Application of Soft Open Point for Flexible Interconnection of Urban Distribution Network

Normally open points (NOPs) in distribution network are used for balancing loads between feeders, reducing network losses, etc. However, circulating current is generated when NOP is closed during feeder interconnection, which may cause protection device maloperation. In this paper, relationship between circulating current and voltage difference at two neighboring substations is first studied. Soft open point (SOP) is then applied at NOP in a distribution network. SOP is able to control active power flowing through the open point. It also provides ancillary service such as reactive power regulation. A SOP based on three-level back-to-back converter is implemented by using RTDS /RSCAD. It is applied to the selected case study. Simulation verifications are provided to show the validity of SOP and its control.