Sensorless Control of Induction Machines—With or Without Signal Injection?

TLDR

Sensorless induction motor drives eliminate shaft speed sensors, offering low cost and high reliability, while vector control requires estimating the magnitude and orientation of the fundamental magnetic flux waves in the stator or rotor. This paper aims to provide an insightful description of sensorless control systems for induction motors using signal flow graphs of complex space vector quantities. The authors extract rotor speed from measured stator currents and terminal voltages, employing open‑loop estimators or closed‑loop observers that differ in accuracy, robustness, and sensitivity to model parameters, and illustrate these techniques with signal flow graphs. Signal injection exploiting the machine’s anisotropic properties yields dynamic performance and steady‑state speed accuracy near zero speed.

Abstract

Controlled induction motor drives without mechanical speed sensors at the motor shaft have the attractions of low cost and high reliability. To replace the sensor, information on the rotor speed is extracted from measured stator currents and from voltages at motor terminals. Vector-controlled drives require estimating the magnitude and spatial orientation of the fundamental magnetic flux waves in the stator or in the rotor. Open-loop estimators or closed-loop observers are used for this purpose. They differ with respect to accuracy, robustness, and sensitivity against model parameter variations. Dynamic performance and steady-state speed accuracy around zero speed range are achieved by signal injection, exploiting the anisotropic properties of the machine. The overview in this paper uses signal flow graphs of complex space vector quantities to provide an insightful description of the systems used in sensorless control of induction motors.