Improved sensorless scalar control by a PLL tracking rotor slotting effects

This paper deals with a simple, computationally not demanding, low cost scalar sensorless control of induction motor drives. The speed estimation has been performed on the basis of a PLL (Phase Locked Loop) algorithm, whose centre bandwith is tuned on-line on the basis of the reference values of the supply and slip frequencies provided to the PWM. This results in the PLL to track properly the machine speed in a very wide speed range. The proposed approach has been tested experimentally on a test set-up. Results show a good behaviour of the scalar sensorless drive in a very wide speed range from rated speed down to as much as 6% of the rated speed.