Evaluation system and method for fuel cell, control system and method for fuel cell, fuel cell system and program

Abstract

To provide an evaluation system for a fuel cell capable of evaluating the fuel cell by evaluating polarization of the fuel cell in real time and quantitatively while keeping accuracy equivalent to a Cole-Cole plot, a control system for a fuel cell capable of controlling the fuel cell on the basis of an evaluation result, and a fuel cell system.SOLUTION: An evaluation system for a fuel cell calculates resistance polarization of the fuel cell by measuring impedance by applying a high frequency current or a high frequency voltage in a fixed frequency during operation of the fuel cell using a solid electrolyte and evaluates the fuel cell by calculating activation polarization and concentration polarization of the fuel cell on the basis of the calculated resistance polarization. A control system for the fuel cell and a fuel cell system control the fuel cell by calculating the activation polarization and the concentration polarization of the fuel cell on the basis of the calculated resistance polarization.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a fuel cell evaluation system and method, a fuel cell control system and method, and a fuel cell system and program, and is particularly suitable for use in fuel cells that use a solid electrolyte, such as a polymer electrolyte fuel cell. [Background technology]

[0002] The voltage of a fuel cell is determined by polarization. Polarization is classified into three categories: activation polarization, resistance polarization, and concentration polarization (also called diffusion polarization). Activation polarization is a voltage drop caused by the consumption of activation energy to promote the reaction of ionization during the oxidation of hydrogen at the anode and the reduction of oxygen at the cathode. Resistance polarization is a voltage drop caused by resistance to the movement of electrons and ions in the electrolyte membrane, electrodes, separators, etc., and increases in proportion to the current. Concentration polarization is a voltage drop caused by the decrease in the concentration of hydrogen and oxygen near the electrodes due to the fuel cell reaction, and is caused by the effect of the rate at which these substances are replenished to the electrodes and the rate at which the products dissipate, and is particularly dominant in the high current range where a lot of fuel is consumed. Figure 17 shows the current-voltage curve (performance curve) of a fuel cell and the relationship between these activation polarization, resistance polarization, and concentration polarization.

[0003] There are various ways to reduce polarization, such as increasing the temperature of the fuel cell to reduce the activation energy when activation polarization increases, increasing the humidity of the electrolyte membrane because it is dry when resistance polarization increases, and increasing the flow rate of the reactant gas when concentration polarization increases. Therefore, if polarization can be evaluated and fed back to control the operation of the fuel cell, it will lead to stable operation of the fuel cell.

[0004] A common method for evaluating the polarization of a fuel cell is a Cole-Cole plot using electrochemical impedance spectroscopy (EIS method), as shown in FIG. 18. In the Cole-Cole plot, a current with a frequency ranging from low to high is applied to the fuel cell, and the impedance obtained by the current is plotted on a complex plane (the horizontal axis is the real part (Re) and the vertical axis is the imaginary part (Im)). However, since the impedance is measured by applying a current with a low frequency in particular, a series of measurements takes a long time. On the other hand, Patent Document 1 proposes a technology that obtains a current index related to the current output by a fuel cell and a voltage index related to the voltage, applies the current index to multiple models to derive multiple polarizations, and compares each of the multiple polarizations with a reference polarization set for each of the multiple polarizations when the voltage index related to the voltage is less than a threshold value, and derives a method for increasing the voltage value output by the fuel cell based on the comparison result. According to Patent Document 1, it is possible to perform measurements while the fuel cell is in operation, but it is difficult to measure polarization while maintaining the same level of accuracy as a Cole-Cole plot.

[0005] Patent Document 2 describes a technique for detecting a specific frequency component by measuring the current and voltage obtained from a fuel cell for a predetermined period of time, and detecting mass transfer resistance (corresponding to concentration polarization). Patent Document 3 proposes a technique for applying a high-frequency (e.g., several kHz to several MHz) AC current to each unit cell of a fuel cell, measuring the series resistance component of the impedance, and determining the amount of water in the fuel cell to control operation. However, both Patent Documents 2 and 3 merely evaluate a single polarization. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2022-82099 [Patent Document 2] JP 2023-39486 A [Patent Document 3] JP 2016-95984 A Summary of the Invention [Problem to be solved by the invention]

[0007] The problem that the present invention aims to solve is to provide a fuel cell evaluation system and method, as well as a program for a fuel cell evaluation method, that can evaluate each polarization of a fuel cell in real time and quantitatively while maintaining the same accuracy as a Cole-Cole plot, thereby enabling fuel cells to be evaluated.

[0008] Another problem that the present invention aims to solve is to provide a fuel cell control system and method, as well as a program for a fuel cell control method, that can quantitatively evaluate each polarization of a fuel cell in real time while maintaining the same accuracy as a Cole-Cole plot, that can control the fuel cell based on the results, and that can thereby achieve stable operation of the fuel cell.

[0009] Yet another problem that the present invention aims to solve is to provide a fuel cell system that can quantitatively evaluate each polarization of a fuel cell in real time while maintaining the same accuracy as a Cole-Cole plot, can control the fuel cell based on the results, and can thereby achieve stable operation of the fuel cell. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention provides: This is a fuel cell evaluation system that calculates the resistance polarization of a fuel cell using a solid electrolyte by applying a fixed-frequency high-frequency current or voltage during operation of the fuel cell and measuring the impedance, and then calculates the activation polarization and concentration polarization of the fuel cell based on the calculated resistance polarization, thereby evaluating the fuel cell.

