KR20230022721A - Method and system for estimating relitive humidity during feul cell stop - Google Patents

Abstract

Disclosed are a method for estimating the relative humidity of a fuel cell stack and a device for estimating the relative humidity of a fuel cell stack using the estimation method. The method includes: a step of checking whether the fuel cell is stopped; an absolute water vapor pressure calculation step of calculating an absolute water vapor pressure according to a change in thermal energy when the fuel cell is stopped; and a step of deriving an estimated relative humidity value using the absolute water vapor pressure according to the change in thermal energy as the current water vapor pressure and using the pre-calculated saturated water vapor pressure at the current temperature.

Description

Relative humidity estimation method and device when fuel cell is stopped {METHOD AND SYSTEM FOR ESTIMATING RELITIVE HUMIDITY DURING FEUL CELL STOP}

The present invention relates to a method and device for estimating relative humidity in a fuel cell system, and more particularly, to a device for estimating relative humidity applicable in a stationary state of a fuel cell without a change in air flow rate and a method for estimating relative humidity using the same.

A fuel cell is an energy conversion device in which chemical energy of hydrogen is converted into electrical energy by an electrochemical reaction between hydrogen and oxygen in a stack, and application fields such as engines and generators of electric mobility are expanding. In addition, as concerns about air pollution gradually increase, the demand for eco-friendly vehicles such as electric vehicles and hydrogen fuel cell vehicles is rapidly increasing.

The present invention relates to a technique for estimating relative humidity in a fuel cell system. Relative humidity in the fuel cell system is calculated by estimated values according to various physical conditions, and techniques for reducing noise are employed.

In particular, according to the conventional relative humidity estimation technology, it is difficult to equally apply the relative humidity estimation logic when the fuel cell is stopped, so there is a problem of applying a fixed relative humidity value. Accordingly, there is a need for a relative humidity estimation technology capable of relatively accurately following the current relative humidity value, rather than a fixed relative humidity value, even when the fuel cell is stopped.

The matters described as the background art above are only for improving understanding of the background of the present invention, and should not be taken as an admission that they correspond to prior art already known to those skilled in the art.

KR 10-1795245 B1

The present invention has been proposed to solve these problems, and is intended to provide a technology for diagnosing the voltage stability state of a stack for each driving condition using variables controllable in vehicle components and preventing fuel cell deterioration according to the diagnosis result. .

Particularly, in preventing fuel cell deterioration, another object of the present invention is to identify the cause and occurrence location of cell performance deterioration and to provide specific diagnosis results such as reversible/irreversible deterioration.

In addition, in the present invention, by performing a suitable deterioration avoidance operation according to the diagnosis result of fuel cell deterioration, the best intra-cell water balance in the fuel cell system is secured and voltage stability is maintained to increase the durability of the fuel cell system. It has another purpose.

To achieve the above object, a method for estimating relative humidity of a fuel cell stack according to the present invention includes the steps of checking whether the fuel cell is stopped; An absolute vapor pressure calculation step of calculating an absolute vapor pressure according to a change in thermal energy by Equation 1 below when the fuel cell is stopped;

Equation 1:

(P _abs : absolute water vapor pressure, P _SatVprT2 : saturated water vapor pressure at the temperature after fuel cell shutdown, T ₁ : stack temperature before fuel cell shutdown, T ₂ : stack temperature after fuel cell shutdown)

and deriving an estimated relative humidity value by using the absolute vapor pressure according to the change in thermal energy as the current vapor pressure and using the pre-calculated saturated vapor pressure at the current temperature.

In the step of checking whether the fuel cell is stopped, it is possible to determine whether the fuel cell is stopped by checking whether the supply air flow rate and whether the air shut-off valve and the air pressure valve are closed.

In the step of checking whether the fuel cell is stopped, when the supply air flow rate change is '0', the air blower is not operating, and both the air blocking valve and the air pressure valve are closed, it may be determined that the fuel cell is stopped.

