Research On PEMFC Emulator Based On Two-phase Four-switch Interleaved Parallel Buck Converter

Proton Exchange Membrane Fuel Cell(PEMFC)is a new type of power generation device that directly converts hydrogen energy into electrical energy.It has the advantages of high efficiency and pollution-free.It is widely used in new energy vehicles,distributed power generation and other fields.However,in related application research,the use of physical stacks will bring a series of complex problems such as the control of auxiliary equipment and hydrogen storage.Therefore,it is possible to build a fuel cell simulator to simulate the output characteristics of a physical stack and directly connect to the load.According to the output characteristics of PEMFC,a two-phase four-switch interleaved parallel topology is designed for the output converter of the simulator,and a control strategy that can realize reference voltage following and branch current sharing is studied.The hardware in the loop simulation platform of the simulator was built through the d SPACE real-time simulation system to realize the accurate simulation of the output characteristics of the physical stack.First,a dynamic model of the PEMFC equivalent circuit is established.Based on the electrochemical mechanism of the fuel cell and the electric double layer effect in a dynamic environment,a dynamic simulation model of a hundred-watt PEMFC was built in Simulink to provide a reference voltage value for the output converter.Secondly,a two-phase four-switch interleaved parallel topology is designed for the output converter.The operating modes and parameter values ??of interleaved parallel converter and multi-switch converter are analyzed.Aiming at the shortcomings of relatively large fluctuations in the branch current of the traditional interleaved parallel topology,the interleaved parallel topology and the multi-switch topology are combined,and a two-phase four-switch interleaved parallel converter is proposed.The model of the converter is built in Simulink,and the simulation results show that this topology can reduce the relative fluctuation of the branch current by increasing the ripple frequency.The prototype of the converter was made to conduct open-loop experiments,and the experimental results proved the correctness of the theoretical analysis and simulation results.Then,for the proposed converter,a fast current sharing control strategy of voltage and current double closed loop based on PI regulator is designed.The reason for the unbalanced branch current caused by the multi-phase parallel structure is explained.Several common parallel current sharing control strategies are analyzed.Among them,the voltage and current double closed-loop control strategy has good current sharing effect and fast dynamic response.The small signal model of the converter is established,and the transfer function is derived from it.Draw the Bode diagram of the transfer function of the current inner loop and the voltage outer loop respectively,and determine the parameters of the PI regulator.The control strategy model is built in Simulink,and the simulation results show that the dual closed-loop control strategy has good robustness to load disturbance,and can realize branch current sharing and reference voltage following.The closed-loop experiment of the converter proves the correctness of the theoretical analysis and simulation results.Finally,based on the d SPACE real-time simulation system,a simulator system platform was built.The composition structure of the simulator system combined with the hardware circuit and control unit is introduced.Explains the design idea of ??the hardware circuit and the operation flow of the control unit in the d SPACE system.The steady-state and dynamic experiments are carried out on the simulator platform,and the comparison with the output characteristics of the physical stack proves that the built simulator has good simulation accuracy.