JP5724911B2 - Fuel cell diagnostic device - Google Patents

Description

  The present invention relates to a fuel cell diagnostic apparatus for diagnosing the state of a polymer electrolyte fuel cell.

  Conventionally, a configuration has been proposed in which the impedance of a fuel cell is measured by an AC impedance method, and the state of the fuel cell is diagnosed based on the measured impedance (see, for example, Patent Document 1).

  In Patent Document 1, impedances in different frequency regions such as a high frequency region and a low frequency region are measured, and a dry / wet state of the fuel cell is diagnosed based on the measured impedance in the high frequency region, and based on the impedance in the low frequency region. Thus, the supply state of the reaction gas supplied to the fuel cell is diagnosed.

JP 2007-12419 A

  By the way, the impedance of the low frequency region in the fuel cell is greatly influenced by the dry / wet state (dry state and wet state) inside the fuel cell and the load variation (change in current density) of the fuel cell in addition to the supply state of the reaction gas. There is a tendency to change.

  For this reason, even if it is attempted to diagnose the supply state of the reaction gas supplied to the fuel cell simply based on the impedance in the low frequency region as in the prior art, it is possible to accurately diagnose the supply state of the reaction gas in the fuel cell. There was a problem that I could not.

  An object of the present invention is to provide a fuel cell diagnostic apparatus capable of accurately diagnosing the supply state of a reaction gas in a fuel cell.

  The present invention is applied to a solid polymer fuel cell (1) in which a plurality of cells (10) that output electric energy by electrochemical reaction of reaction gases such as an oxidant gas and a fuel gas are stacked. The present invention is intended for a fuel cell diagnostic apparatus for diagnosing the state of the above.

  In order to achieve the above object, the present invention provides an AC applying means (431) for applying a low frequency AC signal lower than a predetermined reference frequency and a high frequency AC signal higher than a reference frequency to the fuel cell. ), A voltage detection means (42) for detecting the cell voltage of the target cell (10) to be diagnosed among the plurality of cells, and a local current detection means for detecting a local current flowing through a predetermined local region in the target cell (41), impedance calculation means (432) for calculating the local impedance of the local part of the target cell based on the cell voltage and local current when a low-frequency AC signal is applied by the AC application means, and AC Membrane resistance calculating means (43) for calculating the membrane resistance of the local portion of the target cell based on the cell voltage and local current when the high frequency alternating current signal is applied by the applying means. ), A correction means (434) for correcting the local impedance to calculate the diffusion impedance included in the local impedance, a diagnosis means (435) for diagnosing the supply state of the reaction gas to the fuel cell based on the diffusion impedance, Is provided. Then, the correction means calculates the diffusion impedance by removing the influence of the membrane resistance and the activation resistance of the target cell that changes according to the load fluctuation of the fuel cell from the local impedance.

  According to this, from the local impedance when the low-frequency AC signal is applied, the membrane resistance that changes depending on the dry / wet state (dry state and wet state) of the target cell, and the activation resistance that changes due to the load fluctuation of the fuel cell Since the supply state of the reaction gas in the fuel cell is diagnosed based on the diffusion impedance calculated by removing the influence, the supply state of the reaction gas in the fuel cell can be accurately diagnosed.

  In addition, the code | symbol in the parenthesis of each means described in this column and the claim shows an example of a correspondence relationship with the specific means described in the embodiment described later.

1 is an overall configuration diagram of a fuel cell system according to a first embodiment. 1 is an overall configuration diagram of a fuel cell diagnostic device according to a first embodiment. It is explanatory drawing for demonstrating the output current at the time of applying an alternating current signal. FIG. 3 is an equivalent circuit diagram of a cell according to the first embodiment. It is an equivalent circuit diagram when the supply state of air to the cell becomes an oxygen-deficient state. It is a graph which shows the ideal Cole-Cole plot at the time of changing the supply state of the air to a cell. It is a graph which shows the ideal Cole-Cole plot when the load fluctuation | variation of a fuel cell arises. It is a characteristic view which shows the current-voltage characteristic of a fuel cell. It is a flowchart which shows the flow of the diagnostic process which diagnoses the supply state of the air of the fuel cell which the signal processing apparatus which concerns on 1st Embodiment performs. It is a characteristic view which shows the relationship between the diffusion impedance of a cathode electrode, and oxygen concentration. It is a whole block diagram of the fuel cell diagnostic apparatus which concerns on 2nd Embodiment. It is an equivalent circuit diagram when the supply state of hydrogen to the cell becomes a hydrogen shortage state. It is a flowchart which shows the flow of the diagnostic process which diagnoses the supply state of the hydrogen of the fuel cell which the signal processing apparatus which concerns on 2nd Embodiment performs.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals in the drawings.

(First embodiment)
1st Embodiment of this invention is described based on FIGS. The fuel cell system of this embodiment is applied to a so-called fuel cell vehicle, which is a kind of electric vehicle, and supplies electric power to an electric load such as a vehicle driving electric motor (not shown).

  As shown in the overall configuration diagram of FIG. 1, the fuel cell system includes a solid polymer fuel cell 1 that outputs electrical energy by utilizing an electrochemical reaction between hydrogen and oxygen. The fuel cell 1 outputs electric energy supplied to various electric loads such as an electric motor for driving a vehicle and a secondary battery. The fuel cell 1 is configured as a series connection body in which a plurality of cells 10 serving as basic units are stacked and each cell 10 is electrically connected in series.

