JP6620510B2 - Method and apparatus for estimating hydrogen concentration in fuel cell - Google Patents

Description

  The present invention relates to a hydrogen concentration estimation method and a hydrogen concentration estimation device for a fuel cell.

  In a so-called anode circulation type fuel cell system, it is necessary to detect the hydrogen concentration in the anode gas circulation flow path in order to exhaust the exhaust gas having a low hydrogen concentration to the outside.

  For example, in Patent Document 1, in an anode circulation type fuel cell system, from the pressure loss characteristics of the anode gas circulation flow path in the fuel cell stack 1, the differential pressure between the inlet and outlet of the circulation pump, and the rotation speed of the circulation pump, A method for estimating the hydrogen concentration in the anode gas circulation channel based on the pressure-flow rate characteristics of the circulation pump is described.

JP 2006-310046 A

  In the above-mentioned Patent Document 1, it is assumed that the water vapor content (water vapor fraction) in the anode gas circulation channel is a saturated water vapor fraction when calculating the estimated value of the hydrogen concentration. Therefore, when the actual water vapor fraction deviates from the assumed value, there is a concern that the estimation accuracy of the hydrogen concentration is lowered.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a hydrogen concentration estimation method and a hydrogen concentration estimation apparatus that can estimate the hydrogen concentration in the anode gas circulation flow path with higher accuracy. There is.

  According to an aspect of the present invention, an anode gas temperature in an anode gas circulation channel, a differential pressure between an inlet and an outlet of a circulation pump provided in the anode gas circulation channel, and a circulation pump in a fuel cell system having a fuel cell The gas density in the anode gas circulation channel is estimated based on the pressure loss characteristic of the anode gas circulation channel and the pressure-flow rate characteristic of the circulation pump from the differential pressure, and the relative humidity in the fuel cell is calculated. A fuel cell hydrogen concentration estimation method for estimation is provided. In this fuel cell hydrogen concentration estimation method, the hydrogen concentration is calculated using relative humidity based on the anode gas temperature, the differential pressure, and the gas density.

  Further, according to an aspect of the present invention, a temperature acquisition device that acquires an anode gas temperature in an anode gas circulation channel in a fuel cell system having a fuel cell, and an inlet of a circulation pump provided in the anode gas circulation channel A differential pressure acquisition device that acquires the differential pressure at the outlet, a rotational speed acquisition device that acquires the rotational speed of the circulation pump, a pressure loss characteristic storage device that stores pressure loss characteristics of the anode gas circulation flow path, and a circulation pump A gas density in the anode gas circulation channel is estimated based on the pressure loss characteristic of the anode gas circulation channel and the pressure-flow rate characteristic of the circulation pump from the differential pressure, and a pressure-flow characteristic memory device that stores the pressure-flow rate characteristic. A hydrogen density estimation device for a fuel cell is provided. Further, the hydrogen concentration estimation device includes a relative humidity estimation device that estimates the relative humidity of the fuel cell, and a hydrogen concentration calculation device that calculates the hydrogen concentration using the relative humidity based on the anode gas temperature, the differential pressure, and the gas density. And having.

  According to the present invention, the hydrogen concentration is determined based on the gas density determined from the anode gas temperature in the anode gas circulation channel, the differential pressure of the circulation pump, the rotation speed of the circulation pump, the pressure loss characteristic, and the pressure-flow characteristic of the circulation pump. In the estimation, the relative humidity in the fuel cell is used. Therefore, in the estimation of the hydrogen concentration, the influence of the actual humidity in the fuel cell is taken into account without making a rough approximation assuming that the water vapor content (water vapor fraction) in the anode gas circulation channel is the saturated water vapor fraction. As a result, it is possible to perform an estimation that matches the actual behavior, so that a more accurate hydrogen concentration can be obtained.

FIG. 1 is a schematic diagram of a fuel cell system according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating the configuration of the controller. FIG. 3 shows a pressure loss characteristic map. FIG. 4 shows a pump performance map. FIG. 5 shows a flowchart for explaining the flow of estimating the hydrogen concentration. FIG. 6 shows a graph in which a pressure loss characteristic map and a pump performance map are superimposed. FIG. 7 is a graph showing the relationship between the gas density and the pump differential pressure at the point where the pressure loss characteristic and the pump performance characteristic can be balanced. FIG. 8 shows a map showing the relationship between the HFR value and the relative humidity. FIG. 9 is a Nyquist diagram of the internal impedance of the fuel cell stack according to one embodiment. FIG. 10 shows an example of an equivalent circuit of the fuel cell stack. FIG. 11 shows an ionomer resistance value-relative humidity map. FIG. 12 is a flowchart showing a flow of calculating the electric double layer capacity value of the fuel cell stack according to the embodiment. FIG. 13A is a diagram illustrating an example of an equivalent circuit of a fuel cell stack. FIG. 13B is a diagram illustrating an example of an equivalent circuit of the fuel cell stack. FIG. 14 shows a map showing the relationship between relative humidity and electric double layer capacitance value. FIG. 15 is a flowchart illustrating the flow of hydrogen concentration estimation according to an embodiment. FIG. 16 is a graph schematically showing fluctuations in pump differential pressure when liquid water is present in the fuel cell stack. FIG. 17 is a flowchart for explaining the flow of processing in the presence of liquid water according to an embodiment. FIG. 18 is a diagram schematically showing a configuration of an impedance measuring apparatus according to an embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a schematic diagram of a fuel cell system 100 according to an embodiment of the present invention.

  In the present embodiment, the fuel cell system 100 includes a fuel cell stack 1, an anode gas circulation device 3, an impedance measurement device 5, and a controller 6. In this embodiment, for simplification of the drawing, an anode gas discharge system, a cathode gas supply / discharge system, an electric power system for supplying electric power to a motor, etc., a cooling device for the fuel cell stack 1, and the like. The illustration of the element is omitted.

  The fuel cell stack 1 is a laminated battery in which two or more fuel battery cells (unit cells) are laminated. The fuel cell stack 1 receives the supply of the anode gas and the cathode gas and generates electric power necessary for traveling of the vehicle. The fuel cell stack 1 has an anode electrode side terminal 1A and a cathode electrode side terminal 1B as output terminals for extracting electric power.

  The anode gas circulation device 3 supplies anode gas (hydrogen gas) to the fuel cell stack 1 for circulation. The anode gas circulation device 3 includes a high-pressure tank 31, an anode gas supply passage 32, an anode pressure regulating valve 33, an ejector 34, an anode gas circulation channel 35, a pump inlet side pressure sensor 36, a circulation pump 37, A pump outlet pressure sensor 38 and a temperature sensor 39 are provided.

  The high-pressure tank 31 is a container that stores the anode gas supplied to the fuel cell stack 1 while maintaining the high-pressure state.

  The anode gas supply passage 32 is a passage for supplying the anode gas discharged from the high-pressure tank 31 to the fuel cell stack 1. One end of the anode gas supply passage 32 is connected to the high-pressure tank 31, and the other end is connected to the ejector 34.

  The anode pressure regulating valve 33 is provided in the anode gas supply passage 32 downstream of the high pressure tank 31. The anode pressure regulating valve 33 is controlled to be opened and closed by the controller 6 and adjusts the pressure of the anode gas supplied to the fuel cell stack 1.

  The ejector 34 is provided at a connection portion between the anode gas supply passage 32 and the anode gas circulation passage 35. The ejector 34 recirculates the anode gas from the high-pressure tank 31 and the anode gas discharged from the anode electrode of the fuel cell stack 1 through the anode gas circulation channel 35.

  The anode gas circulation passage 35 is a passage for circulating the anode gas between the anode electrode inlet and the anode electrode outlet of the fuel cell stack 1. When it is detected by the hydrogen concentration estimation method described later that the hydrogen concentration in the anode gas circulation passage 35 is below a certain value, a purge valve (not shown) is opened and the off-gas with a reduced hydrogen concentration is It is discharged into the discharge passage.

