An Improved Passive Anti-islanding Technique for Distributed-generation Photovoltaic Systems

Islanding detection techniques for DGPV are employed in order to determine the status of the electrical grid. In fact, the grid-connected inverter must be stopped once the islanding operating mode is detected according to standards and grid-code limits. Passive anti-islanding techniques monitor grid parameters to detect islanding. One advantage of passive techniques is a lower THD injected into the grid by active techniques. Thus, passive techniques were studied and an improved passive detection technique was proposed in this paper. The ratio of phase variation and the voltage variation at the point of common coupling (PCC) was adopted to detect islanding. In addition, this method combined with the under/over voltage detection and the under/over frequency detection. Then, the proposed technique not only has the merit of low cost and easy to operate, but also has multiple judgment and high reliability. The simulation results under Matlab/Simulink show that the proposed technique is very effective in reducing the non-detection zone and that the islanding operation can be detected more rapidly and effectively than traditional passive techniques, and that it can not misjudge when the load reduce suddenly.