Bypass air flow estimation method and device and in-pile air flow estimation method

Abstract

The invention relates to the technical field of fuel cell engine control, in particular to a bypass air flow estimation method and device and an in-pile air flow estimation method.The bypass air flow estimation method comprises the steps that the corresponding relation among the opening degree of a bypass valve, the actual pressure ratio and the standard condition flow is obtained; obtaining the bypass valve opening degree, the in-stack air pressure, the in-stack air temperature and the environment pressure of the air system of the target fuel cell; the actual pressure ratio of the bypass valve is calculated based on the obtained in-pile air pressure and the environment pressure, and the standard-condition flow of the bypass valve is determined according to the opening degree of the bypass valve, the actual pressure ratio of the bypass valve and the corresponding relation; and determining a correction coefficient based on the in-reactor air temperature, the in-reactor air pressure and the environment pressure, and correcting the standard condition flow by adopting the correction coefficient to obtain the bypass air flow of the bypass valve. The bypass air flow of the bypass valve of the air system of the fuel cell can be estimated, a flow meter does not need to be additionally arranged, and the cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cell engine control, and in particular to a bypass air flow estimation method and device, and a stack air flow estimation method. Background Art

[0002] Fuel cell vehicles are an important development direction for new energy vehicles because they have the advantages of zero emissions, high efficiency and fast hydrogen refueling. The power of fuel cell vehicles is mainly provided by fuel cell engines, which are mainly composed of multiple subsystems such as fuel cell stacks, air supply subsystems, water thermal management subsystems, hydrogen supply subsystems, DCDC, etc. The fuel cell engine needs to ensure a certain flow rate and pressure into the stack. The operating flow rate and pressure of the fuel cell are controlled in a closed loop by adjusting the air compressor speed and the back pressure valve opening.

[0003] In the air system, due to the characteristics of the air compressor, according to the flow-pressure ratio surge curve of the air compressor, when the flow and pressure exceed the surge line, the air compressor will experience obvious surge, which is specifically manifested as surge at low speed, periodic fluctuations in pressure and flow, and obvious noise at high speed.

[0004] In order to achieve surge control of the air system, a bypass valve needs to be added at the stack entry. Surge will reduce the life of the air compressor and affect the stable power output of the fuel cell engine. However, after adding the bypass valve, since the air system only has a mass flow meter at the air filter, the stack entry flow is not equal to the mass flow at the air filter. At this time, the closed-loop control of the air system's stack entry air flow will be uncontrollable. An effective method is to add a mass flow meter at the bypass, but the temperature of the air compressor outlet gas is relatively high. Long-term exposure to high temperature and high humidity conditions will affect the accuracy and stability of the flow meter, and adding a flow meter will increase the cost of the system. Summary of the invention

[0005] The object of the present invention is to provide a bypass air flow estimation method, device and stack air flow estimation method, which can estimate the bypass air flow of a fuel cell air system bypass valve without adding a flow meter, thereby reducing costs.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention provides a bypass air flow estimation method, which is applied to an air system of a fuel cell, comprising:

[0008] Obtain the corresponding relationship between the bypass valve opening, actual pressure ratio and standardized flow rate;

[0009] Obtaining the bypass valve opening, stack air pressure, stack air temperature and ambient pressure of the air system of the target fuel cell;

[0010] The actual pressure ratio of the bypass valve is calculated based on the obtained stack air pressure and the ambient pressure, and the standardized flow rate of the bypass valve is determined according to the obtained bypass valve opening, the calculated actual pressure ratio of the bypass valve and the corresponding relationship;

[0011] A correction coefficient is determined based on the temperature and pressure of the air entering the stack, and the correction coefficient is used to correct the normalized flow rate to obtain the bypass air flow rate of the bypass valve.

[0012] Furthermore, the correction coefficients include a standard temperature correction coefficient, a standard pressure ratio correction coefficient and a relative flow ratio correction coefficient.