  The pump inlet side pressure sensor 36 detects the pressure between the anode gas outlet of the fuel cell stack 1 and the circulation pump 37 in the anode gas circulation passage 35 (hereinafter also referred to as “pump inlet side pressure P1”). It is a sensor.

  The circulation pump 37 functions as a power source for circulating the anode gas in the anode gas circulation passage 35. The circulation pump 37 is provided with a rotation speed sensor 37a for detecting the rotation speed N.

  The pump outlet side pressure sensor 38 is a sensor that detects the pressure between the circulation pump 37 and the ejector 34 in the anode gas circulation passage 35.

  The temperature sensor 39 is provided between the ejector 34 and the fuel cell stack 1 and detects a gas temperature at the anode inlet of the fuel cell stack 1 (hereinafter also referred to as “circulation anode gas temperature T”).

  The impedance measuring device 5 is a device that measures the internal impedance of the fuel cell stack 1 based on the output voltage and output current of the fuel cell stack 1. Specifically, the impedance measuring device 5 controls the output of the fuel cell stack 1 so that the output current and output voltage of the fuel cell stack 1 include an AC signal having a predetermined frequency, and the output voltage value detected at this time and The internal impedance Z is calculated based on the output current value. Further, the impedance measuring device 5 outputs the measured internal impedance Z to the controller 6.

  The controller 6 includes a microcomputer having a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and an input / output interface (I / O interface). The controller 6 includes signals from various sensors such as a current sensor and a voltage sensor (not shown) in addition to detection signals from the pump inlet pressure sensor 36, the rotation speed sensor 37a, the pump outlet pressure sensor 38, and the temperature sensor 39, And a signal from a sensor such as an accelerator stroke sensor for detecting the depression amount of an accelerator pedal (not shown) is input.

  Further, the controller 6 controls the opening degree of the anode pressure regulating valve 33 according to the concentration of hydrogen flowing through the anode gas circulation passage 35 to adjust the pressure and flow rate of the anode gas supplied to the fuel cell stack 1.

  FIG. 2 is a block diagram illustrating the configuration of the controller 6 according to the present embodiment. As shown in the figure, the controller 6 includes a temperature acquisition device 40, a differential pressure acquisition device 41, a rotation speed acquisition device 42, and a pressure loss characteristic storage device that are constituted by the CPU, ROM, RAM, and I / O interface. And a data storage unit 43 as a pressure-flow rate characteristic storage device, a gas density estimation device 44, a relative humidity estimation device 45, and a hydrogen concentration calculation device 46.

  The temperature acquisition device 40 receives and acquires the anode gas temperature T detected by the temperature sensor 39 from the temperature sensor 39.

  The differential pressure acquisition device 41 receives the pump inlet side pressure P1 detected by the pump inlet side pressure sensor 36 and the pump outlet side pressure P2 detected by the pump outlet side pressure sensor 38, and based on these values, the difference is obtained. The pressure ΔP (P2−P1) is acquired.

  The rotation speed acquisition device 42 receives and acquires the rotation speed N of the circulation pump 37 detected by the rotation speed sensor 37a.

  The data storage unit 43 stores a pressure loss characteristic map M1 used for estimating the gas density ρ in the anode gas circulation passage 35 and a pump performance map M2.

  FIG. 3 shows a pressure loss characteristic map M1. As shown in the figure, this pressure loss characteristic map M1 shows the relationship between the circulation flow rate Qs in the anode gas circulation channel 35 and the pressure loss in the anode gas circulation channel 35 as the pressure loss characteristic of the anode gas circulation channel 35. Is a map showing each gas density.

  FIG. 4 shows a pump performance map M2. As shown in the figure, this pump performance map M2 shows the pressure difference ΔP (hereinafter referred to as “pump difference”) between the circulation flow rate Qs in the anode gas circulation passage 35 and the circulation pump 37 as the pump performance characteristic according to the pump rotation speed N. It is also a map showing the relationship with the gas density ρ.

  Based on the pressure loss characteristic map M1 and the pump performance map M2 described above, the gas density estimation device 44 uses the rotational speed N of the circulation pump 37, the circulation flow rate Qs in the anode gas circulation passage 35, and the pump differential pressure ΔP based on the pressure loss characteristic map M1 and the pump performance map M2. The gas density ρ of the anode gas circulation channel 35 is estimated.

  The relative humidity estimation device 45 estimates the relative humidity RH inside the fuel cell stack 1 from the internal impedance Z measured by the impedance measurement device 5 based on a predetermined impedance-relative humidity map.

  The hydrogen concentration calculation device 46 obtains the hydrogen concentration CRH in the anode gas circulation channel 35 based on the circulation anode gas temperature T, the differential pressure ΔP, the gas density ρ, and the relative humidity RH. Here, the “hydrogen concentration CRH in the anode gas” is a value obtained by dividing the flow rate of only hydrogen contained in the anode gas in the anode gas circulation channel 35 by the circulation flow rate Qs of the entire anode gas. means.

  FIG. 5 is a flowchart for explaining the flow of estimating the hydrogen concentration according to this embodiment.

  In step S10, the temperature acquisition device 40 of the controller 6 acquires the anode gas temperature T, the differential pressure acquisition device 41 acquires the differential pressure ΔP, and the rotation speed acquisition device 42 acquires the rotation speed N.

  In step S20, the gas density estimation device 44 estimates the gas density ρ based on the pressure loss characteristic map M1, the pump performance map M2, and the calculated pump differential pressure ΔP. Details of the estimation of the gas density ρ will be described.

  FIG. 6 shows an outline of a graph in which the pressure loss characteristic map M1 and the pump performance map M2 are superimposed. In FIG. 6, for the sake of simplification of the drawing, only a curve in the case of taking three values ρ1 to ρ3 as the value of the gas density ρ is shown. Further, the pump performance map M2 is also shown on the assumption that the pump rotational speed N is a fixed value for simplification of the drawing.

  In FIG. 6, the intersection of the curve of the pressure loss characteristic map M1 (curve that increases as the pump differential pressure ΔP increases) and the curve of the pump performance map M2 (curve that decreases as the pump differential pressure ΔP increases) is This represents an actual characteristic that can balance both characteristics. Therefore, the characteristic that can be actually taken is a curve R connecting the intersections I1, I2, and I3 of both maps M1 and M2.

  FIG. 7 is a graph showing the relationship between the gas density ρ and the pump differential pressure ΔP in the above-described characteristic that balances the pressure loss characteristic and the pump performance characteristic. In the graph, the values of the pump differential pressure ΔP and the gas density ρ at each of the intersections I1, I2, and I3 in which the above-described characteristics are balanced are plotted on a plane, and straight lines obtained from these plots. It is. Therefore, by using this straight line, the gas density ρ adapted to the actual characteristics can be estimated from the detected value of the pump differential pressure ΔP.

  Returning to FIG. 5, in step S <b> 30, the relative humidity estimation device 45 is based on the HFR-relative humidity map from the high frequency impedance (HFR) based on the internal impedance Z measured by the impedance measurement device 5. The relative humidity RH inside the fuel cell stack 1 is estimated.

  Specifically, the impedance measuring device 5 controls the output current of the fuel cell stack 1 so that the output current and output voltage of the fuel cell stack 1 include an AC signal having a sufficiently large frequency ωH of several kHz or more. The DC / DC converter is controlled, and the internal impedance Z (ωH) is calculated as the HFR value based on the detected output current value and output voltage value. This HFR value substantially corresponds to the resistance value of the electrolyte membrane of the fuel cell stack 1. Then, the impedance measuring device 5 transmits this HFR value to the relative humidity estimating device 45 of the controller 6.

  FIG. 8 is an HFR value-relative humidity map showing the relationship between the HFR value and the relative humidity RH inside the fuel cell stack 1. As shown in the figure, the HFR value and the relative humidity RH have a relationship in which the relative humidity RH decreases as the HFR value increases, and the relative humidity RH is uniquely determined when the HFR value is determined. Therefore, the relative humidity estimation device 45 calculates the relative humidity RH from the calculated HFR value based on this HFR-relative humidity map.

