JP2020087763A - Fuel cell monitoring device - Google Patents

Abstract

To provide a technology capable of detecting the state of insufficient supply amount of reaction gas for a fuel battery cell with high accuracy.SOLUTION: A fuel cell monitoring device includes an impedance measurement section for calculating the absolute value of impedance of a fuel battery cell for an AC signal of relatively low frequency, and the phase angle of impedance of a fuel battery cell for an AC signal of relatively high frequency, by applying AC signals of two frequencies to a fuel cell stack, and a determination section for determining that a supply amount of the fuel gas is insufficient, for the fuel battery cell where the absolute value of the impedance is larger than a predetermined first threshold level, or determining that a supply amount of the fuel gas is insufficient for the fuel battery cell where the absolute value of the impedance is smaller than the first threshold level, and for the fuel battery cell where the phase angle of the impedance is larger than a predetermined second threshold level to the negative side.SELECTED DRAWING: Figure 3

Description

The present disclosure relates to a fuel cell monitoring device.

A fuel cell monitoring device that superimposes an AC signal on the output current of a fuel cell, measures the impedance with respect to the AC signal, and uses the measurement result to detect the current state of the fuel cell cells that make up the fuel cell stack is known. Has been. For example, in the fuel cell monitoring device of Patent Document 1, when the absolute value of the impedance of the fuel cell is larger than the absolute value of the reference impedance that is the second threshold+the predetermined value α, the fuel cell is the fuel gas. It is determined that there is a shortage of hydrogen. Further, when the absolute value of the impedance of the fuel cell is smaller than the absolute value of the reference impedance that is the first threshold value-the predetermined value β, the fuel cell is in a state where oxygen, which is the oxidant gas, is insufficient. To determine.

JP, 2017-045648, A

However, in the fuel cell, the supply amount of both the oxidant gas and the fuel gas may be insufficient with respect to the required power generation amount due to, for example, blockage of the gas flow path. In the technique of Patent Document 1 described above, it is specified which of the supply amount of the fuel gas and the oxidant gas is insufficient depending on the magnitude of the absolute value of the impedance with respect to the reference value. It is not possible to detect the situation where the supply amount of both is insufficient. Thus, there is still room for improvement in accurately detecting the state of insufficient supply of the reaction gas to the fuel cell using the impedance measurement result.

One form of the technique of the present disclosure is provided as a fuel cell monitoring device that monitors the supply states of an oxidant gas and a fuel gas in a plurality of fuel cells included in a fuel cell stack. In the fuel cell monitoring device of this aspect, an alternating current signal having two frequencies is applied to the fuel cell stack, and an absolute value of impedance of the fuel battery cell with respect to an alternating current signal having a relatively low frequency and a relatively high frequency are applied. And an impedance measurement unit for calculating the phase angle of the impedance of the fuel cell with respect to the AC signal, and the fuel cell in which the absolute value of the impedance is larger than a predetermined first threshold value or the absolute value of the impedance. When the value of the fuel cell is smaller than the first threshold value and the phase angle of the impedance is larger than the predetermined second threshold value on the negative side, the supply amount of the fuel gas is insufficient. A determination unit for determining. According to the fuel cell monitoring device of this aspect, since the determination is performed using the absolute value of the impedance and the phase angle, it is possible to detect a state in which the supply amount of the fuel gas that cannot be detected only by the determination of the absolute value of the impedance is insufficient. Can be detected. For example, it is possible to detect a state where the supply amounts of both the fuel gas and the oxidant gas are insufficient. Therefore, it is possible to detect with high accuracy the insufficient supply amount of the reaction gas to the fuel cell unit.
The technology of the present disclosure can be implemented in various forms other than the fuel cell monitoring device. For example, a method of monitoring a power generation state of a fuel cell, a method of determining a supply state of a reaction gas in a fuel cell, a control method and a control device of a fuel cell monitoring device, a fuel cell system including the fuel cell monitoring device, and a control method thereof. It can be realized in the form of a computer program that realizes any of the above methods, a non-transitory recording medium that records the computer program, or the like.

1 is a schematic diagram showing a fuel cell system including a fuel cell monitoring device according to a first embodiment. The schematic sectional drawing which shows the structure of a fuel cell. Explanatory drawing which shows the flow of the monitoring process of 1st Embodiment. Explanatory drawing for demonstrating the determination threshold value in 1st Embodiment. Explanatory drawing which shows the flow of the monitoring process of 2nd Embodiment. Explanatory drawing for demonstrating the determination threshold value in 2nd Embodiment.

