COMPARISON AND EFFECTIVENESS OF SLIP MODE FREQUENCY SHIFT AND SANDIA FREQUENCY SHIFT ACTIVE METHODS FOR ISLANDING DETECTION IN SINGLE-PHASE GRID-CONNECTED PHOTOVOLTAIC SYSTEMS. JESR [Internet]. 2025 Jul. 31 [cited 2025 Sep. 13];30(4):7-18. Available from: https://jesr.ub.ro/journal/article/view/472