Stability Analysis of Induction Motor Drives Using Phase-Locked Loop Control System

This paper presents the analysis of an induction motor drive using a phase-locked loop speed control system. A linear continuous model of the drive is developed and the system response is analysed using conventional root locus techniques. Various compensating ``filters'' and feedback signals are considered and the need for addition of derivative feedback is shown. A sampled data model is used to study the effects of discrete phase detector output. Stability limits on speed are predicted. A drive was implemented and experimental results are presented to verify theoretical predictions.