System and method for controlling coolant temperature of a fuel cell

Abstract

The present invention provides a system and method for controlling the coolant temperature of a fuel cell. A coolant temperature control system for a fuel cell stack in a vehicle includes: a controller for determining a real-time target outlet temperature of a fuel cell stack coolant; and a communication device for detecting a fuel cell voltage and a fuel cell current output from the fuel cell stack. The real-time target outlet temperature of the fuel cell stack coolant is determined by the ratio of the input fuel cell heat generated from the fuel cell stack to the fuel cell power, and is used to compensate for the target outlet temperature due to degradation of the fuel cell stack over time. In addition, when the travel distance of the vehicle is greater than a predetermined travel distance, the coolant temperature control system determines to activate a real-time target outlet temperature for evaluating the fuel cell stack coolant.

Description

Technical Field

[0001] The present disclosure relates to systems and methods for controlling coolant temperature in a vehicle, and more particularly to systems and methods for controlling coolant outlet temperature of a fuel cell stack in a vehicle. Background Art

[0002] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0003] Hydrogen fuel cells are an alternative power source to internal combustion engines for vehicles due to zero harmful exhaust emissions, high efficiency and the possibility of producing hydrogen from renewable methods. Multiple fuel cells used as a power source are stacked in a vehicle. The vehicle further includes: a fuel supply system that supplies hydrogen or similar fuel to the fuel cell stack; an air supply system that supplies oxygen, which is an oxidant required for the electrochemical reaction; and a water and thermal management system that regulates the temperature of the fuel cell stack, etc.

[0004] When hydrogen is supplied to the anode of the fuel cell stack and oxygen is supplied to the cathode of the fuel cell stack, hydrogen ions are separated by a catalytic reaction in the anode. The separated hydrogen ions are transferred to the oxidation electrode as the cathode through the electrolyte membrane, and the separated hydrogen ions in the anode produce an electrochemical reaction together with electrons and oxygen in the oxidation electrode, so that electric energy can be obtained. Therefore, in a hydrogen fuel cell vehicle, electricity and heat are generated due to the movement of electrons generated by the above process.

[0005] Through this process, the fuel cell stack generates electrical energy from the electrochemical reaction of hydrogen and oxygen as reactant gases, and discharges heat and water as reaction byproducts. Therefore, the fuel cell system in the vehicle includes a device for controlling the temperature of the fuel cell stack. Generally, the cooling system for maintaining the fuel cell stack at a desired temperature in the fuel cell system for the vehicle widely adopts a coolant type, which cools the fuel cell stack by circulating the coolant through the cooling channel in the fuel cell stack.

[0006] The above information disclosed in this Background section is only for enhancement of understanding of the background of the present disclosure and therefore it may contain information that does not constitute prior art. Summary of the invention

[0007] The present disclosure provides a coolant temperature control system and method for controlling the temperature of a fuel cell (FC) stack in a vehicle.

[0008] According to one aspect of the present disclosure, a coolant temperature control system includes a controller operable to determine a real time target exit temperature of a FC coolant. The controller is configured to compensate for the target exit temperature due to degradation of the FC stack over time. The controller determines an input FC Heat to FC Power ratio generated from the FC stack. The coolant temperature control system further includes a communicating device operable to detect an FC voltage and FC current output from the FC stack. In addition, the controller determines a constant FC Heat to Power ratio and a target FC coolant outlet temperature at the beginning and end of the life of the FC stack for mapping the real time target FC coolant outlet temperature.

[0009] According to another aspect of the present disclosure, when a trip distance of the vehicle is greater than a predetermined travel distance, the controller determines to activate the temperature control system for estimating a real-time target outlet temperature of the FC coolant. The controller sets 30 km as the predetermined travel distance for activating the estimation of the real-time target outlet temperature of the FC coolant.

