CN109916964B - Fuel cell impedance calibration method - Google Patents

Abstract

The application relates to a fuel cell impedance calibration method. The method includes S10, purging the fuel cell by the gas with different humidity under different temperature, and obtaining a plurality of balance internal resistances of the fuel cell; s20, establishing an internal resistance humidity relation model of the balance internal resistance and the humidity of the gas; and S30, obtaining an internal resistance water content relation model of the balance internal resistance and the water content in the fuel cell through a fitting method based on the internal resistance humidity relation model and the humidity water content relation model of the humidity of the gas and the water content in the fuel cell. And establishing a humidity and water content relation model of the humidity and the water content in the fuel cell according to the humidity and water content relation model, and obtaining an accurate internal resistance water content relation model by a fitting method. Therefore, the water content in the fuel cell can be accurately obtained according to the relation model of the balance internal resistance and the internal resistance water content.

Description

Fuel Cell Impedance Calibration Method

technical field

The present application relates to the field of batteries, and in particular, to a method for calibrating the impedance of a fuel cell.

Background technique

The proton exchange membrane hydrogen fuel cell is a clean and efficient energy conversion device. For proton exchange membrane fuel cells, the reaction requires the participation of water, and the effective conduction of protons can only be achieved when the membrane is fully wetted. When the membrane is in a state of water shortage, the conductivity of the proton exchange membrane will appear significantly decline. At the same time, the high water content inside the fuel cell may cause liquid water to accumulate inside, resulting in flooding. Therefore, humidity estimation and control are critical to the efficiency and performance of fuel cell systems. AC impedance is an important test method for fuel cell humidity estimation. Using the AC impedance method, the internal humidity state of the fuel cell can be obtained most conveniently. Among them, the high-frequency impedance represents the internal resistance of the fuel cell membrane, which can be used to evaluate the water content of the fuel cell membrane.

In the traditional method, the relationship between AC impedance and humidity is based on an empirical model, and the error of determining the water content of the membrane through the AC impedance is relatively large.

SUMMARY OF THE INVENTION

Based on this, it is necessary to provide a fuel cell impedance calibration method to solve the problem of large error in estimating the water content of the membrane through the AC impedance.

A fuel cell impedance calibration method, comprising:

S10, at different temperatures, sequentially selecting a plurality of gases with different humidity to purge the fuel cell, and obtain a plurality of equilibrium internal resistances of the fuel cell;

S20, establishing an internal resistance-humidity relationship model of the equilibrium internal resistance and the humidity of the gas;

S30, based on the internal resistance-humidity relationship model, the humidity of the gas and the humidity-water content relationship model of the internal water content of the fuel cell, obtain the equilibrium internal resistance and the internal water content of the fuel cell by a fitting method The internal resistance water content relationship model.

In one embodiment, the step S10 includes:

S110, maintaining the temperature of the fuel cell at the temperature during normal operation;

S120, under each of the measurement temperature conditions, sequentially select a plurality of gases with different humidity to purge the fuel cell, and measure the high-frequency impedance of the fuel cell in real time in each experiment;

S130, when the high-frequency impedance and the gas reach an equilibrium state, obtain a plurality of the balanced internal resistances through the high-frequency impedance.

In one embodiment, in the step S120, the humidity of the gas purging the fuel cell is gradually increased in different measurements.

In one embodiment, the step S130 includes:

S131, after purging the fuel cell by the gas for a certain period of time, stop purging;

S132, when the high-frequency impedance is stabilized after the purging stops, determine a stable value of the high-frequency impedance, and continue to purge the fuel cell with the gas;

S133, repeating steps S131-S132, and determining one of the balanced internal resistances according to the stable value.

S134, selecting different temperatures and the humidity of the gas, and repeating steps S131-S132 to obtain a plurality of the balanced internal resistances.

In one embodiment, in the step S110, the temperature of the fuel cell is maintained for more than half an hour during normal operation.

In one embodiment, in the step S133, the determining one of the balanced internal resistances according to the stable value includes:

When the difference between the stable values measured when two adjacent purging stops balance is not greater than the preset value, the stable value measured after is selected as one of the equilibrium internal resistances;

In one embodiment, before the step S110, it also includes:

S010, the fuel cell is purged with dry gas.

In one embodiment, in the step S010, the time for purging the fuel cell is greater than 2 hours.

In one embodiment, the temperature of the drying gas is not greater than 25°C.

In one embodiment, the humidity water content relationship model is:

λ _eq =0.043+17.81a-39.85a ² +36a ³

a=C _v /C _sat

where a is the water activity, Pv represents the water vapor partial pressure of the current gas, Psat represents the saturated vapor pressure at the current temperature, and λeq represents the equilibrium water content.

