JP4720105B2 - Fuel cell diagnostic device and fuel cell diagnostic method - Google Patents

Description

  The present invention relates to a fuel cell diagnostic device and a fuel cell diagnostic method, and more particularly, to a fuel cell diagnostic device and a fuel cell diagnostic method for a fuel cell system having a DC / DC converter that raises and lowers the voltage of a fuel cell stack.

Conventionally, as an internal resistance device of a fuel cell, an AC impedance measurement device has been provided for each cell module or cell of a stationary fuel cell system such as a distributed power supply device, and an AC impedance when an alternating current of a specific frequency is applied. A technique for measuring (internal resistance) is known (for example, see Patent Document 1).
JP 2002-367650 A

  However, the above-described conventional technology is premised on application to a stationary fuel cell system, and is not considered to be applied to a space-saving fuel cell system such as for a vehicle. Therefore, when the technique of Patent Document 1 is applied to a space-saving fuel cell system, an internal resistance measuring device is provided for each cell module or for each cell, and the entire system needs to be downsized. Regardless, the system becomes large, which is very disadvantageous in terms of layout.

  A first feature of the present invention is a fuel cell diagnostic apparatus for a fuel cell system having a DC / DC converter that raises and lowers the voltage of a fuel cell stack including a plurality of cells, etc., and uses the DC / DC converter as a fuel. Means for applying an alternating current of a predetermined frequency to the battery stack, means for measuring a voltage change of each cell, etc. when an alternating current of a predetermined frequency is applied, and measuring an internal resistance of each cell, etc. The gist of the invention is to have means for detecting an abnormality of each cell or the like from the reactance.

  A second feature of the present invention is a fuel cell diagnostic method for a fuel cell system having a DC / DC converter that steps up and down a voltage of a fuel cell stack including a plurality of cells, etc., and uses the DC / DC converter as a fuel. A step of applying an alternating current of a predetermined frequency to the battery stack, a step of measuring a voltage change of each cell, etc. when an alternating current of a predetermined frequency is applied, and measuring an internal resistance of each cell, etc. The gist of the present invention is a fuel cell diagnostic method including a step of detecting an abnormality for each cell or the like from reactance included therein.

  ADVANTAGE OF THE INVENTION According to this invention, the fuel cell diagnostic apparatus and fuel cell diagnostic method which can miniaturize the whole fuel cell system can be provided.

  Embodiments of the present invention will be described below with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

  As shown in FIG. 1, a fuel cell diagnostic apparatus according to an embodiment of the present invention includes a fuel cell stack 1 including a plurality of cells or cell modules, and a current controller (DC / DC) that steps up and down the voltage of the fuel cell stack 1. The present invention is applied to a vehicle fuel cell system having at least a DC converter 2. The DC / CD converter 2 steps up and down the voltage of the fuel cell stack 1 and adjusts the supply voltage to the auxiliary power source (high voltage battery) 8 and the like.

  The fuel cell diagnostic device applies an alternating current to the fuel cell stack 1 at a predetermined frequency using the DC / DC converter 2 of such a vehicle fuel cell system, and generates a voltage generated for each cell or each cell module at that time. The change is measured to measure the internal resistance, and the abnormality of the fuel cell stack 1 is detected from the obtained internal resistance (AC impedance) and reactance.

  Specifically, the fuel cell diagnostic apparatus uses an AC applying unit that applies an alternating current of a predetermined frequency to the fuel cell stack 1 using the DC / DC converter 2 and each cell when an alternating current of a predetermined frequency is applied. Alternatively, cell voltage detection means 3 (hereinafter referred to as “cell voltage detection device”) that measures a voltage change for each cell module and measures an internal resistance for each cell or each cell module, and reactance included in the internal resistance and the internal resistance. To an abnormality detecting means for detecting an abnormality for each cell or each cell module. Here, the “abnormality detection means” constitutes a part of an electronic control unit (ECU) 4 described later. The DC / DC converter 2 included in the vehicular fuel cell system applies an alternating current of a predetermined frequency to the fuel cell stack 1 as an “alternating current applying means” of the fuel cell diagnostic device.

