Control Strategy of Active Commutated Converter for HVDC transmission system under Unbalanced Grid

An active commutated converter (ACC) topology for HVDC transmission system is introduced. Based on the mathematical model of ACC under two-phase static coordinate system, a novel control strategy which adopts the PR controller for negative sequence component of the grid current elimination and unity power factor operation under unbalanced grid situation is proposed. Besides, the maximum active power that can be transmitted during unbalanced grid fault is also proposed. What’s more, the PR controller are designed. Compared with the traditional control methods, the proposed control strategy can be performed at a low switching frequency and without decoupling process. The results of ACC built in PSCAD/EMTDC validate the correctness and effectiveness of the proposed control strategy.