1. First embodiment:
1-1. Fuel cell system overview:
FIG. 1 is a schematic diagram showing a configuration of a fuel cell system 100 including a fuel cell monitoring device 10 according to the first embodiment. The fuel cell system 100 includes a fuel cell stack 20 that receives a supply of a reaction gas, that is, a fuel gas and an oxidant gas to generate electric power, and causes the fuel cell stack 20 to generate electric power according to a request from an external load 200. The fuel cell monitoring device 10 monitors the supply state of the reaction gas in the fuel cell stack 20 during power generation. In the following, after the configuration of the fuel cell system 100 other than the fuel cell monitoring device 10 is described, the configuration of the fuel cell monitoring device 10 and the monitoring process executed by the fuel cell monitoring device 10 will be described.

In the first embodiment, the fuel cell system 100 is mounted on a fuel cell vehicle and outputs electric power used for traveling of the fuel cell vehicle and electric power consumed by accessories and electric components of the fuel cell vehicle. The power output by the fuel cell system 100 may be used for external power feeding. It should be noted that in other embodiments, the fuel cell system 100 may not be mounted in a fuel cell vehicle. The fuel cell system 100 may be installed in a moving body such as a ship, or may be fixedly installed in a facility such as a building.

1-2. Fuel cell stack configuration:
The fuel cell stack 20 is a polymer electrolyte fuel cell, and generates electricity by an electrochemical reaction between hydrogen, which is a fuel gas, and oxygen, which is an oxidant gas. The fuel cell stack 20 has a stack structure in which a plurality of fuel cell units 21 are stacked. Each of the fuel cells 21 is a power generation element that can generate power even by itself. The fuel cell stack 20 is provided with a manifold (not shown) that is a branch flow path for the reaction gas and the refrigerant connected to each fuel cell 21.

FIG. 2 is a schematic cross-sectional view showing the structure of the fuel cell unit 21. The fuel cell unit 21 includes a membrane electrode assembly 50 that is a power generator. The membrane electrode assembly 50 includes an electrolyte membrane 51 and two electrodes 52 and 53. The electrolyte membrane 51 is a thin film of electrolyte resin that exhibits good proton conductivity in a wet state. The electrolyte membrane 51 is made of, for example, a fluorine-based ion exchange resin. The first electrode 52 and the second electrode 53 are arranged on both surfaces of the electrolyte membrane 51, respectively. The first electrode 52 is an anode to which the fuel gas is supplied, and the second electrode 53 is a cathode to which the oxidant gas is supplied. Each of the electrodes 52 and 53 includes a catalyst layer 54 arranged on the surface of the electrolyte membrane 51, and a gas diffusion layer 55 laminated on the catalyst layer 54. The catalyst layer 54 includes a catalyst for promoting a power generation reaction, and conductive particles carrying the catalyst. As the catalyst, for example, platinum (Pt) can be adopted. Further, as the conductive particles, for example, carbon particles can be adopted. The gas diffusion layer 55 is composed of a porous base material having gas diffusivity and conductivity. The gas diffusion layer 55 can be made of, for example, carbon paper.

The fuel cell unit 21 further includes two separators 61 and 62 sandwiching the membrane electrode assembly 50. The first separator 61 faces the first electrode 52, and the second separator 62 faces the second electrode 53. Each of the separators 61 and 62 is made of, for example, a plate-shaped member having conductivity and gas impermeability such as a metal plate. On the surface of each of the separators 61 and 62 on the side of the membrane electrode assembly 50, a groove forming a gas flow path 63 for guiding a reaction gas is formed. The gas flow path 63 of each fuel cell 21 is connected to a manifold (not shown). Fuel gas flows through the gas flow passage 63 of the first separator 61, and oxidant gas flows through the gas flow passage 63 of the second separator 62. A coolant passage 64 through which a coolant flows is provided on the surface of each of the separators 61 and 62 opposite to the surface on which the gas passage 63 is provided.

Please refer to FIG. The fuel cell stack 20 includes end plates 22 at both ends of the fuel cell stack 21 in the stacking direction. Each end plate 22 is made of, for example, a metal plate. The stacked body of the fuel cells 21 is fastened via the end plate 22 by a fastening member (not shown). Further, the end plate 22 is provided with a connecting portion to which pipes 32, 36, 41, 44 for circulating a reaction gas described later are connected.

A collector plate 23 and an insulating plate 24 are arranged between each end plate 22 and the stacked body of the fuel cells 21. The collector plate 23 is composed of a plate-shaped member having conductivity. The current collector plate 23 is in contact with the stacked body of the fuel battery cells 21, and is electrically connected to each fuel battery cell 21. The current collector 23 functions as a terminal. The fuel cell stack 20 is electrically connected to an external load 200 including a motor, auxiliaries, and electrical components via a collector plate 23. The insulating plate 24 is arranged between the current collector plate 23 and the end plate 22 to electrically insulate the both.