[0011] The fixed frequency of the high frequency current or high frequency voltage applied to the fuel cell is the frequency at the point where the locus of the Cole-Cole plot obtained by measuring the impedance of the fuel cell intersects with the real axis (for example, the frequency at the point where the left end of the semicircular locus in FIG. 18 intersects with the real axis). This fixed frequency is, for example, 1 kHz, but is not limited to this. When calculating the activation polarization and concentration polarization of the fuel cell, in addition to the calculated resistance polarization, the results of the current-voltage characteristics of the fuel cell, which are measured simultaneously when a fixed frequency high frequency current or voltage is applied to the fuel cell, are also used.

[0012] The fuel cell evaluation system may be configured, for example, as follows: an impedance measuring device for measuring the impedance of the fuel cell; a power source for supplying the fuel cell with a high-frequency current or voltage having the fixed frequency; having The method is configured to apply the fixed frequency high frequency current or high frequency voltage from the power source during operation of the fuel cell, measure the impedance with the impedance measuring device, calculate the resistance polarization of the fuel cell, calculate the activation polarization and concentration polarization of the fuel cell based on the calculated resistance polarization, and evaluate the fuel cell based on the calculated resistance polarization, activation polarization, and concentration polarization. In this case, the magnitude relationship between the calculated resistance polarization and a predetermined first reference value is determined, the magnitude relationship between the calculated concentration polarization and a predetermined second reference value is determined, and the magnitude relationship between the calculated activation polarization and a predetermined third reference value is determined, thereby evaluating each polarization and evaluating the fuel cell. The above control of the application of the fixed frequency high frequency current or high frequency voltage, the measurement of the impedance with the impedance measuring device, the calculation and evaluation of each polarization, etc. can be performed by a computer connected between the impedance measuring device and the power source.

[0013] The fuel cell using a solid electrolyte is a polymer electrolyte fuel cell or a solid oxide fuel cell, but is not limited thereto. The fuel cell may be a single fuel cell, which is the smallest power generation unit, or a fuel cell stack in which a plurality of fuel cells are stacked. The reaction gases of the polymer electrolyte fuel cell or the solid oxide fuel cell, i.e., the fuel (reducing agent) and the gas containing oxygen (oxidizing agent), may be conventionally known and are selected as necessary.

[0014] The present invention also provides This is a method for evaluating a fuel cell, which comprises applying a fixed-frequency high-frequency current or voltage during operation of a fuel cell using a solid electrolyte and measuring the impedance to calculate the resistance polarization of the fuel cell, and then calculating the activation polarization and concentration polarization of the fuel cell based on the calculated resistance polarization to evaluate the fuel cell.

[0015] The fuel cell evaluation method is configured, for example, as follows: measuring the voltage of the fuel cell at predetermined time intervals during operation of the fuel cell; determining whether the voltage of the fuel cell measured at the time interval is larger than a predetermined reference voltage; a step of calculating a resistance polarization of the fuel cell by measuring an impedance while applying a high frequency current or voltage of the fixed frequency when the voltage of the fuel cell is determined to be lower than the reference voltage, and calculating an activation polarization and a concentration polarization of the fuel cell based on the resistance polarization; determining whether the calculated resistive polarization is smaller than a predetermined first reference value; A step of determining whether the calculated concentration polarization is smaller than a second reference value determined in advance; determining whether the calculated activation polarization is smaller than a predetermined third reference value; This fuel cell evaluation method omits the steps of measuring the voltage of the fuel cell and judging whether the voltage of the fuel cell is larger than a predetermined reference voltage, and the like, a step of calculating a resistance polarization of the fuel cell by applying a high-frequency current or a high-frequency voltage of the fixed frequency and measuring an impedance, and calculating an activation polarization and a concentration polarization of the fuel cell based on the resistance polarization; determining whether the calculated resistive polarization is smaller than a predetermined first reference value; A step of determining whether the calculated concentration polarization is smaller than a second reference value determined in advance; determining whether the calculated activation polarization is smaller than a predetermined third reference value; The configuration may include:

[0016] The present invention also provides This is a fuel cell control system that calculates the resistance polarization of a fuel cell that uses a solid electrolyte by applying a fixed-frequency high-frequency current or voltage and measuring the impedance during operation of the fuel cell, and then calculates the activation polarization and concentration polarization of the fuel cell based on the calculated resistance polarization, thereby controlling the fuel cell.

[0017] The control system for the fuel cell is configured, for example, as follows: an impedance measuring device for measuring the impedance of the fuel cell; a power source for supplying the fuel cell with a high-frequency current or voltage having the fixed frequency; having The system is configured to calculate the resistance polarization of the fuel cell by applying a high-frequency current or high-frequency voltage of the fixed frequency from the power source while the fuel cell is in operation and measuring the impedance with the impedance measuring device, calculate the activation polarization and concentration polarization of the fuel cell based on the calculated resistance polarization, and control the fuel cell based on the calculated resistance polarization, activation polarization, and concentration polarization.

