Stator-flux-oriented sensorless induction motor drive for optimum low-speed performance

For high-performance AC drives, the speed-sensorless vector control of induction motors has received increasing attention from the standpoints of cost, size, noise immunity, and reliability. This paper presents the speed- and voltage-sensorless drive of vector-controlled induction motors for general-purpose drive applications. The rotor speed is determined by the difference between the synchronous angular frequency and the estimated slip angular frequency, which is estimated by the detected stator current and the stator-flux reference. To improve the low-speed drive characteristics, accurate applied-voltage calculation is proposed under considerations of the compensations for the quantization error in the digital controller, the forward voltage drop of switching devices, and the dead time of the inverter. The experimental studies show the improved drive characteristics