1-3. Components for fuel cell stack power generation:
The fuel cell system 100 further includes a system control unit 25 that controls the operation of the fuel cell stack 20, a fuel gas supply/discharge unit 30 and an oxidant gas supply/discharge unit 40 that supply and discharge a reaction gas to and from the fuel cell stack 20. And The fuel cell system 100 is additionally provided with a coolant supply unit that supplies a coolant to the coolant channel 64 of the fuel cell stack 20, a converter for controlling the output current, a secondary battery, and the like. However, in the present specification, for convenience, illustration and detailed description thereof are omitted.

The system control unit 25 is configured by an ECU (Electronic Control Unit) including at least one processor and a main storage device. The system control unit 25 exerts various functions for controlling the power generation of the fuel cell stack 20 by executing the programs and instructions read by the processor into the main storage device. At least a part of the function of the system control unit 25 may be configured by a hardware circuit. The system control unit 25 also functions as a higher-level control unit of the fuel cell monitoring device 10. The system control unit 25 uses parameters, which will be described later, measured in the fuel cell monitoring device 10, such as the output current of the fuel cell stack 20, the stack voltage Vs, the cell voltage Vc, and the impedance, for operation control of the fuel cell stack 20. May be.

The fuel gas supply/discharge unit 30 includes a high pressure tank 31, a supply pipe 32, an opening/closing valve 33, a regulator 34, and an injector 35 as a fuel gas supply system. The high-pressure tank 31 stores high-pressure fuel gas. The supply pipe 32 connects the high-pressure tank 31 and the anode-side manifold inlet of the fuel cell stack 20 provided on the end plate 22, and guides the fuel gas in the high-pressure tank 31 to the fuel cell stack 20. The on-off valve 33, the regulator 34, and the injector 35 are provided in the supply pipe 32. The system control unit 25 controls opening/closing of the opening/closing valve 33 to control the flow of fuel gas from the high-pressure tank 31 to the supply pipe 32. The regulator 34 adjusts the pressure on the upstream side of the injector 35. The injector 35 injects fuel gas toward the anode side of the fuel cell stack 20 under the control of the system controller 25.

The fuel gas supply/discharge unit 30 further includes a circulation pipe 36, a circulation pump 37, a drain pipe 38, and a drain valve 39 as a fuel gas circulation/discharge system. The circulation pipe 36 is connected to a manifold outlet on the anode side of the fuel cell stack 20 provided on the end plate 22. The circulation pipe 36 is provided with a circulation pump 37. The anode exhaust gas discharged from the fuel cell stack 20 is sent to the supply pipe 32 through the circulation pipe 36 by the circulation pump 37. The drainage pipe 38 is connected to the circulation pipe 36 via a gas-liquid separator (not shown). The drainage pipe 38 separates drainage, which is a liquid component stored in the gas-liquid separator from the anode exhaust gas, into the outside of the fuel cell vehicle. The drain valve 39 is provided in the drain pipe 38. The system control unit 25 controls opening/closing of the drain valve 39 to control drainage of drainage from the drainage pipe 38.

The oxidant gas supply/discharge unit 40 includes a supply pipe 41 and a compressor 43 as a supply system of the oxidant gas. One end of the supply pipe 41 is connected to a cathode-side manifold inlet of the fuel cell stack 20 provided on the end plate 22, and the other end is connected to an air intake (not shown) of a fuel cell vehicle. The compressor 43 is provided in the supply pipe 41, and under the control of the system control unit 25, takes in and compresses air containing oxygen, which is an oxidant gas, and supplies the compressed air to the fuel cell stack 20.

The oxidant gas supply/discharge unit 40 further includes a discharge pipe 44 and a back pressure valve 45 as an oxidant gas discharge system. The exhaust pipe 44 is connected to the manifold outlet on the cathode side of the fuel cell stack 20 provided on the end plate 22, and guides the cathode exhaust gas exhausted from the fuel cell stack 20 to the outside of the fuel cell vehicle. The back pressure valve 45 is provided in the discharge pipe 44. The system control unit 25 controls the opening degree of the back pressure valve 45 to adjust the back pressure of the fuel cell stack 20.

1-4. Configuration of fuel cell monitoring device:
The fuel cell monitoring device 10 includes a monitoring device control unit 11 that controls the entire fuel cell monitoring device 10. The monitoring device control unit 11 executes a monitoring process of monitoring the supply state of the reaction gas in the fuel cells 21 forming the fuel cell stack 20. The monitoring device control unit 11 is configured by a computer including at least one processor and a main storage device. The monitoring device control unit 11 may be configured as a part of the ECU that configures the system control unit 25. The monitoring device control unit 11 exerts various functions for executing the monitoring process by executing the programs and instructions read by the processor on the main storage device.

