time when the load of the fuel cell 20 begins to shift towards the low-load operating point. Hereinafter, the "low-load operating point" refers to a low-load operating condition in which the current density of the fuel cell does not exceed 0.1 [A / cm²]. 2 ] for example.

[0070] Fig. Figure 6 is a diagram representing the cathode backpressure output characteristic curve according to the modified example of the second embodiment. In the fuel cell system according to the modified example, as shown in the drawing, when a low-load request, i.e., a request to shift the load of fuel cell 20 to a low-load operating point X4, is received at a specific time X3, the cathode backpressure sensitivity S, i.e., the slope k of the curve, is determined at a low-load shift time at which the load of fuel cell 20 begins to shift to the low-load operating point X4. The cathode backpressure output characteristic curve is then determined based on the cathode backpressure sensitivity S.The cathode back pressure corresponding to the required output TW is then calculated as the target cathode back pressure TP using the cathode back pressure output characteristic curve, whereupon the cathode back pressure P is controlled to the target cathode back pressure TP.

[0071] The fuel cell system according to this modified example, similar to the fuel cell systems according to the first and second embodiments, can ensure the required output TW more reliably, thereby improving power generation performance. Furthermore, similar to the fuel cell system according to the second embodiment, the accuracy of the cathode backpressure output characteristic curve is increased, enabling a further improvement in power generation performance. Third embodiment

[0072] A fuel cell system according to a third embodiment has an identical hardware configuration to the fuel cell system 10 according to the first embodiment, differing only in the cathode backpressure control processing performed by the control unit 60. The cathode backpressure control processing according to the third embodiment is essentially identical to the cathode backpressure control processing according to the first embodiment, which is described in Fig. 2 is configured and differs only in the content of the processing performed in step S170. In other words, in the cathode backpressure control processing according to the third embodiment, the processing of steps S110 to S160 and S180 to S194 is in Fig. 2 is executed as is, while the processing of step S170 is replaced solely by the characteristic curve estimation processing described below. It should be noted that the hardware configuration of the third embodiment is identical to that of the first embodiment, with identical reference numerals assigned to the corresponding components of the description below.

[0073] Fig. 7 is a flowchart illustrating the characteristic curve estimation processing according to the third embodiment. This characteristic curve estimation processing is performed by the control unit 60 during the in Fig. The cathode backpressure control processing shown in step 2 was performed instead of the processing of step S170. As shown in Fig. Figure 7 shows that when processing initially begins, the control unit 60 acquires an impedance R (step S310). The impedance R is obtained by dividing the voltage detected by the voltage sensor 2b by the current detected by the current sensor 2a.

[0074] Next, the control unit 60 determines whether the obtained impedance R lies within a range extending from a first predetermined value R1 to a second predetermined value R2 (step S315). The first predetermined value R1 is a predetermined positive value, and the second predetermined value R2 is a predetermined positive value greater than the first predetermined value R1. The impedance R indicates the moisture condition of the interior of the fuel cell 20, and if the impedance R is within the range (referred to below as an "acceptable range") extending from the first predetermined value R1 to the second predetermined value R2, this indicates that the moisture condition of the fuel cell 20 is suitable.Furthermore, this shows that if the impedance R is smaller than the first predetermined value R1, the fuel cell 20 is in a flooded state, and if the impedance R is larger than the second predetermined value R2, this shows that the fuel cell 20 is in a dried-out state.

[0075] If the impedance R is determined to be within the permissible range in step S315, the cathode backpressure output characteristic curve is estimated using normal table data (step S320). The "normal table data" is identical to the table data used in step S170 of the first embodiment, and thus an estimation result obtained in step S320 is identical to the result obtained in step S170 of the first embodiment.

[0076] If, on the other hand, it is determined that the impedance R is outside the permissible range in step S315, or in other words, if it is determined that the fuel cell 20 is flooded or dried out, the cathode backpressure output characteristic curve is estimated using corrected tabular data (step S330).

[0077] The "normal table data" is used to extract the data in Fig. The 3 shown cathode backpressure output characteristic curve is used, whereas the “corrected table data” is used to extract a Fig. The cathode backpressure output characteristic curve shown in section 8 is used. Fig. The curves C1, C2, and C3 shown in section 8 are the cathode backpressure output characteristic curves indicated by the normal table data. The dotted lines in Fig. The three curves shown, C1', C2', and C3', are the cathode backpressure output curves indicated by the corrected tabular data. Curves C1', C2', and C3' exhibit a slightly reduced output relative to curves C1, C2, and C3, and the difference between the output B shown by the normal tabular data and the output shown by the corrected tabular data increases as the cathode backpressure P decreases. In other words, curves C1', C2', and C3' are corrected to show cases where the platinum surface area has been reduced compared to curves C1, C2, and C3. Curves C1', C2', and C3' can be determined beforehand by experiment or simulation.

[0078] Therefore, to obtain the previous output TW in the drawing, a larger cathode backpressure P is required on all curves C1', C2', C3' compared to curves C1, C2, C3. For example, TP1' is required instead of TP1, and TP2 is required instead of TP2. In other words, the corrected tabular data has been adjusted such that the magnitude of the cathode backpressure obtained for an identical required output is greater than that of the normal tabular data. One correction amount corresponds to the amount by which the platinum surface area of ​​the fuel cell has been reduced.

[0079] Returning to Fig. 7, following the execution of step S320 or step S330, the characteristic curve estimation processing is temporarily terminated.

[0080] With the fuel cell system according to the third embodiment with the configuration described above, the required output TW can be reliably ensured, similar to the fuel cell system 10 of the first embodiment, thereby improving power generation performance. Furthermore, the following effect is achieved: The fuel cell output corresponds precisely to an effective platinum surface area. The "effective platinum surface area" is determined by the product of a platinum utilization rate, which varies according to an operating condition, and the platinum surface area, which gradually decreases as the usable time increases. An oxidation film state and the flooded state are factors that determine the platinum utilization rate.When the fuel cell 20 is flooded, the platinum utilization rate is reduced by the moisture, leading to a reduction in output. However, according to the third embodiment, this reduction in output can be corrected by increasing the cathode backpressure according to the corrected table data, thus ensuring the required output TW more reliably. Furthermore, when the fuel cell 20 dries out, the cathode backpressure-output characteristic curve decreases, similar to that of the flooded state. Again, the reduction in output can be corrected by increasing the cathode backpressure according to the corrected table data, thus ensuring the required output TW more reliably. This further improves the power generation performance.

[0081] It should be noted that in the third embodiment, the humidity state of the interior of the fuel cell 20 is determined based on the impedance R. However, instead of a third modified example of the third embodiment, a dew point meter can be provided in the fuel cell such that the humidity state is determined based on a measurement result from the dew point meter. According to the first modified example, the humidity state of the fuel cell can be determined with a higher degree of accuracy.

