Fuel cell system and control method thereof

Abstract

A fuel cell system comprises 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 detect, as a gas pressure sensitivity, a ratio of a fluctuation of an output of the fuel cell (20) to a fluctuation of the pressure of the oxidation gas, specify 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 control the pressure of the oxidation gas based on the specified correspondence relationship.

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, controls the air pressure at the cathode inlet and is also available in the prior art (Published Japanese Patent Application No. 2002-42839 (JP 2002-42839 A)). The air pressure at the cathode inlet is controlled by adjusting a backpressure control valve located at the cathode outlet (JP 2002-42839 A and Published Japanese Patent Application No. 2011-29158 (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. SUMMARY OF THE INVENTION

[0004] 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.

[0005] A first aspect of the invention 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 pressure of the oxidation gas and the fuel cell output based on the detected gas pressure sensitivity, and control the pressure of the oxidation gas based on the specified correspondence relationship.

[0006] 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.

[0007] 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.

[0008] 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.

[0009] 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.

[0010] 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.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] A second aspect of the invention is a fuel cell system comprising: a fuel cell; an oxidation gas supply unit configured to supply 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 the ratio of a fluctuation in the 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.

[0023] A third aspect of the invention 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. This method includes: detecting the ratio of a fluctuation in the fuel cell output to a fluctuation in the oxidation gas pressure as a gas pressure sensitivity; specifying a correspondence relationship between the oxidation gas pressure and the fuel cell output based on the detected gas pressure sensitivity; and controlling the oxidation gas pressure based on the specified correspondence relationship. Similar to the fuel cell system according to the first aspect, the control method for a fuel cell system according to this aspect can ensure the required output more reliably, thereby enabling higher power generation performance.

[0024] A fourth aspect of the invention 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 oxidation gas pressure as the gas pressure sensitivity; and estimating the 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

[0025] 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:

[0026] Fig. 1 is a descriptive view that represents a configuration of a fuel cell system as a first embodiment of the invention;

[0027] Fig. 2 is a flowchart that represents a cathode backpressure control process to be performed by the control unit;

[0028] Fig. 3 is a diagram that represents a cathode backpressure output characteristic curve;

[0029] Fig. 4 is a flowchart that represents a cathode backpressure control process according to a second embodiment;

[0030] Fig. 5 is a diagram that represents a cathode backpressure output characteristic curve according to the second embodiment;

[0031] Fig. 6 is a diagram that represents a cathode backpressure output characteristic curve according to a modified example of the second embodiment;

[0032] Fig. 7 is a flowchart that represents a characteristic curve estimation processing according to a third embodiment;

[0033] Fig. 8 is a diagram that represents a cathode backpressure output characteristic curve according to the third embodiment;

[0034] Fig. 9 is a flowchart representing a characteristic curve estimation processing according to a fourth embodiment;

[0035] Fig. 10 is a flowchart that represents a characteristic curve estimation processing according to a second modified example of the fourth embodiment;

[0036] Fig. 11 is a flowchart representing a characteristic curve estimation processing according to a sixth embodiment;

[0037] Fig. 12 is a flowchart representing a humidity control processing according to a seventh embodiment;

[0038] Fig. 13A to Fig. 13D representation views are those that depict a fluctuation of a cathode backpressure output characteristic curve depending on the presence or absence of flooding under the corresponding conditions;

[0039] Fig. 14 is a flowchart that represents an overall control processing according to an eighth embodiment;

[0040] 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;

[0041] 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;

[0042] Fig. 17 is a flowchart representing an overall tax processing according to a ninth embodiment; and

[0043] Fig. 18 is a flowchart that represents an overall tax processing according to a tenth embodiment. DETAILED DESCRIPTION OF THE EXECUTION FORMS

[0044] 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 ​​a platinum electrode catalyst used in the fuel cell. It may therefore be impossible to achieve high power generation performance by implementing a control system such as that described in JP 2002-42839 A. Ensuring a required amount of power generation is also difficult. 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.

[0045] 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.

[0046] Next, the embodiments of the invention will be described. First embodiment

[0047] Fig. 1 is a descriptive view showing a configuration of a fuel cell system 10This represents a first embodiment of the invention. In this embodiment, the invention is applied to a vehicle-mounted power generation system for a fuel cell vehicle. As in Fig. The fuel cell system shown in 1 contains 10 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 the power generation, an oxidation gas piping system 30 , which supplies air to the fuel cell as an oxidation gas 2 supplies, a fuel gas pipeline system 40 , which supplies hydrogen gas as the fuel gas to the fuel cell 20 supplies an electrical power system 50 , which charges or discharges an electrical power to and from the system, a control unit 60, which performs overall control of the entire system, etc.

[0048] The fuel cell 20 It 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 the fuel cell 20The fuel cell comprises 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). A pair of separators is provided to sandwich the cathode and anode electrodes on either side. Fuel gas is fed into one separator, and oxidizer gas is fed into the other separator. As a result of this gas supply, the fuel cell generates 20 an electrical power.

[0049] 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 is a temperature of the fuel cell 20 They are recorded at the fuel cell 20 appropriate.