[0010] According to another aspect of the present disclosure, each of FC heat and FC power (FC Power) is determined by evaluating the detected FC voltage and FC current. The controller estimates FC heat by the following formula: FC heat = [1.25 × (# of FC) - FC voltage] × FC current, and estimates FC power by the following formula: FC power = FC voltage × FC current.

[0011] According to another aspect of the present disclosure, a constant FC heat to FC power ratio is obtained by wherein a maximum FC heat to FC power ratio (Ratio max ) and the minimum FC heat to FC power ratio (Ratio min The target FC coolant outlet temperature is determined by the minimum target FC coolant outlet temperature (T FC_Min ) and the maximum target FC coolant outlet temperature allowed at the end of the life of the FC stack (T FC_Max) is determined. Therefore, the controller determines the slope (m) of the calibration line (calibration line) used for mapping the real-time target outlet temperature of the FC coolant and the x-intercept (X) of the calibration line of the slope by the following formula: and

[0012] According to another aspect of the present disclosure, the controller determines the real-time target outlet temperature of the FC coolant using the determined input FC heat to FC power ratio by the following formula:

[0013] According to another aspect of the present disclosure, the FC voltage and the FC current are detected by a voltage sensor and a current sensor connected between the FC stack and a communication device of the system.

[0014] According to one aspect of the present disclosure, a method for controlling the coolant temperature of a fuel cell (FC) stack of a vehicle having a controller includes the following steps: detecting FC voltage and FC current output from the FC stack; evaluating FC heat and FC power generated by the FC stack using the detected FC voltage and FC current; determining a ratio of input FC heat to FC power generated from the FC stack; determining a constant FC heat to FC power ratio and a target FC coolant outlet temperature at the beginning and end of the life of the FC stack for mapping a real-time target outlet temperature of the FC coolant; and determining a real-time target outlet temperature of the FC coolant for compensating for the target outlet temperature due to degradation of the FC stack based on the operating time of the FC stack.

[0015] According to another aspect of the present disclosure, the method further includes the steps of: evaluating a travel distance of the vehicle; and determining to activate a real-time target outlet temperature for evaluating the FC coolant when the travel distance of the vehicle is greater than a predetermined travel distance. The controller sets 30 km as the predetermined travel distance for activating the real-time target outlet temperature for evaluating the FC coolant.

[0016] Further areas of applicability will become apparent from the description provided herein.It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order that the present disclosure may be better understood, various forms thereof given by way of example will now be described with reference to the accompanying drawings, in which:

[0018] Figure 1A schematic diagram showing a coolant temperature control system for a fuel cell stack according to an exemplary form of the present disclosure;

[0019] Figure 2 is a graph showing a target FC coolant outlet temperature for each ambient temperature according to the related art;

[0020] Figure 3 is an exemplary graph showing voltage degradation of a fuel cell stack at the beginning and end of the life of the fuel cell stack;

[0021] Figure 4 is an exemplary graph showing fuel cell stack durability fleet data over 100,000 km;

[0022] Figure 5 is a graph showing a calibration line for mapping a real-time target FC coolant outlet temperature according to an exemplary form of the present disclosure;

[0023] Figure 6 is a configuration diagram showing a coolant temperature control system for a fuel cell stack according to an exemplary form of the present disclosure; and

[0024] Fig. 7A and Figure 7B are exemplary graphs showing calibration lines for mapping a target FC coolant outlet temperature and a maximum FC coolant outlet temperature, respectively.

[0025] The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. DETAILED DESCRIPTION

[0026] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate the same or corresponding parts and features.

[0027] Although the exemplary form is described as using multiple units to perform the exemplary process, it should be understood that the exemplary process can also be performed by one or more modules. In addition, it should be understood that the term controller refers to a hardware device including a memory and a processor. The memory is configured to store the module, and the processor is specifically configured to execute the module to perform one or more processes described further below.