[0013] Furthermore, the calculation formula of the standard temperature correction coefficient is: Where: a1 is the standard temperature correction coefficient, T std is the standard temperature, T up is the air temperature entering the pile.

[0014] Further, the calculation formula of the standard pressure ratio correction coefficient is: Where: a2 is the standard pressure ratio correction coefficient, P std is the standard pressure, P up is the air pressure entering the pile.

[0015] Further, the calculation formula of the relative flow ratio correction coefficient is: Where: a3 is the relative flow ratio correction coefficient, P down is the environmental pressure, P up is the air pressure entering the pile, and k is the air adiabatic index.

[0016] Furthermore, the bypass air flow rate of the bypass valve The calculation formula is In the formula, is the standard flow rate of the bypass valve, a1 is the standard temperature correction coefficient, a2 is the standard pressure ratio correction coefficient, and a3 is the relative flow ratio correction coefficient.

[0017] Furthermore, a corresponding relationship table between the bypass valve opening, the actual pressure ratio and the standardized flow rate is obtained through a bypass valve calibration test.

[0018] Furthermore, the fuel cell controller collects and obtains the bypass valve opening of the air system, the air pressure entering the stack, the air temperature entering the stack and the ambient pressure.

[0019] In a second aspect, the present invention provides a bypass air flow estimation device, which can execute the steps of the bypass air flow estimation method described above, including:

[0020] The first acquisition module is used to construct a corresponding relationship table between the opening of the bypass valve, the actual pressure ratio and the standardized flow rate.

[0021] The second acquisition module is used to acquire the bypass valve opening, stack-entering air pressure, stack-entering air temperature and ambient pressure of the air system of the target fuel cell.

[0022] The first determination module calculates an actual pressure ratio of the bypass valve based on the acquired stack air pressure and the ambient pressure, and determines a normalized flow rate of the bypass valve according to the acquired bypass valve opening, the calculated actual pressure ratio of the bypass valve and the corresponding relationship.

[0023] The second determination module determines a correction coefficient based on the temperature of the air entering the stack, the pressure of the air entering the stack and the ambient pressure, and uses the correction coefficient to correct the normalized flow rate to obtain a bypass air flow rate of the bypass valve.

[0024] In a third aspect, the present invention provides a method for estimating the air flow rate of a stack, which is applied to an air system of a fuel cell, comprising:

[0025] Obtaining the air filter flow rate and bypass valve working status of the air system of the target fuel cell;

[0026] In response to the bypass valve being in a closed state, the stack air flow rate of the air system of the target fuel cell is an air filter flow rate;

[0027] In response to the bypass valve operating state being open, the inlet air flow of the air system of the target fuel cell is the difference between the air filter flow and the bypass air flow of the bypass valve, and the bypass air flow is obtained using the bypass air flow estimation method described above.

[0028] The present invention has the following unexpected beneficial effects:

[0029] 1. The present invention estimates the inlet air flow rate of the fuel cell air system through a semi-physical empirical model of the valve. Specifically, the bypass valve opening, inlet air pressure, inlet air temperature and ambient pressure of the air system of the target fuel cell are obtained during the actual operation process, and the standardized flow rate of the bypass valve is obtained through the semi-empirical physical model of the valve, that is, the correspondence table between the bypass valve opening, the actual pressure ratio and the standardized flow rate. Then, a correction coefficient is determined according to the inlet air temperature, the inlet air pressure and the ambient pressure. The standardized flow rate is corrected by the correction coefficient to obtain the bypass air flow rate of the bypass valve. On the one hand, the bypass air flow rate is obtained by looking up the table and correcting, and no complicated calculation is required. On the other hand, since the relevant data can be directly collected and obtained by the fuel cell controller, there is no need to add an additional mass flow meter, which reduces the manufacturing cost.

