An Anti-Islanding for Multiple Photovoltaic Inverters using Harmonic Current Injections

Sutthipan Patthamakunchai, Mongkol Konghirun, Wanchak Lenwari

Abstract


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 (h), 5th and 9th harmonics. Due to its excellent algorithm looking at specific frequencies, the Goertzel algorithm is employed in this paper to identify frequency components. This algorithm extracts specific voltage component monitoring the change at the point of common coupling (PCC), as a result the islanding condition can be diagnosed by considering the change in impedance related to injecting harmonics during connecting and islanding condition. 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.


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