Fault diagnosis apparatus for fuel cell electric vehicle and method thereof

Abstract

A fault diagnosis device and method for fuel cell electric vehicles are provided. The device includes: a main relay connected to the fuel cell stack; a power converter connected to the main relay; a heater relay, one end connected to the fuel cell stack and the main relay, and the other end connected to the cathode oxygen consumption (COD) heater; and a fuel cell control unit (FCU) connected to the main relay, the power converter, and the heater relay. When the vehicle enters a shutdown procedure, the FCU diagnoses a fault in the main relay based on the change in stack voltage controlling the opening and closing of the heater relay, and the power of the power converter, which is variablely controlled according to the voltage of the power converter, and outputs a diagnostic result.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2020-0169807, filed with the Korean Intellectual Property Office on December 7, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to a fault diagnosis device and method for fuel cell electric vehicles. Background Technology

[0004] With increasing focus on reducing environmental pollution, research into environmentally friendly energy sources has been actively pursued. Among these, fuel cell systems, which utilize the electrochemical reaction between hydrogen and oxygen, have attracted significant attention. Fuel cell electric vehicles equipped with such systems use electricity generated by the fuel cell to drive an electric motor.

[0005] The stack master relay used in fuel cell electric vehicles cannot be internally diagnosed when a fusion fault occurs. Therefore, existing technology uses a separate function to detect fusion faults in the master relay. However, because the fusion fault of the master relay and the operating delay fault of the cathode oxygen consumption (COD) heater are similar, the master relay fusion fault is often misdiagnosed as a COD heater fault. When the master relay fusion fault is misdiagnosed as a COD heater fault, the cause of the fault cannot be accurately located, and maintenance errors may occur. Furthermore, even if the heater relay is conducting when the master relay fusion fault occurs, the COD heater cannot be operated because it is impossible to forcibly discharge the remaining voltage in the stack. Therefore, the stack's durability may be reduced, and the time required to shut down the vehicle will be longer. Summary of the Invention

[0006] This disclosure aims to address the aforementioned problems in the prior art while maintaining the advantages achieved by the prior art.

[0007] One aspect of this disclosure provides a fault diagnosis apparatus and method for fuel cell electric vehicles for detecting and diagnosing a blown main relay fault in the stack of a fuel cell electric vehicle.

[0008] The technical problems to be solved by this invention are not limited to those described above. Those skilled in the art to which this disclosure pertains should clearly understand from the following description any other technical problems not mentioned herein.

[0009] According to one aspect of this disclosure, a fault diagnosis device for a fuel cell electric vehicle may include a main relay connected to the fuel cell stack. The device may also include a power converter connected to the main relay; and a heater relay, one end connected to the fuel cell stack and the main relay and the other end connected to the cathode oxygen consumption (COD) heater. The device may further include a fuel cell control unit (FCU), the power converter, and the heater relay connected to the main relay. When the vehicle enters a shutdown procedure, the FCU may diagnose a fault in the main relay based on changes in the stack voltage controlling the heater relay to open and close, and the power of the power converter, which is variablely controlled according to the voltage of the power converter, and may output a diagnostic result.

[0010] When the vehicle enters the shutdown procedure, the FCU can monitor the stack voltage for a predetermined period of time starting from the time the heater relay is turned on, in order to determine whether the depletion of the stack voltage is delayed.

[0011] The FCU can detect the first pile voltage after the heater relay is disconnected, and can detect the second pile voltage after the heater relay is turned on. It can also use the first and second pile voltages to calculate the change in pile voltage.

[0012] When the change in stack voltage is less than the reference change, the FCU can primarily determine the fault of the main relay.

[0013] When the change in stack voltage is not less than the reference change, the FCU can determine the operating delay fault of the COD heater.

[0014] The FCU can variably control the output voltage of the power converter to an upper limit voltage and a lower limit voltage.

[0015] When the output voltage of the power converter is variably controlled to the upper limit voltage, the FCU can detect the power of the first power converter. When the output voltage of the power converter is variably controlled to the lower limit voltage, the FCU can also detect the power of the second power converter. The FCU can also make a secondary judgment on the fault of the main relay based on whether the power of the first power converter and the power of the second power converter meet the fault diagnosis conditions of the main relay.

[0016] The FCU can determine a main relay fuse failure when the power of the first power converter is less than the first reference power, and when the power of the second power converter is greater than the first reference power and less than the second reference power.

