Combined Local and Centralized Voltage Control in Active Distribution Networks

A two-level real-time voltage control scheme is proposed to keep voltages within specified limits in distribution grids using distributed generation units (DGUs). It combines a local and a centralized control of their reactive powers. The local control provides fast response after a disturbance, reducing its impact and enhancing voltage quality. The centralized control uses measurements collected throughout the network to bring the voltages inside tighter limits and balance the various DGU contributions. To this purpose, it adjusts in a coordinated way their reactive power set points, taking into account the local controls. This discrete control solves at each time step a multitime-step constrained optimization inspired of model predictive control. The method effectiveness is demonstrated on a 75-bus test system hosting 22 DGUs.