Research On Control Strategy Of Anode And Cathode Pressure Balance Of Fuel Cell Power System

With the acceleration of fuel cell commercialization,fuel cell power system has become the core research and development object in the field of transportation,and power density is the main index to evaluate the performance of power system.Increasing the reaction gas pressure inside the fuel cell stack can effectively improve the output performance of the stack,so as to improve the power density of the power system.Limited by the pressure tolerance of the proton exchange membrane of the stack,the pressure balance control between the anode and cathode of the fuel cell power system is particularly important under dynamic conditions.Improper design may cause permanent damage to the fuel cell stack.Therefore,this thesis will focus on the balance of anode and cathode pressure of fuel cell power system,reduce the pressure fluctuation under dynamic conditions and improve the reliability and safety of fuel cell power system.The main research contents include the following aspects:1.The physical model including fuel cell stack,cathode and anode gas supply system components is established.By analyzing the principle of fuel cell,a physical model describing the operating characteristics of fuel cell stack is established.By analyzing the mechanism of various components in the cathode and anode gas supply system,a physical model describing the characteristics of gas pressure and flow is established.The establishment of the above model provides a basis for the subsequent design and verification of the controller.2.Facing the demand of cathode air supply,the system transfer function identification method and the pressure and flow regulation method based on feedforward decoupling are studied.According to the nonlinear and coupling characteristics of the pressure and flow of the cathode air subsystem,in order to simplify the design of the controller,the transfer function matrix model is used to characterize the relationship between the pressure and flow in the linear region of the working point of the cathode subsystem.By designing the system identification experiment,the m-sequence is used as the excitation signal,and the model parameters are identified by the least square method.According to the identification model,the feedforward compensation decoupling controller is designed and compared with the traditional double PI controller.The experimental results show that the feedforward compensation decoupling control can help to reduce the coupling relationship between pressure and flow,and has good dynamic response ability.In the process of working point change of cathode subsystem,the distance weight method is used to optimize the decoupling effect of feedforward decoupling network at different working points,so as to achieve better decoupling control effect.3.The pressure control algorithm of anode pressure following cathode is designed to realize the pressure balance between anode and cathode.Based on the models of anode components,combined with the characteristics of hydrogen supply and consumption of anode subsystem,the state space model for anode pressure control is established,and the proportional controller and funnel controller based on feedforward are designed.The funnel controller has more advantages in parameter design because of its preset performance.Combined with the pressure control strategy of cathode and anode,the pressure balance control strategy of anode pressure following cathode is formed.The simulation results show that the pressure difference between anode and cathode can be maintained at a low level and has a fast dynamic response speed.