Study On Double-star Multilevel Railway Power Conditioner System Based On YNvd Transformer

In order to solve the power quality problem of negative sequence current and harmonic current in modern high-speed railway power supply system,a double-star multilevel railway power conditioner system based on YNvd balance d transformer was proposed in this paper.This system adopted a novel double-star multilevel railway power conditioner(DS-MRPC).DS-MRPC which consists of four H-Bridge links and corresponding output filter inductors is AC-AC conversion circuit structure and no direct current bus capacitance is required.Different from the conventional railway power conditioner based compensation systems,this system integrated DS-MRPC into the phase-? side flexible taps of YNvd balance transformer instead of into phase-? side feeder via a step-down transformer,thus the initial system costs were reduced significantly.Firstly,this paper discussed and analyzed the development situation of electrified railway at home and abroad,the current situation of power quality problems of electrified railway and the several common power quality problems control methods,then this paper emphatically introduced the current research status of domestic and foreign experts on railway power conditioner(RPC).Secondly,the characteristics of YN/d11 transformer,V/ V transformer,Scott balanced transformer and novel YNvd balanced transformer were analyzed in detail.It is pointed out that the YNvd balanced transformer had the characteristics of strong negative sequence current suppression ability and no direct electrical connection between two-phase output of secondary side,in addition,when the railway power conditioner was applied to the traction power supply system with YNvd balance transformer,the required capacity was relatively small.Following that,structural characteristics of several multilevel railway power conditioner(MRPC)are studied.This paper introduced the structure characteristics of traditional RPC,multiplex RPC,MRPC with two arms,MRPC with three arms,MRPC with four arms and the novel double-star multilevel railway power conditioner in detail.It is pointed out that the structure of DS-MRPC was an AC-AC conversion circuit structure,no direct current bus capacitance is required,and the required number of submodule,power switching device and the submodule capacitance is relatively small.The novel railway power compensation systems based on YNvd balanced transformer and DS-MRPC was worthy of in-depth study.Again,this article analyzed the topology structure and the compensation principle of the double-star multilevel railway power conditioner system based on YNvd transformer.And on the basis of the principle of compensation,the power analysis of the system was carried out in detail.It pointed out that in the situation which regardless of device loss and reactive power,the overall instantaneous power and the four links instantaneous power of DS-MRPC contained only alternating component,there was no DC active component which can make the divergence of the dc capacitor voltage,the DS-MRPC was generally in a state of energy balance.Based on the compensation principle,a comprehensive control strategy was proposed,which consists of the compensation reference current detection operation,the command current tracking control,the circulation suppression,the voltage balance of four H-bridge links and each submodule of H-bridge links.At last,this paper expounded the design principles and methods of main system circuit's important parameter,such as the corresponding output filter inductors of H-bridge links,submodule capacitance of H-bridge links,the number of submodule and the voltage reference of submodule capacitance.Then on the Matlab/Simulink platform,the simulation results showed the feasibility and effectiveness of the proposed system.