Modeling And Control Of PEM Fuel Cell Air Supply System Based On Power Management

The increasingly severe problems of energy shortage and environmental pollution have led to the continuous exploration toward new efficient and clean energy sources,such as solar,wind and hydrogen.Fuel cell,as a novel power-generation device that directly converts chemical energy of gaseous fuel into electric energy,is the most potential alternative to clean energy production during recent decades.Among various types of fuel cells,proton exchange membrane(PEM)fuel cell can produce electricity,heat,water and almost pollution-free emissions through the reaction of oxidant and hydrogen.In fact,it has been widely applied and developed in electric vehicles due to its advantages of high efficiency,high power density,low operation temperature and low noise.However,since PEM fuel cell is a complex system with strong nonlinearities,accurate and effective control actions are required to maintain the stable operation,especially the control for PEM fuel cell air supply system.In addition,we know that drastic changes of the load requirements unavoidably lead to undesirable undershoot and overshoot of the oxygen excess ratio if the demand power is provided only by the PEM fuel cell system.By supplementing the battery and/or supercapacitor to form a PEM fuel cell hybrid system,it can provide an effective solution to this drawback and can eliminate the peak of output power so that it has a smooth output characteristic.This paper focuses on the air supply system of PEM fuel cell,mainly studies the modeling and nonlinear control method of the air supply system,and considers adding auxiliary power battery to improve the control performance of the intake system.The work accomplished in this paper is described as follows:The working principle of the fuel cell system and the composition and control for the air supply subsystem are introduced.The research status of modeling and control of the air supply system and the research status of the fuel cell hybrid power system are summarized and analyzed.According to the characteristics and operating principle of the PEM fuel cell air supply system,based on the mathematical expressions of each module,a PEM fuel cell system model including air supply system and voltage is developed.Then the control-oriented third-order nonlinear air supply system model is compared with the classic Pukrushpan's ninth-order model.Simultaneously,considering the disturbance,parameter uncertainty,measurement noise and unmeasurable cathode pressure of the model,the disturbance observer is designed based on the third-order model,and the following and anti-interference performance of the suggested observer are tested by simulation.Due to strong nonlinearities,large load range and constraints of the air-feed system,a nonlinear model predictive controller(NMPC)for the air supply system is proposed.Based on the deduced nonlinear model and control demand of air supply system,the control problem of air supply system is transformed into an optimal control problem with constraints.Then,the particle swarm optimization(PSO)algorithm is adopted to solve the open-loop optimization problem online at each sampling time,and the optimal solution of the control law is obtained.Subsequently,through the simulation test of the constant oxygen excess ratio and the variable oxygen excess ratio of the intake system by MATLAB,the validity of the NMPC controller is verified.In view of the soft output characteristics of PEM fuel cell system,namely,when the load demand changes rapidly(such as step response),the dynamic response of air supply system is slow.In this paper,the power battery is utilized as the auxiliary power supply to compensate for the lack of the fuel cell output in the case of fast load transitions.Firstly,the Thevenin equivalent circuit model of lithium-ion battery is built,and extended Kalman filter(EKF)is applied to estimate the state of charge(SOC)of battery.Then,a power coordination algorithm is presented to allocate the fuel cell power and battery power,and the effectiveness of the suggested power management strategy is tested.Finally,the effect of the auxiliary power battery on the performance of air supply system is verified by simulation.