Large time-delay decoupling and correction in synchronous complex-vector frame

This study presents an enhanced method for simultaneously achieving optimised disturbance damping and axis-decoupling in high-power converters operating in the synchronous rotating frame. High-power converters are considered here because they are normally constrained to a low-switching-to-fundamental pulse ratio, and hence experience a large control delay as a trade-off. This trade-off lowers bandwidth and phase margin, which in the synchronous frame, are further worsened by cross-coupling between the d - and q -axes. The proposed method, therefore, targets to remove axis-cross-coupling, so that the dynamics and stability of the high-power converter can be significantly improved, even with a large control delay. A procedure for optimising its performances has then been proposed, after evaluating pole-zero trajectories of three critical coefficients associated with filter decoupling, delay decoupling, and phase correction. Such coordinated evaluation using complex-vector models in the synchronous frame has previously not been performed and is hence a major contribution of the study. Simulation and experimental results presented have verified this contribution, the proposed method and its improvement over other recent methods found in the literature.