JP5146639B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system that generates power upon receiving a reaction gas.

  A fuel cell stack is an energy conversion system for causing an electrochemical reaction by supplying a fuel gas and an oxidizing gas to a membrane-electrode assembly and converting chemical energy into electric energy. Among them, a solid polymer electrolyte fuel cell stack using a solid polymer membrane as an electrolyte is easy to downsize at a low cost and has a high output density, so that it is expected to be used as an in-vehicle power source. .

As one of the indexes for optimally controlling the operating state of the fuel cell stack, the AC impedance of the fuel cell stack is used. Since this AC impedance value has a correlation with the wet state of the electrolyte membrane, the wet state of the electrolyte membrane can be detected by measuring the AC impedance value. For example, Japanese Patent Laid-Open No. 7-235324 discloses a method for estimating the water content inside a fuel cell stack based on the AC impedance of the fuel cell stack. If the electrolyte membrane is in excess or insufficient moisture, the output of the fuel cell stack will be reduced due to flooding or dryout phenomenon, so the electrolyte membrane is optimally wet for optimal control of battery operation. Need to be maintained.
JP 7-235324 A

  However, as the aging of the fuel cell stack progresses, the correlation between the AC impedance and the moisture content gradually changes, so the map data showing the correlation between the AC impedance and the moisture content deviates from the actual correlation. Resulting in.

  Therefore, an object of the present invention is to propose a fuel cell system that can solve the above problems and can appropriately correct map data indicating the correlation between the AC impedance and the moisture content.

  In order to solve the above-described problems, a fuel cell system according to the present invention includes a fuel cell, map data indicating a correlation between the AC impedance of the fuel cell and a water content, and a water content calculated by water balance calculation of the fuel cell. And a correction unit that corrects an error in the map data based on the measured value of the AC impedance of the fuel cell.

  Since the correlation between the AC impedance of the fuel cell and the moisture content gradually changes with the aging of the fuel cell, the water content calculated by the water balance calculation of the fuel cell and the measured value of the AC impedance of the fuel cell By using it, the error of the map data can be corrected.

  In the correlation between the AC impedance and the moisture content, there is a dead zone where the AC impedance value does not change when a certain moisture content is exceeded. In the dead zone area, the value of AC impedance is almost constant regardless of the amount of moisture, so the correction unit uses this dead characteristic to correct map data with high accuracy even when the estimation accuracy of moisture is low. it can.

  The correction unit preferably corrects an error in the map data by forcibly shifting the operation state of the fuel cell to the dead zone region. In order to forcibly transition the operating state to the dead zone region, the water balance may be controlled in the direction in which water accumulates inside the fuel cell.

  The correction unit can calculate the water content based on the amount of heat absorbed when the ice inside the fuel cell melts during warm-up operation below freezing. The water content inside the fuel cell is Mw, the amount of heating applied per unit time per unit mass of ice during warm-up operation is Q, and the time required for the ice inside the fuel cell to completely melt and change to water If Δt and the heat of fusion per unit mass of water are Cw, the relationship Mw = Q × Δt / Cw is established.

  According to the present invention, it is possible to appropriately correct map data indicating the correlation between AC impedance and moisture content.

Embodiments according to the present invention will be described below with reference to the drawings.
FIG. 1 shows a system configuration of a fuel cell system 10 according to the present embodiment.
The fuel cell system 10 functions as an in-vehicle power supply system mounted on a fuel cell vehicle. The fuel cell stack 20 generates electric power by receiving supply of reaction gas (fuel gas, oxidant gas), and air as oxidant gas. Gas supply system 30 for supplying the fuel cell stack 20 with hydrogen, fuel gas supply system 40 for supplying hydrogen gas as the fuel gas to the fuel cell stack 20, and power for controlling charge and discharge of power A system 50, a cooling system 60 for cooling the fuel cell stack 20, and a control unit (ECU) 90 for controlling the entire system are provided.

  The fuel cell stack 20 is a solid polymer electrolyte cell stack formed by stacking a plurality of cells in series. In the fuel cell stack 20, the oxidation reaction of the formula (1) occurs at the anode electrode, and the reduction reaction of the equation (2) occurs at the cathode electrode. In the fuel cell stack 20 as a whole, the electromotive reaction of the formula (3) occurs.

