JP2017037758A - Fuel battery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel battery system that can estimate the effective surface area of catalyst with high accuracy during actual operation of a fuel battery.SOLUTION: A fuel battery system 10 estimates a wet state in a fuel battery 20, acquires an output current value and an output voltage value in each of a low current region and a high current region of the fuel battery 20 within a predetermined period before and after the wet state is estimated, calculates the diffusion resistance of oxidant gas in the fuel battery on the basis of the acquired output current value and output voltage value, calculates a first estimation value of the effective surface area of catalyst on the basis of the obtained output voltage value at a predetermined current value in the low current region, and calculates a second estimation value of the effective surface area by referring to a map on the basis of the estimated wet state and the calculated diffusion resistance to calculate a final estimation value of the effective surface area.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a fuel cell system.

  In Patent Document 1, when an increase in the output of the fuel cell is required, the catalyst of the cathode electrode is based on the ratio of the change in the output of the fuel cell to the change in the pressure of the oxidant gas supplied to the cathode electrode of the fuel cell. A technique for calculating the effective surface area is described.

Japanese Patent Application Laid-Open No. 2014-082115

  However, according to the technique disclosed in the above document, the pressure of the oxidant gas is increased while the current value output from the fuel cell is kept constant, and the change in the output of the fuel cell at that time is read. It is considered that the ratio of the change in the output of the fuel cell to the change in the pressure of the agent gas is acquired. In this case, it is considered that the increase in the current value of the fuel cell is started so that the output of the fuel cell reaches the required output after this ratio is acquired. For this reason, it takes a long time for the output of the fuel cell to reach the required output after the increase in the output of the fuel cell is required, compared with the case where the current value is increased immediately after the output increase request. Response characteristics may be deteriorated. Therefore, there is a problem that it is difficult to carry out such a method during actual operation of the fuel cell.

  An object of the present invention is to provide a fuel cell system capable of accurately calculating the effective surface area of a catalyst during actual operation of the fuel cell.

  According to the present invention, a fuel cell including a cathode electrode and an anode electrode, an oxidant gas supply unit that supplies an oxidant gas to the cathode electrode, a fuel gas supply unit that supplies a fuel gas to the anode electrode, A wetness estimation unit for estimating a wet state in the fuel cell, and an output current value and an output voltage value in the low current region and the high current region of the fuel cell, respectively, for a predetermined period before and after the wet state is estimated And the diffusion resistance of the oxidant gas in the fuel cell is calculated based on the acquired acquisition unit and the output current value and output voltage value of the acquired low current region and high current region, respectively. A diffusion resistance calculation unit; a storage unit that stores a map that defines a correspondence relationship between the effective surface area of the catalyst of the cathode electrode and the diffusion resistance for each wet state; and a predetermined current in the acquired low current region Before in value A first estimate of the effective surface area is calculated based on an output voltage value, and a second estimate of the effective surface area is referenced with reference to the map based on the estimated wet state and the calculated diffusion resistance. And a surface area calculator that calculates a final estimated value of the effective surface area based on the first estimated value and the second estimated value.

  Calculate a first estimate of the effective surface area based on the output voltage value in the low current region, calculate the diffusion resistance based on the respective output current value and output voltage value in the low current region and the high current region, A second estimated value of the effective surface area is calculated based on the wet state and the diffusion resistance, and a final estimated value of the effective surface area is calculated based on the first estimated value and the second estimated value. Therefore, the effective surface area of the catalyst can be calculated with high accuracy during actual operation of the fuel cell.

  It is possible to provide a fuel cell system capable of calculating the effective surface area of the catalyst with high accuracy during actual operation of the fuel cell.

It is explanatory drawing which shows the structure of a fuel cell system. It is a flowchart which shows an example of the control which a control unit performs. It is an illustration figure of the map which showed the current voltage characteristic of the fuel cell. It is an example of the map which prescribed | regulated the correspondence of the diffusion resistance and platinum effective surface area previously memorize | stored in the memory | storage part. It is the map which prescribed | regulated the correspondence of the output voltage value in a low electric current area | region, and a platinum effective surface area.

