Research On Single-stage Bidirectional Dual Active Bridge AC-DC Converter

With the development of power electronics technology and the excessive exploitation and consumption of fossil fuels,the utilization of renewable energy has become a research hotspot of society.The research and popularization of new energy vehicles have become a major theme in today’s society.With the increase of new energy vehicle ownership year by year,the bidirectional flow of electric energy between the power grid and the vehicle has become a social trend.In this dissertation,bidirectional AC-DC converter is taken as the research object.The single-stage ac-dc bi-directional converter topology studied in this dissertation is composed of isolation transformer,resonant inductor and capacitor,four-quadrant full bridge switches on the AC side and full bridge circuit on the DC side.The following research work is finished in the dissertation:Because of the two-stage system structure of the traditional bi-directional ac-dc converter,the circuit efficiency is limited and the cost is high.In this dissertation,a new modulation method is proposed.In the modulation strategy,the input current and input voltage completely is made in the same phase in each high-frequency cycle by modulating the duty cycle of the bridge on both sides,so as to realize the automatic power factor correction function,and realize the bidirectional power flow by adjusting the phase shift angle of the bridge on both sides.After analyzing its operating principle,we find that because the voltage duty cycle of the bridge on the dc side varies with input ac voltage,there is a range for all switches realizing soft switching in each power frequency cycle.The relationship between the range and circuit parameters are studied in the dissertation.Compared with another existing modulation strategy of automatic power factor correction,the inductor current is smaller and the transformer utilization ratio is higher.Secondly,according to the above theoretical analysis,the optimized circuit parameters are selected to minimize the loss of the converter.A simulation platform is set up in PSIM to verify the correctness of the modulation method by comparing the simulation results with the theoretical analysis waveform.Finally,the hardware circuit is designed.Calculating the parameters of the circuit,and selecting suitable electronic devices.Setting up the experiment platform and debuging the circuit.Comparing experimental results with theoretical analysis to verify the feasibility of the proposed theory.