H ₂ → 2H ⁺ + 2e ⁻ (1)
(1/2) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (2)
H ₂ + (1/2) O ₂ → H ₂ O (3)

  A voltage sensor 71 for detecting the output voltage of the fuel cell stack 20 and a current sensor 72 for detecting the generated current are attached to the fuel cell stack 20.

  The oxidizing gas supply system 30 includes an oxidizing gas passage 34 through which oxidizing gas supplied to the cathode electrode of the fuel cell stack 20 flows, and an oxidizing off gas passage 36 through which oxidizing off gas discharged from the fuel cell stack 20 flows. . In the oxidizing gas passage 34, an air compressor 32 that takes in the oxidizing gas from the atmosphere via the filter 31, a humidifier 33 for humidifying the oxidizing gas supplied to the cathode electrode of the fuel cell stack 20, and an oxidizing gas supply A throttle valve 35 for adjusting the amount is provided. The oxidizing off gas passage 36 includes a back pressure adjusting valve 37 for adjusting the oxidizing gas supply pressure, and a humidifier 33 for exchanging moisture between the oxidizing gas (dry gas) and the oxidizing off gas (wet gas). Is provided.

  The fuel gas supply system 40 includes a fuel gas supply source 41, a fuel gas passage 45 through which fuel gas supplied from the fuel gas supply source 41 to the anode electrode of the fuel cell stack 20 flows, and fuel discharged from the fuel cell stack 20. A circulation passage 46 for returning the off gas to the fuel gas passage 45, a circulation pump 47 that pumps the fuel off gas in the circulation passage 46 to the fuel gas passage 43, and an exhaust drainage passage 48 that is branched and connected to the circulation passage 47. Have.

  The fuel gas supply source 41 is composed of, for example, a high-pressure hydrogen tank or a hydrogen storage alloy, and stores high-pressure (for example, 35 MPa to 70 MPa) hydrogen gas. When the shut-off valve 42 is opened, the fuel gas flows out from the fuel gas supply source 41 into the fuel gas passage 45. The fuel gas is decompressed to, for example, about 200 kPa by the regulator 43 and the injector 44 and supplied to the fuel cell stack 20.

  The fuel gas supply source 41 includes a reformer that generates a hydrogen-rich reformed gas from a hydrocarbon-based fuel, and a high-pressure gas tank that stores the reformed gas generated by the reformer in a high-pressure state. It may be configured.

  The regulator 43 is a device that regulates the upstream side pressure (primary pressure) to a preset secondary pressure, and includes, for example, a mechanical pressure reducing valve that reduces the primary pressure. The mechanical pressure reducing valve has a housing in which a back pressure chamber and a pressure adjusting chamber are formed with a diaphragm therebetween, and the primary pressure is reduced to a predetermined pressure in the pressure adjusting chamber by the back pressure in the back pressure chamber. It has a configuration for the next pressure.

  The injector 44 is an electromagnetically driven on-off valve capable of adjusting the gas flow rate and gas pressure by driving the valve body directly with a predetermined driving cycle with an electromagnetic driving force and separating the valve body from the valve seat. The injector 44 includes a valve seat having an injection hole for injecting gaseous fuel such as fuel gas, a nozzle body for supplying and guiding the gaseous fuel to the injection hole, and an axial direction (gas flow direction) with respect to the nozzle body. And a valve body that is slidably accommodated and opens and closes the injection hole.

  An exhaust / drain valve 49 is disposed in the exhaust / drain passage 48. The exhaust / drain valve 49 is operated according to a command from the control unit 90, thereby discharging the fuel off-gas containing impurities in the circulation passage 46 and moisture to the outside. By opening the exhaust drain valve 49, the concentration of impurities in the fuel off-gas in the circulation passage 46 is lowered, and the hydrogen concentration in the fuel off-gas circulating in the circulation system can be increased.

  The fuel off gas discharged through the exhaust drain valve 49 is mixed with the oxidizing off gas flowing through the oxidizing off gas passage 34 and diluted by a diluter (not shown). The circulation pump 47 circulates and supplies the fuel off-gas in the circulation system to the fuel cell stack 20 by driving the motor.

