A Control Strategy for VSC under Unbalanced Conditions in AC Distribution Networks

As the integration of renewable energy sources and complex loads increases, modern distribution networks face significant challenges related to unbalanced operation. This paper investigates control strategies for two-level voltage source converters (VSCs) operating under unbalanced conditions in AC distribution networks. A novel dual synchronous reference frame (DDSRF)-based phase-locked loop (PLL) method is proposed to mitigate the adverse effects of double-frequency components introduced by unbalanced conditions. Additionally, a negative sequence current control loop is designed to suppress the impact of negative sequence currents on the safe operation of the VSC. Furthermore, an outer-loop power control strategy that accounts for unbalanced factors is introduced to reduce power fluctuations. Through PSCAD simulations results demonstrate that the proposed strategies significantly enhance VSC control performance and system stability under unbalanced conditions.