Research On Resonant Bidirectional High Gain Isolated DC-DC Converter Based On Wide Band-gap Devices

In recent years,with the improved of energy storage technology and cost reduction,as well as the development of demand side,distributed energy storage is widely used as the inevitable trend of future power grid development.At the same time,with the low voltage storage battery,the diversification of power electronic converter topology and the complexity of system control strategy,distributed energy storage system is developing towards high frequency,high efficiency,miniaturization and controllability.This requires isolated bidirectional DC converter as the core equipment of distributed energy storage system to have the characteristics of high frequency,high gain,high power density,high efficiency and wide voltage gain range.How to improve the power density of bi-directional isolation converter,widen the voltage conversion range of converter and ensure high efficiency power conversion in the full load range of converter has important research significance.For this reason,this paper focuses on the subject of "Isolated Resonance Bidirectional Power Conversion Technology".The research is carried out from two aspects: the wide gain range with high efficiency and realization of high frequency,high efficiency and high power density for converter.It is discussed in detail according to the order of topology design,mathematical modeling,characteristic analysis,parameter optimization and experimental verification.The major works are organized as below:(1)Two novel circuit topologies of high gain bidirectional CLTC and CDT-LC resonant DC-DC converter with dual transformer structure are proposed.The two circuit topologies can realize ZVS and ZCS in full load range to harvest high efficiency.The operating modes and working characteristics of two topologies are introduced.A simplified equivalent analysis method is proposed to simplify the dual transformer structure by using controlled source,and the advantages of CDT-LC in gain feature are qualitatively analyzed.Based on the time-domain analysis method,the corresponding mathematical model is established to discusse the gain feature and soft-switching characteristics for the CDT-LC converter.It is verified that the converter achieves a bi-directional normalized voltage gain of 0.8-1.2 within a narrow frequency range.Its characteristics are very suitable for the bi-directional charging and discharging scenarios distributed energy storage with low-voltage and high-current.Besides,the parameters are designed reasonably to optimize the efficiency at the resonant point,and the optimal parameters are obtained.(2)The high frequency loss model is proposed,and the corresponding loss analysis for CDT-LC is carried out based on parameters and simulation results.The influence of replacing traditional Si devices with Si C devices on the loss of converter is studied.A 2.5k W CDT-LC prototype was established to verify the correctness and accuracy of theoretical analysis.At the same time,compared with other converters,the obvious advantages of CDT-LC converter in operating frequency range,efficiency and gain regulation range are confirmed.(3)An improved multi-CLLC structure for high frequency and high gain environment is proposed.The working mode of the topology is introduced,and a universal mathematical model is established.Detailed implementation conditions of high frequency soft switching and design process of converter parameters are given.In addition,an integrated design method of high-frequency magnetic components is discussed in depth,and a multi-coil optimal wiring method applied to PCB windings is proposed.Finally,the loss analysis and calculation show that the transformer design method has significant effect on improving efficiency.(4)A 400 W Multi-CLLC experimental prototype with rated operating frequency of 1 MHz was established to verify the theoretical analysis.It has achieved high efficiency and high power density.Besides,the influence of Ga N devices on the efficiency improving for converter is analyzed based on the comparative experiments.Also,the problems encountered in the high frequency experiments are analyzed and summarized.And some corresponding improvement methods are put forward.At last,it has proved that the application of isolated resonant bidirectional DC converter in high frequency scenario still has broad research potential and exploration space.