Control of distributed energy resources under switching transient between grid-connected and Islanded operation modes

Abstract

This paper presents control strategies that enable stable operation of electronically coupled distributed energy resources (DERs) that switch between grid-connected and islanded operation modes. First, it is shown that stability of islanded and grid-connected systems, individually, is not a sufficient condition for stability of the switched system. Then controller design problem, for grid-connected and islanded systems, is formulated as controller design for a switched system. Furthermore, robustness and desired transient behavior of the system in the two modes of operation are taken into account. This allows the controller to accurately generates pulse width modulation (PWM) signals so that the real and reactive powers output of the DER track their corresponding references in grid-connected mode. Moreover the control design allows voltages to track their references in islanded operation mode. It is shown that the control scheme ensures system stability during transition between the two modes of operation. To demonstrate the effectiveness of the proposed approach, the control scheme is applied to a detailed nonlinear model of a converter-based DER.