  FIG. 1 is an explanatory diagram showing the configuration of the fuel cell system 10. In this embodiment, the fuel cell system is applied to a vehicle. As shown in FIG. 1, the fuel cell system 10 includes a fuel cell stack (hereinafter referred to as a fuel cell) 20, an oxidant gas piping system 30, a fuel gas piping system 40, a power system 50, and a control unit 60. The fuel cell 20 generates power by receiving supply of the oxidant gas and the fuel gas, and generates electric power accompanying the power generation. The oxidant gas piping system 30 supplies air containing oxygen to the fuel cell 20 as an oxidant gas. The fuel gas piping system 40 supplies hydrogen gas as fuel gas to the fuel cell 20. The power system 50 charges and discharges system power. The control unit 60 performs overall control of the entire system.

  The fuel cell 20 is a solid polymer electrolyte type and has a stack structure in which a large number of single cells (cells) are stacked. The unit cell of the fuel cell 20 has a cathode electrode (air electrode) on one surface of an ion exchange membrane made of an electrolyte and an anode electrode (fuel electrode) on the other surface. For an electrode including a cathode electrode and an anode electrode, for example, platinum Pt is used as a catalyst (electrode catalyst) based on a porous carbon material. A cathode-side gas diffusion layer is disposed on the surface of the cathode electrode, and similarly, an anode-side gas diffusion layer is also disposed on the surface of the anode electrode. Further, a pair of separators are provided so as to sandwich the cathode-side and anode-side gas diffusion layers from both sides. The fuel gas is supplied to the fuel gas flow path of one separator and the oxidant gas is supplied to the oxidant gas flow path of the other separator, so that the fuel cell 20 generates electric power.

  The fuel cell 20 is provided with a current sensor 2a and a voltage sensor 2b for detecting an output current and a voltage, respectively, and a temperature sensor 2c for detecting the temperature of the fuel cell 20.

  The oxidant gas piping system 30 includes an air compressor 31, an oxidant gas supply path 32, a humidification module 33, a cathode off-gas flow path 34, and a motor M 1 that drives the air compressor 31.

  The air compressor 31 is driven by the motor M <b> 1 and compresses air (oxidant gas) containing oxygen taken from outside air and supplies the compressed air to the cathode electrode of the fuel cell 20. A rotation speed detection sensor 3a for detecting the rotation speed is attached to the motor M1. The oxidant gas supply path 32 guides the oxidant gas supplied from the air compressor 31 to the cathode electrode of the fuel cell 20. Cathode off-gas is discharged from the cathode electrode of the fuel cell 20 through the cathode off-gas channel 34.

  The humidification module 33 exchanges moisture between the low-humidity oxidant gas flowing through the oxidant gas supply path 32 and the high-humidity cathode offgas flowing through the cathode offgas flow path 34 and is supplied to the fuel cell 20. Moisten the oxidant gas appropriately. The cathode offgas flow path 34 exhausts the cathode offgas outside the system, and a back pressure adjusting valve A1 is disposed in the vicinity of the cathode electrode outlet. The pressure of the oxidant gas discharged from the fuel cell 20, that is, the cathode back pressure is regulated by the back pressure regulating valve A1. A pressure sensor 3b for detecting the cathode back pressure is attached between the fuel cell 20 and the back pressure adjustment valve A1 in the cathode off gas flow path 34.

  The fuel gas piping system 40 drives a fuel gas supply source 41, a fuel gas supply path 42, a fuel gas circulation path 43, an anode off-gas flow path 44, a hydrogen circulation pump 45, a gas-liquid separator 46, and a hydrogen circulation pump 45. Motor M2.

  The fuel gas supply source 41 is a tank that supplies hydrogen gas, which is a fuel gas, to the fuel cell 20. The fuel gas supply path 42 guides the fuel gas discharged from the fuel gas supply source 41 to the anode electrode of the fuel cell 20, and a tank valve H1, a hydrogen supply valve H2, and an FC inlet valve H3 are arranged in order from the upstream side. Yes. These valves are electromagnetic valves that supply and shut off the fuel gas to the fuel cell 20.

  The fuel gas circulation path 43 recirculates unreacted fuel gas to the fuel cell 20, and a gas-liquid separator 46, a hydrogen circulation pump 45, and a check valve (not shown) are arranged in order from the upstream side. Unreacted fuel gas discharged from the fuel cell 20 is appropriately pressurized by the hydrogen circulation pump 45 and guided to the fuel gas supply path 42. The backflow of the fuel gas from the fuel gas supply path 42 to the fuel gas circulation path 43 is suppressed by a check valve. The anode off gas flow path 44 exhausts the anode off gas containing the hydrogen off gas discharged from the fuel cell 20 and the water stored in the gas-liquid separator 46 to the outside of the system, and an exhaust drain valve H5 is provided.

