COMPARISON AND EFFECTIVENESS OF SLIP MODE FREQUENCY SHIFT AND SANDIA FREQUENCY SHIFT ACTIVE METHODS FOR ISLANDING DETECTION IN SINGLE-PHASE GRID-CONNECTED PHOTOVOLTAIC SYSTEMS. Journal of Engineering Studies and Research, [S. l.], v. 30, n. 4, p. 7–18, 2025. DOI: 10.29081/jesr.v30i4.001. Disponível em: https://jesr.ub.ro/journal/article/view/472. Acesso em: 13 sep. 2025.