Evaluation of Techniques for Cross-Coupling Decoupling Between Orthogonal Axes in Double Synchronous Reference Frame Current Control

Current control in voltage source converters under balanced conditions is often performed by proportional-integral (PI) controllers in a single synchronous reference frame (SRF). The cross-coupling between its dq-axes is usually decoupled by a state-feedback (SF) decoupling technique, and less frequently by an alternative procedure based on complex vectors (CVs). In case of imbalance, the single SRF is commonly replaced by PI controllers in a pair of SRFs rotating with opposite sequences, which is known as double SRF control (DSRFC). It is generally assumed that the SF decoupling strategy can be applied to decouple the cross-coupling between the orthogonal axes of each SRF in DSRFC, as for a single SRF structure. This paper proves that the SF technique does not produce a noticeable improvement in DSRFC, because the terms added to each SRF interfere with those added to the opposite-sequence SRF; in addition, it is shown that the CV decoupling strategy, which has not been applied to DSRFC before, provides an enhancement in axes decoupling for low bandwidth values. Experimental results confirm the theory.