  The electric power system 50 includes a high voltage DC / DC converter 51, a battery 52, a traction inverter 53, an auxiliary machine inverter 54, a traction motor M3, and an auxiliary machine motor M4.

  The high-voltage DC / DC converter 51 can adjust the DC voltage from the battery 52 and output it to the traction inverter 53 side. The DC voltage from the fuel cell 20 or the voltage from the traction motor M3 converted to DC by the traction inverter 53 can be obtained. It can be adjusted and output to the battery 52. The output voltage of the fuel cell 20 is controlled by the high voltage DC / DC converter 51.

  The battery 52 is a chargeable / dischargeable secondary battery, and can be charged with surplus power or supplied with auxiliary power. Part of the direct-current power generated by the fuel cell 20 is stepped up and down by the high-voltage DC / DC converter 51 and charged in the battery 52. The battery 52 is attached with an SOC sensor 5a for detecting the state of charge.

  The traction inverter 53 and the auxiliary inverter 54 convert the DC power output from the fuel cell 20 or the battery 52 into three-phase AC power and supply it to the traction motor M3 and the auxiliary motor M4. The traction motor M3 drives the wheels 71 and 72. The traction motor M3 is provided with a rotation speed detection sensor 5b for detecting the rotation speed. The auxiliary motor M4 is a motor for driving various auxiliary machines, and is a generic term for the motors M1 and M2.

  The control unit 60 includes a CPU, a ROM, and a RAM, and controls each part of the system in an integrated manner based on input sensor signals. Specifically, the control unit 60 makes a request to the fuel cell 20 based on each sensor signal sent from the accelerator pedal sensor 81 that detects the rotation of the accelerator pedal 80, the SOC sensor 5a, and the rotation speed detection sensor 5b. Calculate the output.

  The control unit 60 controls the output voltage and output current of the fuel cell 20 so as to generate this required output. The control unit 60 controls output pulses of the traction inverter 53 and the auxiliary machine inverter 54 to control the traction motor M3, the auxiliary machine motor M4, and the like.

  Here, in the fuel cell 20, the surface area (hereinafter referred to as platinum effective surface area) of the portion effective for power generation of platinum which is a catalyst in the cathode catalyst layer may decrease and the output voltage may decrease. The decrease in the effective platinum surface area may be reduced irreversibly due to, for example, an increase in usage time over time, or may be reduced reversibly due to poisoning or the influence of water. In the present embodiment, the control unit 60 executes control for calculating the platinum effective surface area. This control is executed by the acquisition unit 61, the wetness estimation unit 62, the diffusion resistance calculation unit 63, the surface area calculation unit 64, and the storage unit 65 that are functionally realized by the CPU, the ROM, and the RAM. Details will be described below.

  FIG. 2 is a flowchart illustrating an example of control executed by the control unit 60. This control is repeatedly executed every predetermined time. When the control is started, the acquisition unit 61 determines whether or not the output current value and the output voltage value in each of the low current region and the high current region of the fuel cell 20 are acquired within a predetermined period. (Step S1). The output current value and the output voltage value in the low current region and the high current region are acquired within a predetermined period by the acquisition unit 61 in the following cases, for example. When the accelerator pedal 80 is depressed, the fuel cell 20 accelerates within a few seconds from the stopped state or the idling operation to the high current region. Further, it is during deceleration when the fuel cell 20 shifts from the high current region to the idle operation or the stopped state within a few seconds after the depression amount of the accelerator pedal 80 is decreased. When the operating state of the fuel cell 20 passes through the low current region and the high current region, the acquisition unit 61 can acquire the respective output current values and output voltage values in the low current region and the high current region. The method for acquiring the output current value and the output voltage value will be described in detail below.