The monitoring device control unit 11 has an impedance measurement unit 11i and a determination unit 11j as functional units for executing the monitoring process. The impedance measuring unit 11i calculates the absolute value of impedance and the phase angle for each of the fuel cells 21 to be monitored by the AC impedance method.

The determination unit 11j determines whether or not the supply amount of the reaction gas in the fuel cell 21 is insufficient by using the absolute value of the impedance calculated by the impedance measurement unit 11i and the phase angle. The “insufficient supply amount of reaction gas” here means at least one of the oxidant gas and the fuel gas with respect to the amount of reaction gas theoretically required for the target power generation amount of the fuel cell stack 20. It means that the actual supply is insufficient. Insufficient supply of the reaction gas is often caused by blocking the gas passage 63 or the passage connecting the gas passage 63 and the manifold in some of the fuel cells 21 with the liquid water in the fuel cells 21. It is caused by being done. Details of the impedance measurement process by the impedance measurement unit 11i and the determination process by the determination unit 11j will be described later.

The fuel cell monitoring device 10 further includes a signal superimposing unit 12, a current measuring unit 13, a stack voltage measuring unit 14, a cell voltage measuring unit 15 as hardware for measuring the impedance of the fuel cell stack 20. Equipped with. The signal superimposing unit 12 includes an AC power supply and superimposes an AC signal on the output current of the fuel cell stack 20 under the control of the impedance measuring unit 11i of the monitoring device control unit 11. The current measuring unit 13 measures the output current Is of the fuel cell stack 20 and outputs it to the monitoring device control unit 11. The stack voltage measuring unit 14 measures the stack voltage Vs, which is the voltage of the entire fuel cell stack 20, and outputs it to the monitoring device control unit 11. The stack voltage measuring unit 14 may be omitted. The cell voltage measuring unit 15 measures the cell voltage Vc, which is the voltage of each fuel cell 21, and outputs it to the monitoring device control unit 11.

1-5. Monitoring process:
FIG. 3 is an explanatory diagram showing a flow of the monitoring process in the first embodiment. The fuel cell monitoring device 10 executes this monitoring process at a predetermined cycle while the fuel cell stack 20 is generating power. In the monitoring process of the first embodiment, it is determined whether or not the supply amount of the reaction gas is insufficient for the predetermined determination target fuel cells 21.

In the monitoring process of the first embodiment, all of the fuel cells 21 that make up the fuel cell stack 20 are to be determined. In another embodiment, any n of the N fuel cells 21 forming the fuel cell stack 20 may be selected in advance as a determination target. N and n are arbitrary natural numbers that satisfy N>n. When only some of the fuel cells 21 are to be determined, at least the fuel cells 21 arranged at the ends of the fuel cell stack 20 in the stacking direction may be included in the determination. desirable. This is because the fuel cell 21 arranged at the end portion tends to accumulate liquid water in the gas flow path 63, and tends to cause insufficient supply of the reaction gas.

In step S10, the impedance measuring unit 11i calculates the absolute value of the impedance for low-frequency alternating current and the phase angle of the impedance for high-frequency alternating current for each of the fuel cells 21 to be monitored. The high frequency and the low frequency here are names for distinguishing relative high and low of the frequency, and are concepts different from “low frequency” and “high frequency” in a general sense. Below, the absolute value of the impedance for low-frequency alternating current is also referred to as “low-frequency absolute value”, and the phase angle of the impedance for high-frequency alternating current is also referred to as “high-frequency phase angle”.

The impedance measuring unit 11i first applies two AC signals to the fuel cell stack 20. More specifically, the impedance measuring unit 11i causes the signal superimposing unit 12 to superimpose an AC signal having a low frequency f _L and a high frequency f _{H on} the output current of the fuel cell stack 20. The low frequency f _L is, for example, 18 to 22 Hz, and the high frequency f _H is, for example, 180 to 220 Hz. The impedance measuring unit 11i may simultaneously superimpose the AC signals of the low frequency f _L and the high frequency f _H , or may alternately superimpose them. The impedance measuring unit 11i causes the signal superimposing unit 12 to superimpose a sine wave AC signal corresponding to the magnitude of the current output by the fuel cell stack 20. The effective value of the superimposed alternating current may be, for example, about 5 to 10% of the output current of the fuel cell stack 20.

The impedance measuring unit 11i measures the output voltage waveform of each fuel cell 21 by the cell voltage measuring unit 15 while the signal superimposing unit 12 superimposes the AC signal. Further, the impedance measuring unit 11i measures the output current waveform of the fuel cell stack 20 by the current measuring unit 13. The cell voltage Vc and the output current Is thus obtained are the voltage value/current value of the response current generated by superimposing the AC current. The impedance measuring unit 11i uses the current value of the alternating current superimposed by the signal superimposing unit 12 and the cell voltage Vc, for example, by a fast Fourier transform (FFT) method, to obtain a low frequency absolute value Z _L and a high frequency phase. The angle θ _H is calculated.

