Influence of Induction Machine Loads on Islanding Detection by Inverter-Based Distributed Generation

An inverter-based distributed generation system with an interface unit called power conditioning subsystem (PCS) is required to prevent unintentional islanding immediately. Although the run-on time increases in a local isolated grid that includes an induction machine, the mechanism has not been clarified. In this study, first, an anti-islanding test system used for the PCS certification test in Japan was set up, and it was found that most of the reactive power provided by the PCS to promote frequency deviations was absorbed by the connected induction machine. Second, a modified equivalent circuit of a three-phase induction machine was proposed to simulate their behaviors numerically. The simulation results showed good agreement with the experimental results. Especially, the transient absorption of negative reactive power by the induction machine was accurately reproduced. Third, to investigate the mechanism behind the prolongation of the run-on time, the influence of the inertia of the induction machine was analyzed. It was found that there are worst values of moment of inertia that cause the least frequency fluctuation and the longest run-on time under respective islanding conditions. The results of this study contribute to a better understanding of the behavior and influence of induction machines under an islanding condition.