  The fuel cell stack 1 is formed by stacking fuel cell cells (hereinafter referred to as “cells”) or cell modules that generate power by reacting a fuel gas supplied to an anode electrode and an oxidant gas supplied to a cathode electrode. Become. The oxidant gas (air) supplied to the fuel cell stack 1 is pressurized to a desired pressure by the air compressor 14 after impurities such as dust and oil mist are removed by the filter. And it cools to the driving | running | working appropriate temperature of the fuel cell stack 1 with the cooler 15 downstream of the air compressor 14. FIG. Thereafter, the oxidant gas is humidified by the cathode humidifier 16 downstream of the cooler 15 and supplied to the cathode electrode of the fuel cell stack 1. The pressure of the oxidant gas between the cathode humidifier 16 and the fuel cell stack 1 is measured by a pressure sensor 17. The air compressor 14 pressurizes the oxidant gas by the operation of a predetermined motor 18.

  The fuel gas (hydrogen gas) supplied to the fuel cell stack 1 is supplied from the hydrogen tank 9, adjusted to a predetermined temperature by the heat exchanger 10, and mixed with the fuel gas discharged from the fuel cell stack 1 by the ejector 11. Is done. Thereafter, the fuel gas is humidified by the anode humidifier 7 and supplied to the anode electrode of the fuel cell stack 1. The fuel gas discharged from the fuel cell stack 1 is adjusted to a predetermined pressure by the back pressure control valve and guided to the ejector 11 or the outside of the apparatus. The oxygen sensor 13 detects the oxygen concentration in the fuel gas discharged to the outside of the apparatus.

  A temperature sensor 21, a cell voltage detection device 3, a storage tank 12 and a DC / DC converter 2 are connected to the fuel cell stack 1. The temperature sensor 21 measures the temperature in the fuel cell stack 1. The DC / DC converter 2 is connected to the auxiliary power supply 8. The DC / DC converter 2, auxiliary power supply 8, atmospheric pressure sensor 20, back pressure control valve 6, pressure sensor 17, cell voltage detection device 3 and output controller 19 are each connected to an electronic control unit (ECU) 4, and the ECU 4 Controls the operation of each component. A part of the ECU 4 constitutes the “abnormality detection means” described above. The fuel cell stack 1 supplies electric power to a drive motor 5 as an example of a main load mounted on the vehicle under the control of the ECU 4.

  FIG. 2 shows a portion related to the fuel cell diagnostic apparatus in the fuel cell system of FIG. The fuel cell stack 1 includes n cells or cell modules C1 to Cn. The DC / DC converter 2 steps up and down the voltage of the fuel cell stack 1 and adjusts the supply voltage to the auxiliary power source (high voltage battery) 8. The auxiliary power supply 8 includes a plurality of power supplies connected in series. In the embodiment, the DC / DC converter 2 applies an alternating current with a predetermined frequency to the fuel cell stack 1. And the cell voltage detection apparatus 3 measures the voltage change which arises for every cell or every cell module at that time, and measures internal resistance. Specifically, as shown below, the AC frequency applied to the fuel cell stack 1 is changed, and the internal resistance (AC impedance) is determined from the change in response current and response voltage generated for each cell or cell module at that time. Ask.

  In general, the response voltage E, the response current I, and the impedance Z of the fuel cell stack 1 when an alternating current or an alternating voltage is applied to the fuel cell including the fuel cell stack 1 are expressed by Equations (1) to (3), respectively. I can express.

E = E ₀ expj (ωt + Φ) (1)
I = I ₀ expjωt (2)
Z = E / I = (E ₀ / I ₀ ) expjΦ (3)

Here, ω represents an angular frequency [Hz] (ω = 2πν), and Φ represents an initial phase. Moreover, (3) Formula is shown by (4) Formula as the impedance Z in a R, L, C series circuit.

Z = R + jχ (4)

Here, Z represents impedance [Ω], R represents resistance [Ω] (real part), χ represents reactance (imaginary part), and χ = (ωL−1 / ωC). L represents an inductance component [H]. When the inductance component L exists, a phase difference between the response current I and the response voltage E occurs. Therefore, a phase shift occurs between the response current I and the response voltage E due to a change in frequency, and the reactance component χ changes. When there is no phase difference between the response current I and the response voltage E, the reactance component χ is zero.

