Isolated H-bridge VSC Based 3-phase 4-wire DSTATCOM for power quality improvement

A new topology of DSTATCOM (distribution static compensator) consisting of a H-bridge VSC (voltage source converter) and a star/delta transformer is proposed for power quality improvement in a three-phase four-wire distribution system. The star/delta transformer provides isolation to the H- bridge VSC as well as mitigates the zero sequence current in a three-phase four-wire distribution system. The H-bridge VSC is connected to the secondary of the star/delta transformer for the compensation of reactive power for voltage regulation or for power factor correction along with load balancing and elimination of harmonics currents. In order to optimise the voltage rating of the VSC, the star/delta transformer is designed to have a suitable voltage rating for the secondary windings. This transformer connection provides the selection of ldquooff the shelfrdquo, H-bridge VSC for this application and it also provides isolation for the VSC. The neutral current compensation is achieved without increasing the kVA rating of the star/delta transformer. The number of IGBTs (insulated gate bipolar transistors) required is reduced to half compared to a normal 4-leg VSC and hence the cost is also expected to be reduced. The performance of the proposed three-phase four- wire DSTATCOM system is validated through simulations using MATLAB software with its simulink and power system blockset (PSB) toolboxes.