A sensorless torque control system for induction
motors was developed in this research. The system allows for
fast and precise torque tracking over a wide range of speed.
Unlike most research in the area, the authors used an
induction motor model that adapts its parameters to the
operating conditions. An adaptive sliding mode observer is
developed for speed observation and a cascade of discrete time
sliding mode controllers is used for flux and current control. A
least-square estimation speed estimation method is used at
very low speed (below 20 rpm). Simulation and experimental
results prove the validity of the approach.