  The power system 50 includes a DC / DC converter 51, a battery 52, a traction inverter 53, a traction motor 54, and auxiliary machinery 55. The DC / DC converter 51 boosts the DC voltage supplied from the battery 52 and outputs it to the traction inverter 53, and the DC power generated by the fuel cell stack 20, or the regenerative power collected by the traction motor 54 by regenerative braking. Power conversion means having a function of lowering the voltage of the battery 52 and charging the battery 52. The charge / discharge of the battery 52 is controlled by these functions of the DC / DC converter 51. Further, the operation point (output voltage, output current) of the fuel cell stack 20 is controlled by voltage conversion control by the DC / DC converter 51.

  The battery 52 functions as a surplus power storage source, a regenerative energy storage source during regenerative braking, and an energy buffer during load fluctuations associated with acceleration or deceleration of the fuel cell vehicle. As the battery 52, for example, a secondary battery such as a nickel / cadmium storage battery, a nickel / hydrogen storage battery, or a lithium secondary battery is suitable.

  The traction inverter 53 is, for example, a PWM inverter driven by a pulse width modulation method, and converts a DC voltage output from the fuel cell stack 20 or the battery 52 into a three-phase AC voltage in accordance with a control command from the control unit 90. Thus, the rotational torque of the traction motor 54 is controlled. The traction motor 54 is a three-phase AC motor, for example, and constitutes a power source of the fuel cell vehicle.

  Auxiliary machines 55 are motors (for example, power sources such as pumps) arranged in each part in the fuel cell system 10, inverters for driving these motors, and various on-vehicle auxiliary machines. (For example, an air compressor, an injector, a cooling water circulation pump, a radiator, etc.) is a general term.

  The cooling system 60 includes refrigerant passages 61, 62, 63, and 64 for flowing the refrigerant circulating in the fuel cell stack 20, a circulation pump 65 for pumping the refrigerant, and heat exchange between the refrigerant and the outside air. A radiator 66, a three-way valve 67 for switching the refrigerant circulation path, and a temperature sensor 74 for detecting the refrigerant temperature are provided. During normal operation after the warm-up operation is completed, the refrigerant flowing out of the fuel cell stack 20 flows through the refrigerant passages 61 and 64 and is cooled by the radiator 66, and then flows through the refrigerant passage 63 and flows into the fuel cell stack 20 again. Thus, the three-way valve 67 is controlled to open and close. On the other hand, during the warm-up operation immediately after system startup, the three-way valve 67 is controlled to open and close so that the refrigerant flowing out of the fuel cell stack 20 flows through the refrigerant passages 61, 62, 63 and again into the fuel cell stack 20.

  The control unit 90 is a computer system including a CPU, a ROM, a RAM, an input / output interface, and the like, and functions as a control unit for controlling battery operation. For example, when the control unit 90 receives the activation signal IG output from the ignition switch, the control unit 90 starts the operation of the fuel cell system 10, and the accelerator opening signal ACC output from the accelerator sensor or the vehicle speed output from the vehicle speed sensor. The required power of the entire system is obtained based on the signal VC and the like.

  The required power of the entire system is the total value of the vehicle running power and the auxiliary machine power. Auxiliary power is the power consumed by in-vehicle accessories (humidifiers, air compressors, hydrogen pumps, cooling water circulation pumps, etc.), and equipment required for vehicle travel (transmissions, wheel control devices, steering devices, and suspensions) Power consumed by devices, etc., and power consumed by devices (air conditioners, lighting fixtures, audio, etc.) disposed in the passenger space.

  Then, the control unit 90 determines the distribution of the output power of each of the fuel cell stack 20 and the battery 52, calculates a power generation command value, and makes the power generation amount of the fuel cell stack 20 coincide with the target power. The oxidizing gas supply system 30 and the fuel gas supply system 40 are controlled. Furthermore, the control unit 90 controls the operating point (output voltage, output current) of the fuel cell stack 20 by controlling the DC / DC converter 51 and adjusting the output voltage of the fuel cell stack 20. The control unit 90 outputs, for example, each of the U-phase, V-phase, and W-phase AC voltage command values to the traction inverter 53 as a switching command so that a target torque according to the accelerator opening is obtained, and the traction motor The output torque of 54 and the rotation speed are controlled.