[0050] The oxidation gas piping system 30 contains an air compressor 31 , an oxidation gas supply passage 32 , a humidification module 33 , a cathode exhaust gas flow passage 34 , an M1 engine that powers the air compressor 31 drives, etc.

[0051] The air compressor 31 is driven by a driving force from the motor M1, which is controlled by a control command from the control unit 60is activated to supply oxygen (oxidation gas), which is drawn in from outside air via an air filter (not shown in the figure), and the compressed oxygen to the cathode electrode of the fuel cell. 20 supplies. A speed sensor. 3a The device, which detects the rotational speed (one rotational speed per predetermined time; similar to what follows) of motor M1, is attached to motor M1. The oxidation gas supply passage 32 is a gas flow passage for guiding the air from the air compressor 31 oxygen supplied to the cathode electrode of the fuel cell 20 A cathode exhaust gas is drawn from the cathode electrode of the fuel cell through the cathode exhaust gas flow passage. 34 The cathode exhaust contains the exhaust gas of the oxygen after it has contributed to a fuel cell reaction in the fuel cell. 20 The cathode exhaust contains a substance produced by the cell reaction in the fuel cell. 20It generates moisture and is therefore in a state of high humidity.

[0052] The humidity module 33 moistens the fuel cell 20 supplied oxidation gas suitable by exchanging moisture between the material passing through the oxidation gas supply passage 32 flowing low-moisture oxidation gas and the cathode exhaust gas flow passage 34 flowing high-humidity cathode exhaust. The cathode exhaust flow passage 34 A gas flow passage is used to discharge the cathode exhaust gas to the outside of the system, and a backpressure regulating valve A1 is located near a cathode electrode outlet of the gas flow passage. A pressure (hereinafter referred to as the "cathode backpressure") of the gas flow from the fuel cell is controlled by the gas flow passage. 20 The amount of released oxidation gas is regulated by the back pressure control valve A1. A pressure sensor 3b, which detects the cathode back pressure, is located at the cathode exhaust gas flow passage 34 between the fuel cell 20 and attached to the back pressure regulating valve A1.

[0053] The fuel gas pipeline 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 , an M2 motor to drive the hydrogen circulation pump 45 , etc.

[0054] The fuel gas supply source 41 The fuel gas, such as hydrogen gas, is fed into the fuel cell. 20 to, and is formed, for example, by a high-pressure hydrogen tank, a hydrogen storage tank, or the like. The fuel gas supply passage 42is a gas flow passage for guiding the gas from the fuel gas supply source 41 released fuel gas to the anode electrode of the fuel cell 20 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 path in sequence from an upstream 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 formed, for example, by solenoid valves.

[0055] The fuel gas recirculation passage 43 is a control gas flow passage for recirculating unreacted fuel gas to the fuel cell 20 , and an FC outlet valve H4, the hydrogen circulation pump 45 and the check valve46 are arranged in the gas flow passage in sequence from an upstream side to a downstream side. A low-pressure, unreacted fuel gas supplied by the fuel cell. 20 The hydrogen is delivered and is suitable for use by the hydrogen circulation pump. 45 under pressure, which is exerted by the driving force from the control unit by a control command. 60 The M2 motor is driven, and to the fuel gas supply passage. 42 is supplied. A backflow of fuel cell gas from the fuel gas supply passage. 42 to the fuel gas recirculation passage 43 is passed through the check valve 46 suppressed. The anode exhaust flow passage 44 is a gas flow passage for releasing an anode exhaust containing hydrogen exhaust gas from the fuel cell 20is released to the outside of the system, and a drain valve H5 is arranged in the gas flow passage.

[0056] The electrical power system 50 includes a high-pressure direct current / direct current (DC / DC) converter 51 , a battery 52 , a traction converter 53 , an additional inverter 54 , a traction motor M3, an auxiliary motor M4, etc.

[0057] The high-pressure DC / DC converter 51 is a DC / DC voltage converter with a function for regulating a DC voltage input from the battery 52 and to output the regulated DC voltage to the traction inverter 53 , and a function for controlling a DC voltage input therein from the fuel cell 20 or the traction motor M3 and to output the regulated DC voltage to the battery 52 Charging and discharging the battery 52is achieved through these functions of the high-pressure DC / DC converter 51 Furthermore, an output voltage of the fuel cell is achieved. 20 through the high-pressure DC / DC converter 51 controlled.

[0058] The battery 52 It is a rechargeable / dischargeable secondary battery. Various types of secondary batteries, such as a nickel-hydrogen battery or similar, can be used. The battery 52 It can be charged with an overvoltage under the control of a battery computer (not shown in the figure) and can also supply additional power. Part of the power supplied by the fuel cell 20 The generated DC power is converted by the high-pressure DC / DC converter. 51 be boosted or amplified or downgraded and the battery 52 charged. A SOC sensor 5a , which determines the battery's state of charge (SOC). 52 detected, is connected to the battery 52Appropriate. It should be noted that a rechargeable / dischargeable storage device other than a secondary battery, such as a capacitor, for example, instead of the battery, is required. 52 can be used.

[0059] A traction inverter 53 and the additional inverter 54 are pulse width modulation (PWM) inverters with a pulse width modulation system that controls the DC power output of the fuel cell 20 or the battery 52 The system converts the voltage into three-phase alternating current in response to a given control command and supplies this 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 sensor 5bThe motor that 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 M2 engine, which powers the hydrogen circulation pump, 45 The components that drive the engine, etc., are collectively referred to as the M4 auxiliary engine.