  The DC / DC converter 2 periodically switches the applied AC frequency in a plurality of specific frequency bands when measuring the internal resistance. For example, as shown in FIG. 3A, an alternating voltage or alternating current having a frequency of 10 kHz is applied to the fuel cell stack 1. At this time, there is no phase difference between the response current I and the response voltage E. Thereafter, as shown in FIG. 3B, the frequency of the alternating voltage or alternating current applied to the fuel cell stack 1 is changed to, for example, 1 Hz. At this time, the response current I has no phase difference, but the response voltage E has a phase difference (phase lag).

  When the internal resistance (alternating current impedance) deviates from a predetermined allowable range in a specific frequency band, the cell number and the frequency band where the failure has occurred are detected as a failure has occurred. The “predetermined allowable range” may be obtained experimentally or theoretically.

As shown in FIG. 4, the equivalent circuit of the k-th cell Ck constituting the fuel cell stack 1 includes a resistance component Zctk conductive part of the connected capacitive component C _D and cells in parallel, to which are connected in series And a resistance component ZΩk. k represents an arbitrary natural number of 1 to n.

The AC frequency switched by the DC / DC converter 2 desirably belongs to a specific frequency band as shown in FIG. In other words, the AC frequency is desirably an arbitrary frequency belonging to each frequency band of 5 to 10 kHz, 20 to 40 Hz, and 0.01 to 1 Hz. In the frequency band of 5 to 10 kHz, the resistance component ZΩk of the conductor portion of the cell can be measured. In the frequency band of 20 to 40 Hz, the resistance component Zctk accompanying the electrochemical reaction can be measured. In the frequency band of 0.01 to 1 Hz, the resistance component Z _D k accompanying the movement of the diffused resistance material can be measured. When the resistance component ZΩk increases, a failure such as an electrolyte membrane or a bus bar electrode provided in the fuel cell stack 1 is estimated. When the resistance component Zctk increases, a failure of an electrode reaction promoting material such as an anode electrode, a cathode electrode, or a catalyst included in the fuel cell stack 1 is estimated. When the resistance component Z _D k increases, a failure in the introduction portion of the fuel cell stack 1 is estimated. Resistance component Z _D is capable improved by the operation (purge) for draining water generated by the operation of the back pressure control valve 6 of FIG. 1, when detecting a failure of the resistance component Z _D, solutions such as purging is necessary.

  With reference to FIG. 6, the operation of the fuel cell system and the fuel cell diagnostic apparatus of FIG. 1 will be described.

  (A) In step S01, the ignition switch is turned on. In step S02, the fuel cell stack 1 starts power generation. In step S03, the ECU 4 confirms that the air flow rate QN is substantially the same as the predetermined reference value QN1.

  (B) Thereafter, in step S04, it is confirmed whether or not the temperature T of the fuel cell stack 1 is within a predetermined reference range (T1 <T <T2). In step S05, the DC / DC converter 2 is switched to the AC impedance measurement mode. That is, as described above, the DC / DC converter 2 can apply an alternating current of a predetermined frequency to the fuel cell stack 1 and can periodically switch the applied alternating frequency in a plurality of specific frequency bands. Switch to.

  (C) In step S06, the DC / DC converter 2 applies an AC voltage or an AC current having a frequency of 10 kHz to the fuel cell stack 1, and the cell voltage detector 3 measures the response current I and the response voltage E. Measure AC impedance. In step S07, the cell voltage detection device 3 calculates impedances ZΩ1,..., ZΩn for each cell.

  (D) In step S08, the ECU 4 determines whether each of ZΩ1,..., ZΩn is smaller than the abnormality detection value ZΩ0. In step S09, the resistance component ZΩk having an abnormality detection value ZΩ0 or more is determined to be abnormal in the electrolyte membrane of the corresponding cell, and the cell number k is detected.

  (E) In step S10, the DC / DC converter 2 applies an AC voltage or an AC current having a frequency of 20 Hz to the fuel cell stack 1, and the cell voltage detector 3 measures the response current I and the response voltage E. Measure AC impedance. In step S11, the cell voltage detection device 3 calculates impedances Zct1,..., Zctn for each cell.

  (F) In step S12, the ECU 4 determines whether each of Zct1,..., Zctn is smaller than the abnormality detection value Zct0. In step S13, it is determined that the resistance component Zctk having an abnormality detection value Zct0 or more is abnormal in the anode electrode or cathode electrode of the corresponding cell, and the cell number k is detected.

