阅读说明：本技术 燃料电池堆的性能恢复方法 (Method for recovering performance of fuel cell stack ) 是由 郑圣哲 金钟均 金大钟 郑载元 于 2020-09-02 设计创作，主要内容包括：本公开涉及一种车辆的燃料电池系统中的燃料电池堆的性能恢复方法。该方法包括：利用预定的堆状态判断标准,基于从车辆收集的信息,判断燃料电池堆是否处于可以执行堆性能恢复操作的状态；基于燃料电池系统的操作信息,判断车辆是否处于可以执行堆性能恢复操作的状态；以及当判断燃料电池堆处于可以执行堆性能恢复操作的状态并且车辆处于可以执行堆性能恢复操作的状态时,执行堆性能恢复操作。(The present disclosure relates to a performance recovery method of a fuel cell stack in a fuel cell system of a vehicle. The method comprises the following steps: determining whether the fuel cell stack is in a state in which a stack performance recovery operation can be performed, based on information collected from the vehicle, using a predetermined stack state determination criterion; determining whether the vehicle is in a state in which a stack performance recovery operation can be performed, based on operation information of the fuel cell system; and performing a stack performance recovery operation when it is determined that the fuel cell stack is in a state in which the stack performance recovery operation can be performed and the vehicle is in a state in which the stack performance recovery operation can be performed.)

1. A performance recovery method of a fuel cell stack in a fuel cell system of a vehicle, comprising:

determining, by a controller, whether the fuel cell stack is in a state in which a stack performance recovery operation can be performed, based on information collected from the vehicle, using a predetermined stack state determination criterion;

determining, by the controller, whether the vehicle is in a state in which the stack performance recovery operation can be performed, based on operation information of a fuel cell system; and

by the controller, when it is determined that the fuel cell stack is in a state in which the stack performance recovery operation can be performed and the vehicle is in a state in which the stack performance recovery operation can be performed, the stack performance recovery operation is performed.

2. The method of claim 1, wherein,

determining whether the fuel cell stack is in a state in which a stack performance recovery operation can be performed includes:

calculating an integrated value of a stack current obtained by integrating a current output from the fuel cell stack during operation of the fuel cell system;

comparing the calculated integration value of the stack current with a current integration reference value as a stack state judgment standard; and

when the calculated integrated value of the stack current is larger than the current integration reference value, it is determined that the fuel cell stack is in a state in which the stack performance recovery operation can be performed.

3. The method of claim 2, wherein,

the controller integrates only the stack current above a predetermined lower limit value during operation of the fuel cell system to calculate an integrated value of the stack current.

4. The method of claim 1, wherein,

determining whether the fuel cell stack is in a state in which a stack performance recovery operation can be performed includes:

calculating an accumulated travel distance obtained by accumulating a vehicle travel distance when the output of the fuel cell stack is equal to or greater than a predetermined first output reference value during vehicle travel and operation of the fuel cell system;

comparing the judged accumulated travel distance with a distance reference value as a pile state judgment criterion; and

when the determined accumulated travel distance is greater than the distance reference value, it is determined that the fuel cell stack is in a state in which the stack performance recovery operation can be performed.

5. The method of claim 1, wherein,

determining whether the fuel cell stack is in a state in which a stack performance recovery operation can be performed includes:

during vehicle running and operation of the fuel cell system, calculating an integrated value of a stack current obtained by integrating a current output from the fuel cell stack, and calculating an accumulated running distance obtained by accumulating a vehicle running distance when an output of the fuel cell stack is equal to or greater than a predetermined first output reference value;

comparing the calculated integrated value of the stack current with a current integration reference value as a stack state judgment criterion, and comparing the judged accumulated travel distance with a distance reference value as a stack state judgment criterion; and

when the calculated integrated value of the stack current is larger than the current integration reference value or when the calculated accumulated travel distance is larger than the distance reference value, it is determined that the fuel cell stack is in a state in which the stack performance recovery operation can be performed.

6. The method of claim 1, further comprising:

confirming, by the controller, a fuel cell stop entry count when it is determined that the fuel cell stack is in a state in which the stack performance recovery operation can be performed; and

by the controller, during operation of the fuel cell system, when it is determined that a predetermined condition related to confirmation of the number of times of fuel cell stop entries is satisfied, it is determined whether the vehicle is in a state in which the stack performance recovery operation can be performed.

7. The method of claim 6, wherein,

confirming the number of fuel cell entry stops includes:

determining whether a number of times that a stack voltage is equal to or less than a predetermined voltage reference value when a fuel cell stop occurs within a predetermined time during operation of the fuel cell system is less than a first predetermined number of times; and

determining that the condition related to confirming the number of times the fuel cell stops entering is satisfied when the number of times the stack voltage is equal to or less than the voltage reference value is less than the first predetermined number of times.

8. The method of claim 1, wherein,

determining whether the vehicle is in a state in which the stack performance recovery operation can be performed includes:

it is determined whether the vehicle is in a state in which the stack performance recovery operation can be performed, based on whether the vehicle is in a running state, a state of charge, that is, SOC and dischargeable electric power, of a battery connected to a drive motor to supply electric power to the drive motor, and a stack request output.

9. The method of claim 8, wherein,

under the condition that the vehicle is in a running state, the condition that the SOC of the battery is equal to or greater than a predetermined first SOC reference value, the condition that the dischargeable electric power of the battery is equal to or greater than a predetermined first electric power reference value, and the condition that the stack requested output is less than a predetermined second output reference value,

the controller determines that the vehicle is in a state in which the stack performance recovery operation can be performed.

10. The method of claim 8, wherein,

on the condition that the SOC of the battery is equal to or greater than a predetermined second SOC reference value when the vehicle is in a key-off state and not in a running state,

the controller determines that the vehicle is in a state in which a stack performance recovery operation can be performed.

11. The method of claim 1, wherein,

performing the heap performance recovery operation comprises:

switching a running mode of the vehicle to a battery running mode in which the vehicle runs by driving a drive motor with charging power of a battery;

closing the main relay; and

controlling operation of an electrical load device connected to the fuel cell stack to sweep a voltage of the fuel cell stack to restore performance of the fuel cell stack.

12. The method of claim 11, wherein,

the electric load device includes:

a COD heater for heating the reactor coolant; and

an air compressor that supplies air serving as an oxidizing gas to the fuel cell stack.

13. The method of claim 12, wherein,

during the performance recovery operation of the stack,

the controller turns on the COD heater to scan a voltage of the fuel cell stack, performs cooling control of the COD heater using the stack coolant, and performs on/off control of the air compressor, wherein the air compressor is controlled to be alternately turned on and off.