[0060] The control unit 60 It forms a central processing unit (CPU), a read-only memory (ROM), a working memory (RAM), etc., and forms an overall control system for the corresponding parts of the system based on input sensor signals. In particular, the control unit calculates 60 a required amount of power generation (hereinafter referred to as a “required output”) by the fuel cell 20 , is required based on the corresponding sensor signals from an accelerator pedal sensor 81 , which involves turning an accelerator pedal 80detected by the SOC sensor 5a , the speed sensors 3a , 5b etc. will be transferred.

[0061] The control unit 60 This then controls an output voltage and output current of the fuel cell 20 such that the fuel cell 20 The required output is generated. Furthermore, the control unit controls 60 the traction motor M3 and the auxiliary motor M4 for controlling output pulses and the like of the traction inverter 53 and the additional inverter 54 .

[0062] In the fuel cell 20 Does a platinum surface area decrease when the fuel cell's service life increases? 20 over a period of time, the output voltage decreases. In other words, as the surface area of ​​platinum on the cathode catalyst layer decreases over the fuel cell's operating time, the voltage drops. 20If the power output increases, it becomes impossible to obtain the required output power from the fuel cell. 20 to obtain. This allows the control unit to 60 It is ensured that the required output power can be obtained by estimating the platinum surface area and controlling the backpressure control valve A1 according to the estimated result. This control processing (cathode backpressure control processing) is carried out by the operation of a required output acquisition unit. 61 , a gas pressure sensitivity detection unit 62 , a correspondence relationship calculation unit 63 , a target gas pressure calculation unit 64 and a gas pressure conversion unit 65 to be implemented. The corresponding units 61 until 65 The cathode backpressure control process is described in detail below.

[0063] Fig. 2 is a flowchart that shows a process through the control unit 60 This represents the cathode backpressure control processing. The cathode backpressure control processing is executed repeatedly at predetermined time intervals (for example, every 10 ms). When the processing begins, the control unit determines 60 First, whether an instantaneous point in time (a point in time at which the cathode backpressure control processing is executed) corresponds to a point in time to start increasing the cathode backpressure (a cathode backpressure increase point in time) (Silo step). When a driver makes a load request by pressing down the accelerator pedal 80 created by the air compressor 31The amount of oxidation gas supplied is increased by a control process not shown in the figures, leading to an increase in cathode backpressure. This causes a determination in step S110 as to whether a current time corresponds to the time of the cathode backpressure increase.

[0064] If, at step S110, it is determined that the current time corresponds to the time of the cathode back pressure increase, the control unit proceeds. 60 the processing to step S120, in which the processing is carried out to obtain a cathode back pressure P from the pressure sensor 3p to obtain. Next, the control unit calculates 60 a fluctuation ΔP of the cathode back pressure from a cathode back pressure obtained during the previous execution of the cathode back pressure control processing by subtracting the previous cathode back pressure from the cathode back pressure P obtained in step S110 (step S130).

[0065] Next, the control unit receives 60 an output W of the fuel cell 20 (Step S140). In particular, the control unit determines 60 an output power as output W by obtaining the current from the current sensor 2a and the voltage from the voltage sensor 2b , and the current is multiplied by the voltage. Next, the control unit calculates 60 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 obtained output W (step S150).

[0066] Next, the control unit divides 60The fluctuation ΔW of the output is determined by the fluctuation ΔP of the cathode backpressure, and the resulting quotient is stored 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. Next, the control unit performs 60 the processing to estimate a cathode backpressure output ceroid curve based on the cathode backpressure sensitivity S (step S170).

[0067] 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 is obtained. 20The output W is plotted on the ordinate, corresponding to the cathode backpressure P, resulting in a cathode backpressure-output characteristic curve, represented by curve C1. Curve C1 and curves C2 and C3, described below, can be determined beforehand through experimentation 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.

[0068] 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.

[0069] 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.

[0070] In this embodiment, the cathode backpressure increase time is detected in step S110, and it is then assumed that the cathode backpressure increase time 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. 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 the memory unit. 60 stored and the CPU of the control unit 60The cathode backpressure output characteristic curve is determined 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 associated with that 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.

[0071] Returning to Fig. 2 receives the control unit after executing step S170. 60a required output TW, which is generated by the fuel cell 20 is required (step S180). The required output TW corresponds to a previously mentioned required power generation amount, and as described above, is based on the reading from the accelerator pedal sensor. 81 , the SOC sensor 5a , the speed sensors 3a , 5b etc. calculated from the corresponding sensor signals transmitted.

[0072] Next, the control unit refers to 60 The cathode backpressure output characteristic curve obtained in step S170 is used to calculate a target cathode backpressure TP corresponding 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).

[0073] After executing step S190, the control unit controls 60 The control unit 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 regulating valve A1 (step S192). After executing step S192, the control unit terminates. 60 temporarily the cathode backpressure control processing.

