Adaptive Active Islanding Detection Strategy Enhanced with Fault Ride-Through Capability for Grid-Tied Inverters

The performance requirements of Grid-Tied Inverters (GTI) are regularly updated as the penetration of Distributed Generation (DG) increases. In view of improved reliability, the GTIs are required to add on the feature of low or high voltage ride-through (VRT). However, few studies are available to assess the impact of VRT methods on the existing control of the GTI, especially in terms of the implementation of islanding detection (ID). It is observed that the requirements for low VRT and ID are contradictory i.e., for certain low voltage levels, while low VRT assumes fault in the grid and demands continued operation, ID assumes the system to be islanded and tries to trip or initiate transfer to intentional islanded operation. Hence, it is important that the ID method differentiates between events corresponding to fault in the grid that demands VRT and actual islanding. In this paper, a previously proposed method of ID that makes use of the constancy of a voltage to current ratio in response to a pattern of step changes in active power reference, is adapted to operate with low VRT successfully. It is shown that the method can effectively differentiate between a fault condition that demands VRT and an islanding phenomenon. Also, a method for balanced current injection even during unbalanced operation with current limiting action is devised and implemented. The method is validated through MATLAB/Simulink simulation and the results thereof are presented.