Fuel cell system shutdown purging method and optimal strategy determination method thereof

Abstract

The application relates to a fuel cell system shutdown purging method and an optimal strategy determination method thereof, and the shutdown purging method is as follows: when normal operation of a fuel cell system ends, a purging process is prepared to be executed, working current is reduced to I 吹扫 At this time, the current single piece voltage is monitored by a single piece voltage patrol device CVM and recorded as V0; the single piece voltage reduction amount Delta V of the corresponding purging stage when the purging is completed is calculated; the single piece voltage V1 when the purging is completed is calculated according to the single piece voltage reduction amount Delta V of the purging stage; the purging is stopped when the voltage patrol device CVM monitors that the current single piece voltage is V1, and then the shutdown process is completed. Without using a complicated device to detect the internal resistance value of the stack, only the single piece voltage is monitored by the single piece voltage patrol device, so that whether the purging is completed can be accurately judged. The fuel cell system shutdown purging method adopted by the application is simple and easy to implement, effectively reduces the use cost, and meanwhile, the completion degree of the purging is ensured.

Description

Technical Field

[0001] This invention relates to the field of fuel cells, and specifically to a method for shutting down and purging a fuel cell system and a method for determining the optimal strategy thereon. Background Technology

[0002] During operation, hydrogen and air react to produce water. Although most of this water is expelled with the exhaust gases, water within the membrane electrode assembly (MEA) is difficult to remove. During shutdown, the temperature inside the stack drops, causing the gaseous water to condense into liquid water. In sub-zero ambient temperatures, this liquid water can easily freeze and damage the MEA, affecting the stack's performance and lifespan. Therefore, it is necessary to implement a purging strategy during shutdown to remove as much water as possible from the MEA and ensure performance upon restart.

[0003] During fuel cell system purging, the internal resistance of the stack increases with purging time due to the membrane gradually drying. Current technology typically uses fixed conditions and purging times as the basis for purging decisions, and cannot monitor changes in internal resistance in real time. Purging times should vary depending on operating conditions. As the fuel cell industry develops, DC manufacturers are gradually adding internal resistance measurement capabilities. However, equipment for detecting stack internal resistance is usually very complex and is generally only used in the research and development phase, not yet in practical application.

[0004] In addition, different purging conditions can achieve the final purging effect, but the existing technology lacks a standard for judgment to find the best, resulting in poor purging efficiency.

[0005] Therefore, there is an urgent need to design a shutdown purging method for fuel cell systems and a method for determining the optimal strategy to solve the problems existing in the above-mentioned prior art. Summary of the Invention

[0006] In view of this, the present invention provides a method for shutting down and purging a fuel cell system and a method for determining the optimal strategy. The purpose is to determine the conditions for completing the purging without using complex equipment to detect the internal resistance of the fuel cell stack, and to seek the optimal purging strategy based on the balance between the power consumption of the air compressor and the purging time.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for shutting down and purging a fuel cell system, as detailed below:

[0009] When the fuel cell system finishes normal operation, a purging process is prepared, and the operating current is reduced to I through the fuel cell DC / DC converter. 吹扫 At this time, the current single-chip voltage is monitored by the single-chip voltage detector (CVM) and recorded as V0;

[0010] Calculate the voltage drop ΔV of a single chip during the purging stage when the purging is completed;

[0011] Calculate the single-chip voltage V1 when the purging is completed based on the single-chip voltage drop ΔV during the purging stage.

[0012] When the voltage monitor CVM detects that the current single-chip voltage is V1, it stops purging and then completes the shutdown process.

[0013] Furthermore, the calculation of the single-chip voltage drop ΔV upon completion of the purging process is as follows:

[0014] The voltage drop caused by the increase in proton resistance can be expressed by the following expression:

[0015]

[0016] In the formula, ΔV is the voltage drop of a single chip during the purging stage, and I 吹扫 For the purge current, ΔR H This represents the increase in proton resistance during the purging phase.

[0017] Furthermore, the increase in proton resistance ΔR during the purging phase H The decrease in water content Δλ of the proton exchange membrane is related to the following:

[0018]

[0019] In the formula, k and b are corresponding constants, both of which are related to the thickness and active area of ​​the proton exchange membrane. During the purging stage, the reduction in water content Δλ for a fixed type of proton exchange membrane is a constant value.

[0020] Furthermore, the calculation of the single-cell voltage V1 at the end of the purging process, based on the single-cell voltage drop ΔV during the purging phase, is as follows:

[0021] V1 = V0 - ΔV;

[0022] In the formula, V0 is the current single-cell voltage monitored by the single-cell voltage monitor (CVM) at the start of the fuel cell system shutdown purging.

