Method and device for diagnosing a fault within a fuel cell stack

Abstract

A method for diagnosing a fault of a fuel cell stack (2), the method comprising: Supplying, to the fuel cell stack (2), a plurality of alternating currents with different frequency combinations by an alternating current (AC) generator (12); Measuring, by a processor (13), a distortion rate and impedance of the fuel cell stack (2) for each alternating current, and selecting an optimal frequency based on the measured distortion rate and impedance; Supplying, to the fuel cell stack (2), an alternating current with the selected optimal frequency by the AC power generator; Calculating, by the processor (13), the distortion rate of the fuel cell stack (2) according to the alternating current with the optimal frequency and diagnosing a cell voltage drop based on the calculated distortion rate; and Calculating, by the processor (13), the impedance of the fuel cell stack (2) according to the alternating current with the optimal frequency, the amount of water in the fuel cell stack (2) based on the calculated impedance and diagnosing a cause of the cell voltage drop based on the calculated impedance and amount of water, where: selecting the optimal frequency: Selecting a first frequency of an alternating current corresponding to the largest distortion rate as a first optimal frequency for diagnosing the cell voltage drop based on the distortion rates measured for the respective alternating currents; and Selecting a second frequency of an alternating current corresponding to the largest impedance as a second optimal frequency for diagnosing the cause of the cell voltage drop based on the impedances measured for the respective alternating currents.

Description

BACKGROUND(a) Field of the invention

[0001] The present invention relates to a method and apparatus for diagnosing a fault of a fuel cell stack. (b) Description of the prior art

[0002] A fuel cell is a type of battery that converts chemical energy produced by the oxidation of fuel directly into electrical energy, which can be used by any number of devices. In most cases, a fuel cell is identical to a chemical cell in that it uses an oxidation and reduction reaction to generate energy. However, in a fuel cell, the reactants are intermittently supplied from an external source, and thus the reaction products are continuously removed from a fuel cell system. In a chemical cell, however, the battery reaction is carried out within a closed system.

[0003] Currently, the commercialization of fuel cells has begun because the reaction product of fuel cells is pure water and thus very environmentally friendly. Consequently, research into using fuel cells as a power source for vehicles is of great interest in the automotive industry.

[0004] A fuel cell often consists of a stacked arrangement in which a plurality of unit cells are arranged one next to / on top of the other, referred to in the industry as a fuel cell stack. Electrical energy is generated by supplying each unit cell of the fuel cell stack with hydrogen as fuel and oxygen as an oxidizer. However, if a deterioration in performance or a failure occurs in any one of the unit cells that make up the fuel cell stack, the overall performance of the fuel cell stack deteriorates, and stable operation cannot be achieved.

[0005] In the prior art, the performance of the fuel cell stack is diagnosed by measuring the voltage output by each unit cell of the fuel cell stack. One such diagnostic method includes a total harmonic distortion analysis (THDA) method. The THDA method diagnoses the cell voltage by calculating a distortion rate through frequency analysis of the stack voltage.

[0006] Although the THDA method can easily detect a drop in cell voltage, it is much more difficult to quantitatively measure what caused the drop in cell voltage.

[0007] Furthermore, there is a method for measuring the impedance of the fuel cell stack using electrochemical impedance spectroscopy (EIS). This method applies a current or voltage as a sinusoidal waveform to the fuel cell stack and then measures the current (I) and voltage (V) of the fuel cell stack. The impedance is calculated based on the measured current (I) and voltage (V) of the fuel cell stack.

[0008] However, this method diagnoses the humidity condition by measuring the load on a stack, but does not diagnose the cell voltage drop. Consequently, a separate device such as a space vector modulator (SVM) or a capacitive voltage multiplier (CVM) is required.

[0009] The information disclosed above in this Background section is intended only to enhance the understanding of the background of the invention and may therefore contain information that does not constitute prior art already known to a person of ordinary skill in the art in this country.