14. The method of claim 1, further comprising:

determining, by the controller, whether a predetermined stack performance recovery operation interruption condition is satisfied during the stack performance recovery operation;

judging, by the controller, whether the heap performance recovery operation has been completed when it is judged that the heap performance recovery operation interruption condition is satisfied; and

and changing the stack state judgment standard and ending the stack performance recovery operation by the controller when judging that the stack performance recovery operation is not finished.

15. The method of claim 14, wherein,

determining whether a predetermined stack performance recovery operation interruption condition is satisfied includes:

during the stack performance recovery operation, it is determined that the stack performance recovery operation interruption condition is satisfied when at least one of a condition that a stack is required to output less than a predetermined third output reference value, a condition that a state of charge, SOC, of a battery connected to a drive motor to supply electric power to the drive motor is less than a predetermined third SOC reference value, and a condition that dischargeable electric power of the battery is less than a second power reference value is satisfied.

16. The method of claim 14, wherein,

when the number of executions of the on/off control of the air compressor for sweeping the voltage of the fuel cell stack is less than a second predetermined number during the stack performance recovery operation,

the controller determines that the stack performance recovery operation has not been completed.

17. The method of claim 14, wherein,

when it is determined that the stack performance recovery operation has been completed,

the controller ends the stack performance recovery operation without changing the stack state judgment criterion.

18. The method of claim 17, wherein,

when the number of executions of the on/off control of the air compressor for sweeping the voltage of the fuel cell stack reaches a second predetermined number during the stack performance recovery operation,

the controller determines that the stack performance recovery operation has been completed.

19. The method of claim 16, further comprising:

judging, by the controller, whether the heap performance recovery operation has been completed when it is judged that the heap performance recovery operation interruption condition is not satisfied;

maintaining, by the controller, the stack performance recovery operation when it is determined that the stack performance recovery operation has not been completed; and

ending, by the controller, the stack performance recovery operation when it is determined that the stack performance recovery operation has been completed.

20. The method of claim 19, wherein,

when the number of times of execution of the on/off control of the air compressor reaches the second predetermined number of times during the stack performance recovery operation,

the controller determines that the stack performance recovery operation has been completed.

Technical Field

The present disclosure relates to a performance recovery method of a fuel cell stack, and more particularly, to an operation control method of a fuel cell system capable of recovering performance of a fuel cell stack to improve durability of the fuel cell stack.

Background

A fuel cell (fuel cell) is a power generation device that converts chemical energy in fuel into electrical energy by causing an electrochemical reaction between a fuel gas and an oxidizing gas. Such a fuel cell is widely used as a power source for use in industry, home, and vehicles. The fuel cell may also be used to supply power to small electric/electronic products or portable devices.

Currently, a polymer electrolyte membrane fuel cell (or Proton Exchange Membrane Fuel Cell) (PEMFC) having a high power density is most studied as a fuel cell for vehicles. In the polymer electrolyte membrane fuel cell, hydrogen is used as a fuel gas, and oxygen or air including oxygen is used as an oxidizing gas.

The fuel cell includes a plurality of cells (cells) in which a fuel gas and an oxidizing gas react with each other to generate electric energy. Generally, a plurality of unit cells are stacked in a stack and connected in series with each other to meet an output demand.

A fuel cell for a vehicle requires high output (power). Therefore, in order to satisfy the power demand, several hundreds of single cells that individually generate electric energy are stacked in a stack. A cell assembly formed by stacking and connecting a plurality of unit cells to each other is called a fuel cell stack.

Each unit cell (unit cell) of the polymer electrolyte membrane fuel cell includes: a Membrane Electrode Assembly (MEA) including a polymer electrolyte membrane capable of moving hydrogen ions and catalyst electrode layers integrally attached to opposite surfaces of the polymer electrolyte membrane; a Gas Diffusion Layer (GDL) for supplying reaction gases such as fuel gas and oxidizing gas to the membrane electrode assembly and transmitting generated electric power; a gasket (gasket) for maintaining airtightness of the reaction gas and the coolant; a fastening member for maintaining a proper fastening pressure; and a Bipolar Plate (BP) for moving the reaction gas and the coolant.

The membrane electrode assembly includes a polymer electrolyte membrane capable of moving hydrogen ions and electrode layers, such as an anode (anode) and a cathode (cathode), formed by coating opposite surfaces of the polymer electrolyte membrane with a catalyst for inducing a reaction between hydrogen as a fuel gas and air (or oxygen) as an oxidizing gas.

In each unit cell of the fuel cell, a gas diffusion layer for uniformly distributing the fuel gas and the oxidizing gas is stacked on the outer side of the membrane electrode assembly, i.e., on the outer side of each of the anode and the cathode, and a separation plate for providing channels through which the reaction gas and the coolant flow and supplying the reaction gas to the gas diffusion layer is disposed on the outer side of the gas diffusion layer.

In addition, gaskets for fluid sealing (seal) are provided between the components constituting the unit cells. The gasket may be integrally formed with the membrane electrode assembly or the separator plate.

The above elements constitute a unit cell. A plurality of unit cells are stacked, end plates for supporting the unit cells are then coupled to outermost sides of the stacked unit cells, and the end plates are fastened to the unit cells with fastening members in a state where the unit cell stack is arranged between the end plates, thereby constituting a fuel cell stack.

A fuel cell system installed in a fuel cell vehicle includes a device for supplying a reaction gas to a fuel cell stack, in addition to the fuel cell stack.

Namely, the fuel cell system includes: a fuel cell stack configured to generate electric energy through an electrochemical reaction of a reaction gas; a hydrogen supply device configured to supply hydrogen serving as a fuel gas to the fuel cell stack; an air supply device configured to supply air including oxygen serving as an oxidizing gas to the fuel cell stack; a heat and water management system configured to control an operating temperature of the fuel cell stack and perform heat and water management functions; and a fuel cell system controller configured to control an overall operation of the fuel cell system.

In a conventional fuel cell system, the hydrogen supply device may include a hydrogen storage unit (hydrogen tank), a regulator, a hydrogen pressure control valve, and a hydrogen recycler, the air supply device may include a blower or an air compressor, a humidifier, and the like, and the heat and water management system may include a water collector, an electric water pump (coolant pump), a water tank, a radiator, and the like.

High-pressure hydrogen supplied from a hydrogen storage unit of a hydrogen supply device is depressurized to a predetermined pressure by a regulator and then supplied to a fuel cell stack. At this time, the depressurized hydrogen is supplied to the fuel cell stack in a state where the pressure and the supply amount are controlled according to the operating conditions of the fuel cell stack.

In addition, residual hydrogen unreacted in the fuel cell stack is discharged through an outlet of an anode (hydrogen electrode) of the stack or is recycled to an inlet of the anode of the stack through a hydrogen recycler.

The hydrogen recycler is a device capable of improving the reliability of hydrogen supply and the life of the fuel cell. There are various recycling methods, and a method using an ejector, a method using a blower, and a method using both an ejector and a blower are known.

