Islanding detection and control of islanded single and two-parallel distributed generation units

This thesis experimentally validates the performance of an active islanding detection method under various scenarios. The method actively injects a negative-sequence current through the interface voltage-sourced converter (VSC) of a distributed generation (DG) unit, as a disturbance signal for islanding detection. The estimated magnitude of the corresponding negative-sequence voltage at the PCC is used as the islanding detection signal. It is also analytically shown that the islanding detection method has a non-detection zone (NDZ), and a method to eliminate the NDZ is proposed. Moreover, the effectiveness of the modified method in eliminating the NDZ is verified based on simulation results in PSCAD/EMTDC software environment and experimental tests.;The feasibility of the islanding detection method for islanding detection in two-DG systems is also experimentally investigated. Moreover, based on the analyzed controller, a control strategy for autonomous operation of two-DG systems is proposed, and its performance is experimentally evaluated. Then, adopting the islanding detection method and the proposed control strategy, the viability of smooth transitions from grid-connected modes to autonomous (islanded) modes in two-parallel DG systems is experimentally validated.;Moreover, the performance of an autonomous mode controller for islanded DG units is experimentally evaluated. Based on a robustness analysis, it is shown that the controller which is basically designed for the nominal plant, can maintain the stability of the system despite of significant load uncertainties. Then adopting the islanding detection method and the proposed controller, the viability of uninterruptible operation of a single-DG system subsequent to an islanding event is experimentally validated.