[0017] When the power of the first power converter is greater than or equal to the first reference power, and when the power of the second power converter is less than or equal to the first reference power but greater than or equal to the second reference power, the FCU can determine the operating delay fault of the COD heater.

[0018] The power converter can be implemented as a bidirectional high-voltage DC-DC converter (BHDC).

[0019] According to another aspect of this disclosure, a fault diagnosis method for a fuel cell electric vehicle, including a fuel cell control unit (FCU) connected to a fuel cell stack, a power converter, and a heater relay, may include detecting whether the vehicle has entered a shutdown procedure. The method may further include diagnosing a fault in the main relay when the vehicle enters a shutdown procedure, based on changes in the stack voltage controlling the opening and closing of the heater relay and the power of the power converter, which is variablely controlled based on the voltage of the power converter. The method may further include outputting the fault diagnosis result of the main relay.

[0020] Diagnosing a fault in the main relay may include monitoring the stack voltage for a predetermined period of time starting from the time the heater relay is turned on; and determining whether the depletion of the stack voltage is delayed based on the results of the stack voltage monitoring.

[0021] Diagnosing a fault in the main relay may include: detecting the static voltage when the heater relay is open and closed and calculating the change in stack voltage. Diagnosis may also include determining whether the change in stack voltage is less than a reference change. If the change in stack voltage is less than the reference change, the primary focus may be on identifying a fault in the main relay.

[0022] Fault diagnosis of the main relay can include identifying the operating delay fault of the COD heater when the change in stack voltage is not less than the reference change.

[0023] Fault diagnosis of the main relay may include variably controlling the output voltage of the power converter to an upper limit voltage to detect the power of the first power converter. Diagnosis may also include variably controlling the output voltage of the power converter to a lower limit voltage to detect the power of the second power converter. Furthermore, diagnosis may include a secondary determination of the main relay fault when the power of the first power converter and the power of the second power converter meet the main relay fault diagnosis criteria.

[0024] The secondary determination may include determining a main relay fuse failure when the power of the first power converter is less than the first reference power, and when the power of the second power converter is greater than the first reference power and less than the second reference power.

[0025] The fault diagnosis of the main relay may also include determining the COD heater operation delay fault when the power of the first power converter and the power of the second power converter do not meet the fault diagnosis conditions of the main relay. Attached Figure Description

[0026] The above and other objects, features and advantages of this disclosure should become more apparent from the following detailed description taken in conjunction with the accompanying drawings:

[0027] Figure 1 This is a block diagram illustrating the configuration of a fault diagnosis device for a fuel cell electric vehicle according to an embodiment of the present disclosure;

[0028] Figure 2 This is a flowchart of a fault diagnosis method for fuel cell electric vehicles according to an embodiment of the present invention; and

[0029] Figure 3 This is a diagram illustrating the fault diagnosis effect of a fuel cell electric vehicle according to an embodiment of the present disclosure. Detailed Implementation

[0030] In the following, some embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. When adding reference numerals to components in each drawing, it should be noted that the same numerals are used to denote components that are shown as identical or equivalent components in other drawings. Furthermore, in describing embodiments of the present disclosure, detailed descriptions of well-known features or functions have been omitted to avoid unnecessarily obscuring the spirit of the disclosure.

[0031] In describing components according to embodiments of this disclosure, terms such as first, second, "A", "B", (a), (b), etc., may be used. These terms are intended only to distinguish one component from another, and they do not limit the nature, order, or arrangement of the constituent components. Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as those commonly understood by one of ordinary skill in the art to which this disclosure pertains. Terms defined in general dictionaries should be interpreted as having a meaning consistent with the context in the art. Unless expressly defined in this application as having an ideal or overly formal meaning, such terms should not be interpreted as having an ideal or overly formal meaning. When a component, apparatus, element, etc., of this disclosure is described as having a purpose or performing an operation, function, etc., the component, apparatus, or element should be considered herein as being "configured" to satisfy that purpose or perform that operation or function.

[0032] Figure 1 This is a block diagram illustrating the configuration of a fault diagnosis device for a fuel cell electric vehicle according to an embodiment of the present disclosure.

[0033] Reference Figure 1 The fault diagnosis device for fuel cell electric vehicles may include a fuel cell stack (hereinafter referred to as "stack") 110, a power converter 120, a high-voltage battery 130, a cathode oxygen consumption (COD) heater 140, a fuel cell control unit (FCU) 150, a first main relay RL1, a second main relay RL2 and a heater relay RL3.

