Device for diagnosing a fault of a fuel cell stack

Abstract

Device (1) which diagnoses a fault in a fuel cell stack (2), the device (1) comprising: an alternating current, AC, absorption unit (11) connected to the fuel cell stack (2) and switched based on an applied AC signal to allow a current to flow from the fuel cell stack (2); an AC signal generator (12) configured to generate the AC signal and to supply the generated AC signal to the AC absorption unit (11); and a processor configured to: to measure a stack voltage or a stack current of the fuel cell stack (2); and to diagnose the fault in the fuel cell stack (2) based on the measured stack voltage or stack current, wherein the AC absorption unit (11) comprises: a transistor (TR1), wherein a collector terminal is connected to a first terminal of the fuel cell stack (2), an emitter terminal is connected to a second terminal of the fuel cell stack (2), and a base terminal is connected to an output terminal of the AC signal generator (12); wherein a load (R1) is connected between the first terminal of the fuel cell stack (2) and the second terminal of the fuel cell stack (2), and the stack current output from the fuel cell stack (2) is a summation of an absorption current flowing through the AC absorption unit (11) and a load current flowing through the load (R1).

Description

BACKGROUND(a) Field of the invention

[0001] The present invention relates to a device 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 current state of the 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. 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.

[0006] However, for the above fault diagnosis, a direct current (DC)-DC (DC-DC) converter, which boosts a DC voltage, and a DC-AC (DC-AC) converter, which converts the boosted direct current (DC voltage) to an alternating current (AC voltage), are required to input the alternating current into the fuel cell stack. Since both the above converter and an inverter are required, constructing a device for diagnosing a fault in the fuel cell stack becomes difficult, and a large number of parts are required. Therefore, the product price increases. In addition, the fault diagnosis device requires a capacitor that decouples the alternating current from the direct current when inputting the alternating current. When the alternating current flows through the above capacitor, a signal distortion occurs. As a result, it may be difficult to input the alternating current in a sine wave.The information disclosed above in this 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.

[0007] DE 10 2011 107 182 A1 discloses a system and method for monitoring fuel cells in a fuel cell array. The system includes a sensor circuit, such as a voltage sensor circuit, that monitors a condition of the fuel cells. If the sensor circuit detects a malfunctioning cell, it sends a signal to a tone generator, which generates a frequency signal that switches a load in and out of the cell array. A voltage sensor detects the voltage of the cell array having the frequency signal and sends the detected voltage signal to a tone decoder, which decodes the frequency signal to determine that the fuel cells are malfunctioning.

[0008] DE 11 2006 001 747 T5 discloses a fuel cell system suitable for measuring alternating current impedance. The fuel cell system comprises a stabilizing means for stabilizing power generation in a fuel cell and a means for measuring alternating current impedance after power generation in the fuel cell has been stabilized.

[0009] KR 10 1 090 705 B1 discloses a method for monitoring the condition of a fuel cell stack that responds to a frequency using a diagnostic signal, thereby improving diagnostic analysis performance. SUMMARY

[0010] The present invention provides a fault diagnosis device that can diagnose whether a fuel cell stack has failed using a simpler arrangement.

[0011] An embodiment of the present invention provides a device having the features of claim 1.

[0012] According to an embodiment of the present invention, it may be possible to diagnose a fault in a fuel cell stack using a simpler arrangement. Specifically, even when a DC-DC converter is not used and a DC-AC converter that converts a boosted DC voltage into an alternating current is used, it may be possible to allow a current of the fuel cell stack to be an alternating current. Consequently, a structure of the fault diagnosis device can be simplified, and a relatively small number of parts can be used. Therefore, the production cost of the fault diagnosis device can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an exemplary diagram illustrating a structure of an apparatus that diagnoses a failure in a fuel cell stack according to an embodiment of the present invention; Fig. 2 shows an exemplary graph illustrating a stack current characteristic according to an embodiment of the present invention; and Fig. 3 shows an exemplary graph illustrating a voltage-current characteristic according to an operating state of each cell of a fuel cell stack according to an embodiment of the present invention. DETAILED DESCRIPTION

[0013] 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 power, such as both gasoline-powered and electric-powered vehicles.

