Wei Yingdong

A series voltage compensator based on thyristor-controlled transformer

Series compensation is an important way to improve transmission capability and power controllability of long-distance power delivery systems. Since typical series compensators have some limitations, this paper proposes a novel series voltage compensator based on thyristor-controlled transformer. By special configurations of transformer windings and thyristor converters, it is capable of injecting voltage phasors with adjustable magnitudes and phase angles. Taking the advantage of power semiconductor devices, this compensator responds much faster than mechanical compensators and permits frequent regulations. A SMIB system with two parallel transmission lines are taken as a study case. And simulation results show the injected voltage and regulated power by the compensator, which proves its effectiveness.

Virtual neutral point selection for three-leg railway power quality conditioner

With the development of series connection of IGBTs, the transformerless high-voltage converter becomes an important type utilized in power quality improvement applications. Electric railway is a kind of unbalanced load and the compensators based on three-leg converters are potential solutions for it. This paper proposes a modeling method for three-leg railway power quality conditioner, by means of selecting a virtual neutral point. This method, compared with conventional ways, replaces the two higher actual phase voltages by three lower virtual ones, which helps the converter lower the requirement of dc-link voltage level and the number of series-connected devices by about 30%. Simulation results prove that the control strategy based on this new model represents satisfying performances.