Modeling And Control Strategy Of Power Electronic Traction Transformer

With the increasing coverage of China's electrified railways and the development of high-speed emu,the problem of large volume and heavy weight of transformer equipment in the traditional traction transmission system greatly restricts the development of lightweight and high-speed railways in China.By adopting new Power electronic devices and new high-power converter technology,PETT has effectively realized the miniaturization and lightweight of the equipment,and has the advantages of good controllability,high Power density and high intelligence level,which is of great significance to the future development of China's high-speed railway.Based on power electronic traction transformer as the research object,from the suitable for China's power electronic traction transformer topology structure of traction drive system research,and analysis of the mathematical model and the working principle,on the basis of the input stage,isolation level control strategy as the research key,optimize its resistance to disturbance and the performance of the power quality aspects.The main tasks are as follows.Firstly,the topological structure and mathematical model of power electronic traction transformer are analyzed.Based on the analysis of the working principle of power electronic transformer,the power electronic transformer is divided into three main PET forms,which are single-stage type,two-stage type and three-stage type.Then the input single-phase AC/DC rectifier and isolation stage dc-dc converter are studied,their topology and working principle are analyzed,and the mathematical model is established.Secondly,the control strategy of input level is studied.In order to overcome the shortcoming of using power predictive control strategy in single-phase PWM rectifier,a method of parameter estimation for real-time circuit parameters by adding gradient calculation method into power predictive control is proposed in this paper,and a simulation model is established for simulation analysis.The simulation results show that the power prediction control strategy based on parameter estimation has better stability when the network side voltage of the system breaks down,and the active power and reactive power are more consistent with the reference value,and have better response ability when the referencevalue changes,and the system has stronger anti-interference ability.Thirdly,the voltage balance problem of input-output side is studied.Based on cascaded H bridge output side capacitance voltage imbalance causes were analyzed,and combining with the traditional based on proportional pulse compensation strategy research,on the basis of the proposed fuzzy adaptive PI modified strategy,and through constructing three-level cascaded H bridge,a simulation model of this strategy was verified by internal and external disturbance has good voltage balance effect.Finally,the control strategy of isolation stage DC-DC converter is studied.Through the study of single phase shift control strategy and its working mode,the existing shortcomings are analyzed.Aiming at the problems of slow dynamic response and non-controllable reactive current of single-phase shift control method in DAB,this paper proposes a control strategy based on vector control,and builds a simulation model for the two control strategies.Through simulation analysis,the vector control strategy has better dynamic response ability and can control the reactive current,which has practical engineering value.