Hierarchical Distributed Voltage Optimization Method for HV and MV Distribution Networks

The increasing penetration of distributed photovoltaics (PVs) has brought great challenges to the security and stability of distribution networks (DNs), especially voltage violation. Current voltage optimization methods rarely consider the mutual voltage support between high voltage (HV) and medium voltage (MV) DNs, which may cause PV generation losses in extreme scenarios. Limited by the convergence conditions of common distributed optimization algorithms, mixed integer optimization problem can hardly be calculated in a distributed manner. This paper tries to exert the mutual voltage support capability of HV and MV DNs and realize optimal operation of continuous and discrete voltage regulation devices. Thus, a hierarchical distributed voltage optimization method for HV and MV DNs is proposed in this paper. It is assumed that HV and MV DNs are operated by different control systems and real-time communication between them is available. First, the voltage optimization models of HV and MV DNs are developed to minimize the total cost of voltage adjustment and network losses, which optimize the dispatch of on-load tap changers, reactive power compensators, feeder switches, and distributed PVs. Then the generalized Benders decomposition is applied to solve the mixed integer optimization model in a master-slave distributed manner and the accuracy of LinDistFlow equation is improved through the compensation of peak voltage and boundary power flow in MV DNs. Finally, the effectiveness of proposed method is demonstrated via simulation tests in Jinzhai DNs of China. The results of proposed optimization method are very close to those of global centralized optimization method.