FIG. 2 is an exploded perspective view of the cells 21 constituting the fuel cell stack 20.
The cell 21 includes an electrolyte membrane 22, an anode electrode 23, a cathode electrode 24, and separators 26 and 27. The anode electrode 23 and the cathode electrode 24 are diffusion electrodes having a sandwich structure with the electrolyte membrane 22 sandwiched from both sides. Separators 26 and 27 made of a gas-impermeable conductive member form fuel gas and oxidizing gas flow paths between the anode electrode 23 and the cathode electrode 24 while sandwiching the sandwich structure from both sides. . The separator 26 is formed with a rib 26a having a concave cross section. When the anode electrode 23 comes into contact with the rib 26a, the opening of the rib 26a is closed and a fuel gas flow path is formed. The separator 27 is formed with a rib 27a having a concave cross section. When the cathode electrode 24 comes into contact with the rib 27a, the opening of the rib 27a is closed and an oxidizing gas flow path is formed.

  The anode electrode 23 is composed mainly of a carbon powder carrying a platinum-based metal catalyst (Pt, Pt—Fe, Pt—Cr, Pt—Ni, Pt—Ru, etc.), and a catalyst layer 23a in contact with the electrolyte membrane 22; It has a gas diffusion layer 23b formed on the surface of the catalyst layer 23a and having both air permeability and electronic conductivity. Similarly, the cathode electrode 24 has a catalyst layer 24a and a gas diffusion layer 24b. More specifically, the catalyst layers 23a and 24a are made by dispersing carbon powder carrying platinum or an alloy made of platinum and another metal in a suitable organic solvent, adding an appropriate amount of an electrolyte solution to form a paste, and forming an electrolyte membrane 22 Screen printed on top. The gas diffusion layers 23b and 24b are formed of carbon cloth, carbon paper, or carbon felt woven with carbon fiber yarns. The electrolyte membrane 22 is a proton conductive ion exchange membrane formed of a solid polymer material such as a fluorine resin, and exhibits good electrical conductivity in a wet state. A membrane-electrode assembly 25 is formed by the electrolyte membrane 22, the anode electrode 23, and the cathode electrode 24.

FIG. 3 is an equivalent circuit diagram showing the electrical characteristics of the cell 21.
The equivalent circuit of the cell 21 has a circuit configuration in which R1 is connected in series to a parallel connection circuit of R2 and C. Here, R1 corresponds to the electric resistance of the electrolyte membrane 22, and R2 corresponds to a resistance-converted activation overvoltage and diffusion overvoltage. C corresponds to the electric double layer capacity formed at the interface between the anode electrode 23 and the electrolyte membrane 22 and at the interface between the cathode electrode 24 and the electrolyte membrane 22. When a sine wave current having a predetermined frequency is applied to this equivalent circuit, the voltage response is delayed with respect to the change in current.

  FIG. 4 is a graph showing the AC impedance of the fuel cell stack 20 on a complex plane. The horizontal axis indicates the real part of the AC impedance, and the vertical axis indicates the imaginary part of the AC impedance. ω is the angular frequency of the sinusoidal current.

  When a sine wave signal from high frequency to low frequency is applied to the equivalent circuit shown in FIG. 3, a graph as shown in FIG. 4 is obtained. When the frequency of the sine wave signal is infinitely large (ω = ∞), the AC impedance is R1. The AC impedance when the frequency of the sine wave signal is very small (ω = 0) is R1 + R2. The AC impedance obtained when the frequency of the sine wave signal is changed between a high frequency and a low frequency draws a semicircle as shown in FIG.

  As described above, by using the AC impedance method, it is possible to separately measure R1 and R2 in the equivalent circuit of the fuel cell stack 20. When R1 becomes larger than a predetermined value and the output of the fuel cell stack 20 is reduced, the electrolyte membrane 22 is dried to increase the resistance overvoltage, and the conductivity is reduced. It can be judged as the cause of the decrease. When R2 is larger than a predetermined value and the output of the fuel cell stack 20 is reduced, excessive water is present on the electrode surface and the diffusion overvoltage is increased. I can judge.

