Islanding Detection Search Sequence for Distributed Power Generators Under AC Grid Faults

Grid-connected converters require advanced controllers in order to achieve high performance and meet country-specific anti-islanding standards. This paper presents a novel, high performance islanding search sequence (ISS) technique applied to four islanding detection methods. The salient aspects of the proposed determination technique reside in its fault-tolerant safety redundancy with rapid unintentional islanding detection integrated within: active-reactive power control, maximum power point tracking (MPPT) algorithm, and phase-locked loop routine. The islanding detection search sequence method is successfully implemented within a voltage-oriented inverter controller using a synchronously rotating reference frame. The ISS structure is designed with an adaptive strategy to achieve system stability and minimum impact on power quality, and is applicable to grid-connected distributed power generators. The adaptive search sequence results in fast detection, robust operation, and most importantly, a reduced reactive and active power injection. The proposed control structure and detection methods performance are demonstrated through experimental results of a three-phase, 20-kVA three-level neutral-point-clamped transformerless inverter. The evaluation results on the grid-interactive inverter include the islanding detection method integrated in the MPPT used in renewable energy harvesting applications.