An MRAS - based full Order Luenberger Observer for Sensorless DRFOC of Induction Motors

Sbita Lassaâd and Ben Hamed Mouna
Research Unit of Modeling, Analysis and Control Systems, National Engineering School of Gabès (ENIG)-Tunisia,

Abstract

A new method for the implementation of a sensorless direct flux oriented control of induction motor drives is proposed in this paper. As the induction motor is decoupled if the direct rotor flux is maintained constant and equal to the nominal flux value and the reverse rotor flux is to be fixed at zero value. It is well known that the rotor flux of the induction motor is unmeasured. To cope with this problem and the drawbacks of the sensors, a combination of two observers is used: a full order Luenberger observer to estimate the rotor flux and a model reference adaptative system (MRAS) observer for rotor speed estimation. With the help of the observed (d, q) axis components of the rotor flux, the direct rotor field orientation vector control is implemented. We show by an extensive simulation study that the proposed method for DRFOC is completely satisfactory at low speed region and in field weakening region (high speeds). It is not sensitive to disturbances and parameters mismatch. Observers and control scheme are robust to changes in load torque. The method proposed achieves good performances with an optimal and adaptative gain tuning matrix obtained from the Linear Quadratic Regulator (LQR) design principle. Digital simulation results are presented to show the improvements in performance of the proposed method and the global stability of the MRAS based speed sensorless combined to flux observer scheme with the LQR matrix gain.

 Keywords: Induction motor, Direct rotor field oriented control, Luenberger Observer, MRAS and speed sensorless.

Biographies:

Lassaâd Sbita obtained the doctorate thesis onJuly 1997 in Electrical engineering from ESSTT of Tunis, Tunisia. He works as an associate Professor at the electrical-automatic genuis department of the Natioanl Engineering School of Gabès, Tunsia. He is manager of the research group on electric machine drives in the research Unit MACS-ENIG. His fields of interest include power electronics, machine drives, automatic control, modeling, observation and identication.

Mouna Ben Hamed obtained the Master degree on September 2006 in automatic and intelligent techniques from National engineering School of Gabès. She is a member of the research Unit MACS-ENIG. She is actually preparing the PhD in the field of sensorless induction motor drives. She works actually as assistant professor at the National Engineering School of Gabès-University of Gabès -Tunisia.

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