[0018] The present invention also provides This is a fuel cell control method in which a fixed-frequency high-frequency current or voltage is applied to a fuel cell using a solid electrolyte during operation, the impedance is measured, and the resistance polarization of the fuel cell is calculated, and the activation polarization and concentration polarization of the fuel cell are calculated based on the resistance polarization, thereby controlling the fuel cell.

[0019] The control method for the fuel cell is configured, for example, as follows: measuring the voltage of the fuel cell at predetermined time intervals during operation of the fuel cell; determining whether the voltage of the fuel cell measured at the time interval is larger than a predetermined reference voltage; a step of calculating a resistance polarization of the fuel cell by measuring an impedance while applying a high frequency current or voltage of the fixed frequency when the voltage of the fuel cell is determined to be lower than the reference voltage, and calculating an activation polarization and a concentration polarization of the fuel cell based on the resistance polarization; continuing operation of the fuel cell when it is determined that the voltage of the fuel cell is equal to or higher than the reference voltage; determining whether the calculated resistive polarization is smaller than a predetermined first reference value; a step of taking a measure to reduce the resistive polarization to the first reference value or less when it is determined that the calculated resistive polarization is greater than the first reference value; continuing operation of the fuel cell when it is determined that the calculated resistive polarization is equal to or less than the first reference value; A step of determining whether the calculated concentration polarization is smaller than a second reference value determined in advance; When it is determined that the calculated concentration polarization is greater than the second reference value, a step of reducing the concentration polarization to the second reference value or less is performed; continuing operation of the fuel cell when it is determined that the calculated concentration polarization is equal to or less than the second reference value; determining whether the calculated activation polarization is smaller than a predetermined third reference value; when it is determined that the calculated activation polarization is greater than the third reference value, performing a process to reduce the activation polarization to the third reference value or less; continuing operation of the fuel cell when the calculated activation polarization is determined to be equal to or less than the third reference value; The device is configured to have:

[0020] In the step of performing a process to reduce the resistance polarization to a first reference value or less, for example, the operating temperature of the fuel cell is lowered to reduce the relative humidity, or the flow rate of the reactant gas of the fuel cell is reduced. In the step of performing a process to reduce the concentration polarization to a second reference value or less, for example, the flow rate of the reactant gas of the fuel cell is increased, or the operating temperature of the fuel cell is raised to increase the relative humidity. In the step of performing a process to reduce the activation polarization to a third reference value or less, the operating temperature of the fuel cell is raised. These processes can be performed by conventionally known methods.

[0021] The present invention also provides At least one solid electrolyte fuel cell; This is a fuel cell system that calculates the resistance polarization of the fuel cell by applying a fixed frequency high-frequency current or high-frequency voltage while the fuel cell is in operation and measuring the impedance, and calculates the activation polarization and concentration polarization of the fuel cell based on the calculated resistance polarization, thereby controlling the fuel cell.

[0022] The present invention also provides A program for causing a computer to execute the fuel cell evaluation method described above.

[0023] The present invention also provides A program for causing a computer to execute the above fuel cell control method.

[0024] In the invention of a program for causing a computer to execute the above fuel cell evaluation method and fuel cell control method, what has been described in relation to the invention of the above fuel cell evaluation method and fuel cell control method applies, unless it is contrary to the nature of the invention. Effect of the Invention

[0025] According to this invention, the resistance polarization of the fuel cell is calculated by applying a fixed frequency high frequency current or voltage during operation of the fuel cell and measuring the impedance, and the activation polarization and concentration polarization of the fuel cell are calculated based on the calculated resistance polarization, thereby making it possible to quantitatively evaluate each polarization of the fuel cell in real time while maintaining the same accuracy as a Cole-Cole plot, thereby making it possible to evaluate or control the fuel cell and ultimately to realize stable operation of the fuel cell. [Brief description of the drawings]

[0026] [Figure 1] 1 is a block diagram showing a fuel cell system according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram for explaining a method of separating activation polarization and concentration polarization in the fuel cell system according to the first embodiment of the present invention. [Diagram 3] 3 is a flowchart showing a method for controlling a fuel cell in a fuel cell system according to the first embodiment of the present invention. [Figure 4] FIG. 4 is a block diagram showing a fuel cell evaluation system according to a second embodiment of the present invention. [Diagram 5] 6 is a flowchart showing a fuel cell evaluation method in a fuel cell evaluation system according to a second embodiment of the present invention. [Figure 6] 1 is a block diagram showing a fuel cell system according to an embodiment; [Figure 7] FIG. 1 is a schematic diagram showing an equivalent circuit used in a Cole-Cole plot measured by an EIS method in a comparative example. [Figure 8]FIG. 11 is a schematic diagram showing resistance polarization, activation polarization, and concentration polarization at each measurement point in the embodiment for the 36th cell from the fuel inlet of a 40-cell fuel cell stack. [Figure 9] FIG. 11 is a schematic diagram showing resistance polarization, activation polarization, and concentration polarization at each measurement point in time for the 36th cell from the fuel inlet of a 40-cell fuel cell stack in a comparative example. [Figure 10] 11 is a schematic diagram showing the proportion of each polarization in the total polarization when the load current is changed to 5 A, 10 A, and 15 A in an example. [Figure 11] 13 is a schematic diagram showing the proportion of each polarization in the total polarization when the load current is changed to 5 A, 10 A, and 15 A in the comparative example. [Figure 12] 13 is a schematic diagram showing a change in load current when the load current is increased from 1 A to 20 A at approximately two-minute intervals in a state at measurement time point D in the embodiment. FIG. [Figure 13] FIG. 13 is a schematic diagram showing a change in concentration polarization when the load current is increased as shown in FIG. 12. [Figure 14] 13 is a schematic diagram showing a change in resistance polarization when the load current is increased as shown in FIG. 12. [Figure 15] 13 is a schematic diagram showing a change in activation polarization when the load current is increased as shown in FIG. 12. [Figure 16] 13 is a schematic diagram showing the relationship between concentration polarization and the battery voltage of the 36th cell when the load current is changed to 16 A, 18 A, and 20 A in an example. [Figure 17] FIG. 2 is a schematic diagram showing a current-voltage curve of a fuel cell. [Figure 18] FIG. 2 is a schematic diagram showing an example of a Cole-Cole plot measured by an EIS method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Hereinafter, a mode for carrying out the invention (hereinafter referred to as an "embodiment") will be described with reference to the drawings.

