Field weakening at high and low speed for sensorless vector controlled induction motor drives

This paper investigates field weakening in speed sensorless vector controlled induction motor drives. The sensorless drive uses direct field oriented control with a MRAS based speed and flux observer. The conventional case of field weakening for above rated speed operation is illustrated where the rotor time constant parameter is a function of flux and is derived from self-commissioning. A novel use of field weakening at zero or very low speed is introduced in order to maintain sensorless field orientation at zero/low speed under a wide range of loads.