Islanded-Mode Control of Electronically Coupled Distributed-Resource Units Under Unbalanced and Nonlinear Load Conditions

This paper proposes a voltage- and frequency-control strategy for the islanded operation of dispatchable electronically coupled distributed-resource units, based on a discrete-time mathematical model which is also valid for variable-frequency operation. The proposed control strategy utilizes a combination of deadbeat and repetitive control to enhance the performance of the control system under unbalanced and/or distorted load currents. Moreover, a new approach is proposed to maintain the effectiveness of the repetitive control under variable-frequency operational scenarios. Furthermore, the control strategy employs feedforward compensation techniques to mitigate the impact of load dynamics on the regulation process. The performance of the proposed control strategy is demonstrated for single- and multiunit islanded networks, through digital time-domain simulation studies in the PSCAD/EMTDC software environment.