[0028] First Embodiment [Fuel cell system] FIG. 1 shows a fuel cell system according to a first embodiment. As shown in FIG. 1, the fuel cell system includes a fuel cell 10 using a solid electrolyte, a power source 20 for applying a fixed-frequency high-frequency current or voltage between the anode and cathode of the fuel cell 10, an impedance measuring device 30 for measuring the impedance of the fuel cell 10, and a computer 40 connected between the power source 20 and the impedance measuring device 30. The fuel cell 10 may be a single fuel cell or a fuel cell stack in which a plurality of fuel cells are stacked. The fuel cell 10 is a solid polymer electrolyte fuel cell or a solid oxide fuel cell. The fixed frequency of the power source 20 is, for example, 1 kHz. A program created according to the flowchart shown in FIG. 3 described later is installed in the computer 40, which evaluates the polarization of the fuel cell 10 and controls the fuel cell 10 by feeding back the result. An electronic load 50 is connected to the fuel cell 10.

[0029] In this fuel cell system, a fixed-frequency high-frequency current or voltage is applied between the anode and cathode of the fuel cell 10 by a power source 20 during load-following operation of the fuel cell 10, and the impedance (series resistance) of the fuel cell 10 at this time is measured by an impedance measuring device 30. Meanwhile, as described in detail later, the current-voltage characteristics of the fuel cell 10 are measured simultaneously with the application of the fixed-frequency high-frequency current or voltage. Then, a computer 40 calculates the resistance polarization from the measured impedance, and calculates activation polarization and concentration polarization based on the resistance polarization thus calculated and the measured current-voltage characteristics, and the computer 40 controls the fuel cell 10 based on the obtained resistance polarization, activation polarization, and concentration polarization.

[0030] The calculation methods of the resistance polarization, the activation polarization, and the concentration polarization will now be described in detail.

[0031] If the resistance of the fuel cell 10 is R, the resistance polarization V ohmAccording to Ohm's law, this is the product of the current I flowing through the fuel cell 10 and is expressed by equation (1). V ohm = R × I (1) The resistance R is a constant frequency impedance, i.e., a series resistance, measured by applying a fixed frequency high frequency current or voltage during operation of the fuel cell 10 as described above. Activation polarization V act and concentration polarization V mass To calculate the resistive polarization V ohm Voltage ignoring the voltage drop due to IR-free (expressed as) was calculated using equation (2). V IR-free =V+V ohm (2) Here, V is the voltage output from the fuel cell 10 (cell voltage).

[0032] Figure 2 shows the V IR-free The relationship between the resistive polarization V and the open circuit voltage (OCV voltage) and the Tafel slope is shown in Figure 2. ohm V is the logarithmic representation of the current I after correcting for the effect of IR-free In the low current region of the voltage characteristic, a linear voltage drop is observed, and in the high current region, it gradually becomes nonlinear. The slope of the line in the low current region is the Tafel slope. The voltage drop from the OCV voltage due to this line is the activation polarization V act The area below the line is the concentration polarization V mass The activation polarization V act and concentration polarization V mass is expressed as the following equations (3) and (4). V act =E-(b log(I)+a) (3) V mass =(b log(I)+a)-V IR-free (4) Here, E is the OCV voltage [V] of the fuel cell 10. a and b are fitting parameters in the linear approximation, b is the Tafel slope, and a is the intercept of the linear approximation. In this way, the activation polarization V act and concentration polarization V mass and separate.

[0033] [Fuel cell control method] FIG. 3 is a flow chart showing the control method of this fuel cell.

[0034] As shown in FIG. 3, control is started during the load following operation of the fuel cell 10.

[0035] In step S1, the cell voltage of the fuel cell 10 is measured at a predetermined time interval. The predetermined time interval is, for example, one second, but is not limited to this.

[0036] In step S2, the battery voltage measured in step S1 is compared with a predetermined reference voltage V s The magnitude relationship with is determined.