[0014] Although the embodiment is described as using a plurality of units to perform the example process, it is understood that the example processes may also be performed by one or more modules. Furthermore, it is understood that the term controller refers to a hardware device including a memory and a processor. The memory is configured to store the modules, and the processor is specifically configured to execute said modules to perform one or more processes described below.

[0015] 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).

[0016] 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.

[0017] 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.

[0018] 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.

[0019] Hereinafter, an apparatus for diagnosing a failure in a fuel cell stack according to an embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1 is an exemplary diagram illustrating a structure of an apparatus that diagnoses a failure in a fuel cell stack according to an embodiment of the present invention.

[0020] As in Fig. 1, a device 1 (hereinafter referred to as “fault diagnosis device 1”) that diagnoses a fault in a fuel cell stack 2 according to an embodiment of the present invention may include an alternating current (AC) absorption unit 11 connected to the fuel cell stack 2, an AC signal generator 12 configured to generate an AC signal that drives the AC absorption unit 11, and a diagnosis processing unit 13 configured to perform fault diagnosis by measuring a voltage and a current of the fuel cell stack 2.

[0021] For fault diagnosis of the fuel cell stack 2 and to allow a stack current to have an AC component, the AC absorption unit 11 connected to the fuel cell stack 2, into which a current output from the fuel cell stack 2 flows, may include a transistor TR1. Furthermore, a load unit, that is, a load R1, may be included in or connected to the fault diagnosis device 1. The load R1 briefly refers to all parts that use a current generated by the fuel cell stack 2. The load consumes power of a fuel cell and may include, for example, an inverter, a motor, a DC-DC converter, a battery, and the like.

[0022] A collector terminal of the transistor TR1 can be connected to a first terminal (e.g., + terminal) of the fuel cell stack 2, an emitter terminal can be connected to a second terminal (e.g., - terminal) of the fuel cell stack 2, and a base terminal can be connected to an output terminal of the AC signal generator 12. A terminal on a first side of the load R1 can be connected to the first terminal of the fuel cell stack 2, and a terminal on a second side of the load R1 can be connected to the second terminal of the fuel cell stack 2. Accordingly, the stack current output from the fuel cell stack 2 can flow through the transistor TR1 and through the load R1. A current flowing through the transistor TR1 is called an absorption current, and a current flowing through the load R1 is called a load current.

[0023] Fig. Figure 2 shows an exemplary graph illustrating a stack current characteristic according to an embodiment of the present invention. The absorption current may have an AC component according to a switching operation of the transistor TR1 as shown in Fig. 2(b), and the load current may have a DC component as shown in Fig. 2(c). The stack current output from the fuel cell stack 2 according to an operation of the transistor TR1 can flow through the transistor TR1 and thereby becomes an AC component. Accordingly, as shown in Fig. As shown in Figure 2(a), the stack current can be expressed as a summation of the load current and the absorption current.

[0024] The AC signal generator 12 may be configured to generate an AC signal (or may also be referred to as a control current) that drives the transistor TR1 of the AC absorption unit 11, and may be configured to output the generated AC signal to the base terminal of the transistor TR1. The AC signal may allow the stack current, even with a substantially small amount of current, to be expressed as an AC component. A current flowing in the transistor TR1 may be a current of a gain region of the transistor TR1. Accordingly, a current amplified by a gain rate flows compared to the current applied to the base terminal.

[0025] The AC signal generator 12 may be configured to generate an AC signal according to a control signal output by the diagnostic processing unit 13. The diagnostic processing unit 13 may be configured to adjust a frequency of the current output by the AC signal generator 12 according to the control signal. The AC signal supplied to the transistor TR1 of the AC absorption unit 11 may be designated as I text = I max × sinωt. The frequency ω varies according to the control signal. The AC signal generator 12 may be configured to generate an AC signal of 10 Hz according to, for example, the control signal output from the control current control unit, and may be configured to supply the generated AC signal to the AC absorption unit 11.

[0026] As described above, since the current of the fuel cell stack 2 is required to flow only through the transistor TR1 of the AC absorption unit 11, an amount of current to be introduced into the fuel cell stack 2 is not required. The AC signal input to the base terminal of the transistor TR1 is required to flow only in a form of a sinusoidal waveform, and thus, a structure of the fault diagnosis device 1 can be simplified and the number of parts used can be reduced. Moreover, instead of introducing an alternating current into a direct current, the alternating current can flow directly into the transistor TR1, and thus a decoupling capacitor may not be required. Accordingly, distortion of the alternating current may not occur, and thus it is possible to allow the alternating current to flow close to a sinusoidal waveform.