[0074] If, in step S110, it is determined that the current time does not correspond to the time of the cathode back pressure increase, the control unit determines, on the other hand, 60 , whether the cathode backpressure output characteristic curve has been obtained (step S194). If it is determined below that the cathode backpressure output characteristic curve has been obtained, the control unit 60 the processing to step S180, in which the control unit 60 The system calculates the target cathode back pressure TP in the manner described above using the cathode back pressure output characteristic curve obtained during the above cathode back pressure control processing and the required output TW obtained during the execution of the current cathode back pressure control processing, and controls the cathode back pressure P to the target cathode back pressure TP.

[0075] If step S194 determines that the cathode backpressure output characteristic curve was not obtained, the cathode backpressure control processing is temporarily terminated.

[0076] The processing of step S180 in the cathode backpressure control processing is considered the required output acquisition unit, as described above. 61 ( 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 .

[0077] In the fuel cell system 10According 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 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 decreased, but also when the fuel cell output decreased. 20 This decreases due to a reduction in the platinum surface area resulting from the use of the fuel cell. Therefore, the fuel cell system can be used... 10 According to the first embodiment, the required output TW can be reliably ensured, thereby improving power generation performance. Furthermore, according to the fuel cell system... 10 The cathode back pressure is controlled as the pressure of the oxidation gas, and therefore the oxidation gas control can be implemented with a favorable response behavior. Second embodiment

[0078] Fig. 4 is a flowchart illustrating a cathode backpressure control process 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, this only applies to the cathode backpressure control processing performed by the control unit. The hardware configuration of the second embodiment is identical to that of the first embodiment, and therefore, in the following embodiment, the corresponding components are assigned the same reference numerals.

[0079] 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. Step 4 is replaced. The processing of the remaining steps S120 to S194 is identical. When processing begins, the control unit determines 60 , 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 towards a high-load operating point (a high-load shift point) (step S210). In particular, this shifts, for example, when the driver initiates a high-load request by depressing the accelerator pedal. 80 powerfully displays the load of the fuel cell 20 to the high-load operating point. Hereinafter, the "high-load operating point" refers to a high-load operating condition in which the 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.

[0080] 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.

[0081] This allows the fuel cell system according to the second embodiment to be used similarly to the fuel cell system 10 According to the first embodiment, the required output TW can be ensured more reliably, thereby improving power generation performance. Furthermore, the following effect is achieved. Normally, when the fuel cell's load 20 Since the cathode backpressure output characteristic curve is small, the increasing slope of the 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 fuel cell load changes. 20The operating point begins to shift towards the high-load point, and 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 further improvements in power generation performance.

[0082] It should be noted that in the second embodiment, the cathode backpressure sensitivity S is determined at the time when the load on the fuel cell changes. 20 begins to shift towards the high-load operating point, but instead of 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 20begins to shift towards the low-load operating point. Below, 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.

[0083] 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 demand occurs, i.e., a demand to shift the load of the fuel cell... 20 At a low-load operating point X4, 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 the fuel cell 20The system begins to shift towards the low-load operating point X4. 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, whereupon the cathode backpressure P is controlled to achieve the target cathode backpressure TP.

[0084] 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

[0085] A fuel cell system according to a third embodiment has an identical hardware configuration of the fuel cell system. 10 according to the first embodiment, and differs from it only in the control unit 60The 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.

[0086] Fig. Figure 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. 7 is shown when processing first begins, that the control unit 60 an impedance R (step S310) is obtained. The impedance R is determined by dividing the value by the voltage sensor. 2b voltage detected by the current sensor 2a Received recorded electricity.

[0087] Next, the control unit determines 60, 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 that is greater than the first predetermined value R1.

[0088] The impedance R indicates the humidity level of the fuel cell's interior. 20 and if the impedance R is within the range (hereinafter referred to as an “acceptable range”) extending from the first predetermined value R1 to the second predetermined value R2, this indicates that the moisture state 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 20is in a flooded state, and if the impedance R is greater than the second predetermined value R2, this indicates that the fuel cell 20 is in a dried-out state.

[0089] 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.

[0090] 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 20If the cathode backpressure output characteristic curve is flooded or dried out, it is estimated using corrected tabular data (step S330).

[0091] 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 experimentation or simulation.

[0092] 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.

[0093] Returning to Fig. 7, following the execution of step S320 or step S330, the characteristic curve estimation processing is temporarily terminated.

[0094] The fuel cell system according to the third embodiment with the above configuration can be used similarly to the fuel cell system 10In the first embodiment, the required output TW is reliably ensured, 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 20When 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 tabulated data, and therefore the required output TW can be ensured more reliably. Furthermore, when the fuel cell 20 When the cathode backpressure dries out, the output characteristic curve is similar to that of the flooded state. However, in this case as well, the reduction in output can be corrected by increasing the cathode backpressure according to 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.

[0095] It should be noted that in the third embodiment, the moisture level inside the fuel cell 20The humidity level is determined based on the impedance R, but 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 level is determined based on a measurement result from the dew point meter. According to the first modified example, the humidity level of the fuel cell can be determined with a higher degree of accuracy.

