Multivariable-Controlled Shunt Compensator for Damping Subsynchronous Interactions in Electrical Distribution Networks

Abstract

In recent years, the massive integration of converter-interfaced devices to electrical distribution networks has lead to appearance of poorly-damped subsynchronous interactions in the grid. These oscillation modes amplify electrical disturbances originated from the grid and may cause an interaction between grid elements threatening the system stability. Shunt compensators at the distribution level have already been used to improve the damping of these networks. However, their control system strongly depends on the distribution network dynamics, that is difficult to know at all times. In this paper, a multivariable controller for a shunt compensator is proposed. First, the dynamics of a distribution network with high penetration of electronic interfaces is explored in order to understand the interactions. Then, the controller of the compensator is designed based on an estimated model of the plant so that no previous information of the network is required. This controller is based on a state-feedback controller and a state observer, both designed by using the linear quadratic regulator (LQR) theory. Analytical results and computer simulations are used to verify the effectiveness of the controller. The main findings are validated in a laboratory environment comprising two 15 kW distributed generators, a 15 kW compensator and a 75 kW grid emulator.