A decentralized optimization method based two-layer Volt-Var control strategy for the integrated system of centralized PV plant and external power grid

Abstract

The large-scale integration of centralized photovoltaic (PV) plant (CPVP) is encountering severe challenges. On the one hand, the weak static voltage stability (SVS) of the external power grid (EPG) greatly restricts the maximum transmission power provided by CPVP. On the other hand, voltage limit violation is prone to occur at the end of collecting power lines inside CPVP. Driven by the above voltage issues, this paper proposes a novel two-layer Volt-Var control (VVC) strategy with two timescales for the integrated system consisting of CPVP and EPG. In this VVC strategy, besides the interaction between CPVP and EPG is fully considered, the coupling between transmission network (TN) and distribution network (DN) in EPG is also highly valued. The explicit integrated optimization model is constructed. Two decentralized optimization methods are applied for efficiently solving the integrated optimization problems corresponding to the different control layers, respectively. The operations of various VVC devices are coordinated via the proposed VVC strategy. The simulation results obtained indicate that the proposed two-layer VVC strategy can effectively reduce the voltage limit violation risk inside CPVP, and even in the worst case, the average nodes voltage deviation is only 0.024 p.u. Meanwhile, compared with the case without VVC, the value of the selected average SVS margin index will be reduced by about 33.18%, which means EPG is significantly improved.