[0010] From US 2010 / 0 141 262 A1, a method for diagnosing a fault in a fuel cell stack is also known, comprising: supplying a plurality of alternating currents with different frequency combinations to the fuel cell stack by an AC generator; measuring, by a processor, a distortion rate and impedance of the fuel cell stack for each alternating current, and selecting an optimal frequency based on the measured distortion rate and impedance; supplying an alternating current with the selected optimal frequency to the fuel cell stack by the AC generator; calculating, by the processor, the distortion rate of the fuel cell stack according to the alternating current with the optimal frequency and diagnosing a cell voltage drop based on the calculated distortion rate;and calculating, by the processor, the impedance of the fuel cell stack according to the alternating current with the optimal frequency, and diagnosing a cause of the cell voltage drop based on the calculated impedance and water quantity; OVERVIEW

[0011] It is therefore an object of the present invention to provide a fault diagnosis method and a fault diagnosis apparatus that can diagnose a drop in cell voltage of a fuel cell stack and determine the cause of the drop in cell voltage.

[0012] The object is achieved by a method for diagnosing a fault in a fuel cell stack having the features of claims 1 and 3, as well as a device having the features of claim 4. Advantageous embodiments are the subject of the subclaims.

[0013] An embodiment of the present invention provides a method for diagnosing a failure of a fuel cell stack according to claim 1. More specifically, a plurality of alternating currents are supplied as control currents with different frequency combinations to the fuel cell stack, and a distortion rate and impedance of the fuel cell stack are measured for each alternating current. Based on the measured distortion rate and impedance, an optimal frequency is selected, and an alternating current with the selected optimal frequency is supplied to the fuel cell stack. The distortion rate of the fuel cell stack is then calculated according to the alternating current with the optimal frequency, and a cell voltage drop is calculated based on the calculated distortion rate.Likewise, the impedance of the fuel cell stack is calculated according to the alternating current with the optimal frequency, and a water quantity in the fuel cell stack is calculated based on the calculated impedance, and a cause of the cell voltage drop is diagnosed based on the calculated impedance and the water quantity. Additionally, selecting the optimal frequency includes: selecting a first frequency of an alternating current corresponding to the largest distortion rate as a first optimal frequency for diagnosing the cell voltage drop based on the distortion rates measured for the respective alternating currents; and selecting a second frequency of an alternating current corresponding to the largest impedance as a second optimal frequency for diagnosing the cause of the cell voltage drop based on the impedances measured for the respective alternating currents.

[0014] In some embodiments of the present invention, supplying the plurality of alternating currents to the fuel cell stack may include supplying to the fuel cell stack an alternating current having a first frequency of a first frequency range for diagnosing the cell voltage drop and an alternating current having a second frequency of a second frequency range for diagnosing the cause of the cell voltage drop. In this embodiment, the first frequency and the second frequency may be different from each other.

[0015] Another embodiment of the present invention provides an alternative method for diagnosing a fault of a fuel cell stack according to claim 3.

[0016] More specifically, in this method, both an alternating current having a first optimal frequency of a first frequency range that diagnoses a cell voltage drop and an alternating current having a second optimal frequency of a second frequency range that diagnoses a cause of the cell voltage drop are supplied to the fuel cell stack. Then, a distortion rate is calculated based on a voltage of the fuel cell stack according to the alternating current of the first optimal frequency, and the cell voltage drop is diagnosed based on the calculated distortion rate.Similarly, the impedance is calculated based on the voltage and current of the fuel cell stack according to the alternating current of the second optimal frequency, and the water quantity in the fuel cell stack is calculated based on the calculated impedance. The cause of the cell voltage drop is diagnosed based on the calculated impedance and the water quantity. Diagnosing the cell voltage drop involves diagnosing the cell voltage drop based on a total harmonic distortion analysis (THDA) method, and diagnosing the cause of the cell voltage drop involves measuring the impedance using electrochemical impedance spectroscopy (EIS) and diagnosing the cause of the cell voltage drop.

