CONTROL METHOD FOR A FUEL CELL SYSTEM

Abstract

Control procedure for a fuel cell system, comprising: Deriving, by means of a control, a voltage of a fuel cell stack (10) by charging a high-voltage battery (220); Deriving, by control, the voltage of the fuel cell stack (10) by connecting a fuel cell load device (20) to the fuel cell stack (10) when the voltage of the fuel cell stack (10) is less than a predetermined first reference voltage (V1) when the voltage is derived, wherein the fuel cell load device (20) is a load to discharge a voltage of a fuel cell when starting up or switching off the fuel cell; Adjusting, by means of the control, a voltage of a main bus connection (211) arranged between the fuel cell stack and an inverter (231) to an acceptable minimum voltage (V3) in order to prevent the output power of the fuel cell stack (10) from being supplied to loads other than the fuel cell load device (20) until a voltage of the fuel cell stack (10) reaches a predetermined second reference voltage (V2) based on the connection with the fuel cell load device (20); Diagnosing, by control, an operation of the connected fuel cell load device (20); the diagnosis of the operation of the fuel cell load device (20) includes: Diagnosing, by controlling, the operation of the fuel cell load device (20) based on a rate of decrease of the voltage of the fuel cell stack (10), wherein diagnosing the operation of the fuel cell load device (20) based on the rate of decrease of the voltage of the fuel cell stack (10) includes: Diagnosing, by controlling, the operation of the fuel cell load device (20) based on both a time required for the voltage of the fuel cell stack (10) to reach a certain voltage after the fuel cell load device (20) is connected to the fuel cell stack (10), and on a reference time required for the voltage of the fuel cell stack (10) to reach the certain voltage under normal operation of the fuel cell load device (20), wherein the reference time varies based on a vehicle speed, an amount of air inflow, a water content of the fuel cell stack (10), a crossover state within the fuel cell stack (10) and the voltage of the fuel cell stack (10) when the fuel cell load device (20) is connected to the fuel cell stack (10).

Description

BACKGROUND 1. Field of the invention

[0001] The present invention relates in general to a control method for a fuel cell system and in particular to a control method of a fuel cell system which prevents deterioration of a fuel cell stack and diagnoses a fault in a load for dissipating a residual voltage of the fuel cell stack. 2. Description of the state of the art

[0002] A fuel cell system applicable to a hydrogen fuel cell vehicle, a type of environmentally friendly vehicle, consists of a fuel cell stack for generating electricity from an electrochemical reaction of reactant gases; a hydrogen supply system designed to supply hydrogen as fuel to a fuel cell stack; an air supply system designed to supply gas, including oxygen as an oxidizing agent in electrochemical reactions; and a heat and water management system designed to circulate water and maintain an optimal fuel cell stack temperature for propulsion by releasing heat, which is a byproduct of the electrochemical reactions within it.

[0003] Fig. Figure 1 shows an exemplary schematic view representing a complete fuel cell system. As in Fig. As shown in Figure 1, the fuel cell system 100 can comprise a fuel cell stack 10, a fuel cell load device 20, an air blower 30, a humidifying device (humidifier) ​​40, air shut-off valves 35 and 45 at an inlet and outlet, a drain valve 42, a purge valve 44, a water separator 50, a hydrogen recirculation device 55, a hydrogen supply valve 57, a cooler 60, and a thermostat 65. The air shut-off valves 35 and 45 at the inlet and outlet prevent air from entering the fuel cell stack after a fuel cell vehicle is shut down. The drain valve 42 is located in a hydrogen discharge line to remove water generated at an anode, and the purge valve 44 adjusts hydrogen concentrations at the anode and discharges hydrogen to an air outlet to dilute the air.

[0004] The fuel cell load device 20, which reduces the voltage of the fuel cell stack 10 to dissipate the voltage, is connected to the fuel cell stack 10 both during and after the fuel cell vehicle is shut down to remove oxygen from within the fuel cell stack 10. The oxygen flowing into the fuel cell stack 10 is removed along with any residual hydrogen from the anode, as the fuel cell load device 20 consumes power. However, insufficient hydrogen may prevent complete oxygen consumption, and therefore a wake-up procedure is used to periodically supply hydrogen to the anode.

[0005] In other words, unlike a motor vehicle with an internal combustion engine, the fuel cell system 100 requires a post-processing procedure that reduces the voltage of the fuel cell stack 10 by removing residual air within the fuel cell stack 10 after the fuel cell vehicle is switched off. This post-processing procedure prevents deterioration of the fuel cell stack 10, thus avoiding the risk of hazards from high voltages. If a voltage builds up due to the presence of oxygen at the anode, carbon corrosion can occur at the cathode. Therefore, it is necessary to remove the oxygen within the fuel cell stack 10 and prevent any additional oxygen from entering. If additional oxygen does enter the fuel cell stack, its removal is required.As a result, when a vehicle is switched off, the system stops the supply of oxygen, intentionally consumes the remaining oxygen for a load current using the fuel cell load device 20, and reduces the voltage.

[0006] Furthermore, DE 10 2010 047 436 A1 discloses a control method for a fuel cell system, comprising: deriving, by means of a control system, a voltage of a fuel cell stack by charging a high-voltage battery; and deriving, by means of the control system, the voltage of the fuel cell stack by connecting a fuel cell load device to the fuel cell stack, if the voltage of the fuel cell stack is less than a predetermined first reference voltage when the voltage is derived.

[0007] JP 2014 - 082 856 A is a fuel cell system characterized in that it comprises: a fuel cell attached to a vehicle, provided with a gas flow path and generating energy by supplying a reaction gas to the gas flow path; a collision prediction device that predicts the possibility of a collision of the vehicle; a discharge device that discharges the fuel cell and a control device that causes the fuel cell to be discharged by the discharge device when the collision prediction means predicts that the possibility of a collision is high.

[0008] In KR 10 2006 0 108 341 A, a fuel cell system with at least one fuel cell for generating electrical energy by an electrochemical reaction of a fuel containing hydrogen, which is supplied to both surfaces of an electrolyte membrane, and hydrogen containing hydrogen supplied to a cathode electrode, is described, in which an external load coupled to the fuel cell is electrically disconnected according to an operating stop signal for the fuel cell.

[0009] JP 2001 - 229 951 A also shows a fuel cell system with: a power controller that controls the power generated by a fuel cell and the power stored in a battery; a circulation pump for a hydrogen circulation system consisting of a hydrogen separator and the fuel cell; a circulation pump that generates power by means of residual hydrogen in the hydrogen circulation system while water vapor circulates to the hydrogen circulation system when the system is stopped; and a residual hydrogen purge device for reducing the residual hydrogen concentration in the hydrogen circulation system by applying a voltage to the fuel cell from the battery while vapor circulates in the hydrogen circulation system, and residual hydrogen in the hydrogen circulation system is electrochemically transported from the fuel electrode side to the air electrode side of the fuel cell. OVERVIEW

[0010] It is an object of the present invention to provide a control method for a fuel cell system that can reduce the voltage of the fuel cell stack using a battery and a fuel cell load device and can diagnose a malfunction of the fuel cell load device.

[0011] The problem is solved by a control method for a fuel cell system with the features of claim 1. Advantageous further developments are found in the dependent claims.