The hydrogen recycler recycles unreacted hydrogen unused in the anodes of the fuel cell stack to the anodes (hydrogen electrodes) of the stack through a recycle pipe to reuse the hydrogen.

In addition, in the fuel cell, the more the amount of foreign substances such as nitrogen, water, and steam that move to the anode through the electrolyte membrane in the stack, the less the amount of hydrogen in the anode, and thus the reaction efficiency is reduced. Therefore, a hydrogen purge valve installed in the stack anode exhaust line may be opened to purge hydrogen.

Meanwhile, the durability life of the fuel cell stack is a very important factor for ensuring the marketability of the fuel cell vehicle. Therefore, various efforts have been competitively made in order to prevent the degradation of the fuel cell stack and increase the durability life of the fuel cell stack, and various studies have been made on the cause of the degradation of the stack.

Further, in recent years, commercial vehicles such as buses or trucks, as well as automobiles, have increasingly demanded fuel cell systems. As a result, a control technique capable of improving the durability of the fuel cell system is becoming a focus of attention. In particular, research has been actively conducted to be able to minimize degradation of a fuel cell stack in a fuel cell system.

In conjunction with the durability of the fuel cell stack, stack degradation can be largely classified into reversible degradation and irreversible degradation. This deterioration occurs for various reasons, and a representative cause of reversible deterioration is the generation of platinum catalyst oxide (Pt — OH).

The platinum catalyst oxide functions as a factor of reversible deterioration at an early stage of its generation. However, in the case where the oxide continuously remains in the stack, the oxide is converted into a factor of irreversible deterioration by an unexpected chemical reaction, which causes the durability of the stack to be irreparably deteriorated.

Therefore, it is necessary to remove the oxide to restore the performance of the fuel cell stack. In order to ensure the durability of the stack, a recovery operation of periodically removing the oxide causing reversible deterioration at an appropriate time is required (minimizing the reduction in durability also leads to an increase in stack efficiency).

As a method for recovering performance of a fuel cell stack by removing an oxide, a method of inducing a reduction reaction by stack potential fluctuation, i.e., voltage sweep (sweeparing), is known.

In addition, it is advantageous to keep the exposure voltage low for a long time to efficiently perform the stack performance recovery operation in the voltage scanning manner, and it is known that the improvement effect is remarkable in the case where the voltage fluctuation is repeatedly caused.

However, when the stack performance recovery operation mode is applied to the vehicle, the following problems are encountered.

First, it is necessary to determine whether the vehicle is in a state in which an operation to recover the performance of the fuel cell stack can be performed using the voltage sweep method. Basically, the fuel cell stack must output current at any time according to the driver's request based on the characteristics of the fuel cell stack in the vehicle. Therefore, in order to perform a plurality of voltage sweeps while satisfying the above-described requirements, an accurate determination criterion for ensuring the stack performance recovery operation time is required, and the determination must take into account both the state of the vehicle and the state of the fuel cell stack.

In addition, as for the means for controlling the voltage sweep, it is generally difficult to cause voltage fluctuation in a state where no load is present, and even in the case where a voltage is formed, it takes a long time for discharging (lowering the voltage). Therefore, a means for causing voltage fluctuation quickly and efficiently is required.

In addition, in order to maximize the effect of improving durability by the recovery operation, it is necessary to maintain the fuel cell stack at a low voltage for a long time. Further, it is necessary to perform the recovery operation in a low voltage state a plurality of times in succession. However, in the case where the recovery operation has not been completed due to the driver's output request or the vehicle condition, it is necessary to judge this and reflect it in the next recovery operation in order to maximize the effect of the recovery operation.

The information disclosed in the background section above is for the purpose of aiding in the understanding of the background of the disclosure, and should not be taken as an admission that the information forms any part of the prior art.

Disclosure of Invention

The present disclosure is proposed to solve the above-mentioned problems associated with the prior art, and an object of the present disclosure is to provide a performance recovery method of a fuel cell stack, which accurately determines whether a stack is in a state in which a stack performance recovery operation can be performed and whether a vehicle is in a state in which a stack performance recovery operation can be performed, thereby appropriately ensuring a performance recovery operation time during vehicle traveling and more efficiently performing voltage sweep and stack performance recovery.

In an aspect of the present disclosure, a performance recovery method of a fuel cell stack in a fuel cell system of a vehicle may include: determining, by the controller, whether the fuel cell stack is in a state in which a stack performance recovery operation can be performed, based on information collected from the vehicle, using a predetermined stack state determination criterion; determining, by the controller, whether the vehicle is in a state in which a stack performance recovery operation can be performed, based on operation information of the fuel cell system; and performing, by the controller, the stack performance recovery operation when it is determined that the fuel cell stack is in a state in which the stack performance recovery operation can be performed and the vehicle is in a state in which the stack performance recovery operation can be performed.

Other aspects and preferred embodiments of the disclosure are discussed below.

It will be understood that the term "vehicle" or "vehicular" or other similar terms as used herein include motor vehicles in general, such as passenger vehicles including Sport Utility Vehicles (SUVs), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid vehicles, hydrogen-powered vehicles, and other alternative fuel (e.g., fuel derived from resources other than petroleum) vehicles. As referred to herein, a hybrid vehicle is a vehicle having two or more power sources, such as gasoline-powered and electric-powered vehicles.

The above and other features of the present disclosure are discussed below.

Drawings

The above and other features of the present disclosure will now be described in detail with reference to certain exemplary embodiments thereof as illustrated in the accompanying drawings, which are given by way of illustration only, and thus are not limiting of the present disclosure, and wherein:

fig. 1 is a view schematically showing main components of a power grid structure of a fuel cell system that performs a fuel cell stack performance recovery operation according to an aspect of the present disclosure;

FIG. 2 is a flow chart illustrating an overall process for fuel cell stack performance recovery according to an aspect of the present disclosure;

FIG. 3 is a flow diagram illustrating a method of determining whether a heap is in a state that requires a heap performance recovery operation in accordance with an aspect of the present disclosure;

FIG. 4 is a flow chart illustrating a method of confirming a number of fuel cell shut downs according to an aspect of the present disclosure;

FIG. 5 is a flow chart illustrating a method of determining whether a vehicle is in a state in which a stack performance recovery operation may be performed, according to an aspect of the present disclosure;

FIG. 6 is a flow diagram illustrating a method of determining whether a heap performance recovery operation has completed and, when not completed, changing heap status determination criteria, in accordance with an aspect of the present disclosure; and

fig. 7 is a diagram illustrating an example of changing the heap status determination criteria according to an aspect of the present disclosure.

It should be understood that the drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the disclosure. The specific design features of the present disclosure, including, for example, specific dimensions, orientations, locations, and shapes, are set forth in part in the disclosure herein to be determined by the particular intended application and use environment.

In the drawings, like reference characters designate like or equivalent parts of the disclosure throughout the various views.

