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Islanding detection is a mandatory feature for grid-connected inverters. The effectiveness of passive islanding detection methods (IDMs) is usually demonstrated by means of nondetection zones (NDZs) represented in a power mismatch space (ΔP versus ΔQ). Active frequency drifting IDMs have been shown to provide improved performance but their theoretical NDZ cannot be described in the ΔP versus ΔQ space for a general RLC load. This paper shows that a load parameter space based on the values of the quality factor and resonant frequency of the local load (Qf versus f0) can be used in these cases. It employs a single curve to represent the NDZ of frequency drifting IDMs for any RLC loads. Equations that represent NDZs of three common active IDMs in the Qf versus f0 load parameter space are derived and it is shown that the slip mode frequency shift and the Sandia frequency shift IDMs can be designed to guarantee islanding detection for equivalent RLC loads with a quality factor smaller than a design value. The accuracy of the NDZs is verified with simulation and experimental results.
Date of Publication: March 2006