FIG. 5 shows functional blocks of the control unit 90.
The control unit 90 includes an operation control unit 91, a voltage command unit 92, an AC impedance measurement unit 93, map data 94, and a correction unit 95. The operation control unit 91 is a control means for controlling each part (the oxidizing gas supply system 30, the fuel gas supply system 40, the power system 50, and the cooling system 60) related to the battery operation control, and optimally controls the operation state. As one of the indexes for achieving this, the AC impedance of the fuel cell stack 20 is used. The voltage command unit 92 outputs a voltage command value to the DC / DC converter 51. The AC impedance measuring unit 93 calculates the AC impedance based on the voltage response and current response of the fuel cell stack 20. The map data 94 holds the correlation between the AC impedance of the fuel cell stack 20 and the amount of water. The map data 94 is used, for example, as a reference for appropriately adjusting the dry state of the electrolyte membrane 22 by supplying scavenging gas into the fuel cell stack 20 when the operation is stopped, and the maximum output power of the fuel cell stack 20. It is used for the calculation. The correction unit 95 corrects the map data 94 after taking into account the shift in the correlation between the alternating current impedance and the moisture amount due to aging and the like.

The AC impedance measurement of the fuel cell stack 20 by the control unit 90 is performed according to the following procedure.
(1) The voltage command unit 92 generates a voltage command value obtained by superimposing a sine wave signal on a predetermined DC voltage, and outputs the voltage command value to the DC / DC converter 51.
(2) The DC / DC converter 51 operates based on the voltage command value, converts the DC power stored in the battery 52 into AC power, and applies a sine wave signal to the fuel cell stack 20.
(3) The AC impedance measuring unit 93 samples the response voltage detected by the voltage sensor 71 and the response current detected by the current sensor 72 at a predetermined sampling rate, performs a fast Fourier transform process (FFT process), The response voltage and the response current are divided into a real component and an imaginary component, respectively, and the FFT-processed response voltage is divided by the FFT-processed response current to calculate the real component and the imaginary component of the AC impedance. The distance r from the origin and the phase angle θ are calculated. The AC impedance of the fuel cell stack 20 can be calculated by measuring the response voltage and the response current while continuously changing the frequency of the sine wave signal applied to the fuel cell stack 20.

  In addition, since the electric current which flows through the fuel cell stack 20 is accompanied by the movement of the electric charge by a chemical reaction, if the amplitude of an alternating current signal is increased, the reaction amount (gas utilization rate) with respect to the supply gas amount will fluctuate. If there is a change in the gas utilization rate, an error may occur in the measurement of the AC impedance. Therefore, the AC component of the signal applied to the fuel cell stack 20 during the AC impedance measurement is preferably about several percent of the DC component.

  FIG. 6 is an explanatory diagram of map data 94 showing the correlation between AC impedance and moisture content. The horizontal axis represents the AC impedance of the fuel cell stack 20, and the vertical axis represents the amount of water inside the fuel cell stack 20. In general, the greater the amount of moisture, the higher the conductivity of the electrolyte membrane 22, so the AC impedance tends to decrease. On the other hand, the smaller the amount of moisture, the lower the conductivity of the electrolyte membrane 22, so the AC impedance tends to increase.

  The characteristic curve 94A shows the correlation between the AC impedance and the moisture content when the service life is relatively short. The characteristic curve 94B shows the correlation between the AC impedance and the amount of water in a period when the service life is relatively long. It has been found that the correlation between the AC impedance and the amount of water becomes almost equal to that obtained when the entire characteristic curve is translated in the direction of the horizontal axis when the service life becomes longer and the aging progresses. In order to correct the correlation error between the alternating current impedance and the water amount due to the aging of the fuel cell stack 20 using such characteristics, the alternating current impedance corresponding to a specific water amount is determined by the above procedure. By obtaining the difference (impedance error) between the actual measurement value obtained by measurement and the theoretical value of the AC impedance calculated from the map data 94, the characteristic curve 94A before correction is translated in the horizontal axis direction by the difference. A corrected characteristic curve 94B can be obtained.

  By the way, in the correlation between the AC impedance and the moisture content, there is a dead zone where the AC impedance value becomes almost constant when a certain moisture content is exceeded. For example, regarding the characteristic curve 94A, when the water content exceeds W1, the value of the AC impedance does not change while maintaining Z1 (minimum AC impedance). Similarly, for the characteristic curve 94B, when the water content exceeds W1, the value of the AC impedance does not change while maintaining Z2 (minimum AC impedance). If such insensitive characteristics are used, even if some estimation error is included in the water content, the AC impedance calculated from the measured value of the AC impedance measured under the condition of the water content W1 or more and the map data 94 is used. By obtaining the difference from the theoretical value of the map data 94, the map data 94 can be corrected easily and with high accuracy.