[0037] In step S2, the measured battery voltage is V s or more, i.e. battery voltage ≥ V s If so, normal operation is continued in step S3, and it is determined in step S4 whether operation is to be ended. If operation is to be continued, the process returns to step S1, and if not, operation is ended.

[0038] In step S2, the measured battery voltage is V s Lower, i.e. battery voltage <V s If it is determined that the resistance polarization V of the fuel cell 10 is greater than the resistance polarization V of the fuel cell 10, the polarization of the fuel cell 10 is measured in step S5. Specifically, a fixed frequency high frequency current or voltage is applied from the power source 20, and the impedance is measured by the impedance measuring device 30, and the resistance polarization V of the fuel cell 10 is calculated based on the above-mentioned equations (1) to (4). ohm Calculate the resistance polarization V ohm Activation polarization V of the fuel cell 10 based on act and concentration polarization V mass Calculate.

[0039] In step S6, the calculated resistance polarization V ohm and a predetermined first reference value V1.

[0040] In step S6, the resistive polarization V ohm is less than V1, i.e., V ohm If it is determined that V1 is not greater than V2, normal operation is performed in step S7.

[0041] In step S6, the resistive polarization V ohm is greater than V1, i.e., V ohm If it is determined that V1 is greater than V2, then in step S8, the resistive polarization V ohm V1 or less, that is, V ohm Measures are then taken to reduce the voltage V to ≦V1, and normal operation is resumed. This measure may involve, for example, lowering the operating temperature of the fuel cell 10 to lower the relative humidity, or reducing the flow rate of the reactant gas in the fuel cell 10.

[0042] In step S9, the calculated concentration polarization V mass and a predetermined second reference value V2.

[0043] In step S9, the concentration polarization V mass is equal to or less than the second reference value V2, i.e., V ohm If it is determined that V is less than or equal to V2, normal operation is carried out in step S10.

[0044] In step S9, the concentration polarization V mass is greater than V2, i.e., V mass If it is determined that V2 is greater than V, then in step S11, the concentration polarization V mass V2 or less, that is, V mass Measures are then taken to reduce the relative humidity to V≦V2, and normal operation is resumed. This measure may involve, for example, increasing the flow rate of the reactant gas in the fuel cell 10, or raising the operating temperature of the fuel cell 10 to increase the relative humidity.

[0045] In step S12, the calculated activation polarization V act and a predetermined third reference value V3.

[0046] In step S12, the activation polarization V act is equal to or less than the third reference value V3, i.e., Vact If it is determined that V is less than or equal to V3, normal operation is performed in step S3.

[0047] In step S12, the activation polarization V act is greater than V3, i.e., V act If it is determined that V3 is greater than V3, the activation polarization V act V3 or less, that is, V act ≦V3, and the process returns to normal operation in step S3. In this process, for example, the operating temperature of the fuel cell is increased.

[0048] The calculated resistive polarization V in step S6 ohm and V1, and the concentration polarization V calculated in step S9 mass and V2, and the activation polarization V calculated in step S12 act The order in which the magnitude relationship between V1 and V2 is determined is not limited to the above order, and may be any order.

[0049] As described above, according to the first embodiment, a high-frequency current or voltage with a fixed frequency of, for example, 1 kHz is applied to the fuel cell 10 during operation, and the impedance is measured by the impedance measuring device 30 to obtain the series resistance, which is used to calculate the resistance polarization. The concentration polarization and activation polarization are calculated from the resistance polarization thus calculated, making it possible to evaluate the resistance polarization, concentration polarization, and activation polarization in real time and quantitatively while maintaining the same accuracy as a Cole-Cole plot, even when the load current value fluctuates. Then, the fuel cell 10 is controlled based on the evaluation results, so that the resistance polarization, concentration polarization, and activation polarization can be maintained below their respective reference values, thereby realizing stable operation of the fuel cell 10 and improving the lifetime of the fuel cell 10.

[0050] Second embodiment [Fuel cell evaluation system] Fig. 4 shows a fuel cell evaluation system according to a second embodiment. As shown in Fig. 4, the fuel cell evaluation system includes a power source 20 connected between the anode and cathode of a fuel cell 10 for applying a fixed-frequency high-frequency current or voltage, an impedance measuring device 30 connected between the anode and cathode of the fuel cell 10 for measuring the impedance of the fuel cell 10, and a computer 40 connected between the power source 20 and the impedance measuring device 30. An electronic load 50 is connected to the fuel cell 10. The fixed frequency of the power source 20 is, for example, 1 kHz. A program created according to the flowchart shown in Fig. 5 described later is installed in the computer 40, and the polarization of the fuel cell 10 is evaluated to evaluate the fuel cell 10.

[0051] In this fuel cell evaluation system, a fixed-frequency high-frequency current or voltage is applied between the anode and cathode of the fuel cell 10 by a power source 20 during load-following operation of the fuel cell 10, and the impedance of the fuel cell 10 at that time is measured by an impedance measuring device 30. Meanwhile, simultaneously with the application of the fixed-frequency high-frequency current or voltage, the current-voltage characteristics of the fuel cell 10 are measured. Then, a computer 40 calculates the resistance polarization from the measured impedance, and based on the resistance polarization thus calculated and the measured current-voltage characteristics, the activation polarization and concentration polarization are calculated, and the obtained resistance polarization, activation polarization, and concentration polarization are evaluated, thereby evaluating the fuel cell 10.