[0034] Stack 110 can generate electrical energy through an electrochemical reaction between hydrogen supplied from a hydrogen tank (not shown) and oxygen collected from outside air. Stack 110 may include two catalyst electrodes, in other words, an anode and a cathode. When hydrogen and oxygen are supplied to the anode and cathode respectively, the anode can separate the hydrogen into protons, namely hydrogen ions and electrons. Hydrogen ions can move across the electrolyte layer to the cathode and combine with oxygen in the cathode to produce water. Electrons generate an electric current through an external circuit. In other words, electrical energy can be generated due to the potential difference between the anode and cathode. The electrical energy generated by stack 110 can be used as driving energy for an electric motor (not shown).

[0035] The power converter 120 can convert power output from or input to the high-voltage battery 130. For example, the power converter 120 can convert the voltage output from the high-voltage battery 130 into the voltage required to drive a motor to output the converted voltage. Furthermore, the power converter 120 can convert the voltage output from the stack 110 into the charging voltage required to charge the high-voltage battery 130. This power converter 120 can be implemented as a bidirectional high-voltage DC-DC converter (BHDC).

[0036] The power converter 120 can change its output voltage under the command of the FCU 150. The power converter 120 can adjust the output voltage to an upper or lower limit voltage. Here, the upper and lower limits voltage can be preset to the maximum and minimum operating voltages of the power converter 120.

[0037] The first main relay RL1 and the second main relay RL2 can be arranged between the stack 110 and the power converter 120. The first main relay RL1 and the second main relay RL2 can be collectively referred to as the stack main relays. The first main relay RL1 can be connected to the negative (-) terminal of the stack 110 and the second main relay RL2 can be connected to the positive (+) terminal of the stack 110. In the specification, the first main relay RL1 and the second main relay RL2 can be used interchangeably with the negative (-) main relay and the positive (+) main relay, respectively.

[0038] The high-voltage battery 130 can store (charge) electrical energy generated by the stack 110 or can emit (discharge) the stored electrical energy. The high-voltage battery 130 can receive power converted by the power converter 120 or can transmit the stored power to the power converter 120.

[0039] When the fuel cell is turned on (started) and off (stopped or shut down), the COD heater 140 can function as an internal resistance load to forcibly discharge the residual voltage in the stack 110, thereby improving the durability of the stack 110. In other words, the COD heater 140 can remove residual oxygen and hydrogen in the stack 110 during vehicle start-up and shutdown to prevent stack 110 degradation.

[0040] COD heater 140 can be connected to the negative (-) terminal of the first main relay RL1 and stack 110, and can also be connected to one end of heater relay RL3. The other end of heater relay RL3 can be connected to the positive (+) terminal of stack 110 and the second main relay RL2. Heater relay RL3 can be turned on or off upon command from FCU 150.

[0041] The FCU 150 can connect to the power converter 120, the first main relay RL1, the second main relay RL2, and the heater relay RL3 via an in-vehicle communication network. The in-vehicle communication network can be implemented as a Controller Area Network (CAN), a Media-Oriented System Transmission (MOST) network, a Local Interconnect Network (LIN), Ethernet, or Flexray.

[0042] FCU 150 can control the on and / or off of the first main relay RL1 and / or the second main relay RL2, and can control the power converter 120 to drive the drive motor (not shown) through power transfer and power conversion between the stack 110 and the high-voltage battery 130.

[0043] FCU 150 can activate main relays RL1 and RL2 to operate the high-voltage system. Furthermore, in situations requiring operation of the COD heater 140 to control the depletion of residual voltage in the stack 110 via the COD heater 140 (e.g., fuel cell start-up / stop and other drive conditions), FCU 150 can deactivate the second main relay RL2 and activate the heater relay RL3.

[0044] When the depletion of the stack voltage is delayed when the fuel cell electric vehicle is shut down, the FCU 150 can diagnose a main relay blowout fault. When the second main relay RL2 blows, the COD heater 140 cannot function regardless of the control of the heater relay RL3, and because current is continuously supplied from the high-voltage battery 130, voltage depletion may be delayed. The FCU 150 can send commands for each drive condition to control the on and / or off of the main relays RL1 and RL2 and the heater relay RL3, control the voltage of the power converter 120, and perform power transfer and conversion.