  Specifically, as shown in FIG. 2, each cell 10 includes a membrane electrode assembly (MEA: Membrane Electrode) in which a pair of catalyst electrode layers 100b and 100c are arranged on both side surfaces of an electrolyte membrane 100a made of a solid polymer. Assembly) 100 and a pair of separators 101 and 102 sandwiching the membrane electrode assembly 100.

  Of the pair of separators 101 and 102, the separator 101 facing the anode electrode 100b has a hydrogen inlet 101a for introducing hydrogen as a fuel gas, a hydrogen channel 101c for supplying hydrogen to the anode electrode 100b, and a hydrogen channel 101c. A hydrogen outlet portion 101b for deriving hydrogen from is formed.

  Of the pair of separators 101 and 102, the separator 102 facing the cathode electrode 100c has an air inlet portion 102a for introducing air as an oxidant gas, an air channel 102c for supplying oxygen to the cathode electrode 100c, air An air outlet portion 102b for leading air from the flow path 102c is formed. Each of the separators 101 and 102 has an inlet portion 101a and an outlet port of each of the inlet portions 101a and 102a so that the flow direction of hydrogen flowing through the hydrogen flow channel 101c and the flow direction of air flowing through the air flow channel 102c are opposed to each other. Portions 101b and 102b are formed.

Each cell 10 is supplied with hydrogen and air, and as shown below, causes a reaction gas such as hydrogen and oxygen to undergo an electrochemical reaction to output electric energy.
(Anode electrode) H ₂ → 2H ⁺ + 2e ⁻
(Cathode electrode) 2H ⁺ + 1 / 2O ₂ + 2e ⁻ → H ₂ O
Returning to FIG. 1, the fuel cell 1 and various electric loads are electrically connected via a DC-DC converter 2 capable of transmitting electric power in both directions. The DC-DC converter 2 controls the flow of electric power from the fuel cell 1 to various electric loads or from the various electric loads to the fuel cell 1.

  In addition, the fuel cell diagnostic device 4 is connected to a cell 10 to be diagnosed (hereinafter referred to as a target cell 10) among the cells 10. This fuel cell diagnostic device 4 diagnoses the air supply state in the vicinity of the air outlet portion 102b (hydrogen inlet portion 101a), which is a local portion of the target cell 10 on the downstream side of the air flow (downstream side of the oxidant gas flow). It is. The local site on the downstream side of the air flow is a site closer to the air outlet 102b than to the air inlet 102a. The details of the fuel cell diagnostic device 4 will be described later.

  In the fuel cell 1, air supply pipe 20 that supplies air to the fuel cell 1, surplus air that has undergone an electrochemical reaction in the fuel cell 1, and generated water accumulated on the cathode electrode 100 c side from the fuel cell 1 to the outside air. An air discharge pipe 21 for discharging is connected. The air supply pipe 20 communicates with the air inlet portion 102a of each cell 10 via an air supply manifold (not shown) formed inside the fuel cell 1, and the air discharge pipe 21 is connected to the inside of the fuel cell 1. Are communicated with the air outlet portion 102b of each cell 10 through an air discharge manifold (not shown) formed in the above.

  An air pump 22 for pumping air sucked from the atmosphere to the fuel cell 1 is provided at the most upstream portion of the air supply pipe 20, and an air pressure in the fuel cell 1 is adjusted in the air discharge pipe 21. An air pressure regulating valve 23 is provided. In the present embodiment, the air pump 22 and the air pressure regulating valve 23 constitute air supply means for supplying air of a predetermined flow rate and pressure to the fuel cell 1.

  The fuel cell 1 also includes a hydrogen supply pipe 30 that supplies hydrogen to the fuel cell 1, and a small amount of hydrogen that has undergone an electrochemical reaction in the fuel cell 1 and generated water accumulated on the anode electrode 100 b side. A hydrogen discharge pipe 31 is connected to discharge from the outside to the outside air. The hydrogen supply pipe 30 communicates with the hydrogen inlet portion 101a of each cell 10 through a hydrogen supply manifold (not shown) formed inside the fuel cell 1, and the hydrogen discharge pipe 31 is connected to the inside of the fuel cell 1. The hydrogen outlet manifold 101 (not shown) is connected to the hydrogen outlet portion 101 b of each cell 10.

  A high-pressure hydrogen tank 32 filled with high-pressure hydrogen is provided at the uppermost stream portion of the hydrogen supply pipe 30, and is supplied to the fuel cell 1 between the high-pressure hydrogen tank 32 and the fuel cell 1 in the hydrogen supply pipe 30. A hydrogen pressure regulating valve 33 for adjusting the hydrogen pressure is provided. In the present embodiment, the hydrogen pressure regulating valve 33 constitutes a fuel gas side gas supply means for supplying hydrogen at a desired pressure to the fuel cell 1.

  The hydrogen discharge pipe 31 is provided with an electromagnetic valve 34 that opens and closes at predetermined time intervals in order to discharge the produced water together with a small amount of hydrogen to the outside air. In the above-described electrochemical reaction, although generated water is not generated on the anode electrode 100b side, the generated water that has permeated the electrolyte membrane 100a from the cathode electrode 100c side may accumulate on the anode electrode 100b side. For this reason, in this embodiment, the hydrogen discharge piping 31 and the solenoid valve 34 are provided.