[0096] Furthermore, in step S315 of the first embodiment, an AND condition is performed to determine that the impedance R is not less than the first predetermined value R1 and not greater than the second predetermined value R2. However, instead of a second modified example of the first embodiment, a determination can be made simply as to 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. Furthermore, as a third modified example of the third embodiment, a determination can be made simply as to whether the impedance R is smaller than the predetermined value R1. With this configuration, the cathode backpressure output characteristic curve can be estimated using the corrected tabulated data when the fuel cell is flooded. 20It should be noted that in the third embodiment, identical corrected table data are used in both the flooded and dried-out 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.

[0097] Furthermore, in the third embodiment, the determination of whether the fuel cell 20 is flooded or dried out, based on the impedance R, but a fourth modified example of the third embodiment can instead determine whether the fuel cell is flooded or dried out. 20 flooded or dried out, based on the temperature of the fuel cell 20 execute, which are determined by the temperature sensor 2cis detected. Similar effects according to the third embodiment are obtained with the fourth modified example.

[0098] 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 section 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

[0099] A fuel cell system according to a fourth embodiment differs from the fuel cell system 10 According to the third embodiment, this applies only to the characteristic curve estimation processing performed by the control unit, and is identical 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.

[0100] Fig. Figure 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. 2 shown cathode backpressure processing instead of the processing of step170 executed. As in Fig. As shown in 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 a no-load load is received. The magnitude of the no-load load approximates a load received in an open (OC) circuit state. In this embodiment, the determination of whether the fuel cell 20 in the idle state, by determining whether the voltage sensor 2b The detected voltage was above a predetermined voltage continuously for at least a predetermined time. Below, if it is determined that the fuel cell 20Not 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 Fig. 7, and the values ​​of the normal table data are also identical.

[0101] If in step S410 it is determined that the fuel cell 20 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 above configuration, similar to the fuel cell system... 10According to the first embodiment, the required output TW can be ensured more reliably, thereby improving power generation performance. Furthermore, the following effect is achieved: During idle operation, power generation is continuously performed at a high voltage, thus increasing the platinum oxidation film thickness until it reaches a predetermined level, leading to a reduction in the data usage rate. In the fourth embodiment, the reduction in output caused by the reduced platinum usage rate can be corrected by increasing the cathode backpressure with the corrected table data, thus ensuring the required output TW more reliably. This further improves power generation performance.

[0102] 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.

[0103] 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. 10 shows, a determination is carried out as to whether the fuel cell 20is in a temporary operating state (step S410). In the temporary operating state, where a reaction gas (the oxidation gas and the fuel gas) is supplied to the fuel cell. 20 The system is repeatedly started and stopped intermittently, maintaining a lower voltage continuously. Consequently, the amount of platinum oxide in the cell decreases to a predetermined level, thereby increasing the platinum utilization rate to almost 100%. Below, if it is determined that the fuel cell... 20 In the temporary operating state in step S510, the cathode backpressure output characteristic curve with the normal data is similar to step S420. Fig. 9 is estimated. On the other hand, if it is determined that the fuel cell 20 In the temporary operating state determined in step S510, the cathode backpressure output characteristic curve is calculated with the corrected table data similarly to step S430. Fig. 9 was estimated. In this way, the required TW expenditure can be ensured more reliably. Fifth embodiment

[0104] 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 is obtained, the estimated cathode backpressure output characteristic curve is stored in a non-volatile memory, for example an electrically erasable programmable read memory (EPROM) located in the control unit 60 is contained, stored, 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.

[0105] 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

[0106] 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 = A Pti O (1 – θ)(P O2 / P ref )exp(–αFη / RT) (1) 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 overpotential, “R” is a gas constant and “T” is the fuel cell temperature.

[0107] In equation (1), a value for the cathode platinum surface area can be obtained by 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 for the cathode AC current density i O is a fixed value determined during the design phase of the fuel cell.

[0108] 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.

[0109] A value of the required partial pressure of oxygen P O2 can be achieved by multiplying the value obtained from the pressure sensor 3b The measured cathode back pressure P is obtained 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. It should be noted that "kPa-abs" is a unit-representing absolute pressure. The charge transfer coefficient α, the Faraday constant F, and the gas constant T each take on 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 measured by the voltage sensor. 2b The fuel cell temperature T is obtained by the temperature sensor. 2c receive.

[0110] 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 with 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 2. 170 .

[0111] As in Fig. As shown in 11, the control unit receives, when processing first starts, the control unit 60 This fuel cell temperature T from the temperature sensor 2c (S610). Next, the control unit receives 60 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 determines 60 the cathode platinum surface area type based on the one in step S160 of Fig. 2. Determine the cathode backpressure sensitivity S (step S630). As described above, the type of cathode platinum surface area can be calculated from the cathode backpressure sensitivity S.

[0112] Next, the control unit determines 60Whether 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 of operation, 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).

[0113] If step S640 determines that the platinum utilization rate is unknown, the control unit 60 the processing to step S650, where the update processing is performed, and subsequently the cathode backpressure control of Fig. 2. The update process is executed from the beginning. It is performed to remove the platinum oxide layer from the cathode catalyst layer. In particular, the fuel cell voltage is adjusted. 20 to a threshold that is predefined as a recovery target voltage by the DC / DC converter 51The voltage is set and reduced. A converter command voltage is then maintained at the threshold in such a way that the oxide layer is blown away, resulting in an oxidation utilization rate of 100% or more, and thereby increasing the efficiency of the DC / DC converter. 51 The resulting voltage reduction is eliminated. In this way, the cell voltage of the fuel cell is restored. 20 The gas is reduced to a reduced zone, thereby reducing or removing the oxidation layer on the surface of the Pt catalyst. It should be noted that the oxidation gas is expelled by fully opening the backpressure control valve A1 and the speed of the compressor motor M1. 31 is maximized.