[0052] The methods of calculating the resistance polarization, the activation polarization, and the concentration polarization are the same as those in the first embodiment.

[0053] [Fuel cell evaluation method] FIG. 5 is a flow chart showing the method for evaluating this fuel cell.

[0054] As shown in FIG. 5, the evaluation begins during load following operation of the fuel cell 10.

[0055] In step S21, the cell voltage of the fuel cell 10 is measured at a predetermined time interval. The predetermined time interval is, for example, one second, but is not limited to this.

[0056] In step S22, the battery voltage and V s The magnitude relationship with is determined.

[0057] The battery voltage measured in step S22 is V s or more, i.e. battery voltage ≥ V s If so, the evaluation is terminated.

[0058] The battery voltage measured in step S22 is V s Lower, i.e. battery voltage <V s If it is determined that the resistance polarization V ohm , activation polarization V act and concentration polarization V mass The calculation of each polarization is performed in the same manner as in the first embodiment.

[0059] In step S24, the calculated resistance polarization V ohm Determine the magnitude relationship between V and V1, and calculate the resistance polarization V ohm Evaluation will be conducted.

[0060] In step S25, the calculated concentration polarization V mass Determine the magnitude relationship between V and V2, and calculate the concentration polarization V mass Evaluation will be conducted.

[0061] In step S26, the calculated activation polarization V act Determine the magnitude relationship between V and V3, and determine the activation polarization V act Evaluation will be conducted.

[0062] The calculated resistive polarization V in step S24 ohm and V1, and the concentration polarization V calculated in step S25 massand V2, and the activation polarization V calculated in step S26 act The order in which the magnitude relationship between V1 and V2 is determined is not limited to the above order, and may be any order.

[0063] In this manner, each polarization of the fuel cell 10 can be evaluated, and thus the fuel cell 10 can be evaluated.

[0064] According to the second embodiment, a high-frequency current or voltage of a fixed frequency, for example 1 kHz, is applied to the fuel cell 10 while the fuel cell 10 is in operation, and the impedance is measured by the impedance measuring device 30 to determine the series resistance, thereby calculating the resistance polarization. The concentration polarization and activation polarization are calculated from the resistance polarization thus calculated, thereby making it possible to evaluate the resistance polarization, concentration polarization, and activation polarization in real time and quantitatively while maintaining the same accuracy as a Cole-Cole plot, and even when the load current value fluctuates, thereby enabling the fuel cell 10 to be evaluated.

[0065] [Example] A prototype fuel cell system was constructed and then operated to conduct evaluation experiments.

[0066] This fuel cell system is shown in Fig. 6. As shown in Fig. 6, in this fuel cell system, a 40-cell open cathode solid polymer fuel cell stack 11 with a rated output of 500 W was used as the fuel cell 10. A bipolar power supply 21 connected to a function generator 22 generating a fixed frequency signal was used as the power source 20. An impedance analyzer ALDAS-F manufactured by Hioki E.E. Corporation was used as the impedance measuring device 30. The series resistance was calculated by continuously measuring the impedance (series resistance) at a constant frequency during operation of the fuel cell stack 11 by applying a high-frequency current of a fixed frequency (1 kHz) using the logging plot of the ALDAS-F. The high-frequency current was set to 0.1 A.

[0067] As a comparative example, a Cole-Cole plot was made by the EIS method. In the Cole-Cole plot, measurements were made at frequencies from 100 mHz to 10 kHz. Curve fitting was performed on the Cole-Cole plot thus obtained using fuel cell evaluation software Zview2 (Scribner Associates). For the curve fitting, an equivalent circuit shown in FIG. 7, which can be easily compared with the method of the embodiment, was used, and the series resistance R s , charge transfer resistance R act , mass transfer resistance R mass The calculated R s , R act and R mass From these, the resistance polarization, activation polarization, and concentration polarization can be calculated, respectively.

[0068] 8 and 9 show polarization values ​​at each measurement point obtained by the method of the embodiment and the method of the comparative example for the 36th cell from the fuel inlet of a 40-cell fuel cell stack 11 at a load current of 10A. Measurement points A, B, C, and D respectively indicate A: before the first operation, B: after the first operation, C: before the second operation, and D: after the second operation. Such an operation performed after a long period of stopped state of the fuel cell stack 11 is hereinafter referred to as activation operation. The activation operation can be used to activate the warm-up air and catalyst, and can bring the fuel cell stack 11 into a state where it can perform its original performance. Comparing FIG. 8 with FIG. 9, it can be seen that with both methods, the resistive polarization V ohm and activation polarization V act is decreasing. Concentration polarization V mass Regarding A, the concentration polarization V mass is the V obtained by the method of the embodiment. mass However, it can be seen that the tendency of each polarization to decrease due to activation operation can be captured by the method of the embodiment. In the polarization evaluation of the 36th cell, it can be said that the method of the embodiment showed a similar tendency to the method of the comparative example. Resistance polarization V due to activation operation ohm and activation polarization V actThe decrease in is believed to be due to the fact that the electrolyte membrane became dry and impurities were introduced due to the long period of non-operation, but the electrolyte membrane became moist and the impurities were removed during the first operation period A and B and the second operation period C and D. As described above, the improvement in the operating performance of the fuel cell stack 11 due to the activation operation could be evaluated using the method according to the embodiment.

