A Bidirectional Three-level DC-DC Converter For Hybrid Energy Source Electric Vehicles

Energy is the driving force of human development and progress.However,the demand for fossil resources has increased rapidly with the development of industry in recent years,resulting in energy shortage,environmental pollution and other issues.Therefore,it is necessary to develop clean energy,promote energy change,and achieve sustainable development.Developing electric vehicles is the best way to solve the problem of energy shortage and environmental problems.Bidirectional DC-DC converter,as the core component of hybrid energy source electric vehicles,plays an important role in power conversion and energy transfer.In this paper,a bidirectional three level DC-DC converter is proposed for the application of hybrid energy source electric vehicles based on the study of domestic and foreign various bidirectional DC-DC converters.The proposed converter can avoid extreme duty cycle while achieving a high voltage-gain.The modulation strategy and operation principle of the converter under Buck mode and Boost mode are analyzed in detail.In the aspect of control strategy,the capacitor voltage balance control strategy and the inductor current ripple optimization strategy are put forward.In addition,a bidirectional power flow control strategy is proposed for the hybrid energy source system.Finally,an experimental prototype of bidirectional three level DC-DC converter is built,whose rated power is 1.2kW,and the corresponding prototype experiments are carried out.The correctness of the operation principle of the converter and the feasibility and effectiveness of the control strategy are verified by observing the output characteristics under different duty cycles,the voltage stress of the power switches,the inductor current ripple characteristics and the bidirectional power flow of the proposed converter.