Closed-Loop MRAS speed observer for linear induction motor drives

This paper presents a Closed-Loop Model Reference Adaptive System (CL-MRAS) speed observer developed for linear induction motor (LIM) drives. Starting from the structure of the CL-MRAS speed observer in literature, It is based on a LIM dynamic model taking into consideration the dynamic end-effects. Particularly, the following aspects are original: it employs the voltage and current models of the LIM considering the dynamic end effects, it proposes a net thrust model including the braking force caused by the dynamic end-effects, it considers the friction load of the LIM drive experimentally obtained with off-line tests. The proposed sensorless technique has been tested on a purposely developed experimental set-up. Results show that the CL-MRAS observer permits the drive to operate down to the speed of 0.02 m/s, i.e. about 0.03 % of the rated speed, which is about 10 times lower than the minimum working speed achieved with other observers implemented on the same LIM drive, like the TLS EXIN full-order Luenberger Observer and the TLS EXIN Kalman Filter.