Research On Current Stress And Dynamic Response Optimization Strategy Of Dual Active Bridge DC-DC Converter

With the increasing global energy and environmental problems,the importance of new energy generation such as photovoltaic and wind power has become increasingly important.As natural factors such as sunlight and wind are not under human control,photovoltaic and wind power generation has a distinctly random nature and often requires energy storage devices to suppress their fluctuations.Dual Active Bridge(DAB)DC-DC converters are extremely suitable for energy storage systems due to their high-power density,bidirectional energy transmission and electrical isolation,and have therefore received extensive attention and research.This thesis investigates the minimum current stress and dynamic response speed of the Dual Active Bridge DCDC converter and investigates it’s control strategy to improve the transfer’s efficiency and accelerate the dynamic response speed.In this thesis,the operating principle,power transfer characteristics,current stress characteristics and reactive power characteristics of the DAB DC-DC converter are analyzed in detail,and the minimum current stress of the DAB DC-DC converter for extended phase shift control and triple phase shift control is investigated.Secondly,in order to speed up the dynamic response of the DAB DC-DC converter,this thesis focuses on the direct power control method and further analyses the virtual direct power control method.Direct power control passes the output voltage difference through a PI controller to obtain a given output power,thus speeding up the dynamic response.However,this method improves the dynamic response speed of the system for the case of input voltage change,and has very limited effect for the case of load change.The dynamic response of the system is further improved by a virtual direct power control method for load variations,while also eliminating sensitivity to inductor parameters.In order to reduce the current stress amplitude in the DAB DC-DC converter simultaneously,a virtual direct power-minimum current stress optimized strategy is proposed in the thesis.The method analyses and refines the power and current stress models of the DAB DC-DC converter under EPS control and TPS control,and derives the optimal shift compared to the range of combinations and transmitted powers for the optimized control strategy by means of the Lagrange multiplier method.Finally,an experimental prototype of the DAB DC-DC converter is built to verify the proposed virtual direct power-minimum current stress control scheme.The steadystate and dynamic test results show that the virtual direct power-minimum current stress control scheme has a smaller current stress amplitude and faster dynamic response than the conventional dynamic performance-minimum current stress and direct powerminimum current stress schemes,verifying the feasibility of the theoretical analysis.