  In order to improve the correction accuracy of the map data 94, it is desirable that the water content estimation accuracy inside the fuel cell stack 20 is as high as possible. As a method for estimating the water content, for example, a method of calculating the water content using the heat of melting of water is applied at start-up below freezing point, and the power generation state (air flow rate, air pressure is applied at normal temperature operation). The water content can be applied by a water balance calculation theoretically derived based on the power generation current, stack temperature, and the like.

FIG. 7 shows the temperature change of the fuel cell stack 20 at the time of starting below freezing.
Time t1 indicates a point in time when the ignition switch is switched from OFF to ON and an activation instruction is input to the control unit 90. When the control unit 90 detects that the stack temperature at startup is below freezing point, the control unit 90 starts the warm-up operation until the stack temperature reaches a predetermined temperature. In the warm-up operation, the fuel cell stack 20 may be warmed up by increasing the self-heat generation amount of the fuel cell stack 20 by performing low-efficiency operation with lower power generation efficiency than in normal operation, or dedicated operation The fuel cell stack 20 may be warmed up using the warming-up device.

The control unit 90 calculates the heating amount Q applied per unit time per unit mass of ice based on the temperature rise from time t1 until time t2 until the stack temperature reaches the melting point Tm of ice. Then, the control unit 90 measures the time required for the ice in the fuel cell stack 20 to completely melt and change to water, that is, the elapsed time Δt from time t2 to time t3. When the water content in the fuel cell stack 20 is Mw and the heat of fusion per unit mass of water is Cw, the following equation (4) is established.
Mw = Q × Δt / Cw (4)

FIG. 8 shows a water balance calculation model of the fuel cell stack 20 during normal temperature operation.
The control unit 90 calculates the generated water amount W1 [g / sec] by multiplying the FC current value 201 measured using the current sensor 72 by the gain 204. The gain 204 is a constant having a value of the number of stack cells / LVFF / 2 × 18. Here, LVFF is a Faraday constant (96500 C / mol). The control unit 90 calculates the water vapor pressure U1 from the FC temperature 202 measured using the temperature sensor 74 and the water saturated steam characteristic map data 205, and uses an air pressure sensor (not shown) to produce an air pressure value 109 (hereinafter referred to as the air pressure value 109). , Referred to as an air pressure value U2). Then, the control unit 90 substitutes the arguments U1 and U2 into the function 208, and calculates the partial pressure ratio V1 of water vapor and air.

  The control unit 90 calculates the air consumption A1 [mol / sec] by multiplying the FC current value 201 measured using the current sensor 72 by the gain 207. The gain 207 is a constant having a value of stack cell number / LVFF / 4. The control unit 90 uses an air flow rate sensor (not shown) disposed in the vicinity of the oxidant off-gas outlet of the fuel cell stack 20 to call an air flow rate value 203 (hereinafter referred to as an air flow rate value A2 [mol / sec]). )). Then, the control unit 90 calculates the air flow rate V2 that has been taken away and converted into moisture by the air flow rate A2-the air consumption amount A1. The control unit 90 substitutes the arguments V1 and V2 for the multiplication function 210, and multiplies the return value by the gain 211, thereby calculating the carry-off water amount W2 [g / sec]. The gain 211 is a constant having a value of 18. The carry-off water amount W2 is multiplied by a gain 213 having a value of −1, so that the sign is −.

  The control unit 90 calculates the water vapor exchange rate X1 corresponding to the air flow rate A2 based on the humidification module water vapor exchange rate map data 212. The control unit 90 assigns arguments W1 and W2 to the MIN function 214, and sets the return value to X2. The MIN function 214 is a function that returns a value that takes the minimum value among a plurality of arguments. The control unit 90 substitutes the arguments X1 and X2 for the multiplication function 215, and sets the return value as the humidified water amount W3 [g / sec]. The control unit 90 substitutes arguments W1, −W2, and W3 into the addition function 216, and uses the return value (W1−W2 + W3) as the amount of water 217 remaining in the fuel cell stack 20.