[0082] Furthermore, in step S315 of the first embodiment, an AND operation is performed to determine whether the impedance R is less than the first predetermined value R1 and not greater than the second predetermined value R2. Instead of a second modified example of the first embodiment, a determination can be made simply whether the impedance R is greater than the predetermined second value R2. With this configuration, the cathode backpressure output characteristic curve can be estimated using the corrected tabular data when the fuel cell 20 is flooded. Additionally, as a third modified example of the third embodiment, a determination can be made simply whether the impedance R is less than the predetermined value R1. With this configuration, the cathode backpressure output characteristic curve can be estimated using the corrected tabular data when the fuel cell 20 is dried out.It should be noted that in the third embodiment identical corrected table data are used in both the flooded and dried states, but separate corrected table data with different differences to the cathode backpressure output characteristic curves determined from the normal table data can be used instead.

[0083] Furthermore, in the third embodiment, the determination of whether the fuel cell 20 is flooded or dry is performed based on the impedance R, but a fourth modified example of the third embodiment can instead perform the determination of whether the fuel cell 20 is flooded or dry based on the temperature of the fuel cell 20, which is detected by the temperature sensor 2c. Similar effects according to the third embodiment are obtained with the fourth modified example.

[0084] Furthermore, in the third embodiment and its corresponding modified examples, step S170 of the first embodiment is combined with the one described in Fig. The processing shown in step 7 is replaced, but as a fifth modified example of the third embodiment, step S170 can be used instead ( Fig. 4) the second embodiment with the in Fig. The processing shown in 7 can be replaced. According to the fifth modified example, similar effects are obtained according to the second embodiment, and in addition, the required output TW can be ensured more reliably, even if the fuel cell 20 is flooded or dried out. Fourth embodiment

[0085] A fuel cell system according to a fourth embodiment differs from the fuel cell system 10 according to the third embodiment only in the characteristic curve estimation processing performed by the control unit, and is identical to it in both software and hardware configuration. Since the hardware configuration of the fourth embodiment is identical to that of the third embodiment and therefore to the first embodiment, the identical reference numerals used in the first embodiment have been assigned to the corresponding parts of the following description.

[0086] Fig. 9 is a flowchart illustrating the characteristic curve estimation processing according to the fourth embodiment. The characteristic curve estimation processing is performed by the control unit 60 during the in Fig. The cathode backpressure processing shown in step 2 was performed instead of the processing of step 170. As shown in Fig. As shown in Figure 9, when processing begins, a determination is made as to whether the fuel cell 20 is in an idle state (step S410). The idle state is a state in which the fuel cell 20 receives an idle load. The magnitude of the idle load approximates a load received in an open-circuit (OC) state. In this embodiment, the determination of whether the fuel cell 20 is in the idle state is made by determining whether the voltage detected by the voltage sensor 2b has been above a predetermined voltage continuously for at least a predetermined time. Subsequently, if it is determined that the fuel cell 20 is not in the idle state, the cathode backpressure output characteristic curve is estimated using the normal table data (S420). The processing of step S420 is identical to the processing of step S320 in Figure 9. Fig. 7, and the values ​​of the normal table data are also identical.

[0087] If, in step S410, it is determined that fuel cell 20 is in the idle state, the cathode backpressure output characteristic curve is estimated using the corrected table data (step S430). The processing of step S430 is essentially identical to the processing of step S330 in Fig. 7, and therefore, as in Fig. Figure 8 shows the cathode backpressure output characteristic curve estimated with the corrected table data, displaying curves with a reduced output relative to the outputs C2, C3 of the normal table data. The in Fig. Curves C1', C2', and C3' shown are cathode backpressure output characteristic curves corresponding to the flooded or dried-out state. Therefore, the curves C1', C2', and C3' of the table data corrected in step S430 differ in shape from the curves C1', C2', and C3' of the corrected table data used in step S330. In particular, the corrected table data used in step S430 is aligned with the idle state, and therefore different data are derived from those obtained in step S320. Fig. 7 used corrected table data. However, as described above, the corrected table data shows curves with a reduced output relative to curves C1, C2, C3 of the normal table data. With the fuel cell system according to the fourth embodiment with the configuration described above, the required output TW can be ensured more reliably, similar to the fuel cell system 10 according to the first embodiment, and thus the power generation performance can be improved. In addition, the following effect is obtained: During idle operation, power generation is performed continuously at a high voltage, and therefore the oxidation film of the platinum increases and subsequently reaches a fixed amount, leading to a reduction in the data utilization rate.In the fourth embodiment, a reduction in output caused by the reduction in the platinum utilization rate can be corrected by increasing the cathode backpressure using the corrected table data, and therefore the required output TW can be ensured more reliably. This allows the power generation performance to be improved even further.

[0088] It should be noted that in the fourth embodiment, step S170 of the first embodiment involves the processing of Fig. 9 is replaced, but instead, step S170 can be used as a first modified example of the fourth embodiment ( Fig. 4) the second embodiment with the in Fig. The processing shown in 9 can be replaced. According to the first modified example, similar effects of the second embodiment are obtained, and in addition, the required output can be ensured more reliably, even during an idle state.

[0089] Furthermore, as a second modified example of the fourth embodiment, the processing of step S410 in the first modified example of the fourth embodiment can be replaced with a configuration in which, as in Fig. Figure 10 shows a determination being made as to whether the fuel cell 20 is in an intermittent operating state (step S410). In the intermittent operating state, a feed of reaction gas (the oxidation gas and the fuel gas) to the fuel cell 20 is repeatedly started and stopped intermittently, and a lower voltage is continuously maintained. Accordingly, the amount of platinum oxide layer decreases and reaches a defined value, thereby increasing the platinum utilization rate to almost 100%. Below, if it is determined in step S510 that the fuel cell 20 is in the intermittent operating state, the cathode backpressure output characteristic curve with normal data similar to that of step S420 is shown. Fig. 9 is estimated. If, on the other hand, it is determined that the fuel cell 20 is in the temporary operating state in step S510, the cathode backpressure output characteristic curve with the corrected table data is similar to step S430 of Fig. 9 was estimated. In this way, the required TW expenditure can be ensured more reliably. Fifth embodiment

[0090] In the fuel cell system according to the first to fourth embodiments, the processing, which extends from the acquisition of the cathode backpressure sensitivity S to the estimation of the cathode backpressure output characteristic curve, is performed at a predetermined time, whereupon the target cathode backpressure TP is calculated according to the required output TW by referencing the cathode backpressure output characteristic curve. In an alternative configuration, the estimated cathode backpressure output characteristic curve can be used continuously for a predetermined period, such as a day or a week. This configuration can be used in a fuel cell system according to a fifth embodiment. In a case where the fifth embodiment is applied to the first embodiment, for example, if the cathode backpressure output characteristic curve is initially calculated in step S170 of Fig. 2, the estimated cathode backpressure output characteristic curve is stored in a non-volatile memory, for example an electrically erasable programmable read memory (EPROM) contained in the control unit 60, which retains its memory contents even after a power supply to the fuel cell system has been switched off, and for a predetermined time only steps S180 to S192 of Fig. 2 during the cathode backpressure control processing. In other words, the target cathode backpressure TP is calculated using the cathode backpressure output characteristic curve stored in the EPROM in step S190. After a predetermined period has elapsed, the cathode backpressure output characteristic curve is updated by executing steps S110 to S194 of Fig. 2 is updated, after which the updated cathode backpressure output characteristic curve is used continuously for the next predetermined period.