The method for calibrating the impedance of the fuel cell provided in the embodiments of the present application firstly purges the fuel cell with gases of different humidity at different temperatures, and obtains multiple equilibrium internal resistances of the fuel cell. The internal resistance-humidity relationship model is established through the equilibrium internal resistance and the humidity. The relationship between the equilibrium internal resistance and the humidity can be established according to the internal resistance-humidity relationship model. According to the humidity-water content relationship model, a humidity-water content relationship model between the humidity and the internal water content of the fuel cell can be established, so the relationship between the equilibrium internal resistance and the internal water content of the fuel cell can be established through the humidity . The accurate relationship model of internal resistance water content can be obtained by fitting method. Therefore, the internal water content of the fuel cell can be accurately obtained according to the relationship model between the equilibrium internal resistance and the water content of the internal resistance.

Description of drawings

FIG. 1 is a flowchart of a fuel cell impedance calibration method provided by an embodiment of the present application;

Fig. 2 is the relationship diagram of the equilibrium internal resistance and the humidity of the gas provided by the embodiment of the present application;

FIG. 3 is a high-frequency impedance and time relationship diagram provided by an embodiment of the present application;

FIG. 4 is a fitting curve diagram of the equilibrium internal resistance and the equilibrium water content provided by the embodiment of the present application.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present application clearer, the following examples will further describe the fuel cell impedance calibration method of the present application in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present application, but not to limit the present application.

The serial numbers themselves, such as "first", "second", etc., for the components herein are only used to distinguish the described objects, and do not have any order or technical meaning. The "connection" and "connection" mentioned in this application, unless otherwise specified, include both direct and indirect connections (connections). In the description of this application, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", The orientation or positional relationship indicated by "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description , rather than indicating or implying that the referred device or element must have a particular orientation, be constructed and operate in a particular orientation, and therefore should not be construed as a limitation on the present application.

In this application, unless otherwise expressly stated and defined, a first feature "on" or "under" a second feature may be in direct contact with the first and second features, or the first and second features indirectly through an intermediary touch. Also, the first feature being "above", "over" and "above" the second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is level higher than the second feature. The first feature being "below", "below" and "below" the second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature has a lower level than the second feature.

Referring to FIG. 1 , an embodiment of the present application provides a fuel cell impedance calibration method. The method includes:

S10, at different temperatures, sequentially selecting a plurality of gases with different humidity to purge the fuel cell, and obtain a plurality of equilibrium internal resistances of the fuel cell;

S20, establishing an internal resistance-humidity relationship model of the equilibrium internal resistance and the humidity of the gas;

S30, based on the internal resistance-humidity relationship model, the humidity of the gas and the humidity-water content relationship model of the internal water content of the fuel cell, obtain the equilibrium internal resistance and the internal water content of the fuel cell by a fitting method The internal resistance water content relationship model.

Referring to FIG. 2 , in step S10 , a certain temperature may be selected first, and then gases with different humidity may be selected at the temperature to purge the fuel cell multiple times. At the same time, the real-time measurement of the high-frequency impedance of the fuel cell is performed. When the high-frequency impedance of the fuel cell remains stable, the equilibrium internal resistance at which the fuel cell reaches an equilibrium state is determined.

In the step S20, according to one of the temperature, one of the humidity and one of the equilibrium internal resistances, a point may be determined on the relationship between the humidity and the equilibrium internal resistance. According to a plurality of the temperatures, a plurality of the humidity, and a plurality of the equilibrium internal resistances, a plurality of points may be determined in the relationship diagram of the humidity and the equilibrium internal resistance, and a plurality of the equilibrium internal resistances and the equilibrium internal resistances may be determined. The relationship curve of humidity can thus be used as the relationship model of the internal resistance humidity.

In the step S30, through the internal resistance-humidity relationship model, the corresponding relationship between the humidity and the equilibrium internal resistance can be obtained. Through the humidity-water content relationship model, the corresponding relationship between the humidity and the water content inside the fuel cell can be obtained. Therefore, by using the humidity as a medium, the relationship between the equilibrium internal resistance and the water content inside the fuel cell can be established. Correspondence. Through the fitting method, the water content relationship model of internal resistance can be determined, and then the accurate internal water content of the fuel cell can be obtained through the equilibrium internal resistance.

The method for calibrating the impedance of the fuel cell provided in the embodiments of the present application firstly purges the fuel cell with gases of different humidity at different temperatures, and obtains multiple equilibrium internal resistances of the fuel cell. The internal resistance-humidity relationship model is established through the equilibrium internal resistance and the humidity. The relationship between the equilibrium internal resistance and the humidity can be established according to the internal resistance-humidity relationship model. According to the humidity-water content relationship model, a humidity-water content relationship model between the humidity and the internal water content of the fuel cell can be established, so the relationship between the equilibrium internal resistance and the internal water content of the fuel cell can be established through the humidity . The accurate relationship model of internal resistance water content can be obtained by fitting method. Therefore, the internal water content of the fuel cell can be accurately obtained according to the relationship model between the equilibrium internal resistance and the water content of the internal resistance.