[0045] The FCU 150 may include communication circuitry 151, processor 152, and memory 153. Communication circuitry 151 may transmit (send) control signals to at least one of the power converter 120, first main relay RL1, second main relay RL2, and heater relay RL3 using an in-vehicle communication network. Furthermore, communication circuitry 151 may receive status signals (e.g., on or off signals) transmitted from at least one of the power converter 120, first main relay RL1, second main relay RL2, and heater relay RL3.

[0046] Processor 152 performs overall control of FCU 150. Processor 152 can be implemented as at least one of Application-Specific Integrated Circuit (ASIC), Digital Signal Processor (DSP), Programmable Logic Device (PLD), Field-Programmable Gate Array (FPGA), Central Processing Unit (CPU), Microcontroller, and Microprocessor. Memory 153 can be a non-transitory storage medium that stores instructions executed by processor 152. Memory 153 can store data generated according to the operation of processor 152 and can store various setting information. Memory 153 can be implemented as at least one of storage media (recording media), such as flash memory, hard disk, Random Access Memory (RAM), Static RAM (SRAM), Read-Only Memory (ROM), Programmable ROM (PROM), Electrically Erasable Programmable ROM (EEPROM), Erasable Programmable ROM (EPROM), and registers.

[0047] Processor 152 can determine whether the vehicle has entered a shutdown procedure. Processor 152 can receive information (signals) that provide notification that the vehicle has entered a shutdown procedure from a higher-level controller (e.g., vehicle control unit (VCU) or sensors via communication circuit 151.

[0048] When the vehicle enters the shutdown procedure, the processor 152 can activate the heater relay RL3 to operate the COD heater 140. In this case, the COD heater 140 can discharge any remaining voltage in the stack 110. The processor 152 can monitor the output voltage (i.e., stack voltage) of the stack 110 for a predetermined time T starting from the time the heater relay RL3 is activated. In this case, the processor 152 can use a voltage sensor, voltmeter, etc., to monitor the stack voltage.

[0049] Processor 152 can determine whether the stack voltage is greater than a reference voltage during a predetermined time period. When the static voltage is greater than the reference voltage during the predetermined time period, processor 152 can determine that the stack main relay may have failed. When the static voltage drops to equal to or less than the reference voltage within the predetermined time period, processor 152 can determine that the stack main relay (or main relay) is normal.

[0050] When the static voltage exceeds a reference voltage within a predetermined time, processor 152 can perform preliminary fault diagnosis to determine if the main relay has failed. Processor 152 can monitor changes in stack voltage by controlling the opening and closing of heater relay RL3 to preliminarily determine if the main relay has failed. Processor 152 can change heater relay RL3 from the closed state to the open state to detect the first stack voltage, and can change heater relay RL3 from the open state to the closed state to detect the second stack voltage. Processor 152 can use the first and second stack voltages to calculate the change in stack voltage. Processor 152 can determine whether the change in static voltage is less than a reference change to preliminarily determine if the main relay or COD heater 140 has failed. Here, the reference change can be preset based on experimental values. When the change in static voltage is greater than or equal to the reference change, processor 152 can determine that COD heater 140 has failed.

[0051] When the change in static voltage is less than a reference change, processor 152 can perform secondary fault diagnosis. Processor 152 can variably control the output voltage (power converter voltage) of power converter 120 to monitor the output power (power converter power) of power converter 120. Processor 152 can control power converter 120 to output an upper limit voltage. At this time, processor 152 can use a power sensor or the like to detect the first power converter power. Furthermore, processor 152 can control power converter 120 to output a lower limit voltage, and can detect the second power converter power when the power converter voltage is at the lower limit voltage. Processor 152 can determine whether the power converter power meets the main relay fault diagnosis conditions to secondaryly determine whether the main relay or COD heater 140 is faulty. When the power converter power meets the main relay fault diagnosis conditions, processor 152 can determine (locate) a main relay fuse failure. When the power converter power does not meet the main relay fault diagnosis conditions, processor 152 can determine that the COD heater 140 has failed. In other words, when the power of the first power converter is less than the first reference power, and the power of the second power converter is greater than the first reference power and less than the second reference power, the processor 152 can determine that the second main relay RL2 has a blown fuse. Simultaneously, when the power of the first power converter is greater than or equal to the first reference power, or when the power of the second power converter is less than or equal to the first reference power and greater than or equal to the second reference power, the processor 152 can determine that the COD heater 140 has an operating delay fault.

