Improved torque and speed estimation in sensorless induction motor drive

Sensorless vector control methods for induction motor drives are widely used not only to control systems into which the torque or speed sensor cannot be installed due to their environment, but also to achieve precise control of general purpose inverter systems. A new simple and accurate algorithm is presented in this paper. An accurate mathematical model of the induction motor is used for obtaining the relations of torque and speed variation with stator current. These relations are simulated by sixth order polynomial equations using the fitting method. The current coefficients of these polynomials are also simulated by eighth order polynomial equations function of frequency. So, torque and speed estimation is obtained by the digital measurement of stator current and frequency with reduced computational burden. Comparison of the computed results and experimental measurements are performed which verify the validity and accuracy of the proposed algorithm.