[0091] As described above, the cathode backpressure output characteristic curve, determined on the basis of the cathode backpressure sensitivity S, corresponds to the platinum surface area and therefore does not change significantly over a few days. This allows the target cathode backpressure TP to be calculated with a high degree of accuracy, similar to the fuel cell system according to the fifth embodiment. Furthermore, the cathode backpressure output characteristic curve only needs to be calculated once per predetermined period, thus improving the processing response. It should be noted that the configuration of the fifth embodiment can be applied similarly to any of the second to fourth embodiments, as well as the first embodiment. Sixth embodiment

[0092] Next, a sixth embodiment is described. The sixth embodiment comprises an identical hardware configuration to the first embodiment, and therefore, in the following description, the identical reference numerals to those of the first embodiment are assigned to the corresponding components. In the first embodiment, the cathode backpressure output characteristic curve is pre-estimated by preparing a plurality of cathode backpressure output characteristic curves in the tabular data, and then a cathode backpressure output characteristic curve is selected based on the cathode backpressure sensitivity S. In the sixth embodiment, on the other hand, the cathode backpressure output characteristic curve is estimated using a formula for determining the current density. First, the current density generated by the fuel cell is considered. The current density can be determined from the following equation (1). i=APtio(1−θ)(Po2 / Pref)exp(−αFη / RT) where i is the current density, “A Pt “the cathode platinum surface area is, “i O “ is a cathode alternating current density, “θ” is an oxidation layer ratio, “P O2 “a required oxidation partial pressure is, “P ref “ is a reference oxidation concentration, “α” is a charge transfer coefficient, “F” is a Faraday constant, “η” is a cathode overvoltage, “R” is a gas constant and “T” is the fuel cell temperature.

[0093] In equation (1), a value of the cathode platinum surface area A can be obtained. Ptby estimating the cathode backpressure sensitivity S determined in the first embodiment. As described in the first embodiment, the cathode backpressure output characteristic curve varies in shape according to a platinum surface area, and its shape is estimated by the cathode backpressure sensitivity S. Estimating the cathode backpressure output characteristic curve is therefore equivalent to estimating the cathode platinum surface area. A value of the cathode AC current density io is a fixed value determined during the design phase of the fuel cell.

[0094] An oxidation layer ratio θ is an unknown value. A value (1-θ) indicates the platinum usage rate. As noted above, strictly speaking, the platinum usage rate is determined by the oxidation layer state and the flooded state, but in the sixth embodiment, the value (1-θ) indicates the platinum usage rate assuming no flooding has occurred. Therefore, if a platinum usage rate (1-θ) is not already known, an update process is performed to remove the oxidation layer (oxidation layer ratio θ=0), thus fixing the platinum usage rate (1-θ) to a known value.

[0095] A value of the required partial pressure of oxygen P O2 can be obtained by multiplying the cathode back pressure P detected by pressure sensor 3b by a predetermined oxygen ratio (for example, 0.21). A value of the reference oxygen concentration P Refis an oxygen concentration under reference conditions, and 100 (kPa-abs) is conventionally used. Note that "kPa-abs" is a unit-representing absolute pressure. The charge transfer coefficient α, the Faraday constant F, and the gas constant T each assume fixed values. A value, the cathode overvoltage η, is obtained by subtracting an actual voltage from an open-circuit voltage (OCV). The "actual voltage" is a single-cell voltage obtained from voltage sensor 2b. The fuel cell temperature T is obtained from temperature sensor 2c.

[0096] Fig. 11 is a flowchart representing a characteristic curve estimation processing according to the sixth embodiment. In the sixth embodiment, the processing is related to the cathode backpressure control processing of the first embodiment, which is described in Fig. 2 is shown, essentially identical, but the processing of step S170 in Fig. Step 2 is replaced by the characteristic curve estimation processing. In other words, the cathode backpressure estimation processing according to the sixth embodiment is identical to the cathode backpressure control processing according to the first embodiment, except for step 170.

[0097] As in Fig. As shown in Figure 11, when processing first starts, the control unit 60 receives the fuel cell temperature T from the temperature sensor 2c (S610). Next, the control unit 60 receives a cell voltage V from the voltage sensor 2b and determines the cathode overvoltage η by subtracting the cell voltage V from the OCV (step S620). Next, the control unit 60 determines the cathode platinum surface area A. Pt based on the one in step S160 of Fig. 2. Determine cathode backpressure sensitivity S (step S630). As described above, the cathode platinum surface area A Pt calculated from the cathode backpressure sensitivity S.

[0098] Next, control unit 60 determines whether the platinum user rate is known (step S640). As described above, after power is generated at a low voltage (on a high voltage) following an idle (OC avoidance) period, the platinum oxide layer thickness reaches a fixed amount (or a large side), and therefore the value of θ is essentially zero if the platinum user rate is known. Furthermore, after power is generated within a certain fixed voltage range (a low voltage) following, for example, intermittent operation (a natural voltage drop), the platinum layer thickness reaches a fixed amount (or a small side). Therefore, θ reaches a value of, for example, 0.5 if the platinum user rate is known.This means that the determination in step S640, whether the platinum user rate is known, is carried out by determining whether the power was generated at a low voltage (a high voltage) or whether the power was generated at a specified voltage range (a low voltage).

[0099] If step S640 determines that the platinum utilization rate is unknown, control unit 60 transfers the processing to step S650, where the update processing is performed, and subsequently the cathode backpressure control is initiated. Fig. 2. The update process is executed from the beginning. It is performed to remove the platinum oxide layer from the cathode catalyst layer. Specifically, the cell voltage of the fuel cell 20 is reduced to a threshold that is predefined as a recovery setpoint voltage by the DC / DC converter 51. A converter command voltage is then maintained at the threshold such that the oxide layer is blown away, resulting in an oxidation utilization rate of 100% or higher, and thereby eliminating the voltage reduction generated by the DC / DC converter 51. In this way, the cell voltage of the fuel cell 20 is reduced to a reduced zone, thereby reducing or removing the oxide layer on the surface of the Pt catalyst.It should be noted that the oxidation gas is blown away by fully opening the back pressure control valve A1 and the speed of the motor M1 of the compressor 31 is maximized.

