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To be connected to the utility grid, renewable energy systems must provide high quality power, guarantee safe interaction with the grid, and be protected from abnormal operating conditions, including islanding. The paper presents islanding protection methods relevant to the Hydrogen Research Institute's photovoltaic/wind hybrid system, and the particularities of grid-connected inverters. A commercial system is tested to make sure its utility disconnect, over/under voltage and over/under frequency protection systems operate properly. Grid-connected inverters are classified based on commutation technique and an overview of islanding protection methods is presented.