[0012] A control method of a fuel cell system according to an embodiment of the present invention may comprise: deriving the voltage of a fuel cell stack by charging a high-voltage battery; deriving the voltage of the fuel cell stack by connecting a fuel cell load device to the fuel cell stack when the voltage of the fuel cell stack is less than a predetermined first reference voltage (V1) when the voltage is derived, wherein the fuel cell load device is a load to discharge a voltage of the fuel cell upon start-up or shutdown of the fuel cell; adjusting, by the control method, a voltage of a main bus terminal arranged between the fuel cell stack and an inverter to an acceptable minimum voltage (V3) to preventthat the output power of the fuel cell stack is provided to loads other than the fuel cell load device until a voltage of the fuel cell stack reaches a predetermined second reference voltage (V2), based on the connection to the fuel cell load device. The control method further comprises: diagnosing, by the controller, an operation of the connected fuel cell load device, wherein diagnosing the operation of the fuel cell load device includes: diagnosing, by the controller, the operation of the fuel cell load device based on a rate of decrease in the voltage of the fuel cell stack, wherein diagnosing the operation of the fuel cell load device based on the rate of decrease in the voltage of the fuel cell stack includes: diagnosing, by the controller,The operation of the fuel cell load device is based on both the time required for the fuel cell stack voltage to reach a specific voltage after the fuel cell load device is connected to the fuel cell stack, and a reference time required for the fuel cell stack voltage to reach the specific voltage under normal operation of the fuel cell load device. The reference time varies based on vehicle speed, airflow rate, fuel cell stack water content, crossover conditions within the fuel cell stack, and the fuel cell stack voltage when the fuel cell load device is connected to the fuel cell stack.

[0013] If the high-voltage battery cannot be charged, if an accident involving the fuel cell vehicle is detected, or if the time required for a fuel cell stack to reach a predetermined first reference voltage exceeds a specified first reference time, charging of the high-voltage battery can be stopped and the second derivation can be performed. The high-voltage battery may not be charged under certain circumstances, including if the high-voltage battery fails, a power converter connected to the high-voltage battery fails, the high-voltage battery's state of charge (SOC) exceeds a specified SOC, or a power source for charging the high-voltage battery is insufficient.When the fuel cell load device is connected to the fuel cell stack, if the voltage of the fuel cell stack is reduced so that it is less than a predetermined second reference voltage (V2), the second derivation process can be terminated.

[0014] The control procedure may further include setting the voltage of a main bus terminal, located between the fuel cell stack and an inverter, to an acceptable minimum voltage (V3) to prevent the fuel cell stack's output power from being supplied to loads other than the fuel cell load device until the fuel cell stack voltage reaches a predetermined second reference voltage (V2), as specified in the connection to the fuel cell load device. Setting the main bus terminal voltage to the acceptable minimum voltage (V3) can maintain the main bus terminal voltage at an initial value, and when the fuel cell stack voltage reaches the predetermined second reference voltage (V2), the main bus terminal voltage can be reduced to the acceptable minimum voltage (V3).

[0015] Setting the main bus terminal voltage to the acceptable minimum voltage (V3) can maintain the main bus terminal voltage higher than the voltage of a fuel cell stack. Furthermore, setting the main bus terminal voltage to the acceptable minimum voltage (V3) can involve disconnecting the fuel cell stack from the main bus terminal by switching off a main relay before connecting it to the fuel cell load device. The acceptable minimum voltage (V3) can be lower than the first reference voltage and higher than the minimum voltage required to operate a power converter connected to the high-voltage battery or high-voltage components connected to the main bus terminal.

[0016] Prior to the first derivation process, the control procedure may further include stopping the supply of air to the fuel cell stack after increasing the voltage of the fuel cell stack above the first reference voltage by supplying air to the fuel cell stack. Prior to the second derivation process, the control procedure may further include disconnecting the fuel cell stack from a main bus connection located between the fuel cell stack and an inverter by switching off a main relay.

[0017] A control method of a fuel cell system according to a further embodiment of the present invention may include: connecting a fuel cell load device to a fuel cell stack; and diagnosing the operation of the connected fuel cell load device.

[0018] Diagnosing the operation of the fuel cell load device can further include diagnosing that the fuel cell load device is failing if a difference between a set current value and a current value flowing into the fuel cell load device, or a difference between the set current value and a value of the fuel cell stack's output current, exceeds predefined tolerances. The set current value is calculated based on both the voltage of the fuel cell stack and a resistance value of the fuel cell load device. The tolerances can each be predefined based on the resolution of a sensor that detects the current value flowing into the fuel cell load device and the resolution of a sensor configured to detect the fuel cell stack's output current value.

[0019] Diagnosing the operation of the fuel cell load device based on the rate of voltage decrease of the fuel cell stack can involve diagnosing the operation of the fuel cell load device based on both the voltage of the fuel cell stack after a specific time period following connection of the fuel cell load device to the fuel cell stack, and a reference voltage that the fuel cell stack reaches after the specified time period under normal operation of the fuel cell load device. The reference voltage can vary based on vehicle speed, the amount of airflow, the water content of the fuel cell stack, a crossover condition within the fuel cell stack, or the voltage of the fuel cell stack at the moment the fuel cell load device is connected to it.

[0020] Additionally, the operation of the fuel cell load device can be diagnosed based on at least one of the following: the current delivered by the fuel cell stack and the current flowing into the fuel cell load device when the voltage of the fuel cell stack is greater than a predetermined voltage. The operation of the fuel cell load device can also be diagnosed based on the rate of voltage decrease of the fuel cell stack when the voltage of the fuel cell stack is less than a predetermined voltage.

[0021] The fuel cell load device can be connected to the fuel cell stack when the fuel cell stack voltage is lower than a predetermined first reference voltage, when the fuel cell stack voltage is derived by charging a high-voltage battery; and diagnostics of the fuel cell load device's operation can be terminated when the fuel cell stack voltage drops below a predetermined second reference voltage. The predetermined voltage can be higher than the predetermined second reference voltage and lower than the predetermined first reference voltage.

[0022] If the voltage of the fuel cell stack is greater than the specified voltage, or if a difference between a set current value and a current value flowing into the fuel cell load device, or a difference between the set current value and a value of an output current of the fuel cell stack, is greater than specified tolerances, it can be determined that the fuel cell load device has failed, where the set current value is calculated based on the voltage of the fuel cell stack and a resistance value of the fuel cell load device.If the voltage of the fuel cell stack is lower than the specified voltage, the operation of the fuel cell load device can be diagnosed based on both a time required for the voltage of the fuel cell stack to reach a specific voltage from a diagnostic start time, and a reference time required for the voltage of the fuel cell stack to reach the specific voltage under normal operation of the fuel cell load device.

[0023] The reference time can vary based on vehicle speed, airflow rate, fuel cell stack water content, crossover conditions within the fuel cell stack, or the fuel cell stack voltage at the moment the fuel cell load device is connected. The preset voltage can be higher than the specified voltage. If the fuel cell stack voltage is lower than the preset voltage, the operation of the fuel cell load device can be diagnosed based on both the fuel cell stack voltage after a specified time has elapsed from the diagnostic start time and a reference setpoint voltage after a specified time has elapsed under normal fuel cell load device operation.

[0024] The reference voltage can vary based on vehicle speed, airflow rate, fuel cell stack water content, crossover state within the fuel cell stack, or the fuel cell stack voltage at the moment the fuel cell load device is connected. The specified voltage can be higher than the reference voltage. Furthermore, once the diagnostics of the fuel cell load device's operation are complete, the control procedure can include storing results based on the diagnostic status in a memory.