In the step of checking whether the fuel cell is stopped, if it is determined that the fuel cell is not stopped, calculating an absolute vapor pressure according to the flow rate according to Equation 2 below; and

Equation 2:

A step of deriving an estimated relative humidity value using the absolute vapor pressure according to the flow rate as the current vapor pressure and using the pre-calculated saturated vapor pressure at the current temperature; may be performed.

The saturated water vapor pressure at the current temperature may be calculated by Equation 3 below according to the stack temperature after the fuel cell is stopped.

Equation 3:

(P _SatVpr : saturation vapor pressure, T: stack temperature)

The stack temperature may be determined by an arithmetic mean of a stack inlet temperature and a stack outlet temperature.

An apparatus for estimating the relative humidity of a fuel cell stack of the present invention includes a temperature sensor for detecting the temperature of the fuel cell stack; a pressure sensor that detects the pressure of the fuel cell stack; A relative humidity estimator for estimating the relative humidity of the fuel cell stack from information including the stack temperature detected by the temperature sensor and the stack pressure detected by the pressure sensor;

The relative humidity estimator calculates the absolute water vapor pressure according to the change in thermal energy by Equation 1 when the fuel cell is stopped, sets the absolute vapor pressure according to the change in thermal energy as the current vapor pressure, and calculates the saturated vapor pressure at the current temperature calculated in advance. It is configured to derive an estimated value of relative humidity using

According to the method and apparatus for estimating relative humidity during fuel cell shutdown of the present invention, a new estimation method capable of estimating relative humidity in consideration of the water vapor pressure and temperature at the outlet of the cathode even when there is no fluidity of gas due to fuel cell shutdown is proposed. do.

In particular, according to the method and apparatus for estimating relative humidity when the fuel cell is stopped, the relative humidity of the fuel cell stack can be estimated even when the fuel cell is stopped, and thus the followability of the relative humidity can be improved even when the fuel cell is stopped.

Therefore, according to the present invention, it is possible to reduce the time delay related to tracking the relative humidity, which may occur when the fuel cell is restarted after stopping the fuel cell, and thus has an effect of improving the output of the fuel cell system.

1A is an air supply system of a fuel cell system during normal running;
1B is an air supply system when the fuel cell is stopped.
2 is a graph showing a time delay for estimating the relative humidity that occurs when the relative humidity is output as a fixed value when the fuel cell is stopped;
3A is a block diagram of an air supply system in a normal driving state in an air supply system of a fuel cell system to which an apparatus for estimating relative humidity when a fuel cell is stopped according to an embodiment of the present invention is applied;
3B is a configuration diagram of an air supply system when a fuel cell is stopped in an air supply system of a fuel cell system to which an apparatus for estimating relative humidity when a fuel cell is stopped according to an embodiment of the present invention is applied;
4 is a flowchart of a method for estimating relative humidity when a fuel cell is stopped according to an embodiment of the present invention.
5 is a flowchart of a method for estimating relative humidity when a fuel cell is stopped according to another embodiment of the present invention.
6 is a graph showing that relative humidity followability is improved by a method for estimating relative humidity when a fuel cell is stopped according to an embodiment of the present invention.

Hereinafter, a method and system for preventing deterioration of a fuel cell stack according to various embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

A fuel cell vehicle goes through a process of stopping and resuming power generation of a fuel cell, if necessary, during operation, which is called a fuel cell stop and a fuel cell restart. In a fuel cell vehicle, such a process of stopping and restarting the fuel cell is repeated according to a driver's requested output.

In order to secure the performance of the fuel cell system, it is important to properly manage the humidity of the electrolyte membrane in the fuel cell stack, and for this, air supplied to the cathode of the stack is properly humidified to maintain an appropriate level of relative humidity. The air supplied to the cathode is humidified by a humidifier, and the relative humidity in the stack may vary according to the amount of humidified air supplied.

FIG. 1A is a block diagram of an air supply system of a fuel cell system during normal driving, and is intended to explain a model for estimating a relative humidity value at a cathode outlet based on a change in flow rate of the air supply system during normal driving.