[0028] In addition, the control logic of the present disclosure may be formed as non-transitory computer readable media on a computer readable medium containing executable program instructions executed by a processor, controller, etc. Examples of computer readable media include, but are not limited to, ROM, RAM, compact disc (CD)-ROM, magnetic tapes, floppy disks, flash drives, smart cards, and optical data storage devices.

[0029] Figure 1 A coolant temperature control system 10 is shown for a fuel cell (FC) stack 12 in a vehicle. Figure 1 In the example of FIG. 1 , the temperature control system 10 is shown in a vehicle having a fuel cell stack 12, but the temperature control system 10 may also be used to cool any other structure having a fuel cell stack 12. Figure 1 As shown in the figure, the temperature control system 10 includes: a radiator 14 and a cooling fan 15, which receive heated coolant from the fuel cell stack 12 and discharge heat from the coolant to the outside; a coolant pipeline 16, which is arranged between the fuel cell stack 12 and the radiator 14 to circulate the coolant; and a coolant pump 18, which is used to pump the coolant received from the radiator and deliver the pumped coolant to the fuel cell stack 12 through the coolant pipeline 16.

[0030] like Figure 1 As shown in , the temperature control system 10 further includes a flow meter 21 for measuring and / or controlling the amount of coolant, a coolant inlet temperature sensor 22 for measuring the temperature of the coolant entering the fuel cell stack 12, and a coolant outlet temperature sensor 24 for measuring the temperature of the coolant coming out of the fuel cell stack 12. Each of the flow meter 21, the coolant inlet temperature sensor 22, and the coolant outlet temperature sensor 24 is directly or indirectly connected to a controller 20 including a central processing unit (CPU) in the vehicle. The controller 20 further includes a communication device 25 for communicating with the flow meter 21 and the sensors 22 and 24. In Figure 1 In FIG. 1 , the coolant inlet temperature sensor 22 is located upstream of the fuel cell stack 12 , and the coolant outlet temperature sensor 24 is located downstream of the fuel cell stack 12 .

[0031] In addition, the communication device 25 in the controller 20 communicates with a current sensor 26 for measuring the current output from the fuel cell stack 12 and a voltage sensor 28 for measuring the voltage output from the fuel cell stack 12, such as Figure 1Thus, the controller 20 receives all data from each of the coolant inlet temperature sensor 22 and the coolant outlet temperature sensor 24, the current sensor 26 and the voltage sensor 28, and the flow meter 21, and controls all operations of the temperature control system 10 of the fuel cell stack 12, including the temperature and amount of the coolant flow.

[0032] generally, Figure 1 The temperature control system 10 in the system controls the operation by setting a target temperature of the coolant at the outlet of the fuel cell stack 12. In the system 10, the controller 20 can detect the coolant outlet temperature by communicating with the coolant outlet temperature sensor 24, compare the measured temperature with a predetermined target temperature, or control the operation of the temperature control system for mapping the target temperature.

[0033] In the existing temperature control system as the related art, Figure 2 A diagram showing a fixed target coolant outlet temperature of a fuel cell stack for each ambient temperature is shown by the operation of the control system. Figure 2 As shown in , the calibration of the mapping used for the control system is based on the performance of the fuel cell stack at the beginning of its useful life, and we have found that it does not take into account stack degradation, such as end-of-life performance, because the target coolant outlet temperature of the fuel cell stack for each ambient temperature is fixed at the beginning of life performance. In addition, the target fuel cell coolant outlet temperature can be controlled based on the ambient temperature, which is independent of the degradation of the fuel cell stack. For example, the target fuel cell coolant outlet temperature is reduced on hot days to avoid a dry-out phenomenon of the fuel cell stack. Therefore, Figure 2 The current mapping control system of the target coolant outlet temperature in the control system may be inadequate because the current system for controlling the target coolant outlet temperature does not take into account the degradation of the fuel cell stack during its service life.