Step S20 is a determination process of determining whether or not the supply amount of the fuel gas is insufficient. In step S20, the determination unit 11j determines whether or not the low-frequency absolute value Z _L is greater than a predetermined determination threshold Zs+α for each determination target fuel cell 21. Hereinafter, Zs of the determination thresholds is also referred to as “impedance reference value Zs”. Zs is a value determined for each stoichiometric ratio of the reaction gas, and is a low frequency absolute value expected to be measured when the reaction gas is normally supplied to the fuel cell 21 at the stoichiometric ratio. It is the reference value shown. The “reaction gas stoichiometric ratio” is the ratio of the actual reaction gas supply amount to the reaction gas supply amount that is theoretically required for the power generation amount of the fuel cell stack 20. The time when the stoichiometric ratio of the reaction gas in the fuel cell 21 is smaller than 1.0 is when the supply amount of the reaction gas is insufficient in the fuel cell 21. In the first embodiment, the determination threshold Zs+α is the first threshold for determining whether or not the supply amount of the fuel gas is insufficient.

When the supply amount of the fuel gas is insufficient while the supply amount of the oxidant gas is not insufficient, an oxidation reaction of carbon occurs on the cathode side to compensate for the insufficient proton, and the reaction resistance increases. Therefore, in this case, Z _L increases compared to the normal state where neither the fuel gas nor the oxidant gas is insufficient. Therefore, in step S20, the determination unit 11j determines that the fuel cell 21 that satisfies the relationship of Z _L >Zs+α has an insufficient supply amount of only the fuel gas. Α of the determination threshold value Zs+α is a positive real value determined in advance by an experiment, and defines an allowable range on the plus side with respect to the impedance reference value Zs which is assumed not to cause a shortage of the supply amount of the fuel gas. ..

If there is a fuel cell 21 that has been determined to have an insufficient supply amount of only fuel gas in step S20, a process for eliminating the shortage of fuel gas is executed in step S25. Specifically, the monitoring device control unit 11 requests the system control unit 25 to execute the process of increasing the supply amount of the fuel gas from the present amount. If there is no fuel battery cell 21 for which it is determined that the supply amount of only the fuel gas is insufficient in step S20, or after the process of step S25 is executed, the determination unit 11j determines the determination of step S30. Do it.

Step S30 is a determination process for determining whether or not the supply amount of the oxidizing gas is insufficient. In step S30, the determination unit 11j determines whether or not the absolute value Z _{L of the} impedance is smaller than the determination threshold value Zs−β for each fuel cell 21 to be determined. When the oxidant gas is insufficient in the state where the supply amount of the fuel gas is not insufficient, the oxidation-reduction reaction of the protons moved to the cathode side occurs, so that the reaction resistance decreases. Therefore, Z _L is lower than in the normal state where neither the fuel gas nor the oxidant gas is insufficient. Therefore, in step S30, the determination unit 11j determines that the supply amount of only the oxidant gas is insufficient in the fuel cells 21 satisfying the relationship of Z _L <Zs−β. Β of the determination threshold value Zs−β is a positive real value that has been experimentally determined in advance, and is on the negative side with respect to the impedance reference value Zs that is assumed not to cause insufficient supply of the oxidizing gas. Specify the range.

If there is a fuel cell 21 in which it is determined in step S30 that the supply amount of only the oxidant gas is insufficient, a process for eliminating the deficiency of the oxidant gas is executed in step S35. Specifically, the monitoring device control unit 11 requests the system control unit 25 to execute the process of increasing the supply amount of the oxidant gas from the present amount. After executing the process of step S35, the determination unit 11j ends the monitoring process. In step S30, when there is no fuel battery cell 21 satisfying the relationship of Z _L <Zs−β, the determination unit 11j performs the determination in step S40.

Step S40 is a determination process for determining whether or not the supply amounts of the fuel gas and the oxidant gas are insufficient. In step S40, the determination unit 11j determines whether or not the high frequency phase angle θ _H is smaller than the determination threshold θs−γ for each fuel cell 21 to be determined. Since the high frequency phase angle θ _H is a negative value, the determination in step S40 may be restated as determining whether the high frequency phase angle θ _H is larger than the determination threshold θs−γ on the negative side. The phase angle reference value θs is a value determined for each stoichiometric ratio of the reaction gas, and the high frequency expected to be measured when the reaction gas is normally supplied to the fuel cell 21 at the stoichiometric ratio. It is a reference value indicating a phase angle. The determination threshold value θs−γ in step S40 is a second threshold value for determining whether or not the supply amount of the fuel gas is insufficient. γ is a positive real value that is experimentally determined in advance, and defines a negative side allowable range with respect to the phase angle reference value θs.

