Discrete-Time Current Regulator for AC Machine Drives

Abstract

In a practical alternating current (ac) machine drive system, a zero-order hold equivalent discrete-time machine model motivates the development of a direct discrete-time current regulator structure. However, it is complicated to establish the direct discrete-time current regulator for asymmetric machine<xref ref-type="fn" rid="fn1">¹</xref><fn id="fn1"><label>¹</label> Asymmetric machine denotes a ac salient machine in this article, whereas the symmetric machine denotes a ac non-salient machine. </fn> model due to the involvement of complex matrix exponential related to unequal machine inductance parameters. In order to overcome this barrier, a novel direct discrete-time current regulator based on the flux model is proposed, where a modified ac machine model considering delay compensation is developed and a new feed-forward voltage compensation is designed to eliminate the matrix exponential. In addition, a discrete-time flux observer is proposed and can work in the proposed current regulator to suppress the adverse one-step delay effect on the feed-forward voltage compensation and current regulator. The theoretical analysis has shown that the proposed discrete-time current regulator and flux observer have good parameter robustness and stability. Also, the experimental verification is performed on an ac machine drive test rig.