[0114] On the other hand, if step S640 determines that the platinum utilization rate is known, the control unit estimates 60the cathode backpressure output characteristic curve with 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 to determine 60 a correspondence relationship between the required oxygen partial pressure P O2 and 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. O2The 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.

[0115] This allows the fuel cell system according to the sixth embodiment to be used similarly to the fuel cell system 10 According to the first embodiment, the required output TW can be ensured more reliably, thereby improving power generation performance. Furthermore, with the fuel cell system according to the sixth embodiment, the cathode backpressure output characteristic curve is determined using a formula, 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.

[0116] 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 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

[0117] 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, it further differs 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 following description.

[0118] 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 first performs the following steps. 60 the processing to determine the cathode back pressure P from the pressure sensor 3b (Step S710). Next, the control unit receives 60 the actual output W of the fuel cell 20 (Step S720). In particular, the control unit determines 60 The output power is defined 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.

[0119] Next, the control unit compares 60The actual cathode backpressure sensitivity is compared to an estimated cathode backpressure sensitivity S, and an actual output absolute is compared to 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.

[0120] 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, the flooding in the fuel cell is determined to be stopped. 20 occurs, and therefore a flood avoidance process is executed (step S740).

[0121] 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.

[0122] The flood prevention processing of step S740 is executed to prevent flooding caused by the humidification module. 33 to reduce the amount of humidification applied under normal conditions. It should be noted that flood prevention processing is not necessarily limited to this configuration and can also be implemented with other methods, such as increasing the initial temperature of the fuel cell. 20. In particular, 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.

[0123] 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.

[0124] Fig. Figure 13 is a descriptive view showing the variation of the cathode backpressure output characteristic curve as a function of the presence or absence of flooding under the corresponding states. The states are the corresponding combinations of high and low platinum utilization rates and large and small effective platinum surface areas.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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

[0130] 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 battery condition 52 is improved by a single control process. This overall control is achieved by the control unit. 60 executed.

[0131] Fig. Figure 14 is a flowchart representing overall control processing according to an eighth embodiment. The overall control processing is performed repeatedly by the control unit. 60 The process is executed at predetermined time intervals. As shown in the figures, when processing begins, the control unit performs the following actions. 60 the processing to achieve the corresponding states of the fuel cell 20 and the battery 52 to record and assess (step S810). The control unit 60 For example, it records the state of the fuel cell 20 by estimating the amount of moisture in the fuel cell 20 by determining their impedance value and the amount of moisture, whether the fuel cell 20 is dried out or flooded. Furthermore, the control unit, for example, detects 60 the battery condition 52 by determining a deterioration state of the battery52 from a voltage measurement obtained during startup.

[0132] Next, the control unit determines 60 a suitable area of ​​the battery's SOC based on the fuel cell's states 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 a value stored in the battery. 52 The remaining amount of electricity is obtained from the amount of electricity stored in the battery when the battery is fully charged. It should be noted that the battery's state of charge (SOC) can be defined as a chargeable amount rather than a remaining capacity. The "acceptable range" is a range within which the battery 52can be used effectively. The permissible range changes according to the state of the fuel cell. 20 as well as the condition of the battery 52 The permissible range is continuously increased when an internal state of the fuel cell is affected. 20 has worsened.

[0133] Next, the control unit performs 60 a process for reading the battery's SOC 52 from (step S830). In particular, the SOC is based on a charging / discharging current of the battery. 52 calculated, which is detected by a battery current sensor (not shown). Next, the control unit determines 60 Step S840 determines whether the state of charge (SOC) obtained in step S830 is within an acceptable range obtained in step S820. If step S840 determines that the SOC is not within the appropriate range, a required charge / discharge amount is calculated to shift the battery's SOC. 52in the appropriate area (step S850).

[0134] After executing step S850, the control unit determines 60 Fluctuations (fluctuation amounts) of the cathode back pressure and a cathode flow rate required for the output TW from the fuel cell 20 is required, is necessary to achieve a magnitude that is increased by the battery charge / discharge amount determined in step S850 (step S860). The "cathode flow rate" is a flow rate of the fluid to the fuel cell. 20 supplied oxidizing gas.

[0135] Fig. Figure 15 is a diagram illustrating the correspondence relationship between the cathode backpressure P and the cathode flow rate L during the execution of the cathode backpressure control process. When the accelerator pedal is pressed, the pressure is determined by the pressure of the cathode backpressure. 80If the operating state is depressed in such a way that it shifts from point Xa to point Xb with the cathode backpressure control processing 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 drawing. 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.

[0136] Fig. Figure 16 is a time diagram showing a fluctuation in the cathode back pressure P, the cathode flow rate L, and the fuel cell output W. 20 This represents the accelerator pedal. It is assumed that the accelerator pedal 80at time t1 is suppressed to such an extent that the output W of the fuel cell 20 The required output TW is reached at time t2. A 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.