[0017] Yet another embodiment of the present invention provides an apparatus for diagnosing a fault of a fuel cell stack according to claim 4. More specifically, the apparatus comprises an alternating current (AC) injector connected to the fuel cell stack and applying an alternating current to a current flowing from the fuel cell stack to a load. The apparatus also comprises an AC generator configured to generate the alternating current.A diagnostic processor is also configured to measure a voltage and a current of the fuel cell stack to diagnose a cell voltage drop of the fuel cell stack and to diagnose the cause of the cell voltage drop based on the measured voltage and current, wherein the diagnostic processor is configured to select a first frequency of an alternating current corresponding to a largest distortion rate as a first optimal frequency to diagnose the cell voltage drop based on the distortion rates measured for the respective alternating currents; and to select a second frequency of an alternating current corresponding to a largest impedance as a second optimal frequency to diagnose the cause of the cell voltage drop based on the impedance measured for the respective alternating currents.

[0018] In some embodiments, the AC generator may supply an AC current having a first optimal frequency of a first frequency range for diagnosing the cell voltage drop and an AC current having a second optimal frequency of a second frequency range for diagnosing the cause of the cell voltage drop.

[0019] Furthermore, the diagnostic processor may include: an optimal frequency selection section configured to select the first optimal frequency for diagnosing the cell voltage drop and the second optimal frequency for diagnosing the cause of the cell voltage drop; an AC control section configured to control the AC generator; a distortion rate calculation section configured to measure the voltage of the fuel cell stack and calculate a distortion rate of the fuel cell stack based on the measured voltage; and an impedance / water calculation section configured to measure the voltage and current of the fuel cell stack and the amount of water in the fuel cell stack based on the calculated impedance and calculate an impedance based on the measured voltage and current.and a diagnostic section configured to diagnose the cell voltage drop of the fuel cell stack based on the distortion rate and to diagnose the cause of the cell voltage drop based on the impedance and the water amount;

[0020] According to one embodiment of the present invention, it is possible to simultaneously measure a cell voltage drop of a fuel cell stack and determine the cause of the cell voltage drop. Also, by simultaneously diagnosing the cell voltage drop and the cause of the cell voltage drop using a single device, it is possible to reduce the size of a device for diagnosing the failure of the fuel cell stack and reduce the cost of producing the device. It is also possible to more accurately diagnose the failure of the fuel cell stack by obtaining an optimal frequency for diagnosing the cell voltage drop of the fuel cell stack and the cause of the cell voltage drop at the same time. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram showing a structure of an apparatus for diagnosing a failure of a fuel cell stack according to an embodiment of the present invention. Fig. 2A-C show graphs illustrating a stack current characteristic according to an embodiment of the present invention. Fig. 3 is a diagram illustrating a structure of a diagnostic processor according to an embodiment of the present invention. Fig. 4 shows a graph illustrating a voltage-current characteristic according to an operating state of each cell of a fuel cell stack. Fig. 5 shows a flowchart of a method for diagnosing a fault of a fuel cell stack according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] In the following detailed description, certain embodiments of the present invention have been shown and described for purposes of illustration only. As those skilled in the art would appreciate, the described embodiments may be modified in various ways without departing from the spirit or scope of the present disclosure. Accordingly, the drawings and description are to be considered as illustrative and not restrictive. Like reference characters designate like elements throughout the description.

[0022] Throughout this specification, unless expressly stated otherwise, the word "comprise / include" or variations such as "comprises / includes" or "comprising / having" shall be construed as including the elements mentioned but not excluding any other elements.

[0023] It should be noted that the term "vehicle" or "vehicle-" or other synonymous terms as used herein includes motor vehicles in general, such as passenger cars including sports utility vehicles (SUVs), buses, trucks, various utility vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles, and other alternative fuel vehicles (e.g., fuel derived from sources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of propulsion, such as both gasoline-powered and electric-powered vehicles.

[0024] Additionally, it is understood that the methods described below are executed by at least one controller including a specially configured processor (e.g., fault diagnostic device 1). The term "controller" refers to a hardware device comprising a memory and a processor. The memory is configured to store program instructions, and the processor is specifically configured to execute said program instructions to perform one or more processes described further below.

