Gas-electricity coordination control and water content constraint management method for hydrogen fuel cell

Abstract

The invention discloses a hydrogen fuel cell gas-electricity coordination control and water content constraint management method, which belongs to the technical field of fuel cells, and comprises the following steps: analyzing the influence of different load working conditions and different gas supply flows and pressures on membrane water content, and establishing a cross-membrane transmission water mass flow equation; a nonlinear coupling relation between an air loop and a DC-DC converter is considered, and a fuel cell gas-electric loop dynamic model is constructed; aiming at dynamic response characteristics on different time scales presented by the coupling system, a control instruction is designed based on a nonlinear backstepping method, and coordination control of the gas-electric coupling loop of the hydrogen fuel cell is completed; finally, aiming at the problem that fluctuation of the membrane water content affects the service life of the system, a reference adjustment algorithm is introduced, reference signals are corrected in real time, and safety constraint management of the membrane water content is achieved. The influence of rapid load change on the voltage and membrane water content of the fuel cell system can be reduced, and the operation stability and safety of the system are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of fuel cells, and in particular relates to a method for gas-electricity coordinated control and water content constraint management of a hydrogen fuel cell. Background Art

[0002] The proton exchange membrane fuel cell is a complex system with multiple time scales and multiple physical fields coupled. Its operation is affected by multiple physical processes such as gas flow, electrochemical reaction, membrane water transfer and heat transfer. During the operation of the fuel cell, the dynamic response of the gas supply system plays a vital role. Due to the large mechanical inertia of components such as the air compressor and the lag in gas flow regulation, the system responds slowly to load changes. Especially under conditions with large load fluctuations, the rapid regulation of the DC-DC converter on the current can easily lead to drastic fluctuations in the oxygen concentration inside the stack, the membrane water content and the output voltage, which in turn causes oxygen starvation, flooding and membrane dryness, affecting the efficiency and service life of the system. Therefore, in order to reduce the impact of rapid load changes on system performance and ensure the stability and safety of the system under various conditions, it is urgent to carry out research related to the safety control of the fuel cell gas-electricity-water coupling system. This research can effectively improve the dynamic and steady-state performance of the system, enhance the operating efficiency of the fuel cell and extend its service life.

[0003] The DC-DC control strategy in the existing fuel cell system relies on the linear feedback method. In realizing the fuel cell voltage output control task, it fails to fully consider the impact of the system nonlinear characteristics and gas dynamic response on the membrane water content and output voltage, making it difficult to meet the performance requirements under complex dynamic loads. In addition, the existing work on the control of proton exchange membrane fuel cells focuses on the control of a single gas supply system, and usually ignores the real-time regulation of the membrane water content inside the stack. The stability of the membrane water content is crucial to the performance, life and safety of the fuel cell. The water management problem of proton exchange membrane fuel cells involves complex water transfer mechanisms and multi-scale dynamic processes, which makes water management a very challenging research problem. Summary of the invention

[0004] Focusing on the multi-time scale and strong coupling characteristics of the gas dynamics and load current dynamics of proton exchange membrane fuel cells, and the problem of membrane water content fluctuations inside the stack under different load conditions and gas supplies, in order to further improve the safety and efficiency of the fuel cell system operation, the present invention provides a hydrogen fuel cell gas-electricity coordinated control and water content constraint management method, aiming to achieve coordinated control between the gas supply circuit and the DC-DC converter, and safe constraint adjustment of the membrane water content under different load conditions.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for gas-electricity coordinated control and water content constraint management of a hydrogen fuel cell comprises the following steps:

[0007] Step 1: Analyze the effects of different load conditions, gas flow rates and pressures on membrane water content The mass flow equation of water transported across the membrane is established by considering the electroosmotic drag and reverse diffusion of water inside the stack.

