Islanding detection method for single-phase distributed generation systems based on inverters

The detection of the islanding condition of a distributed generation system is crucial for safety reason, as discussed in IEEE Standards, and specifically required by some national codes. Several anti-islanding methods have been investigated and classified as passive (measurement of the natural effects of islanding) and active (based on the measurement of the effects due to transients or harmonics deliberately introduced in the system). In case the power drained by the load matches the power generated by the DG inverter the effect of islanding are small and the passive detection methods fail. However the active methods that have been developed to overcome these limits create disturbances that can interact with those generated by other DG systems. In this paper a new anti-islanding method is proposed. It exploits the natural sensitivity to disturbances of a grid voltage sensorless control to highlight islanding condition. The adopted grid voltage sensorless control is adapted to a single-phase system with the use of resonant controllers on the basis of the internal model control law: a resonant controller-based observer results. Then a Kalman-filter-based algorithm is used to detect the islanding condition on the basis of the energy mismatch between the estimated 3^rd and 5^th harmonics and the real ones. Simulation and experimental results support the analysis.