[0034] Figure 3 A graph 30 is shown of the degradation of the fuel cell stack 12 during its service life. The graph 30 shows the fuel cell voltage versus fuel cell current in the fuel cell stack 12 during its service life in a vehicle. A graph 32 shows the fuel cell voltage versus fuel cell current at the beginning of the service life, and another graph 34 shows the fuel cell voltage versus fuel cell current at the end of the service life of the fuel cell stack 12 in a vehicle. Figure 3As shown in , a decrease in voltage output of the fuel cell stack occurs during its service life. Therefore, as the voltage of the fuel cell stack 12 in the vehicle degrades over mileage, the fuel cell stack 12 generates more waste heat due to the degradation of the fuel cell stack 12.

[0035] According to an exemplary form of the present disclosure, the heat of the fuel cell stack 12 generated during fuel cell stack operation is calculated by the following first equation E1, FC Heat Generated = [1.25×(# of Fuel Cells)-FC Voltage (Volts)]×FC Current, where # of Fuel Cells represents the number of fuel cells installed in the fuel cell stack 12. In E1, if the fuel cell voltage degrades, the heat of the fuel cell stack 12 naturally increases. In addition, if the fuel cell voltage degrades and therefore the heat of the fuel cell stack 12 increases, the fuel cell stack 12 pulls more current. Therefore, the fuel cell coolant temperature control system currently used is inadequate because the heat generated from the fuel cell stack 12 keeps increasing during the service life of the fuel cell stack 12 and at the end of its service life.

[0036] Figure 4 A graph of fuel cell durability fleet data over 100,000 km is shown, with the fuel cell coolant outlet temperature fixed at its target at the start of lifetime performance. Figure 4 The first data 42 in the graph represents the maximum fuel cell coolant outlet temperature, and the second data 44 represents the average fuel cell coolant outlet temperature. Both the first data 42 and the second data 44 show almost constant values ​​over 100,000 km. Therefore, the heat value of the fuel cell stack itself is difficult to explain the health status of the fuel cell stack, such as degradation. However, the third data 46 represents the ratio of fuel cell (FC) heat to fuel cell (FC) power over 100,000 km. Figure 4 As shown in , the FC heat to FC power ratio increases significantly over time. Therefore, this ratio can be used to indicate the health of the fuel cell stack. The FC heat to FC power ratio is calculated by dividing the FC heat calculated according to the first equation E1 by the FC power calculated according to the second equation E2 (FC power = FC voltage × FC current). Figure 4 As shown in , at the beginning of the useful life of the fuel cell stack, the FC heat to FC power ratio is about 60%, and the ratio increases to about 75% over 100,000 km. Therefore, as described above, the heat generated by the fuel cell stack 12 during its useful life increases due to the degradation of the fuel cell stack 12, and the excess heat can be evaluated by the FC heat to FC power ratio.

[0037] Figure 5 A diagram for mapping the real-time target FC coolant outlet temperature is shown. Figure 5 Ratio max The maximum FC heat to FC power ratio at which the fuel cell stack is considered to end its life is expressed as Ratio min represents the minimum FC heat to FC power ratio where the fuel cell stack life is considered to begin, T FC_Min represents the minimum FC coolant outlet temperature allowed at the beginning of the life of the fuel cell stack 12, T FC_Max represents the maximum FC coolant temperature allowed at the end of the life of the fuel cell stack 12, Ratio input represents the real-time input FC heat to FC power ratio, and T FC_Target represents a real-time target FC coolant outlet temperature based on the current input FC Heat to FC Power ratio. Thus, the target FC coolant outlet temperature in the system 10 is dynamically determined based on the real-time input FC heat to FC Power ratio during the service life of the fuel cell stack 12.

