Abstract
This paper addresses the problem of optimizing the voltage profile of radially-operated distribution systems by acting on the active and reactive powers provided by distributed energy resources (DERs). A novel voltage optimization procedure is proposed by adopting a decentralized control strategy. To this aim, a centralized voltage optimization problem (VOP), minimizing the distance of all the nodal voltages from their reference values, is firstly formulated as a strictly-convex quadratic program. Then, the centralized VOP is rewritten by partitioning the network into voltage control zones (VCZs) with pilot nodes. To overcome the lack of strictly convexity determined by the reduction to the pilot nodes, the dual centralized VOP working on the augmented Lagrangian function is reformulated and iteratively solved by the method of multipliers. Finally, a fully-distributed VOP solution is obtained by applying a distributed algorithm based on the auxiliary problem principle, which allows for solving in each VCZ a quadratic programming problem of small dimension and to drive the VCZ solutions toward the overall optimum by an iterative coordination process that requires to exchange among the VCZs only scalar values. The effectiveness and feasibility of the proposed method have been demonstrated via numerical tests on the IEEE 123-bus system.
Highlights
The proper selection of the voltage control strategy and architecture, the adequate settings of local controllers and, in the near future, the coordination of the transmission system operators (TSOs) and distribution system operators (DSOs) are the many challenges that need to be faced for voltage control in smart grids [1]
With respect to the voltage optimization problem (VOP) (1), it is turned into a convex constrained quadratic programming problem providing local minimum points; this is due to the objective function that, considering only pilot nodes (PNs), remains convex but not in a strictly sense
A distributed algorithm based on the auxiliary problem principle (APP) has been proposed in this paper to solve the voltage optimization problem (VOP) in distribution networks with distributed energy resources (DERs) according to a decentralized approach
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. By reducing the size of the problem to be solved in each VCZ, computing facilities will process a limited amount of data; information exchange and communication infrastructure will cover limited network areas with the great advantage of lower investment costs and higher resilience to faults and cyber attacks Despite of these undoubtable advantages, decentralised approaches provide a sub-optimal solution with respect to the centralized one.
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