Analysis and design of a series voltage compensator for three-phase unbalanced sources

Voltage unbalance typically present a three-phase AC supply systems adversely affects power system components, static converters, electric drive systems, electric machines, etc. connected to the system. The authors describe a method to eliminate this unbalance by means of a voltage compensator connected in series with the supply through transformers. The technique is based on extracting the negative sequence voltage component of the supply and canceling it in order to obtain balanced voltages. The positive sequence component is then adjusted to achieve voltage regulation. It is shown that the compensation can be achieved with low-kVA inverters and that harmonic injection is reduced to a minimum. Implementation principles, design equations, and a design example are presented. Simulated and experimental results confirm the theoretical concept and feasibility of the proposed system