[0038] exist Figure 5 In the present invention, the controller 20 in the temperature control system 10 of the vehicle evaluates the calibration line based on the parameters determined at the beginning and end of the life of the fuel cell stack 12 for mapping the real-time target FC coolant outlet temperature. As described above, the parameters used to calculate the calibration line are determined by the constant FC heat to FC power ratio at the beginning and end of the life of the fuel cell stack 12 and the FC coolant outlet temperature allowed at each of the beginning and end of the life of the fuel cell stack 12. Figure 5 The evaluation calibration line in is used to compensate for the degradation of the fuel cell stack 12 during its service life. Therefore, the real-time target FC coolant outlet temperature can be obtained by following Figure 5 Therefore, the controller 20 in the coolant temperature control system 10 can dynamically determine the target FC coolant outlet temperature of the excess heat of the fuel cell stack 12 due to its degradation.

[0039] like Figure 5 As shown in , the real-time target FC coolant outlet temperature is determined along the calibration line and calculated using the current input FC heat and FC power ratio by the following third equation E3:

[0040] Where m represents the slope of the calibration line of the graph, and X represents the intercept of the calibration line of the slope. The slope m of the calibration line is calculated by the following fourth equation E4, And the intercept X of the calibration line of the slope is calculated by the following fifth equation E5,

[0041] The fuel cell stack 12 in the vehicle generates electrical energy through an electrochemical reaction of hydrogen and oxygen as reaction gases, and discharges heat and water as reaction byproducts. Since water, one of the byproducts, changes its amount and state according to the real-time driving conditions of the vehicle including temperature and pressure, etc., it is difficult to estimate the internal phenomena of the fuel cell stack 12. According to the driving conditions of the vehicle, water keeps changing its state in the form of steam, saturated solution and ice. It affects the characteristics of electrons and gases, wherein the water with changed state passes through the separator channel, gas diffusion layer, catalyst layer, membrane, etc. (not shown) of the fuel cell stack 12. Therefore, due to the change in the state of water, a "flooding" phenomenon in which water overflows and a "dry-out" phenomenon in which water is lacking occur in the fuel cell stack 12. Therefore, it can also be determined that the water used in Figure 5 The real-time target FC coolant outlet temperature is mapped on the calibration line in order to avoid dry-out and flooding of the fuel cell stack 12 .

[0042] Figure 6 1 is an exemplary flow chart 100 showing the operation of the controller 20 in the temperature control system 10 according to the present disclosure. As shown in the flow chart 100, if the travel distance of the vehicle is greater than a predetermined distance (e.g., 30 km), the controller 20 determines the real-time target or maximum FC coolant outlet temperature using the current input FC heat to FC power ratio. However, if the travel distance of the vehicle is less than the predetermined distance, the controller 20 for evaluating the real-time target or maximum FC coolant outlet temperature may not be activated because the current input FC heat to FC power ratio becomes inaccurate under battery-only operation such as low fuel cell operation.

[0043] In step S101, the controller 20 starts operating the dynamic target FC coolant outlet temperature system. In step S102, the controller 20 communicates with the current sensor 26 for detecting the current output from the fuel cell stack 12, the voltage sensor 28 for detecting the voltage output from the fuel cell stack 12, and the speed sensor 23 for detecting the speed of the vehicle (shown in FIG. Figure 1 In step S103, the controller 20 calculates the FC heat value by the first equation E1 and the FC power value by the second equation E2 using the collected data from step S102. In addition, in step S104, the controller 20 calculates the travel distance of the vehicle in the current trip of the vehicle using the collected vehicle speed data.

[0044] In step S105, the controller 20 calculates the total FC heat energy value over time during vehicle travel by integrating all calculated data from step S103. In step S106, the controller 20 calculates the total FC power value over time during vehicle travel by integrating all calculated data from step S103. In step S107, the controller 20 calculates the current input FC heat to FC power ratio during the current trip of the vehicle.

