Tuning of multivariable PI robust controllers for the decentralized voltage regulation in grid-connected distribution networks with Distributed Generation

Abstract

This paper deals with the voltage control problem in grid-connected electric distribution networks with Distributed Generators (DGs). The proposed solution adopts a decentralized approach to regulate the voltage amplitude of the nodes to which the DGs are connected without any communication links among the DGs. A generalized Multi-Input Multi-Output (MIMO) model of the distribution system is employed to design a diagonal matrix of PI controllers acting on the reactive power injected or absorbed by the DGs. The solution of a constrained minimization nonlinear problem in the frequency domain gives the tuning of the PI parameters ensuring system stability with nominal plant and robust stability with respect to both uncertainty affecting the nominal plant and disconnection of a DG. In the case of DGs represented by Photo-Voltaic systems, a case study reports the results of numerical simulations obtained with reference to a distribution network with feeders, sub-feeders and PV systems; the results confirm the validity of the presented design technique. Finally, the proposed PI controllers are compared with the ones designed on the basis of phase margin specifications.