Study Of Railway Static Power Conditioner

High-speed railway traction power supply system has the disadvantages ofheavy unbalanced three phase, large harmonics and reactive power. Compared toconventional power quality adjustment device, based on back-to-back converter,railway static power conditioner (RPC), establish a link between the upper arm andthe down arm, can effective ly balance the load between two arms, compensate theharmonic current and reactive power. which as a whole to achieve optimum runningcondition.This paper studies the harmonics current characteristics of SS4electriclocomotive generated in operation. Through the analys is of two commonly usedtraction transformer (Scott transformer and YN, d11transformer),including wiring,electrical quantities’ relationship between primary and secondary side and relativecompensation of the total capacity, a overall structure of the RPC compensatingsystem based on Scott transformer has been settled down. The reactive powercompensation and negative sequence harmonic princip le has been described, as wellas the voltage, current and power flow relationship between the system.Through the analys is of steady-state operation of RPC, the principle of energyexchange between RPC and the traction power supply system is got, by theoptimization of the RPC main circuit parameters, a single-phase harmonic currentdetection method faced with electrified railway is determined, a system-levelcontrol strategy is designed according to the overall control means of RPC. Throughthe simulation of two load cases, it can be clearly seen that RPC has greatimprovement of the power quality for electrified railway, such as balancing the loadcurrent of two bridge arm, reducing the content of negative sequence current,ameliorating the three-phase current imbalance and compensating reactive andharmonic current of the two leg.As the conventional PI control is difficult to trace the waveform, an improvedcontrol scheme was applied in this paper. The whole design was provided, thesystem stability, non-randomized harmonic interference, steady-state error wasanalyzed to obtain the general stability conditions of the system. The improvedcontrol scheme can effectively eliminate the negative sequence current andthree-phase voltage fluctuations of the primary side, as well as improve the powerfactor and harmonic filter, so that electrified railway power quality proble ms can beresolved perfectly. Analysis and simulation results testify the effectiveness of theproposed control scheme.