In one embodiment, the step S10 includes:

S110, maintaining the temperature of the fuel cell at the temperature during normal operation;

S120, under each measurement temperature condition, select a plurality of gases with different humidity to purge the fuel cell, and measure the high-frequency impedance of the fuel cell in each experiment in real time;

S130, when the high-frequency impedance and the gas reach an equilibrium state, obtain a plurality of the balanced internal resistances through the high-frequency impedance.

In the step S110, hot water may be supplied to the fuel cell through a hot water supply device, so that the temperature of the fuel cell may be maintained at the temperature when the fuel cell is operating. In one embodiment, the fuel cell is maintained between 60°C and 80°C.

In one embodiment, the temperature of the fuel cell is maintained for more than half an hour during normal operation. The temperature of the fuel cell is maintained between 60° C. and 80° C. for more than half an hour, thus ensuring the stability of the temperature of the fuel cell.

In the step S120, at a determined measurement temperature, a plurality of gases with different humidity may be sequentially selected to purge the fuel cell. The humidity may be relative humidity, which is subject to the protective vapor pressure of the fuel cell at the current temperature. The humidity may be the water vapor pressure of the front gas. During each measurement, the high frequency impedance of the fuel cell is measured in real time.

In one embodiment, in the step S120, the humidity of the gas purging the fuel cell is gradually increased in different measurements. Based on the current saturated vapor pressure of the fuel cell, gases with a humidity of 10%-100% of the saturated vapor pressure from small to large can be sequentially selected to carry out purging experiments one by one.

Referring to FIG. 3, in the step S130, when the fuel cell is purged with gas, the internal state of the fuel cell will be unstable. The high-frequency impedance of the fuel cell shows significant fluctuations in the purge state. Since the internal state of the fuel cell is unstable, the high-frequency impedance of the fuel cell at this time does not reflect the membrane impedance of the fuel cell well. After the purging is stopped, the high-frequency internal resistance of the fuel cell begins to drop rapidly, and the equilibrium internal resistance can be determined according to the high-frequency internal resistance.

In one embodiment, the step S130 includes:

S131, after purging the fuel cell by the gas for a certain period of time, stop purging;

S132, when the high-frequency impedance is stabilized after the purging stops, determine a stable value of the high-frequency impedance, and continue to purge the fuel cell with the gas;

S133, repeating steps S131-S132, and determining one of the balanced internal resistances according to the stable value.

S134, selecting different temperatures and the humidity of the gas, and repeating steps S131-S132 to obtain a plurality of the balanced internal resistances.

In the step S132, after the purging is stopped, the high-frequency internal resistance of the fuel cell begins to drop rapidly and is finally maintained at a stable value.

In the step S133, in order to avoid insufficient internal balance of the fuel cell, a gas with the same humidity may be selected to purge the fuel cell again under the same temperature condition. That is, steps S131-S132 are repeated to ensure that the balance internal resistance does not change much or does not change any more. At this time, a set of data of the equilibrium internal resistance and the corresponding humidity can be obtained.

In one embodiment, the determining one of the balanced internal resistances according to the stable value includes:

When the difference between the stable values measured when the balance between adjacent two purges is stopped is not greater than a preset value, the stable value measured later is selected as one of the equilibrium internal resistances. In one embodiment, the preset value is the degree of change of the stable value obtained from two consecutive measurements. In one embodiment, when the change of the stable value of the subsequent measurement relative to the stable value of the previous measurement is not greater than 5%, the stable value of the subsequent measurement may be determined to be the equilibrium internal resistance.

In the step S134, different parameters of the temperature and the humidity of the gas are selected, and the above steps are repeated again to obtain multiple sets of the equilibrium internal resistance and the humidity data.

In one embodiment, before the step S110, it also includes:

S010, the fuel cell is purged with dry gas. In order to prevent the remaining water in the fuel cell membrane and the remaining water in the catalyst layer from affecting the estimation results, it is necessary to first remove the reserved water inside the fuel cell. The reserved water can be purged by the drying gas. In one embodiment, since the saturated vapor pressure of water is related to temperature, a dry gas with 0% humidity is used for purging at a lower temperature, thereby minimizing the presence of moisture in the fuel cell.

In one embodiment, in the step S010, the time for purging the fuel cell is greater than 2 hours. Therefore, it can be ensured that the inside of the fuel cell is sufficiently dry and the test is accurate.

In one embodiment, the temperature of the drying gas is not greater than 25°C. Therefore, the moisture carried by the dry gas can be reduced as much as possible to ensure the accuracy of the measurement.

