An anti-islanding for multiple photovoltaic inverters using harmonic current injections

Islanding phenomenon is one of the major concerns in the distributed generator (DG) systems. Islanding occurs when one or more DGs supplied local loads without connecting to the grid utility. This unintentional condition must be detected with the minimum time possible to prevent the hazardous effects to a person worked in the system or equipment connected to the network. The two main methods of anti-islanding are passive and active methods. The passive methods are excellent in the speed of detection and power quality. However, the passive have relatively large non-detection zone (NDZ). On the other hands, the active methods have less relatively small NDZ and still provide a good speed of detection. This paper proposes an anti-islanding technique for multiple grid-connected inverters in photovoltaic (PV) system based on an active method. By injecting harmonic currents with the same or different harmonic orders and monitoring the change at the point of common coupling (PCC), the islanding condition can be diagnosed. Due to its excellent algorithm looking at specific frequencies, the Goertzel algorithm is employed in this paper to identify frequency components. Simulation results using PSIM software confirm the effectiveness to the technique in accordance with the requirements of the interconnection standards, IEEE Std. 1547 and IEEE Std. 929–2000.