  FIG. 3 is an exemplary diagram of a map showing the current-voltage characteristics of the fuel cell 20. FIG. 3 shows a plurality of IV curves C1 to C4 stored in the storage unit 65 in advance. IV curves C1 to C4 indicate current-voltage characteristics (IV characteristics) that can be taken by the fuel cell 20 and are calculated in advance through experiments. The IV characteristics of the fuel cell 20 change according to the operating state. The IV curves C1 to C4 will be described later.

  The output current value and output voltage value in the low current region are obtained as follows. A reference current value IK set in the low current region is stored in advance in the storage unit 65, and this reference current value IK is acquired as an output current value in the low current region. The output voltage value in the low current region is acquired as the output voltage value of the fuel cell 20 when the output current value detected by the current sensor 2a reaches the reference current value IK. Here, the reference current value IK is set to a value larger than the output current value in the idle operation state of the fuel cell 20. FIG. 3 illustrates the case where the output voltage value V1 in the low current region is acquired and the case where the output voltage value V4 larger than the output voltage value V1 is acquired. Here, since the output voltage value in the low current region is an actual measurement value, the output voltage values V1 and V4 are not necessarily on the IV curves C1 and C4, respectively, as shown in FIG. There is.

  The output current value and output voltage value in the high current region are obtained as follows. A reference voltage value VKL set in the high voltage range corresponding to the high current range is stored in the storage unit 65 in advance, and this reference voltage value VKL is acquired as an output voltage value in the high current range. The output current value in the high current region is acquired as the output current value of the fuel cell 20 when the output voltage value detected by the voltage sensor 2b reaches the reference voltage value VKL. FIG. 3 illustrates the case where the output current value I1 in the high current region is acquired and the case where the output current value I4 smaller than the output current value I1 is acquired. Here, as described above, since the output current value in the low current region is an actual measurement value, the output current values I1 and I4 are not necessarily on the IV curves C1 and C4, respectively, as shown in FIG. It may be approximate.

  As shown in FIG. 3, the operation allowable region in which the operation of the fuel cell 20 is allowed is defined by the designed upper limit current value UI and lower limit voltage value LV. The upper limit current value UI and the lower limit voltage value LV are defined in consideration of ensuring normal operation on the fuel cell system 10 side, and the maximum current value and minimum It is not a voltage value.

  The “low current region” is a region where the output current of the fuel cell 20 is relatively small and the output voltage is relatively large. The low current region corresponds to, for example, a region in the first half of the region between the point where the current value becomes zero and the upper limit current value UI. The low current region is a region in which the voltage decreases mainly due to the influence of the activation overvoltage among the activation overvoltage, resistance overvoltage, and concentration overvoltage that are causes of the voltage decrease of the fuel cell 20. The “medium current region” is a region where the output current and voltage of the fuel cell 20 are relatively medium. The middle current region is a region where the voltage decreases mainly due to the effect of resistance overvoltage. The “high current region” is a region where the output current of the fuel cell 20 is relatively large and the output voltage is relatively small. The high current region corresponds to a region in the latter half of the region between the point where the current value becomes zero and the upper limit current value UI. The high current region is a region where the voltage decreases mainly due to the influence of concentration overvoltage. The activation overvoltage is a decrease in voltage mainly due to activation energy consumed when oxygen is reduced at the cathode electrode. The resistance overvoltage is a decrease in voltage due to the internal resistance of the electrolyte membrane, catalyst layer, gas diffusion layer, separator, and current collector in the fuel cell 20. The concentration overvoltage is a decrease in voltage due to an increase in gas diffusion resistance due to moisture supplied to the cells of the fuel cell 20 or generated water generated in the cells.

  In the flowchart of FIG. 2, if a negative determination is made in step S1, the control unit 60 ends the present control. If an affirmative determination is made in step S1, the wetness estimation unit 62 acquires the output current value and the output voltage value in each of the low current region and the high current region within a predetermined period, and then acquires them in step S1. The wet state in the fuel cell 20 is estimated based on the output voltage value at a predetermined current value in the low current region of the fuel cell 20 (step S2). Specifically, the wetness estimation unit 62 estimates that the wet state is excessively humid when the output voltage value at the reference current value IK in the low current region is equal to or higher than the threshold value VK, and when the output voltage value is lower than the threshold value VK, the wet state. Is assumed to be normal. The case where the wet state is excessively humidified is a case where flooding has occurred, for example. The estimated wet state is stored in the storage unit 65. Thus, when the output voltage value in the low current region is relatively high, the moist state is estimated to be overhumidified, and when it is relatively low, the reason that it is estimated to be normal is as follows. The larger the output voltage value in the low current region, the smaller the activation overvoltage. The decrease in activation overvoltage is considered to be related to an increase in ion conduction in the ionomer due to an increase in the amount of water in the fuel cell 20. For this reason, it is considered that the greater the output voltage value in the low current region, the greater the amount of water in the fuel cell 20. FIG. 3 illustrates a case where the output voltage value V4 is equal to or greater than the threshold value VK and the output voltage value V1 is less than the threshold value VK.