  The fuel cell system is provided with a control device 5 as power generation control means for performing various controls. This control device 5 controls the operation of various electric actuators constituting the fuel cell system based on various input signals, and is composed of a well-known microcomputer comprising a CPU, ROM, RAM, etc. and its peripheral circuits. Has been.

  Connected to the input side of the control device 5 of the present embodiment are a fuel cell diagnostic device 4, a vehicle start switch (not shown) for instructing the control device 5 to start operation of the fuel cell 1, and the like. Output signals from the diagnosis device 4 and the vehicle start switch are input.

  On the other hand, various electric actuators such as the air pump 22, the air pressure regulating valve 23, the hydrogen pressure regulating valve 33, and the electromagnetic valve 34 described above are connected to the output side of the control device 5. It is controlled by the control signal.

  Next, the fuel cell diagnostic device 4 of the present embodiment will be described. As shown in the main part configuration diagram of FIG. 2, the fuel cell diagnostic device 4 includes a local current sensor 41, a voltage sensor 42, and a signal processing device 43.

  The local current sensor 41 is disposed adjacent to a local portion (in the present embodiment, in the vicinity of the air outlet portion 102b and the hydrogen inlet portion 101a) on the downstream side of the air flow where the air supply state in the target cell 10 is likely to be insufficient. It is a local current detection means for detecting a current (local current) flowing in a local region corresponding to the downstream side of the flow. As the local current sensor 41, a known current sensor using a shunt resistor or a Hall element can be used.

  The voltage sensor 42 is voltage detection means for detecting the cell voltage of the target cell 10. The local current sensor 41 and the voltage sensor 42 are connected to the signal processing device 43, and output signals from the sensors 41 and 42 are input to the signal processing device 43.

  The signal processing device 43 executes control processing and arithmetic processing based on various input signals, and includes a well-known microcomputer composed of a CPU, ROM, RAM, etc. and its peripheral circuits.

  The signal processing device 43 includes a signal applying unit 431 that applies an AC signal (AC current) to the output current of the fuel cell 1, an impedance calculating unit 432 that calculates a local impedance of a local portion of the target cell 10, A membrane resistance calculation unit 433 that calculates the membrane resistance of the electrolyte membrane 100a at the local site, a correction unit 434 that calculates the diffusion impedance included in the local impedance by correcting the calculation result of the impedance calculation unit 432, and air to the fuel cell 1 ( A diagnostic unit 435 for diagnosing the supply state of (oxygen) is provided.

  The signal applying unit 431 constitutes an AC applying unit that applies an AC signal having a predetermined frequency to the output current of the fuel cell 1. As a result, as shown in the explanatory diagram of FIG. 3, the output current of the fuel cell 1 is superimposed on the direct current component (current value I) with the alternating current component (amplitude ΔI) of the frequency f.

  The signal application unit 431 according to the present embodiment generates a low-frequency AC signal that is lower than a predetermined reference frequency (for example, 100 Hz) and a high-frequency AC signal that is higher than the reference frequency for the output current of the fuel cell 1. The synthesized AC signal can be applied.

  Specifically, in this embodiment, the signal application unit 431 applies an AC signal obtained by synthesizing a high-frequency signal of 0.5 kHz to several hundred kHz and a low-frequency signal of 0.1 Hz to 100 Hz. Like to do. In addition, as a low-frequency signal, from the inflection point where two semicircular trajectories intersect in a Cole-Cole plot showing a change in local impedance on a complex plane when an AC signal is applied with a variable frequency. It is desirable to set a frequency region that exhibits a high impedance. The AC signal applied by the signal applying unit 431 is preferably within 10% of the output current of the fuel cell 1 so as not to affect the power generation state of the fuel cell 1.

  The impedance calculation unit 432 applies the local signal of the target cell 10 based on the detection values of the local current sensor 41 and the voltage sensor 42 when the signal application unit 431 applies the AC signal to the output current of the fuel cell 1. Impedance calculating means for calculating local impedance at the site is configured.

The impedance calculation unit 432 according to the present embodiment individually extracts an alternating current component corresponding to a high frequency signal and an alternating current component corresponding to a low frequency signal by a fast Fourier transform process or the like, and corresponds to the high frequency signal. Each of the high frequency impedance Z _H and the low frequency impedance Z _L corresponding to the low frequency signal can be calculated.

Film resistance calculation section 433, using a high frequency impedance Z _H, constitutes a film resistance calculation means for calculating the film resistance Rpem of the electrolyte membrane 100a in the local site of the target cell 10. It should be noted that the high frequency impedance Z _H, since it has a correlation to the membrane resistance of the electrolyte membrane 100a, it is possible to calculate the membrane resistance from the high frequency impedance Z _H.

Correcting unit 434, the low frequency impedance Z _L, the film resistance of the target cell 10, and to eliminate the effect of activation resistance of the target cell 10 that changes according to the load variation of the fuel cell 1 (the change of the required output) Thus, the correction means calculates the diffusion impedance of the cathode electrode 100c, which changes in accordance with the supply state of air to the target cell 10. A method for calculating the diffusion impedance of the cathode electrode 100c in the correction unit 434 will be described later.

  Based on the diffusion impedance of the cathode electrode 100c calculated by the correction unit 434, the diagnosis unit 435 diagnoses whether the air supply state of the fuel cell 1 is in an insufficient state or an appropriate state. Is configured.