[0030] 2. The present invention obtains the inflow air flow rate by comprehensively calculating the air filter flow rate and the bypass valve working state of the air system of the target fuel cell. By subtracting the bypass flow rate from the air filter flow rate, the inflow air flow rate when the bypass valve is opened can be obtained, thereby ensuring the closed-loop control of the inflow air flow rate when the bypass valve is opened. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention.

[0032] Figure 1 A schematic flow chart of a bypass air flow estimation method according to an embodiment of the present invention is shown.

[0033] Figure 2 A schematic structural diagram of a fuel cell air system according to an embodiment of the present invention is shown.

[0034] Figure 3 A curve diagram of the relative flow ratio coefficient according to an embodiment of the present invention is shown.

[0035] Figure 4 A schematic structural diagram of a bypass air flow estimation device according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0036] The following will describe the embodiments of the present invention with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention, not for limiting the scope of protection of the present invention.

[0037] In one embodiment, see Figure 1 As shown, the present invention provides a bypass air flow estimation method, which is applied to the air system of a fuel cell, comprising:

[0038] Obtain the corresponding relationship between the bypass valve opening, actual pressure ratio and standardized flow rate.

[0039] The bypass valve opening, stack air pressure, stack air temperature and ambient pressure of the air system of the target fuel cell are obtained.

[0040] The actual pressure ratio of the bypass valve is calculated based on the obtained stack air pressure and the ambient pressure, and the standardized flow rate of the bypass valve is determined according to the obtained bypass valve opening, the calculated actual pressure ratio of the bypass valve and the corresponding relationship.

[0041] A correction coefficient is determined based on the temperature and pressure of the air entering the stack, and the correction coefficient is used to correct the normalized flow rate to obtain the bypass air flow rate of the bypass valve.

[0042] The present invention estimates the inlet air flow rate of the fuel cell air system through a semi-physical empirical model of the valve, specifically, obtains the bypass valve opening, inlet air pressure, inlet air temperature and ambient pressure of the air system of the target fuel cell during actual operation, and obtains the standardized flow rate of the bypass valve through the semi-empirical physical model of the valve, that is, the correspondence table between the bypass valve opening, the actual pressure ratio and the standardized flow rate, and then determines the correction coefficient according to the inlet air temperature, the inlet air pressure and the ambient pressure, and uses the correction coefficient to correct the standardized flow rate to obtain the bypass air flow rate of the bypass valve. On the one hand, the bypass air flow rate is obtained by looking up the table and correcting, and no complicated calculation is required; on the other hand, since the relevant data can be directly collected and obtained by the fuel cell controller, there is no need to add an additional mass flow meter, which reduces the manufacturing cost.

[0043] The following is a detailed analysis and description of each step of the bypass air flow estimation method of the present invention.

[0044] Constructing a corresponding relationship table between the bypass valve opening, actual pressure ratio and standardized flow is the core foundation of the entire estimation process. Under different load requirements and environmental conditions, the bypass valve opening is finely adjusted, and the corresponding actual pressure ratio and standardized flow are accurately measured and recorded with the help of high-precision pressure sensors and flow measurement equipment. Filtering algorithms are used to remove noise data, and methods such as multivariate linear regression are used to fit and analyze the data, so as to establish a scientific and accurate corresponding relationship table.

[0045] Obtaining the bypass valve opening, stack air pressure, stack air temperature and ambient pressure of the target fuel cell air system is an important prerequisite for ensuring the accuracy of the estimation. The bypass valve opening can be directly obtained through the feedback signal of the electronic control system, which intuitively reflects the degree of opening of the bypass line. The stack air pressure and stack air temperature not only affect the electrochemical reaction rate inside the fuel cell, but are also closely related to the physical properties of the gas. Ambient pressure refers to the external environmental pressure of the fuel cell, which is an important reference for calculating the actual pressure ratio. Its value will vary with factors such as altitude and climatic conditions. In order to obtain high-precision data, the selected sensor must have good stability, accuracy and rapid response capabilities, and must be calibrated and maintained regularly to ensure the reliability of the data.

