Sequence-decoupled resonant controller for three-phase grid-connected inverters

This paper proposes a set of sequence-decoupled resonant controllers constructed with an easy-to-implement structure. It shows that either positive-sequence or negative-sequence components of three-phase unbalanced AC signals can be regulated individually in the stationary frame, while conventional and widely used resonant controllers cannot separately cope with these two sequences. Consequently, the extraction of the corresponding sequence component is not necessary for an individual sequence's control. Moreover, controllers designed for positive and negative sequences can be assigned with different gains to meet practical applications. The principle of new sequence-decoupled resonant controllers is described based on a multi-state-variable structure. In addition, the relation with conventional resonant controllers is investigated. The controllers are found to be equivalent when dealing with both sequences together. Furthermore, two examples are presented to show the application of the proposed controller. The effectiveness of the proposed new controller and its performance in the two system applications are verified by experiments.