[0025] Furthermore, the control logic of the present invention may be embodied as non-transitory computer-readable media on a computer-readable medium comprising executable program instructions executed by a processor, controller, or the like. Examples of computer-readable storage media include, but are not limited to, ROM, RAM, compact disc (CD)-ROMs, magnetic tapes, floppy disks, flash drives, smart cards, and optical data storage devices. The computer-readable recording medium may also be decentralized in network-coupled computer systems such that the computer-readable medium is stored and executed in a distributed manner, e.g., by a telematics server or a controller area network (CAN).

[0026] Furthermore, the terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting of the invention. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It is further understood that the terms "comprise" and / or "comprising," when used in this specification, describe the presence of the specified features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more features, integers, steps, operations, elements, components, and / or groups thereof. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed elements.

[0027] Unless expressly stated or evident from the context, the term "approximately" as used herein is understood to be within a range of standard tolerance in the art, for example, within 2 standard deviations of the mean values. "Approximately" can be understood to be within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise indicated by the context, all numerical values ​​provided herein are modified by the term "approximately."

[0028] Hereinafter, a method and an apparatus for diagnosing a failure of a fuel cell stack according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0029] Fig. 1 is a diagram illustrating a structure of an apparatus for diagnosing a failure of a fuel cell stack according to an embodiment of the present invention. As shown in Fig. 1, a device 1 (hereinafter referred to as “fault diagnosis device 1”) that diagnoses a fault of a fuel cell stack 2 according to an embodiment of the present invention includes an alternating current (AC) introduction device 11 (AC injector 11) connected to the fuel cell stack 2, an AC generator 12 configured to generate an AC signal for driving the AC introduction device 11, and a diagnosis processor configured to perform fault diagnosis and measurement of impedance and water amount by measuring a voltage and a current of the fuel cell stack 2.

[0030] As an exemplary manner for performing fault diagnosis of the fuel cell stack 2, the AC introduction device 11 (connected to the fuel cell stack 2) may include electronic devices (e.g., transistors) to allow a stack current to have an AC component. Meanwhile, a load R1 may be connected to the fault diagnosis device 1. The load R1 refers to all parts that use electric power generated by the fuel cell stack 2. The load consumes power from a fuel cell and may include, for example, an inverter, a motor, a direct current (DC) to DC (DC-DC) converter, a battery, and the like.

[0031] In addition, a terminal on one side of the load R1 can be connected to the first terminal of the fuel cell stack 2 and a terminal on the other side of the load R1 can be connected to the second terminal of the fuel cell stack 2.

[0032] Accordingly, the stack current output from the fuel cell stack 2 and the current output from the AC injection device 11 are added together and flow through the load R1. The current output from the AC injection device 11 is called the injection current, and the current flowing through the load R1 is called the load current.

[0033] Fig. 2A-C show graphs illustrating a stack current characteristic according to an embodiment of the present invention. In the illustrative graph, the injection current output from the AC injection device 11 has an AC component according to an operation of the AC generator 12, as shown in Fig. 2B, and the load current has a DC component, as shown in Fig. 2C. As shown in Fig. 2C, the load current can be expressed as a summation of the stack current and the injection current.

[0034] The AC generator 12 generates an AC signal for driving the AC introducing device 11. The AC generator 12 generates an AC signal according to a control signal output from the diagnostic processor 13.

[0035] The diagnostic processor 13, on the other hand, measures a voltage and current output by the fuel cell stack 2. That is, the stack voltage and current output, and diagnoses a cell voltage drop based on the measured voltage and current. The diagnostic processor 13 also measures an impedance and a water quantity, and is thus able to deduce the cause of the cell voltage drop based on this impedance and water quantity.

[0036] Fig. 3 is a diagram illustrating a structure of the diagnostic processor 13 according to an embodiment of the present invention. As shown in Fig. 3, the diagnostic processor 13 according to an embodiment of the present invention includes an AC control section 131, an optimal frequency selection processing section 132, a distortion rate calculation section 133, an impedance / water calculation section 134, and a diagnostic section 135.

