Study of a STATCOM used for unbalanced current compensation caused by a high speed railway (HSR) sub-station

The sub-stations of the high speed railway connected to the high voltage three phase network, are considered as pollutant loads, disrupting power grids. The major problem of these sub-stations is the unbalance caused by the connection between two phases of high voltage network. This connection leads to an unbalanced current, this current is decomposed into two sequences (positive and negative), creating negative sequence voltage in different points of the network. The parallel VSI STATCOM is one of the modern compensation solutions for the negative sequence current. It allows injecting currents in the sub-station connection point in order to get a balanced network. This paper describes the structure, control strategy, and performance of a VSI STATCOM.