In step S40, when there is the fuel battery cell 21 that satisfies the relationship of θ _H <θs−γ, the determination unit 11j determines that the supply amount of both the fuel gas and the oxidant gas is the target power generation amount of the fuel cell stack 20. It is determined to be insufficient. The reason for this will be described later. If there is a fuel battery cell 21 that satisfies the relationship of θ _H <θs−γ, the monitoring device control unit 11 notifies the system control unit 25 of the current supply amounts of both the fuel gas and the oxidant gas in step S45. Request execution of a process to increase the number. After performing step S45, the monitoring device control unit 11 ends the monitoring process.

FIG. 4 is an explanatory diagram showing experimental results for verifying changes in the low frequency absolute value Z _L and the high frequency phase angle θ _H when the stoichiometric ratio of the fuel gas and the oxidant gas to the fuel cell stack 20 is changed. In the upper part of FIG. 4, a graph showing the time variation of the stoichiometric ratio of the oxidant gas and the fuel gas is shown. In this stoichiometric ratio graph, the time change of the fuel gas is shown by the solid line, and the time change of the oxidant gas is shown by the broken line. In the middle part of FIG. 4, a graph showing the change over time of the low frequency absolute value Z _L is shown. The graph of the low frequency absolute value Z _L exemplifies the allowable range defined by the impedance reference value Zs and α, β included in the determination thresholds in step S20 and step S30. In the lower part of FIG. 4, a graph showing the time variation of the high frequency phase angle θ _H is shown. In this graph, the vertical axis indicating the value of the high frequency phase angle θ _H indicates the negative direction. The graph of the high frequency phase angle θ _H illustrates the phase angle reference value θs included in the determination threshold value in step S40 and the allowable range defined by γ. The time axes of the respective graphs of the stoichiometric ratio, the low frequency absolute value Z _L , and the high frequency phase angle θ _H in FIG. 4 correspond to each other.

The graph of FIG. 4 was obtained in the following experiment. In this experiment, first, the stoichiometric ratio of both the fuel gas and the oxidant gas is greater than 1.0 and the supply amount of both the fuel gas and the oxidant gas is not insufficient for one or more fuel cells 21. Power generation was started in a normal state. After that, the stoichiometric ratio of the oxidant gas was gradually decreased in stages until the cell voltage Vc decreased to 0V. Next, after the cell voltage Vc is reduced to 0V, the stoichiometric ratio of the fuel gas is gradually reduced while maintaining the stoichiometric ratio of the oxidant gas at a value smaller than 1.0. The experiment was terminated when Vc became around -0.2V.

In the normal state, the low frequency absolute value Z _L and the high frequency phase angle θ _H are substantially constant near the reference values Zs and θs, respectively. When the stoichiometric ratio of the fuel gas is higher than 1.0 and the stoichiometric ratio of the oxidant gas is lower than 1.0, the low frequency absolute value Z _L sharply decreases stepwise, and conversely, the high frequency phase angle θ _H rises sharply in steps. This is because the above-described redox reaction of the protons occurs at the cathode due to insufficient supply of only the oxidizing gas. Therefore, when the low frequency absolute value Z _L is smaller than the allowable range with respect to the impedance reference value Zs, that is, when it is smaller than the determination threshold value Zs-β in step S30, the supply of the oxidant gas is performed. It can be determined that only the quantity is insufficient. As shown in the graph of FIG. 4, β has a determination threshold value Zs-β of which the stoichiometric ratio of the fuel gas is larger than 1.0 and the stoichiometric ratio of the oxidant gas is 1.0 to 1.2. It is desirable that the value be set to a value corresponding to the absolute value of the low frequency when it is between.

When the stoichiometric ratio of the oxidant gas is smaller than 1.0 and the supply amount thereof is insufficient and the stoichiometric ratio of the fuel gas is lower than 1.0, the low frequency absolute value Z _L is plotted against the vertical axis. It sharply rises at an acute angle. This is because, as described above, the oxidation reaction of carbon occurs on the cathode side, and the reaction resistance increases more than in the normal state. This means that even if the low frequency absolute value Z _L is lower than the determination threshold value Zs+α in step S20, the supply amount of the fuel gas is insufficient when the supply amount of the oxidant gas is insufficient. It indicates that it may be in a state.