Detailed Description

Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily practice the present disclosure. However, the present disclosure is not limited to the embodiments disclosed herein, and may be embodied in various different forms.

Unless otherwise indicated, the terms "comprising" and "comprises" as described herein should not be construed as excluding other elements, but rather as further including such other elements.

First, the present disclosure relates to a performance recovery method of a fuel cell stack capable of improving durability of the fuel cell stack by preventing irreversible degradation of the fuel cell stack of a fuel cell system mounted in a fuel cell vehicle.

According to an aspect of the present disclosure, a logic for determining whether a current vehicle is in a state in which an operation to recover performance of a fuel cell stack can be performed using information such as an integrated value of a stack current, an accumulated travel distance, a fuel cell stop (fuel cell stop) entry number, a state of charge (SOC) of a battery, a dischargeable power of the battery, and a stack required output is disclosed.

According to an aspect of the present disclosure, a method of efficiently causing voltage fluctuations using an air compressor and a Cathode Oxygen Depletion (COD) heater is disclosed. In order to achieve electrical isolation between the high-voltage battery and the COD heater during voltage fluctuations, control of the main relay is also performed.

According to an aspect of the present disclosure, a time at which the recovery operation has not been completed due to the driver's output request or the condition of the vehicle is determined and reflected in the next stack performance recovery operation to maximize the effect of the stack performance recovery operation.

Fig. 1 is a view schematically showing the main components of a power grid structure of a fuel cell system that performs a fuel cell stack performance recovery operation according to an aspect of the present disclosure.

Referring to fig. 1, a fuel cell system mounted in a fuel cell vehicle includes: a fuel cell stack 10 serving as a main power source (electric power source) of the vehicle; a high-voltage battery (main battery) 16 serving as an auxiliary power source of the vehicle; a bidirectional high voltage DC/DC converter (BHDC)15 connected to the high voltage battery 16 to control an output of the high voltage battery 16; an inverter 12 connected to the fuel cell stack 10 and a main bus terminal as an output side of the high-voltage battery 16; a drive motor 13 connected to the inverter 12; and a controller 17 configured to control the operation of the fuel cell system.

The controller 17 of the fuel cell system according to the exemplary embodiment of the present disclosure may be a processor (e.g., a computer, a microprocessor, a CPU, an ASIC, a circuit system, a logic circuit, etc.). The controller 17 may be implemented by a non-transitory memory storing, for example, a program, a software instruction reproduction algorithm, or the like that controls the operation of various components of the fuel cell vehicle when executed, and a processor configured to execute the program, the software instruction reproduction algorithm, or the like. Here, the memory and the processor may be implemented as separate semiconductor circuits. Alternatively, the memory and processor may be implemented as a single integrated semiconductor circuit. The processor may be embodied as one or more processors.

In fig. 1, reference numeral 14 denotes a COD heater 14 connected to the main bus terminal to operate by the output (output current) of the fuel cell stack 10 to heat the stack coolant, and reference numeral 18 denotes an air compressor configured to supply air serving as an oxidation gas to the fuel cell stack 10. These are also components of the fuel cell system.

According to an aspect of the present disclosure, the COD heater 14 and the air compressor 18 may be used as a means of sweeping the stack voltage (to fluctuate the voltage) during operation to restore the performance of the fuel cell stack 10.

As shown in fig. 1, in the fuel cell system, a fuel cell stack 10 as a main power source and a high-voltage battery 16 as an auxiliary power source are connected in parallel to an inverter 12/drive motor 13 as a load in the system through main bus terminals.

In addition, a converter 15 connected to the high-voltage battery 16, i.e., a bidirectional high-voltage DC/DC converter (BHDC), is connected to the main bus terminals, which are the output sides of the fuel cell stack 10, so that the outputs of the fuel cell stack 10 and the high-voltage battery 16 can be controlled by controlling the voltage of the bidirectional high-voltage DC/DC converter 15 (the output voltage output to the main bus terminals).

In addition, a main relay 11 configured to selectively connect the fuel cell stack to a main bus terminal is mounted on an output side of the fuel cell stack 10.

In addition, the drive motor 13 is a motor configured to drive the vehicle. The inverter 12 is connected to the output sides of the fuel cell stack 10 and the high-voltage battery 16 via the main bus terminals, and performs phase (phase) conversion on the electric power supplied from the fuel cell stack 10 and/or the high-voltage battery 16 to drive the drive motor 13.

According to an aspect of the present disclosure, the controller 17 controls the overall operation of the components of the fuel cell system. For example, the controller 17 controls the operations of the main relay 11, the inverter 12, the COD heater 14, the converter 15 and the air compressor 18.

According to an aspect of the present disclosure, a method of controlling an operation of an electrical load device connected to a fuel cell stack to receive power from the fuel cell stack and thus consume the power of the fuel cell stack, that is, an electrical load device configured to function as an electrical load with respect to the fuel cell stack, to scan (sweeparing) a stack voltage is used as a stack performance recovery method. At this time, the operation of the electric load device is controlled by the controller 17.

That is, when the controller 17 outputs a control signal for scanning the stack voltage during the stack performance recovery operation, the operation of the electrical load device is controlled according to the control signal output by the controller 17 to scan the stack voltage.

As described above, in the present disclosure, the COD heater 14 and the air compressor 18 may be used as an electrical load device for sweeping the stack voltage, and the controller 17 controls the operations of the COD heater 14 and the air compressor 18 such that the stack voltage is swept during the stack performance recovery operation.

The stack performance recovery operation will be described in detail below.

Fig. 2 is a flowchart illustrating an overall process for fuel cell stack performance recovery according to an aspect of the present disclosure, in which a process for stack performance recovery operation of a fuel cell system is controlled according to an aspect of the present disclosure.

The fuel cell stack performance recovery operation according to an aspect of the present disclosure is performed by the controller 17 based on information collected from the vehicle, and the controller 17 may be a fuel cell system controller configured to control the overall operation of the fuel cell system.

According to an aspect of the present disclosure, the controller 17 is configured to execute the entire process for fuel cell stack performance recovery shown in fig. 2 and execute detailed logic of each process shown in fig. 3 to 6.

As shown in fig. 2, a performance recovery method of a fuel cell stack according to an aspect of the present disclosure includes the following processes: the controller 17 determines whether the stack is in a state in which the stack performance recovery operation can be performed (S10); the controller 17 determines whether the vehicle is in a state in which the stack performance recovery operation can be performed (S30); and when each of the stack and the vehicle is in a state in which the stack performance recovery operation can be performed, the controller 17 performs the stack performance recovery operation (S40).

In addition, the performance recovery method of a fuel cell stack according to an aspect of the present disclosure may further include the following process: after the process of determining whether the stack is in a state in which the stack performance recovery operation can be performed, and before the process of determining whether the vehicle is in a state in which the stack performance recovery operation can be performed, the controller 17 confirms the number of fuel cell stop entries (S20).

