Research On MPPT And Grid-connected Control Of PEMFC Distributed Generation System

Proton exchange membrane fuel cell is a new type of power generation device,which has attracted much attention in the field of distributed power generation due to its clean and efficient characteristics.However,PEMFC cannot generate stable DC power.It is expensive to produce and difficult to coordinate with the distribution network as a distributed power source.Therefore,the output power of PEMFC needs to be controlled to meet the grid-connected indicators while obtaining the maximum power.This paper proposes a maximum power point tracking(MPPT)algorithm based on the equivalent sliding mode control(SMC),and proposes a double closed-loop controller based on grid-connected indicators where the multi-group fuzzy genetic algorithm(MPFGA)is utilized to adjust the parameters of the controller.The system works well under both grid-connected and independent operation modes.Firstly,based on the electrochemical mechanism of the fuel cell,a 5k W-class PEMFC simulation model is built.The effects of stack temperature and membrane water content on the output voltage and output power of PEMFC are analyzed.It provides a model reference for the power conversion and inverter control system design of 5k W-class PEMFC distributed generation system.Secondly,in order to improve the utilization rate of PEMFC,the maximum power point tracking technology of the front-stage of the power generation system is studied.Three traditional MPPT control methods are analyzed from the theoretical and simulation perspectives.Aiming at the disadvantages of the traditional algorithm’s large stability error and amplitude of chatter,an SMC algorithm was proposed to implement MPPT,and the stability and accessibility of the sliding surface are proved.Simulations verify that the proposed controller has better dynamic and steady-state performance under constant and changing temperature.Then,the rear-stage inverter and its control strategy is designed to meet the grid-connected requirements.The voltage type full-bridge inverter topology,unipolar SPWM modulation method and LCL grid-connected filter are selected.The voltage and current double closed-loop PI controller with grid voltage feedforward is designed to achieve grid-connected operation.The parameters of the controller are calculated using a typical second-order system design method,and the simulation results show that the parameters obtained basically meet the grid connection requirements.Finally,PEMFC,the front-stage DC/DC converter circuit and the rear-stage inverter circuit are connected to build a single-phase distributed power generation system model based on a 5k W-class PEMFC.A multi-group fuzzy genetic algorithm(MPFGA)and a new fitness function are proposed to adjust the controller parameters in grid-connected and independent operation modes.The simulation verifies that the system can meet the grid connection index and maintain the maximum power output under the changing temperature.