The Dynamic Modeling And Optimal Control Of Proton Exchange Membrane Fuel Cell System

Against the backdrop of carbon peaking and carbon neutrality,hydrogen energy has received extensive attention as a renewable and clean energy source.Proton exchange membrane fuel cell(PEMFC)is fueled by hydrogen,and it has quickly become one of the most promising green energy conversion devices,in advantage of its high efficiency,zero emissions,and low noise.However,PEMFC systems exhibit complex characteristics of strong nonlinearity,multiple constraints,and frequent disturbances during operation,which make it difficult for conventional control methods to deliver satisfactory control performance.In addition,PEMFC system is a complex system with multiple inputs and multiple outputs,and the output power is tightly related to the operation mode.This paper focuses on the dynamic modeling and optimal control of the fuel cell system.Based on the inherent characteristics of PEMFC system,advanced control strategies are designed to achieve stable and efficient operation.The major contributions of current work are proposed as follows:1.Combined with the mechanism model and the empirical formula,a complete nonlinear dynamic model of PEMFC system is established in the Simulink platform.This model thoroughly considers the complex relationship between the stack and the auxiliary equipment,constructs dynamic models of associated auxiliary equipment such as air circuits,cooling water circuits and humidification circuits,and improves the voltage model related to the flooding phenomenon.The PEMFC model can accurately reflect the relation among the output voltage,the relative humidity of the cathode channel,and the operating temperature with varying the external current(load),air compressor voltage,cooling water mass flow,and humidification electrical power.The constructed PEMFC model is proven to be suitable for simulation and controller design.2.To mitigate the frequent disturbances caused by external load,advanced control strategies are proposed for PEMFC,such as active disturbance rejection control of oxygen excessive ratio,relative humidity control strategy based on the water content inside the cathode channel,and feedforward model predictive control of stack temperature.In view of the limitations of hygrometer measurement,it is innovatively proposed to use the water content inside the cathode channel as a soft measurement feedback signal,which improves the control accuracy of the cathode relative humidity and effectively avoids the flooding phenomenon.The simulation and experimental results have verified the disturbance rejection performance and setpoint tracking ability of these proposed control systems.3.To deal with the tight relationship between the output voltage and the relative humidity,and the strong nonlinearity caused by the external current,a multi-model predictive control method with weighted controller output membership is proposed for PEMFC,where multivariable predictive control is adopted to solve the coupling between the output voltage and relative humidity.This method handles the system nonlinearity by weighting the controller output by membership,and amplifies external currents into the predictive model to predict the influence of disturbance.Through the simulation cases of setpoint tracking and variable load,it is verified that the proposed control method can quickly eliminate the disturbance on the output variables caused by the variable load,and effectively solve the model mismatch caused by the system nonlinearity.4.To achieve the economic operation of PEMFC,a two-layer optimal control algorithm for maximum net power is proposed.A nonlinear optimization problem is developed to maximize the net power(the difference between power output and the power consumption of the auxiliary equipment)by optimizing the air compressor voltage,the humidification power,and the cooling water mass flow.Therefore,the optimal setpoints can be obtained under the given operating condition in the upper layer,whereas the lower layer guarantees the setpoint tracking.5.In order to reduce the frequent adjustment of control variables,and consider the net power in the objective function of the controller,a zone economic predictive control method of PEMFC with single-layer control structure is proposed.In comparison to the zone predictive model control,the simulation result shows that the zone economic model predictive control can effectively improve the net power and the net efficiency of PEMFC system.