(G) In step S14, the DC / DC converter 2 applies an AC voltage or an AC current having a frequency of 1 Hz to the fuel cell stack 1, and the cell voltage detector 3 measures the response current I and the response voltage E. Measure AC impedance. In step S15, the cell voltage detection device 3 calculates impedances Z _D 1,..., Z _D n for each cell.

(H) In step S16, the ECU 4 determines whether each of Z _D 1,..., Z _D n is smaller than the abnormality detection value Z _D 0. In step S17, it is determined that the resistance component Z _D k that is equal to or greater than the abnormality detection value Z _D 0 is abnormal in the anode electrode or cathode electrode of the corresponding cell, and the cell number k is detected.

  (L) In step S18, the DC / DC converter 2 is switched to the normal control mode different from the AC impedance measurement mode, and the operation of the fuel cell diagnostic device is completed.

  As described above, the DC / DC converter 2 provided in the vehicle fuel cell system is used to superimpose an alternating current on the fuel cell stack 1 at a predetermined frequency, and a voltage change is performed for each cell or each cell module at that time. The internal resistance is measured and the abnormality of the fuel cell is detected from the obtained impedance and reactance. Thereby, it is not necessary to separately provide an AC impedance (internal resistance) measuring device for each cell or each cell module, and the entire system can be reduced in size.

  Further, the DC / DC converter 2 measures the internal resistance in some specific frequency bands by periodically changing the switching frequency at any frequency belonging to some specific frequency bands when measuring the internal resistance. Thus, it is possible to estimate the cause of the increase in resistance.

(Other embodiments)
As described above, the present invention has been described by way of one embodiment. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples, and operational techniques will be apparent to those skilled in the art.

  For example, the cell voltage detection device 3 is connected to a main load (such as the drive motor 5) on which the fuel cell stack 1 is mounted after the ignition switch (IGN) of the vehicle on which the vehicle fuel cell system is mounted is turned on. It is desirable to measure the internal resistance until a state where power supply is started (Ready state) or after the ignition switch is turned off until the fuel cell stack 1 stops generating power. The fuel cell stack 1 supplies electric power to a main load such as a drive motor 5 via the DC / DC converter 2 during traveling. Therefore, the current at the time of measuring the internal resistance cannot be changed arbitrarily.

  Further, based on the diagnosis result by the internal resistance measurement after the ignition switch is turned on, the supply flow rate of the fuel gas and the oxidant gas to the fuel cell stack 1, the fuel gas and the oxidant gas in the fuel cell stack 1 It is desirable to correct the opening of the back pressure control valve that controls the pressure and the water pressure of the humidifying water that humidifies the electrolyte membrane included in the fuel cell stack. That is, the back pressure control valve 6 for controlling the supply flow rate of the fuel gas or the oxidant gas, the pressure of the fuel gas in the fuel cell stack 1 and the wetness of the electrolyte membrane based on the diagnosis result by the AC impedance measurement when the IGN is on. Correct the water pressure used for the operation. Thereby, it is possible to suppress a decrease in fuel cell performance due to deterioration of the anode electrode, the cathode electrode and the electrolyte membrane.

  Further, the cell voltage detection device 3 measures the internal resistance when the supply flow rates of the fuel gas and the oxidant gas to the fuel cell stack 1 substantially coincide with the predetermined flow rates. That is, the alternating current is measured when the flow rate of the fuel gas or the oxidant gas substantially matches the predetermined flow rate. Thereby, the power generation state of the fuel cell stack 1 can be controlled and compared with the abnormality determination reference value, and the accuracy can be improved.

  Furthermore, the cell voltage detection device 3 measures the internal resistance when the temperature of the fuel cell stack 1 is within a predetermined range. That is, the internal resistance is measured when the temperature of the fuel cell stack 1 is within a predetermined range. Thereby, the power generation state of the fuel cell stack 1 can be controlled and compared with the abnormality determination reference value, and the accuracy is improved.

  Furthermore, the fuel cell diagnostic apparatus and method according to the present invention can be applied not only to a vehicle fuel cell system but also to other space-saving fuel cell systems, and have a remarkable effect.