[0008] Step 2: Considering the coupled behavior of gas flow and pressure in the air supply system, as well as the coupled dynamics between the air circuit and the DC-DC converter, a gas-electric multi-circuit nonlinear dynamic model is constructed;

[0009] Step 3: Combine the gas-electric multi-circuit nonlinear dynamic model of step 2 to derive the control strategy based on the backstepping method and design the air compressor input voltage of the air circuit respectively. , back pressure valve opening instruction and the DC-DC converter duty cycle , forming a closed-loop control system to achieve coordinated control of the fuel cell gas-electric coupling system;

[0010] Step 4: Linearly discretize the closed-loop control system formed in step 3 to predict the state information of membrane humidity, and design a cascade reference adjustment algorithm based on this to adjust the flow reference value in turn. , Pressure reference value and load current reference Make corrections to complete the safe constraint management of membrane water content.

[0011] Compared with the prior art, the present invention has the following beneficial effects:

[0012] (1) In the process of DC-DC regulation, the present invention takes into account the influence of the slow time scale of the air supply system on the output performance of the fuel cell, and can reduce the fluctuation amplitude of the output voltage of the fuel cell system and the water content of the stack membrane when the load changes rapidly, thereby improving the operating efficiency and reliability of the system.

[0013] (2) The present invention achieves safe constraint management of membrane water content by indirectly correcting the reference signal values ​​of flow, pressure and current, effectively avoiding fault conditions such as flooding and membrane drying, which is beneficial to maintaining the output performance of the fuel cell and effectively extending the service life of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A flow chart of a method for gas-electricity coordinated control and water content constraint management of a hydrogen fuel cell according to the present invention;

[0015] Figure 2 A fuel cell output voltage diagram of a hydrogen fuel cell gas-electricity coordinated control and water content constraint management method of the present invention;

[0016] Figure 3 A reference signal correction diagram for a hydrogen fuel cell gas-electricity coordinated control and water content constraint management method of the present invention;

[0017] Figure 4 The present invention discloses a membrane water content constraint situation of a hydrogen fuel cell gas-electricity coordinated control and water content constraint management method. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the protection scope of the present invention.

[0019] like Figure 1 As shown, the hydrogen fuel cell gas-electricity coordinated control and water content constraint management method of the present invention includes the following steps:

[0020] Step 1: Analyze the effects of different load conditions, gas flow rates and pressures on membrane water content The mass flow equation of water transported across the membrane is established by considering the electroosmotic drag and reverse diffusion of water inside the stack.

[0021] Step 2: Considering the coupled behavior of gas flow and pressure in the air supply system, as well as the coupled dynamics between the air circuit and the DC-DC converter, a gas-electric multi-circuit nonlinear dynamic model is constructed;

[0022] Step 3: Combine the system dynamic model in step 2 (i.e., the gas-electric multi-circuit nonlinear dynamic model) to derive the control strategy based on the backstepping method and design the air compressor input voltage of the air circuit respectively. and back pressure valve opening command and the DC-DC converter duty cycle , forming a closed-loop control system ( Figure 1 (not shown) to achieve coordinated control of the fuel cell gas-electric coupling system;

[0023] Step 4: Linearly discretize the closed-loop control system formed in step 3 to predict the state information of membrane humidity, and design a cascade reference governor (RG) algorithm based on this information to adjust the flow-pressure reference vector value in turn. and load current reference Correction is made to complete the safety constraint management of membrane water content. is the flow reference value, is the pressure reference value.

[0024] Specifically, the step 1 includes:

[0025] Analysis of the effects of different load conditions, gas flow rates and pressures on membrane water content The corresponding mathematical characterization equation is derived as follows:

[0026] ;

[0027] in, Relative humidity, is the water vapor mass at the cathode of the stack, is the gas constant of water vapor, is the stack temperature, is the cathode flow channel volume, is the saturated vapor pressure;

[0028] Considering the electroosmotic drag and back diffusion of water, the mass flow rate of water transported across the membrane is It is expressed as:

[0029] ;

[0030] in, is the molar mass of water, is the proton exchange membrane area, is the number of fuel cells, and are the electroosmotic drag water mass flow rate and the reverse diffusion water mass flow rate, respectively.