The air supply system is configured to take in external air and supply it to the cathode, and the air passing through the cathode can be discharged to the outside. To this end, the air supply system includes an air blower for compressed and delivered external air, and an air shut-off valve may be installed at the cathode inlet side to block air inflow to the cathode. Also, although not shown, a humidifier for humidifying supplied air to have an appropriate humidity may be included at a front end of the cathode inlet. Air compressed and delivered through the air blower is introduced into the cathode through the air shutoff valve, and may be discharged to the outside through the air pressure valve at the outlet of the cathode.

In particular, in the case of FIG. 1A , the fuel cell vehicle is in a normal running state, the air blower rotates (for example, 15,000 rpm or more) to supply air, and the air shutoff valve and the air pressure valve are both open.

In the "normal driving" state of FIG. 1A, an open system state in which the inflow and discharge of outside air continuously occurs, and there is a flow rate error due to air flow at the inlet and outlet ends of the cathode. Therefore, in such an open system state, it is possible to estimate a relative humidity (RH) value based on a change in flow rate.

In this flow rate-based relative humidity estimation method, the relative humidity is calculated by calculating the absolute vapor pressure according to the flow rate at the outlet of the cathode and the saturated vapor pressure at the current temperature. At this time, the absolute vapor pressure at the cathode outlet means the current vapor pressure calculated according to the flow rate at the cathode outlet.

Relative humidity estimation based on flow rate change can be calculated from Equations 1 to 3 below.

First, the relative humidity can be calculated by Equation 1 below based on the saturated vapor pressure and the current vapor pressure.

In addition, the absolute vapor pressure according to the flow rate at the outlet of the cathode can be calculated by Equation 2 below, which means the current vapor pressure for calculating the relative humidity.

(P _CaOutVpr : water vapor pressure at the cathode outlet, P _CaOutTot : total pressure at the cathode outlet, m _CaOutVpr : water vapor flow rate at the cathode outlet, M _Air : air molecular weight, m _CaOutAir : air flow rate at the cathode outlet, M _H2O : water molecular weight)

In addition, the saturation vapor pressure (PSatVpr) for calculating the relative humidity is a function of the stack internal temperature (T) and can be calculated by Equation 3 below.

(P _SatVpr : saturation vapor pressure, T: stack temperature)

On the other hand, FIG. 1B shows an air supply system in a “fuel cell stop” state. As shown in FIG. 1B, in the "fuel cell stop" state, the air blower is in a stopped state (rotational speed of 0 rpm), and both the air shutoff valve and the air pressure valve are closed. That is, the air supply system in the "fuel cell stop" state is in a closed system state, and there is no change in flow rate at the inlet and outlet of the cathode.

Therefore, since there is no change in the air flow rate when the fuel cell is stopped, it is not possible to apply the relative humidity estimation logic based on the flow rate change, and temporarily apply a fixed value (eg, 20%) as the relative humidity estimation value. do.

In a system that maintains an average humidity of 70 to 80%, it takes more than a certain level of time to change from a fixed estimated relative humidity of 20% to a value of 70 to 80% that is suitable for driving a fuel cell.

In this regard, FIG. 2 is a graph illustrating an example in which output degradation occurs due to a time delay required for the relative humidity value to reach an actual calculated value from a fixed value (20%) after the fuel cell is stopped.

As shown in FIG. 2, in the fuel cell stop section, the estimated relative humidity value is determined as a preset fixed value (20% in the example of FIG. 2), and after the fuel cell stop is released, the relative humidity value is actually changed from the fixed value. There will be a time delay to reach the calculated value.

Due to this time delay, since the target stoichiometric ratio (SR) value in the corresponding section is set relatively low, a problem occurs in that the amount of air supplied is less than the amount of air actually required. Therefore, a required level of output cannot be obtained due to the decrease in the flow rate of the supply air, and thus, the decrease in output occurs at the point in time when the stop of the fuel cell is canceled.

