A combined central and local voltage control strategy of soft open points in active distribution networks

With the increasing penetration of distributed generation (DG), the risk of voltage violations in active distribution networks (ADNs) has become a major concern for the system operator. Soft open point (SOP) is a flexible power electronic device which can realize accurate active and reactive power flow control. This paper proposes a combined central and local operation strategy of SOPs to realize voltage control in ADNs. The active power of SOPs is centrally adjusted based on the information and forecasting throughout the network, which aims to maintain the voltage within the limits in the global optimization. And the local control of reactive power based on real-time measurements can rapidly respond to the frequent voltage violations caused by the fluctuations of DG outputs. The potential benefits of SOPs are fully explored to reduce power losses and improve voltage profile of ADNs. By applying convex relaxation, the original mixed-integer nonlinear programming (MINLP) model is converted into an effectively solved mixed-integer second-order cone programming (MISOCP) model. Case studies on the PG&E 69-node distribution system are conducted to verify the effectiveness of the proposed method