  The wet state may be estimated before acquiring the output current value and the output voltage value in the low current region and acquiring the output current value and the output voltage value in the high current region. That is, the order of the output current value and the output voltage value in the low current region and the high current region are not limited as long as they are acquired within a predetermined period before and after the wet state is estimated. The term “within the predetermined period” refers to a period in which a change in the effective platinum surface area caused by a change in the poisoning amount of platinum or a change in the wet state can be ignored. That is, within the predetermined period is a period in which it can be considered that the effective platinum surface area does not change greatly even when the output of the fuel cell 20 changes as described above.

Subsequently, the diffusion resistance calculation unit 63 calculates the diffusion resistance of the gas in the fuel cell 20 based on the output current value and the output voltage value in each of the low current region and the high current region acquired in step S1. Calculate (step S3). Specifically, the diffusion resistance is calculated based on Equation 1 below.
Gas diffusion resistance = (4F × Po ₂ ) / (10RT × I) (1)
In this equation, F is a Faraday constant. Po ₂ is the oxygen partial pressure. R is a gas constant. T is temperature. I is a limit current value, and a voltage of 0.15 V is supplied by supplying hydrogen gas / air to the anode electrode and the cathode electrode through a gas diffusion layer having a porous flow path in MEA (Mebrane Electrode Assembly), respectively. Is the current density when. The calculated diffusion resistance is stored in the storage unit 65. The diffusion resistance means difficulty in diffusing oxidant gas in the fuel cell 20. The limit current value is acquired by the diffusion resistance calculation unit 63 under a predetermined condition in order to acquire the gas diffusion resistance, and will be described in detail below.

  The limit current value is outside the operation allowable range shown in FIG. For this reason, it is acquired as follows. The diffusion resistance calculation unit 63 grasps the current-voltage characteristics of the fuel cell 20 based on the output current value and the output voltage value in each of the low current region and the high current region acquired in step S1. Next, the diffusion resistance calculation unit 63 specifies an IV curve that is closest to the grasped current-voltage characteristic among the plurality of IV curves C1 to C4. The IV curves C1 to C4 are calculated in advance for each operation state of the fuel cell 20 and stored in the storage unit 65. The number of IV curves stored in the storage unit 65 is not limited to four. The diffusion resistance calculation unit 63 refers to the identified IV curve and a map that prescribes the correlation between the IV curve and the limit current value stored in advance in the storage unit 65, and acquires the limit current value. FIG. 3 shows limit current values IM1 to IM4 corresponding to the IV curves C1 to C4, respectively, for easy understanding. For example, when the output voltage value V1 in the low current region and the output current value I1 in the high current region are acquired, the IV curve C1 is specified and the limit current value IM1 is acquired. When the output voltage value V4 in the low current region and the output current value I4 in the high current region are acquired, the IV curve C4 is specified and the limit current value IM4 is acquired.

  Therefore, in this embodiment, the limit current value is acquired without actually causing the fuel cell 20 to output the limit current value. For example, if the limit current value is actually output to the fuel cell 20, the limit current value is not the optimum condition for power generation, and thus power generation efficiency may be reduced. Further, when the fuel cell 20 outputs a limit current value when the maximum output is requested, a predetermined period is required until the limit current value is output, and the output responsiveness may be lowered. As described above, when the limit current value is actually output to the fuel cell 20, there is a possibility of affecting the operation. In the present embodiment, since the limit current value is acquired without causing such a problem, the influence on the operation as described above can be prevented. The order of execution of steps S2 and S3 does not matter.