In this case, the controller 17 performs the subsequent process, that is, performs the stack performance recovery operation, only when it satisfies that each of the stack and the vehicle is in a state in which the stack performance recovery operation can be performed and a condition relating to the number of times the fuel cell stops entering is satisfied.

In addition, the performance recovery method of a fuel cell stack according to an aspect of the present disclosure may further include the following process: the controller 17 determines whether the stack performance recovery operation has been completed (S50); and when the stack performance recovery operation has not been completed, the controller 17 changes the stack state judgment criterion (S60).

According to an aspect of the present disclosure, when the controller 17 determines that the stack performance recovery operation has been completed or the stack state determination criteria is changed, the controller 17 ends the stack performance recovery operation (S70).

In the following description, the stack refers to the fuel cell stack 10 of the fuel cell system mounted in the fuel cell vehicle, the fuel cell in the fuel cell stop refers to the fuel cell stack, and the recovery of the performance of the stack refers to the recovery of the performance of the fuel cell stack.

In addition, the stack performance recovery operation may refer to an operation of the fuel cell system that recovers the performance of the fuel cell stack, and control of the operation of the fuel cell system for stack performance recovery is performed by the controller 17.

In addition, according to an aspect of the present disclosure, the voltage sweep refers to sweeping the voltage of the fuel cell stack 10, and the voltage sweep and the voltage fluctuation may be understood to have the same meaning.

FIG. 3 is a flow diagram illustrating a method of determining whether a heap is in a state in which heap performance recovery operations may be performed in accordance with an aspect of the present disclosure. The heap being in a state in which a heap performance recovery operation can be performed may refer to the heap being in a state in which it is necessary to perform the heap performance recovery operation, and in order to enter the heap performance recovery operation, it must first be determined whether the heap is in a state in which it is necessary to perform the heap performance recovery operation.

According to an aspect of the present disclosure, the stack performance recovery operation manner is a manner of recovering reversible deterioration of the fuel cell stack 10 due to the catalyst oxide, and the more the number of uses of the fuel cell stack 10, the more the catalyst oxide is generated. Therefore, in the heap status judgment criterion, it is important how many times the heap has been used.

Therefore, according to an aspect of the present disclosure, the state of the stack for entering the stack performance recovery operation is determined based on the integrated value of the stack current or the accumulated travel distance of the vehicle traveling at the stack output above a predetermined level.

At this time, during the operation of the fuel cell system, the controller 17 calculates and uses an integrated value that integrates the stack current above the lower limit value I1. In fig. 3, I1 denotes the lower limit value, which is a value preset in the controller 17 to remove the noise value of the stack current, and which may be set to a smaller value that can distinguish the noise value.

As described above, according to an aspect of the present disclosure, in calculating the integrated value of the stack current, the lower limit value I1 of the integrated stack current is applied to remove a noise value, and the integrated value of the stack current is calculated when the stack output, i.e., the stack current, is the lower limit value I1 or more (S11 and S13).

The controller 17 is configured to integrate only the stack current (stack output) equal to or larger than the lower limit I1 when calculating the integrated value of the stack current.

In addition, in calculating the accumulated running distance, during running of the vehicle and operation of the fuel cell system, the controller 17 accumulatively calculates the running distance of the vehicle when the stack output is equal to or greater than the predetermined first output reference value I2 (S12 and S14). Here, the stack output may be a stack current.

That is, the cumulative travel distance of the vehicle traveling at the stack current equal to or higher than the first output reference value I2 is calculated. In fig. 3, I2 denotes a first output reference value, which is a value used to cumulatively calculate the travel distance of the vehicle when the stack 10 is used, and may be set to a value capable of representing the stack output.

According to an aspect of the present disclosure, as described above, only the travel distances of the vehicle when the stack current is above the first output reference value I2 are accumulated to calculate the accumulated travel distance. As described above, in fig. 3, both the lower limit value I1 and the first output reference value I2 may be values set for the stack current.

According to an aspect of the present disclosure, at least one of an integrated value of a stack current or an accumulated travel distance may be utilized. When the integrated value of the stack current is greater than the predetermined current integration reference value Q1 or the accumulated running distance is greater than the predetermined distance reference value D1, the controller 17 determines that the stack is in a state in which the stack performance recovery operation needs to be performed (S15).

When it is determined that the stack is in a state in which it is necessary to perform the stack performance recovery operation, the controller 17 resets (reset) the integrated value of the stack current or the accumulated travel distance (S16), and performs a subsequent process for stack performance recovery, that is, a process of confirming the number of times the fuel cell stops entering (S20).

In fig. 3, Q1 represents the current integral reference value, and D1 represents the distance reference value. Q1 and D1 are both heap state judgment criteria for judging the number of times the heap has been used, and the entry period and execution period of the heap performance recovery operation are judged based on these values.

Several techniques have been proposed to be able to monitor the state of the stack 10, and most utilize a way of estimating the gradient in the stack current-voltage characteristic. However, in order to estimate reliable values in this manner, the stack must operate in various current regions.

However, in the case where the vehicle is driven mainly in the local current region according to the driving style of the driver, it is not possible to determine whether the stack performance recovery operation needs to be performed.

In an actual commercial vehicle, a sudden change in stack output may reduce the durability of the vehicle, and the vehicle may be subjected to thermal shock due to a large amount of heat generated in the vehicle. Therefore, a heap fixed point operation strategy is employed in many cases. Therefore, the way of estimating the gradient in the stack current-voltage characteristic curve is not suitable for determining the stack state.

Fig. 4 is a flow chart illustrating a method of confirming a Fuel Cell Stop (Fuel Cell Stop) entry number in accordance with an aspect of the present disclosure. According to an aspect of the present disclosure, as described above, a manner is employed for performance recovery operations through stack voltage sweeping.

However, during the running of the fuel cell vehicle, a fuel cell stopped state may occur, and the stack voltage may decrease to a low potential due to natural discharge in the fuel cell stopped state. As described above, in the case where the stack voltage is lowered due to the stop of the fuel cell and thus a voltage variation above a predetermined level occurs, an effect of recovering the stack performance is achieved.

Therefore, according to an aspect of the present disclosure, the controller 17 may be configured to repeatedly generate the fuel cell stop state within a predetermined time during the operation of the fuel cell system, and thus determine that the stack performance recovery operation is not required when the number of times the stack voltage decreases below the predetermined voltage reference value V1 is equal to or greater than the first predetermined number of times C1.

If not, that is, in step S21 of fig. 4, when the number of times the stack voltage falls below the predetermined voltage reference value V1 while the fuel cell is stopped is less than the first predetermined number of times C1 within the predetermined time, the controller 17 resets the number of times the stack voltage is equal to or less than the voltage reference value V1 after the predetermined time (S22), and performs the subsequent process for the stack performance recovery, that is, the process of determining whether the vehicle is in a state in which it is possible to enter the stack performance recovery operation (S30).