[0037] The AC control section 131 outputs a control signal to the AC generator 12 to diagnose the failure of the fuel cell stack 2 and to generate an AC current to diagnose a cause of a cell voltage drop.

[0038] In some embodiments of the present invention, a plurality of alternating currents of different frequency ranges may be used to diagnose a cell voltage drop and the cause of the cell voltage drop. A distortion rate may be calculated in this embodiment to diagnose the fault of the fuel cell stack 2, and the cell voltage drop may be diagnosed based on the calculated distortion rate. A frequency range (e.g., a first frequency range) for the above fault diagnosis is, for example, 10 Hz. On the other hand, an impedance of the fuel cell stack 2 may be measured to diagnose the cause of the cell voltage drop. A frequency range (e.g., a second frequency range) for the above impedance measurement is, for example, approximately 300 Hz.Accordingly, according to one embodiment of the present invention, AC signals of the first frequency range and the second frequency range can be used to diagnose the fault and the cause of the cell voltage drop. For this purpose, for example, by selecting three adjacent frequencies (e.g., approximately 10 Hz, 8 Hz, and 12 Hz) from the first frequency range, by selecting three adjacent frequencies (e.g., approximately 300 Hz, 290 Hz, and 310 Hz) from the second frequency range, and by combining three frequencies selected from the first frequency range with three frequencies selected from the second frequency range, it is possible to use a plurality of control AC currents to diagnose the fault of the fuel cell stack 2 and the cause of the cell voltage drop according to one embodiment of the present invention.For example, it is possible to use an alternating current of a combination of approximately 10Hz and approximately 300Hz, an alternating current of a combination of approximately 8Hz and approximately 290Hz, and an alternating current of a combination of approximately 12Hz and approximately 310Hz.

[0039] As described above, a plurality of alternating currents comprising a plurality of alternating currents of different frequency ranges can be used. Control signals can be generated to enable the generation of the plurality of alternating currents. These generated control signals are output to the alternating current generator 12. Accordingly, the alternating current generator 12 generates different AC signals, i.e., alternating currents, according to the control signals and then supplies and introduces the generated alternating currents to the stack current through the AC introduction device 11.For example, according to a control signal output from the AC control section 131, the AC generator 12 may generate a first AC power of a combination of approximately 10 Hz and approximately 300 Hz, may generate a second AC power of a combination of approximately 8 Hz and approximately 290 Hz, and may generate a third AC power of a combination of approximately 12 Hz and approximately 310 Hz.

[0040] The optimal frequency selection processing section 132 selects an optimal frequency for diagnosing the cell voltage drop and diagnoses the cause of the cell voltage drop from the plurality of alternating currents (including an AC signal of the first frequency range and an AC signal of the second frequency range) supplied to the fuel cell stack 2 for fault diagnosis.

[0041] The distortion rate calculation section 133 measures the stack voltage of the fuel cell stack 2 according to the alternating current and calculates a distortion rate based on the measured stack voltage. For this section 133, total harmonic distortion analysis (THDA) can be used as a method for calculating the distortion rate.

[0042] Fig. Figure 4 shows a graph illustrating a voltage-current characteristic according to an operating state of each cell of a fuel cell stack. Generally, when a current having a sinusoidal waveform is supplied to the fuel cell stack 2, a voltage of a cell operating normally in the fuel cell stack 2 varies in a linear portion of the graph, as indicated by a dashed line. Fig. 4, and a voltage of a cell operating abnormally in the fuel cell stack 2 varies in a non-linear section as shown by a solid line of Fig. 4. Accordingly, it can be determined that a voltage of a normal cell exhibits little distortion according to a current change, whereas a voltage of an abnormal cell exhibits a significant voltage amplitude and significant distortion according to a cell current change. Accordingly, it is possible to diagnose whether the fuel cell stack 2 is defective by calculating a distortion rate through frequency analysis of the stack current and diagnosing whether the cell voltage has dropped based on the calculated distortion rate.

