Distributed generation has been greatly introduced into electrical power systems during the last several decades. Providing protection against islanding is probably one of the most challenging issues addressed in distributed generation applications. The positive feedback anti-islanding scheme for inverter-based distributed generators has gained wide acceptance. This scheme has a destabilizing effect on the supply system. Although a single inverter's destabilizing force is small, the collective impact of the destabilizing force produced by a large number of distributed generators may be significant. This impact may make the anti-islanding scheme less effective or may cause problems to the supply power system.

The objective of this thesis is to determine the impact of inverter-based distributed generators on power systems and the interactions among the distributed generators due to the positive feedback anti-islanding control. Four related topics are covered in the thesis. First, small-signal models representing the interconnected inverter-based distributed generation systems and the associated anti-islanding actions are established. These models provide the analytical tools for the work conducted in the other topics. The models' validity is evaluated by using electromagnetic transient simulation programs. Second, the nature and characteristics of a single inverter's impact on power systems are investigated. The relationship between the positive feedback anti-islanding control strength and the single distributed generator power transfer capability is quantified. Third, the nature and characteristics of the collective impact of multiple inverters and their anti-islanding activities on power systems arc studied. The small-signal stability of the distributed generation system with multiple inverters and the interferences among the generators are analyzed. Last, the islanding protection performance of the positive feedback anti-islanding scheme is evaluated in terms of the stability.