[0046] The actual pressure ratio of the bypass valve is calculated based on the obtained air pressure entering the reactor and the ambient pressure. The calculation formula is: actual pressure ratio = ambient pressure / air pressure entering the reactor. The actual pressure ratio clearly shows the pressure change of the gas on both sides of the bypass valve and is a key indicator for judging the gas flow trend. Based on the obtained bypass valve opening and the calculated actual pressure ratio, the corresponding standardized flow rate is queried in the pre-built corresponding relationship table.

[0047] The correction coefficient is determined based on the inlet air temperature, inlet air pressure and ambient pressure, and the standard flow is corrected using the correction coefficient to finally obtain the bypass air flow of the bypass valve. The corrected flow data can more truly reflect the bypass air flow under actual operating conditions, providing reliable data support for the precise control of the fuel cell air system.

[0048] The bypass air flow estimation method described in the present invention can adapt to complex and changeable operating conditions through comprehensive consideration and precise calculation of multiple parameters, provide a scientific basis for the optimal control of the fuel cell air system, and effectively promote the application and development of fuel cell technology in the field of clean energy.

[0049] In this embodiment, see Figure 2 As shown, the air system of the fuel cell includes a fuel cell stack 1, an air filter 2, an air compressor 3, an intercooler 4, a stop valve 5, a back pressure valve 6 and a bypass valve 7. The air filter 2, the air compressor 3, the intercooler 4 and the stop valve 5 are connected to the air inlet end of the fuel cell stack 1 in sequence, the back pressure valve 6 is connected to the air outlet end of the fuel cell stack 1, the pipeline between the stop valve 5 and the fuel cell stack 1 is connected to the pipeline between the back pressure valve 6 and the fuel cell stack 1 through the bypass valve 7, the air filter 2 is provided with a flow meter 8 for collecting the air filter flow, and the pipeline between the stop valve 5 and the air inlet end of the fuel cell stack 1 is provided with a pressure sensor 9 for collecting the inlet pressure of the fuel cell stack.

[0050] As a preferred embodiment of the present invention, the correction coefficient includes a standard temperature correction coefficient, a standard pressure ratio correction coefficient and a relative flow ratio correction coefficient.

[0051] Furthermore, the calculation formula of the standard temperature correction coefficient is: Where: a1 is the standard temperature correction coefficient, T std is the standard temperature, T up is the air temperature entering the pile.

[0052] Furthermore, the calculation formula of the standard pressure ratio correction coefficient is: Where: a2 is the standard pressure ratio correction coefficient, P std is the standard pressure, P up is the air pressure entering the pile.

[0053] Furthermore, the calculation formula of the relative flow ratio correction coefficient is:

[0054] Where: a3 is the relative flow ratio correction coefficient, P down is the environmental pressure, P up is the air pressure entering the pile, and k is the air adiabatic index.

[0055] For example, see Figure 3 , shows a curve diagram of the relative flow ratio coefficient. It can be seen from the figure that the relative flow ratio coefficient is related to the pressure ratio Pr.

[0056] As a preferred embodiment of the present invention, the bypass air flow rate of the bypass valve is The calculation formula is:

[0057] In the formula, is the standard flow rate of the bypass valve, a1 is the standard temperature correction coefficient, a2 is the standard pressure ratio correction coefficient, and a3 is the relative flow ratio correction coefficient.

[0058] As a preferred embodiment of the present invention, the corresponding relationship between the opening of the bypass valve, the actual pressure ratio and the standardized flow rate is obtained through a bypass valve calibration test.

[0059] The bypass valve calibration test specifically includes the following steps:

[0060] Step 1: Preparation of test equipment: The test equipment includes an actuator capable of accurately controlling the opening of the bypass valve, a high-precision pressure sensor for measuring the air pressure entering the stack and the ambient pressure, a flow measurement device (such as a mass flow meter) for measuring the normalized flow, and a data acquisition component for real-time recording of various data during the test.