In fig. 4, V1 denotes a voltage reference value that is used to specify a voltage level at which the effect of the stack performance recovery operation can be achieved due to the fuel cell stop, and may be set to a low voltage at which the effect of the stack performance recovery operation can be achieved.

According to an aspect of the present disclosure, when the stack voltage is decreased to the voltage reference value V1 at the time of the stop of the fuel cell, the effect of the stack performance recovery operation can be achieved. Specifically, when the number of times that the stack voltage falls below the voltage reference value V1 is less than the first predetermined number of times C1 while the fuel cell is stopped, the subsequent process for the recovery of the stack performance is continuously performed.

In fig. 4, C1 represents the minimum number of times required to achieve the effect of the stack performance recovery operation, i.e., the first predetermined number of times C1. When the number of times the stack voltage falls below the voltage reference value V1 within the predetermined time is less than the first predetermined number of times C1, the controller 17 determines that the effect of the stack performance recovery operation cannot be achieved, and performs the subsequent process for stack performance recovery.

Normally, the fuel cell is brought to a stop in a state where there is no stack output. Therefore, in the previous stack state confirmation process, when the integrated value of the stack current is larger than the current integration reference value Q1 or the accumulated running distance is larger than the distance reference value D1, a state in which the fuel cell is stopped can be avoided to some extent according to the stack output condition at that time.

Further, since it takes a long time for the stack voltage to decrease below the voltage reference value V1 only due to a natural voltage drop at the time of stopping the fuel cell, there is not a high possibility that the stack voltage decreases below the voltage reference value V1 at the time of stopping the fuel cell occurs a plurality of times within a predetermined time.

Therefore, the process of confirming the number of times the fuel cell stops entering is not a necessary process that must be performed during the operation of recovering the performance of the fuel cell stack.

That is, when the controller 17 determines that the stack 10 is in a state that requires entry into the stack performance recovery operation, the logic may be configured to determine whether the vehicle is in a state that can enter the stack performance recovery operation after confirming the process of stopping the entry number of fuel cells. In contrast, the controller 17 can confirm the vehicle state immediately after confirming the stack state without performing the process of confirming the number of times the fuel cell stops entering.

Fig. 5 is a flowchart illustrating a method of determining whether a vehicle is in a state in which a stack performance recovery operation may be performed, according to an aspect of the present disclosure. According to an aspect of the present disclosure, the controller 17 is configured to confirm whether the vehicle is in a state in which the stack performance recovery operation can be performed according to the logic shown in fig. 5.

That is, when it is determined in the process S10 that the stack is in a state in which entry into the performance recovery operation is required, and it is confirmed in the process S20 that the number of fuel cell stop entries is counted and it is determined that the stack is in a state in which execution of the stack performance recovery operation is required, the controller 17 determines in the subsequent process S30 whether the vehicle is in a state in which the stack performance recovery operation can be executed (see fig. 2).

Since the vehicle basically has to generate an output desired by the driver, it is confirmed whether the vehicle can run without the output of the stack 10, and when the vehicle can run without the output of the stack, the stack performance recovery operation must be performed in the subsequent process.

In this process, the controller 17 confirms whether the vehicle can run without the output of the stack 10. If the vehicle can travel without the output of the stack 10, the controller 17 determines that the vehicle is in a state in which the stack performance recovery operation can be performed.

Referring to fig. 5, the detailed steps of the process of determining whether the vehicle is in a state in which the stack performance recovery operation can be performed are shown.

As shown in fig. 5, the controller 17 determines whether the vehicle is running in a start (key on) state (S31), and in the case of the vehicle running, compares the SOC of the high-voltage battery (main battery) 16 connected to the drive motor to supply electric power to the drive motor with a predetermined first SOC reference value S1 (S32).

Here, when the SOC of the high-voltage battery 16 is equal to or greater than the first SOC reference value S1, the controller 17 compares the dischargeable electric power of the high-voltage battery 16 with a predetermined first electric power reference value W1 (S33).

Subsequently, when the dischargeable electric power of the high-voltage battery 16 is equal to or greater than the first electric power reference value W1, the controller 17 compares the current stack required output determined while the fuel cell system is operating with a predetermined second output reference value I3 (S34). Subsequently, when the stack requested output is smaller than the second output reference value I3, the controller 17 determines that the vehicle is in a state in which the stack performance recovery operation can be performed even if the vehicle is running.

That is, when the condition that the vehicle will run in the startup state, the condition that the SOC of the high-voltage battery 16 is equal to or greater than the first SOC reference value S1, the condition that the dischargeable electric power of the high-voltage battery 16 is equal to or greater than the first electric power reference value W1, and the condition that the stack requested output is less than the second output reference value I3 are all satisfied, the controller 17 determines that the vehicle is in a state in which the stack performance recovery operation can be performed even if the vehicle is running.

On the other hand, when the vehicle is in a key-off state instead of a running state, the controller 17 compares the SOC of the high-voltage battery 16 with the second SOC reference value S2 (S35), and determines that the vehicle is in a state in which the stack performance recovery operation can be performed when the SOC of the high-voltage battery 16 is equal to or greater than the second SOC reference value S2.

As described above, the controller 17 confirms whether the vehicle is running, whether the vehicle is in a start/stop (on/off) state, the SOC of the high-voltage battery (main battery) 16, the dischargeable electric power of the high-voltage battery 16, and the stack required output to determine whether the vehicle is in a state in which the stack performance recovery operation can be performed.

Here, the stack requested output may refer to a current value requested by the stack as a value determined by the operation information of the fuel cell system. A method of determining the current stack required output from the operation information of the fuel cell system is known in the art, and a detailed description thereof will be omitted.

In fig. 5, S1 denotes the first SOC reference value. When the vehicle is running in the startup state, the controller 17 determines that the stack performance recovery operation can be performed only when the SOC of the high-voltage battery 16 is equal to or greater than the first SOC reference value S1.

Whether the SOC of the high-voltage battery 16 is equal to or greater than the first SOC reference value S1 is information on whether the vehicle can run using the high-voltage battery 16 without the output of the stack 10. The higher the SOC of the high-voltage battery 16, the longer the performance recovery operation time.

However, in the case where the first SOC reference value S1 is set to an excessively high value and cannot be reached during traveling, the stack performance recovery operation may not be performed, and therefore, it is necessary to set the first SOC reference value S1 to an appropriate value (e.g., S1 — 60%).

In fig. 5, W1 denotes a first power reference value, which is a value set in the controller 17 to determine that the vehicle can run using the high-voltage battery 16, and which can be set to a value equal to or greater than the average required output of the drive motor 13.