On the other hand, when the stoichiometric ratio of the fuel gas reaches 1.0 while the supply amount of the oxidant gas is insufficient, the high frequency phase angle θ _H exceeds the phase angle reference value θs and sharply decreases. Therefore, when the high frequency phase angle θ _H is smaller than the allowable range of the phase angle reference value θs, that is, when it is smaller than the determination threshold value θs−γ in step S40, the supply of the oxidant gas is performed. It can be determined that both the amount and the supply amount of the fuel gas are insufficient. As shown in the graph of FIG. 4, γ is when the determination threshold value θs−γ is such that the stoichiometric ratios of the fuel gas and the oxidant gas are between 0.9 and 1.0. It is desirable to set the value to correspond to the high frequency phase angle of.

Here, the insufficient supply amount of the fuel gas is a cause of irreversible deterioration in the catalyst layer 54, such as separation of the catalyst due to oxidation of carbon contained in the catalyst layer 54 and reduction of the reaction area due to aggregation of the catalyst. Become. According to the monitoring process of the first embodiment, even if the shortage of the supply amount of the fuel gas is not detected by the determination of the low frequency absolute value Z _L only, the determination of the fuel gas of the fuel gas is performed by the determination using the high frequency phase angle θ _H. The supply shortage can be detected and countermeasures can be taken early. Therefore, it is possible to suppress the irreversible deterioration of the catalyst in the catalyst layer 54 without the insufficient supply of the fuel gas being detected.

1-6. Summary of the first embodiment:
As described above, according to the fuel cell monitoring device 10 of the first embodiment, the supply amount of the fuel gas is insufficient together with the supply amount of the oxidant gas by using the low frequency absolute value Z _L and the high frequency phase angle θ _H. It is possible to detect the running state. Therefore, it is possible to detect with high accuracy the insufficient supply amount of the reaction gas to the fuel cell 21. Further, for example, it is possible to suppress the occurrence of defects caused by the insufficient supply amount of the fuel gas in the fuel cell 21, such as the decrease in the power generation efficiency of the fuel cell stack 20 and the deterioration of the catalyst described above.

2. Second embodiment:
FIG. 5 is an explanatory diagram showing a flow of monitoring processing in the second embodiment. The monitoring process of the second embodiment is executed by the fuel cell monitoring device 10 having the same configuration as described in the first embodiment. The fuel cell monitoring device 10 is mounted on the fuel cell system 100 having the same configuration as described in the first embodiment. The flow of the monitoring process of the second embodiment is almost the same as the monitoring process of the first embodiment, except that the determination process of step S32 is added after the determination process of step S30.

As described below, in the monitoring process of the second embodiment, a condition for detecting a state in which the supply amounts of both the fuel gas and the oxidant gas are insufficient is added. In the monitoring process of the second embodiment, when it is determined in step S30 that the relationship of Z _L <Zs−β is satisfied, the determination process of step S32 is performed. Step S32 is a determination process using the high frequency phase angle θ _H to determine whether the supply amount of the oxidizing gas is insufficient or the supply amounts of the fuel gas and the oxidizing gas are insufficient. Specifically, in step S32, the determination unit 11j are high frequency phase angle theta _H is, the determination threshold [theta] s + [delta] whether the difference is less than, i.e., high frequency phase angle theta _H is greater or not to the negative side than the decision threshold [theta] s + [delta] To judge. δ is an experimental value that can be detected in advance so that the state where the supply amount of both the fuel gas and the oxidant gas is insufficient is detected before the high-frequency phase angle θ _H reaches the phase angle reference value θs. It is a positive real value defined in. In the second embodiment, the determination threshold θs−γ in step S40 has a function as a second threshold for determining whether or not the supply amount of the fuel gas is insufficient in addition to the determination threshold θs+δ in step S32.

In step S32, when the relationship of θ _H <θs+δ is satisfied, the determination unit 11j determines that the supply amounts of the fuel gas and the oxidant gas are insufficient. In this case, the monitoring device control unit 11 executes the process for eliminating the insufficient supply amount of the fuel gas and the oxidizing gas in step S45 described in the first embodiment. When the relationship of θ _H <θs+δ is not satisfied in step S32, the determination unit 11j determines that only the supply amount of the oxidizing gas is insufficient. In this case, the monitoring device control unit 11 executes the process for eliminating the insufficient supply amount of the oxidant gas in step S35 described in the first embodiment.

FIG. 6 is an explanatory diagram for explaining the determination threshold value θs+δ in step S32. FIG. 6 is substantially the same as FIG. 4 referred to in the first embodiment, except that δ is illustrated and a range in which the shortage of the supply amounts of the fuel gas and the oxidant gas is detected is added.