  Subsequently, the surface area calculation unit 64 calculates a platinum effective surface area with reference to a map preliminarily stored in the storage unit 65 and defining a correspondence relationship between the diffusion resistance and the platinum effective surface area (step S4). FIG. 4 is an example of a map that prestores the correspondence between the diffusion resistance and the platinum effective surface area stored in the storage unit 65. This map is calculated in advance through experiments and stored in the storage unit 65. In the fuel cell 20 in the initial state, since the platinum effective surface area is large and the diffusion resistance is small, the correspondence between the two is located in the lower right of the map of FIG. However, due to reversible and irreversible performance degradation accompanying the operation of the fuel cell 20, the effective platinum surface area decreases and the diffusion resistance increases, and the correspondence between the two shifts to the upper left of the map of FIG. The way of transition varies depending on the wet state. For this reason, the map shown in FIG. 4 defines a plurality of curves D1 and D4 corresponding to the wet state. Curves D1 and D4 respectively define the relationship between the diffusion resistance and the platinum effective surface area when the fuel cell 20 is in a normal and excessive humid state. The diffusion resistance and the platinum effective surface area have a negative correlation for the following reason. This is because when the effective surface area of platinum decreases due to, for example, platinum poisoning, the diffusion resistance increases because the gas necessary for the reaction tends to concentrate on the remaining part of the platinum surface.

  Referring to the curves D1 and D4, when the effective surface area of platinum is the same in the case where the wet state is normal and in the case of excessive humidification, the diffusion resistance is larger in the case of excessive humidification. This is because in the case of excessive humidification, the diffusion of gas is inhibited by the amount of water in the fuel cell 20, that is, the diffusion resistance increases.

  The surface area calculation unit 64 selects one of the curves D1 and D4 based on the wet state of the fuel cell 20 estimated in step S2, and plots the value of the diffusion resistance calculated in step S3 on the selected curve. Determine the effective platinum surface area. In this way, the platinum effective surface area is calculated based on the diffusion resistance in consideration of the wet state of the fuel cell 20. For example, when the limit current value IM1 is acquired and the wet state is estimated to be normal, the value obtained by plotting the diffusion resistance value K / IM1 calculated based on the limit current value IM1 on the curve D1 is platinum. Calculated as the effective surface area S1. Similarly, when the limiting current value IM4 is acquired and the wet state is estimated to be excessive humidification, the value obtained by plotting the diffusion resistance value K / IM4 calculated based on the limiting current value IM4 on the curve D4 Is calculated as a platinum effective surface area S4. Here, K is a coefficient, and is defined as K = (4F × Po2) / (10RT) based on the above equation (1). Note that the platinum effective surface area calculated in step S4 corresponds to the second estimated value.

  Next, the surface area calculation unit 64 calculates the platinum effective surface area based on the output voltage value in the low current region acquired in step S1 (step S5). FIG. 5 is a map that defines the correspondence between the output voltage value in the low current region and the platinum effective surface area. This map is calculated in advance by experiments and stored in the storage unit 65. The output voltage value in the low current region and the platinum effective surface area are approximately proportional to each other. The larger the platinum effective surface area, the larger the output voltage value in the low current region. This is because a large output voltage value in a low current region means that the activation overvoltage is small, and the smaller the poisoning amount to platinum and the larger the platinum effective surface area, the smaller the activation overvoltage. For example, the value when the output voltage value V1 is plotted on the curve of the map of FIG. 5 is calculated as the platinum effective surface area S1 ′. Similarly, a value obtained by plotting the output voltage value V4 on the curve of the map is calculated as the platinum effective surface area S4 ′. Note that the platinum effective surface area calculated in step S5 corresponds to the first estimated value.

  Here, since the effective platinum surface areas S1 and S1 ′ are calculated by different methods in steps S4 and S5, respectively, the values are often different. The same applies to the platinum effective surface areas S4 and S4 ′. Accordingly, the surface area calculation unit 64 executes the following processing.

  The surface area calculator 64 calculates the final platinum effective surface area based on the platinum effective surface area calculated based on steps S4 and S5 (step S6). Specifically, the average platinum effective surface area calculated in steps S4 and S5 is calculated as the final platinum effective surface area. The final platinum effective surface area is stored in the storage unit 65, and the final platinum effective surface area stored in the storage unit 65 is updated each time the control in steps S1 to S6 is repeatedly executed. Thereby, the control unit 60 can control the operation state of the fuel cell 20 based on the final platinum effective surface area stored in the storage unit 65.

