Slip-frequency controlled induction motor drives using digital phase-locked-loop control system

This paper presents a novel speed control scheme for an induction motor drive using digital phase-locked-loop. The slip-frequency control of induction motor is used to provide better performance characteristics of the motor and the phase-locked-loop technique is employed to provide extremely accurate speed regulation. The drive system is described and the control circuitry is outlined. An analytical model is developed and root locus analysis is used to evaluate the suitability of different feedbacks. An experimental model using a 5 HP induction motor is built and tested. System response is presented and compared for different filters in the feedback control system. Excellent speed regulation in the order of 0.01 per cent and a wide lock range have been obtained.