Next, a procedure for correcting the map data 94 indicating the correlation between the AC impedance and the moisture content will be described with reference to FIG.
The control unit 90 determines whether or not the accumulated operation time of the fuel cell stack 20 has exceeded a predetermined threshold (step 901). If the accumulated operation time exceeds the threshold value (step 901; YES), there is a possibility that the fuel cell stack 20 has deteriorated over time. Therefore, as a preliminary preparation for correcting the map data 94, the fuel cell stack The water content inside 20 is calculated (step 902). The method for calculating the water content may be a method using the heat of fusion described above or a method using the water balance calculation model described above.

  If the water content obtained by calculation is less than W1 (step 903; NO), the control unit 90 controls the water balance in the direction in which water is accumulated in the fuel cell stack 20 (step 904). Specifically, the control unit 90 performs a control operation for increasing the FC current 201, a control operation for increasing the humidification amount to the oxidizing gas by the humidifier 33, and the like, thereby generating the generated water amount W1 or the humidified water amount. Increase W3. Further, the control operation for lowering the FC temperature 202 and the control operation for increasing the air pressure value 206 may be performed to reduce the amount W2 of the carried away water. The control unit 90 can function as a water balance control means for controlling the water balance flowing into and out of the fuel cell stack 20.

  When the water content exceeds W1 (step 903; YES), the control unit 90 measures the AC impedance of the fuel cell stack 20 (step 905). Since the alternating current impedance measured at this time is the alternating current impedance in the dead zone, the value is constant regardless of the water content. The control unit 90 corrects the map data 94 based on the difference between the actual measurement value of the AC impedance in the dead zone and the theoretical value of the AC impedance calculated from the map data 94 (step 906). At this time, it is preferable to correct the map data 94 in consideration of the temperature characteristics of the fuel cell stack 20.

  According to the present embodiment, since the map data 94 is corrected using the insensitive characteristic in the correlation between the AC impedance and the moisture content, the map data 94 can be corrected with high accuracy even if the estimation accuracy of the moisture content is low. .

  In the above-described embodiment, the usage form in which the fuel cell system 10 is used as the in-vehicle power supply system is illustrated, but the usage form of the fuel cell system 10 is not limited to this example. For example, the fuel cell system 10 may be mounted as a power source of a mobile body (robot, ship, aircraft, etc.) other than the fuel cell vehicle. Further, the fuel cell system 10 according to the present embodiment may be used as a power generation facility (stationary power generation system) such as a house or a building.

1 is a system configuration diagram of a fuel cell system according to an embodiment. It is a disassembled perspective view of a cell. It is an equivalent circuit diagram which shows the electrical property of a cell. It is the graph which displayed the alternating current impedance of the fuel cell stack on the complex plane. It is a functional block diagram of a control unit. It is explanatory drawing of the map data which shows correlation with alternating current impedance and a moisture content. It is a graph which shows the temperature change of the fuel cell stack at the time of starting below freezing. It is explanatory drawing which shows the water balance calculation model of the fuel cell stack at the time of normal temperature driving | operation. It is a flowchart which shows the process routine for correct | amending the map data which show the correlation of alternating current impedance and a moisture content.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Fuel cell system 20 ... Fuel cell stack 90 ... Control unit 91 ... Operation control part 92 ... Voltage command part 93 ... AC impedance measurement part 94 ... Map data 95 ... Correction part

Claims (3)

A fuel cell;
Map data indicating the correlation between the AC impedance of the fuel cell and the amount of water,
A correction unit that corrects an error in the map data based on the water content calculated by the water balance calculation of the fuel cell and the measured value of the AC impedance of the fuel cell;
The correction unit corrects an error in the map data based on an actual measurement value of the AC impedance of the fuel cell in a dead zone where the AC impedance is substantially constant when the water content is equal to or greater than a predetermined value . The fuel cell system according to claim 1,
The said correction | amendment part is a fuel cell system which correct | amends the error of the said map data by forcibly making the operating state of the said fuel cell change to the said dead zone area | region. A fuel cell;
Map data indicating the correlation between the AC impedance of the fuel cell and the amount of water,
A correction unit that corrects an error in the map data based on a moisture content calculated based on a heat amount absorbed when the ice inside the fuel cell melts at a sub-freezing start time and an actual measurement value of the AC impedance of the fuel cell ; ,
A fuel cell system comprising:

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