  Next, a method for calculating the diffusion impedance of the cathode electrode 100c in the correction unit 434 will be described. First, an equivalent circuit of the cell 10 according to the present embodiment will be described with reference to the equivalent circuit diagram of FIG.

  As shown in FIG. 4, the equivalent circuit of the cell 10 according to the present embodiment has a configuration in which the membrane resistance Rpem of the electrolyte membrane 100a is connected in series to the composite circuit that constitutes the electrodes 100b and 100c. In the present embodiment, the anode electrode 100b is configured by a composite circuit in which an electric double layer capacitance (capacitor component) Can is connected in parallel to a series-connected activation resistor Rct_an and diffusion impedance Zan, and the cathode electrode 100c is connected in series. Further, it is composed of a composite circuit in which an electric double layer capacitance (capacitor component) Cca is connected in parallel to the activation resistance Rct_ca and the diffusion impedance Zca. In addition, although resistance of each separator 101,102 exists inside a cell, since the said resistance is not influenced by the dry / wet state inside a cell, the load fluctuation of the fuel cell 1, and the supply state of a reactive gas, this implementation It is omitted in the form.

  Here, when the air supply state to the cell 10 is insufficient and the hydrogen supply state of the cell 10 is appropriate, the activation resistance Rct_an of the anode electrode 100b, the diffusion impedance Zan, and the electric two Since the multilayer capacitance Can is smaller than the activation resistance Rct_ca, the diffusion impedance Zca, and the electric double layer capacitance Cca of the cathode electrode 100c, the cell 10 can be expressed by an equivalent circuit diagram shown in FIG.

  FIG. 6 shows a case where the load of the fuel cell 1 is constant, the dry / wet state in the cell 10 is in an appropriate state, and the supply state of air to the cell 10 is changed when the hydrogen supply state is in an appropriate state. It is a chart which shows an ideal Cole-Cole plot. FIG. 6 is a characteristic diagram showing a change in local impedance on a complex plane when an AC signal from a high frequency to a low frequency is applied using the equivalent circuit of the cell 10 shown in FIG.

As shown in FIG. 6, when the supply state of air to the cell 10 changes from the proper state to the insufficient state, the local impedance of the cell 10 tends to increase or decrease according to the change in the oxygen concentration on the cathode electrode 100 c side. For example, the low frequency impedance Z _L when the supply state is starved of air to the cell 10, the supply state of the air to the cell 10 is larger than when the proper state. Therefore, based on the change in the low frequency impedance Z _L, it is conceivable to diagnose the state of supply of air to the cell 10.

  However, in the actual cell 10, even if the air supply state is maintained in an appropriate state, when the wet and dry state in the cell 10 changes, the local impedance of the cell 10 increases or decreases due to the change in the membrane resistance Rpem.

  In the actual cell 10, even if the air supply state is maintained in an appropriate state, when the load fluctuation of the fuel cell 1 occurs, the local impedance of the cell 10 tends to increase or decrease. This is because the potential of the cathode electrode 100c changes due to the change in the generated current of the fuel cell 1 due to the load variation of the fuel cell 1, and the degree of catalytic activity at the cathode electrode 100c (ease of reaction between oxygen and proton). The reason is that the activation resistance Rct_ca indicating the change is changed.

  Here, FIG. 7 shows an ideal Cole-Cole plot when the load variation of the fuel cell 1 occurs when the dry and wet state in the cell 10 is in an appropriate state and the supply state of air and hydrogen is in an appropriate state. It is a chart. This chart is a characteristic diagram showing a change in local impedance on a complex plane when an AC signal from a high frequency to a low frequency is applied using the equivalent circuit of the cell 10 shown in FIG.

  As shown in FIG. 7, when the load of the fuel cell 1 changes from a low load to a high load, the local impedance of the cell 10 tends to decrease due to a decrease in the activation resistance Rct_ca of the cathode electrode 100c.

Therefore, in the present embodiment, the membrane resistance Rpem of the electrolyte membrane 100a that is affected by the dry and wet state of the cell 10 and the activation resistance Rct_ca of the cathode electrode 100c that changes due to the influence of the load fluctuation of the fuel cell 1 are calculated. using the value, followed by removal of the influence of the effects of wet and dry state of the cell 10 from the low frequency impedance Z _L, and load fluctuation of the fuel cell 1.

Here, membrane resistance Rpem of the electrolyte membrane 100a calculates the membrane resistance Rpem from the high frequency impedance _{Z H} having correlation. Specifically, the real part Re (Z _H ) of the high-frequency impedance Z _H is calculated as the membrane resistance Rpem.

  The activation resistance Rct_ca of the cathode electrode 100c is calculated by dividing the change amount of the activation overvoltage included in the change amount of the cell voltage when the low-frequency AC signal is applied by the change amount of the local current. Specifically, the activation resistance Rct_ca of the cathode electrode 100c can be calculated using the following formulas F1 and F2.

Rct_ca = ΔVa / Δi... F1
ΔVa = B × log {(I + ΔI) / ΔI}... F2
However, ΔVa indicates a change in the activation overvoltage of the catalyst electrode layer (cathode electrode 100c) that changes according to the AC signal applied to the output current of the fuel cell 1, and Δi indicates a low frequency in the output current of the fuel cell 1. Represents the amplitude (change amount) of the alternating current component when the alternating current signal is applied, I represents the current value of the direct current component when the low frequency alternating current signal is applied to the output current of the fuel cell 1, and B represents the fuel cell. A Tafel slope of 1 is shown.

