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.