[0025] According to one embodiment of the present invention, the fuel cell system control method can improve the durability of the fuel cell system by dissipating residual oxygen from the fuel cell stack. Additionally, the method can reduce the risk of damage from high voltages by lowering the voltage of the fuel cell stack. The method can also maintain stability during vehicle restarts and improve the vehicle's fuel efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The above and further tasks, features and other advantages of the present invention will become clearer from the following detailed description in conjunction with the accompanying drawings. The figures show: Fig. 1 an exemplary schematic view representing a fuel cell system in accordance with the state of the art as a whole; Fig. 2 an exemplary block diagram of a power network of a fuel cell system according to an embodiment of the present invention; Fig. 3 an exemplary block diagram of a power network of a fuel cell system according to a further embodiment of the present invention; Fig. 4A and Fig. 4B Exemplary flowcharts illustrating a control method of a fuel cell system according to an embodiment of the present invention; Fig. 5 an exemplary block diagram of a power network of a fuel cell system according to an embodiment of the present invention; Fig. 6 an exemplary block diagram of a power network of a fuel cell system according to a further embodiment of the present invention; Fig. 7A and Fig. 7B Exemplary views showing a process for discharging the voltage of a fuel cell stack using a high-voltage battery or a process for disabling the process for discharging the voltage of the fuel cell stack using the high-voltage battery according to an embodiment of the present invention; Fig. 8 an exemplary graph showing changes in voltage and current over time when a fuel cell is switched off, according to an embodiment of the present invention; Fig. 9 An exemplary flowchart illustrating a method for diagnosing the operation of a fuel cell load device using a current value determined by a Fig. 5 shown first current sensor is detected according to an embodiment of the present invention; Fig. 10 An exemplary flowchart illustrating a procedure for diagnosing the operation of a fuel cell load device using a current value determined by a Fig. 6 second current sensor is detected, according to an embodiment of the present invention; Fig. 11A and Fig. 11B according to an embodiment of the present invention, graphene which, when a fuel cell load device is in normal operation and when the fuel cell load device fails, represents a time required to reach a certain voltage or a voltage after a certain period of time according to changes in the voltage of a fuel cell stack; Fig. 12 an exemplary flowchart illustrating a method for diagnosing the operation of a fuel cell load device according to an embodiment of the present invention; Fig. 13 an exemplary flowchart illustrating a method for diagnosing the operation of a fuel cell load device according to a further embodiment of the present invention; and Fig. 14 and Fig. 15 Flowcharts according to an embodiment of the present invention, which represent a control method of a fuel cell system according to further embodiments of the present invention. DETAILED DESCRIPTION

[0027] It is understood that the term "vehicle" or "vehicle-" or other equivalent expressions as used herein include 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 include hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other vehicles using alternative fuels (for example, fuel derived from sources other than petroleum). As referenced herein, a hybrid vehicle is a vehicle that has two or more sources of propulsion, such as both gasoline-powered and electric-powered vehicles.

[0028] Although the exemplary embodiment is described as using a plurality of units to perform the exemplary process, it is understood that the exemplary processes can also be performed by one or more modules. Furthermore, it is understood that the term "controller" refers to a hardware device comprising 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, which are described below.

[0029] Furthermore, the control logic of the present invention can be implemented as non-volatile, computer-readable media on a computer-readable medium comprising executable program instructions that are 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 can also be decentralized in networked computer systems, allowing the computer-readable medium to be stored and executed in a distributed manner, for example, by a telematics server or a controller area network (CAN).

[0030] The terminology used herein is intended for the purpose of describing certain embodiments and is not intended to limit the invention. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly indicates otherwise. It is further understood that the expressions "possess" and / or "possessing," when used in this description, describe the presence of the specified features, numbers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more features, numbers, steps, operations, elements, components, and / or groups thereof. As used herein, the expression "and / or" includes any and all combinations of one or more of the associated listed elements.

[0031] Unless expressly stated otherwise or evident from the context, the term "approximately" as used herein is understood to mean that the value lies within a range of standard tolerances in the prior art, for example, within two standard deviations of the mean values. "Approximately" may be understood to mean that the value lies 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".

[0032] Specific structural or functional descriptions in the embodiments of the present invention, disclosed in this description or application, are provided only to illustrate the embodiments of the present disclosure. These descriptions can be given in various forms and should not be considered limited to the embodiments described in the description or application.

[0033] Certain embodiments are illustrated in the drawings and described in detail in the description or application because the embodiments of the present invention can have various forms and modifications. It is understood, however, that there is no intention to limit the embodiments of the present invention to the specific embodiments shown, but rather that it is intended to cover all modifications, equivalents, and alternatives that are included within the scope of protection of the present invention.

[0034] Although the terms "first", "second", etc. may be used herein to describe different elements, these elements should not be limited by these terms. These terms are used merely to distinguish one element from another. For example, a first element could be referred to as a second element, and similarly, a second element could be referred to as a first element, without altering the scope of the present invention.

[0035] It is understood that when an element is described as being "coupled" or "connected" to another element, it may be directly coupled or connected to the other element, or there may be intermediate elements. In contrast, when an element is described as being "directly coupled" or "directly connected" to another element, there are no intermediate elements. Other words used to describe the relationship between elements should be interpreted similarly (for example, "between" versus "directly between," "adjacent" versus "directly adjacent," etc.).

[0036] Unless otherwise specified, all terms used herein (including technical and scientific terms) have the same meanings as those normally understood by a person skilled in the art in the field to which this invention belongs. It is further understood that terms such as those defined in commonly used dictionaries should be interpreted in a manner consistent with their meaning in the context of the prior art and not in an idealized or overly formal sense, unless expressly provided herein.

[0037] Reference is now made to the drawings, in which the same reference symbols are used throughout the various drawings to denote the same or similar components.

[0038] Fig. Figure 2 shows an exemplary block diagram of a power network of a fuel cell system according to an embodiment of the present invention, and Fig. Figure 3 shows an exemplary block diagram of a power network of a fuel cell system according to a further embodiment of the present invention. As in Fig. 2 and Fig. As shown in Figure 3, a fuel cell-battery hybrid system for a vehicle can comprise: a fuel cell 10 as a main power source and a high-voltage battery (main battery) 220 as an auxiliary power source, which can be connected in parallel via a main bus connector 211; a bidirectional direct current-to-direct current (DC / DC) converter (e.g.BHDC: Bidirectional high-voltage DC / DC converter) 221, which is connected to the high-voltage battery 220 to adjust the output power of the high-voltage battery 220; an inverter 231, which is connected to the main bus terminal 211 on the output side of both the fuel cell 10 and the high-voltage battery 220; a drive motor 232, which is connected to the inverter 231; a high-voltage load 233 inside the vehicle, excluding the inverter 231 and the drive motor 232; a low-voltage battery (auxiliary battery) 240 and a low-voltage load 241; a low-voltage DC / DC converter (e.g. LDC: Low-voltage DC / DC converter) 242, which connects the low-voltage battery 240 to the main bus terminal 211, which is configured to convert a high voltage to a low voltage; and a fuel cell load device 20.