As shown in FIG. 8, the Tafel slope B is a predetermined current value when the current-voltage characteristic of the fuel cell 1 corrected for the voltage drop due to the membrane resistance Rpem of the electrolyte membrane 100 a of the cell 10 is represented by a Tafel plot. The voltage change rate in the region of α (for example, 0.1 A / cm ² ) or less is shown.

  Further, the diffusion impedance Zca of the cathode electrode 100c is calculated using the equivalent circuit shown in FIG. Specifically, the diffusion impedance Zca of the cathode electrode 100c can be calculated using the following formula F3.

Zca = 1 / [{1 / (Z _L −Rpem)} − j × ω × Cca] −Rca_ca... F3
However, j represents an imaginary unit, ω (= 2πf) represents the angular frequency of the AC signal applied, and Cca represents the electric double layer capacitance (capacitor component) of the cathode electrode 100c.

  Here, as the electric double layer capacity Cca of the cathode electrode 100 c, the capacity component of the catalyst electrode layer (cathode electrode 100 c) at the local site of the cell 10 can be used. In addition, what is necessary is just to use the value (value of the electric double layer capacity | capacitance in a catalyst electrode layer) previously quantified using the cyclic voltamentary (CV) measurement for the capacity | capacitance component of the cathode electrode 100c.

  Next, in the fuel cell system according to the above configuration, a process for diagnosing the supply state of air to the target cell 10 executed by the fuel cell diagnostic device 4 will be described with reference to the flowchart of FIG. The control routine shown in FIG. 9 starts when the vehicle start switch is turned on and the fuel cell 1 is in a power generation state.

  When the fuel cell 1 is in a power generation state, the signal applying unit 431 of the signal processing device 43 applies an AC signal obtained by combining the high frequency signal and the low frequency signal to the output current of the fuel cell 1 (S10). ).

Subsequently, output signals from the local current sensor 41 and the voltage sensor 42 are read (S20). Based on the detection values of the local current sensor 41 and the voltage sensor 42, the impedance calculation unit 432 of the signal processing device 43 calculates the local impedance at the local site of the target cell 10 (S30). In the process of step S30, the high frequency impedance Z _H and the low frequency impedance Z _L are calculated.

At film resistance calculation unit 433 of the signal processor 43, using a high frequency impedance _{Z H,} calculating the membrane resistance Rpem of the electrolyte membrane 100a (S40). In the present embodiment, the real part Re (Z _H ) of the high frequency impedance Z _H is calculated as the film resistance Rpem.

  Subsequently, the correction unit 434 of the signal processing device 43 calculates the activation resistance Rct_ca of the cathode electrode 100c using the above-described mathematical formulas F1 and F2 (S50).

Furthermore, by the correction unit 434 of the signal processing unit 43 performs correction to calculate the diffusion impedance Zca the cathode electrode 100c from the low frequency impedance _{Z L} (S60). Specifically, the diffusion resistance Zca of the cathode electrode 100c is calculated by substituting the membrane resistance Rpem calculated in step S40 and the activation resistance Rct_ca calculated in step S50 into the above-described equation F3.

  Subsequently, in the diagnosis unit 435 of the signal processing device 43, whether or not the absolute value Abs (Zca) of the diffusion impedance Zca of the cathode electrode 100c calculated in the process of step S60 is larger than a predetermined determination threshold Abs (Zca_ref). Is determined (S70). This determination threshold value Abs (Zca_ref) is determined based on the absolute value Abs (Zca) of the diffusion impedance of the cathode electrode 100c when the supply state of air becomes insufficient.

  When it is determined in step S70 that the absolute value Abs (Zca) of the diffusion impedance Zca of the cathode electrode 100c is equal to or less than the determination threshold Abs (Zca_ref) (S70: NO), the air supply state is in an appropriate state. (S70), and the diagnosis process is terminated.

  On the other hand, when it is determined that the absolute value Abs (Zca) of the diffusion impedance Zca of the cathode electrode 100c is larger than the determination threshold value Abs (Zca_ref) (S70: YES), it is diagnosed that the air supply state is insufficient. (S90), and the diagnosis process is terminated. In this case, for example, by increasing the rotation speed of the air pump 22 and increasing the supply amount of air, the air shortage state can be solved. Note that the air shortage state includes not only a state where the air supply amount is insufficient, but also a state where the air amount contributing to power generation in the target cell 10 is insufficient due to, for example, flooding or the like. is there.

According to the embodiment described above, the effect of wet and dry condition in a subject cell 10 from the low frequency impedance Z _L, which is the local impedance, and to remove the influence of load fluctuation of the fuel cell 1, the diffusion impedance of the cathode electrode 100c Zca Therefore, the air supply state of the fuel cell 1 is diagnosed based on the diffusion impedance Zca. Therefore, the air shortage state and the appropriate state of the fuel cell 1 can be accurately diagnosed.

  In the present embodiment, when diagnosing the supply state of air to the fuel cell 1, the air shortage state and the appropriate state of the fuel cell 1 are accurately diagnosed based on the diffusion impedance Zca of the cathode electrode 100c. However, it is not limited to this.

  For example, when diagnosing the supply state of air to the fuel cell 1, the oxygen concentration of air supplied to the local portion of the target cell 10 may be estimated based on the diffusion impedance Zca of the cathode electrode 100c. .

