Research On Three-phase Dual Active Bridge DC-DC Converter For V2G

In recent years,with the rapid development and popularization of new energy vehicles,a large number of electric vehicles disorderly fast charging increase the load fluctuation of the power grid,which increases the construction cost of the power grid and brings a severe test to the stable operation of the power grid.V2G(Vehicle-to-Grid)technology can help vehicles coordinate with power grid,and realize the peak load cutting and valley filling of power grid through the energy feedback from vehicle to power grid.As the key part of V2 G technology,the performance of high-power bidirectional charging station directly affects the realization of V2 G.Three-phase dual active bridge converter has the advantages of large power capacity,bidirectional energy flow,and soft switching,which is suitable for high-power bidirectional energy applications.However,it also has the problems of low efficiency caused by backflow power under light load or voltage mismatch conditions.In order to solve the above problems,it takes three-phase dual active bridge converter as the research object in this thesis,mainly studies the performance improvement and optimization.Firstly,the topology and working principle of three-phase dual active bridge are studied.The power transmission and soft switching characteristics under phase shift control and three degrees of freedom duty cycle control are analyzed,and the influence of duty cycle on the performance of the converter is studied.Secondly,according to the different combinations of phase voltage waveforms,the three degrees of freedom duty cycle control mode is divided into three categories and 17 kinds.The modes with poor performance are eliminated by simplified analysis.The boundary conditions and switching conditions of 11 remaining working modes are solved,and the transmission power,current stress,and current RMS of each working mode are analyzed.In order to improve the performance of the converter,the current stress and current RMS are optimized,respectively.The Lagrange multiplier method is used to solve the optimal control trajectory of current stress under each mode.By synthesizing various modes,the minimum current stress operation method in the full power range is proposed.The numerical optimization method is used to solve the problem with the current RMS as the objective,and the minimum operation mode of current RMS in the full power range is obtained.The calculation results show that both of them take triangle wave control methods and phase-shifting control methods in low power and high power section respectively.Finally,V2 G high-power bidirectional DC-DC converter parameters are designed,and a prototype of three-phase dual active bridge converter with 400V-750 V input,750 V output and 30 k W power is built.The experimental results show that the current optimization control method can effectively reduce the current stress and current RMS of the converter.It also improves the efficiency under light load.