[0031] Specifically, the step 2 includes:

[0032] Considering the coupled behavior of gas flow and pressure in the air supply system, revealing the air compressor speed in the air supply system , supply manifold pressure , the mass of oxygen at the cathode of the stack , nitrogen quality , water vapor quality , and the return manifold pressure The mutual influence between them is further analyzed. The coupling dynamics between the air circuit and the DC-DC converter is further analyzed. According to the law of conservation of gas mass and the working principle of the DC-DC converter circuit, the nonlinear dynamic model of the gas-electric multi-circuit is derived as follows:

[0033] ;

[0034] in, The vector representation of , The vector representation of , is the fuel cell current, is the fuel cell output voltage, , and express , and The first derivative of represents the cathode gas pressure, is the air compressor outlet gas flow rate, is the DC-DC output voltage, , Respectively represent the air compressor input voltage and back pressure valve opening control command, represents the duty cycle, are the fuel cell gas-electric coupling system model parameters, is the inductance value of the DC-DC converter, is the resistance value, is the capacitance value.

[0035] Specifically, the step 3 includes:

[0036] Combined with the air-electric coupling dynamic model in step 2, the flow-pressure tracking error of the air path is defined as , the current tracking error of the DC-DC converter ,in, is the flow-pressure vector, is the flow-pressure reference value, is the fuel cell current reference value, and the virtual controlled variable and stabilization function are designed as follows:

[0037] ;

[0038] in, and are the virtual controlled variables of the flow-pressure control loop and the current control loop, and They are and The stabilization function of is the process variable, and They are and The first derivative of , is a positive design parameter, with a superscript is the matrix transpose symbol;

[0039] Define the flow-pressure tracking error of the virtual controlled variable and virtual controlled variable current tracking error In order to realize the tracking control of flow-pressure-current state, the air path control input signal is designed and duty cycle update rate for:

[0040] ;

[0041] in, and They are and The first derivative of is the process variable, , are positive design parameters respectively.

[0042] Specifically, step 4 includes:

[0043] The closed-loop control system formed in step 3 is linearly discretized to obtain the prediction model:

[0044] ;

[0045] in, is the system matrix, express The state quantity of the closed-loop control system at any moment, express The output value of the closed-loop control system at time Indicates the flow-pressure-current reference signal value to be corrected;

[0046] Design vector reference regulation algorithm to obtain flow-pressure reference value correction signal :

[0047] ;

[0048] in, To optimize the parameters, is the system state and reference signal set that satisfies the membrane water content constraint, diag represents the diagonal matrix, Express satisfaction The minimum value under the condition i=1,2; represents the Euclidean norm;

[0049] Design scalar reference adjustment algorithm to obtain current reference value correction signal :

[0050] ;

[0051] in, Indicates that the optimization parameters are met Maximum value under the conditions.

[0052] In summary, the designed cascade reference regulation algorithm is used to correct the flow-pressure reference vector and the reference current respectively, while satisfying the water content constraint management, reducing the correction of the current reference value and reducing the impact on the output voltage and power of the fuel cell system.

[0053] Example:

[0054] This embodiment takes a proton exchange membrane fuel cell system as an example, and the system parameters are shown in Table 1, which are used to define the specific fuel cell system. Considering the characteristics of the system such as multi-time scale, multi-physical field coupling, and strong nonlinearity, it is necessary to realize the multi-stage loop coordinated control and membrane water content safety constraint management under variable load conditions based on nonlinear control methods.

[0055] Table 1

[0056] The specific steps of this embodiment are as follows:

[0057] Step 1: Analyze the effects of different load conditions, gas flow rates and pressures on membrane water content Considering the electroosmotic drag and reverse diffusion of water inside the stack, the membrane water content is deduced Mathematical characterization equation and water mass flow rate transmitted across the membrane .