[0137] 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.

[0138] 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 the fuel cell 20The required output TW is set at time t4, which is earlier than 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 time t2, at which the cathode back pressure P reaches the target 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 match 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.

[0139] After executing step S860, the control unit executes 60 The cathode backpressure control processing (step S870) and the cathode flow rate control processing (step S880) are performed. 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 by 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 varied by varying the speed of the motor M1 of the air compressor. 31controlled. 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.

[0140] 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.

[0141] The fuel cell system according to the eighth embodiment with the above configuration can be used similarly to the fuel cell system 10According to the first embodiment, the required output TW can be ensured more reliably, 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.

[0142] 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.

[0143] 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

[0144] A fuel cell system according to a ninth embodiment differs from the fuel cell system 10 According to the eighth embodiment, the difference lies solely 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 the first embodiment, the identical reference numerals used in the first embodiment are assigned to the corresponding components in the following description.

[0145] 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. 60executed at predetermined time intervals. This overall tax processing includes identical steps S810, S870, and S880 to the overall tax processing as described in Fig. The eighth embodiment shown in Figure 14 differs from it in that steps S920 to S930 are used instead of steps S820 to S860. Fig. 14 are planned. The control unit 60 determines whether the condition of the fuel cell 20 based on the state of the fuel cell estimated in step S810 20 is favorable (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 the cathode flow rate is determined such that the required output TW from the fuel cell 20 is required to reach a magnitude that is increased by the power output of an auxiliary device that is operated to maintain the state of the fuel cell.20 to improve (step S930). 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 below such that the in Fig. The performance increase shown in section 16 corresponds to the performance of the operated auxiliary device.

[0146] After executing step S930, the control unit 60 The cathode backpressure control processing (step S870) and the cathode flow control processing (step S880) are executed. 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 oscillation mode determined in step S930. After step S880 is executed, the overall control processing is temporarily terminated. If, in step S920, it is determined that the state of the fuel cell 20On the other hand, if it is inexpensive, processing continues to step S870 without executing step S930.

[0147] The fuel cell system according to the ninth embodiment with the above configuration can be used similarly to the fuel cell system 10 According to the first embodiment, the required output TW can be ensured more reliably, 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 when 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 maintain the state of the fuel cell, is also increased. 20To improve performance, this surplus is then used to supplement the system. This ensures that a balance between power demand and supply is maintained throughout the entire fuel cell system. Tenth embodiment

[0148] A fuel cell system according to a tenth embodiment differs from the fuel cell system 10 According to the ninth embodiment, the only difference lies in the overall control processing performed by the control unit, and it 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.

[0149] 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 Executed at predetermined time intervals. As shown in the drawing, when processing starts, the control unit receives... 60 First, the impedance R (step S1010). The impedance R is determined by dividing the voltage by the voltage sensor. 2b voltage detected by the current sensor 2a Received recorded electricity.

[0150] Next, the control unit determines 60The third embodiment determines whether the obtained impedance R is greater than a second predetermined value R2 (step S1020) and whether the impedance R is less than a first predetermined value R1 (< R2). The first predetermined value R1 and the second predetermined value R2 are identical in the third embodiment. If, in steps S1020 and S1030, it is determined that the impedance R lies within a suitable range (R2 ≤ R ≤ R1) extending from the first predetermined value R1 to the second predetermined value R2 (negative determinations in both S1020 and S1030), the processing proceeds to step S870. In steps S870 and S880, the cathode backpressure control processing and the cathode flow rate control processing are carried out in an identical manner as in the eighth embodiment, which is described in Fig. As shown in 14, it is executed.

[0151] If, at step S1030, it is determined that the impedance R is smaller than the first predetermined value R1, it is also determined that the amount of moisture is excessively large (i.e., it is determined that flooding has occurred), and therefore the control unit 60 The processing proceeds to step S1040. At step S1040, the control unit determines... 60 The manner in which the cathode back pressure P and the cathode flow rate L are varied (the oscillation speed / the 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 the time at which 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.

[0152] 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.

[0153] After executing step S1040 or S1050 similarly, if a negative determination is executed in step S1030, the control unit 60the processing to step S870. By performing steps S870 and S880, the cathode back pressure P and the cathode flow rate L are varied in the manner determined in step S1040.

[0154] 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.

[0155] 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.

[0156] 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

[0157] In the above embodiments, the cathode backpressure sensitivity S, which serves as a pressure sensitivity, is based on the pressure (cathode backpressure) of the fuel cell. 20 the emitted oxidation gas is determined, but instead the pressure sensitivity can be based on the pressure of the gas flowing to the fuel cell. 20The pressure sensitivity can be determined based on the supplied oxidation gas. It can also be determined based on the pressure of the oxidation gas in an oxidation gas flow passage provided within a fuel cell. Furthermore, the pressure sensitivity can be determined based on the pressure difference between an oxidation gas supply port and an oxidation gas discharge port. Modified Example 2

[0158] 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

[0159] 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

[0160] In the above embodiments and the modified examples, functions that are implemented by software can also be implemented by hardware, such as separate electronic circuits.

