Complete Stability of Reduced-Order and Full-Order Observers for Sensorless IM Drives

In this paper, reduced-order observers for flux and speed estimation of sensorless induction-motor drives are analyzed. All gain selections, which give stability for all operating conditions, including the regeneration mode (called complete stability), are found. Furthermore, it is shown that full-order observers, under the assumption of fast stator-current dynamics, have equivalent implementations as reduced-order observers. Consequently, all gain selections of the full-order observer gains for which complete stability is obtained, under the assumption stated, are also found. A number of previously proposed full-order observers are analyzed within the developed framework, generally showing agreement between the full- and reduced-order models.