  Specifically, a control map that defines the correspondence between the diffusion impedance Zca of the cathode electrode 100c and the oxygen concentration is stored in a storage unit such as a ROM of the signal processing device 43, and the cathode electrode 100c calculated in step S60 is stored. Based on the diffusion impedance Zca, the oxygen concentration can be estimated with reference to the control map. Since the oxygen concentration tends to decrease as the absolute value of the diffusion impedance Zca of the cathode electrode 100c increases, the control map stored in the storage unit increases as the diffusion impedance Zca of the cathode electrode 100c increases. It is specified that the oxygen concentration is lowered.

Here, when occurring load change in the fuel cell 1, the estimation result and estimating the oxygen concentration based on the diffusion impedance Zca the cathode electrode 100c, estimation result to estimate the oxygen concentration based on the low frequency impedance Z _L The following results were obtained when an experiment was compared.

10 (a) shows the relationship between the absolute value and the estimated oxygen concentration of the low frequency impedance Z _L of the object cell 10 when the load change in the fuel cell 1 is generated, FIG. 10 (b), the fuel cell 1 shows the relationship between the absolute value of the diffusion impedance Zca of the cathode electrode 100c and the estimated oxygen concentration when a load change occurs.

As shown in FIG. 10, the estimated oxygen concentration corresponding to the low frequency impedance Z _L of the target cell 10, whereas there is a tendency to undergo the influence of load fluctuation of the fuel cell 1, the diffusion impedance Zca the cathode electrode 100c The corresponding estimated oxygen concentration was almost unaffected by the load fluctuation of the fuel cell 1.

  As described above, if the oxygen concentration in the target cell 10 is estimated from the diffusion impedance Zca of the cathode electrode 100c, the oxygen concentration can be accurately estimated without separately preparing a dedicated gas concentration sensor.

(Second Embodiment)
In the present embodiment, an example in which the signal processing device 43 of the fuel cell diagnostic device 4 diagnoses the supply state of hydrogen to the cell 10 will be described. In the fuel cell diagnostic device 4 of the present embodiment, as shown in the main part configuration diagram of FIG. It is arranged adjacent to a local site on the downstream side of the flow (in the present embodiment, in the vicinity of the hydrogen outlet portion 101b and the air inlet portion 102a) and detects a current (local current) flowing in the local site corresponding to the downstream side of the hydrogen flow. Yes.

When diagnosing state of supply of hydrogen into the cell 10 as in this embodiment, as in the case of diagnosing the state of supply of air to the cell 10, the influence of wet and dry conditions in the cell 10 from the low frequency impedance Z _L, It is necessary to remove the influence of the load fluctuation of the fuel cell 1.

Therefore, in the present embodiment, the membrane resistance Rpem that changes due to the influence of the wet and dry state in the cell 10 and the activation resistance Rct_an of the anode electrode 100b that changes due to the influence of the load fluctuation of the fuel cell 1 are calculated, and each calculated value is used. Te, followed by removal of the influence of impact and load fluctuation of the fuel cell 1 of the wet and dry state in the cell 10 from the low frequency impedance Z _L.

  Here, the activation resistance Rct_an of the anode electrode 100b can be calculated using the following formulas F4 and F5.

Rct_an = ΔVa / Δi... F4
ΔVa = B × log {(I + ΔI) / ΔI}... F5
However, ΔVa indicates a change in the activation overvoltage of the catalyst electrode layer (anode electrode 100b) that changes in accordance with an AC signal applied to the output current of the fuel cell 1, and Δi indicates a low frequency in the output current of the fuel cell 1. Represents the amplitude (change amount) of the alternating current component when the alternating current signal is applied, I represents the current value of the direct current component when the low frequency alternating current signal is applied to the output current of the fuel cell 1, and B represents the fuel cell. A Tafel slope of 1 is shown.

  Here, when the supply state of hydrogen to the cell 10 is insufficient and the supply state of air to the cell 10 is appropriate, the activation resistance Rct_ca of the cathode electrode 100c, the diffusion impedance Zca, and the electricity Since the double layer capacitance Cca is smaller than the activation resistance Rct_an, the diffusion impedance Zan, and the electric double layer capacitance Can of the anode electrode 100b, the cell 10 can be expressed by an equivalent circuit diagram shown in FIG.

  In the present embodiment, the diffusion impedance Zan of the anode electrode 100b is calculated using the equivalent circuit shown in FIG. Specifically, the diffusion impedance Zan of the anode electrode 100b can be calculated using the following formula F6.

Zan = 1 / [{1 / (Z _L −Rpem)} − j × ω × Can] −Rct_an... F6
However, j represents an imaginary unit, ω (= 2πf) represents the angular frequency of the AC signal applied, and Can represents the electric double layer capacitance (capacitor component) of the anode electrode 100b. As the electric double layer capacity Can of the anode electrode 100b, a capacity component of the catalyst electrode layer (anode electrode 100b) at a local portion of the cell 10 can be used.

  Next, in the fuel cell system according to the above configuration, the process of diagnosing the supply state of hydrogen to the target cell 10 executed by the fuel cell diagnostic device 4 will be described with reference to the flowchart of FIG.

