Impedance sensitivity-based corrective method for online voltage control in smart distribution grids

With the rapid increase in hosting large penetration levels of Distributed Generation (DG), voltage stability problem has raised a main concern for distribution networks. This study proposes a new centralized voltage control method following a security purpose for active distribution grids. The method is based on a sensitivity analysis to optimally dispatch the control variables. The sensitivity analysis uses a Thevenin-based load impedance margin (TLIM) derived from the nodal measurements to take into the consideration the changes in the system operation, especially those caused by the rapid-response devices of DGs. Sensitivity of load and equivalent impedances to control variables is investigated via the derivation of nodal voltage and current with respect to control variables. Accordingly, the contribution of each control variable in change TLIM and, hence, in voltage control can accurately be obtained. The changes of the impedances of pilot bus, which has the smallest value among all the TLIMs, are formulated in a multi-step optimization problem in terms of impedance sensitivities for the optimal dispatch of controls. The proposed sensitivities and their application in voltage control are successfully validated by a 11-kV distribution grid including 77 bus and hosting 22 DG units. Simulation results show the validity and the accuracy of the proposed sensitivity method in voltage control during different scenarios.