  Returning to FIG. 5, in step S40, the hydrogen concentration calculation device 46 sets the circulating anode gas temperature T, the pump inlet side pressure P1, the gas density ρ estimated in step S20, and the relative humidity RH estimated in step S30. Based on this, the hydrogen concentration CRH in the anode gas circulation passage 35 is calculated. Details of the method for calculating the hydrogen concentration CRH will be described.

  The hydrogen concentration calculation device 46 calculates a hydrogen concentration CRH as a hydrogen fraction based on the following equation (1).

  Here, in the formula, a, b, and c mean a hydrogen fraction (hydrogen concentration), a nitrogen fraction, and a water vapor fraction in the anode gas in the anode gas circulation channel 35, respectively. The hydrogen fraction “a”, the nitrogen fraction “b”, and the water vapor fraction “c” are the ratios of the hydrogen component, the nitrogen component, and the water vapor component to the entire anode gas in the anode gas circulation passage 35, respectively. In the present embodiment, the main component of the anode gas can be considered to be substantially occupied by hydrogen, nitrogen, and water vapor, so that the sum of these is 1 as shown in Equation (3).

Furthermore, in Formula (1), MH2, MN2, and MH2O mean the molecular weight of a hydrogen molecule, the molecular weight of a nitrogen molecule, and the molecular weight of water, respectively. “T” means the above-described circulating anode gas temperature T. “TN” means a temperature in a standard state, and its value is, for example, 273 [K]. Further, “P” means the above-described pump inlet side pressure P1. “PN” means the pressure in the standard state, and the value is, for example, 1.0 × 10 ⁵ [pa].

  Therefore, MH2, MN2, MH2O, TN, and PN are known values. The circulating anode gas temperature T is a value detected by the temperature sensor 39, and the pump inlet side pressure P 1 is a value detected by the pump inlet side pressure sensor 36. Further, the gas density ρ is the value estimated in step S20. Therefore, in the above formula (1), the unknowns are only the hydrogen fraction a, the nitrogen fraction b, and the water vapor fraction c. Further, considering the above formula (3), if either one of the nitrogen fraction b and the water vapor fraction c is determined, the hydrogen fraction a can be obtained.

  In this embodiment, the water vapor fraction c is calculated based on the above equation (2). Psat in the formula (2) means a saturated water vapor pressure. The saturated water vapor pressure Psat can be uniquely determined according to the value of the circulating anode gas temperature T. Therefore, the water vapor fraction c is calculated from the saturated water vapor pressure Psat, the pump inlet side pressure P1, and the relative humidity RH estimated in step S30. In particular, in the present embodiment, as can be clearly understood from the equation (2), by multiplying the saturated water vapor pressure Psat by the relative humidity RH, the actual fuel cell stack 1 with respect to the water vapor fraction c. The humidity inside is reliably reflected. Therefore, the water vapor fraction c can be calculated with high accuracy.

  Therefore, in the present embodiment, the hydrogen fraction a, that is, the hydrogen concentration CRH can be calculated based on the equations (1) to (3).

  As described above, according to the hydrogen concentration estimation method for a fuel cell according to the present embodiment described above, the following effects can be obtained.

  In the fuel cell hydrogen concentration estimation method according to the present embodiment, the anode gas temperature T in the anode gas circulation channel 35 and the anode gas circulation channel 35 are provided in the fuel cell system 100 having the fuel cell stack 1 as a fuel cell. The pressure difference ΔP between the inlet and outlet of the circulation pump 37 and the rotation speed N of the circulation pump 37 are acquired (step S10 in FIG. 5), and the pressure loss characteristic M1 of the anode gas circulation passage 35 and the circulation pump are obtained from the difference pressure ΔP. The gas density ρ in the anode gas circulation passage 35 is estimated based on the pressure-flow rate characteristic M2 (step S20 in FIG. 5). Further, in this method for estimating the hydrogen concentration of the fuel cell, the relative humidity RH in the fuel cell stack 1 is estimated (step S30 in FIG. 5), and the relative humidity is determined based on the anode gas temperature T, the differential pressure ΔP, and the gas density ρ. The hydrogen concentration is calculated using RH (step S40 in FIG. 5).

  In the present embodiment, the controller 6 acquires the anode gas temperature T in the anode gas circulation passage 35 in the fuel cell system 100 having the fuel cell stack 1, and the inlet and outlet of the circulation pump 37. The differential pressure acquisition device 41 that acquires the differential pressure ΔP of the pressure, the rotational speed acquisition device 42 that acquires the rotational speed N of the circulation pump 37, and the pressure loss characteristic storage device M1 that stores the pressure loss characteristics of the anode gas circulation passage 35. A pressure-flow rate characteristic storage device M2 for storing the pressure-flow rate characteristic of the circulation pump 37, a pressure loss characteristic M1 of the anode gas circulation passage 35 based on the differential pressure ΔP, and a pressure-flow rate characteristic M2 of the circulation pump. A gas density estimation device 44 for estimating the gas density ρ in the anode gas circulation flow path 35 and a relative humidity estimation for estimating the relative humidity RH of the fuel cell stack 1 A location 45, the anode gas temperature T, the differential pressure [Delta] P, and on the basis of the gas density [rho, functions as a hydrogen concentration calculating unit 46 for calculating the hydrogen concentration CRH using RH relative humidity.

  According to this embodiment, it is determined from the anode gas temperature T in the anode gas circulation passage 35, the differential pressure ΔP of the circulation pump 37, the rotational speed of the circulation pump 37, the pressure loss characteristic M1, and the pressure-flow characteristic M2 of the circulation pump. In estimating the hydrogen concentration based on the gas density ρ, the relative humidity RH is used. Therefore, in the estimation of the hydrogen concentration CRH, the influence of the actual humidity in the fuel cell stack 1 is taken into consideration without performing a rough approximation assuming that the water vapor fraction in the anode gas circulation passage 35 is the saturated water vapor fraction. Since it is possible to perform an estimation that matches the actual behavior, a more accurate hydrogen concentration CRH can be obtained.

  Further, in the fuel cell hydrogen concentration estimation method according to the present embodiment, the internal impedance Z of the fuel cell is measured, and the relative humidity RH is obtained based on the internal impedance Z. In particular, in the present embodiment, the impedance measuring device 5 measures the internal impedance Z, and the relative humidity estimating device 45 obtains the relative humidity RH based on the internal impedance Z (step S30 in FIG. 5). Thereby, the relative humidity RH can be easily obtained using the predetermined relationship between the internal impedance Z and the relative humidity RH.

  In particular, in the method for estimating the hydrogen concentration of the fuel cell according to the present embodiment, the internal impedance Z is a high frequency impedance (HFR value) measured using the frequency ωH in the high frequency band for obtaining the HFR. That is, the impedance measuring device 5 measures the internal impedance Z using the frequency in the frequency band for obtaining the HFR. Thus, the relative humidity RH can be obtained with higher accuracy by using the HFR value strongly correlated with the wetness in the fuel cell stack 1 for the calculation of the relative humidity RH.

(Second Embodiment)
Hereinafter, a second embodiment will be described. In each of the embodiments described below, the same reference numerals are used for portions that perform the same functions as those of the above-described first embodiment, and repeated descriptions are appropriately omitted.

  In this embodiment, in determining the relative humidity RH in step S30 of FIG. 5, the ionomer resistance Rion derived from the electrolyte component in the catalyst layer of the fuel cell constituting the fuel cell stack 1 is used instead of the HFR value. Is used. Below, the calculation method of ionoma resistance Rion is demonstrated.

  FIG. 9 is a Nyquist diagram of the internal impedance Z of the fuel cell stack 1 according to the present embodiment. In particular, in FIG. 9, an impedance curve (also referred to as an equivalent circuit impedance curve C1) determined by applying measured values of state quantities (reaction resistance value and electric double layer capacity value) of the fuel cell stack 1 to a predetermined simple equivalent circuit, In addition, an impedance curve (also referred to as an actual impedance curve C2) based on an actual measurement value of internal impedance measured in advance under a predetermined condition is shown.