In one embodiment, the humidity water content relationship model is:

λ _eq =0.043+17.81a-39.85a ² +36a ³

a=P _v /P _sat

where a is the water activity, Pv represents the water vapor partial pressure of the current gas, Psat represents the saturated vapor pressure at the current temperature, and λeq represents the equilibrium water content, that is, the internal water content of the fuel cell corresponding to the equilibrium internal resistance. The relationship between the humidity and the equilibrium water content at the current temperature can be determined through the humidity-water content relationship model.

Wherein, the internal resistance water content relationship model can be selected from the following relationship:

R _mem =F(λ _mem )

where R _mem represents the high frequency impedance and λ represents the water content. R represents the contact internal resistance of the fuel cell, and a, b, c, d, and R are all unknown constants.

Referring to FIG. 4 , the equilibrium internal resistance and the equilibrium water content obtained in the above-mentioned embodiments can be obtained by fitting the specific values of the a, b, c, d, and R, and thus the Internal resistance water content relationship model.

In one embodiment, the specific values of a, b, c, d, and R can also be obtained through the polynomial fitting of the water activity.

The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity, all possible combinations of the technical features in the above-described embodiments are not described. However, as long as there is no contradiction between the combinations of these technical features, All should be regarded as the scope described in this specification.

The above-mentioned embodiments only represent several embodiments of the present application, and the descriptions thereof are relatively specific and detailed, but should not be construed as a limitation of the scope of this patent. It should be pointed out that for those skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which all belong to the protection scope of the present application. Therefore, the scope of protection of the patent of the present application shall be subject to the appended claims.

Claims (9)

1. A method for calibrating impedance of a fuel cell, comprising:

s10, selecting a plurality of gases with different humidity to purge the fuel cell in sequence at different temperatures, and obtaining a plurality of balance internal resistances of the fuel cell;

s20, establishing an internal resistance humidity relation model of the balance internal resistance and the humidity of the gas;

s30, obtaining an internal resistance water content relation model of the balance internal resistance and the water content in the fuel cell through a fitting method based on the internal resistance humidity relation model and the humidity water content relation model of the humidity of the gas and the water content in the fuel cell;

the humidity water content relation model is as follows:

λ_eq＝0.043+17.81a-39.85a²+36a³

a＝P_v/P_sat

wherein a is water activity, Pv represents the current water vapor partial pressure of the gas, Psat represents the saturated vapor pressure at the current temperature, and λ eq represents the equilibrium water content;

the internal water-blocking content relation model is

R_mem＝F(λ_mem)

Wherein R is_memRepresents high frequency impedance, λ represents water content, R represents contact internal resistance of the fuel cell, and a, b, c, d, R are unknown constants.

2. The fuel cell impedance calibration method according to claim 1, wherein the step S10 includes:

s110, maintaining the temperature of the fuel cell at the temperature of the normal operation;

s120, selecting a plurality of gases with different humidity to purge the fuel cell under each temperature measuring condition, and measuring the high-frequency impedance of the fuel cell in each experiment in real time;

s130, when the high-frequency impedance and the gas reach a balance state, obtaining a plurality of balance internal resistances through the high-frequency impedance.

3. The fuel cell impedance calibration method according to claim 2, wherein in the step S120, the humidity of the gas for purging the fuel cell is gradually increased in different measurements.

4. The fuel cell impedance calibration method according to claim 2, wherein the step S130 includes:

s131, after the fuel cell is purged for a certain time by the gas, stopping purging;

s132, determining a stable value of the high-frequency impedance after the purging stops stabilizing, and continuing to purge the fuel cell through the gas;

s133, repeating the steps S131-S132, and determining the balanced internal resistance according to the stable value;

s134, selecting different temperatures and the humidity of the gas, and repeating the steps S131 to S132 to obtain a plurality of balance internal resistances.

5. The method for calibrating the impedance of a fuel cell according to claim 2, wherein in step S110, the temperature of the fuel cell is maintained for more than half an hour during normal operation.

6. The method for calibrating impedance of a fuel cell according to claim 4, wherein said step S133, said determining a balanced internal resistance according to said stable value comprises:

and when the difference of the stable values measured when the two adjacent purges stop balancing is not larger than a preset value, selecting the measured stable value as the balancing internal resistance.

7. The method for calibrating the impedance of a fuel cell according to claim 2, wherein the step S110 is preceded by the steps of:

and S010, purging the fuel cell through dry gas.

8. The method for calibrating the impedance of a fuel cell according to claim 7, wherein in the step S010, the time for purging the fuel cell is more than 2 hours.

9. The fuel cell impedance calibration method of claim 7, wherein the temperature of the dry gas is not greater than 25 ℃.

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