[0069] 10 and 11 show the results of measuring the percentage of each polarization in the total polarization of the 36th cell when the load current is set to 5 A, 10 A, and 15 A at the measurement point D, using the method of the embodiment and the method of the comparative example. mass The ratio of the resistive polarization V ohm The proportion of activated polarization V act However, in the comparative example, when the load current value increases, the resistance polarization V ohm The proportion of activated polarization V act The proportion of increased. When looking at each load current value, differences were also seen between the two methods. As mentioned above, this is thought to be due to a problem with accuracy caused by the equivalent circuit (see Figure 7) used in the curve fitting of Zview2 not being able to reproduce the complex electrochemical reactions of the fuel cell. The method of the embodiment, which does not rely on fitting information, was able to evaluate the improvement in operating performance due to activation operation and the change in polarization characteristics associated with an increase in the load current value.

[0070] When load fluctuations occurred during operation, polarization evaluation was performed using the method of the embodiment. At measurement point D, the load current was increased from 1 A to 20 A at intervals of about 2 minutes, as shown in FIG. 12. Using the method of the embodiment, a high-frequency current of a constant frequency (1 kHz) was applied at the same time as the current-voltage characteristics were measured, and the series resistance R s The obtained R s The resistance polarization was calculated from the above, and the activation polarization and concentration polarization were calculated based on the calculated resistance polarization, and each polarization was evaluated.

[0071] Figures 13, 14, and 15 show the transitions of concentration polarization, resistance polarization, and activation polarization, respectively. In addition to the results of the 36th cell, Figures 13, 14, and 15 also show the results of the 4th, 6th, 10th, 18th, and 28th cells. In the concentration polarization shown in Figure 13, the concentration polarization started to increase when the load current value reached 10A around 1000s (see Figure 12), and the 36th cell increased significantly compared to the other cells. From this, it is considered that the 36th cell has a defect due to the inhibition of the diffusion of the reaction gas, such as the blockage of the flow path due to the increase in the generated water. In addition, Figure 16 shows the concentration polarization and the cell voltage of the 36th cell when the load current values ​​are 16A, 18A, and 20A. Since the concentration polarization decreased at the same time as the cell voltage increased due to the hydrogen purge in the fuel cell, it can be said that the concentration polarization was evaluated by the method of the embodiment.

[0072] The resistive polarization shown in Figure 14 gradually increases as the load current value increases. Among them, the resistive polarization increases significantly in cell 36. This suggests that the electrolyte membrane of cell 36 is damaged, or some other problem is caused by the resistance of the fuel cell.

[0073] The activation polarization shown in Figure 15 depends on the load current value and the battery voltage in the low current range where the Tafel slope was calculated. Therefore, the activation polarization is the largest for the 36th cell, and in the high current range, there is no significant difference in the activation polarization between the 6th cell, the 10th cell, and the 18th cell, which are low voltage cells.

[0074] As described above, each polarization during operation of the fuel cell stack 11 could be evaluated.

[0075] Although the embodiment and examples of the present invention have been specifically described above, the present invention is not limited to the above-described embodiment and examples, and various modifications based on the technical concept of the present invention are possible.

[0076] For example, the numerical values, shapes, structures, arrangements, etc. given in the above-mentioned embodiments and examples are merely examples, and numerical values, shapes, structures, arrangements, etc. different from these may be used as necessary. [Explanation of symbols]

[0077] 10: fuel cell, 11: fuel cell stack, 20: power supply, 21: bipolar power supply, 22: function generator, 30: impedance measuring device, 40: computer, 50: electronic load

Claims

1. A fuel cell evaluation system that calculates the resistance polarization of a fuel cell using a solid electrolyte by applying a fixed frequency high-frequency current or voltage and measuring the impedance while the fuel cell is in operation, and then calculates the activation polarization and concentration polarization of the fuel cell based on the calculated resistance polarization, thereby evaluating the fuel cell.

2. 2. The fuel cell evaluation system according to claim 1, wherein said fixed frequency is a frequency at a point where a locus of a Cole-Cole plot obtained by measuring the impedance of said fuel cell intersects with a real axis.

3. 3. The fuel cell evaluation system according to claim 2, wherein said fixed frequency is 1 kHz.

4. an impedance measuring device for measuring the impedance of the fuel cell; a power source for supplying the fuel cell with a high-frequency current or voltage having the fixed frequency; having The fuel cell evaluation system according to any one of claims 1 to 3, further comprising: applying a high-frequency current or high-frequency voltage of the fixed frequency from the power source while the fuel cell is in operation, measuring the impedance with the impedance measuring device, thereby calculating the resistance polarization of the fuel cell; calculating the activation polarization and concentration polarization of the fuel cell based on the calculated resistance polarization; and evaluating the fuel cell based on the calculated resistance polarization, activation polarization, and concentration polarization.

