Sensorless control of induction motor drives

TLDR

Sensorless induction motor drives are attractive because they eliminate mechanical speed sensors, offering low cost and high reliability, while vector control requires estimating the magnitude and orientation of the fundamental magnetic flux waves. This paper presents an overview of sensorless control systems for induction motors using signal flow graphs of complex space vector quantities. Rotor speed information is extracted from measured stator voltages and currents, employing open‑loop estimators or closed‑loop observers, as illustrated by the signal flow graphs. The reviewed methods differ in accuracy, robustness, and sensitivity to model parameter variations, yet dynamic performance and steady‑state speed accuracy at low speeds can be achieved by exploiting parasitic machine effects.

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 the information on the rotor speed is extracted from measured stator voltages and currents at the 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 in the low-speed range can be achieved by exploiting parasitic effects 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.