A new hybrid anti-islanding algorithm in grid connected three-phase inverter system

Passive and active methods are two major categories of anti-islanding approaches which are being widely used in grid-connected distributed generation (DG) systems. Passive anti-islanding techniques have no negative impact on the inverter's performance however large non-detection zone is the shortcoming of these techniques. On the other hand, active approaches have smaller non-detection zone, but these active approaches inevitably have negative impact on inverter's performance. To solve these problems, a new hybrid of both passive and active anti-islanding algorithm is proposed in this paper. A covariance index is used as a passive indicator to activate an active anti-islanding action, adaptive reactive power shift action, which can intelligently vary the output reactive power of the DG system to realize the anti-islanding protections. Both simulation and experimental results have demonstrated that this new algorithm can provide a fast anti-islanding protection while assure the zero or the least perturbation in inverter's grid-connected operation.