In the method and apparatus for estimating relative humidity during fuel cell shutdown according to the present invention, a fixed value for relative humidity is not used during fuel cell shutdown in order to solve the problem of output degradation due to time delay that may occur after the fuel cell shutdown is canceled. Instead, we present a new technique for estimating the relative humidity by considering the temperature inside the stack and the amount of evaporation inside the stack.

In this regard, FIGS. 3A and 3B illustrate an air supply system to which an apparatus for estimating relative humidity when a fuel cell is stopped according to an embodiment of the present invention is applied. In particular, FIG. 3A shows the configuration and state of the air supply system in a normal running state, and FIG. 3B shows the configuration and state of the air supply system when the fuel cell is stopped. In addition, FIG. 4 shows a flowchart of a method for estimating relative humidity when a fuel cell is stopped according to an embodiment of the present invention.

3A and 3B include an air supply system 100 that is basically the same as the previously described configurations of FIGS. 1A and 1B. Therefore, since the configuration of the air blower 110, the air shutoff valve 120, the cathode 130, and the air pressure valve 140 have been described above, detailed descriptions thereof will be omitted.

FIG. 3A, like FIG. 1A, shows a general driving state in which the fuel cell operates, the air blower rotates (for example, 15,000 rpm or more) to supply air, and the air shutoff valve and the air pressure valve are both open. represents the open state.

On the other hand, in FIG. 3b, as in FIG. 1b, the air supply system is shown in the “fuel cell stop” state. As shown in FIG. 3B, in the "fuel cell stop" state, the air blower is in a stopped state (rotational speed of 0 rpm), and both the air shutoff valve and the air pressure valve are closed. The air supply system in the "fuel cell stop" state is in a closed system state, and there is no change in flow rate at the inlet/outlet end of the cathode, so a relative humidity estimation technique that does not depend on the change in flow rate is applied.

Referring to FIGS. 3A and 3B , an apparatus for estimating the relative humidity of a fuel cell stack according to an embodiment of the present invention includes a temperature sensor 150 and a pressure sensor 160 for measuring the temperature in the stack and a fuel cell system internal It may be configured to further include a data storage unit 200 for storing various data and an RH estimator 300 for estimating relative humidity.

In this regard, the data storage unit 200 may be a memory device provided separately from the processor, such as a data buffer in the processor or a flash memory for processing calculations. In the data storage unit, various information that is a basis for executing a control algorithm of the fuel cell system may be stored, and the RH estimator (relative humidity estimator) may obtain necessary information from the data storage unit. However, such a data storage unit is not an essential element in implementing the present invention, and the RH estimator can directly receive information necessary for estimating the relative humidity from specific components in the fuel cell system. For example, the RH estimator may receive values for stack temperature and stack pressure detected from a temperature sensor and a pressure sensor, respectively. In addition, the RH estimator is connected to the air blower 110, the air shutoff valve 120, and the air pressure valve 140, and information such as whether the air blower is operating or not, valve opening and closing, etc. can be directly input from each component. .

Therefore, the apparatus for estimating the relative humidity of a fuel cell stack according to a preferred embodiment of the present invention can be applied without limitation as long as the relative humidity estimation method as shown in FIGS. 4 and 5 can be applied using the internal information of the stack. should be interpreted as

An apparatus for estimating relative humidity of a fuel cell stack according to the present invention is characterized in that the relative humidity value is calculated by considering the saturation vapor pressure that changes when the fuel cell is stopped and the amount of evaporation inside the stack through the RH estimator.

In particular, the RH estimator in the preferred embodiment of the present invention calculates the absolute water vapor pressure according to the amount of evaporation, and calculates the relative humidity using the calculated absolute vapor pressure according to the amount of evaporation as the current water vapor pressure.

Looking in detail at the principle of calculating the relative humidity in the RH estimator, as described in Equation 1 above, the relative humidity is calculated as the ratio of the current water vapor pressure and the saturated water vapor pressure at the current temperature. Here, the saturated vapor pressure at the current temperature may be calculated by calculating the saturated vapor pressure according to the inside of the stack.