According to an aspect of the present disclosure, the controller 17 determines that the vehicle can run using the high-voltage battery 16 when the dischargeable electric power of the high-voltage battery 16 is equal to or greater than the first electric power reference value W1.

In fig. 5, I3 denotes a second output reference value, which is compared with the stack required output I3 and set to a low value in the controller 17, to determine that the output required by the vehicle can be provided by the high-voltage battery 16 and that the stack required output is small (e.g., the second output reference value is 5A).

In fig. 5, S2 denotes the second SOC reference value. When the vehicle is not running and is in a key-off state, the controller 17 determines that the stack performance recovery operation may be performed when the SOC of the high-voltage battery 16 is equal to or greater than the second SOC reference value S2.

In a key-off state where the vehicle is not running, it is sufficient to ensure only a low SOC of the battery required to perform the stack performance recovery operation (air compressor on/off control, etc.), and therefore the second SOC reference value S2 may be set to a value lower than the first SOC reference value S1 (e.g., S2-25%).

FIG. 6 is a flow diagram illustrating a method of determining whether a heap performance recovery operation has completed and changing heap status determination criteria when not completed in accordance with an aspect of the present disclosure.

As shown in fig. 1, the controller 17 executes a predetermined stack performance recovery operation process when it is satisfied that each of the stack and the vehicle is in a state in which the stack performance recovery operation can be performed and a condition relating to the number of times the fuel cell stops entering is satisfied.

According to an aspect of the present disclosure, stack performance recovery may be achieved by operating the COD heater 14 while repeatedly controlling the on/off of the air compressor 18 to sweep the stack voltage.

That is, the controller 17 performs the stack performance recovery operation shown in fig. 6 when it is satisfied that the stack is in a state in which the stack performance recovery operation can be performed, when it is confirmed that the result of the number of fuel cell stop entries satisfies the predetermined condition, and when it is satisfied that the vehicle is in a state in which the stack performance recovery operation can be performed.

During the stack performance recovery operation, first, the vehicle running mode is switched to the high-voltage battery running mode (the stack output for running is limited) (S41). The high-voltage battery running mode is a mode in which the vehicle runs by battery discharge, and is a mode in which the drive motor 13 is driven with the charging power of the high-voltage battery 16 instead of the generated power of the fuel cell stack 10 so that the vehicle runs.

Subsequently, the controller 17 turns off the main relay 11 of the fuel cell system (S42), turns on the COD heater 14(S43), performs cooling control of the COD heater (S44), and controls the hydrogen supply pressure to be the predetermined target pressure H1 or more (S45).

At this time, when the main relay is turned off by the controller 17, the electrical path formed from the high voltage battery 16 may be blocked when the COD heater is turned on.

As described above, when the COD heater 14 is turned on while the stack performance recovery operation is performed in the state where the main relay 11 is turned off, the COD heater 14 can be used as an electrical load that consumes stack power.

In addition, the cooling control process of the COD heater 14 may be a process of controlling the temperature of the COD heater to prevent overheating of the COD heater. Concurrently with the cooling control of the COD heater 14, the controller 17 causes the coolant pump (not shown) to operate at a rotational speed above a predetermined rotational speed (RPM), and controls the operation of the coolant bypass valve to maintain its opening degree toward the COD heater at a predetermined level.

At this time, the rotation speed of the coolant pump and the opening degree of the coolant bypass valve toward the COD heater are set to prevent the COD heater from overheating when the stack performance recovery operation is performed, based on the heat generation capacity of the COD heater 14.

In addition, the controller 17 controls a hydrogen pressure control valve (not shown) and the like to maintain the pressure of hydrogen supplied to the fuel cell stack 10, i.e., a hydrogen supply pressure, above a predetermined target pressure H1. During the stack performance recovery operation, it is sufficient to maintain the hydrogen supply pressure at the pressure required to generate the stack voltage and the current due to the operation of the COD heater 14 as the load.

Therefore, the target pressure H1 during the stack performance recovery operation may be set to the value of the basic target pressure level at the time of normal operation (for example, the target pressure of 130 kPa).

In addition, in a state where the cooling control of the COD heater 14 is performed, the controller 17 scans the stack voltage to recover the stack performance. To scan the stack voltage, the air compressor 18 is on/off controlled (S46).

That is, the controller 17 controls the operation of the air compressor 18 such that the air compressor 18 is alternately turned on and off. When the air compressor is turned on, it is sufficient to supply only the amount of air capable of generating voltage to the stack 10, and therefore, the air compressor 18 is controlled at the basic operation level at the time of normal operation.

In addition, when the controller 17 controls the operation of the air compressor 18 such that the air compressor 18 is alternately turned on and off, the holding time of each of the turning on and off may be individually applied. In order to maximize the effect of the stack performance recovery operation, the time to hold the low potential is important, and thus the off hold time may be set longer than the on hold time.

The controller 17 counts the number of times of execution of the on/off control of the air compressor while repeatedly controlling the air compressor 18 to be turned on and off. Basically, when the number of times the on/off control of the air compressor, which is counted in step S52 of fig. 6, is performed reaches the second predetermined number of times C2, the controller 17 determines that the stack performance recovery operation has been completed.

In addition, while repeatedly controlling the air compressor 18 to be turned on and off, the controller 17 determines whether the stack performance recovery operation interruption condition is satisfied or not, based on the operation information of the fuel cell system collected from the vehicle (S51).

When the stack performance recovery operation interruption condition is satisfied, it is determined whether the stack performance recovery operation has been completed (S52). Even if the stack performance recovery operation interruption condition is satisfied in step S51 and therefore the stack performance recovery operation must be interrupted, when it is determined in step S52 that the stack performance recovery operation has not been completed, the controller 17 ends the stack performance recovery operation after changing the stack state determination criterion in step S60 (S70).

On the other hand, when it is judged in step S51 that the stack performance recovery operation interruption condition is satisfied, and when it is judged in step S52 that the stack performance recovery operation has been completed, the controller 17 immediately ends the stack performance recovery operation without changing the stack state judgment criterion (S70).

When it is judged in step S51 that the stack performance recovery operation interruption condition is not satisfied during the stack performance recovery operation, the controller 17 maintains the stack performance recovery operation until the stack performance recovery operation is completed (no in step S53). At this time, the controller 17 counts the number of executions of the on/off control of the air compressor 18, and when the number of executions of the on/off control of the air compressor 18 counted in step S53 reaches the second predetermined number of times C2, it is judged that the stack performance recovery operation has been completed, and the stack performance recovery operation is ended (S70).

According to an aspect of the present disclosure, the stack performance recovery operation interruption condition may be a condition that the stack required output is equal to or greater than the third output reference value during the stack performance recovery operation, a condition that the SOC of the high-voltage battery 16 is less than the third SOC reference value, or a condition that the dischargeable power of the high-voltage battery 16 is less than the second power reference value.

