Design And Research Of Control Strategy For Dual Active DC-DC Converter Based On PET

With the rapid development of new energy and renewable energy power generation technologies,Power Electronic Transformer(PET)equipments are widely used in distributed smart grids,track traction and other occasions.The components of PET have become an important part of green energy strategy in our country because of its advantages of efficient energy utilization.Therefore,the study of bidirectional isolated DC-DC converter which as the core device of PET has a great significance in promoting the interaction between distributed energy and power grid.Specific study highlights are as follows:1.In this thesis,according to the characteristics of typical topology for dual active bridge(DAB)DC-DC converter,the working principle and steady state characteristics of DAB converter with single phase shift(SPS)control and dual phase shift(DPS)control are studied respectively.It is found that DAB converter with SPS control has inherent power reflux phenomenon and the problem of excessive current stress.Furthermore,this thesis finds that DAB converter with DPS control can eliminate power reflux by adjusting phase,but the current stress of DAB converter still needs to be further optimized.And then,this thesis proposes corresponding control methods based on the theoretical analysis of SPS control.And the theoretical analysis of the three control modes is verified through simulation built by Simulink software.2.In this thesis,considering the problems of power reflux phenomenon and current stress for DAB converter which will increase the loss of switching device and reduce the energy transmission efficiency of the system,a new triple phase shift(TPS)control method is proposed.The control principle of triple phase shift(TPS)control and the operation mode and steady state characteristics of DAB converter are analyzed and studied in detail.And the reflux power and current stress of DAB converters under the TPS control are researched.It is found that the adjusting range of the transmission power is wider for TPS control compared to the DPS control and SPS control,and the phenomenon of power reflux can be eliminated by adjusting three phase-shifting controls,which has more significant advantages in reducing inductance current peak value and reducing system reactive power,etc.Moreover,TPS control mode can be simulated and verified by establishing simulation through Simulink software.3.At last,a 10kW DAB converter experimental platform is successfully constructed in this thesis.The electrical parameters and technical indicators of the experimental device are designed in detail,and the switch devices are selected according to the relevant parameters and indicators,and the high-frequency transformer,protection circuit and driving circuit are designed.The control board and control program of the experimental platform are introduced in detail.The running test of DAB experimental platform under three modulation modes is completed,and the experimental results verify the accuracy of the theoretical analysis in this paper.