The Study And Emulation On The Power Quality Control Of The Power System For Railway Traction

As a large power single phase rectified load, the electric traction load has many disadvantages like heavy distortion, acute fluctuation and severe asymmetry. The safe and economic operation of power systems is badly influenced. A novel power supply system for railway traction is presented in this paper, where the active power filters (APF) is utilized to eliminate the disadvantages of the system that is widely adopted at present. By compensating the negative, reactive and harmonic current simultaneously, the proposed system can avoid deteriorating the problem of the power quality.In corresponding to the asymmetrical transformers that is used in the traction supply system, one scheme is developed to realize the proposed balance electrical system (BED). The structure of APF suitable for implementing the BED is proposed, on a survey of the existing topology of the passive, active and hybrid filters, and the current, voltage, multi-level and cascade converters.An evaluation on most of methods proposed by other publication for generating the reference current/voltage is done in the paper, and the characteristic and applicability of these methods are analyzed. A high-speed and simple reference generating method is suggested, which can extract the positive sequence voltage from the asymmetrical, distorted source voltage, and the reference current can be generated by utilizing this voltage. Meanwhile, PWM control mode based on the triangular-wave modulation and set sideband control mode are analyzed and researched in detail. According to the practical requirements, a state optimal vector control strategy in which the correlation among the legs is harnessed is developed, leading to the result of low switching frequency, higher switching efficiency and accuracy.Through analyzing the general requirements on the design parameters of the BED, the relationship of the APF parameters is found, and the design method of the main circuit of APF is proposed. In corresponding to the features of the electrified railway traction power supply system, a traction power System Simulation model with BED is established in the PSCAD/EMTDC environment. Comprehensive research is done on the reactive power compensation and harmonic characteristics of the BED, and the correctness and feasibility of the system structure, control strategy and parameter calculation method are confirmed by the simulation results obtained.