[0023] The present invention also provides an optimal strategy determination method based on the above-described fuel cell system shutdown and purging method, wherein the optimal strategy determination method is as follows:

[0024] S1. Set a maximum limit t for the purging time of a specific fuel cell system. lim ;

[0025] S2. During the purging phase, different air compressor purging speeds are set at certain intervals, and the fuel cell system shutdown purging method is executed sequentially in order of increasing air compressor purging speed. The power consumption of the corresponding air compressor is calculated, and the purging time is recorded.

[0026] S3. When the air compressor purging speed is a certain value, the corresponding purging time is less than or equal to the maximum limit t of the purging time. lim When this is the case, the optimal strategy for the shutdown purging method is to determine the air compressor purging speed and the corresponding purging time.

[0027] Furthermore, in step S2, different air compressor purging speeds are set at certain intervals during the purging phase, and the fuel cell system shutdown purging method is executed sequentially according to the air compressor purging speed from small to large. The power consumption of the corresponding air compressor is calculated, and the purging time is recorded as follows:

[0028] S2-1. Set the initial purging speed of the air compressor to N0, execute the fuel cell system shutdown purging method, and simultaneously obtain the purging air mass flow rate m and the air pressure P at the air compressor inlet. 前 Air pressure P at the air compressor outlet 后 and the air temperature T at the air compressor inlet 前 Calculate the current power consumption of the air compressor. Record the current purging time t0;

[0029] S2-2. Restore the fuel cell system to normal operation for 30 minutes to ensure the proton exchange membrane is fully wetted; set the air compressor purging speed to N. n The fuel cell system shutdown and purging method is executed, and the purging air mass flow rate m and the air pressure P at the air compressor inlet are obtained simultaneously. 前 Air pressure P at the air compressor outlet 后 and the air temperature T at the air compressor inlet 前 Calculate the current power consumption of the air compressor. Record the current purging time t n ;

[0030] S2-3. The purging time t n And the maximum limit of purging time t lim Comparison, if t n >t lim Then set the air compressor purging speed to N. n+1 And N n+1 >N n Repeat step S2-2; if t n ≤t lim Enter S3.

[0031] Furthermore, the specific calculation method for the power consumption of the air compressor is as follows:

[0032]

[0033] In the formula, T 前 The air temperature at the compressor inlet is represented by m; the purge air mass flow rate is represented by η; and the efficiency is represented by p, which is obtained from the compressor characteristic curve. r The pressure ratio represents the air compressor's pressure, P, which is the air pressure at the compressor's outlet. 后 Pressure P at the air compressor inlet 前 The ratio of .

[0034] Furthermore, the purge air mass flow rate m is obtained from a mass flow meter installed at the air compressor inlet, and the air pressure P at the air compressor inlet is... 前 The air pressure P at the air compressor outlet is obtained from a pressure sensor installed at the air compressor inlet. 后 The air temperature T at the air compressor inlet is obtained from a pressure sensor located at the air compressor outlet. 前 The temperature data is obtained from a temperature sensor located at the air compressor inlet.

[0035] Compared with the prior art, the beneficial effects of the present invention are:

[0036] (1) This invention is based on the proton resistance R caused by the decrease in water content inside the proton exchange membrane during the purging process. H The increase in proton resistance causes a voltage drop. By accurately calculating the voltage drop during the purging process, the increase in proton resistance eliminates the need for complex equipment to detect the internal resistance of the fuel cell stack. Instead, a single-chip voltage monitor (CVM) is used to monitor the voltage of each chip, which accurately determines whether the purging is complete. Voltage monitoring ensures that the water in the membrane electrode assembly is reduced to the required level. The fuel cell system shutdown purging method adopted in this invention is simple and easy to implement, effectively reduces operating costs, and ensures the completion of the purging process.

[0037] (2) Based on the voltage drop to determine whether the purging is complete, this invention makes an optimization judgment based on the purging time and the power consumption of the air compressor. Based on the relevant parameter values ​​obtained by the fuel cell system during the shutdown purging process, the power consumption of the air compressor is accurately calculated. Under the condition of ensuring the purging time, the power consumption of the air compressor is minimized as much as possible. The balance point between the purging time and the power consumption of the air compressor is selected as the optimal strategy for the shutdown purging method. Under the same purging current, the purging time of the fuel cell system is guaranteed, and the energy loss caused by excessive power consumption of the air compressor is avoided, thereby improving the purging efficiency.

