Research On Typical Topologies Of Dual Active Bridge Bidirectional DC-DC Converter

This paper introduces the application background and research status of Dual Active Bridge (DAB) bidirectional DC-DC converter, which serves as core circuit widely used in distributed sources integration and power electronic transformer. This paper mainly focuses on Voltage-Fed, Current-Fed and resonant type of DAB topologies and corresponding Phase-Shift control strategies. Power transmission, soft-switching and power backflow characteristics of the converter has been deeply analyzed. Comparison of three typical topologies is completed.High frequency equivalent model of Voltage-Fed Dual Active Bridge has been established. In order to solve the drawbacks of narrow soft-switching region and high reactive power under Single-Phase-Shift when terminal voltage does not match, put forward a novel type of Extended-Phase-Shift control strategy which keeps volt-second area in primary and secondary side balance. This control strategy could enhance the flexibility of power regulation, simplify the closed-loop control strategy, expand soft-switching regions, and reduce current stress and backflow power of the system at the same time.Current-Fed Dual Active Bridge is fit for occasions that require low current ripple. With secondary full-bridge PWM duty-ratio control, an electronic transformer is added into the equivalent circuit, which could keep voltage amplitude matching in primary and secondary side when terminal voltage of the converter fluctuates. It reduces the current peak of leakage inductance. Dual-PWM-plus-Phase-Shift control has been put forward, based on decoupling control of duty ratio and phase shift, realizes the soft-switching in wide voltage range and reduces circulation loss of the system.Based on the research of LCL resonant network, its application in LCL resonant Dual Active Bridge is realized. Under Dual-Phase-Shift control, voltage and current in primary and secondary side are in phase, which could eliminate reactive power and backflow power. Under time-domain waveform analysis, equivalent model of each harmonic is established, quantitative expression of each waveform in the cavity is deduced, ratio of each harmonic transmission power relate to fundamental harmonic transmission active power is calculated, and power transmission characteristics of the converter is further studied through fundamental harmonic approximation method.On the basis of working principle and parameter design method, universal experimental platform of Dual Active Bridge bidirectional DC-DC converter rated 3.6 kW has been developed. Experimental results of Characteristic waveform and backflow power are well coincide with theoretical analysis. Aiming at solving common problems when input and output voltage of the converter does not match, Phase-Shift control strategies mentioned above could achieve soft-switching in wide voltage and load range, reduce the current stress and backflow power, therefore the operating efficiency of the converter is improved.