When the stoichiometric ratio of the oxidant gas is less than 1.0 and the supply amount of the oxidant gas is insufficient, when the stoichiometric ratio of the fuel gas is decreased from a value greater than 1.0, the stoichiometric ratio of the fuel gas is reduced. The high-frequency phase angle θ _H begins to decrease before the ratio reaches 1.0. While the stoichiometric ratio of the fuel gas is maintained at 1.0, the high frequency phase angle θ _H decreases more gently than when the stoichiometric ratio of the fuel gas is less than 1.0. It is considered that this is because the field where the oxidation reaction of carbon on the cathode side, which causes the decrease of the high frequency phase angle θ _H , occurs gradually expands. This means that in the state where the high frequency phase angle θ _H is smaller than θs−γ which is one of the second threshold values, the carbon oxidation reaction due to the insufficient supply of the fuel gas is remarkable on the cathode side of the fuel cell unit 21. It indicates that it may be in progress.

According to the monitoring process of the second embodiment, even if the high frequency phase angle is not smaller than the determination threshold value θs−γ in step S40, when the relationship of θH<θs+δ is satisfied in step S32, it is determined that the fuel gas A state where the supply amount of the oxidizing gas is insufficient is detected. Therefore, the supply amount shortage of the fuel gas and the oxidant gas can be detected at an earlier stage than that in the first embodiment, so that the supply amount shortage of the fuel gas can be eliminated earlier. Response measures can be taken. As shown in FIG. 6, δ is a value corresponding to the high frequency phase angle when the determination threshold θs+δ is such that the stoichiometric ratio of the oxidant gas is smaller than 1.0 and the stoichiometric ratio of the fuel gas is 1.0. It is desirable to be set so that

As described above, according to the fuel cell monitoring apparatus 10 that executes the monitoring process of the second embodiment, the high frequency phase angle θ _H at which the state where the supply amounts of both the fuel gas and the oxidant gas are insufficient is detected. The range has been expanded. Therefore, it is possible to detect an insufficient supply amount of the fuel gas and the oxidant gas at an earlier stage. In addition, according to the fuel cell monitoring device 10 of the second embodiment, it is possible to achieve various operational effects similar to those described in the first embodiment.

3. Other:
In the above embodiment, some or all of the functions and processes realized by software may be realized by hardware. Further, some or all of the functions and processing realized by hardware may be realized by software. As the hardware, for example, various circuits such as an integrated circuit, a discrete circuit, or a circuit module in which those circuits are combined can be used.

The technology of the present disclosure is not limited to the above-described embodiments, examples, and modified examples, and can be implemented with various configurations without departing from the spirit of the invention. For example, the technical features in the embodiments, examples, and modifications corresponding to the technical features in each mode described in the section of the outline of the invention are to solve some or all of the above problems, or In order to achieve some or all of the above-mentioned effects, it is possible to appropriately replace or combine them. Further, the technical features are not limited to those described as not essential in the present specification, and may be appropriately deleted if the technical features are not described as essential in the present specification. Is possible.

10... Fuel cell monitoring device, 11... Monitoring device control unit, 11i... Impedance measuring unit, 11j... Judgment unit, 12... Signal superimposing unit, 13... Current measuring unit, 14... Stack voltage measuring unit, 15... Cell voltage measuring unit , 20... Fuel cell stack, 21... Fuel cell, 22... End plate, 23... Current collecting plate, 24... Insulating plate, 25... System control unit, 30... Fuel gas supply/discharge unit, 31... High pressure tank, 32... Supply pipe, 33... Open/close valve, 34... Regulator, 35... Injector, 36... Circulation pipe, 37... Circulation pump, 38... Drain pipe, 39... Drain valve, 40... Oxidizing gas supply/discharge section, 41... Supply pipe, 43... Compressor, 44... Exhaust pipe, 45... Back pressure valve, 50... Membrane electrode assembly, 51... Electrolyte membrane, 52... First electrode, 53... Second electrode, 54... Catalyst layer, 55... Gas diffusion layer, 61 ... 1st separator, 62... 2nd separator, 63... Gas channel, 64... Refrigerant channel, 100... Fuel cell system, 200... External load, Zs... Impedance reference value, θs... Phase angle reference value θ

Claims (1)

A fuel cell monitoring device for monitoring a supply state of an oxidant gas and a fuel gas in a plurality of fuel cell units included in a fuel cell stack,
By applying an AC signal of two frequencies to the fuel cell stack, the absolute value of the impedance of the fuel cell with respect to the AC signal of the relatively low frequency and the absolute value of the impedance of the fuel cell with respect to the AC signal of the relatively high frequency. An impedance phase angle, and an impedance measurement unit that calculates,
The fuel cell in which the absolute value of the impedance is larger than a predetermined first threshold value, or the absolute value of the impedance is smaller than the first threshold value and the phase angle of the impedance is predetermined. A determination unit that determines that the supply amount of the fuel gas is insufficient in the fuel cells that are larger than the threshold value to the negative side;
And a fuel cell monitoring device.

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