[0038] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description and the drawings. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 A diagram illustrating a method for shutting down and purging a fuel cell system according to an embodiment of the present invention is shown.

[0041] Figure 2 The graph shows the changes in internal resistance and voltage over time during the purging process of the fuel cell system according to an embodiment of the present invention.

[0042] Figure 3 The diagram shows the change in proton resistance with purging time when the rotational speed of the air compressor changes according to an embodiment of the present invention. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] This invention provides a method for shutting down and purging a fuel cell system, such as... Figure 1 As shown, the shutdown purging method is as follows:

[0045] When the fuel cell system finishes normal operation, a purging process is prepared, and the operating current is reduced to I through the fuel cell DC / DC converter. 吹扫 At this time, the current single-chip voltage is monitored by the single-chip voltage detector (CVM) and recorded as V0;

[0046] Calculate the voltage drop ΔV of a single chip during the purging stage when the purging is completed;

[0047] Calculate the single-chip voltage V1 when the purging is completed based on the single-chip voltage drop ΔV during the purging stage.

[0048] When the voltage monitor CVM detects that the current single-chip voltage is V1, it stops purging and then completes the shutdown process.

[0049] The calculation of the single-chip voltage drop ΔV when the purge is completed is as follows:

[0050] During the fuel cell system purging procedure, as the water content within the proton exchange membrane gradually decreases, the internal resistance gradually increases, while the stack voltage gradually decreases. Specifically... Figure 2 As shown, during purging, the internal resistance gradually increases and the corresponding voltage gradually decreases, which is caused by changes in the internal water content.

[0051] In the voltage loss of the fuel cell stack, the activation loss E act And Ohm loss E ohm and concentration loss E conc The composition, in which the voltage drop Δv of the fuel cell stack is expressed as:

[0052] Δv=E act +E ohm +E conc ;

[0053] The voltage drop Δv of the fuel cell stack is the product of the voltage drop per cell ΔV and the number of cells in the stack.

[0054] Since the current is small and constant during purging, the activation loss E is considered to be... act and concentration loss E conc The effect is constant; that is, the voltage loss during the purging phase is entirely due to the ohmic loss E. ohm This is caused by the ohmic resistance R. ohm From proton resistance R H Electronic resistance R e and contact resistance R C Composition, ohmic resistance R ohm The expression is:

[0055] R ohm =R H +R e +R C ;

[0056] During the purging phase, the operating current is very low and remains constant. Under the same current, the electronic resistance R... e and contact resistance R C It is fixed, therefore the proton resistance R is mainly due to the decrease in water content within the proton exchange membrane. H The voltage drop caused by the increase in proton resistance. Therefore, the voltage drop caused by the increase in proton resistance has the following expression:

[0057]

[0058] In the formula, ΔV is the voltage drop of a single chip during the purging stage, and I 吹扫 For the purge current, ΔR HThis represents the increase in proton resistance during the purging phase.

[0059] The increase in proton resistance ΔR during the purging phase H The decrease in water content Δλ of the proton exchange membrane is related to the following:

[0060]

[0061] In the formula, k and b are corresponding constants, both of which are related to the thickness and active area of ​​the proton exchange membrane.

[0062] According to experimental tests, the increase in proton resistance ΔR during different purging stages... H The relationship between the decrease in water content of the corresponding proton exchange membrane, Δλ, and the above formula is obtained through data fitting.

[0063] During the purging process, the decrease in water content λ of a fixed type of proton exchange membrane is often a constant value. Therefore, the increase in proton resistance ΔR during the purging stage... H The voltage drop ΔV of a single chip during the purging stage is a constant value.

[0064] For a specific type of proton exchange membrane, its water content λ changes from 14 to 2 during the purging phase. Therefore, based on the decrease in water content Δλ = 14 - 2, the increase in proton resistance ΔR during the purging phase can be calculated. H Combined with the purging current I 吹扫 The voltage drop ΔV of a single chip during the purging stage is also calculated to be a constant value.

[0065] The calculation of the single-cell voltage V1 at the completion of purging is based on the single-cell voltage drop ΔV during the purging phase, as detailed below:

[0066] V1 = V0 - ΔV;

[0067] In the formula, V0 is the current single-cell voltage monitored by the single-cell voltage monitor (CVM) when the fuel cell system shutdown purging begins.

