Improved Positive and Negative Sequence Double Loop Control Strategy for Cascaded STATCOM under Grid Voltage Imbalance

Aiming at the issue of reactive power and negative sequence current compensation of cascaded static synchronous compensator (STATCOM) and the problems of DC-side voltage equalization under grid voltage imbalance, an improved positive and negative sequence double loop control method is proposed. Through the independent control of positive and negative sequence active and reactive power, the global voltage regulation control of the device is realized while realizing reactive and negative sequence current compensation. A phase-injection voltage is applied between the phases to balance the phase-to-phase power and achieve phase-tophase voltage equalization. The simulation results evidence that the proposed method can not only well compensate the reactive power and negative sequence current, in case of unbalanced grid voltage well, but also effectively solve the DC side voltage balance problem.