Meanwhile, in calculating the current vapor pressure, it is noted that in the present invention, since the air shutoff valve and the air pressure valve remain closed when the fuel cell is stopped, the inside of the stack becomes a closed system maintaining a sealed state. That is, since the inside of the stack is in a sealed state, a factor that changes the absolute vapor pressure existing at the outlet of the cathode is the amount of evaporation, and the saturation vapor pressure changes according to the temperature inside the stack. The change in evaporation is equal to the heat energy absorbed by the liquid as it evaporates.

In estimating the relative humidity at the outlet of the cathode when the fuel cell is stopped, the formulas for calculating water vapor pressure and relative humidity by an Assman hygrometer as shown in Equations 4 and 5 below can be used. In the equation below, the absolute vapor pressure can be calculated through the difference between the thermal energy taken from the wet bulb thermometer and the thermal energy from the dry bulb thermometer.

(e: water vapor pressure, E: saturated vapor pressure at dry-bulb temperature, E': saturated vapor pressure at wet-bulb temperature, t: dry-bulb temperature, t': wet-bulb temperature, p: air pressure at the time, A: constant (wet-bulb no-icing: 0.50, wet-bulb no-icing : 0.44)

Regarding Equations 4 and 5 above, since the difference in heat energy taken away is equal to the amount of evaporation, it can be said that 'wet bulb temperature = temperature after fuel cell shutdown' and 'dry bulb temperature = temperature before fuel cell shutdown'.

Through this, when Equations 4 and 5 above are applied to the system in a stopped state of the fuel cell, Equations 6 and 7 can be derived.

(P _abs : current water vapor pressure (absolute vapor pressure according to the amount of evaporation), P _SatVprT2 : saturated water vapor pressure at the temperature after fuel cell shutdown, T ₁ : stack temperature before fuel cell shutdown, T ₂ : stack temperature after fuel cell shutdown)

(P _abs (evaporation amount): Absolute vapor pressure according to the amount of evaporation, P _SatVpr (stack temperature): saturated vapor pressure according to the temperature inside the stack)

On the other hand, in calculating Pabs, since the change in saturated water vapor pressure before and after fuel cell shutdown is not very large, the saturated water vapor pressure (P _SatVprT2 ) at the temperature after fuel cell shutdown applied to Equation 6 is the temperature before fuel cell shutdown calculated in advance. The saturation vapor pressure at P _SatVprT1 may be applied instead.

In this regard, the saturation vapor pressure before and after stopping the fuel cell is a value determined according to the stack temperature, and may be calculated according to Equation 3 above. In this regard, the stack temperature may be detected by the temperature sensor 150, and in the case of a system in which temperature sensors are attached to the inlet and outlet of the stack, the stack temperature is determined by the arithmetic average of the stack inlet temperature and the stack outlet temperature. can

Through such a relative humidity estimation formula, in the apparatus and method for estimating the relative humidity of a fuel cell stack according to a preferred embodiment of the present invention, the change according to the temperature and the amount of evaporation, which are currently variable elements, to the absolute water vapor pressure immediately before the fuel cell is stopped. By applying this, it is possible to improve the accuracy of estimating the relative humidity at the outlet of the cathode when the fuel cell is stopped.

Hereinafter, a method for estimating relative humidity of a fuel cell stack according to a preferred embodiment of the present invention will be described in detail with reference to FIGS. 4 and 5 .

Referring to FIG. 4 , in the method for estimating the relative humidity of a fuel cell stack according to an embodiment of the present invention, a step of calculating a saturation vapor pressure at a current temperature (S402) is performed in a situation in which starting is completed and driving is performed (S401). can In this step, the saturation vapor pressure at the stack temperature before the Fc Stop state is calculated.

Thereafter, in the method for estimating the relative humidity of the fuel cell stack according to the present invention, it is checked whether the fuel cell is stopped (S403), and when the fuel cell is stopped, the absolute water vapor pressure is calculated according to the change in thermal energy according to Equation 6 above. Step S405 may be performed.