[0039] Here, both the fuel cell 10 as a primary power source and the high-voltage battery 220 as an auxiliary power source can be connected in parallel via the main bus connection 211 with system-internal loads, such as the inverter 231, the drive motor 232, etc. The bidirectional DC / DC converter 221, which is connected to the high-voltage battery, can be connected to the main bus connection 211 on the output side of the fuel cell 10, and consequently, it may be possible to adjust the output power of the fuel cell 10 and the high-voltage battery 220 by setting a voltage of the bidirectional DC / DC converter 221 (e.g., an output voltage at the main bus connection).

[0040] The fuel cell 10 can include a diode 213 at one of its output terminals to prevent reverse current, and a relay 214 to optionally connect the fuel cell 10 to the main bus terminal 211. The relay 214 can be located in the Fig. The power grid shown in section 2 must be arranged, but it does not necessarily have to be in the grid shown in the diagram. Fig. The power network shown in section 3 is arranged as follows. Relay 214 in Fig. The fuel cell load device 20 can be configured to connect the fuel cell 10 to the main bus during the idle stop / restart process of the fuel cell system and while the vehicle is being driven under normal operation of the fuel cell 10 (e.g., operation without faults), and to disconnect the fuel cell 10 from the main bus after the vehicle's ignition is switched off (key off) (e.g., normal shutdown) or an emergency shutdown. The fuel cell load device 20 can be a load for dissipating a voltage from the fuel cell after the fuel cell has been started up and shut down. The fuel cell 10 and the fuel cell load device 20 can be connected to each other via a fuel cell load relay 25.

[0041] The fuel cell system in Fig. 3 eliminates relay 214, therefore it may be possible to avoid the cost of the relay and the noise caused by its operation. However, to switch off the fuel cell's output power, which is a role for relay 214 in Fig. As shown in Figure 2, the system should maintain a voltage across the bidirectional DC / DC converter 221 that is greater than the open-circuit voltage of the fuel cell stack and a limit load of both the high-voltage load 233 and the low-voltage load 241 that is within the permissible output power of the high-voltage battery without relay 214. Additionally, to reduce the time required to build up a high voltage when the fuel cell shuts down, it is necessary to dissipate the voltage. If relay 214 is included in the system, it may be possible to prevent a high voltage from building up at the bus terminal by switching off relay 214.

[0042] Fig. 4A and Fig. Figure 4B shows exemplary flowcharts illustrating a control method of a fuel cell system according to an embodiment of the present invention. Fig. 4 represents a control method in which the fuel cell system may include a main relay 214 which is configured to prevent any output power from the fuel cell from being provided to a main bus terminal while Fig. 4B represents a control procedure in which the fuel cell system does not include the main relay 214. In particular, a fuel cell controller (FCU) may be set up to execute the respective steps in the flowchart, or multiple controllers / regulators for each component within the fuel cell system, which are connected to the fuel cell controller, may be set up to execute the process.

[0043] With reference to Fig. 4A and Fig. 4B, when the fuel cell system 100 is switched off (S401), the control can be configured to determine whether the voltage of the fuel cell stack 10 is less than a predetermined first reference voltage (V1) (S403). If the voltage of the fuel cell stack 10 is less than the predetermined first reference voltage (V1), air can be supplied to the fuel cell stack 10 (S405), and the voltage of the fuel cell stack 10 can be increased until it is greater than the first reference voltage (V1) (S407), at which point the supply of air to the fuel cell stack can be stopped (S409). If the voltage of the fuel cell stack is greater than the first reference voltage (V1), the supply of air to the fuel cell stack can be prevented, and the air supply process can be terminated (S409).

[0044] In other words, stopping the air supply can be performed independently of the fuel cell voltage. However, if the voltage of the fuel cell stack 10 is substantially low, the control system can be configured to supply air to the fuel cell stack 10 to raise its voltage above the first reference voltage (V1) and then stop the air supply. If the fuel cell is shut down during the idle-stop process, the voltage of the fuel cell stack 10 is already low, and thus it can be difficult to diagnose whether the fuel cell load device 20 is operating. To diagnose whether the fuel cell load device is operating, it may be necessary to operate the fuel cell load device in a state where the voltage of the fuel cell stack 10 is as high as a certain threshold.Therefore, after air is supplied to the fuel cell stack to increase the voltage of the fuel cell stack to a certain level, the supply of air can be stopped.

[0045] After the air supply is stopped, the control system can be configured to determine whether the high-voltage battery 220 may be charged, or whether the fuel cell vehicle accident has not occurred (S411). Whether the high-voltage battery 220 may be charged can be determined based on at least one condition selected from the group consisting of: whether the high-voltage battery 220 has failed, whether the bidirectional DC / DC converter 221 connected to the high-voltage battery 220 has failed, whether the state of charge (SOC) of the high-voltage battery 220 is greater than a predetermined SOC, and whether a power source for charging the high-voltage battery 220 is insufficient.

[0046] In response to the determination that the high-voltage battery 220 may be charged, the voltage of the fuel cell stack can be consumed by charging the high-voltage battery 220, and thus the voltage of the fuel cell stack 10 can be reduced (S413). When the voltage of the fuel cell stack 10 is reduced, the control system can be configured to determine whether the voltage of the fuel cell stack 10 is less than the predetermined first reference voltage (V1) or whether the charging time of the high-voltage battery 220 is greater than a predetermined time period (T1) (S415). If the voltage of the fuel cell stack 10 is less than the predetermined first reference voltage (V1) or if the charging time of the high-voltage battery 220 is greater than the predetermined time period (T1), the charging of the high-voltage battery can be stopped (S417).

[0047] As in Fig. As shown in Figure 4B, for the system comprising the main relay 214, if the voltage of the fuel cell stack 10 is less than the specified first reference voltage, or if the charging time of the high-voltage battery is greater than the specified time (T1), the fuel cell stack 10 can be disconnected from the main bus terminal 211 by switching off the main relay 214 (S416), and the voltage of the main bus terminal 211 can be reduced to achieve a third reference voltage (V3), which can be specified to be approximately equal to or less than the first reference voltage (V1) (S417). Stopping the high-voltage battery 220 can be determined based on conditions including the voltage of the main bus terminal 211, the maximum voltage derived from the fuel cell stack that can be attributed to charging the high-voltage battery, and the like.The process for discharging the voltage of the fuel cell stack 10, which is attributable to charging the high-voltage battery 220, and the process for discharging the voltage of the fuel cell stack 10, which is attributable to operating the fuel cell load device 20, cannot be performed simultaneously.

[0048] More precisely, to prevent power from being delivered to the loads (e.g., high-voltage battery, auxiliary machinery, etc.) except for the fuel cell load device 20, the voltage of the main bus terminal 211 can be reduced to the specified third reference voltage. Furthermore, the fuel cell stack can be connected to the fuel cell load device 20 (S419). The operation of the fuel cell load device 20 can be diagnosed while the fuel cell load device 20 is connected to the fuel cell stack 10 (S421). In other words, the control system can be configured to diagnose or determine whether the fuel cell load device 20 is operating correctly and without faults, in accordance with its design purpose.

[0049] If the voltage of the fuel cell stack is reduced below a predetermined second reference voltage (V2) (S423), the diagnostic process can be terminated and the diagnostic results can be stored in memory (S425). Then, the voltage of the main bus terminal 211 can be reduced to the predetermined third reference voltage (V3) by adjusting the voltage of the power converter, the bidirectional DC / DC converter 221 (S427). The voltage of the main bus terminal 211 can be reduced to the predetermined third reference voltage to determine, based on the result of the fuel cell load device 20 diagnostics (which can indicate whether the fuel cell load device is failing), whether a warning light, etc., should be activated. This information is then read from memory the next time the vehicle is started after being switched off.

