Research On A Current-type Bidirectional DC-DC Resonant Converter

With the overexploitation and waste of traditional fossil energy,its reserves have been difficult to meet the needs of future social construction.In order to realize the efficient use of energy and the sustainable development of society,some new energy power generation technology has gradually become a hot topic of social concern.DC micro-grid is widely used for its low cost and low loss.Based on the application background of Energy Storage System(ESS)of DC micro-grid,this thesis studies a current-type bidirectional DC-DC resonant converter as the interface of energy storage device,and analyzes its working principle,working characteristics and dynamic control strategies in depth.This thesis summarizes the research significance and current situation of the bidirectional DC-DC converters used in DC micro-grid energy storage system,and points out that the bidirectional DC-DC converters have the problem of narrow voltage regulation range,large input current ripple and difficulty in implementing soft switching.In order to settle the problems mentioned above and ulteriorly make progress in improving working performance of the converters,this thesis studies a current-type bidirectional DC-DC resonant converter and adds auxiliary inductor to the original topology.The working principle of the converter is studied,the switching state of its different modes is analyzed in detail,and the function expressions of input inductive current,resonant circuit current and resonant capacitor voltage are derived by KCL and KVL.Under Fixed-frequency Pulse Width Modulation(FPWM),the voltage gain,the input current ripple and Zero Voltage Switching(ZVS)characteristics of the converter are analyzed using time domain analysis and First Harmonic Approximation(FHA).The results show that the current-type converter can achieve high voltage gain ratio and suppression of input current ripple.The addition of auxiliary inductor reduces the difficulty of the switching tubes to realize ZVS,and the current stress of the primary side switching tubes without affecting the high voltage gain performance of the converter.The effectiveness of topological improvement is verified by simulation.In view of the variable application of voltage and load of energy storage system,the dynamic response performance of the converter is studied in this thesis.The simulation is carried out under the condition of input voltage or load mutation,and the results show that the dynamic response of the converter is slow when the traditional dual-closed-loop PI is adjusted,which cannot meet the situation of emergency cut-off of energy storage device.Therefore,a Model Predictive Control(MPC)strategy is proposed,a discrete model of the converter is established,and the simulation result analysis of the MPC is completed: Compared with the dual-closed-loop PI regulation,the dynamic response speed of MPC is faster and more advantageous.In this thesis,an experimental prototype with a rated power of 160 W is built and debugging is completed.The performance and control strategies are verified by the prototype,and the experimental results show that the improvement of topology and control strategies is reasonable and feasible.