When the fuel cell 1 is in a power generation state, the signal applying unit 431 of the signal processing device 43 applies an AC signal obtained by synthesizing the high-frequency and low-frequency signals to the output current of the fuel cell 1 (S10). Output signals from the sensor 41 and the voltage sensor 42 are read (S20). And based on the detected value of each sensor 41 and 42, the local impedance in the local site | part of the object cell 10 is calculated in the impedance calculation part 432 of the signal processing apparatus 43 (S30). At film resistance calculation unit 433 of the signal processor 43, using a high frequency impedance _{Z H,} calculating the membrane resistance Rpem of the electrolyte membrane 100a (S40).

  Subsequently, the correction resistance 434 of the signal processing device 43 calculates the activation resistance Rct_an of the anode electrode 100b using the above-described mathematical formulas F4 and F5 (S100).

Furthermore, by the correction unit 434 of the signal processing unit 43 performs correction to calculate the diffusion impedance Zan of the anode electrode 100b from the low frequency impedance _{Z L} (S110). Specifically, the diffusion resistance Zan of the anode electrode 100b is calculated by substituting the membrane resistance Rpem calculated in step S40 and the activation resistance Rct_an calculated in step S100 into the above-described equation F6.

  Subsequently, whether or not the absolute value Abs (Zan) of the diffusion impedance Zan of the anode electrode 100b calculated in the process of step S110 is larger than a predetermined determination threshold Abs (Zan_ref) in the diagnosis unit 435 of the signal processing device 43. Is determined (S120). This determination threshold value Abs (Zan_ref) is determined based on the absolute value Abs (Zan) of the diffusion impedance of the anode electrode 100b when the hydrogen supply state becomes insufficient.

  When it is determined in step S120 that the absolute value Abs (Zan) of the diffusion impedance Zan of the anode electrode 100b is equal to or less than the determination threshold Abs (Zan_ref) (S120: NO), the hydrogen supply state is in an appropriate state. (S130), and the diagnosis process is terminated.

  On the other hand, when it is determined that the absolute value Abs (Zan) of the diffusion impedance Zan of the anode electrode 100b is larger than the determination threshold value Abs (Zan_ref) (S120: YES), it is diagnosed that the hydrogen supply state is insufficient. (S140), and the diagnosis process is terminated. In this case, for example, by reducing the opening degree of the hydrogen pressure regulating valve 33 and reducing the supply amount of hydrogen from the high-pressure hydrogen tank 32, the excessive hydrogen state can be eliminated.

According to the embodiment described above, the effect of wet and dry condition in a subject cell 10 from the low frequency impedance Z _L, which is the local impedance, and the influence of load fluctuation of the fuel cell 1 by removing the diffusion impedance Zan of the anode electrode 100b Since the hydrogen supply state of the fuel cell 1 is diagnosed based on the calculation and the diffusion impedance Zan, the hydrogen shortage state and the appropriate state of the fuel cell 1 can be diagnosed accurately.

  A control map that defines the correspondence between the diffusion impedance Zan of the anode electrode 100b and the hydrogen concentration is stored in a storage unit such as a ROM of the signal processing device 43, and the diffusion impedance Zan of the anode electrode 100b calculated in step S110 is stored. Based on the above, the hydrogen concentration may be estimated with reference to the control map. In this case, the hydrogen concentration can be accurately estimated without separately preparing a dedicated gas concentration sensor.

(Other embodiments)
As mentioned above, although embodiment of this invention was described, this invention is not limited to this, For example, it can deform | transform variously as follows.

  (1) In each of the above-described embodiments, the example in which the diffusion impedance of each of the electrodes 100b and 100c is calculated using the equivalent circuits shown in FIGS. 5 and 12 is described. However, the present invention is not limited to this, and other equivalent circuits are used. The diffusion impedance of each electrode 100b, 100c may be calculated.

  Also, the activation resistance of each electrode 100b, 100c is calculated not only using the formulas F1, F2, F4, F5 but also using other formulas, or the DC component included in the activation resistance and the output current of the fuel cell 1 in advance The activation resistance may be calculated using a control map that defines the relationship with the AC component.

  (2) In each of the above-described embodiments, the example in which the supply state of the reaction gas (hydrogen, air) to the cell 10 is diagnosed using the absolute value of the diffusion impedance of each electrode 100b, 100c has been described. It is not limited to.

  For example, the supply state of the reaction gas to the cell 10 may be diagnosed using the phase difference or frequency characteristic of the diffusion impedance. In this case, each determination threshold value may be determined based on the phase difference of the diffusion impedance and the frequency characteristics when the supply state of the reaction gas becomes insufficient.

  Further, the gas concentration (oxygen concentration, hydrogen concentration) may be calculated from the diffusion impedance, and the supply state of the reaction gas (hydrogen, air) to the cell 10 may be diagnosed using the calculated gas concentration. In this case, each determination threshold value may be determined based on the gas concentration when the supply state of the reaction gas becomes insufficient.

  (3) In each of the above-described embodiments, an example in which the signal applying unit 431 of the signal processing device 43 applies an AC signal obtained by combining a high-frequency signal and a low-frequency signal to the output current of the fuel cell 1. However, the present invention is not limited to this. For example, the signal applying unit 431 of the signal processing device 43 may apply a high frequency signal and a low frequency signal to the output current of the fuel cell 1 at different timings.

  (4) In the first embodiment described above, the single local current sensor 41 is disposed adjacent to the vicinity of the air outlet portion 102b of the target cell 10, and the impedance calculation unit 432 calculates the local impedance near the air outlet portion 102b. Although an example has been described, the present invention is not limited to this.