[0050] The first reference voltage (V1) can be set such that it lies within the voltage operating range of the power converter 221. Additionally, the first reference voltage can be set such that it represents a substantially lower value for the fuel cell vehicle's fuel efficiency, while it can be set such that it represents a substantially higher value for diagnosing whether the fuel cell load device 20 is failing. The third reference voltage (V3) can be a reference voltage for reducing the voltage of the main bus terminal 211 to maintain stability for restarting, and can be set such that it represents a minimum voltage for driving the loads (e.g., auxiliary machines, etc.) in the fuel cell system 100 within the voltage operating range of the power converter 221.The first reference voltage (V1) can be approximately equal to or greater than the third reference voltage (V3). Additionally, the third reference voltage (V3) can be greater than the minimum voltage required to operate the power converter 221 connected to the high-voltage battery 220 or high-voltage components connected to the main bus terminal 211.

[0051] The fuel cell system 100, which does not include the main relay 214, may omit the process of reducing the voltage of the main bus terminal 211 (S417) before stopping the charging of the high-voltage battery 220, or if the system performs step S417, the system may be configured to prevent the power of the fuel cell stack 10 from being delivered to the loads including the high-voltage battery 220, with the exception of the fuel cell load device 20.

[0052] Fig. Figure 5 shows an exemplary block diagram of a power network of a fuel cell system according to an embodiment of the present invention and Fig. Figure 6 shows an exemplary block diagram of a power network of a fuel cell system according to a further embodiment of the present invention. The description of the same components and configurations that are shown in Figure 6 is similar to those in Figure 6. Fig. The figures shown in point 3 are omitted. With reference to Fig. 5. The fuel cell system can be used in Fig. 5 further comprising a first current sensor 27 configured to detect the magnitude of a current flowing to the fuel cell load device 20. Current sensors adapted to the current range flowing to the fuel cell load device can be used as the first current sensors 27. The in Fig. The fuel cell system shown in Figure 6 can include a second current sensor 29, configured to detect an output current of the fuel cell stack 10, instead of the first current sensor 27 for sensing the current flowing to the fuel cell load device 20. In particular, since the output current of the fuel cell stack 10 can have a larger range than the current flowing to the fuel cell load device 20, the second current sensor can be capable of performing a high-resolution current measurement.

[0053] Fig. 7A and Fig. Figure 7B shows exemplary views illustrating a process for deriving the voltage of a fuel cell stack 10 using a high-voltage battery 220 and a process for disabling the process of deriving the voltage of the fuel cell stack 10 using the high-voltage battery 220. Deriving the voltage of the fuel cell stack 10 using the high-voltage battery 220 can be performed until the voltage reaches the predetermined third reference voltage (V3). The voltage of the main bus terminal 211 can be reduced over time, but the acceptable minimum voltage can be limited to the third reference voltage (V3) (e.g., the voltage of the main bus terminal can be set to an acceptable minimum voltage (V3)).The third reference voltage or the acceptable minimum voltage (V3) can be specified such that it is the lower value between the minimum operating voltage of the bidirectional DC / DC converter 221 and the minimum drive voltage of the high-voltage load 233.

[0054] Fig. Figure 7B illustrates when the voltage of the main bus terminal 211 is maintained over time, or when the minimum voltage limit of the main bus terminal 211 varies and the voltage of the main bus terminal 211 is reduced based on the varying minimum voltage limit. The minimum voltage limit can be determined to be the greater of the value between the voltage of the fuel cell stack 10 and the third reference voltage (V3) in order to keep the voltage of the main bus terminal 211 higher than the output voltage of the fuel cell stack 10, thereby preventing the output power of the fuel cell stack 10 from being supplied to the loads except for the fuel cell load device 20.

[0055] Fig. Figure 8 shows an example graph illustrating changes in voltage and current over time when a fuel cell is switched off. Section 1 represents a section in which the voltage of the fuel cell stack 10 is derived by charging the high-voltage battery 220, and Section 2 represents a section in which the voltage of the fuel cell stack 10 is derived using the fuel cell load device 20. Section 2 allows for the diagnosis of the operation of the fuel cell load device 20. Furthermore, Section 2 allows the main relay 214 to be switched off to prevent the high-voltage battery 220 from being charged by the fuel cell stack 10 or to prevent the output power of the fuel cell stack 10 from being supplied to the auxiliary machinery.Additionally, a reduction of the voltage of the main bus terminal 211 can be deactivated using the bidirectional DC / DC converter 221 and the in . Fig. Voltage regulation 2 shown in 7B can be carried out.

[0056] Fig. Figure 9 shows an exemplary flowchart illustrating a procedure for diagnosing the operation of a fuel cell load device 20 using a current value determined by the Fig. The first current sensor 27 shown in section 5 is detected. Fig. Figure 10 shows an exemplary flowchart illustrating a method for diagnosing the operation of a fuel cell load device 20 using a current value determined by the Fig. The second current sensor shown in section 6 is detected.

[0057] With reference to Fig. 9 and Fig. 10 The control method according to an embodiment of the present invention can include diagnosing the operation of the fuel cell load device 20 connected to the fuel cell stack 10, and diagnosing the operation of the fuel cell load device 20 can include calculating an estimated current value (I est ) based on both the voltage of the fuel cell stack 10 and a resistance value of the fuel cell load device 20 (S701, S801). If the difference between the estimated current value (I est ) and a value of the current flowing into the fuel cell load device 20 (I real-load ) or the difference between the estimated current value (I est ) and a value of the output current of the fuel cell stack 10 (I real-fuelcellIf the current value (K, M) is greater than a predefined tolerance (S703, S803), the controller can be configured to determine that the fuel cell load device 20 fails (S705, S805). The predefined tolerance (K, M) can be set differently based on the resolution of the first current sensor 27 of the fuel cell load device 20 and the resolution of the second current sensor 29 of the fuel cell stack 10.

[0058] Fig. 11A and Fig. Figure 11B shows exemplary graphs that, when the fuel cell load device is in normal operation (e.g., when no fault or failure occurs) and when the fuel cell load device fails, represent a time required to reach a certain voltage or a voltage after a certain time period based on changes in the voltage of the fuel cell stack.

[0059] With reference to Fig. 11A can be used to diagnose the operation of the fuel cell load device 20 based on the rate of decrease of the voltage of the fuel cell stack 10. The operation of the fuel cell load device 20 can be diagnosed based on both the time required for the voltage of the fuel cell stack 10 to reach a certain voltage (V11) after the fuel cell load device 20 is connected to the fuel cell stack 10, and a reference time (T_f) required for the voltage of the fuel cell stack 10 to reach the certain voltage (V11) under the normal operation of the fuel cell load device 20.

[0060] With reference to Fig. 11B can be used to diagnose the operation of the fuel cell load device based on the rate of decrease of the voltage of the fuel cell stack. The operation of the fuel cell load device 20 can be diagnosed based on both the voltage of the fuel cell stack 10 when a certain time period (T11) has elapsed after the fuel cell load device 20 has been connected to the fuel cell stack, and a reference voltage (V_f) that the fuel cell stack 10 reaches when the certain time period (T11) has elapsed, under the normal operation of the fuel cell load device 20.

