Transformerless DC traction power conversion system design for light-rail-transit (LRT)

Malaysia Light Rail Transit (LRT) traction network is fed by 750 V DC system. A rectifier transformer (zigzag transformer) and a twelve-pulse traction rectifier are the main equipment to step down and rectify the AC power. In order to eliminate the bulky rectifier transformer in the conventional design, this paper presents a feasibility study on a two-stage power conversion system using purely power electronics converters. The proposed system consists of a six-pulse controlled rectifier, low-pass filter and a buck converter. The six-pulse controlled rectifier will step down and rectify the 33 kV AC grid. The generated DC voltage will be filtered and fine-tuned to reach the desired DC voltage level using a 2 kHz buck converter. The design of the proposed system will be fully discussed and simulated using MATLAB/Simulink. Simulation results with full analysis are enclosed.