A Novel Magnetizing-Curve Identification and Computer Storage Technique for Induction Machines Suitable for Online Application

Field orientation control of an induction machine often requires variable flux operation in either energy optimization mode or field-weakening mode above base speed. One way to generate accurate d-axis stator current reference at all operating points demands accurate knowledge about the magnetizing curve of the machine. This paper proposes a simple and accurate technique to identify the magnetizing curve, which assumes a synchronously rotating stator current axis as the d-axis. The proposed method can be implemented with the same hardware available for normal operation of the drive. The effect of parameter variation on the curve identification accuracy is also discussed. A “piecewise mixed model of approximation” is proposed to store the magnetizing curve in the processor memory for online application. The number of sections required by the proposed technique for accurate representation of the curve reduces drastically, compared to the widely used “piecewise linear model.” Different experiments performed on a practical machine validate the proposed concept.