Research On Dual-Active-Bridge DC/DC Converter For Power Electronic Transformer

The promotion of new energy power generation and distributed power supply has greatly promoted the development of smart grid.Traditional power frequency transformers can no longer meet their performance requirements.Power Electronic Transformer(PET)is considered to be used to replace power frequency transformers.Ideal electrical equipment,it is an intelligent power electronic equipment with electrical isolation,voltage conversion,power regulation and control,and renewable energy grid-connected functions.It is the smart,flexible and diverse development of the future power grid.Core components.Dual Active Bridge(DAB)DC/DC converters,which are intermediate stages of power electronic transformers,have attracted wide attention due to their high power density,modular structure,simple and feasible control strategy,and power bidirectional transmission.This paper takes the dual active full-bridge DC/DC converter as the research object.Firstly,the working principle of three control strategies(phase shift control,single PWM phase shift control,dual PWM phase shift control)for converters is introduced in detail,and the mathematical expression of power transfer of converters under different control modes is derived.Secondly,the loss model of the converter is analyzed.System losses are mainly concentrated in four aspects: switching loss,magnetic loss,line loss and return power;magnetic loss,line loss and return power can be reduced by reducing the inductor peak current;soft switching technology can be applied to dual active bridge DC converters.The switching loss is reduced to greatly improve the system efficiency.Therefore,the boundary conditions of the soft switching technology implemented by different control strategies are mainly studied.Based on the above research,the dual-active bridge DC/DC converter has high return current and high peak inductor current at light load,which can not realize the problem of soft switching.An optimal control method based on dual PWM phase shift control is proposed.The phasor analysis method is used to establish the mathematical model of system transmission power,return power and inductor current,to clarify the physical meaning of each control quantity,reduce the computational complexity of the traditional integral method modeling process,and analyze the phasor diagram ofthe voltage of the dual PWM phase shift control terminal.The voltage change region is obtained;the voltage triangle concept is proposed,and the optimal combination of the phase shift angle of the optimized control strategy is obtained,the peak value of the inductor current is reduced,and the system return power is reduced;and the on-state of the converter is reduced by combining the soft switch on condition Loss,ultimately improving the output efficiency of the system.Finally,the simulation model of dual active bridge DC converter is built in MATLAB/Simulink,and the proposed optimal control strategy based on dual PWM phase shift is simulated.The simulation results show that the optimized control strategy can solve the problem of large peak inductor current and obvious power reflow at light load.When the load changes from light load to rated load,the dual PWM phase shift control has higher The work efficiency is up to 90.25%,and the average transmission efficiency is above 87.67%,which proves the validity and correctness of the control strategy.