[0061] Step 2: Set the test conditions: According to the actual operating conditions that the fuel cell may face, determine a series of bypass valve openings, stack air pressures and ambient pressure combinations. For example, the bypass valve opening is adjusted from 0% to 100% at preset intervals (such as 5%); the stack air pressure and ambient pressure are set according to the actual conditions at different altitudes and different loads.

[0062] Step 3, data collection: Under each set of working conditions, wait for the system to run stably for a period of time to ensure the accuracy of the measured data, and then use the data acquisition component to record the bypass valve opening, the air pressure entering the reactor, the ambient pressure, and the corresponding standardized flow rate. The data collection process needs to be repeated many times to obtain enough data points.

[0063] Step 4: Calculate the actual pressure ratio: Based on the collected inlet air pressure and ambient pressure, calculate the actual pressure ratio under each working condition according to the formula "actual pressure ratio = ambient pressure / inlet air pressure".

[0064] Step 5: Data processing and relational table construction.

[0065] Data cleaning: Since the test process may be affected by external interference and other factors, the collected data may contain noise or outliers. Therefore, it is necessary to clean the collected data and remove those obviously unreasonable data points.

[0066] Data fitting: Use appropriate mathematical methods (such as multivariate linear regression, polynomial fitting, etc.) to fit the cleaned data to find out the mathematical relationship between the bypass valve opening, actual pressure ratio and standardized flow rate.

[0067] Construct a relationship table: Convert the fitted mathematical relationship into a corresponding relationship table. Specifically, discretize the bypass valve opening and the actual pressure ratio, divide the intervals according to a certain interval, and then find the corresponding standardized flow value in each interval and fill it into the relationship table. With this setting, in actual applications, you can quickly get the standardized flow corresponding to different bypass valve openings and different actual pressure ratios by querying the corresponding relationship table.

[0068] As a preferred embodiment of the present invention, the bypass valve opening degree, the air pressure entering the stack, the air temperature entering the stack and the ambient pressure of the air system are collected and acquired through the fuel cell controller.

[0069] In one embodiment, see Figure 4 As shown, the present invention provides a bypass air flow estimation device, which can execute the steps of the bypass air flow estimation method mentioned above. The estimation device 10 includes a first acquisition module 11, a second acquisition module 12, a first determination module 13 and a second determination module 14.

[0070] The first acquisition module 11 is used to acquire the corresponding relationship between the opening of the bypass valve, the actual pressure ratio and the standardized flow rate.

[0071] The second acquisition module 12 is used to acquire the bypass valve opening, the stack-entering air pressure, the stack-entering air temperature and the ambient pressure of the air system of the target fuel cell.

[0072] The first determination module 13 calculates the actual pressure ratio of the bypass valve based on the acquired stack air pressure and the ambient pressure, and determines the standardized flow rate of the bypass valve according to the acquired bypass valve opening, the calculated actual pressure ratio of the bypass valve and the corresponding relationship.

[0073] The second determination module 14 determines a correction coefficient based on the temperature of the air entering the stack, the pressure of the air entering the stack and the ambient pressure, and uses the correction coefficient to correct the normalized flow rate to obtain the bypass air flow rate of the bypass valve.

[0074] In one embodiment, the present invention provides a method for estimating the air flow rate of a stack, which is applied to an air system of a fuel cell, comprising:

[0075] Obtaining the air filter flow rate and bypass valve working status of the air system of the target fuel cell;

[0076] In response to the bypass valve being in a closed state, the stack air flow rate of the air system of the target fuel cell is an air filter flow rate;

[0077] In response to the bypass valve operating state being open, the inlet air flow of the air system of the target fuel cell is the difference between the air filter flow and the bypass air flow of the bypass valve, and the bypass air flow is obtained using the bypass air flow estimation method described above.

[0078] The above embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Any equivalent substitution or change made by a person skilled in the art based on the present invention is within the protection scope of the present invention.

