Reduction in rating of voltage source converter of DSTATCOM using a zig-zag transformer

In this paper, a new topology of DSTATCOM using three single-phase VSCs (voltage source converters) integrated with a zig-zag transformer is employed for the power quality improvement in three-phase four-wire distribution systems. The zig-zag transformer is used for providing a path to the zero sequence fundamental as well as harmonics currents. In order to optimize the voltage rating of the VSCs, the zig-zag transformer is designed to have a tertiary winding for integrating the VSCs. This new topology of DSTATCOM (Distribution Static Compensator) provides the voltage regulation or power factor correction by reactive power compensation, harmonics compensation, load balancing and neutral current compensation in three-phase four-wire distribution system. This topology has the advantages of the use of `off the shelf´ VSC, reduced kVA rating, optimum voltage rating of VSCs and hence less cost. The VSCs are integrated with a zig-zag transformer to realise a single unit by designing a set of third winding in the transformer. The performance of the proposed DSTATCOM system is demonstrated under linear and nonlinear balanced and unbalanced loads by simulation using MATLAB with its Simulink and simpower systems (SPS) tool boxes.