Design and Analysis of PLL Speed Estimator for Sensorless Rotor-Flux Oriented Control of Induction Motor Drives

Speed sensorless control of induction motors, used in high-performance adjustable speed drives, is highly desirable because of increased mechanical robustness, reliability, especially in hostile environments, and low cost. In this paper, a second-order phase-locked loop (PLL) based speed estimator, detecting the phase angle of the rotor-flux vector, is presented and analyzed for speed estimation of the induction motor over a wide speed range. The rotor-flux has been estimated by a model reference adaptive flux observer using the current and voltage model of the induction motor. Mathematical analysis and apposite simulation results for a 355 kW IM drive are presented to validate the presented speed and flux estimation methods.