Improved Complex-Coefficient Rotor Flux Observer with Offset Estimator for Sensorless Induction Motor Drives

The voltage model-based flux observer is widely used in induction motor sensorless drive systems. Conventional rotor flux observer suffers from DC offset and high-order harmonics, which degrade the estimation performance of rotor speed and position. To address the above issue, an improved complex-coefficient flux observer is proposed in this article, along with a detailed dynamic performance analysis of the proposed observer. Compared with the conventional complex-coefficient observer, the proposed observer can effectively suppress high-order harmonics. To further eliminate DC offset, an offset estimator with frequency adaptive gain is proposed. Owing to the designed adaptive gain obtained from the small signal model of the offset observer, the offset estimation error can converge rapidly at different operating frequencies. The effectiveness of the proposed flux observer and offset observer is verified through a series of experiments on a 1.5-kW induction motor sensorless drive platform.