Hybrid Traction Power Quality Compensation System in electrified railway for nominal rating reduction of three-phase converter power switches

Abstract

Since AC traction loads are usually large single-phase loads with a non-linear nature, they create power quality problems, such as high contents of Negative Sequence Current (NSC), low power factor, harmonic injection, etc. To overcome above issues, a Hybrid Traction Power Quality Compensation System (HTPQCS) based on a three-phase Full-Bridge Converter (FBC) and two Static VAR Compensators (SVCs) is proposed in this paper. The proposed structure will considerably reduce the initial investment cost of compensation system and nominal rating of FBC power switches. In this study, the FBC is used to transfer active power from one section to adjacent section and suppress harmonic currents. The SVCs are applied to compensate reactive power and suppress the third and fifth harmonic currents. In this paper firstly, the operating principle of NSC compensation is discussed step by step. Then, the proposed control strategies for SVC and FBC are presented. Finally, simulation results demonstrate the correctness and validity of the proposed structure and compensation strategy and also show that HTPQCS could compensate all power quality problems. The simulation is carried out using MATLAB/Simulink software.