Zoning Evaluation for Voltage Optimization in Distribution Networks with Distributed Energy Resources

Abstract

This paper deals with the problem of the voltage profile optimization in a distribution system including distributed energy resources. Adopting a centralized approach, the voltage optimization is a non-linear programming problem with large number of variables requiring a continuous remote monitoring and data transmission from/to loads and distributed energy resources. In this study, a recently-proposed Jacobian-based linear method is used to model the steady-state operation of the distribution network and to divide the network into voltage control zones so as to reformulate the centralized optimization as a quadratic programming of reduced dimension. New clustering methods for the voltage control zone definition are proposed to consider the dependence of the nodal voltages on both active and reactive powers. Zoning methodologies are firstly tested on a 24-nodes low voltage network and, then, applied to the voltage optimization problem with the aim of analyzing the impact of the R/X ratios on the zone evaluation and on the voltage optimization solution.Energies 2019, 12, 390 2 of 28 without requiring any information exchange. The result is a globally non-optimal control solution. Undoubtedly, this is the lowest-cost solution to start involving DERs in the voltage control of existing distribution networks. Unfortunately, the absence of coordination may introduce technical problems related to the interaction among controllers or even system instability [3,4].In a centralized control, a central control unit, located at the substation level, firstly solves a system voltage optimization/control problem by receiving measurements from all the nodes of the network; then, it sends the optimal set-points back to the local controller of both DERs and conventional Volt/Var devices. This approach yields the optimal solution but its implementation is very expensive requiring a large communication infrastructure with adequate bandwidth to exchange information quickly and accurately [5][6][7][8].In a distributed control, the controllers of both DERs and conventional Volt/Var devices use measurements at PCC to achieve local voltage regulation as in a local control but they also exchange information with the controllers of the neighboring nodes. This approach aims at overcoming the technical problems of the local control while limiting the investments for the communication infrastructure [9,10].In a decentralized approach, the distribution system is usually partitioned into voltage control zones (VCZs). Each VCZ contains nodes weakly coupled with the nodes belonging to other VCZs from an electrical point of view; in the 'electric center' of a VCZ is placed the pilot node (PN), whose voltage variation best represents the variation of the voltage in the VCZ. In each VCZ a centralized control is present whereas the coordination is obtained by a distributed control among the PNs. This approach guarantees the optimal solution for each VCZ and it requires a communication infrastructure lighter than the centralized control [11,12].The div...

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