On the control of main substations between transmission and distribution systems

A new method called flexible active-reactive optimal power flow (A-R-OPF) has been recently developed to deal with power systems including entities such as distributed generation (DG) units and battery storage systems (BSSs). It was shown that bidirectional flows of active and reactive power/energy will be more and more exchanged in the case of connected power systems. This brings additional challenges in terms of optimal control and safe operations. The purpose of this paper is twofold. First, we introduce a new sensitivity analysis method incorporating the original flexible A-R-OPF method with an on-load-tap-changer (OLTC) transformer control system. Second, we study the impacts of reverse A-R-OPF and different disturbances on the feasibility of the whole system. Analyses are carried out by considering a real distribution system with wind DG units and BSSs. It is demonstrated that allowing and/or restricting reverse A-R-OPF can violate the feasibility of traditional control systems. This fact needs to be considered in connected power systems for optimal and reliable operations.