Research On Performance Optimization Of Dual Active Bridge DC-DC Converter

The dual-active-bridge(DAB)DC-DC converter is widely used in microgrids,energy routers and other occasions due to their electrical isolation,high power density,two-direction energy flow,and easy realization of soft switching.However,when the voltage of the DAB converter is not matched,the efficiency will be reduced due to the large reflux power and current stress.Aiming at the above-mentioned problems,this paper proposes an optimization method based on the phase-shift coordinate transformation under the extended phase-shift modulation to optimize the reflux power and current stress to improve the efficiency of the converter.First,the commutation state and operating characteristics of the DAB converter under single-phase-shift modulation are introduced.When the voltage does not match,the reflux power and current stress of the DAB converter are large,which will reduce the efficiency of the converter.In order to solve the problem that single-phase-shift modulation has only one degree of freedom and cannot be optimized,the internal-phase-shift is introduced,extended phase-shift modulation is proposed,and its working characteristics are analyzed.Then,under the extended phase-shift modulation,a reflux power optimization method based on the phase shift coordinate transformation is proposed,which achieves the optimal reflux power.And it can achieve zero reflux power within a certain range of the transmission power.The proposed reflux power optimization scheme based on coordinate transformation simplifies the mathematical model of the transmission power and ensures that the transmission power increases monotonously with the outward phase-shift after coordinate transformation,so there is no need to detect the load current.It can directly select the optimized operation trajectory of reflux power according to the size of the outward phase-shift after the coordinate transformation.When the load,output given voltage or input voltage changes suddenly,it can freely switch among the optimized operation trajectories and quickly restore the stability.Next,a current stress optimization scheme based on the phase-shift coordinate transformation is proposed,which can achieve the optimal current stress in the full power range.Compared with the proposed reflux power optimization scheme,the switch tubes of the current stress optimization scheme can achieve soft switching and the reflux power is small at light load,so the current stress optimization scheme has a better efficiency optimization effect.Both schemes can achieve soft switching under heavy load,and the current stress is approximately equal.So the reflux power optimization scheme has a better efficiency optimization effect because of the lower reflux power.Finally,the software and hardware design of the DAB converter is carried out,and an experimental platform is built to verify the proposed optimization scheme of reflux power and current stress based on the phase-shift coordinate transformation.The experimental results show the effectiveness of the proposed scheme.