[0027] Meanwhile, the diagnosis processing unit 13 may be configured to measure a stack voltage and / or a stack current of the fuel cell stack 2, and to diagnose whether the fuel cell stack 2 has failed based on the measured stack voltage and / or stack current. Furthermore, an operation of an apparatus that diagnoses a failure in a fuel cell stack according to an embodiment of the present invention will be described based on the above arrangement.

[0028] To diagnose the fault of the fuel cell stack 2, the fault diagnosis device 1 may be configured to generate an alternating current of a predetermined frequency and supply the generated alternating current to the AC absorption unit 11. An AC signal of a predetermined frequency, for example, 10 Hz, output from the AC signal generator 12 is supplied to the transistor TR1 of the AC absorption unit 11. The transistor TR1 may be configured to perform an on / off switching operation, and the stack current output from the fuel cell stack 2 may flow through the AC absorption unit 11. In addition, the stack current may flow through the load R1.

[0029] Accordingly, the stack stream input to the diagnosis processing unit 13 can be as shown in Fig. 2, an absorption current of an AC component flowing through the transistor TR1 and a load current of a DC component flowing through the load R1. The diagnostic processing unit 13 may be configured to measure a stack voltage and a stack current, and to diagnose a fault in the fuel cell stack 2 based on the measured stack voltage and the measured stack current. For example, the diagnostic processing unit 13 may be configured to measure the stack voltage, calculate a distortion rate based on the measured stack voltage, and diagnose a fault in the fuel cell stack 2 based on the calculated distortion rate. Total harmonic distortion analysis (THDA) may be used as a method for calculating the distortion rate.

[0030] Fig. 3 shows an exemplary graph illustrating a voltage-current characteristic according to an operating state of each cell of a fuel cell stack.

[0031] In general, when supplying a current of a sine waveform to the fuel cell stack 2, a voltage of a cell operating normally (e.g., no fault) in the fuel cell stack 2 may vary in a linear range as shown by a dashed line of Fig. 3, and a voltage of a cell operating abnormally (e.g., with error) in the fuel cell stack 2 may vary in a non-linear range, as shown by a solid line of Fig.3. Accordingly, a voltage of a normal cell may have reduced distortion according to a current change, whereas a voltage of an abnormal cell may have increased voltage amplitude and increased distortion based on a change in cell current. Accordingly, it may be possible to diagnose a fault in the fuel cell stack 2 by calculating a distortion rate using frequency analysis of the stack current and diagnosing whether the cell voltage has decreased based on the calculated distortion rate. As an example of the above fault diagnosis method, other methods (e.g., a method of measuring an impedance based on the stack voltage and stack current to thereby diagnose a fault in the fuel cell stack 2) may be used.

[0032] While this invention has been described in connection with what are presently considered to be practical embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but on the contrary is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

[1] Device (1) which diagnoses a fault in a fuel cell stack (2), the device (1) comprising: an alternating current, AC, absorption unit (11) connected to the fuel cell stack (2) and switched based on an applied AC signal to allow a current to flow from the fuel cell stack (2); an AC signal generator (12) configured to generate the AC signal and to supply the generated AC signal to the AC absorption unit (11); and a processor configured to: to measure a stack voltage or a stack current of the fuel cell stack (2); and to diagnose the fault in the fuel cell stack (2) based on the measured stack voltage or stack current, wherein the AC absorption unit (11) comprises: a transistor (TR1), wherein a collector terminal is connected to a first terminal of the fuel cell stack (2), an emitter terminal is connected to a second terminal of the fuel cell stack (2), and a base terminal is connected to an output terminal of the AC signal generator (12); wherein a load (R1) is connected between the first terminal of the fuel cell stack (2) and the second terminal of the fuel cell stack (2), and the stack current output from the fuel cell stack (2) is a summation of an absorption current flowing through the AC absorption unit (11) and a load current flowing through the load (R1). [2] Device (1) according to claim 1, wherein: the AC signal generator (12) changes a frequency and an amplitude based on a control signal output from a diagnosis processing unit (13) to generate the AC signal.

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