  In the figure, the equivalent circuit impedance curve C1 is indicated by a broken line, and the actually measured impedance curve C2 is indicated by a solid line. Here, only a part of each impedance curve is shown for simplification of the drawing.

となる。 FIG. 10 shows an example of a simple equivalent circuit of the fuel cell stack 1. As shown in the figure, the simplified equivalent circuit includes an electrolyte membrane resistance component of the fuel cell stack 1, a reaction resistance at the electrodes (cathode electrode and anode electrode), and an electric double layer capacitance component of the electrode. The expression of the internal impedance Z obtained based on the simple equivalent circuit is

It becomes.

  However, ω means frequency, Rmem means electrolyte membrane resistance value, Ract means reaction resistance value, Cdl means electric double layer capacity, and j means imaginary unit.

  Here, the internal impedance measuring device 5 measures the internal impedances Z (ω1) and Z (ω2) at two frequencies ω1 and ω2 belonging to a predetermined low frequency band. Then, the relative humidity estimating device 45 of the controller 6 applies these frequencies ω1 and ω2 and the internal impedances Z (ω1) and Z (ω2) to the above equation (4), thereby reacting resistance value Ract and electric double layer capacitance value. Obtain Cdl.

  Specifically, for the reaction resistance value Ract and the electric double layer capacitance value Cdl, the impedance measurement values Z (ω1) and Z (ω2) at the two frequencies ω1 and ω2 are substituted into the equation (4) to obtain It is obtained by obtaining the electric double layer capacitance value Cdl, the reaction resistance Ract, and the electrolyte membrane resistance value Rmem from four expressions obtained by separating the obtained expression into a real part and an imaginary part.

  When the reaction resistance value Ract and the electric double layer capacitance value Cdl thus obtained are applied to the equation (4), an arc-shaped equivalent circuit impedance curve C1 shown by a broken line in FIG. 10 is obtained.

  On the other hand, the measured impedance curve C2 is a curve drawn by plotting a plurality of measured impedance values on the complex plane by measuring the impedance of the fuel cell stack 1 at a plurality of frequencies. In addition, since this measured impedance curve C2 usually requires measured values of internal impedance at a large number of frequencies, it is difficult to create the fuel cell stack 1 in a state where it is mounted on the vehicle. Therefore, as the measured impedance curve C2, for example, data created by experimentally measuring impedance in advance for a fuel cell stack of the same type as the fuel cell stack 1 is used. Here, the measured value of the internal impedance at a sufficiently large frequency ωH (the intersection of the curve C2 and the real axis in the figure) is the HFR value.

  The actually measured impedance curve C2 substantially coincides with the equivalent circuit impedance curve C1 in a relatively low-frequency arc region. However, the measured impedance curve C2 forms a linear portion in the relatively high frequency non-arc region L1, and deviates from the equivalent circuit impedance curve C1.

  The reason why such a non-arc region L1 is formed is that, in the equivalent circuit impedance curve C1 set based on the simple equivalent circuit as described above, the influence of the ionomer resistance based on the distribution in the thickness direction of the fuel cell is present. This is because the error due to the effect of the ionomer resistance is increased in the high frequency region because it is not taken into consideration.

  From the above, in the portion on the real axis where the frequency ω is maximized, the electrolyte membrane resistance value Rmem, which is the value of the intersection of the equivalent circuit impedance curve C1 and the real axis, and the intersection of the measured impedance curve C2 and the real axis. By taking the difference from the HFR value, which is a value, the ionomer resistance value Rion can be obtained. The ionomer resistance value Rion thus determined does not include electron transport resistance components such as bulk resistance and contact resistance, and is more sensitive to the relative humidity RH of the fuel cell stack 1 than the HFR value. Become. That is, by using the ionomer resistance value Rion for calculating the relative humidity RH, the obtained relative humidity RH becomes more accurate.

  FIG. 11 shows an ionomer resistance value-relative humidity map showing the relationship between the ionomer resistance value Rion and the relative humidity RH inside the fuel cell stack 1. The ionomer resistance value-relative humidity map is stored in the relative humidity estimation device 45 in advance. As shown in the figure, the ionomer resistance value Rion and the relative humidity RH have a relationship in which the relative humidity RH decreases as the ionomer resistance value Rion increases, and the relative humidity RH is uniquely determined when the ionomer resistance value Rion is determined. Therefore, the relative humidity estimating device 45 can calculate the relative humidity RH from the calculated ionomer resistance value Rion based on this HFR-relative humidity map.

  As described above, according to the hydrogen concentration estimation method for a fuel cell according to the present embodiment described above, the following effects can be obtained.

  In the fuel cell hydrogen concentration estimation method according to this embodiment, the ionomer resistance value Rion derived from the electrolyte component in the catalyst layer of the fuel cell stack 1 is calculated from the internal impedance Z, and the relative humidity RH is calculated based on the ionomer resistance value Rion. Ask for. That is, in the present embodiment, the relative humidity estimation device 45 of the controller 6 calculates the ionomer resistance Rion derived from the electrolyte component in the catalyst layer of the fuel cell stack 1 from the internal impedance Z measured by the impedance measuring device. Further, the relative humidity estimation device of the controller 6 obtains the relative humidity RH based on the ionomer resistance Rion.

  As described above, by calculating the relative humidity RH using the ionomer resistance value Rion having higher sensitivity with respect to the relative humidity RH of the fuel cell stack 1, a more accurate estimated value of the relative humidity RH is obtained. be able to. Therefore, the accuracy of the hydrogen concentration CRH calculated based on the high-accuracy relative humidity RH is further improved.

(Third embodiment)
Hereinafter, the third embodiment will be described.

  In the present embodiment, in obtaining the relative humidity RH in step S30 of FIG. 5, the electric double layer capacity value Cdl of the fuel cell stack 1 is used instead of the HFR value. Hereinafter, a method for calculating the electric double layer capacitance value Cdl will be described.

  FIG. 12 is a flowchart showing a flow of calculation of the reaction resistance value Ract, c of the cathode electrode.

  In step S31, the controller 6 sets an equivalent circuit model of the fuel cell stack 1 shown in FIG. 13A. In this embodiment, the equivalent circuit includes a reaction resistance value Ract, a and electric double layer capacitance value Cdl, a of the anode electrode, a reaction resistance value Ract, c and electric double layer capacitance value Cdl, c of the cathode electrode, and The electrolyte membrane resistance value Rmem is included.

  Here, the reaction resistance value Ract, a of the anode electrode increases or decreases according to the reaction of the anode gas at the anode electrode, and the reaction proceeds due to a factor that the reaction does not proceed smoothly, for example, the anode gas is insufficient. The resistance value Ract, a increases. Therefore, when a sufficient amount of anode gas is supplied to the anode electrode and hydrogen is not insufficient, the reaction resistance value Ract, a of the anode electrode is larger than the reaction resistance value Ract, c of the cathode electrode. Small. Therefore, the reaction resistance component of the anode electrode can be ignored.

  Furthermore, the electric double layer capacity value Cdl, a of the anode electrode is modeled to represent the electric capacity of the anode electrode in the fuel cell stack 1. Therefore, the electric double layer capacitance value Cdl, a is determined based on various factors such as the material and size of the anode electrode. Here, it is known that the electric double layer capacitance value Cdl, a of the anode electrode is less sensitive to a low frequency (several hundred Hz or less) than the electric double layer capacitance value Cdl, c of the cathode electrode. In particular, in the frequency belonging to the specific frequency band assumed in the present embodiment, the contribution of the electric double layer capacitance value Cdl, c to the value of the internal impedance is very small. Therefore, the electric double layer capacity component of the anode can be ignored.

  Thus, since the reaction resistance component of the anode electrode and the electric double layer capacity component of the anode electrode can be ignored, the equivalent circuit model of the fuel cell stack 1 is substantially the same as that of the cathode electrode as shown in FIG. 13B. It can be regarded as a circuit including only the reaction resistance value Ract, c, the electric double layer capacitance value Cdl, c, and the electrolyte membrane resistance value Rmem.