[0100] On the other hand, if in step S640 the platinum utilization rate is determined to be known, the control unit 60 estimates the cathode backpressure output characteristic curve using equation (1) (step S660). As described above, the variables in equation (1) are the cathode platinum surface area A Pt , the oxidation layer ratio θ, the required oxygen partial pressure P O2 , the cathode overvoltage η and the fuel cell temperature T, and these variables, except for the required oxygen partial pressure P, are O2 , determined in steps S610 to S650. This allows the control unit 60 to establish a correspondence between the required oxygen partial pressure P. O2and the current density i by introducing the corresponding variables determined in steps S610 to S650 into equation (1). The cathode backpressure output characteristic curve is then derived from the correspondence relationship by converting the required oxygen partial pressure P. O2 The cathode back pressure P is determined by converting the current density i into the output W. After step S660 is executed, the characteristic curve estimation processing is temporarily terminated.

[0101] This allows the fuel cell system according to the sixth embodiment to ensure the required output TW more reliably, similar to the fuel cell system 10 according to the first embodiment, thereby improving power generation performance. Furthermore, the cathode backpressure output characteristic curve is determined using a formula in the fuel cell system according to the sixth embodiment, and therefore the tabular data representing a majority of the cathode backpressure output characteristic curves do not need to be pre-stored. This saves storage resources.

[0102] It should be noted that in the sixth embodiment, step S170 of the first embodiment is replaced by the processing of Fig. 11 is replaced, but it can be used as a modified example of the sixth embodiment instead step S170 ( Fig. 4) the second embodiment with the in Fig. The processing shown in section 11 can be replaced. According to this modified example, similar effects to the second embodiment are obtained, and additional memory resources can be saved. Seventh embodiment

[0103] A fuel cell system according to a seventh embodiment comprises an identical hardware configuration to the fuel cell system 10 according to the sixth embodiment, and the cathode backpressure control processing performed by the control unit ( Fig. 2, Fig. 11) is also identical. The fuel cell system according to the seventh embodiment differs from the fuel cell system 10 according to the sixth embodiment in that it incorporates the humidity control processing as software. It should be noted that if the hardware configuration of the seventh embodiment is identical to that of the first embodiment, the identical reference numerals to those of the first embodiment are assigned to the corresponding components in the description below.

[0104] Fig. Figure 12 is a flowchart illustrating the humidity control processing according to the seventh embodiment. The humidity control processing is started after the processing to control the cathode back pressure P to the setpoint cathode back pressure TP in step S192 of the cathode back pressure control processing is executed ( Fig. 2, Fig. 11) When processing begins, the control unit 60 first performs the processing to obtain the cathode back pressure P from the pressure sensor 3b (step S710). Next, the control unit 60 obtains the actual output W of the fuel cell 20 (step S720). Specifically, the control unit 60 determines the output power as the output W by obtaining the current and voltage respectively from the current sensor 2a and the voltage sensor 2b, and then by multiplying the current by the voltage.

[0105] Next, control unit 60 compares an actual cathode backpressure sensitivity with an estimated cathode backpressure sensitivity S and compares an actual output absolute with an estimated output absolute to determine whether the actual cathode backpressure sensitivity matches the estimated cathode backpressure sensitivity and whether the output absolute matches the estimated output absolute (step S730). The actual cathode backpressure sensitivity and the actual output absolute are derived from the actual cathode backpressure P obtained in step S710 and the actual output W obtained in step S720. The estimated cathode backpressure sensitivity S and the estimated output absolute are derived from the values ​​obtained in the cathode backpressure control processing of Fig. 2 estimated cathode backpressure output characteristic curve determined (especially in step S760 of Fig. 11 determined). Below, “matches” includes not only a case where the values ​​are completely identical, but also a case where the values ​​differ within a permissible range. As described above, the cathode backpressure sensitivity is the slope at a predetermined time (for example, the time to start in order to increase the cathode backpressure) on the characteristic curve, indicating a variation in the fuel cell output W relative to the cathode backpressure P. The output absolute value is an absolute value of the output W on the characteristic curve at the predetermined time.

[0106] If step S730 determines that the actual cathode backpressure sensitivity matches the estimated cathode backpressure sensitivity and the actual output absolute matches the estimated output absolute, the cathode backpressure control processing is temporarily terminated. Conversely, if step S730 determines that the actual cathode backpressure sensitivity does not match the estimated cathode backpressure sensitivity and / or the actual output absolute does not match the estimated output absolute, flooding is determined to be occurring in fuel cell 20, and therefore flood avoidance processing is executed (step S740).

[0107] As described above, the platinum utilization rate is determined by the oxidation layer state and the flooded state. In the sixth embodiment, the cathode backpressure control processing is executed assuming that flooding has not occurred. In the seventh embodiment, on the other hand, instead of assuming that flooding has not occurred, it is determined that flooding has occurred if the actual cathode backpressure sensitivity and the actual output absolute, derived from the actual cathode backpressure P and the actual output W, differ from the estimated cathode backpressure sensitivity S and the estimated output absolute, determined from the cathode backpressure output characteristic curve estimated in the cathode backpressure control processing. In this case, the flood avoidance processing is executed.In other words, flood avoidance processing is executed when step S730 determines that the actual cathode backpressure sensitivity does not match the estimated cathode backpressure sensitivity and / or the actual output absolute does not match the estimated output absolute.

[0108] The flooding prevention processing of step S740 is executed to reduce the amount of humidification applied by the humidification module 33 under normal conditions. It should be noted that the flooding prevention processing is not necessarily limited to this configuration and can also be executed in another process, such as increasing the initial temperature of the fuel cell 20. Specifically, in a case where a coolant flow passage carrying a coolant flowing through the interior of the fuel cell passes through a radiator provided along a cooling fan, the internal temperature is increased by stopping the cooling fan.

[0109] As described, the fuel cell output corresponds to the effective platinum surface area, and the effective platinum surface area is determined by the platinum utilization rate and the platinum surface area. This describes below how the cathode backpressure output characteristic curve varies depending on whether flooding has occurred when corresponding magnitudes of the platinum utilization rate and platinum surface area vary.

[0110] Fig. Figure 13 is a descriptive view showing a fluctuation of the cathode backpressure output characteristic curve depending on the presence or absence of flooding under the corresponding conditions.

[0111] The states are the corresponding combinations of high and low platinum utilization rates and large and small effective platinum surface areas.