[0058] Step 2: Considering the coupled behavior of gas flow and pressure in the air supply system, as well as the coupled dynamics between the air circuit and the DC-DC converter, a gas-electric multi-circuit nonlinear dynamic model is constructed. The specific model parameters are shown in Table 2.

[0059] Table 2

[0060] Step 3: Define the flow, pressure, and current tracking errors of the system, and design the control command signals of the air compressor input voltage and back pressure valve opening, as well as the duty cycle update rate of the DC-DC converter based on the nonlinear backstepping method. The specific design parameters are: , , , .

[0061] Step 4: Linearly discretize the closed-loop control system formed in step 3, design a cascade reference adjustment algorithm, and adjust the flow-pressure reference vector value in turn. and load current reference Make corrections to complete the safe constraint management of membrane water content.

[0062] In order to verify the effectiveness of the multi-loop coordinated control and water management designed in the present invention, the above algorithm is simulated and verified. Under variable load conditions, the output voltage of the fuel cell under the coordinated control strategy of the gas-electric coupling system is as follows: Figure 2 As shown in the figure, the solid line represents coordinated control, and the dashed line represents a control strategy that does not consider gas dynamics. The simulation results show that the total overshoot and offset of the output voltage are reduced by 11.21%. To verify the designed reference adjustment algorithm, the membrane humidity is constrained between 0.5 and 0.98. The correction results of the current, pressure, and flow reference signal values ​​are shown in the figure below. Figure 3 The constraint results of membrane humidity are shown in Figure 4 As shown, the dotted line and solid line represent the change of membrane humidity with load with and without the RG correction algorithm. The simulation results show that the designed correction algorithm can achieve safe constraint management of membrane water content. So far, the gas-electric coordinated control and water content constraint management of hydrogen fuel cells are completed.

[0063] Although the above describes the illustrative specific embodiments of the present invention to facilitate the understanding of the present invention by those skilled in the art, and it should be clear that the present invention is not limited to the scope of the specific embodiments, for those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

Claims

1. A method for gas-electricity coordinated control and water content constraint management of a hydrogen fuel cell, characterized in that: The following steps are involved: Step 1: Analyze the effects of different load conditions, gas flow rates and pressures on membrane water content The mass flow equation of water transported across the membrane is established by considering the electroosmotic drag and reverse diffusion of water inside the stack. Step 2: Considering the coupled behavior of gas flow and pressure in the air supply system, as well as the coupled dynamics between the air circuit and the DC-DC converter, a gas-electric multi-circuit nonlinear dynamic model is constructed; Step 3: Combine the nonlinear dynamic model of the gas-electric multi-circuit in step 2 to derive the control strategy based on the backstepping method and design the air compressor input voltage of the air circuit respectively. , back pressure valve opening instruction and the DC-DC converter duty cycle , forming a closed-loop control system to achieve coordinated control of the fuel cell gas-electric coupling system; Step 4: Linearly discretize the closed-loop control system formed in step 3 to predict the state information of membrane humidity, and design a cascade reference adjustment algorithm based on this to adjust the flow reference value in turn. , pressure reference value and load current reference Make corrections to complete the safe constraint management of membrane water content.

2. A hydrogen fuel cell gas-electricity coordinated control and water content constraint management method according to claim 1, characterized in that: The step 1 comprises: Analysis of the effects of different load conditions, gas flow rates and pressures on membrane water content The corresponding mathematical characterization equation is derived as follows: ； in, Relative humidity, is the water vapor mass at the cathode of the stack, is the gas constant of water vapor, is the stack temperature, is the cathode flow channel volume, is the saturated vapor pressure.

3. A hydrogen fuel cell gas-electricity coordinated control and water content constraint management method according to claim 2, characterized in that: The step 1 also includes: Considering the electroosmotic drag and back diffusion of water, the mass flow rate of water transported across the membrane It is expressed as: ； in, is the molar mass of water, is the proton exchange membrane area, is the number of fuel cells, and are the electroosmotic drag water mass flow rate and the reverse diffusion water mass flow rate, respectively.

