A novel islanding detection method based on digital PLL for grid-connected converters

Phase-locked technique is necessary for grid-connected converters to exchange power with grid. This paper presented a digital phase-locked loop (DPLL) algorithm based on phase adjusting at positive zero-crossing of every cycle. And then, an islanding detection method was proposed based on the DPLL into which a phase deviation was induced via modifying the phase-locked error. The results of simulations and experiments validated the feasibility and effectiveness of the DPLL algorithm and the islanding detection method, and the practicalities of the proposed methods have been verified in a photovoltaic grid-connected converter.