[0112] If the platinum utilization rate is high and the effective platinum surface area is large, as in Fig. As shown in Figure 13A, the cathode backpressure sensitivity (the slope) does not vary regardless of whether flooding is present (dashed line) or not (solid line), whereas the output absolute value is smaller when flooding is present than when flooding is not. If the platinum utilization rate is high and the effective platinum surface area is small, as in Fig. As shown in Figure 13B, both the cathode backpressure sensitivity (the slope) and the output absolute value are smaller when flooding is present than when flooding is absent. If a platinum utilization rate is small and the effective platinum surface area is large, as in Figure 13B, the following applies: Fig. As shown in Figure 13C, both the cathode backpressure sensitivity (the slope) and the output absolute value are smaller when flooding is present than when flooding is absent. When the platinum utilization rate is low and the effective platinum surface area is small, as in Figure 13C, the following applies: Fig. As shown in Figure 13D, the output absolute value does not vary greatly, regardless of whether flooding is present (dotted line) or absent (solid line), whereas the cathode backpressure sensitivity (the slope) is smaller when flooding is present than when flooding is absent.

[0113] It is therefore obvious that by comparing the corresponding values ​​of the cathode backpressure sensitivity (the slope) and the output absolute value, when flooding is not present, when flooding is present, the presence of flooding can be determined on the basis of at least one of the detection results, even if the corresponding magnitudes of the platinum utilization rate and platinum surface area vary.

[0114] With the fuel cell system according to the seventh embodiment with the aforementioned configuration, the required output TW can be ensured more reliably, similar to the fuel cell system of the sixth embodiment, thereby improving power generation performance. Furthermore, with the fuel cell system according to the seventh embodiment, a flooding event can be handled by preventing flooding, thus enabling a further improvement in power generation performance.

[0115] It should be noted that in the seventh embodiment, similar to the sixth embodiment, step S170 of the first embodiment involves the processing of Fig. 11 is replaced, but it can be used as a modified example of the seventh embodiment instead step S170 ( Fig. 4) the second embodiment with the in Fig. The processing shown in Figure 11 can be replaced. According to this modified example, similar effects to the second embodiment are obtained, and additionally, memory resources can be saved, and a further improvement in power generation performance can be achieved by avoiding flooding.

[0116] Furthermore, in the seventh embodiment, the cathode backpressure output characteristic curve is determined using a formula, but similar to the first embodiment, a configuration can be used in which the tabular data representing a plurality of the cathode backpressure output characteristic curves are pre-stored in memory and a desired cathode backpressure output characteristic curve is selected from it based on the cathode backpressure sensitivity S, or in other words, the original configuration of step S170 in Fig. 2, can be used instead. Similar to this configuration, flooding can be avoided, thus enabling a further improvement in power generation performance. Eighth embodiment

[0117] A fuel cell system according to an eighth embodiment comprises an identical hardware configuration to the fuel cell system 10 according to the first embodiment. It should be noted that in the following description, the identical reference numerals to those of the first embodiment are assigned to the corresponding hardware components. In the eighth embodiment, the fuel cell output is ensured at the same time when a state of the battery 52 is improved by a single control process. This overall control is performed by the control unit 60.

[0118] Fig. Figure 14 is a flowchart illustrating overall control processing according to an eighth embodiment. The overall control processing is performed repeatedly by the control unit 60 at predetermined time intervals. As shown in the figures, when processing begins, the control unit 60 performs the processing to detect and assess the corresponding states of the fuel cell 20 and the battery 52 (step S810). For example, the control unit 60 detects the state of the fuel cell 20 by estimating the amount of moisture in the fuel cell 20 from its impedance value and by determining from the amount of moisture whether the fuel cell 20 is dry or flooded. Furthermore, for example, the control unit 60 detects the state of the battery 52 by determining the deterioration state of the battery 52 from a voltage measurement obtained during startup.

[0119] Next, the control unit 60 determines a suitable range for the battery's state of charge (SOC) based on the states of the fuel cell 20 and the battery 52, which are estimated in step S810 (step S820). The "SOC" is an index indicating the amount of power remaining in the battery and is defined below as a value obtained by dividing the amount of electricity remaining in the battery 52 by the amount of electricity stored in the battery when the battery is fully charged. It should be noted that the battery's SOC can be defined as a chargeable amount rather than a remaining capacity. The "acceptable range" is a range within which the battery 52 can be used effectively. The acceptable range changes according to the state of the fuel cell 20 and the state of the battery 52.The permissible range is continuously increased if an internal condition of the fuel cell 20 deteriorates.

[0120] Next, the control unit 60 performs processing to read the state of charge (SOC) of battery 52 (step S830). Specifically, the SOC is calculated based on a charge / discharge current of battery 52, which is detected by a battery current sensor (not shown). Next, the control unit 60 determines whether the SOC obtained in step S830 is within an acceptable range obtained in step S820 (step S840). If step S840 determines that the SOC is not within the acceptable range, a required charge / discharge amount is determined to shift the SOC of battery 52 into the acceptable range (step S850).

[0121] After executing step S850, the control unit determines 60 fluctuations (fluctuation magnitudes) of the cathode back pressure and a cathode flow rate necessary for the required output TW from the fuel cell 20 to achieve a magnitude increased by the battery charge / discharge amount determined in step S850 (step S860). The "cathode flow rate" is the flow rate of the oxidation gas supplied to the fuel cell 20.

[0122] Fig. Figure 15 is a diagram illustrating a correspondence relationship between the cathode backpressure P and a cathode flow rate L during the execution of the cathode backpressure control process. When the accelerator pedal 80 is depressed such that an operating state is shifted from point Xa to point Xb by the cathode backpressure control process according to the first embodiment, the operating state is shifted along a path indicated by an arrow α in the diagram. According to the eighth embodiment, on the other hand, the operating state is shifted along a path indicated by an arrow β in the diagram. In other words, as shown by arrow β, the ratio of an increase in the cathode flow rate L to an increase in the cathode backpressure P is controlled to be greater than that shown by arrow α in the first embodiment.

[0123] Fig. Figure 16 is a time diagram representing a fluctuation in the cathode back pressure P, the cathode flow rate L, and the output W of the fuel cell 20. It is assumed that the accelerator pedal 80 is depressed at time t1 such that the output W of the fuel cell 20 reaches the required output TW at time t2. The timing of time t1 corresponds to point Xa in Fig. 15, and a timing of time t2 corresponds to point Xb in Fig. 15. Dotted lines in the drawing indicate a variation according to the first embodiment, while solid lines in the drawing indicate a variation according to the eighth embodiment.

[0124] As shown in the drawing, during the transition time from time t1 to time t2, the cathode back pressure P changes according to the first embodiment to increase temporarily over time, whereas according to the eighth embodiment, the cathode back pressure P varies and increases with a delay relative to the first embodiment. However, it should be noted that the time t2 at which the cathode back pressure P reaches the target cathode back pressure TP required to achieve the required output TW is identical in both the first and eighth embodiments.Meanwhile, the cathode flow rate L changes according to the eighth embodiment to increase earlier than that of the first embodiment, and a time at which the cathode flow rate L reaches a target cathode flow rate TL required to achieve the required output TW is set at a time t3 which is earlier than the time t2 at which the cathode flow rate L reaches the target cathode flow rate TL according to the first embodiment.