4. A hydrogen fuel cell gas-electricity coordinated control and water content constraint management method according to claim 3, characterized in that: The step 2 comprises: Considering the coupled behavior of gas flow and pressure in the air supply system, revealing the air compressor speed in the air supply system , Air supply manifold pressure , Stack cathode oxygen quality , Nitrogen quality , Water vapor quality and return manifold pressure The mutual influence between them is further analyzed. The coupling dynamics between the air circuit and the DC-DC converter is further analyzed. According to the law of conservation of gas mass and the working principle of the DC-DC converter circuit, the nonlinear dynamic model of the gas-electric multi-circuit is derived as follows: ； in, The vector representation of , represents a vector element, The vector representation of , and is a vector element, is the fuel cell current, is the fuel cell output voltage, , and express , and The first derivative of , represents the cathode gas pressure, is the air compressor outlet gas flow rate, is the DC-DC output voltage, and Respectively represent the air compressor input voltage and back pressure valve opening control command, represents the duty cycle, are the model parameters of the fuel cell gas-electric coupling system, is the inductance value of the DC-DC converter, is the resistance value, is the capacitance value.

5. A hydrogen fuel cell gas-electricity coordinated control and water content constraint management method according to claim 4, characterized in that: The step 3 comprises: Combined with the gas-electric multi-circuit nonlinear dynamic model in step 2, the flow-pressure tracking error of the air path is defined as , the current tracking error of the DC-DC converter ,in, is the flow-pressure vector, is the flow-pressure reference value, For the fuel cell current reference value, design the virtual controlled variable and stabilization function: ； in, and are the virtual controlled variables of the flow-pressure control loop and the current control loop, and They are and The stabilization function of is the process variable, and They are and The first derivative of , is a positive design parameter, with a superscript is the matrix transpose symbol.

6. A hydrogen fuel cell gas-electricity coordinated control and water content constraint management method according to claim 5, characterized in that: The step 3 also includes: Define the flow-pressure tracking error of the virtual controlled variable and virtual controlled variable current tracking error In order to realize the tracking control of flow-pressure-current state, the air path control input signal is designed and duty cycle update rate for: ； in, and They are and The first derivative of is the process variable, , are positive design parameters respectively.

7. A hydrogen fuel cell gas-electricity coordinated control and water content constraint management method according to claim 6, characterized in that: The step 4 comprises: The closed-loop control system formed in step 3 is linearly discretized to obtain the prediction model: ； in, is the system matrix, express The state quantity of the closed-loop control system at any moment, express The output value of the closed-loop control system at time Indicates the flow-pressure-current reference signal value to be corrected, is the flow-pressure reference value correction signal, It is the current reference value correction signal.

8. A hydrogen fuel cell gas-electricity coordinated control and water content constraint management method according to claim 7, characterized in that: In step 4, the cascade reference adjustment algorithm includes a vector reference adjustment algorithm; Design vector reference regulation algorithm to obtain flow-pressure reference value correction signal : ； in, To optimize the parameters, k represents the kth moment, is the system state and reference signal set that satisfies the membrane water content constraint, diag represents the diagonal matrix, Indicates that the optimization parameters are met The minimum value under the condition, i=1,2; represents the Euclidean norm.

9. A hydrogen fuel cell gas-electricity coordinated control and water content constraint management method according to claim 8, characterized in that: In step 4, the cascade reference adjustment algorithm includes a scalar reference adjustment algorithm; Design scalar reference adjustment algorithm to obtain current reference value correction signal : ； in, Indicates that the optimization parameters are met Maximum value under the conditions.

10. A hydrogen fuel cell gas-electricity coordinated control and water content constraint management method according to claim 9, characterized in that: Flow reference value , pressure reference value A flow-pressure reference vector is constructed, and the flow-pressure reference vector and the reference current are respectively corrected using the designed cascade reference adjustment algorithm. While satisfying the water content constraint management, the adjustment of the current reference value is reduced, thereby reducing the impact on the output voltage and power of the fuel cell system.

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