[0068] This invention is based on the proton resistance R caused by the decrease in water content within the proton exchange membrane during the purging process. H The increase in proton resistance causes a voltage drop. By accurately calculating the voltage drop during the purging process, the increase in proton resistance eliminates the need for complex equipment to detect the internal resistance of the fuel cell stack. Instead, a single-chip voltage monitor (CVM) is used to monitor the voltage of each chip, which accurately determines whether the purging is complete. Voltage monitoring ensures that the water in the membrane electrode assembly is reduced to the required level. The fuel cell system shutdown purging method adopted in this invention is simple and easy to implement, effectively reduces operating costs, and ensures the completion of the purging process.

[0069] When executing a fuel cell system shutdown purging procedure, different purging conditions, such as varying airflow rates, can occur under the same purging current, resulting in inconsistent purging times. However, for automotive applications, purging time is a crucial factor and should be minimized as much as possible. Airflow rate, on the other hand, is related to the air compressor speed, which in turn is related to the air compressor's power consumption. Therefore, during shutdown purging, air compressor power consumption should be taken into account to avoid excessive energy loss.

[0070] like Figure 3 As shown in the figure, under the same purging current, when the speed of the air compressor changes, the proton resistance based on the voltage drop strategy changes with the purging time. It can be seen from the figure that the air compressor speeds corresponding to curves ①②③④ increase in turn, the corresponding air compressor power consumption also increases in turn, and the corresponding purging completion time decreases in turn.

[0071] Based on this, the present invention proposes to optimize the shutdown purging strategy using two boundary conditions: the power consumption of the air compressor and the purging time. A specific embodiment of the present invention also provides a method for determining the optimal strategy based on the above-mentioned fuel cell system shutdown purging method, the optimal strategy determination method being as follows:

[0072] S1. Set a maximum limit t for the purging time of a specific fuel cell system. lim ;

[0073] S2. During the purging phase, different air compressor purging speeds are set at certain intervals, and the fuel cell system shutdown purging method is executed sequentially in order of increasing air compressor purging speed. The power consumption of the corresponding air compressor is calculated, and the purging time is recorded.

[0074] S3. When the air compressor purging speed is a certain value, the corresponding purging time is less than or equal to the maximum limit t of the purging time. lim When this is the case, the optimal strategy for the shutdown purging method is to determine the air compressor purging speed and the corresponding purging time.

[0075] Step S2 is as follows:

[0076] S2-1. Set the initial purging speed of the air compressor to N0, execute the fuel cell system shutdown purging method, and simultaneously obtain the purging air mass flow rate m and the air pressure P at the air compressor inlet. 前 Air pressure P at the air compressor outlet 后 and the air temperature T at the air compressor inlet 前 Calculate the current power consumption of the air compressor. Record the current purging time t0;

[0077] S2-2. Restore the fuel cell system to normal operation for 30 minutes to ensure the proton exchange membrane is fully wetted; set the air compressor purging speed to N.n The fuel cell system shutdown and purging method is executed, and the purging air mass flow rate m and the air pressure P at the air compressor inlet are obtained simultaneously. 前 Air pressure P at the air compressor outlet 后 and the air temperature T at the air compressor inlet 前 Calculate the current power consumption of the air compressor. Record the current purging time t n ;

[0078] S2-3. The purging time t n And the maximum limit of purging time t lim Comparison, if t n >t lim Then set the air compressor purging speed to N. n+1 And N n+1 >N n Repeat step S2-2; if t n ≤t lim Enter S3.

[0079] Air compressor purging speed N n Where n takes the value of a positive integer, and N n+1 >N n >N0.

[0080] The specific calculation method for the power consumption of an air compressor is as follows:

[0081]

[0082] In the formula, T 前 The air temperature at the compressor inlet is represented by m; the purge air mass flow rate is represented by η; and the efficiency is represented by p, which is obtained from the compressor characteristic curve. r The pressure ratio represents the air compressor's pressure, P, which is the air pressure at the compressor's outlet. 后 Pressure P at the air compressor inlet 前 The ratio of .

[0083] The purge air mass flow rate m is obtained from the mass flow meter installed at the air compressor inlet, and the air pressure P at the air compressor inlet is also measured. 前 The air pressure P at the air compressor outlet is obtained from a pressure sensor installed at the air compressor inlet. 后 The air temperature T at the air compressor inlet is obtained from a pressure sensor located at the air compressor outlet. 前 The temperature data is obtained from a temperature sensor located at the air compressor inlet.

