Research On Dual Active Bridge DC-DC Converter

In order to solve the problem that the intermittent and unstable renewable energy impacts the operation of the power grid,it is a feasible solution to form an AC-DC hybrid micro-grid with new energy generation equipment and energy storage devices and power grid.Due to its high power density,bidirectional energy transfer and easy realization of soft switching,dual active bridge(DAB)DC-DC converter has been widely used in microgrid and other applications,and has become a research hotspot in recent years.In this paper,the control strategy of DAB DC-DC converter is studied to improve transmission efficiency and speed up dynamic response.Firstly,this paper introduces the working principle and characteristics of DAB DC-DC converter under single-phase-shift(SPS)control,and points out that the current stress is too large and the soft-switching range is small when the input and output voltage are not matched in this control mode.Then the working principle and characteristics of the converter under extended-phaseshift(EPS)control,double-phase-shift(DPS)control and triple-phase-shift(TPS)control are introduced.To solve the problem of excessive current stress in SPS control,an optimal control strategy of minimum current stress is proposed under three control modes.Compared with SPS control,the minimum current control in full power range is realized.The current stress characteristics and soft switching characteristics of EPS control scheme,DPS control scheme and TPS control scheme are compared.The comparison results show that compared with DPS control scheme,EPS control and TPS control scheme can achieve smaller current stress control and larger soft switching range,they can achive soft switching in the whole load range.Then in order to speed up the dynamic response,a internal direct power scheme is proposed,which can achieve faster dynamic response.Combining the scheme with the minimum current stress scheme,the steady-state performance and dynamic performance of the converter are optimized simultaneously.Finally,an experimental prototype of dual active bridge DC-DC converter is built.The hardware and software design of the platform are introduced.The experiments of the minimum current stress optimization scheme and the direct power control scheme in the loop are carried out on the platform.The experimental results verify the correctness of the theoretical analysis.