Two-Layer Collaborative Architecture for Distributed Volt/Var Optimization and Control in Power Distribution Systems

For large-scale distribution networks (DNs) with distributed generations (DGs), the conventional centralized Volt/Var optimization and control (VOC) have high demand for online computing resources and efficiency. This paper proposes a new decision-making method for the distributed VOC (D-VOC) based on a two-layer collaborative architecture. First, for a distributed equivalent load system with on-load tap changer (OLTC), this paper studies how to minimize the active power loss and reach the target voltage of load side for the equivalent load system. Second, a concept of virtual soft controller (VSC) is presented based on the distributed equivalent load system, and the local optimal control strategies of VSCs are designed to realize the D-VOC in DNs. On this basis, a two-layer collaborative architecture for the D-VOC is designed. VSCs could be built in virtual or real deployment at nodes where reactive power sources or reactive power compensation devices are equipped, and they are at the bottom layer of the architecture. VSCs upload their distributed decision results to the local control center (LCC) which is at the top layer of the architecture. The LCC systematically verifies and authorizes each VSC to execute its own operational instruction. Case study on the modified PG & E 69-bus distribution grid shows that the method is feasible and has satisfactory efficiency.