[0061] In other words, once the fuel cell load device 20 is operational, its operation can be diagnosed based on whether the time required for the fuel cell stack voltage to reach the specified voltage (V11) is greater than the reference time, and whether the fuel cell stack voltage after the specified time (T11) is greater than the reference voltage. The time required to reach the specified voltage (V11) and the voltage the fuel cell stack can reach after the specified time (T11) can vary based on the fuel cell stack output voltage when the fuel cell load device 20 is operating (that is, the fuel cell stack voltage at startup to provide the output power of the fuel cell stack 10 to the fuel cell load device 20).Additionally, the failure criterion of the fuel cell load device 20, based on the output voltage of the fuel cell stack, can be variable during operation. Both the time required to reach the specified voltage and the voltage that the fuel cell stack can achieve can increase as the vehicle speed increases. The times can also be increased if airflow is detected and if the fuel cell stack 10 is in a drying state where humidification of the fuel cell stack 10 is insufficient (e.g., the internal resistance of the fuel cell increases). Furthermore, the times can be decreased if hydrogen crossover occurs. Consequently, taking into account the external environment and the degree of degradation of the fuel cell stack 10, the reference voltage and the reference time duration can be modified.In particular, if the vehicle speed, the amount of airflow, the degree of dehydration and the hydrogen crossover rate are increased, the diagnostics of the operation of the fuel cell load device 20 may be deactivated.

[0062] With reference to Fig. 11A and Fig. 11B It may be possible to diagnose, based on the time required to reach a specific voltage or based on the voltage after a specific time period, which can be changed by the output voltage of the fuel cell stack 10 (e.g., the voltage when the diagnosis begins), whether the fuel cell load device 20 is operating normally or is faulty. The criterion for determining the normal or fault state may include offsets such as L1, L2.

[0063] Fig. Figure 12 shows an exemplary flowchart illustrating a method for diagnosing the operation of a fuel cell load device according to an embodiment of the present invention, and Fig. Figure 13 shows an exemplary flowchart illustrating a method for diagnosing the operation of a fuel cell load device according to a further embodiment of the present invention.

[0064] Fig. 12 and Fig. Figure 13 shows the procedure for diagnosing the fault of the fuel cell load device 20, in which the current sensors 27, 29 are used in contrast to the one in Fig. 9 and Fig. The method shown in Figure 10, which diagnoses the failure in the fuel cell load device 20 using the value detected by the current sensor, is not used. If the system does not include the current sensors 27, 29, the failure in the fuel cell load device 20 can be diagnosed using the rate of voltage decrease of the fuel cell stack 10.

[0065] In other words, after the fuel cell load device 20 is connected to the fuel cell stack 10, the control can be set up to determine whether the time required for the voltage of the fuel cell stack to reach the specified voltage (V11) is greater than the reference time period, or whether the voltage of the fuel cell stack 10 is greater than the reference voltage when the specified time period has elapsed, and thus the control can be set up to determine whether the fuel cell load device 20 has failed.

[0066] With reference to Fig. 12 may include diagnosing the operation of the fuel cell load device 20: determining whether the elapsed time after connection to the fuel cell load device 20 is greater than a specified time limit (S901); determining whether the actual voltage value of the fuel cell stack is greater than the reference voltage (V_f) when the elapsed time is greater than the specified time limit (S903); and diagnosing the operation of the fuel cell load device 20 (S905, S907).If the elapsed time is greater than the specified time limit and if the actual voltage value of the fuel cell stack 10 is greater than the reference voltage (V_f) of the normal state, it can be determined that the fuel cell load device 20 has failed, i.e., is not in the normal operating state (S905), whereas if the actual voltage value of the fuel cell stack 10 is less than the reference voltage (V_f), it can be determined that the fuel cell load device 20 is operating normally (S907).

[0067] Furthermore, with reference to Fig. 12. Diagnosing the operation of the fuel cell load device 20 includes: after connection with the fuel cell load device 20, determining whether the voltage of the fuel cell stack 10 reaches a specific voltage (V11, V12) (S901); determining whether the time required for the voltage of the fuel cell stack 10 to reach the specific voltage (V11, V12) is greater than the reference time duration (T_f) (S903); and diagnosing the operation of the fuel cell load device 20 (S905, S907).If the voltage of the fuel cell stack 10 reaches the specified voltage (V11) and if the time required for the voltage of the fuel cell stack 10 to reach the specified voltage (V11) is greater than the reference time period (T_f) of the normal state, it can be determined that the fuel cell load device 20 has failed, i.e., is not in a normal operating state (S905), whereas if the time required for the voltage of the fuel cell stack 10 to reach the specified voltage (V11) is less than the reference time period (T_f), it can be determined that the fuel cell load device 20 is operating normally (S907).

[0068] With reference to Fig. 13 may include diagnosing the operation of the fuel cell load device 20: setting a reference voltage (V_f) of the fuel cell stack 10, which represents the achievable voltage when a certain time period (T11) has elapsed after connection to the fuel cell load device 20 under normal operation of the fuel cell load device 20 (S1001); determining whether the certain time period has elapsed after connection to the fuel cell load device 20 (S1003); and diagnosing the operation of the fuel cell load device (S1007, S1009) according to the difference between the voltage of the fuel cell stack 10 and the reference voltage (V_f) (S1005) when the certain time period (T11) has elapsed after connection to the fuel cell load device.

[0069] In other words, the fuel cell load device 20 can first be connected to the fuel cell stack 10, and the reference voltage can be preset as the voltage that the fuel cell stack can reach after a specific time interval (T11) has elapsed following the connection (when the voltage decreases due to the normal operation of the fuel cell load device 20). The control system can then be configured to determine whether the specific time interval (T11) has elapsed (S1003), and the voltage of the fuel cell stack 10 detected after the specific time interval (T11) can be compared to the reference voltage (S1005). If the difference between the detected voltage and the reference voltage is greater than the offset (L2), it can be determined that the fuel cell load device has failed (S1007).

[0070] Additionally, with reference to Fig. 13. Diagnosing the operation of the fuel cell load device 20 includes: setting a reference time period (T_f) representing the time required for the voltage of the fuel cell stack 10 to reach a specific voltage (V11) under normal operation of the fuel cell load device 20 (S1001); determining whether the voltage of the fuel cell load device 20 reaches the specific voltage (V11) (S1003); and diagnosing the operation of the fuel cell load device (S1007, S1009) according to the difference between the reference time period (T_f) and the actual time required for the voltage of the fuel cell stack 10 to reach the specific voltage (V11) (S1005).

[0071] In other words, the fuel cell load device 20 can first be connected to the fuel cell stack 10, and the reference time (T_f) can be preset. This reference time represents the time required to reduce the voltage of the fuel cell stack 10 to the specified target voltage after connection under normal operation of the fuel cell load device 20. Furthermore, the control system can be configured to determine whether the voltage of the fuel cell stack has been reduced to the specified voltage (S1003), and the time required to reduce the voltage of the fuel cell stack 10 to the specified voltage can be compared with the reference time (S1005).If the difference between the reference time and the time required to reduce the voltage of the fuel cell stack 10 to the specified voltage is greater than the specified tolerance (L1), it can be determined that the fuel cell load device 20 has failed (S1007). If the difference between the reference time and the time required to reduce the voltage of the fuel cell stack 10 to the specified voltage is less than the specified tolerance (L1), it can be diagnosed that the fuel cell load device 20 is operating normally (S1009).