[0043] Meanwhile, the impedance / water calculation section 134 measures the stack voltage and stack current of the fuel cell stack 2 according to the alternating current, measures the impedance based on the measured stack voltage and stack current, and measures the water quantity based on the measured impedance. If an AC loss exists within the fuel cell stack 2, this indicates that a response characteristic varies according to a frequency when an AC variation occurs. By measuring the impedance and / or water quantity as a characteristic of the response characteristic, it is possible to quantitatively understand a loss within the fuel cell stack 2, that is, the cause of the cell voltage drop. For example, a humidification state of the fuel cell stack 2, namely the water quantity, also greatly affects the performance and may act as a cause of the cell voltage drop.

[0044] The impedance can be calculated by supplying an alternating current or an alternating voltage of a sinusoidal waveform to the fuel cell stack 2 and then calculating the stack current and the stack voltage, performing a Fourier transform of the measured current and voltage, and dividing a current value (I) of a predetermined frequency (w) by a voltage value (v) of the predetermined frequency in a frequency spectrum of the Fourier-transformed current and voltage.

[0045] Meanwhile, the diagnosis section 135 diagnoses the cell voltage drop based on the distortion rate calculated by the distortion rate calculation section 133 and diagnoses the cause of the cell voltage drop based on the impedance and the water amount calculated by the impedance / water calculation section 134.

[0046] The diagnostic processor 13 constructed in the above-mentioned structure can be configured / constructed in the form of a microprocessor.

[0047] Next, a method for diagnosing a failure of a fuel cell stack according to an embodiment of the present invention will be described based on the above structure / arrangement.

[0048] Fig. Figure 5 shows a flowchart of a method for diagnosing a fault of a fuel cell stack according to an embodiment of the present invention. The fault diagnosis device 1 uses a plurality of alternating currents, including a plurality of alternating currents of different frequency ranges, to diagnose the fault of the fuel cell stack 2 and to diagnose a cause of a cell voltage drop.

[0049] The fault diagnosis device 1 supplies the plurality of alternating currents to the fuel cell stack 2 and measures a distortion rate and impedance and water amount based on a stack voltage and a stack current output from the fuel cell stack 2 (S100 and S110).

[0050] For example, when using a first alternating current of a combination of approximately 10 Hz and approximately 300 Hz, a second alternating current of a combination of approximately 8 Hz and approximately 290 Hz, and a third alternating current of a combination of approximately 12 Hz and approximately 310 Hz, the first alternating current through the third alternating current are sequentially supplied to the fuel cell stack 2, the stack voltage and current are measured according to each supplied alternating current, and the distortion rate, impedance, and water quantity are measured based on the measured stack voltage and current. As a result, the distortion rate, impedance, and water quantity are measured for each alternating current. In this case, the above distortion rate, impedance, and water quantity calculation procedures can be performed a total of three times.

[0051] For example, the first alternating current of approximately 10 Hz is supplied to the stack current through the AC injection device 11. Accordingly, the first alternating current is included in the stack current output from the fuel cell stack 2 and flows along the load R1. The diagnostic processor 13 measures the stack voltage and stack current and diagnoses whether the fuel cell stack 2 is defective based on the measured stack voltage and stack current.

[0052] The diagnostic processor 13 measures the stack voltage and calculates the distortion rate based on the measured stack voltage. Also, since the first alternating current of the combination of 10 Hz and 300 Hz is supplied to the AC induction device 11 according to frequency conversion, the diagnostic processor 13 measures the stack voltage and current, and measures the impedance and water quantity based on the measured stack voltage and current. The above processes are also performed similarly with respect to the second alternating current and the third alternating current.

[0053] As described above, when the above distortion rate and impedance and water amount calculation processes are performed a plurality of times according to all alternating currents, that is, when the distortion rate and impedance and water amount calculation processes are performed a predetermined number of times (for example, three times according to the number of alternating currents), the optimal frequency selection processing section 132 selects an optimal frequency of an alternating current for optimal diagnosis (S120 and S130).

