Active islanding of a current-controlled converter-interfaced DG

Islanding of a voltage source converter (VSC) equipped DG unit is considered in this paper. Some internal controller signals are implemented in the islanding detection method in order to provide a robust operation. Particularly, the estimated frequency of the grid voltage along with a point of common coupling (PCC) voltage regulator and a dynamic reference-current limiter are proposed for islanding detection algorithm. Using a PCC-voltage regulator adds the active, or dynamic, property for the detection algorithm and increases its reliability. Moreover, implementing a dynamic current limiter, a robust operation is achieved. Through the proper design of the current limiter, the DG unit can have the ability to ride-through voltage dips with magnitudes above a certain limit, which can be set according to the grid codes, and detect islanding if the voltage decreases beyond that limit. The algorithm has also been verified for the case of island motor loads, which is considered as the worst case since dynamic loads affect the grid states in the case of islanding.