  Therefore, in the following, for simplification of the sign, the sign of the reaction resistance value Ract, c of the cathode electrode is simply described as “Ract”, and the sign of the electric double layer capacitance value Cdl, c of the cathode electrode is simply “Cdl”. Describe.

  Returning to FIG. 12, in step S <b> 32, the relative humidity estimation device 45 of the controller 6 sets an expression for the internal impedance Z based on the equivalent circuit shown in FIG. 13B. Therefore, the equation of the internal impedance Z obtained is in agreement with the above equation (4).

  In step S33, the relative humidity estimation device 45 extracts the imaginary part Zim of the above equation (4). The imaginary part Zim is as follows.

  In step S34, the relative humidity estimation device 45 calculates the electric double layer capacitance value Cdl of the cathode electrode from the extracted imaginary part Zim of the internal impedance. Specifically, with respect to the above equation (5), the frequencies ω1 and ω2 (several Hz to several tens of Hz), and the imaginary part Zim of the internal impedance Z measured by the impedance measuring device 5 based on these frequencies ω1 and ω2 ( Substituting ω1) and Zim (ω2), obtain two equations for Cdl and Ract as unknowns, and solve them to obtain the electric double layer capacitance value Cdl.

  In particular, the above formula (5) can be transformed into the following formula (6).

Therefore, on the coordinate plane in which the vertical axis is −1 / ωZim and the horizontal axis is 1 / ω ² , the two frequencies ω1 and ω2 and the imaginary part Zim (ω1) and Zim (ω2) of the impedance are plotted to obtain a straight line. Drawing and finding the intercept of this straight line makes this intercept equal to Cdl. Thereby, the electric double layer capacitance value Cdl of the cathode electrode can be easily calculated.

  FIG. 14 shows a relative humidity-electric double layer capacity value map showing the relationship between the relative humidity RH of the fuel cell stack 1 and the electric double layer capacity value Cdl of the cathode electrode. This relative humidity-electric double layer capacitance value map is stored in advance in the relative humidity estimation device 45. As shown in the drawing, the electric double layer capacitance value Cdl and the relative humidity RH of the cathode electrode increase as the electric double layer capacitance value Cdl increases, and if the electric double layer capacitance value Cdl is determined, the relative humidity RH. Is uniquely determined. Accordingly, the relative humidity estimation device 45 calculates the relative humidity RH from the calculated electric double layer capacitance value Cdl based on the electric double layer capacitance value-relative humidity map. In particular, when an amorphous carbon material such as ketjen black is used as the electrode material of the fuel cell stack 1, the correlation between the electric double layer capacitance value Cdl and the relative humidity RH appears more clearly.

  As described above, according to the hydrogen concentration estimation method for a fuel cell according to the present embodiment described above, the following effects can be obtained.

  In the fuel cell hydrogen concentration estimation method according to the present embodiment, the electric double layer capacity value Cdl of the fuel cell stack 1 is calculated from the internal impedance Z, and the relative humidity is obtained based on the electric double layer capacity value Cdl. That is, in the present embodiment, the relative humidity estimation device 45 of the controller 6 functions as an electric double layer capacitance value device that calculates the electric double layer capacitance value Cdl of the fuel cell stack 1 from the internal impedance Z measured by the impedance measurement device. Furthermore, the relative humidity estimation device of the controller 6 obtains the relative humidity RH based on the electric double layer capacitance value Cdl.

  Thereby, in addition to the HFR value and the ionomer resistance value Rion, a method for calculating the relative humidity RH of the fuel cell stack 1 can be provided, so that the HFR value and ionomer can be determined according to the operating conditions of the fuel cell stack 1 and the like. The relative humidity RH can be obtained in a situation where it is easier to obtain the electric double layer capacitance value Cdl than the resistance value Rion.

  In the present embodiment, the relative humidity RH is obtained using the electric double layer capacity value Cdl of the cathode electrode. For example, the electric double layer capacity of the entire fuel cell stack 1 is also taken into account in consideration of the electric double layer capacity value of the anode electrode. The relative humidity RH may be obtained from the relationship between the capacity and the relative humidity RH.

(Fourth embodiment)
The fourth embodiment will be described below. In the present embodiment, in estimating the hydrogen concentration CRH, it is determined whether or not liquid water is present in the fuel cell stack 1, and if liquid water is present, the above-described calculation of the hydrogen concentration CRH is not performed. . When liquid water is present in the fuel cell stack 1 in a certain amount or more, the pressure loss characteristic of the anode gas circulation passage 35 varies greatly, so that the pressure loss characteristic does not conform to the pressure loss characteristic map M1 described above. Accordingly, in this case, there is a possibility that a large error is included in the estimated hydrogen concentration CRH, so that the hydrogen concentration CRH is not calculated and another estimated value is used as the hydrogen concentration CRH.

  Hereinafter, “liquid water is present in the fuel cell stack 1” means that the liquid water is present in the fuel cell stack 1 in such an amount as to change the pressure loss characteristics of the anode gas circulation passage 35. This does not include the case where there is a small amount of liquid water that does not affect the pressure loss characteristics.

  FIG. 15 is a flowchart illustrating the flow of estimating the hydrogen concentration according to this embodiment.

  As shown in the figure, in step S50, as in step S10 of FIG. 5, the temperature acquisition device 40 of the controller 6 acquires the anode gas temperature T, the differential pressure acquisition device 41 acquires the differential pressure ΔP, and the rotational speed. The acquisition device 42 acquires the rotation speed N. In the present embodiment, in particular, the differential pressure acquisition device 41 of the controller 6 obtains the pump inlet side pressure detection value and the pump outlet side pressure detection value from the pump inlet side pressure sensor 36 and the pump outlet side pressure sensor 38 every predetermined time dt. The pump differential pressure ΔP is calculated every predetermined time dt.

  In step S51, the differential pressure acquisition device 41 calculates the fluctuation of the pump differential pressure ΔP every predetermined time dt. Specifically, the absolute value | ΔP (t + dt) −ΔP (t) | of the difference between the pump differential pressure ΔP (t) at a certain time t and the pump differential pressure ΔP (t + dt) at the time t + dt is defined as the differential pressure fluctuation δP. calculate.

  In step S52, the controller 6 determines whether or not the differential pressure fluctuation δP is larger than a predetermined value. If it is determined that the differential pressure fluctuation δP is greater than the predetermined value, the process proceeds to step S53, and the controller 6 determines that liquid water is present in the fuel cell stack 1. On the other hand, when it is determined that the differential pressure fluctuation δP is equal to or less than the predetermined value, the process proceeds to step S54, and the controller 6 determines that there is no liquid water in the fuel cell stack 1.

  FIG. 16 is a graph schematically showing the fluctuation of the pump differential pressure ΔP when liquid water is present in the fuel cell stack 1. As shown in the figure, when liquid water is present in the fuel cell stack 1, the pump differential pressure ΔP vibrates greatly. Therefore, in this case, the value of the differential pressure fluctuation δP also increases and becomes larger than the predetermined value. Note that this predetermined value is a value determined in advance by experiments or the like as a value that the differential pressure fluctuation δP cannot reach in the state where no liquid water exists in the fuel cell stack 1.

  Returning to FIG. 15, if it is determined in step S53 that liquid water is present in the fuel cell stack 1, the controller 6 sets the previous estimated value as the estimated value of the hydrogen concentration CRH in step S55 as the liquid water presence process. Is done. That is, when liquid water is present in the fuel cell stack 1, the accuracy of the calculation of the hydrogen concentration CRH in step S40 of FIG. 5 cannot be maintained due to the change in the pressure loss characteristic of the anode gas circulation passage 35 described above. Therefore, the previous hydrogen concentration CRH estimated in a state where no liquid water is present in the fuel cell stack 1 is set as an estimated value of the hydrogen concentration CRH.

