Vector control system for induction motor without speed sensor at very low speed

The paper describes a vector control system for an induction motor operating in the very low speed range without a speed sensor. The system uses only current sensors in a closed loop control with rotor speed estimation and a PWM voltage source inverter. Online rotor speed estimation is based on utilizing a parallel model reference adaptive control system (MRAC). The modified flux model for speed estimator uses an ω_e-adaptation scheme, where the inputs estimated are ω_r and ω_s, reference command voltage signal V*_ds and V*_qs, and measured line current components I_ds and I_qs. The estimated flux components in this model can be compensated from the effects of offset errors on integral. The designed speed identification algorithm is then chosen to satisfy Popov´s hyperstability criterion. It can be compensated to the parameter variations and torque fluctuation with speed estimation in less then 63 rad/sec. The suggested control strategy and estimation method have been validated by simulation study. In the simulation, the proposed speed sensorless vector control system at very low speed range are shown to operate very well in spite of variable rotor time constant and load, without change the controller parameters