  As described above, since the final platinum effective surface area is calculated using the platinum effective surface area calculated by different methods in steps S4 and S5, a decrease in calculation accuracy is suppressed. Here, the platinum effective surface area is one of the factors that determine the electrochemical reaction of the fuel cell 20, that is, the output performance of the fuel cell 20. For this reason, the fuel cell 20 can be optimally controlled based on the platinum effective surface area in which a decrease in calculation accuracy is suppressed. Further, when the amount of platinum used for the cathode electrode is reduced in order to reduce the manufacturing cost, it is important to suppress a decrease in the calculation accuracy of the platinum effective surface area.

  The final platinum effective surface area is calculated by calculating, for example, the smaller or larger platinum effective surface area as the final platinum effective surface area among the platinum effective surface areas calculated in steps S4 and S5. Also good. Further, for example, an average value of a value obtained by multiplying one of the platinum effective surface areas calculated in steps S4 and S5 by (1 + k) and a value obtained by multiplying the other by (1-k) is obtained as a final platinum effective surface area. May be calculated as In this case, k is a constant that takes a value of 0 <k <1.

  Further, as described above, the wet state used in the calculation of the platinum effective surface area in step S4 is based on the output voltage value at a predetermined current value in a low current region that can be acquired during the actual operation of the fuel cell 20. Presumed. Further, the diffusion resistance is calculated based on the output current value and the output voltage value in the low current region and the high current region, respectively. Also in the calculation in step S5, the calculation is based on the output voltage value at a predetermined current value in the low current region that can be acquired during the actual operation of the fuel cell 20. As described above, since the platinum effective area is calculated based on the output current value and the output voltage value that can be acquired during the actual operation of the fuel cell 20, the effective surface area of the catalyst can be accurately estimated even during the operation of the fuel cell 20. The order of execution of steps S4 and S5 does not matter.

  Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

  The wet state may be estimated based on impedance. For example, when the impedance resistance component acquired by the acquisition unit 61 is greater than or equal to a predetermined threshold, the wet state is estimated to be normal, and when the impedance resistance component is lower than the predetermined threshold, the wet state is overhumidified. The state may be estimated. Here, for the impedance, for example, the resistance component of the impedance of the fuel cell 20 is measured using an AC impedance method. When the frequency of the current applied to the fuel cell 20 is large (ω = ∞), the impedance is an electrolyte membrane resistance, and thereby a wet state can be estimated.

  As shown in FIG. 4, two curves D1 and D4 corresponding to a normal wet state and an overhumidified state are shown, but the corresponding relationship between the effective platinum surface area and the diffusion resistance is wet for each wet state. There may be three or more curves defined for each state. In this case, the effective platinum surface area can be calculated with higher accuracy.

  The catalyst in the cathode catalyst layer may be other than pure platinum, for example, a platinum alloy.

DESCRIPTION OF SYMBOLS 10 Fuel cell system 20 Fuel cell 30 Oxidant gas piping system 40 Fuel gas piping system 60 Control unit 61 Acquisition part 62 Wet estimation part 63 Diffusion resistance calculation part 64 Surface area calculation part 65 Storage part

Claims (1)

A fuel cell comprising a cathode and an anode;
An oxidant gas supply unit for supplying an oxidant gas to the cathode electrode;
A fuel gas supply unit for supplying fuel gas to the anode electrode;
A wetness estimation unit for estimating a wet state in the fuel cell;
An acquisition unit that acquires an output current value and an output voltage value in each of a low current region and a high current region of the fuel cell within a predetermined period before and after the wet state is estimated;
A diffusion resistance calculation unit that calculates a diffusion resistance of the oxidant gas in the fuel cell based on the output current value and the output voltage value of the acquired low current region and high current region, respectively;
A storage unit storing a map that defines the correspondence between the effective surface area of the catalyst of the cathode electrode and the diffusion resistance for each wet state;
A first estimated value of the effective surface area is calculated based on the output voltage value at a predetermined current value in the acquired low current region, and based on the estimated wet state and the calculated diffusion resistance A surface area for calculating a second estimated value of the effective surface area with reference to the map and calculating a final estimated value of the effective surface area based on the first estimated value and the second estimated value. A fuel cell system comprising: a calculation unit;

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