[0125] A fluctuation of the output W according to the eighth embodiment is as shown in the drawing, and a timing at which the output W of fuel cell 20 sets the required output TW at a time t4 that is earlier than the time t2 according to the first embodiment. In other words, the timing at which the output W reaches the required output TW is earlier than the time t2 at which the cathode back pressure P reaches the set cathode back pressure TP. A shaded area in the drawing denotes a power increase Wadd relative to the first embodiment, obtained by advancing the timing at which the output W reaches the required output TW. The power increase Wadd is defined to be the same as the battery charge / discharge amount determined in step S850. In other words, at step S860 of Fig. 14 A method is determined in which the cathode back pressure P and the cathode flow rate L are varied (a fluctuating rotational speed / a delay time) such that the output W is as in the Fig. 15 and Fig. 16 varies.

[0126] After executing step S860, the control unit 60 performs the cathode backpressure control processing (step S870) and the cathode flow rate control processing (step S880). In the cathode backpressure control processing and the cathode flow rate control processing, the cathode backpressure P and the cathode flow rate L are controlled according to the fluctuation pattern determined in step S860. The cathode backpressure control processing is implemented using an identical processing routine to that of the first embodiment. It should be noted that the cathode backpressure control processing according to the first embodiment can be replaced by the cathode backpressure control processing according to the second embodiment. In the cathode flow control processing, the cathode flow rate is controlled by varying the speed of the motor M1 of the air compressor 31.In the drawing, step S880 is executed after step S870 has been executed; however, this is for the sake of clarity, and in reality, step S870 and step S880 are executed in parallel.

[0127] After steps S870 and S880 are executed, the overall control processing is temporarily terminated. However, if S840 determines that the SOC is within the appropriate range, processing proceeds to step S870 to execute the cathode backpressure control and cathode flow rate control without executing steps S850 and S860.

[0128] With the fuel cell system according to the eighth embodiment with the aforementioned configuration, the required output TW can be ensured more reliably, similar to the fuel cell system 10 according to the first embodiment, thereby improving power generation performance. Furthermore, with the fuel cell system according to the eighth embodiment, the fuel cell output W reaches the required output TW earlier than the point at which the cathode back pressure P reaches the target cathode back pressure TP, and therefore excess power corresponding to the power increase Wadd can be obtained. The battery charge / discharge amount is then supplemented with this excess. This allows a balance between power demand and supply to be maintained throughout the entire fuel cell system.

[0129] It should be noted that in the eighth embodiment, it is determined that the battery is in a non-favorable state when the state of charge (SOC) deviates from the suitable range, but the invention is not necessarily limited thereto. It can be determined that, as long as the battery is in a non-favorable state, the cathode current rate L is increased at an earlier time to provide the necessary additional power to improve the battery's state of charge.

[0130] Furthermore, the way in which the cathode back pressure P and the cathode flow rate L are varied is not based on the information in the Fig. 15 and Fig. The pattern shown in 16 is limited, and as long as the power increase Wadd is maintained compared to the first embodiment, the vibration speed and delay time may differ from those in the Fig. 15 and Fig. 16 differentiators. Ninth embodiment

[0131] A fuel cell system according to a ninth embodiment differs from the fuel cell system 10 according to the eighth embodiment only in the overall control processing performed by the control unit, and is identical in both software and hardware configuration. Since the hardware configuration of the ninth embodiment is identical to that of the eighth embodiment and therefore to that of the first embodiment, the identical reference numerals used in the first embodiment are assigned to the corresponding components in the following description.

[0132] Fig. Figure 17 is a flowchart illustrating the overall control processing according to the ninth embodiment. The overall control processing is performed repeatedly by the control unit 60 at predetermined time intervals. This overall control processing includes identical steps S810, S870, and S880 to the overall control processing according to the embodiment shown in Figure 17. Fig. The eighth embodiment shown in Figure 14 differs from it in that steps S920 to S930 replace steps S820 to S860. Fig. 14 are provided. The control unit 60 determines whether the state of fuel cell 20 is favorable based on the state of fuel cell 20 estimated in step S810 (step S920). If it is subsequently determined that the state of the fuel cell is not favorable, an oscillation of the cathode back pressure and cathode flow rate is determined such that the required output TW from fuel cell 20 reaches a magnitude increased by an amount of power from an auxiliary device operated to improve the state of fuel cell 20 (step S930). Subsequently, the manner in which the cathode back pressure P and the cathode flow rate L are varied (the oscillation speed / the delay time) is determined such that the in Fig. The performance increase shown in section 16 corresponds to the performance of the operated auxiliary device.

[0133] After step S930 is executed, the control unit 60 performs the cathode backpressure control processing (step S870) and the cathode flow control processing (step S880). During the cathode backpressure control processing and the cathode flow rate control processing, the cathode backpressure P and the cathode flow rate L are controlled according to the oscillation mode determined in step S930. After step S880 is executed, the overall control processing is temporarily terminated. Conversely, if step S920 determines that the state of the fuel cell 20 is favorable, the processing proceeds to step S870 without executing step S930.

[0134] With the fuel cell system according to the ninth embodiment with the aforementioned configuration, the required output TW can be ensured more reliably, similar to the fuel cell system 10 according to the first embodiment, thereby improving power generation performance. Furthermore, with the fuel cell system according to the ninth embodiment, the fuel cell output W reaches the required output TW at an earlier timing than the timing at which the cathode back pressure P reaches the target cathode back pressure TP, and therefore excess power corresponding to the power increase Wadd can be obtained. The power of the auxiliary device, which is operated to improve the condition of the fuel cell 20, is subsequently supplemented with this excess. This allows a balance between power demand and supply to be maintained throughout the entire fuel cell system. Tenth embodiment

[0135] A fuel cell system according to a tenth embodiment differs from the fuel cell system 10 according to the ninth embodiment only in the overall control processing performed by the control unit, and is identical in both software and hardware configuration. Since the hardware configuration of the tenth embodiment is identical to that of the eighth embodiment and therefore to the first embodiment, the identical reference numerals used in the first embodiment have been assigned to the corresponding components in the following description.

[0136] Fig. Figure 18 is a flowchart illustrating the overall control processing according to the tenth embodiment. The overall control processing is performed repeatedly by the control unit 60 at predetermined time intervals. As shown in the drawing, when the processing starts, the control unit 60 first receives the impedance R (step S1010). The impedance R is obtained by dividing the voltage detected by the voltage sensor 2b by the current detected by the current sensor 2a.