[0054] The optimal frequency selection processing section 132 selects a frequency at which the largest distortion rate and the largest impedance and water quantity are calculated based on the distortion rates and impedances measured for the respective alternating currents. Here, the alternating current supplied to the fuel cell stack functions as a test current for frequency selection. In this case, a frequency at which the largest distortion rate is calculated and a frequency at which the largest impedance and water quantity are calculated may be different from each other. For example, among the distortion rates corresponding to the first to third alternating currents, a distortion rate corresponding to the first alternating current may be the largest. Among the impedances corresponding to the first to third alternating currents, an impedance corresponding to the third alternating current may be the largest.As described above, the alternating current frequency corresponding to the maximum distortion rate and the maximum impedance is selected as the optimal frequency. The frequency corresponding to the maximum distortion rate is selected as the optimal frequency (e.g., first optimal frequency) for diagnosing cell voltage drop, and the frequency corresponding to the maximum impedance is selected as the optimal frequency (e.g., second optimal frequency) for diagnosing the cause of cell voltage drop.

[0055] As described above, when the optimal frequencies are selected, the fault diagnosis device 1 essentially performs a fault diagnosis of the fuel cell stack 2 based on the selected optimal frequencies. That is, the fault diagnosis device 1 generates an alternating current including a combination of the first optimal frequency and the second optimal frequency, supplies the generated alternating current to the AC introducing device 11 (S140), measures the stack voltage, and calculates the distortion rate based on the measured stack voltage. Then, the fault diagnosis device 1 diagnoses the cell voltage drop based on the calculated distortion rate (S150 and S160).

[0056] Also, the fault diagnosis device 1 can measure the stack voltage and stack current, can measure the impedance based on the measured stack voltage and stack current, can measure the water amount based on the measured impedance, and can diagnose the cause of the cell voltage drop based on the measured impedance and water amount (S150 and S170).

[0057] The above-mentioned embodiments of the present invention are not only constituted by an apparatus and a method. Alternatively, the above-mentioned embodiments may be constituted by a program that performs functions corresponding to the configuration of the embodiments of the present invention, or a recording medium on which the program is recorded. These embodiments can be readily developed from the description of the above-mentioned embodiments by one of ordinary skill in the art to which the present invention belongs.