In this regard, as shown in FIG. 4, in checking whether the fuel cell is stopped, it is possible to determine whether the fuel cell is stopped by checking whether the supply air flow rate has changed, whether the air blower is operating, and whether the air shutoff valve and the air pressure valve are closed. Yes (S404). Therefore, in the RH estimator, it is finally checked whether the supply air flow rate change is '0', the air blower operation is stopped, the air shutoff valve, and the air pressure valve are all closed to reverify whether the fuel cell is stopped. can Although not shown, if it is determined that the fuel cell is not in the stopped state according to the reverification, it is possible to return to a step of checking again whether the fuel cell is in the stopped state by reconfirming a control command or the like.

When the absolute vapor pressure is calculated through step S405, a step of deriving an estimated value of relative humidity based on the calculated value (S420) is performed.

In this step, as in Equation 7 above, the absolute water vapor pressure according to the calculated thermal energy change is set as the current water vapor pressure, and the estimated relative humidity is derived using the previously calculated saturated water vapor pressure at the current temperature. At this time, the value previously calculated in step S402 may be used as the saturation vapor pressure at the current temperature.

Meanwhile, if it is determined in step S403 that the fuel cell is not in a stopped state, a step of calculating the absolute water vapor pressure according to the flow rate (S412) is performed, and a step of deriving an estimated value of relative humidity based on the calculated absolute water vapor pressure is performed ( S420). In this case, it is also possible to verify whether the fuel cell is normally driven by checking the supply air flow rate, whether the air blower is operating, and whether the air shutoff valve and the air pressure valve are open (S411).

5 is a flowchart of a method for estimating relative humidity when a fuel cell is stopped according to another embodiment of the present invention.

Each step of FIG. 5 is substantially the same as the step of the embodiment of FIG. 4 except for the step of calculating the saturation vapor pressure at the temperature after the fuel cell is stopped (Fc Stop) in step 505 .

Therefore, in the case of completion of startup and driving (S501), calculating the saturated vapor pressure at the current temperature (S502), checking whether the fuel cell is stopped (S403), whether or not the supply air flow rate has changed, whether or not the air blower is operating, and The step of verifying whether the fuel cell is stopped by checking whether the air shutoff valve and the air pressure valve are closed (S404) and the step of calculating the absolute vapor pressure according to the change in thermal energy (S506) are the same as the respective corresponding steps. . Similarly, can be implemented. The step of verifying whether the fuel cell is normally operated (S511), the step of calculating the absolute vapor pressure different from the flow rate (S512), and the step of deriving the estimated relative humidity (S520) are also substantially the same as the corresponding steps of FIG. 4 .

However, in the case of the example of FIG. 5, unlike the example of FIG. 4, the saturated vapor pressure at the stack temperature after the fuel cell is stopped is calculated in addition to the calculated value of the saturated vapor pressure according to the stack temperature before the fuel cell is stopped, and the calculated value There is a difference in that is applied to the calculation of the absolute vapor pressure (Pabs) by the change in thermal energy (S506) and the derivation of the estimated relative humidity (S520).

6 is a graph showing that relative humidity followability is improved by a method for estimating relative humidity when a fuel cell is stopped according to an embodiment of the present invention.

Referring to FIG. 6 , it can be confirmed that there is an effect of improving the output of the fuel cell system by shortening the time delay since the followability of the relative humidity is improved compared to using a fixed value of the relative humidity in the fuel cell stop section. .

Although shown and described in relation to specific embodiments of the present invention, it is known in the art that the present invention can be variously improved and changed without departing from the technical spirit of the present invention provided by the claims below. It will be self-evident to those skilled in the art.