[0045] In step S108, the controller 20 determines whether the travel distance of the vehicle is greater than a predetermined distance in the current trip of the vehicle, which is used to activate the system 10 to evaluate the real-time target FC coolant outlet temperature. For example, the predetermined travel distance of the vehicle is 30km for activating the system 10 to determine the real-time target FC coolant outlet temperature. However, the predetermined travel distance in other forms according to the present disclosure can be changed. If the controller 20 determines that the travel distance of the vehicle is greater than the predetermined travel distance, the controller 20 activates in step S109 to calculate the real-time target or maximum FC coolant outlet temperature. However, if the controller 20 determines in step S108 that the travel distance is not greater than the predetermined travel distance, the controller 20 does not activate for evaluating the real-time target or maximum FC coolant outlet temperature, and does not proceed to the next step.

[0046] In step S110, the controller 20 calculates the real-time target or maximum FC coolant outlet temperature using the third equation E3 by using the data calculated in step S107. In addition, in step S110, the controller 20 determines a calibration line for compensating for degradation of the fuel cell stack 12 and mapping the real-time target FC coolant outlet temperature, such as Figure 5 As described above, the calibration line is calculated by using the determined data through the fourth equation E4 and the fifth equation E5, and along Figure 5 Therefore, in step S111 , the real-time target FC coolant outlet temperature calculated in step S110 is determined as a new target FC coolant outlet temperature.

[0047] refer to Fig. 7A and Figure 7B , which show graphs for mapping each of the target FC coolant outlet temperature and the maximum FC coolant outlet temperature according to an exemplary form of the present disclosure. Based on data of the FC heat to FC power ratio obtained at the beginning and end of the life of the fuel cell stack 12, determining Fig. 7A and Figure 7B The two maps in are used to map the target FC coolant outlet temperature and the maximum FC coolant outlet temperature, respectively. Fig. 7AA calibration line is shown as an example for mapping the real-time target FC coolant outlet temperature. Fig. 7A If the current input FC heat to FC power ratio approaches 80% because the fuel cell stack is reaching end of life, the controller 20 reduces the target FC coolant outlet temperature of the system 10 to compensate for excess heat generated by the fuel cell stack 12 due to degradation. Figure 7B A calibration line is shown for mapping the maximum FC coolant outlet temperature. Figure 7B If the input FC heat to FC power ratio approaches 80% as the fuel cell stack reaches end of life, the controller 20 reduces the maximum FC coolant outlet temperature of the system 10 to avoid damage to the fuel cell stack 12 due to overheating caused by degradation of the fuel cell stack 12 .

[0048] While the present disclosure has been described in connection with what are presently considered to be practical exemplary forms, it is to be understood that the disclosure is not limited to the forms disclosed, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the present disclosure.

Claims

1. A coolant temperature control system for a fuel cell stack in a vehicle, the coolant temperature control system comprising: a controller operable to determine a real-time target outlet temperature of a fuel cell coolant, the controller being configured to compensate for the target outlet temperature due to degradation of the fuel cell stack over time, the controller determining a ratio of input fuel cell heat to fuel cell power generated from the fuel cell stack; as well as a communication device operable to detect a fuel cell voltage and a fuel cell current output from the fuel cell stack; wherein the controller determines a fuel cell heat to fuel cell power ratio and a target outlet temperature of the fuel cell coolant that are constant at the beginning and end of the life of the fuel cell stack for mapping a real-time target outlet temperature of the fuel cell coolant, wherein the constant fuel cell heat to fuel cell power ratio is determined by the maximum fuel cell heat to fuel cell power ratio Ratio considered to be at the end of the life of the fuel cell stack max and wherein the minimum fuel cell heat to fuel cell power ratio Ratio is considered at the beginning of the life of the fuel cell stack min Sure, The target outlet temperature of the fuel cell coolant is obtained by calculating the minimum target outlet temperature T of the fuel cell coolant allowed at the beginning of the life of the fuel cell stack. FC_Min and the maximum target outlet temperature T of the fuel cell coolant allowed at the end of the life of the fuel cell stack FC_Max Sure, The controller determines the slope m of a calibration line for mapping the real-time target outlet temperature of the fuel cell coolant and the x-intercept X of the calibration line of the slope by the following formula: and The controller uses the determined fuel cell input heat to fuel cell power ratio Ratio through the following formula: input To determine the real-time target outlet temperature T of the fuel cell coolant FC_Target :

2. The coolant temperature control system according to claim 1, wherein: When the travel distance of the vehicle is greater than a predetermined travel distance, the controller determines to activate the temperature control system for evaluating a real-time target outlet temperature of the fuel cell coolant.

