An improved control strategy of STATCOM for grid voltage unbalance compensation

An improved dual-loop control strategy is proposed in this paper to improve the static synchronous compensator (STATCOM) operation performance under grid voltage unbalance conditions. In the proposed method, the second order harmonic resonant control blocks are added on the positive sequence control blocks to form the outer controller, and the negative sequence current references can be generated for STATCOM to eliminate voltage unbalance at point of common coupling(PCC). In order to accurately track the current reference values, the resonant control blocks are paralleled with PI controllers in inner controller in which the PI controllers are mainly designed for dc component error free control, and the resonant blocks are mainly designed for the second order harmonic component tracking. Simulation results verify the correctness and effectiveness of the improved control strategy.