  Thus, it should be understood that the present invention includes various embodiments and the like not described herein. Therefore, the present invention is limited only by the invention specifying matters according to the scope of claims reasonable from this disclosure.

1 is a block diagram illustrating a fuel cell system and a fuel cell diagnostic apparatus according to an embodiment of the present invention. It is a block diagram which shows the part in connection with a fuel cell diagnostic apparatus among the fuel cell systems of FIG. FIGS. 3A and 3B are graphs showing examples of response current and response voltage generated for each cell or each cell module when alternating current is applied to the fuel cell stack 1. It is a circuit diagram which shows the equivalent circuit of the cell which comprises a fuel cell stack. It is a table | surface which shows the example of the specific frequency band to which the alternating frequency switched by a DC / DC converter belongs. It is a flowchart which shows the operation | movement procedure of the fuel cell system of FIG. 1, and a fuel cell diagnostic apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell stack 2 ... DC / DC converter 3 ... Cell voltage detection means (cell voltage detection apparatus)
4 ... ECU (electronic control unit)
DESCRIPTION OF SYMBOLS 5 ... Drive motor 6 ... Back pressure control valve 7 ... Anode humidifier 8 ... Auxiliary power supply 9 ... Hydrogen tank 10 ... Heat exchanger 11 ... Ejector 12 ... Storage tank 13 ... Oxygen sensor 14 ... Air compressor 15 ... Cooler 16 ... Cathode humidifier 17 ... Pressure sensor 18 ... Motor 19 ... Output controller 20 ... Atmospheric pressure sensor 21 ... Temperature sensor χ ... Reactance component C _D ... Capacitance component C1-Cn ... Cell or cell module E ... Response voltage I ... Response current L ... Inductance component T ... Temperature Z _D k, Zctk, ZΩk ... Resistance component Z ... Impedance k ... Cell number

Claims (7)

A fuel cell diagnostic apparatus for a fuel cell system having a DC / DC converter for stepping up and down a voltage of a fuel cell stack including a plurality of cells or cell modules,
AC applying means for applying an alternating current of a predetermined frequency to the fuel cell stack using the DC / DC converter;
A cell voltage detecting means for measuring a voltage change for each cell or cell module when an alternating current of the predetermined frequency is applied and measuring an internal resistance for each cell or each cell module;
An abnormality detection means for detecting an abnormality for each cell or each cell module from the internal resistance and reactance included in the internal resistance.   2. The fuel cell diagnostic apparatus according to claim 1, wherein when measuring the internal resistance, the AC applying unit switches the frequency of the AC to be applied in a plurality of specific frequency bands.   The cell voltage detecting means is a period from when an ignition switch of a vehicle on which the vehicle fuel cell system is mounted is turned on until the fuel cell stack starts to supply power to a main load mounted on the vehicle, or The fuel cell diagnostic apparatus according to claim 1 or 2, wherein the internal resistance is measured after the ignition switch is turned off until the fuel cell stack stops generating power.   Based on the diagnosis result of the internal resistance measurement after the ignition switch is turned on, the supply flow rate of the fuel gas and the oxidant gas to the fuel cell stack, the fuel gas and the oxidant gas in the fuel cell stack The fuel cell according to any one of claims 1 to 3, wherein an opening of a back pressure control valve for controlling pressure and a water pressure of humidified water for humidifying an electrolyte membrane included in the fuel cell stack are corrected. Diagnostic device.   5. The cell voltage detection means measures the internal resistance when the supply flow rates of the fuel gas and oxidant gas to the fuel cell stack substantially coincide with a predetermined flow rate. The fuel cell diagnostic device according to any one of the preceding claims.   6. The fuel cell diagnostic apparatus according to claim 1, wherein the cell voltage detection unit measures the internal resistance when the temperature of the fuel cell stack is within a predetermined range. A fuel cell diagnostic method for a fuel cell system having a DC / DC converter for stepping up and down a voltage of a fuel cell stack including a plurality of cells or cell modules,
Applying an alternating current of a predetermined frequency to the fuel cell stack using the DC / DC converter;
Measure the voltage change for each cell or cell module when applying alternating current of the predetermined frequency to measure the internal resistance for each cell or cell module,
An abnormality for each cell or each cell module is detected from the internal resistance and reactance included in the internal resistance.

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