[0052] When fault diagnosis is complete, processor 152 can store diagnostic codes indicating the diagnosed fault in memory 153 and output the diagnostic codes on an output device (e.g., display, dashboard, etc.). When a positive (+) main relay fuse fault is located (determined), processor 152 can store the diagnostic code corresponding to the fault in memory 153 and display the diagnostic code on the display. When a fault is determined in COD heater 140, processor 152 can store diagnostic codes indicating a fault in COD heater 140 in memory 153 and turn on the warning light indicating a running delay fault in COD heater 140 on the dashboard.

[0053] Figure 2 This is a flowchart illustrating a fault diagnosis method for a fuel cell electric vehicle according to an embodiment of the present disclosure.

[0054] Reference Figure 2 In S100, Figure 1 The FCU 150 can determine whether the vehicle has entered a shutdown procedure. When Figure 1 When stack 110 begins to shut down, FCU 150 can be disconnected. Figure 1 The second main relay RL2 can be turned on. Figure 1 The heater relay RL3 is used to operate Figure 1 COD heater 140. COD heater 140 can discharge the remaining voltage in stack 110.

[0055] When the vehicle enters the shutdown procedure, in S110, FCU 150 can monitor the output voltage (hereinafter referred to as "stall voltage") of stack 110 during a predetermined time Tl starting from the time when heater relay RL3 is turned on. FCU 150 can use a voltage sensor or the like to monitor the stack voltage.

[0056] In S120, FCU 150 can determine whether the stack voltage is greater than the reference voltage. When the quiescent voltage is greater than the reference voltage during a predetermined time period, FCU 150 can determine that the stack voltage has not been properly depleted. In other words, when the quiescent voltage is greater than the reference voltage within a predetermined time period, FCU 150 can determine that the depletion of the stack voltage is delayed.

[0057] When the stack voltage is greater than the reference voltage, in S130, FCU 150 can control the off / on switching of heater relay RL3 to monitor the change in stack voltage. FCU 150 can disconnect heater relay RL3 and then reconnect it. When heater relay RL3 is disconnected, FCU 150 can detect the stack voltage (first stack voltage) using a voltmeter, voltage sensor, etc., and can detect the stack voltage (second stack voltage) when heater relay RL3 is connected. FCU 150 can use the first and second stack voltages to calculate the voltage amount in the stack voltage.

[0058] In S140, FCU 150 can determine whether the change in stack voltage is less than a reference change. Because when the change in stack voltage is less than the reference change, the COD heater 140 cannot be operated due to a main relay fuse failure, so FCU 150 can preliminarily determine that the main relay has failed.

[0059] When the change in stack voltage is less than the reference change, FCU 150 can be variably controlled in S150. Figure 1 The output voltage of the power converter 120. When a failure of the main relay is initially determined, the FCU 150 can control the upper and lower limits of the output voltage of the power converter 120. When the output voltage of the power converter 120 drops to the lower limit voltage, the stack voltage decreases, so the FCU 150 can shorten the time taken to discharge the remaining voltage of the stack 110 despite the main relay fuse failure.

[0060] In S160, FCU 150 can monitor the output power of power converter 120 based on the variable control of the voltage of power converter 120. When the power converter voltage is at the upper limit voltage, FCU 150 can detect the first power converter power, and when the power converter voltage is at the lower limit voltage, it can detect the second power converter power.

[0061] In S170, FCU 150 can determine whether the power of power converter 120 meets the main relay fault diagnosis conditions. FCU 150 can determine whether the power of the first power converter is less than the first reference power, and whether the power of the second power converter is greater than the first reference power and less than the second reference power.

[0062] When the power of the power converter 120 meets the main relay fault diagnosis conditions, in S180, the FCU 150 can determine that the main relay is blown. When the power of the first power converter is less than the first reference power, and when the power of the second power converter is greater than the first reference power and less than the second reference power, the FCU 150 can determine that the positive (+) main relay RL2 is blown.

[0063] When a main relay fuse failure is determined, in S190, FCU 150 can store and display the diagnostic code corresponding to the determination result. FCU 150 can store the diagnostic code... Figure 1 The diagnostic code can be stored in the memory 153 and can be output on a display device such as a monitor or dashboard.