[0072] The reference setpoint voltage after a specified time period and the reference time period required to reach that specified voltage can vary depending on the voltage of the fuel cell stack 10 when the fuel cell load device 20 is connected to the fuel cell stack 10. Furthermore, the reference time period and the reference voltage can increase as the speed of the fuel cell vehicle increases. Additionally, if airflow is detected and the fuel cell stack 10 is in a drying state where humidification of the fuel cell stack is insufficient, the reference time period and the reference voltage can increase. Finally, if the hydrogen crossover rate of the membrane of the fuel cell containing the fuel cell stack is increased, the reference time period and the reference voltage can decrease.

[0073] Fig. 14 and Fig. Figure 15 shows exemplary flowcharts illustrating a control method for a fuel cell system according to further embodiments of the present invention. Steps S1103 to S1107 in Fig. 14 and the steps from S1203 to S1207 in Fig. 15 are the same as the steps from S801 to S805 in Fig. 10. The steps from S1109 to S1113 in Fig. 14 and the steps from S1209 to S1215 in Fig. 15 are the same as the steps from S901 to S907 in Fig. 12 or steps S1003 to S1009 in Fig. 13. Therefore, descriptions of the previously mentioned steps are omitted.

[0074] The in Fig. 14 and Fig. The control procedure shown in Figure 15 modifies the procedure for diagnosing the operation of the fuel cell load device 20 according to whether the voltage of the fuel cell stack is greater or less than a predetermined voltage (V4) when the diagnosis of the operation of the fuel cell load device 20 is started. In other words, the voltage of the fuel cell stack 10 can be measured and compared with the predetermined voltage (V4) (S1101, S1201). If the voltage of the fuel cell stack 10 is greater than the predetermined voltage (V4), the estimated current value (I) can be est ) are calculated based on both the voltage of the fuel cell stack 10 and the resistance value of the fuel cell load device 20 (S1103, S1203). Then, when the difference between the estimated value (I est ) and the output current value of the fuel cell stack 10 (I real-fuelcellIf the value is greater than a specified tolerance (K) (S1105, S1205), it can be diagnosed that the fuel cell load device 20 has a fault (S1107, S1207).

[0075] Furthermore, if the voltage of the fuel cell stack 10 is lower than the specified voltage (V4), the operation of the fuel cell load device 20 using the Fig. 12 or Fig. The procedure described in Figure 13 can be used to diagnose the problem. In other words, if the voltage of the fuel cell stack 10 is less than the specified voltage (V4), the operation of the fuel cell load device 20 can be diagnosed based on both the time required for the voltage of the fuel cell stack to reach the specified voltage after the fuel cell load device 20 is connected to the fuel cell stack 10 (e.g., elapsed time) and the reference time (T_f), which represents the time required for the voltage of the fuel cell stack to reach the specified voltage under normal operation of the fuel cell load device 20.

[0076] Additionally, if the voltage of the fuel cell stack 10 is less than the specified voltage (V4), the operation of the fuel cell load device 20 can be diagnosed based on both the voltage of the fuel cell stack when the specified time period has elapsed after the fuel cell load device 20 has been connected to the fuel cell stack 10, and the reference voltage (V_f) that the fuel cell stack 10 reaches when the specified time period has elapsed, under the normal operation of the fuel cell load device 20.

[0077] Diagnosing the operation of the fuel cell load device 20 using the current sensor can be more accurate than diagnosing it based on the degree of voltage decay over time. However, considering the range in which the current sensor is set up for measurement, if the magnitude of the current flowing into the fuel cell load device 20 is significant, its operation can be diagnosed using the current sensor. Conversely, if the current flowing into the fuel cell load device 20 is so small that it cannot be detected by the current sensor, its operation can be diagnosed by the degree of voltage decay over time.

[0078] The specified voltage (V4) can be set such that it is greater than both the specified voltage (V11) and the reference voltage (V_f) that the fuel cell stack 10 reaches when the specified time period (T11) has elapsed under the normal operation of the fuel cell load device 20. Additionally, as in Fig. As shown in Figure 8, the specified voltage (V4) can have a value between the first reference voltage (V1) and the second reference voltage (V2). Additionally, the specified voltage (V4) can be greater than L2, which represents the tolerance (offset). As described above, since the current-measuring method can be more accurate than the method that measures the rate of voltage decay, the specified voltage (V4) can serve as the reference voltage, making the rate-of-voltage-measuring method useful.

[0079] According to one embodiment of the present invention, the control method of the fuel cell system can improve the durability of the fuel cell system by removing residual oxygen from the fuel cell stack. Furthermore, the method eliminates the risk of damage from high voltages by reducing the voltage of the fuel cell stack. Additionally, the method can maintain stability during vehicle restarts and can improve the vehicle's fuel efficiency.

