A Unified Observer for Smooth Speed-Sensorless Drive Control of Induction Machines at Full Speed Range

This paper proposes a novel unified observer that combines a modified low-frequency signal injection (LFSI) estimator and an adaptive full-order (AFO) flux observer for smooth sensorless control of nonsalient induction machines at full speed range. The unified observer adopts the same architecture as the AFO, i.e., comprising a rotor speed estimator and a flux observer. The speed estimator dynamics are enforced by an error signal from either the modified LFSI or the AFO, based on a switching signal indicating the system’s observability at an operation point. In order to achieve a smooth transition during the switch, the LFSI channel is modified to enable the switching on the speed estimate derivative rather than the conventional approach of switching on the speed signal. A thorough theoretical analysis is provided. Simulations and experiments validate that the proposed unified observer results in smooth operation over the full speed range.