3. The coolant temperature control system according to claim 2, wherein: The controller sets 30 km as the predetermined driving distance for activation to evaluate the real-time target outlet temperature of the fuel cell coolant.

4. The coolant temperature control system according to claim 1, wherein: The fuel cell heat and the fuel cell power are each determined by evaluating the sensed fuel cell voltage and the fuel cell current.

5. The coolant temperature control system according to claim 4, wherein: The controller estimates the fuel cell heat by the following formula: Fuel cell heat = [1.25×(# of fuel cells)-fuel cell voltage]×fuel cell current, and estimates the fuel cell power by the following formula: Fuel cell power = fuel cell voltage×fuel cell current, where # of fuel cells represents the number of fuel cells installed in the fuel cell stack.

6. The coolant temperature control system according to claim 1, wherein: The fuel cell voltage and the fuel cell current are detected by a voltage sensor and a current sensor connected between the fuel cell stack and the communication device of the system.

7. A method for controlling a coolant temperature of a fuel cell stack of a vehicle having a controller, the method comprising the steps of: detecting a fuel cell voltage and a fuel cell current output from the fuel cell stack; evaluating fuel cell heat and fuel cell power generated by the fuel cell stack using the detected fuel cell voltage and fuel cell current; determining a ratio of input fuel cell heat to fuel cell power generated from the fuel cell stack; determining a fuel cell heat to fuel cell power ratio and a target outlet temperature of the fuel cell coolant that are constant at the beginning and end of the life of the fuel cell stack for mapping a real-time target outlet temperature of the fuel cell coolant; as well as determining a real-time target outlet temperature of the fuel cell coolant for compensating for a target outlet temperature due to degradation of the fuel cell stack over time, wherein the constant fuel cell heat to fuel cell power ratio is determined by the maximum fuel cell heat to fuel cell power ratio Ratio considered to be at the end of the life of the fuel cell stack max and wherein the minimum fuel cell heat to fuel cell power ratio Ratio is considered at the beginning of the life of the fuel cell stack min Sure, The target outlet temperature of the fuel cell coolant is obtained by calculating the minimum target outlet temperature T of the fuel cell coolant allowed at the beginning of the life of the fuel cell stack. FC_Min and the maximum target outlet temperature T of the fuel cell coolant allowed at the end of the life of the fuel cell stack FC_Max Sure, The controller determines the slope m of a calibration line for mapping the real-time target outlet temperature of the fuel cell coolant and the x-intercept X of the calibration line of the slope by the following formula: and The controller uses the determined fuel cell input heat to fuel cell power ratio Ratio through the following formula: input To determine the real-time target outlet temperature T of the fuel cell coolant FC_Target :

8. The method according to claim 7, further comprising the steps of: evaluating a travel distance of the vehicle; as well as When the travel distance of the vehicle is greater than a predetermined travel distance, it is determined to activate a real-time target outlet temperature for evaluating the fuel cell coolant.

9. The method according to claim 8, wherein: The controller sets 30 km as the predetermined driving distance for activation to evaluate the real-time target outlet temperature of the fuel cell coolant.

10. The method according to claim 7, wherein: The controller estimates the fuel cell heat by the following formula: Fuel cell heat = [1.25×(# of fuel cells)-fuel cell voltage]×fuel cell current, and estimates the fuel cell power by the following formula: Fuel cell power = fuel cell voltage×fuel cell current, where # of fuel cells represents the number of fuel cells installed in the fuel cell stack.

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