Research On DC-DC Converter Control Technology For Solid State Transformer

As a new type of power electronic device,Solid State Transformer(SST)can achieve power factor correction,reactive power compensation,voltage adjustment and other functions,in addition to the traditional power transformer.The Bi-directional Full-Bridge DC-DC converter,which is an important part of solid state transformer,not only can decouple the power and load,but also provides the interface for the DC power generation.The converter consists of two symmetrical H-bridge and a high frequency transformer,using phase-shifting control technology can control the output power,and can control the two-way flow of energy,high power density,wide adjustable range and easy to realize soft-switching.But the traditional single-phase-shifting control can cause a great deal of backflow power and current stress,and reduce the conversion efficiency.In order to eliminate the backflow power of bi-directional full-bridge DC-DC converter,this paper analyzes the mechanism of backflow power under single-phase-shifting control,and then do research on new LCL resonant network bi-directional DC-DC converter,the topology can eliminate backflow power,reduce the current stress,but failed to achieve soft-switching which cause large loss on heave load.After the study of the dual-phase-shifting control,find the relationship between the output power and the inner and outer phase-shifting and soft switching condition,then proposed Voltage-Type dual-phase-shifting control strategy to achievethe minimum backflow power,and its correctness is proved by Simulink simulation.The detailed design of 150 W bi-directional full-bridge DC-DC converter experimental platform,mainly including the design of high frequency transformer,power switch design,control circuit and controller design,through the experiment of voltage-type dual-phase-shifting control can not only eliminate backflow power and reduce the current stress,but also the realize soft-switching,have better the conversion efficiency in different output power,prove the effectiveness of the proposed control method.