Claims

[1] A method for diagnosing a fault of a fuel cell stack (2), the method comprising: Supplying, to the fuel cell stack (2), a plurality of alternating currents with different frequency combinations by an alternating current (AC) generator (12); Measuring, by a processor (13), a distortion rate and impedance of the fuel cell stack (2) for each alternating current, and selecting an optimal frequency based on the measured distortion rate and impedance; Supplying, to the fuel cell stack (2), an alternating current with the selected optimal frequency by the AC power generator; Calculating, by the processor (13), the distortion rate of the fuel cell stack (2) according to the alternating current with the optimal frequency and diagnosing a cell voltage drop based on the calculated distortion rate; and Calculating, by the processor (13), the impedance of the fuel cell stack (2) according to the alternating current with the optimal frequency, the amount of water in the fuel cell stack (2) based on the calculated impedance and diagnosing a cause of the cell voltage drop based on the calculated impedance and amount of water, where: selecting the optimal frequency: Selecting a first frequency of an alternating current corresponding to the largest distortion rate as a first optimal frequency for diagnosing the cell voltage drop based on the distortion rates measured for the respective alternating currents; and Selecting a second frequency of an alternating current corresponding to the largest impedance as a second optimal frequency for diagnosing the cause of the cell voltage drop based on the impedances measured for the respective alternating currents. [2] The method of claim 1, wherein: supplying the plurality of alternating currents to the fuel cell stack (2) comprises supplying, to the fuel cell stack (2), an alternating current having a first frequency of a first frequency range for diagnosing the cell voltage drop and an alternating current having a second frequency of a second frequency range for diagnosing the cause of the cell voltage drop, wherein the plurality of alternating currents have the first frequency and the second frequency which are different from each other. [3] A method for diagnosing a fault of a fuel cell stack (2), the method comprising: Supplying, to the fuel cell stack (2), an alternating current having a first optimal frequency of a first frequency range for diagnosing a cell voltage drop and an alternating current having a second optimal frequency of a second frequency range for diagnosing a cause of the cell voltage drop, by an alternating current (AC) generator (12); Calculating, by a processor (13), a distortion rate based on a voltage of the fuel cell stack (2) according to the alternating current of the first optimal frequency and diagnosing the cell voltage drop based on the calculated distortion rate; and Calculating, by the processor (13), an impedance based on the voltage and a current of the fuel cell stack (2) according to the alternating current of the second optimal frequency and the amount of water in the fuel cell stack (2) based on the calculated impedance and diagnosing the cause of the cell voltage drop based on the calculated impedance and amount of water, wherein: diagnosing the cell voltage drop comprises diagnosing the cell voltage drop based on a Total Harmonic Distortion Analysis (THDA) method, and Diagnosing the cause of the cell voltage drop includes measuring the impedance using electrochemical impedance spectroscopy (EIS) and diagnosing the cause of the cell voltage drop. [4] Device (1) for diagnosing a fault of a fuel cell stack (2), the device (1) comprising: an alternating current (AC) introduction device connected to the fuel cell stack (2) and applying an alternating current to a current flowing from the fuel cell stack (2) to a load (R1); an alternating current (AC) generator (12) arranged to generate the applied alternating current; and a diagnostic processor (13) configured to measure a voltage and a current of the fuel cell stack (2) to diagnose a cell voltage drop of the fuel cell stack (2) and to diagnose a cause of the cell voltage drop based on the measured voltage and the measured current, wherein the diagnostic processor (13) is configured to: selecting a first frequency of an alternating current corresponding to a largest distortion rate as the first optimal frequency to diagnose the cell voltage drop based on the distortion rates measured for the respective alternating currents; and selects a second frequency of an alternating current corresponding to a largest impedance as the second optimal frequency to diagnose the cause of the cell voltage drop based on the impedance measured for the respective alternating currents. [5] Device (1) according to claim 4, wherein: the diagnostic processor (13) comprises: an optimal frequency selection processor configured to select the first optimal frequency for diagnosing the cell voltage drop and the second optimal frequency for diagnosing the cause of the cell voltage drop; an AC control section configured to control the AC generator; a distortion rate calculation section configured to measure the voltage of the fuel cell stack (2) and to calculate a distortion rate of the fuel cell stack (2) based on the measured voltage; an impedance / water calculation section configured to measure the voltage and current of the fuel cell stack (2) and to calculate the impedance based on the measured voltage and current and the amount of water in the fuel cell stack (2) based on the calculated impedance; and a diagnostic section configured to diagnose the cell voltage drop of the fuel cell stack (2) based on the distortion rate and to diagnose the cause of the cell voltage drop based on the impedance and the water amount. [6] Device (1) according to claim 5, wherein: the AC introduction device (11) comprises electronic devices arranged to supply an alternating current according to an alternating signal output from the AC generator. [7] A non-transitory computer-readable medium comprising program instructions executed by a processor (13), the computer-readable medium comprising: Program instructions that measure a distortion rate and impedance of the fuel cell stack (2) for each alternating current and select an optimal frequency based on the measured distortion rate and impedance; Program instructions that control a supply of an alternating current at the selected optimum frequency by an alternating current (AC) generator (12); Program instructions that calculate the distortion rate of the fuel cell stack (2) according to the alternating current with the optimal frequency and diagnose a cell voltage drop based on the calculated distortion rate; and Program instructions that calculate the impedance of the fuel cell stack (2) according to the alternating current with the optimal frequency and diagnose a cause of the cell voltage drop based on the calculated impedance, where the program instructions for selecting the optimal frequency include: Program instructions that select a first frequency of an alternating current corresponding to the highest distortion rate as the first optimal frequency to diagnose cell voltage drop based on the distortion rates measured for the respective alternating currents; and Program instructions that select a second frequency of an alternating current corresponding to the greatest impedance as the second optimal frequency to diagnose the cause of the cell voltage drop based on the impedance measured for the respective alternating currents.

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