[0064] When the static voltage is not greater than the reference voltage in S120, FCU 150 can determine that main relays RL1 and RL2 are normal in S200. When the stack voltage drops to equal to or less than the reference voltage due to normal depletion of the stack voltage within a predetermined time, FCU 150 can determine that main relays RL1 and RL2 are normal. In other words, when there is no delay in the depletion of the stack voltage, FCU 150 can determine that main relays RL1 and RL2 are normal.

[0065] In S140, when the change in stack voltage is not less than the reference change, or in S170, when the power of power converter 120 does not meet the main relay fault diagnosis conditions, FCU 150 can locate a heater fault (heater operation delay fault) in S210. When the stack voltage is depleted through normal operation of COD heater 140, because the change in stack voltage is much greater than the reference change, FCU 150 can determine a heater operation delay fault when the change in stack voltage is greater than or equal to the reference change. FCU 150 can determine a heater operation delay fault when the power of the first power converter is greater than or equal to the first reference power, or when the power of the second power converter is less than the first reference power but greater than or equal to the second reference power. When a heater operation delay fault is determined, FCU 150 can output a warning indicating the fault through an output device (e.g., display, speaker, etc.).

[0066] Figure 3 This is a diagram illustrating the fault diagnosis effect of a fuel cell electric vehicle according to an embodiment of the present disclosure.

[0067] Reference Figure 3 ,when Figure 1 When the positive (+) main relay RL2 of stack 110 experiences a fuse failure, the positive (+) main relay RL2 can be disconnected and the circuit can be reconnected. Figure 1 The heater relay RL3. However, because Figure 1 The COD heater 140 was not operating, so the stack voltage could remain above the reference voltage V1 for a certain period of time T1 without being properly depleted.

[0068] when Figure 1 FCU 150 execution Figure 1When the power converter 120 is under constant voltage control, because the output current of the power converter 120 is a constant current output, the power of the power converter can be output as a fixed value. At this time, the power of the power converter may be lower than the first reference power.

[0069] Based on these results, the fault diagnosis device for fuel cell electric vehicles can monitor changes in stack voltage by controlling the opening / closing of the heater relay RL3, and monitor the power converter power by controlling the variable control of the power converter voltage. Therefore, stack main relay blowout faults can be accurately detected.

[0070] According to embodiments of this disclosure, the fault diagnosis device can detect a blown fuse in the main relay connected to the positive (+) terminal of the fuel cell stack. Therefore, appropriate fail-safe operation can prevent a reduction in stack durability.

[0071] Furthermore, according to embodiments of this disclosure, the fault diagnosis device can diagnose a blown fuse fault in the positive (+) main relay. Therefore, maintenance errors due to incorrect diagnosis of a COD heater relay fault can be prevented, and the continued operation of the positive (+) main relay in a blown fuse fault state can be prevented.

[0072] Furthermore, according to embodiments of this disclosure, even if the COD heater is not operating, when the vehicle starts or stops due to a blown positive (+) main relay, the fault diagnosis device can shorten the time spent draining the remaining voltage in the stack by controlling the voltage of the power converter. Additionally, the fault diagnosis device can prevent a reduction in stack durability due to the COD heater not operating. Therefore, maintenance costs associated with replacing the fuel cell can be saved.

[0073] While this disclosure has been described above with reference to embodiments and accompanying drawings, it is not limited thereto. Those skilled in the art to which this disclosure pertains can make various modifications and changes to the embodiments without departing from the spirit and scope of this disclosure as claimed in the appended claims. Therefore, the embodiments of this disclosure are provided to explain the spirit and scope of this disclosure, and not to limit the spirit and scope of the invention. Thus, the spirit and scope of this disclosure are not limited by these embodiments. The scope of protection of this invention should be determined by the appended claims, and all technical ideas within the scope of equivalent claims should be included within the scope of protection of this disclosure.

Claims

1. A failure diagnosis device for a fuel cell electric vehicle, the failure diagnosis device comprising: a main relay connected to a fuel cell stack; a power converter connected to the main relay; a heater relay connected at one end to the fuel cell stack and the main relay and connected at the other end to a cathode oxygen-consuming heater; and a fuel cell control unit connected to the main relay, the power converter, and the heater relay, wherein, when the vehicle enters a shutdown procedure, the fuel cell control unit diagnoses a failure of the main relay based on an amount of change in a stack voltage according to control of turning off and on of the heater relay, and a power of the power converter according to variable control of a voltage of the power converter, and outputs a diagnosis result; wherein the fuel cell control unit variably controls an output voltage of the power converter to an upper limit voltage and a lower limit voltage; wherein, when the output voltage of the power converter is variably controlled to the upper limit voltage, the fuel cell control unit detects a first power converter power, when the output voltage of the power converter is variably controlled to the lower limit voltage, a second power converter power, and whether the first power converter power and the second power converter power satisfy a main relay failure diagnosis condition is judged twice to determine a failure of the main relay.

