Research On Efficiency Optimization Method Of Dual Bridge Series Resonant DC/DC Converter

Dual Bridge Series Resonant DC/DC converter(DBSRC)can be used as an interface device in a DC microgrid to connect energy storage systems,new energy power generation systems,and DC loads to the DC bus.It plays an important role in the efficient operation of the microgrid.It isn’t easy to accurately model and analyzes DBSRC.Currently,the Fundamental Harmonic Approximation(FHA)analysis method is usually used for modeling.However,the FHA analysis method can only obtain approximate solutions,and the resulting errors have not been thoroughly studied.Therefore,this paper focuses on studying the accurate model and efficiency optimization method of DBSRC in the time domain(TD)analysis method and the effective way to reduce the calculation amount of the efficiency optimization control algorithm.This thesis first analyzes the working process and circuit characteristics of DBSRC under Single Phase Shift(SPS)control and establishes an accurate time-domain model using the TD analysis method.On this basis,the error between the solution conclusion of the TD analysis method and the solution conclusion of the FHA analysis method is systematically analyzed,which provides a reference for the optimization design of the converter.Research shows that the transmission power obtained by the FHA analysis method has a severe error under light load when it deviates working frequency from the resonance frequency.Secondly,this thesis analyzes the main factors affecting the efficiency of DBSRC and systematically analyzes the relationship between switch current stress,current RMS value,soft-switching range,switching resonance frequency ratio,and voltage conversion ratio;based on the TD analysis method,In conclusion,this paper proposes an efficiency optimization control method based on frequency conversion and phase shifting.Compared with the fixed frequency SPS control,the optimization control method can achieve high efficiency in the entire power range.At the same time,efficiency optimization is achieved by comparing the TD analysis method and the FHA analysis method.The difference in effect demonstrates that the FHA analysis method has sufficient accuracy in efficiency optimization;on this basis,the time domain current RMS values optimization,the Fundamental Harmonic Approximation current RMS values optimization,the time domain current peak optimization,and the switching current stress are used respectively.Optimization and other methods have completed the research on efficiency optimization and compared the effects of the four efficiency optimization methods.The study shows that the variable frequency plus phase-shift control method proposed in this paper has a very immediate optimization effect under the four efficiency modes.Next,this thesis analyzes the working characteristics of DBSRC under the control of Triple Phase Shift(TPS)and derives the minimum current trajectory(MCT)based on the FHA analysis method,using the least square method and piecewise linear,respectively.The optimization method simplifies the optimization trajectory of MCT and obtains two efficiency optimization methods,including FIT Minimum Current Trajectory(FIT＿MCT)and Piecewise-Linear(PL＿MCT).The simplified method can reduce the computational complexity of the control algorithm to ensure the efficiency optimization effect.Finally,this thesis introduces the DBSRC experimental bench design process,including designing the key material model parameters of the main circuit,the design of the high-frequency transformer,the resonant capacitor of the resonant tank,and the design of the resonant inductance.A 1.5k W DBSRC experimental bench based on IGBT power devices was built to complete the experimental verification of the research conclusions of this paper.