  On the other hand, when it is determined that there is no liquid water in the fuel cell stack 1 as in step S54, the hydrogen concentration CRH is calculated in step S56 as in step S40 of FIG. Is the estimated value of the hydrogen concentration CRH.

  As described above, according to the hydrogen concentration estimation method for a fuel cell according to the present embodiment described above, the following effects can be obtained.

  In the method for estimating the hydrogen concentration of the fuel cell according to the present embodiment, it is determined whether or not liquid water exists in the fuel cell stack 1. If it is determined that liquid water exists in the fuel cell stack 1, Time processing (step S55 in FIG. 15) is performed. That is, in the present embodiment, when the controller 6 determines that liquid water is present in the fuel cell stack 1 and the liquid water presence determination device that determines whether liquid water is present in the fuel cell stack 1, It functions as a liquid water presence treatment device that performs a predetermined liquid water presence treatment.

  Here, the “process when liquid water is present” means that the hydrogen concentration CRH is not limited to the process of setting the previous estimated value as the hydrogen concentration CRH (step S55 in FIG. 15) as in the present embodiment. Arbitrary processes such as a process of giving up the calculation and a process of setting a predicted value of the hydrogen concentration CRH as an estimated value of the hydrogen concentration CRH are included.

  As a result, when liquid water is present in the fuel cell stack 1, the calculation of the hydrogen concentration CRH is not performed in a situation where the pressure loss characteristic of the anode gas circulation passage 35 is greatly fluctuating, and an error is caused. Obtaining an estimate of a high hydrogen concentration CRH is prevented.

  In particular, in the present embodiment, when liquid water is present in the fuel cell stack 1, by setting the hydrogen concentration CRH estimated in the absence of the liquid water as the estimated value of the hydrogen concentration CRH, The estimation of the hydrogen concentration CRH can be continued even in a situation where liquid water is present in the fuel cell stack 1.

(Fifth embodiment)
Hereinafter, a fifth embodiment will be described. In addition, the same code | symbol is attached | subjected to the element similar to 4th Embodiment, and the description is abbreviate | omitted.

  In the present embodiment, as the above-described process in the presence of liquid water, the process of flying the liquid water in the fuel cell stack 1 and the anode gas circulation channel 35 is performed by increasing the number of revolutions of the circulation pump 37, and then the fuel cell The hydrogen concentration CRH in the stack 1 is calculated.

  FIG. 17 is a flowchart for explaining the flow of processing when liquid water is present according to the present embodiment. In addition, since the process shown by this flowchart is an aspect of the process at the time of liquid water presence of step S55 shown in FIG. 15, it is a premise that the process of step S50-step S53 is performed.

  As shown in the figure, in step S60, the controller 6 increases the number of revolutions of the circulation pump 37 to make the circulation pump 37 "high-speed operation". Here, by setting the circulation pump 37 at a high speed, liquid water in the fuel cell stack 1 and the anode gas circulation passage 35 is blown off, and the water content thereof is reduced. In the following, with respect to the “high rotation operation” in which the rotation speed of the circulation pump 37 is increased, the operation at the rotation speed before the rotation speed of the circulation pump 37 is increased is referred to as “normal rotation operation”.

  In step S61, the controller 6 calculates the hydrogen concentration CRH in the high rotation operation state. Specifically, the controller 6 calculates the hydrogen concentration CRH by a method similar to the method described in step S40 of FIG. Hereinafter, the calculated hydrogen concentration CRH is also referred to as “high rotation hydrogen concentration CRH1”.

  In step S62, the controller 6 determines whether or not the differential pressure fluctuation δP is smaller than a predetermined value. The differential pressure fluctuation δP is calculated by a method similar to the method described in step S51 of FIG. The predetermined value is a value determined in advance by experiments or the like as a value considered that the differential pressure fluctuation δP cannot reach when there is no liquid water in the fuel cell stack 1.

  When it is determined that the differential pressure fluctuation δP is equal to or greater than the predetermined value, the high speed operation of the circulation pump 37 is maintained. On the other hand, if it is determined that the differential pressure fluctuation δP is smaller than the predetermined value, the process proceeds to step S63.

  In step S63, the controller 6 decreases the rotation speed of the circulation pump 37 and returns to the normal rotation operation.

  In step S64, the controller 6 calculates the hydrogen concentration CRH in the normal rotation operation state. Specifically, the controller 6 calculates the hydrogen concentration CRH by a method similar to the method described in step S40 of FIG. Hereinafter, the hydrogen concentration CRH calculated in the normal rotation operation state is also referred to as “normal rotation hydrogen concentration CRH2”.

  In step S65, the controller 6 determines whether or not the high rotation hydrogen concentration CRH1-normal rotation hydrogen concentration CRH2 is smaller than a predetermined value. This predetermined value is determined from the viewpoint of whether the high rotation hydrogen concentration CRH1 and the normal rotation hydrogen concentration CRH2 are substantially the same in consideration of factors such as measurement errors, and is a value that is relatively close to zero. It is.

  Therefore, when it is determined that the high rotation hydrogen concentration CRH1 and the normal rotation hydrogen concentration CRH2 are equal to or higher than a predetermined value, the pressure of the anode gas circulation channel 35 is still in the fuel cell stack 1 and the anode gas circulation channel 35. Assuming that the liquid water that affects the loss characteristics remains, the process returns to step S60, and the circulation pump 37 is again operated at a high speed.

  On the other hand, if it is determined that the high rotation hydrogen concentration CRH1 and the normal rotation hydrogen concentration CRH2 are less than the predetermined value, the liquid water in the fuel cell stack 1 and the anode gas circulation channel 35 is supplied to the anode gas circulation channel. Assuming that the pressure loss has been reduced to an extent that does not affect the pressure loss characteristics of 35, the process proceeds to step S66.

  In step S66, the controller 6 determines whether or not the time during which the high rotation hydrogen concentration CRH1-normal rotation hydrogen concentration CRH2 continues to be less than the predetermined value in step S65 has passed the predetermined time. .

  Here, the predetermined time is that the high rotation hydrogen concentration CRH1 to the normal rotation hydrogen concentration CRH2 temporarily becomes less than a predetermined value due to factors such as measurement errors. This time is set to prevent erroneous determination that liquid water is no longer present, even though the liquid water in the passage 35 is not sufficiently reduced.

  Therefore, if the controller 6 determines that the predetermined time has not elapsed, the determination that the high rotation hydrogen concentration CRH1−the normal rotation hydrogen concentration CRH2 in step S65 is less than the predetermined value is an erroneous determination due to a measurement error or the like. Therefore, the process from step S60 is performed.

  On the other hand, when determining that the predetermined time has elapsed, the controller 6 proceeds to step S67.

  In step S67, the controller 6 sets the normal rotation hydrogen concentration CRH2 as an estimated value of the current hydrogen concentration CRH. The high rotation hydrogen concentration CRH1 may be set as an estimated value of the current hydrogen concentration CRH.

  As described above, according to the hydrogen concentration estimation method for a fuel cell according to the present embodiment described above, the following effects can be obtained.

  In the method for estimating the hydrogen concentration of the fuel cell according to the present embodiment, the process when liquid water is present (step S55 in FIG. 15) performs a high-speed operation step (FIG. 17) in which a high-speed operation is performed by increasing the rotational speed of the circulation pump 37. Step S60), a high-rotation operation calculation step (step S61 in FIG. 17) for calculating the hydrogen concentration (high-rotation hydrogen concentration CRH1) during the high-rotation operation, and a differential pressure fluctuation δP in the circulation pump 37 is predetermined. After becoming less than the value, the normal rotation operation step (step S63 in FIG. 17) in which the rotation speed of the circulation pump 37 is decreased to perform the normal rotation operation, and the hydrogen concentration during the normal rotation operation (normal rotation hydrogen concentration CRH2). The normal rotation operation calculation step (step S64 in FIG. 17) for performing the calculation, and the high rotation hydrogen concentration CRH1 and the normal rotation hydrogen concentration CRH2 are actual for a predetermined time. When the determination step (step S65 in FIG. 17) for determining whether or not they coincide with each other and the determination step determines that they coincide with each other, the normal rotation hydrogen concentration CRH2 or the high rotation hydrogen concentration CRH1 is The coincidence determination processing step that is set as the estimated value of the current hydrogen concentration, when it is determined that they do not coincide in the determination step, the high-rotation operation time calculation step, the normal rotation operation step, the normal rotation operation time calculation step, And a mismatch determination processing step for performing a determination step.

