Control aspects of the dynamic negative sequence current injection of type 4 wind turbines

State-of-the-art distributed generation with a fully rated converter only injects positive sequence current into unbalanced faults. Recently, both publications and draft standards have suggested that the injection of negative sequence reactive current into unbalanced faults can have benefits for the power system. This paper discusses a selection of control aspects that are important for negative sequence current injection: negative sequence angle detection, converter current limitation, and voltage recovery after fault clearing. The impact of these control aspects, and negative sequence current injection in general, on the power system is also considered in the discussion.