[0137] Next, the control unit 60 determines whether the obtained impedance R is greater than a second predetermined value R2 (step S1020), and determines whether the impedance R is less than a first predetermined value R1 ( <R2) ist (Schritt S1030). Der erste vorbestimmte Wert R1 und der zweite vorbestimmte Wert R2 nehmen identische Werte bei der dritten Ausführungsform ein. Wenn in Schritt S1020 und Schritt S1030 bestimmt wird, dass die Impedanz R innerhalb eines geeigneten Bereichs (R2 ≤ R ≤ R1) liegt, der sich von dem ersten vorbestimmten Wert R1 zu dem zweiten vorbestimmten Wert R2 (negative Bestimmungen sowohl in S1020 als auch in S1030) erstreckt, schreitet die Verarbeitung zu Schritt S870 fort. Bei den Schritten S870 und S880 werden die Kathodengegendrucksteuerverarbeitung und die Kathodenströmungsratensteuerverarbeitung auf einer identischen Weise wie bei der achten Ausführungsform, die in Fig. As shown in 14, it is executed.

[0138] If, at step S1030, it is determined that the impedance R becomes smaller than the first predetermined value R1, it is also determined that a moisture content is excessively high (i.e., it is determined that flooding has occurred), and therefore the control unit 60 proceeds to step S1040. At step S1040, the control unit 60 determines how the cathode back pressure P and the cathode flow rate L are varied (the oscillation speed / delay time), similar to the eighth and ninth embodiments, such that the cathode flow rate L reaches the target cathode flow rate TL at an earlier time than when the cathode back pressure P reaches the target cathode back pressure TP. The power increase Wadd initially obtained in this way by increasing the cathode flow rate L ( Fig. 16) corresponds to the performance of an auxiliary device that is operated to improve the flooded condition.

[0139] Meanwhile, if in step S1020 it is determined that the impedance R is greater than the second predetermined value R2, it is determined that the moisture content is excessively low (i.e., it is determined that the fuel cell is dry), and therefore processing proceeds to step S1050. In step S1050, a cathode control procedure is determined such that the timing at which the cathode back pressure P reaches the target cathode back pressure TP is earlier than the timing at which the cathode flow rate L reaches the target cathode flow rate TL. In other words, the relationship between the cathode back pressure P and the cathode flow rate L is reversed from that of the eighth embodiment such that the way in which the cathode back pressure P is varied coincides with the way in which the "cathode flow rate L" is varied. Fig. 16 varies, and the way in which the cathode flow rate L is varied corresponds to the way in which the “cathode back pressure P” in Fig. 16 varies. Accordingly, the timing at which the cathode flow rate L reaches the target cathode flow rate TL corresponds to time t2, and the timing at which the cathode back pressure P reaches the target cathode back pressure TP corresponds to time t3, which is earlier than time t2. The increase in performance obtained by first increasing the cathode back pressure P in this way corresponds to the performance of an auxiliary device operated to improve the dried-out state.

[0140] After executing step S1040 or S1050, or similarly if a negative determination is made in step S1030, the control unit 60 proceeds to step S870. By executing steps S870 and S880, the cathode back pressure P and the cathode flow rate L are varied in the manner determined in step S1040.

[0141] With the fuel cell system according to the tenth embodiment with the aforementioned configuration, the required output TW can be ensured more reliably, similar to the fuel cell system according to the first embodiment, and therefore the power generation performance can be improved. Furthermore, with the fuel cell system according to the tenth embodiment, the fuel cell output W reaches the required output TW at an earlier timing than the timing at which the cathode back pressure P reaches the target cathode back pressure TP, and therefore the excess power corresponding to the power increase Wadd can be obtained. The power of the auxiliary device required to improve the flooded state is subsequently supplemented with this excess. This allows a balance between power demand and supply to be maintained throughout the entire fuel cell system.Furthermore, if the fuel cell dries out, the driest state can be improved, and therefore the balance between power demand and supply can be maintained in a similar way throughout the entire fuel cell system.

[0142] It should be noted that the corresponding embodiments from the eighth to the tenth embodiment can be combined. In particular, two embodiments selected from the eighth to the tenth embodiment can be combined, or all three embodiments can be combined.

[0143] The invention is not limited to the first to tenth embodiments and their modified examples described above, and can be implemented in various forms within a scope that does not deviate from its subject matter. For example, the following modifications can be implemented. Modified Example 1

[0144] In the foregoing embodiments, the cathode backpressure sensitivity S, which serves as a pressure sensitivity, is determined based on the pressure (cathode backpressure) of the oxidation gas discharged by the fuel cell 20. However, the pressure sensitivity can alternatively be determined based on the pressure of the oxidation gas supplied to the fuel cell 20. The pressure sensitivity can also be determined based on the pressure of the oxidation gas in an oxidation gas flow passage provided in a cell of the fuel cell. Furthermore, the pressure sensitivity can be determined based on a pressure difference between an oxidation gas supply port and an oxidation gas discharge port. Modified Example 2

[0145] In the above embodiments, the fuel cell is a solid polymer fuel cell; however, it can also be a different type of fuel cell than a solid polymer fuel cell. Modified Example 3

[0146] In the foregoing embodiments, the fuel cell system to which the invention is applied is installed in a vehicle, such as a motor vehicle, but it can also be installed in various moving bodies (a motorized bicycle, a ship, an aircraft, a robot, or the like) as well as in a vehicle. Furthermore, the invention is not limited to a fuel cell system installed in a moving body and can also be applied to a stationary fuel cell system or a portable fuel cell system. Modified example 4

[0147] In the foregoing embodiments and the modified examples, functions that are implemented by software can also be implemented by hardware, such as separate electronic circuits.

[0148] The invention can be realized as a vehicle equipped with a fuel cell system according to the invention, a computer program or a storage medium for acting as a computer to perform functions according to the steps of a control method for the fuel cell system according to the invention, etc.