  In particular, in this embodiment, the controller 6 serving as the liquid water presence determination device described in the fourth embodiment includes a high rotation operation execution unit that executes a high rotation operation in which the number of rotations of the circulation pump 37 is increased, and a high rotation speed. A high-rotation operation calculation execution unit that calculates the high-revolution hydrogen concentration CRH1 during operation, and after the differential pressure fluctuation δP in the circulation pump 37 becomes less than a predetermined value, the rotation speed of the circulation pump 37 is decreased. The normal rotation operation execution unit that executes normal rotation operation, the normal rotation operation calculation execution unit that executes calculation of the normal rotation hydrogen concentration CRH2 during normal rotation operation, the high rotation hydrogen concentration CRH1 and the normal rotation hydrogen concentration CRH2 A determination unit that determines whether or not they substantially match each other for a predetermined time, and a normal rotation hydrogen concentration CRH2 or a high When it is determined that the coincidence determination processing unit that sets the current hydrogen concentration CRH1 as the estimated value of the current hydrogen concentration does not coincide with the determination step, the high-rotation operation time calculation step, the normal rotation operation step, It functions as a non-coincidence determination processing unit that performs a calculation step during normal rotation operation and a determination step.

  Thereby, when liquid water exists in the fuel cell stack 1, the liquid water in the fuel cell stack 1 can be blown by performing a high rotation operation in which the rotation speed of the circulation pump 37 is increased. In particular, in the present embodiment, the high rotation operation is repeated until the high rotation hydrogen concentration CRH1 and the normal rotation hydrogen concentration CRH2 substantially coincide with each other. Accordingly, since the hydrogen concentration CRH can be estimated after the liquid water does not exist in the fuel cell stack 1, the hydrogen concentration CRH can be obtained in a state where the pressure loss characteristic of the anode gas circulation passage 35 has greatly fluctuated. It is possible to more reliably prevent the occurrence of an estimation error by executing the estimation.

(Sixth embodiment)
The sixth embodiment will be described below. In addition, the same code | symbol is attached | subjected to the element similar to the element of embodiment already demonstrated.

  In this embodiment, when measuring the internal impedance of the fuel cell stack 1, the current I is supplied to the fuel cell stack 1 from a predetermined measurement current source instead of a configuration in which an AC signal is superimposed on the output current I and the output voltage V. Then, a so-called excitation current application method for calculating the internal impedance Z = V / I based on the supply current I and the output voltage V to be output is performed.

  FIG. 18 is a block diagram showing a schematic configuration of the impedance measuring apparatus 5 according to the present embodiment.

  As illustrated, the impedance measuring device 5 is connected to the intermediate terminal 1C in addition to the positive electrode terminal (cathode electrode side terminal) 1B and the negative electrode terminal (anode electrode side terminal) 1A of the fuel cell stack 1. The part connected to the midway terminal 1C is grounded as shown in the figure.

  Then, the impedance measuring device 5 includes a positive-side voltage detection sensor 210 that detects the positive-side AC potential difference V1 of the positive-electrode terminal 1B with respect to the intermediate terminal 1C, and a negative-electrode side that detects the negative-side AC potential difference V2 of the negative terminal 1A with respect to the intermediate terminal 1C. Voltage detection sensor 212.

  Further, the impedance measuring device 5 applies an alternating current I2 to a positive side AC power supply unit 214 that applies an alternating current I1 to a circuit that includes the positive terminal 1B and the intermediate terminal 1C, and an alternating current I2 to a circuit that includes the negative terminal 1A and the intermediate terminal 1C. The negative side AC power supply unit 216, the controller 218 for adjusting the amplitude and phase of the AC current I1 and AC current I2, and the internal impedance of the fuel cell stack 1 based on the positive side AC potential differences V1, V2 and the AC currents I1, I2 And an operation unit 220 that performs an operation of Z.

  In the present embodiment, the controller 218 adjusts the amplitude and phase of the alternating current I1 and the alternating current I2 so that the positive AC potential difference V1 and the negative AC potential difference V2 are equal. The controller 218 may be configured by the controller 6 shown in FIG.

  The arithmetic unit 220 includes hardware such as an A / D converter and a microcomputer chip (not shown) and a software configuration such as a program for calculating impedance, and the positive terminal AC potential difference V1 is divided by the AC current I1, and the halfway terminal 1C Is calculated by dividing the negative side AC potential difference V2 by the alternating current I2 to calculate the internal impedance Z2 from the intermediate terminal 1C to the negative terminal 1A. Further, the calculation unit 220 calculates the total internal impedance Z of the fuel cell stack 1 by taking the sum of the internal impedance Z1 and the internal impedance Z2.

  According to the fuel cell state estimation method according to the above-described embodiment, the following effects can be obtained.

  In the fuel cell state estimation method according to the present embodiment, the controller 218 of the impedance measuring device 5 outputs the alternating currents I1 and I2 to the fuel cell stack 1 configured as a laminated battery, and the positive terminal 1B of the fuel cell stack 1 The positive side AC potential difference V1 which is a potential difference obtained by subtracting the potential of the intermediate terminal 1C from the potential of the negative electrode, and the negative side alternating current which is a potential difference obtained by subtracting the potential of the intermediate terminal 1C from the potential of the negative electrode terminal 1A of the fuel cell stack 1 The alternating currents I1 and I2 are adjusted based on the potential difference V2, and the internal impedance Z of the fuel cell stack 1 is calculated based on the adjusted alternating currents I1 and I2, the positive side AC potential difference V1 and the negative side AC potential difference V2. .

  In particular, the controller 218 detects the alternating current I1 applied by the positive AC power supply unit 214 so that the positive AC potential difference V1 on the positive electrode side of the fuel cell stack 1 substantially matches the negative AC potential difference V2 on the negative electrode side. And the amplitude and phase of the alternating current I2 applied by the negative-side AC power supply unit 216 are adjusted. Thereby, since the positive electrode side AC potential difference V1 and the negative electrode side AC potential difference V2 become equal, the positive electrode terminal 1B and the negative electrode terminal 1A become substantially equipotential. Therefore, since the alternating currents I1 and I2 for impedance measurement are prevented from flowing to a load such as a traveling motor, the influence of the power generation by the fuel cell stack 1 on the impedance measurement is prevented.

  Further, when the fuel cell stack 1 performs measurement of internal impedance under the power generation state, the measurement AC potential is superimposed on the voltage generated by the power generation, so that the positive-side AC potential difference V1 and the negative-side AC Although the value of the potential difference V2 itself increases, the phase and amplitude itself of the positive side AC potential difference V1 and the negative side AC potential difference V2 do not change, so that the fuel cell stack 1 is highly accurate as in the case where the fuel cell stack 1 is not in the power generation state. Impedance Z can be measured.

  The embodiment of the present invention has been described above. However, the above embodiment only shows a part of application examples of the present invention, and the technical scope of the present invention is limited to the specific configuration of the above embodiment. Absent.

