Optimal Control Of A Solid Oxide Fuel Cell System

Solid Oxide Fuel cell(SOFC)is a power generation device which converts chemical energy from fossil fuel to electric energy.It has the advantages of high efficiency,zero emission and low noise.It is regarded as the most promising green power generation device in the 21 st century.At present,the research on SOFC system is mainly focused on the safe and stable operation,which is less involved in the optimization of efficiency,cost and other performance while the system is running stably.In particular,the optimal control of SOFC systems with fault or uncertain parameters has not been studied in the literature.Therefore,this thesis mainly concentrates on the optimal control of SOFC system under fault state and uncertain parameters.The main research contents are as follows:(1)Building SOFC system Model.Firstly,a modularization method is adopted to build the peripheral facilities of SOFC system(air compressor,heat exchanger,combustion chamber,mixer,bypass valve),and the core component(stack)which are based on the principles of energy conservation,mass conservation,thermodynamics and thermoeconomics.Then according to corresponding technological processes,the subsystems are connected to form an independent SOFC power generation system.The next step is to fit the fault state and uncertain state of the system by adding fault coefficients and random noise to the model.Finally,using MATLAB/SIMULINK simulation tool,the dynamic mathematical models of SOFC system with different structures and processes are built,and the V-I curve simulation is carried out.The results show that the mathematical model presented in this paper can accurately reflect the output characteristics of the system.(2)Proposing the optimal fault tolerant control strategy for the air compressor failure in SOFC system.The strategy includes four modules: optimization module,fault diagnosis module,switching module and control module.In the optimization module,the efficiency and unit cost of the system are optimized by using the fast non dominant sorting genetic algorithm(NSGA-II)and the ideal solution evaluation method(TOPSIS),so that the system can be obtained the optimal operating points(fuel utilization ratio,air excess ratio,current,anode inlet temperature and cathode inlet temperature)in normal and fault states under different load power.In the fault diagnosis module,a diagnosis method based on model residuals is used to compare the output temperature of air compressor model in normal state with that of air compressor in actual system.Then on-line diagnose whether the system is in the normal state or the air compressor failure state.According to the current state of the system,the switching module selects the appropriate optimal operating point as the target reference value for the control in real time,and transmits the reference value to the control module.Four PID controllers are used to track and control the system power,air excess ratio,anode inlet temperature and cathode inlet temperature.The simulation results show that,in different states,the optimal fault tolerant control strategy can ensure the optimal system efficiency and unit cost,and track the inlet temperature of the anode,the inlet temperature of anode and the air excess ratio at the target reference value in the case of optimal system efficiency and unit cost.(3)Proposing a robust optimal control strategy for uncertain SOFC systems.A robust optimal control strategy is proposed for uncertain SOFC systems.Firstly,load current is chosen as the uncertain parameter of SOFC system,and the range of uncertain parameters is obtained by Monte Carlo method.Then,based on the known uncertain interval,using the two-space particle swarm optimization method to optimize the efficiency of uncertain SOFC systems,and get the corresponding optimal operating points.The optimal operation points are taken as the target reference values to be tracked.Finally,the high order sliding mode controller and two feed-forward controllers are used to track and control the reference value of fuel utilization ratio,air excess ratio and reactor temperature.