100: air supply system
110: air blower
120: air shutoff valve
130: cathode
140: air pressure valve
150: temperature sensor
160: pressure sensor
200: data storage unit
300: RH estimator

Claims (11)

Checking whether the fuel cell is stopped;
An absolute vapor pressure calculation step of calculating an absolute vapor pressure according to a change in thermal energy by Equation 1 below when the fuel cell is stopped;
Equation 1:

(P _abs : absolute water vapor pressure, P _SatVprT2 : saturated water vapor pressure at the temperature after fuel cell shutdown, T ₁ : stack temperature before fuel cell shutdown, T ₂ : stack temperature after fuel cell shutdown)
Deriving an estimated relative humidity value by using the absolute vapor pressure according to the change in thermal energy as the current vapor pressure and using the pre-calculated saturated vapor pressure at the current temperature;
Relative humidity estimation method of a fuel cell stack comprising a.
The method of claim 1,
In the step of checking whether the fuel cell is stopped,
A method for estimating the relative humidity of a fuel cell stack, characterized in that determining whether the fuel cell is stopped by checking the supply air flow rate and whether an air shutoff valve and an air pressure valve are closed.
The method of claim 2,
In the step of checking whether the fuel cell is stopped,
A method for estimating relative humidity when a fuel cell is stopped, characterized in that it is determined that the fuel cell is stopped when the supply air flow rate change is '0', the air blower is not operating, and both the air shutoff valve and the air pressure valve are closed. .
The method of claim 1,
In the step of checking whether the fuel cell is stopped, if it is determined that the fuel cell is not stopped, calculating an absolute vapor pressure according to the flow rate according to Equation 2 below; and
Equation 2:

Deriving an estimated relative humidity value using the absolute vapor pressure according to the flow rate as the current vapor pressure and using the pre-calculated saturated vapor pressure at the current temperature;
Method for estimating relative humidity of a fuel cell stack, characterized in that is performed.
The method of claim 1,
The saturated water vapor pressure at the current temperature is obtained by Equation 3 below according to the stack temperature after the fuel cell is stopped.
Equation 3:

(P _SatVpr : saturation vapor pressure, T: stack temperature)
A method for estimating the relative humidity of a fuel cell stack, characterized in that it is calculated.
The method of claim 5,
The method of estimating relative humidity of a fuel cell stack, characterized in that the stack temperature is determined by an arithmetic average of a stack inlet temperature and a stack outlet temperature.
a temperature sensor that detects the temperature of the fuel cell stack;
a pressure sensor that detects the pressure of the fuel cell stack;
A relative humidity estimator for estimating the relative humidity of the fuel cell stack from information including the stack temperature detected by the temperature sensor and the stack pressure detected by the pressure sensor;
The relative humidity estimator,
When the fuel cell is stopped, the absolute water vapor pressure according to the change in thermal energy is calculated by Equation 1 below,
Equation 1:

(P _abs : absolute water vapor pressure, P _SatVprT2 : saturated water vapor pressure at the temperature after fuel cell shutdown, T ₁ : temperature before fuel cell shutdown, T ₂ : temperature after fuel cell shutdown)
An apparatus for estimating relative humidity of a fuel cell stack configured to derive an estimated relative humidity value by using an absolute vapor pressure according to the change in thermal energy as a current vapor pressure and using a pre-calculated saturated vapor pressure at a current temperature.
The method of claim 7,
The relative humidity estimator determines whether the fuel cell is stopped by checking the supply air flow rate and whether the air shutoff valve and the air pressure valve are closed.
The method of claim 8,
The relative humidity estimator determines that the fuel cell is stopped when the supply air flow rate change is '0', the air blower is not operating, and both the air shutoff valve and the air pressure valve are closed. humidity estimator.
The method of claim 7,
The saturation vapor pressure at the current temperature is obtained by Equation 2 below according to the stack temperature after the fuel cell is stopped.
Equation 2:

(P _SatVpr : saturation vapor pressure, T: stack temperature)
An apparatus for estimating relative humidity of a fuel cell stack, characterized in that the calculation.
The method of claim 10,
The temperature sensor includes a stack inlet temperature sensor and a stack outlet temperature sensor,
The stack temperature is determined by an arithmetic average of a stack inlet temperature detected by the stack inlet temperature sensor and a stack outlet temperature detected by the stack outlet temperature sensor.

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