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

Abstract

This study presents an enhanced method for simultaneously achieving optimised disturbance damping and axisdecoupling 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.

A Deadbeat PI Controller With Modified Feedforward for PMSM Under Low Carrier Ratio

“…To improve the performance of the controller and realize the decoupling function, jωrLsidq is introduced into the feedforward term of the PI controller, and the motor model is simplified to R-L form in SRF. However, when the motor operates at low carrier ratio, the decoupling capability of the PI controller is limited because of timedelay [23]. The feedforward with the current prediction proposed in [24] is added to eliminate time delay.…”