5. 5. The fuel cell evaluation system according to claim 4, further comprising: a step of determining whether the calculated resistance polarization is greater than a predetermined first reference value; a step of determining whether the calculated concentration polarization is greater than a predetermined second reference value; and a step of determining whether the calculated activation polarization is greater than a predetermined third reference value.

6. A method for evaluating a fuel cell, comprising: applying a fixed-frequency high-frequency current or voltage during operation of a fuel cell using a solid electrolyte, measuring the impedance, calculating the resistance polarization of the fuel cell, and calculating the activation polarization and concentration polarization of the fuel cell based on the calculated resistance polarization, thereby evaluating the fuel cell.

7. measuring the voltage of the fuel cell at predetermined time intervals during operation of the fuel cell; determining whether the voltage of the fuel cell measured at the time interval is larger than a predetermined reference voltage; a step of calculating a resistance polarization of the fuel cell by applying a high frequency current or voltage of the fixed frequency and measuring an impedance when the voltage of the fuel cell is determined to be lower than the reference voltage, and calculating an activation polarization and a concentration polarization of the fuel cell based on the resistance polarization; determining whether the calculated resistive polarization is smaller than a predetermined first reference value; determining whether the calculated concentration polarization is smaller than a second reference value; determining whether the calculated activation polarization is smaller than a third reference value; The method for evaluating a fuel cell according to claim 6, comprising:

8. A fuel cell control system that calculates the resistance polarization of a fuel cell using a solid electrolyte by applying a fixed frequency high-frequency current or voltage and measuring the impedance during operation of the fuel cell, and calculates the activation polarization and concentration polarization of the fuel cell based on the calculated resistance polarization, thereby controlling the fuel cell.

9. an impedance measuring device for measuring the impedance of the fuel cell; a power source for supplying the fuel cell with a high-frequency current or voltage having the fixed frequency; having 9. The fuel cell control system according to claim 8, further comprising: a power supply that applies a high-frequency current or high-frequency voltage of the fixed frequency during operation of the fuel cell, and an impedance measuring device that measures the impedance to calculate the resistance polarization of the fuel cell; a calculation of activation polarization and concentration polarization of the fuel cell based on the calculated resistance polarization; and control of the fuel cell based on the calculated resistance polarization, activation polarization, and concentration polarization.

10. A method for controlling a fuel cell comprising the steps of: applying a fixed-frequency high-frequency current or voltage during operation of a fuel cell using a solid electrolyte, measuring the impedance, calculating the resistance polarization of the fuel cell, and calculating the activation polarization and concentration polarization of the fuel cell based on the resistance polarization, thereby controlling the fuel cell.

11. measuring the voltage of the fuel cell at predetermined time intervals during operation of the fuel cell; determining whether the voltage of the fuel cell measured at the time interval is larger than a predetermined reference voltage; a step of calculating a resistance polarization of the fuel cell by applying a high frequency current or voltage of the fixed frequency and measuring an impedance when the voltage of the fuel cell is determined to be lower than the reference voltage, and calculating an activation polarization and a concentration polarization of the fuel cell based on the resistance polarization; continuing operation of the fuel cell when it is determined that the voltage of the fuel cell is equal to or higher than the reference voltage; determining whether the calculated resistive polarization is smaller than a predetermined first reference value; a step of performing a process of reducing the resistive polarization to the first reference value or less when it is determined that the calculated resistive polarization is greater than the first reference value; continuing operation of the fuel cell when it is determined that the calculated resistive polarization is equal to or less than the first reference value; determining whether the calculated concentration polarization is smaller than a second reference value; a step of performing a process for reducing the concentration polarization to the second reference value or less when it is determined that the calculated concentration polarization is greater than the second reference value; continuing operation of the fuel cell when it is determined that the calculated concentration polarization is equal to or less than the second reference value; determining whether the calculated activation polarization is smaller than a third reference value; when it is determined that the calculated activation polarization is greater than the third reference value, performing a process to reduce the activation polarization to the third reference value or less; continuing operation of the fuel cell when it is determined that the calculated activation polarization is equal to or less than the third reference value; The method for controlling a fuel cell according to claim 10, comprising:

12. 12. The fuel cell control method of claim 11, wherein in the step of taking measures to reduce the resistance polarization to the first reference value or below, the operating temperature of the fuel cell is lowered to lower the relative humidity or the flow rate of the reactant gas of the fuel cell is reduced; in the step of taking measures to reduce the concentration polarization to the second reference value or below, the flow rate of the reactant gas of the fuel cell is increased or the operating temperature of the fuel cell is raised to raise the relative humidity; and in the step of taking measures to reduce the activation polarization to the third reference value or below, the operating temperature of the fuel cell is raised.

13. At least one solid electrolyte fuel cell; A fuel cell system that calculates the resistance polarization of the fuel cell by applying a fixed frequency high-frequency current or high-frequency voltage while the fuel cell is in operation and measuring the impedance, and calculates the activation polarization and concentration polarization of the fuel cell based on the calculated resistance polarization, thereby controlling the fuel cell.

14. 8. A program for causing a computer to execute the fuel cell evaluation method according to claim 6 or 7.

15. A program for causing a computer to execute the fuel cell control method according to any one of claims 10 to 12.

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