A Novel Traction Supply System for Urban Rail Transportation with Bidirectional Power Flow and Based on PWM Rectifier

The application of conventional traction supply system for urban railway transportation implies huge energy waste and electrical pollution, in which the energy regenerated from the braking of vehicles cannot be feedback into AC grid. What´s more, its DC output voltage fluctuates seriously with external loads, and AC harmonics on the grid side forms electrical pollution to the outside. This paper proposes a novel traction supply system for urban rail transportation, based on a multi-paralleled structure of PWM rectifiers. Fully exerting the merits of the PWM rectifier, such as a controllable DC output characteristic, less harmonics on grid side, availability of unity power factor as well as the capability of bi-directional power flow, our novel system overcomes the defects of its conventional counterpart. Under the Phase-shift Space Vector Pulse Width Modulation (PS-SVPWM) mechanism, the equivalent switching frequency of the system can be further reduced. Another adopted mechanism in the system is balance control of the PWM rectifier modules´ loads. A subsystem for remote control and monitoring of the system is also developed with Ethernet technology and virtual instrument theory. The design has been testified with experiments on a prototype set up in lab, and related results are given in the last part of this paper.