Claims

[1] Control procedure for a fuel cell system, comprising: Deriving, by means of a control, a voltage of a fuel cell stack (10) by charging a high-voltage battery (220); Deriving, by control, the voltage of the fuel cell stack (10) by connecting a fuel cell load device (20) to the fuel cell stack (10) when the voltage of the fuel cell stack (10) is less than a predetermined first reference voltage (V1) when the voltage is derived, wherein the fuel cell load device (20) is a load to discharge a voltage of a fuel cell when starting up or switching off the fuel cell; Adjusting, by means of the control, a voltage of a main bus connection (211) arranged between the fuel cell stack and an inverter (231) to an acceptable minimum voltage (V3) in order to prevent the output power of the fuel cell stack (10) from being supplied to loads other than the fuel cell load device (20) until a voltage of the fuel cell stack (10) reaches a predetermined second reference voltage (V2) based on the connection with the fuel cell load device (20); Diagnosing, by control, an operation of the connected fuel cell load device (20); the diagnosis of the operation of the fuel cell load device (20) includes: Diagnosing, by controlling, the operation of the fuel cell load device (20) based on a rate of decrease of the voltage of the fuel cell stack (10), wherein diagnosing the operation of the fuel cell load device (20) based on the rate of decrease of the voltage of the fuel cell stack (10) includes: Diagnosing, by controlling, the operation of the fuel cell load device (20) based on both a time required for the voltage of the fuel cell stack (10) to reach a certain voltage after the fuel cell load device (20) is connected to the fuel cell stack (10), and on a reference time required for the voltage of the fuel cell stack (10) to reach the certain voltage under normal operation of the fuel cell load device (20), wherein the reference time varies based on a vehicle speed, an amount of air inflow, a water content of the fuel cell stack (10), a crossover state within the fuel cell stack (10) and the voltage of the fuel cell stack (10) when the fuel cell load device (20) is connected to the fuel cell stack (10). [2] Control method according to claim 1, wherein if the high-voltage battery (220) is not allowed to be charged when an accident of the fuel cell vehicle is detected or when a period required for a voltage of a fuel cell stack (10) to reach a predetermined first reference voltage is greater than a predetermined first reference time period, charging of the high-voltage battery (220) is stopped and the second derivation process is carried out. [3] Control method according to claim 2, wherein the high-voltage battery (220) may not be charged under certain circumstances, which include when the high-voltage battery (220) fails, when a power converter connected to the high-voltage battery (220) fails, when a state of charge (SOC) of the high-voltage battery (220) is greater than a predetermined SOC, or when a power source for charging the high-voltage battery (220) is insufficient. [4] Control method according to claim 1, wherein, when the fuel cell load device (20) is connected to the fuel cell stack (10), when a voltage of the fuel cell stack (10) is reduced so that the voltage is less than a predetermined second reference voltage (V2), the second derivation process is terminated. [5] Control method according to claim 1, wherein adjusting the voltage of the main bus terminal (211) to the acceptable minimum voltage (V3) maintains the voltage of the main bus terminal (211) at an initial value, and when the voltage of the fuel cell stack (10) reaches the predetermined second reference voltage (V2), the voltage of the main bus terminal (211) decreases to the acceptable minimum voltage (V3). [6] Control method according to claim 1, wherein adjusting the voltage of the main bus terminal (211) to the acceptable minimum voltage (V3) keeps the voltage of the main bus terminal (211) greater than a voltage of a fuel cell stack (10). [7] Control method according to claim 1, wherein adjusting the voltage of the main bus terminal (211) to the acceptable minimum voltage (V3) comprises: Disconnecting, by the control, the fuel cell stack (10) from the main bus connection (211) by switching off a main relay before connecting to the fuel cell load device (20). [8] Control method according to claim 1, wherein the acceptable minimum voltage (V3) is less than the first reference voltage and greater than a minimum voltage for operating a power converter connected to the high-voltage battery (220) or high-voltage components connected to the main bus terminal (211). [9] Tax procedure according to claim 1, further comprising: Stop, by control, the supply of air to the fuel cell stack (10) after increasing the voltage of the fuel cell stack (10) so that it is greater than the first reference voltage, by supplying air to the fuel cell stack (10). [10] Tax procedure according to claim 1, further comprising: Disconnecting, by means of the control, the fuel cell stack (10) from a main bus connection (211) arranged between the fuel cell stack (10) and an inverter by switching off a main relay. [11] Control method according to claim 5, wherein the acceptable minimum voltage (V3) is less than the first reference voltage and greater than a minimum voltage for operating a power converter connected to the high-voltage battery (220) or high-voltage components connected to the main bus terminal (211). [12] Control method according to claim 6, wherein the acceptable minimum voltage (V3) is less than the first reference voltage and greater than a minimum voltage for operating a power converter connected to the high-voltage battery (220) or high-voltage components connected to the main bus terminal (211). [13] Control method according to claim 1, wherein diagnosing the operation of the fuel cell load device (20) comprises: Diagnosing, by means of the control, a failure of the fuel cell load device (20) when a difference between a set current value and a current value flowing into the fuel cell load device (20) or a difference between the set current value and a value of the output current of the fuel cell stack (10) is greater than specified tolerances, wherein the set current value is calculated based on both the voltage of the fuel cell stack (10) and a resistance value of the fuel cell load device (20). [14] Control method according to claim 13, wherein the tolerances are predetermined based on a resolution of a sensor configured to sample the current value flowing into the fuel cell load device (20) and a resolution of a sensor configured to sample the output current value of the fuel cell stack (10). [15] Control method according to claim 1, wherein diagnosing the operation of the fuel cell load device (20) based on the rate of decrease of the voltage of the fuel cell stack (10) comprises: Diagnosing, by controlling, the operation of the fuel cell load device (20) based on both the voltage of the fuel cell stack (10) when a certain period of time has elapsed after the fuel cell load device (20) has been connected to the fuel cell stack (10), and on a reference voltage that the fuel cell stack (10) reaches after the certain period of time under normal operation of the fuel cell load device (20). [16] Control method according to claim 15, wherein the reference voltage varies on the basis of a vehicle speed, an amount (magnitude) of an air inflow, a water content of the fuel cell stack (10), a crossover state within the fuel cell stack (10) and the voltage of the fuel cell stack (10) when the fuel cell load device (20) is connected to the fuel cell stack (10). [17] Control method according to claim 1, wherein the diagnosis of the operation of the fuel cell load device (20) is carried out based on at least one selected from the group consisting of: a current supplied by the fuel cell stack (10) and a current flowing into the fuel cell load device (20) when the voltage of the fuel cell stack (10) is greater than a predetermined voltage. [18] Control method according to claim 1, wherein the diagnosis of the operation of the fuel cell load device (20) is carried out on the basis of the rate of a decrease in the voltage of the fuel cell stack (10) when the voltage of the fuel cell stack (10) is less than a predetermined voltage. [19] Tax procedure according to claim 1, wherein: the connection of the fuel cell load device (20) to the fuel cell stack (10) is carried out when the voltage of the fuel cell stack (10) is less than a predetermined first reference voltage, when the voltage of the fuel cell stack (10) is derived by charging a high-voltage battery (220); and the diagnosis of the operation of the fuel cell load device (20) is terminated when the voltage of the fuel cell stack (10) is reduced to less than a predetermined second reference voltage, where the voltage of the fuel cell stack (10) is greater than the specified second reference voltage and less than the specified first reference voltage. [20] Tax procedure according to claim 17, further comprising: Diagnosing, by means of the control, that the fuel cell load device (20) is failing, wherein the set current value is calculated as a function of the voltage of the fuel cell stack (10) and a resistance value of the fuel cell load device (20), if the voltage of the fuel cell stack (10) is greater than the specified voltage, if a difference between a set current value and a current value flowing into the fuel cell load device (20) or a difference between the set current value and a value of an output current of the fuel cell stack (10) is greater than specified tolerances. [21] Control method according to claim 18, wherein, when the voltage of the fuel cell stack (10) is less than the predetermined voltage, the operation of the fuel cell load device (20) is diagnosed based on both a time required for the voltage of the fuel cell stack (10) to reach a certain voltage from a diagnostic start time, and a reference time required for the voltage of the fuel cell stack (10) to reach the certain voltage under normal operation of the fuel cell load device (20). [22] Control method according to claim 21, wherein the reference time varies based on a vehicle speed, an amount of air inflow, a water content of the fuel cell stack (10), a crossover state within the fuel cell stack (10) and the voltage of the fuel cell stack (10) when the fuel cell load device (20) is connected to the fuel cell stack (10), wherein the predetermined voltage is greater than the determined voltage. [23] Tax procedure according to claim 18, further comprising: Diagnosing, by controlling, the operation of the fuel cell load device (20) based on both a voltage of the fuel cell stack (10) when a certain time period has elapsed from the start time of the diagnosis, and on a reference setpoint voltage when the certain time period has elapsed under normal operation of the fuel cell load device (20) when the voltage of the fuel cell stack (10) is less than the specified voltage. [24] Control method according to claim 23, wherein the reference voltage varies based on a vehicle speed, an amount of air inflow, a water content of the fuel cell stack (10), a crossover state within the fuel cell stack (10) or the voltage of the fuel cell stack (10) when the fuel cell load device (20) is connected to the fuel cell stack (10), wherein the predetermined voltage is greater than the reference voltage. [25] Tax procedure according to claim 1, further comprising: When the diagnosis of the operation of the fuel cell load device (20) is completed, the control system stores the results according to the completion of the diagnosis in a memory. [26] Tax procedure according to claim 18, wherein: the connection of the fuel cell load device (20) to the fuel cell stack (10) is carried out when the voltage of the fuel cell stack (10) is less than a predetermined first reference voltage, when the voltage of the fuel cell stack (10) is derived by charging a high-voltage battery (220); and The diagnosis of the operation of the fuel cell load device (20) is terminated when the voltage of the fuel cell stack (10) is reduced to less than a predetermined second reference voltage.

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