Research On Bidirectional DC-DC Converter Based On Optimal Negative Current Control

With the energy consumption and environmental pollution issues become increasingly serious,new energy vehicle with its high efficiency,energy saving,energy diversity,environmental friendly and other great advantages,has received more and more attention,and have a broad space for development in the future of the automotive industry.Because the bidirectional DC-DC converter can not only provide energy,but also recover energy,improve the driving performance and energy utilization rate of electric vehicles,plays a very important role in the electric vehicle power system,it has a very important theoretical significance and engineering value to develop a bidirectional DC-DC converter with high performance.The bidirectional DC-DC converter is studied in this dissertation.In order to achieve high efficiency and high power density,reduce the inductor current and output current ripples,improve the dynamic performance and steady-state performance of the converter,soft switching technique,multiphase interleaved parallel technique and inductor magnetic coupled technique are applied respectively.And an optimal negative current control strategy is used,the working efficiency of the bidirectional DC-DC converter is further improved by optimizing the size of the inductor negative current,reducing the conduction loss and core loss of the converter.The main work of this dissertation is as follows:Firstly,based on the introduction of the research significance and research status of bidirectional DC-DC converter,the operational principle of bidirectional DC-DC converter is analyzed in detail in this dissertation.And the implementation of multiphase interleaved parallel technique,inductor magnetic coupled technique,soft switching technique and the optimal negative current control strategy in bidirectional DC-DC converter are introduced.Secondly,the theoretical analysis and control strategy of bidirectional DC-DC converter are modeled and simulated by using MATLAB/Simulink software.The simulation waveforms of the bidirectional DC-DC converter with individual and coupled inductor and optimal negative current control strategy are compared and analyzed respectively.The simulation results verify the correctness of the theoretical analysis and the feasibility of the optimal negative current control strategy.Finally,the hardware circuit and software system of the bidirectional DC-DC converter are designed,and a 12.5k W experimental prototype is built with DSP TMS320F28035 as its control core.The experimental waveforms of fixed frequency and variable frequency control in different load conditions and implementation of optimal negative current control of the bidirectional DC-DC converter are analyzed respectively.And the working efficiency in the whole load range is tested.The experimental results show that the optimal negative current control strategy improves the working efficiency of the converter,and with the decrease of the output power,the amplitude of the work efficiency increases gradually,which verifies the correctness and feasibility of the theoretical analysis of the optimal negative current control strategy.