[0161] 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 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. [2] Fuel cell system according to claim 1, wherein the gas pressure control unit is configured to receive a required output required by the fuel cell, calculates a pressure of the oxidation gas corresponding to the required output by comparing the required output with the correspondence relationship and controls the pressure of the oxidation gas to the required gas pressure. [3] Fuel cell system according to claim 1 or 2, further comprising a storage unit which stores tabular data in which correspondence relationships between the pressure of the oxidation gas and the output of the fuel cell are each assigned to individual values ​​of the gas pressure sensitivity, wherein the gas pressure control unit is configured such that it specifies the correspondence relationship between the pressure of the oxidation gas and the output of the fuel cell by selecting the correspondence relationship which corresponds to the detected gas pressure sensitivity from the tabular data. [4] Fuel cell system according to one of claims 1 to 3, further comprising a back pressure regulating valve configured to control the pressure of the oxidation gas discharged from the cathode electrode outlet of the fuel cell, wherein the gas pressure control unit is configured to control the pressure of the oxidation gas by adjusting an opening of the back pressure regulating valve. [5] Fuel cell system according to any one of claims 1 to 4, wherein the gas pressure control unit is configured to detect the gas pressure sensitivity and to specify the correspondence relationship between the pressure of the oxidation gas and the output of the fuel cell at the time of start-up to increase the pressure of the oxidation gas. [6] Fuel cell system according to any one of claims 1 to 4, wherein the gas pressure control unit is configured to detect the gas pressure sensitivity and to specify the correspondence relationship between the pressure of the oxidation gas and the output of the fuel cell at a time when a load of the fuel cell begins to shift to an operating point with a predetermined load. [7] Fuel cell system according to any one of claims 1 to 6, wherein: the fuel cell contains an electrode catalyst; The correspondence relationship between the pressure of the oxidation gas and the output of the fuel cell comprises a first correspondence relationship and a second correspondence relationship, wherein the second correspondence relationship is defined such that a quantity of the pressure of the oxidation gas in the second correspondence relationship corresponding to an identical output of the fuel cell is greater than a quantity of the pressure of the oxidation gas in the first correspondence relationship, and the magnitude of the cathode backpressure obtained with an identical required output is greater than that of the normal table data, The gas pressure control unit is configured to specify the correspondence relationship by selecting the first correspondence relationship when the fuel cell is not in a predetermined operating state in which a utilization rate of platinum contained in the electrode catalyst decreases, and selects the second correspondence relationship when the fuel cell 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. [9] Fuel cell system according to claim 7, wherein the predetermined operating point is an idle state of the fuel cell. [10] Fuel cell system according to any one of claims 1 to 9, further comprising a non-volatile memory configured to continuously store the correspondence relationship between the pressure of the oxidation gas and the output of the fuel cell specified by the gas pressure control unit after a power supply to the fuel cell has been switched off, wherein the gas pressure control unit is configured to control the pressure of the oxidation gas within a predetermined period on the basis of the correspondence relationship stored in the non-volatile memory. [11] Fuel cell system according to any one of claims 1 to 6, further comprising a flooding determination unit configured to determine whether flooding has occurred in the fuel cell by comparing a specific gas pressure sensitivity, determined by the gas pressure control unit with an actual gas pressure sensitivity, with an actual gas pressure sensitivity derived from an actual pressure of the oxidation gas and an actual output of the fuel cell, and 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] Fuel cell system according to claim 11, wherein, when the flooding determination unit determines that flooding has occurred, the flooding determination unit is configured to perform the processing to avoid flooding. [13] Fuel cell system according to any one of claims 2 to 6, further comprising: a battery; and a gas flow rate control unit configured to control a 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 at an earlier time than at a time when the pressure of the oxidation gas reaches a set gas pressure. [14] Fuel cell system according to claim 13, further comprising a SOC determination unit configured to detect a state of charge of the battery, wherein it is determined that the battery is in a predetermined state when the detected state of charge deviates from a predetermined range. [15] Fuel cell system according to any one of claims 2 to 6, further comprising a gas flow rate control unit configured to control a 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 output of the fuel cell reaches the required output at an earlier time than at a time when the pressure of the oxidation gas reaches the target gas pressure. [16] Fuel cell system according to claim 15, wherein it is determined that the fuel cell is in the predetermined state when flooding occurs in the fuel cell. [17] 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 as gas pressure sensitivity a ratio of a fluctuation of a fuel cell output to a fluctuation of the oxidation gas pressure and to estimate a platinum surface area of ​​the cathode electrode based on the detected gas pressure sensitivity. [18] 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: Capturing the ratio of a fluctuation in the output of the fuel cell to a fluctuation in the pressure of the oxidation gas as a gas pressure sensitivity; Specifying a correspondence relationship between the pressure of the oxidation gas and the output of the fuel cell based on the measured gas pressure sensitivity; and Controlling the pressure of the oxidation gas based on the specified correspondence relationship. [19] 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: Controlling the pressure of the oxidation gas; Determining the ratio of a fluctuation in the fuel cell output to a fluctuation in the pressure of the oxidation gas as a gas pressure sensitivity; and Estimating a platinum surface area of ​​the cathode electrode based on the measured gas pressure sensitivity.