2. The failure diagnosing apparatus according to claim 1, wherein When the vehicle enters the shutdown procedure, the fuel cell control unit monitors the stack voltage for a predetermined time from a time of turning on of the heater relay to determine whether depletion of the stack voltage is delayed.

3. The failure diagnosing apparatus according to claim 1, wherein The fuel cell control unit detects a first stack voltage after turning off the heater relay and a second stack voltage after turning on the heater relay, and calculates the amount of change in the stack voltage using the first stack voltage and the second stack voltage.

4. The failure diagnosing apparatus according to claim 3, wherein When the amount of change in the stack voltage is less than a reference amount of change, the fuel cell control unit preliminarily determines a failure of the main relay.

5. The failure diagnosing apparatus according to claim 4, wherein When the amount of change in the stack voltage is not less than the reference amount of change, the fuel cell control unit determines a delay in operation of the cathode oxygen-consuming heater.

6. The failure diagnosing apparatus according to claim 1, wherein When the first power converter power is less than a first reference power, and when the second power converter power is greater than the first reference power and less than a second reference power, the fuel cell control unit determines a failure of the main relay to be blown.

7. The failure diagnosing apparatus according to claim 6, wherein When the first power converter power is greater than or equal to the first reference power, or when the second power converter power is less than or equal to the first reference power and greater than or equal to the second reference power, the fuel cell control unit determines a delay in operation of the cathode oxygen-consuming heater.

8. The failure diagnosing apparatus according to claim 1, wherein The power converter is implemented as a bidirectional high-voltage DC-DC converter.

9. A failure diagnosis method for a fuel cell electric vehicle including a main relay connected to a fuel cell stack, a power converter connected to the main relay, a heater relay having one end connected to the fuel cell stack and the main relay and the other end connected to a cathode oxygen consuming heater, and a fuel cell control unit connected to the main relay, the power converter, and the heater relay, the failure diagnosis method comprising: detecting whether a vehicle enters a shutdown procedure; when the vehicle enters the shutdown procedure, diagnosing a failure of the main relay based on a variation amount of a stack voltage according to control of the heater relay to be turned off and turned on, and a power of the power converter according to variable control of a voltage of the power converter; and outputting a result of the failure diagnosis of the main relay; controlling an output voltage of the power converter variably to an upper limit voltage to detect a first power converter power; controlling the output voltage of the power converter variably to a lower limit voltage to detect a second power converter power; and when the first power converter power and the second power converter power satisfy a main relay failure diagnosis condition, secondarily determining a failure of the main relay. the failure diagnosis of the main relay includes:

10. The failure diagnosis method according to claim 9, wherein monitoring the stack voltage for a predetermined time from a time when the heater relay is turned on; and determining whether depletion of the stack voltage is delayed based on a result of the monitoring of the stack voltage. the failure diagnosis of the main relay includes:

11. The failure diagnosis method according to claim 9, wherein detecting a static voltage at the time when the heater relay is turned off and turned on and calculating the variation amount of the stack voltage; determining whether the variation amount of the stack voltage is less than a reference variation amount; and when the variation amount of the stack voltage is less than the reference variation amount, preliminarily determining a failure of the main relay. the failure diagnosis of the main relay includes:

12. The failure diagnosis method according to claim 11, wherein when the variation amount of the stack voltage is not less than the reference variation amount, determining an operation delay failure of the cathode oxygen consuming heater. the secondarily determining includes:

13. The failure diagnosis method according to claim 9, wherein when the first power converter power is less than a first reference power, and when the second power converter power is greater than the first reference power and less than a second reference power, determining a fuse failure of the main relay. the failure diagnosis of the main relay further includes:

14. The failure diagnosis method according to claim 9, wherein when the first power converter power and the second power converter power do not satisfy the main relay failure diagnosis condition, determining an operation delay failure of the cathode oxygen consuming heater. ​

Images