Coordinated control of tie switch and soft normally open point for harnessing flexibility in active distribution systems

Abstract

Integration of renewable energy source (RES) increases the volatility and uncertainty of active distribution systems while the limited line capacity hampers the accommodation of RES. Soft normally open point (SNOP) has the capability to control the power flow between distribution feeders accurately which can mitigate line congestion. SNOP is an effective flexibility resource in active distribution systems. However, currently it is impossible to replace all traditional tie switch by the SNOP considering the high cost of SNOP. In this paper, a coordinated control strategy considering the coexistence of tie switch and SNOP is proposed, in which a bi-level model is built. An index weighing the static insecurity probability is defined as the bridge between the two layers of the bi-level model. By solving the mixed integer nonlinear programming problem, the coordination between tie switch and SNOP is realized accounting for different characteristics of the two types of devices. Simulation results on a 33-bus test system demonstrate the effectiveness of the coordinated control strategy.