Claims

[1] Fuel cell system, characterized by that it has: a fuel cell (20); an oxidizing gas supply unit (30) configured to supply an oxidizing gas to a cathode electrode of the fuel cell (20); and a gas pressure control unit (60) configured to repeatedly execute control processing comprising detecting a ratio of a fluctuation in an output of the fuel cell (20) to a fluctuation in the pressure of the oxidizing gas as a gas pressure sensitivity at a predetermined time during operation of the fuel cell (20), specifying a characteristic curve indicating a correspondence relationship between the pressure of the oxidizing gas and the output of the fuel cell (20) based on the detected gas pressure sensitivity, and controlling the pressure of the oxidizing gas based on the specified characteristic curve. [2] The fuel cell system according to claim 1, wherein the gas pressure control unit (60) is configured to obtain a required output required from the fuel cell (20), calculate, as a target gas pressure, a pressure of the oxidizing gas corresponding to the required output by comparing the required output with the characteristic curve, and control the pressure of the oxidizing gas to the target gas pressure. [3] The fuel cell system according to claim 1 or 2, further comprising a storage unit (60) that stores table data in which characteristic curves indicating correspondence relationships between the pressure of the oxidizing gas and the output of the fuel cell (20) are respectively associated with individual values ​​of the gas pressure sensitivity, wherein the gas pressure control unit (60) is configured to specify the characteristic curve by selecting a characteristic curve corresponding to the detected gas pressure sensitivity from the table data. [4] The fuel cell system according to any one of claims 1 to 3, further comprising a back pressure regulating valve (A1) configured to regulate the pressure of the oxidizing gas discharged from the cathode electrode outlet of the fuel cell (20), wherein the gas pressure control unit (60) is configured to control the pressure of the oxidizing gas by adjusting an opening of the back pressure regulating valve (A1). [5] The fuel cell system according to any one of claims 1 to 4, wherein the predetermined timing corresponds to a timing of starting to increase the pressure of the oxidizing gas. [6] The fuel cell system according to any one of claims 1 to 4, wherein the predetermined time corresponds to a time at which a load of the fuel cell (20) begins to shift to an operating point with a predetermined load. [7] Fuel cell system, characterized by that it has: a fuel cell (20); an oxidizing gas supply unit (30) configured to supply an oxidizing gas to a cathode electrode of the fuel cell (20); and a gas pressure control unit (60) configured to detect, as a gas pressure sensitivity, a ratio of a fluctuation in an output of the fuel cell (20) to a fluctuation in the pressure of the oxidizing gas, specify a correspondence relationship between the pressure of the oxidizing gas and the output of the fuel cell (20) based on the detected gas pressure sensitivity, and control the pressure of the oxidizing gas based on the specified correspondence relationship, wherein: the fuel cell (20) contains an electrode catalyst; the correspondence relationship between the pressure of the oxidizing gas and the output of the fuel cell (20) includes a first correspondence relationship and a second correspondence relationship, wherein the second correspondence relationship is set such that a magnitude of the pressure of the oxidizing gas in the second correspondence relationship corresponding to an identical output of the fuel cell (20) is greater than that of the pressure of the oxidizing gas in the first correspondence relationship, and the gas pressure control unit (60) is configured to specify the correspondence relationship by selecting the first correspondence relationship when the fuel cell (20) is not in a predetermined operating state in which a utilization rate of platinum contained in the electrode catalyst decreases, and select the second correspondence relationship when the fuel cell (20) is in the predetermined operating state. [8] Fuel cell system according to claim 7, wherein the predetermined operating point is a flooded state of the fuel cell (20). [9] A fuel cell system according to claim 7, wherein the predetermined operating point is an idle state of the fuel cell (20). [10] The fuel cell system according to any one of claims 1 to 6, further comprising a non-volatile memory (60) configured to continuously store the characteristic curve specified by the gas pressure control unit (60) after a power supply of the fuel cell system is turned off, wherein the gas pressure control unit (60) is configured to control the pressure of the oxidizing gas within a predetermined period based on the characteristic curve stored in the non-volatile memory (60). [11] Fuel cell system, characterized by that it has: a fuel cell (20); an oxidizing gas supply unit (30) configured to supply an oxidizing gas to a cathode electrode of the fuel cell (20); and a gas pressure control unit (60) configured to detect, as a gas pressure sensitivity, a ratio of a fluctuation in an output of the fuel cell (20) to a fluctuation in the pressure of the oxidizing gas, specify a correspondence relationship between the pressure of the oxidizing gas and the output of the fuel cell (20) based on the detected gas pressure sensitivity, and control the pressure of the oxidizing gas based on the specified correspondence relationship; and a flooding determination unit (60) configured to determine whether flooding has occurred in the fuel cell (20) by comparing a specific gas pressure sensitivity determined from the correspondence relationship between the pressure of the oxidizing gas and the output of the fuel cell (20) specified by the gas pressure control unit (60) with an actual gas pressure sensitivity derived from an actual pressure of the oxidizing gas and an actual output of the fuel cell (20), and by comparing a specific output absolute value, which is an absolute value of the output corresponding to the specific gas pressure sensitivity, with an actual output absolute value. [12] The fuel cell system according to claim 11, wherein, when the flooding determination unit (60) determines that the flooding has occurred, the flooding determination unit (60) is configured to execute the processing for avoiding the flooding. [13] The fuel cell system of claim 2, further comprising: a battery (52), wherein a suitable range of a state of charge of the battery (52) varies according to a state of the fuel cell (20); and a gas flow rate control unit (60) configured to control a flow rate of the oxidizing gas such that, when the gas pressure control unit (60) controls the pressure of the oxidizing gas while the battery (52) is in a predetermined state, the output of the fuel cell (20) reaches the required output at an earlier timing than a timing at which the pressure of the oxidizing gas reaches a target gas pressure. [14] The fuel cell system according to claim 13, further comprising an SOC determination unit (5a) configured to detect the state of charge of the battery (52), wherein it is determined that the battery (52) is in a predetermined state when the detected state of charge deviates from the appropriate range. [15] The fuel cell system according to claim 2, further comprising a gas flow rate control unit (60) configured to control a flow rate of the oxidizing gas such that, when the gas pressure control unit (60) controls the pressure of the oxidizing gas while the fuel cell (20) is in a predetermined state, the output of the fuel cell (20) reaches the required output at an earlier timing than a timing at which the pressure of the oxidizing gas reaches the target gas pressure. [16] The fuel cell system according to claim 15, wherein it is determined that the fuel cell (20) is in the predetermined state when flooding occurs in the fuel cell (20). [17] Fuel cell system, comprising: a fuel cell (20); an oxidizing gas supply unit (30) configured to supply an oxidizing gas to a cathode electrode of the fuel cell (20); a gas pressure control unit (60) configured to control a pressure of the oxidizing gas; and a platinum surface area estimation unit (60) configured to detect, as gas pressure sensitivity, a ratio of a fluctuation in an output of the fuel cell (20) to a fluctuation in the pressure of the oxidizing gas, and to estimate a platinum surface area of ​​the cathode electrode based on the detected gas pressure sensitivity. [18] A control method for a fuel cell system including a fuel cell (20) and an oxidizing gas supply unit (30) configured to supply an oxidizing gas to a cathode electrode of the fuel cell (20), the method comprising: characterized by is that it has: repetitive execution of a control processing, with: detecting a ratio of a fluctuation of an output of the fuel cell (20) to a fluctuation of a pressure of the oxidizing gas as a gas pressure sensitivity at a predetermined time during operation of the fuel cell (20); specifying a characteristic curve indicating a correspondence relationship between the pressure of the oxidizing gas and the output of the fuel cell (20) based on the detected gas pressure sensitivity; and Controlling the pressure of the oxidizing gas based on the specified characteristic curve. [19] A control method for a fuel cell system including a fuel cell (20) and an oxidizing gas supply unit (30) configured to supply an oxidizing gas to a cathode electrode of the fuel cell (20), the method comprising: characterized by is that it has: Controlling a pressure of the oxidizing gas; detecting a ratio of a fluctuation of an output of the fuel cell (20) to a fluctuation of the pressure of the oxidizing gas as a gas pressure sensitivity; and Estimating a platinum surface area of ​​the cathode electrode based on the detected gas pressure sensitivity.

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