Abstract
Massive integration of distributed generators with inherently high intermittency and volatility leads to frequent voltage violations. Thus, an appropriate voltage/Var control (VVC) is essential for the secure and economic operation of distribution systems. The increasing penetrations of rooftop photovoltaic units strengthens the coupling between the medium and low voltage (MV-LV) distribution networks spatially, causes temporal interference of VVCs with each other on different timescales, and worsens the network unbalance profile especially on the LV sides. To address this challenge, this study proposes a spatial-temporal coordinated VVC for MV-LV unbalanced distribution networks. Based on 'decomposition-coordination' principle, the developed strategy consists of three modules of real-time evaluation of reactive capability of LV feeders, long-short-time coordinated VVC of MV network, and parallel short-time VVC of LV feeders. Based on the proposed strategy, the VVC optimization problems for these modules are formulated and jointly solved by mixed-integer second-order cone programming and linear programming methods, to minimize the voltage deviations within the MV-LV unbalanced distribution systems in real time. Finally, based on the joint simulation platform of MATLAB and Python, the effectiveness and superiority of the proposal are numerically verified on a real Australian distribution system.