Claims

1. A bypass air flow estimation method, characterized in that: Air systems for fuel cells, including: Obtain the corresponding relationship between the bypass valve opening, actual pressure ratio and standardized flow rate; Obtaining the bypass valve opening, stack air pressure, stack air temperature and ambient pressure of the air system of the target fuel cell; The actual pressure ratio of the bypass valve is calculated based on the obtained stack air pressure and the ambient pressure, and the standardized flow rate of the bypass valve is determined according to the obtained bypass valve opening, the calculated actual pressure ratio of the bypass valve and the corresponding relationship; A correction coefficient is determined based on the temperature of the air entering the stack, the pressure of the air entering the stack and the ambient pressure, and the correction coefficient is used to correct the normalized flow rate to obtain the bypass air flow rate of the bypass valve.

2. The bypass air flow estimation method according to claim 1, characterized in that: The correction coefficients include a standard temperature correction coefficient, a standard pressure ratio correction coefficient and a relative flow ratio correction coefficient.

3. The bypass air flow estimation method according to claim 2, characterized in that: The calculation formula of the standard temperature correction coefficient is: Where: a1 is the standard temperature correction coefficient, T std is the standard temperature, T up is the air temperature entering the pile.

4. The bypass air flow estimation method according to claim 2, characterized in that: The calculation formula of the standard pressure ratio correction coefficient is: Where: a2 is the standard pressure ratio correction coefficient, P std is the standard pressure, P up is the air pressure entering the pile.

5. The bypass air flow estimation method according to claim 2, characterized in that: The calculation formula of the relative flow ratio correction coefficient is: Where: a3 is the relative flow ratio correction coefficient, P down is the environmental pressure, P up is the air pressure entering the pile, and k is the air adiabatic index.

6. The bypass air flow estimation method according to claim 2, characterized in that: Bypass air flow rate of the bypass valve The calculation formula is In the formula, is the standard flow rate of the bypass valve, a1 is the standard temperature correction coefficient, a2 is the standard pressure ratio correction coefficient, and a3 is the relative flow ratio correction coefficient.

7. The bypass air flow estimation method according to claim 1, characterized in that: Through the bypass valve calibration test, the corresponding relationship table between the bypass valve opening, actual pressure ratio and standardized flow rate is obtained.

8. The bypass air flow estimation method according to claim 1, characterized in that: The bypass valve opening of the air system, the air pressure entering the stack, the air temperature entering the stack and the ambient pressure are collected and obtained through the fuel cell controller.

9. A bypass air flow estimation device, characterized in that: The steps of the bypass air flow estimation method according to any one of claims 1 to 8 can be performed, including: A first acquisition module is used to obtain a corresponding relationship table between the opening of the bypass valve, the actual pressure ratio and the standardized flow rate; A second acquisition module is used to acquire the bypass valve opening, stack air pressure, stack air temperature and ambient pressure of the air system of the target fuel cell; The first determination module calculates the actual pressure ratio of the bypass valve based on the acquired stack air pressure and the ambient pressure, and obtains the corresponding normalized flow rate of the bypass valve by looking up a table according to the acquired bypass valve opening and the calculated actual pressure ratio of the bypass valve; The second determination module determines a correction coefficient based on the temperature of the air entering the stack, the pressure of the air entering the stack and the ambient pressure, and uses the correction coefficient to correct the normalized flow rate to obtain a bypass air flow rate of the bypass valve.

10. A method for estimating air flow into a stack, characterized in that: Air systems for fuel cells, including: Obtaining the air filter flow rate and bypass valve working status of the air system of the target fuel cell; In response to the bypass valve being in a closed state, the stack air flow rate of the air system of the target fuel cell is an air filter flow rate; In response to the bypass valve operating state being open, the inlet air flow of the air system of the target fuel cell is the difference between the air filter flow and the bypass air flow of the bypass valve, and the bypass air flow is obtained by the bypass air flow estimation method according to any one of claims 1 to 8.

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