Control limit of speed sensorless field-oriented drive for induction motor based on phase difference

Speed sensorless field-oriented control strategies that estimate rotor speed are being researched and many methods have been presented. However, in general, complex calculations are necessary to estimate the rotor speed. In this paper, an original sensorless field-oriented control method for induction motor using easy and simple speed estimation is presented. In the proposed method, the motor speed is estimated by measuring the command frequency and the phase difference between the stator current vector and the stator voltage vector. By comparing the measured values with a table of data measured beforehand, the rotor speed can be estimated satisfactorily through simple calculations. However, there are control limits in this method. The authors clarify the control limit of speed sensorless field-oriented drive for an induction motor based on phase difference by calculating T-type equivalent circuit.