That is, according to an aspect of the present disclosure, during the stack performance recovery operation in which the air compressor 18 is repeatedly controlled to turn on and off to sweep the stack voltage, the controller 17 compares the stack required output with the third output reference value, compares the SOC of the high-voltage battery 16 with the third SOC reference value, and compares the dischargeable power of the high-voltage battery 16 with the second power reference value. The controller 17 determines that the stack performance recovery operation interruption condition is satisfied when the stack required output is equal to or greater than the third output reference value, the SOC of the high-voltage battery 16 is less than the third SOC reference value, or the dischargeable electric power of the high-voltage battery 16 is less than the second electric power reference value.

As described above, when it is judged that the stack performance recovery operation interruption condition is satisfied during the stack performance recovery operation, the controller 17 ends the stack performance recovery operation. At this time, when the number of times of execution of the on/off control of the air compressor 18 after the start of the stack performance recovery operation is less than the second predetermined number of times C2, the controller 17 determines that the stack performance recovery operation has not been completed, changes the stack state determination criterion for the next stack performance recovery operation (S60), and ends the stack performance recovery operation (S70).

However, when the stack performance recovery operation interruption condition is satisfied, when the number of times the on/off control of the air compressor 18 is performed has reached the second predetermined number of times C2, the controller 17 determines that the stack performance recovery operation has been completed, and immediately ends the stack performance recovery operation without changing the stack state determination criterion (S70).

In the stack performance recovery operation interruption condition, the third output reference value is a reference value for determining a case where the stack output is required due to the stack performance recovery operation, and may be set in the controller 17 to a value higher than the second output reference value I3 in step S34 of the vehicle state determination process of fig. 5.

In the stack performance recovery operation interruption condition, the third SOC reference value is a reference value for determining excessive decrease in the SOC of the high-voltage battery 16. When the stack performance recovery operation is continuously performed and therefore the SOC of the high-voltage battery 16 is excessively lowered, normal operation in the high-voltage battery running mode may not be possible.

Therefore, when the SOC of the high-voltage battery 16 is less than the third SOC reference value, the controller 17 determines that the stack performance recovery operation interruption condition is satisfied, and ends the stack performance recovery operation to prevent the normal operation from being impossible in the high-voltage battery running mode.

According to an aspect of the present disclosure, the third SOC reference value S3 must be set in the controller 17 to a value lower than the first SOC reference value S1 in step S32 of the vehicle state determination process of fig. 5, and may be set to the same value as the second SOC reference value S2 in step S35 of the vehicle state determination process of fig. 5, or a value smaller than the second SOC reference value S2 by a predetermined value or less (e.g., S2 and S3-25%).

In the stack performance recovery operation interruption condition, the second power reference value is a reference value for determining that the dischargeable power of the high-voltage battery 16 is excessively decreased. When the dischargeable electric power of the high-voltage battery 16 excessively decreases, normal operation in the high-voltage battery running mode may not be possible.

Therefore, when the dischargeable electric power of the high-voltage battery 16 is smaller than the second electric power reference value, the controller 17 determines that the stack performance recovery operation interruption condition is satisfied, and ends the stack performance recovery operation to prevent the normal operation from being impossible in the high-voltage battery running mode.

According to an aspect of the present disclosure, the dischargeable electric power of the high-voltage battery 16 is changeable according to the temperature and voltage of the high-voltage battery 16, and the like, and the controller 17 may determine the dischargeable electric power of the high-voltage battery 16 based on information on the temperature and voltage of the high-voltage battery 16 collected by a detection element such as a sensor.

Methods of determining the dischargeable power of the high-voltage battery 16 are known in the art, and a detailed description thereof will be omitted.

According to an aspect of the present disclosure, the second power reference value may be set in the controller 17 to a value lower than the first power reference value W1 in step S33 of the vehicle state determination process of fig. 5.

According to an aspect of the present disclosure, the number of times of execution of the on/off control of the air compressor may be defined in such a manner that the number of times of execution of the on/off control of the air compressor is 1 when the on and off of the air compressor 18 are respectively maintained for the respective predetermined maintaining times once.

In addition, the second predetermined number of times C2 is a number of times set to determine whether the stack performance recovery operation has been completed. As described above, when the number of times the on/off control of the air compressor is performed has reached the second predetermined number of times C2, the controller 17 may determine that the stack performance recovery operation has been completed.

Ending the heap performance recovery operation refers to returning to a state before performing the heap performance recovery operation. When the stack performance recovery operation ends, all of steps S41 to S46 that were started at the time of the stack performance recovery operation of fig. 6 end, and switch to the normal travel mode.

Meanwhile, even if the predetermined stack performance recovery operation interruption condition is satisfied and thus the stack performance recovery operation must be ended, the change of the stack state judgment criterion in step S60 is performed when the number of times of execution of the on/off control of the air compressor 18 does not reach the second predetermined number of times C2, that is, when the stack performance recovery operation has not been completed.

At this time, when the heap performance recovery operation has not been completed, the heap state judgment criterion is changed so that the next heap performance recovery operation is executed earlier than this time. Here, the stack state judgment criterion may be the current integral reference value Q1 as a criterion for judging the integrated value of the stack current in the stack state judgment process of fig. 3, the distance reference value D1 as a criterion for judging the accumulated travel distance, or both the current integral reference value Q1 and the distance reference value D1.

Fig. 7 is a diagram illustrating an example of changing the heap status determination criteria according to an aspect of the present disclosure. In the graph of fig. 7, the minimum reference may be a lower limit value of the current integral reference value Q1 or a lower limit value of the distance reference value D1.

According to an aspect of the present disclosure, when the number of executions of the on/off control of the air compressor 18 has not reached the second predetermined number of times C2 even though the stack performance recovery operation interruption condition is satisfied, the reference values Q1 and D1 may be decreased by a predetermined value so that the next stack performance recovery operation is executed earlier than this time.

According to an aspect of the present disclosure, if the reference value for the heap state judgment is set to a very small value, the recovery operation may be entered too frequently after the heap performance recovery operation has not been completed. Therefore, an appropriate reference value above the predetermined level is set through a preliminary test and evaluation process.

The two reference values Q1 and D1 may be set to different values. The graph of fig. 7 shows an example of two reference values.

As is apparent from the above description, according to the performance recovery method of a fuel cell stack of an aspect of the present disclosure, it is possible to accurately determine whether the stack is in a state in which the stack performance recovery operation can be performed and whether the vehicle is in a state in which the stack performance recovery operation can be performed, thereby appropriately ensuring the performance recovery operation time during vehicle traveling, enabling voltage sweep and stack performance recovery to be performed more efficiently, and enabling irreversible degradation of the fuel cell stack to be suppressed, thereby improving the durability of the fuel cell stack.

The present disclosure has been described in detail with reference to the preferred embodiments thereof. However, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined in the claims and their equivalents.