Three-level Two-phase To Singlephase Converter For Advanced Cophase Traction Power Supply System

The co-phase power supply system can solve reactive power,harmonic and negative sequence etc.power quality problems of existing traditional traction supply system,and can reduce the half quantities of neutral sections.But the system cannot connect the whole traction network.Based on the co-phase power supply system,the advanced co-phase traction power supply system can cancel neutral sections between traction substations,and connect the whole traction network.The current research on the advanced co-phase traction power supply system utilizes power electronic devices mostly based on the three-phase to single-phase converter to replace traction transformers.It is generally applicable to newly-built railway.In this paper,an advanced co-phase traction power supply system is proposed for the existing traction substation.Most of traction transformers transform the three-phase electric power into two-phase electricity,which is required by the railway traction system.Therefore,using the existing traction transformer,the advanced co-phase traction power supply system based on three level two-phase to single-phase converter is designed.Firstly,the basic model is introduced for the designed advanced co-phase traction power supply system and the two-phase to single-phase PWM converter topology is briefly analyzed.The topology,mathematical model and control strategy of three level single-phase PWM rectifier are studied in detail.The single-phase PWM rectifier based on the transient current control,makes system work at unit power factor.Because the system not only needs to transmit active energy,but also needs to compensate the reactive power of locomotive loads,the single phase dq decoupling control strategy is adopted to adjust power factor arbitrarily in the traction network.Secondly,the common types of traction transformers and the connection forms are introduced,and the electrical characteristics of YNvd traction transformer is introduced in detailed.It is concluded that the current of the three-phase power grid will balance,if the currents of the auxiliary side of the transformer are equal and have the same phase with corresponding voltage separately.In addition,the master-slave current sharing control strategy based on the parallel rectifiers is studied.Single phase rectifier based on transient current control,single phase rectifier based on single phase dq decoupling control,single-phase parallel rectifiers and two-phase to singlephase converter are built by the way of simulation and experiment respectively.The simulation results and experimental results all verify the validity and correctness of the transient current control,the single phase dq decoupling control and the master-slave current sharing control strategy.Meanwhile,it verifies that the system has the ability of bidirectional transmission of active power,compensates the reactive power,and makes the three-phase power grid work at the unit power factor.