  For example, a plurality of local current sensors 41 may be used, these may be arranged adjacent to a plurality of local parts of the target cell 10, and the local impedance of the plurality of local parts may be calculated by the impedance calculation unit 432. In this case, it is possible to diagnose the air supply state at a plurality of local sites of the target cell 10.

  Similarly, in the second embodiment described above, a plurality of local current sensors 41 are used, these are arranged adjacent to the plurality of local parts of the target cell 10, and the impedance calculation unit 432 calculates the local impedance of the plurality of local parts. You may make it do. In this case, it becomes possible to diagnose the supply state of hydrogen in a plurality of local parts of the target cell 10.

  Further, the local current sensor 41 is disposed adjacent to the vicinity of the air outlet portion 102b and the vicinity of the hydrogen outlet portion 101b of the target cell 10, and the impedance calculation unit 432 determines the local impedances near the air outlet portion 102b and the vicinity of the hydrogen outlet portion 101b. You may make it calculate. According to this, it becomes possible to diagnose the supply state of hydrogen and air in the target cell 10.

  (5) Although the configuration in which the voltage sensor 42 detects the voltage of the target cell 10 is desirable as in the above-described embodiments, for example, the voltage sensor 42 may detect the voltage of the entire fuel cell 1. Good.

  (6) In each of the above-described embodiments, the example in which the signal applying unit 431 of the signal processing device 43 applies AC signals having two different frequencies to the output current of the fuel cell 1 has been described. For example, AC signals having three or more different frequencies may be applied.

  (7) In each of the above-described embodiments, the example in which the AC signal is applied to the output current of the fuel cell 1 by the signal applying unit 431 of the signal processing device 43 has been described. An AC signal may be applied to the output current of the fuel cell 1 by the DC converter 2. In this case, the number of parts of the fuel cell diagnostic device 4 can be reduced.

  (8) In each of the above-described embodiments, the example in which the fuel cell diagnostic device 4 of the present invention is applied to a device for diagnosing the state of the fuel cell 1 mounted on the fuel cell vehicle has been described. Further, the present invention may be applied to a device for diagnosing the state of a mobile object such as a portable generator or the installation type fuel cell 1.

(9) In the above embodiments, an example has been described of calculating the real part of the high frequency impedance _{Z H} Re of _{(Z H)} as the membrane resistance Rpem of the electrolyte membrane 100a, is not limited to this, for example, high-frequency impedance _{Z H} absolute value Abs the _{(Z H)} may be calculated as membrane resistance Rpem of the electrolyte membrane 100a.

1 fuel cell 10 cell 41 local current sensor (local current detection means)
42 Voltage sensor (voltage detection means)
431 AC signal application unit (AC application means)
432 Impedance calculation unit (impedance calculation means)
433 Membrane resistance calculation unit (membrane resistance calculation means)
434 Correction unit (correction means)
435 diagnostic unit (diagnostic means)

Claims (5)

The present invention is applied to a polymer electrolyte fuel cell (1) in which a plurality of cells (10) that output electric energy by electrochemical reaction of reaction gases such as an oxidant gas and a fuel gas are stacked. A fuel cell diagnostic device for diagnosing,
AC applying means (431) for applying a low frequency AC signal lower than a predetermined reference frequency and a high frequency AC signal higher than the reference frequency to the fuel cell;
Voltage detection means (42) for detecting a cell voltage of a target cell (10) to be diagnosed among the plurality of cells;
Local current detection means (41) for detecting a local current flowing through a predetermined local site in the target cell;
Impedance calculation means (432) for calculating local impedance of the local part of the target cell based on the cell voltage when the low-frequency AC signal is applied by the AC application means and the local current;
Membrane resistance calculation means (433) for calculating the film resistance of the local part of the target cell based on the cell voltage and the local current when the high frequency AC signal is applied by the AC application means; ,
Correction means (434) for correcting the local impedance and calculating a diffusion impedance included in the local impedance;
Diagnostic means (435) for diagnosing the supply state of the reaction gas to the fuel cell based on the diffusion impedance,
The correction means calculates the diffusion impedance by removing the influence of the membrane resistance and the activation resistance of the target cell that changes in accordance with load fluctuations of the fuel cell from the local impedance. Fuel cell diagnostic device.   The correction means divides the change amount of the activation overvoltage included in the change amount of the cell voltage when the low-frequency AC signal is applied by the AC application means by the change amount of the local current. The fuel cell diagnostic apparatus according to claim 1, wherein an activation resistance is calculated.   The correction means calculates the change in the activation overvoltage using the Tafel slope of the fuel cell, the value of the DC component of the output current output from the fuel cell, and the amplitude of the AC component of the AC signal. The fuel cell diagnostic apparatus according to claim 2.   The correction means is configured by connecting the membrane resistance in series to a composite circuit in which the electric double layer capacitance in the catalytic electrode layer of the target cell is connected in parallel to the activation resistance and the diffusion impedance connected in series. 4. The fuel cell diagnostic apparatus according to claim 1, wherein the diffusion impedance is calculated based on an equivalent circuit of the cell.   5. The fuel cell diagnostic apparatus according to claim 4, wherein the correcting means uses a value of an electric double layer capacity in a catalyst electrode layer of the target cell measured in advance as the electric double layer capacity.

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