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This paper presents an efficient algorithm to solve the multi-objective (MO) voltage control problem in distribution networks. The proposed algorithm minimizes the following three objectives: voltage variation on pilot buses, reactive power production ratio deviation, and generator voltage deviation. This work leverages two optimization techniques: fuzzy logic to find the optimum value of the reactive power of the distributed generation (DG) and Pareto optimization to find the optimal value of the pilot bus voltage so that this produces lower losses under the constraints that the voltage remains within established limits. Variable loads and DGs are taken into account in this paper. The algorithm is tested on an IEEE 13-node test feeder and the results show the effectiveness of the proposed model. [ABSTRACT FROM AUTHOR]

• A centralized online method for voltage control following a security purpose is proposed for active distribution grids. • Sensitivity of the load and the equivalent impedances of a load bus to control variables is investigated. • The load impedance margin TLIM is used as a target for voltage control in distribution networks. • A multi-step optimization problem in terms of impedance sensitivities is formulated. • The contribution of each DG unit in change the impedances is carried out. 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. [ABSTRACT FROM AUTHOR]