DESCRIPTION OF SYMBOLS 1 Fuel cell stack 1A Negative electrode terminal 1B Positive electrode terminal 1C Midway terminal 6 Controller 35 Anode gas circulation flow path 36 Pump inlet side pressure sensor 37 Circulation pump 37a Rotational speed sensor 38 Pump outlet side pressure sensor 39 Temperature sensor 40 Temperature acquisition device 41 Differential pressure Acquisition device 42 Rotational speed acquisition device 43 Data storage unit 44 Gas density estimation device 45 Relative humidity estimation device 100 Fuel cell system 210 Positive electrode side voltage detection sensor 212 Negative electrode side voltage detection sensor 214 Positive electrode side AC power supply unit 216 Negative electrode side AC power supply unit 218 Controller 220 arithmetic unit

Claims (16)

Obtaining an anode gas temperature in an anode gas circulation channel in a fuel cell system having a fuel cell, a differential pressure between an inlet and an outlet of a circulation pump provided in the anode gas circulation channel, and a rotation speed of the circulation pump;
Based on the pressure loss characteristic of the anode gas circulation channel and the pressure-flow rate characteristic of the circulation pump from the differential pressure, the gas density in the anode gas circulation channel is estimated,
Estimating the relative humidity in the fuel cell;
A method for estimating a hydrogen concentration in a fuel cell, wherein the hydrogen concentration in the anode gas circulation channel is calculated using the relative humidity based on the anode gas temperature, the differential pressure, and the gas density. The hydrogen concentration estimation method according to claim 1,
Measuring the internal impedance of the fuel cell;
A hydrogen concentration estimation method for obtaining the relative humidity based on the internal impedance. The hydrogen concentration estimation method according to claim 2,
A hydrogen concentration estimation method for measuring the internal impedance by using a frequency in a frequency band for obtaining HFR. The hydrogen concentration estimation method according to claim 2,
The ionomer resistance derived from the electrolyte component in the catalyst layer of the fuel cell is calculated from the internal impedance,
A hydrogen concentration estimation method for obtaining the relative humidity based on the ionomer resistance. The hydrogen concentration estimation method according to claim 2,
Calculate the electric double layer capacity value of the fuel cell from the internal impedance,
A hydrogen concentration estimation method for obtaining the relative humidity based on the electric double layer capacity value. A hydrogen concentration estimation method according to any one of claims 1 to 5,
Determining whether liquid water is present in the fuel cell;
A hydrogen concentration estimation method for performing processing when a predetermined amount of liquid water is present when it is determined that liquid water is present in the fuel cell. The hydrogen concentration estimation method according to claim 6,
When the liquid water is present,
A high rotation operation step of performing a high rotation operation in which the number of rotations of the circulation pump is increased;
A calculation step during high rotation operation for calculating the hydrogen concentration during the high rotation operation;
A normal rotation operation step of performing a normal rotation operation by decreasing the rotation speed of the circulation pump after the fluctuation of the differential pressure in the circulation pump becomes less than a predetermined value;
A calculation step during normal rotation operation for calculating the hydrogen concentration during the normal rotation operation;
A determination step of determining whether or not the calculated value of the hydrogen concentration in the high rotation operation and the calculated value of the hydrogen concentration in the normal rotation operation substantially coincide with each other for a predetermined time;
If it is determined that the values match in the determination step, the match determination for setting the calculated value of the hydrogen concentration in the normal rotation operation or the calculated value of the hydrogen concentration in the high rotation operation as an estimated value of the current hydrogen concentration Processing steps;
When it is determined in the determination step that they do not match, again, the high rotation operation time calculation step, the normal rotation operation step, the normal rotation operation time calculation step, and the mismatch determination processing step for performing the determination step,
A hydrogen concentration estimation method including In the hydrogen concentration estimation method for a fuel cell according to any one of claims 2 to 7,
The fuel cell is configured as a laminated battery,
Output alternating current to the laminated battery,
Obtained by subtracting the potential of the halfway portion from the positive side AC potential difference, which is a potential difference obtained by subtracting the potential of the middle portion of the multilayer battery from the positive side potential of the laminated battery, and the potential of the negative side of the laminated battery. Adjusting the alternating current based on the negative electrode AC potential difference that is a potential difference,
A method for estimating a hydrogen concentration in a fuel cell, wherein the internal impedance of the stacked battery is calculated based on the adjusted AC current, the positive-side AC potential difference, and the negative-side AC potential difference. A temperature acquisition device for acquiring an anode gas temperature in an anode gas circulation channel in a fuel cell system having a fuel cell;
A differential pressure acquisition device for acquiring a differential pressure between an inlet and an outlet of a circulation pump provided in the anode gas circulation channel;
A rotational speed acquisition device for acquiring the rotational speed of the circulation pump;
A pressure loss characteristic storage device for storing the pressure loss characteristic of the anode gas circulation channel;
A pressure-flow characteristic storage device for storing the pressure-flow characteristic of the circulation pump;
A gas density estimation device for estimating a gas density in the anode gas circulation channel based on the pressure loss characteristic of the anode gas circulation channel and the pressure-flow rate characteristic of the circulation pump from the differential pressure;
A relative humidity estimation device for estimating the relative humidity of the fuel cell;
A hydrogen concentration calculation device that calculates the hydrogen concentration in the anode gas circulation channel using the relative humidity based on the anode gas temperature, the differential pressure, and the gas density;
An apparatus for estimating the hydrogen concentration of a fuel cell. The hydrogen concentration estimation apparatus according to claim 9,
Further comprising an impedance measuring device for measuring the internal impedance of the fuel cell;
The relative humidity estimation device is a hydrogen concentration estimation device that obtains the relative humidity based on the internal impedance. The hydrogen concentration estimation apparatus according to claim 10,
The impedance measuring device is
A hydrogen concentration estimation apparatus that measures the internal impedance using a frequency in a frequency band for obtaining HFR. The hydrogen concentration estimation apparatus according to claim 10,
An ionomer resistance calculating device that calculates an ionomer resistance derived from an electrolyte component in the catalyst layer of the fuel cell from the internal impedance;
The relative humidity estimation device is a hydrogen concentration estimation device that obtains the relative humidity based on the ionomer resistance. The hydrogen concentration estimation apparatus according to claim 10,
An electric double layer capacity value device for calculating an electric double layer capacity value of the fuel cell from the internal impedance;
The relative humidity estimation device is a hydrogen concentration estimation device for obtaining the relative humidity based on the electric double layer capacity value. The hydrogen concentration estimation apparatus according to any one of claims 9 to 13,
A liquid water presence determination device for determining whether liquid water is present in the fuel cell;
When it is determined that liquid water is present in the fuel cell, a liquid water presence treatment device that performs a predetermined liquid water presence treatment;
A hydrogen concentration estimation apparatus having The hydrogen concentration estimation apparatus according to claim 14,
The liquid water presence determination device is
A high-speed operation execution unit for executing a high-speed operation with an increased number of rotations of the circulation pump;
A high-speed operation calculation execution unit that executes the calculation of the hydrogen concentration during the high-speed operation;
A normal rotation operation execution unit that performs normal rotation operation by reducing the rotation speed of the circulation pump after the fluctuation of the differential pressure in the circulation pump becomes less than a predetermined value;
A normal rotation operation calculation execution unit for calculating the hydrogen concentration during the normal rotation operation;
A determination unit that determines whether or not the calculated value of the hydrogen concentration in the high rotation operation and the calculated value of the hydrogen concentration in the normal rotation operation substantially coincide with each other for a predetermined time;
If it is determined that the values match in the determination step, the match determination for setting the calculated value of the hydrogen concentration in the normal rotation operation or the calculated value of the hydrogen concentration in the high rotation operation as an estimated value of the current hydrogen concentration A processing unit;
When it is determined in the determination step that they do not match, again, the high-rotation operation time calculation step, the normal rotation operation step, the normal rotation operation time calculation step, and the mismatch determination processing unit that performs the determination step;
A hydrogen concentration estimation apparatus having In the fuel cell hydrogen concentration estimation apparatus according to any one of claims 9 to 15,
The fuel cell is configured as a laminated battery,
The impedance measuring device is
Output alternating current to the laminated battery,
Obtained by subtracting the potential of the halfway portion from the positive side AC potential difference, which is a potential difference obtained by subtracting the potential of the middle portion of the multilayer battery from the positive side potential of the laminated battery, and the potential of the negative side of the laminated battery. Adjusting the alternating current based on the negative electrode AC potential difference that is a potential difference,
A hydrogen concentration estimation apparatus that calculates the internal impedance of the stacked battery based on the adjusted AC current, the positive-side AC potential difference, and the negative-side AC potential difference.

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