[0084] This invention, based on voltage drop as a criterion for determining whether purging is complete, optimizes the process by considering purging time and air compressor power consumption. Using relevant parameter values ​​acquired during the fuel cell system's shutdown purging process, it accurately calculates air compressor power consumption. While ensuring sufficient purging time, it minimizes air compressor power consumption, selecting the optimal balance between purging time and air compressor power consumption as the optimal strategy for the shutdown purging method. Under the same purging current, this approach ensures both sufficient purging time for the fuel cell system and avoids energy loss due to excessive air compressor power consumption, thereby improving purging efficiency.

[0085] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for determining the optimal strategy for a fuel cell system shutdown purging method, characterized in that, The method for determining the optimal strategy is as follows: S1. Set a maximum limit on the purging time for a specific fuel cell system. ; S2. During the purging phase, different air compressor purging speeds are set at certain intervals, and the fuel cell system shutdown purging method is executed sequentially in order of increasing air compressor purging speed. The power consumption of the corresponding air compressor is calculated, and the purging time is recorded. The specific method for shutting down and purging the fuel cell system is as follows: When the fuel cell system finishes normal operation, a purging process is prepared, and the operating current is reduced to [value missing] via the fuel cell DC / DC converter. At this time, the current single-chip voltage is monitored by the single-chip voltage monitor (CVM) and recorded as follows: ; Calculate the voltage drop of a single chip during the corresponding purging stage when purging is complete. ; Based on the voltage drop of a single chip during the purging phase Calculate the single-chip voltage when purging is complete. ; When the voltage monitor (CVM) detects that the current single-chip voltage is Stop purging and then complete the shutdown process; Step S2 is as follows: S2-1. Set the initial purging speed of the air compressor to... Perform the fuel cell system shutdown and purging method, and simultaneously obtain the purging air mass flow rate. Air pressure at the air compressor inlet Air pressure at the air compressor outlet and the air temperature at the air compressor inlet Calculate the current power consumption of the air compressor. Record the current purging time. ; S2-2. Restore the fuel cell system to normal operation for 30 minutes to ensure the proton exchange membrane is fully wetted; set the air compressor purging speed to [value missing]. Perform the fuel cell system shutdown and purging method, and simultaneously obtain the purging air mass flow rate. Air pressure at the air compressor inlet Air pressure at the air compressor outlet and the air temperature at the air compressor inlet Calculate the current power consumption of the air compressor. Record the current purging time. ; S2-3. Purging time and the maximum limit of purging time In comparison, if Then set the air compressor purging speed to ,and Repeat step S2-2; if Enter S3; S3. When the air compressor purging speed is a certain value, the corresponding purging time is less than or equal to the maximum limit of the purging time. When this is the case, the optimal strategy for the shutdown purging method is to determine the air compressor purging speed and the corresponding purging time.

2. The optimal strategy determination method as described in claim 1, characterized in that, The calculation of the single-chip voltage drop upon completion of the purge is described. The details are as follows: The voltage drop caused by the increase in proton resistance can be expressed by the following expression: ； In the formula, This refers to the voltage drop per chip during the purging phase. For purging current, This represents the increase in proton resistance during the purging phase.

3. The optimal strategy determination method as described in claim 2, characterized in that, The increase in proton resistance during the purging phase The reduction in water content of the proton exchange membrane The following relationship exists: ； In the formula, and For the corresponding constant, and All of these are related to the thickness and active area of ​​the proton exchange membrane. During the purging phase, the reduction in water content for a fixed type of proton exchange membrane... It is a constant value.

4. The optimal strategy determination method as described in claim 3, characterized in that, The amount of voltage drop per chip during the purging phase Calculate the single-chip voltage when purging is complete. The details are as follows: ； In the formula, This refers to the current cell voltage monitored by the cell voltage monitor (CVM) at the start of the fuel cell system shutdown purging.

5. The optimal strategy determination method as described in claim 4, characterized in that, The specific calculation method for the power consumption of an air compressor is as follows: ； In the formula, This represents the air temperature at the air compressor inlet. Represents the purge air mass flow rate; Efficiency is represented by the characteristic curve of the air compressor. The pressure ratio represents the air compressor's pressure at the compressor outlet. Pressure at the air compressor inlet The ratio of .

6. The optimal strategy determination method as described in claim 5, characterized in that, purge air mass flow rate The air pressure at the air compressor inlet is obtained from a mass flow meter installed at the air compressor inlet. The air pressure at the air compressor outlet is obtained from a pressure sensor installed at the air compressor inlet. The air temperature at the air compressor inlet is obtained from a pressure sensor located at the air compressor outlet. The temperature data is obtained from a temperature sensor located at the air compressor inlet.

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