Sensorless Control of Induction Machines at Low and Zero Speed by Using PWM Harmonics for Rotor-Bar Slotting Detection

This paper presents the use of the inherent high-frequency pulsewidth modulation (PWM) harmonics for sensorless control of ac machines. The amplitude and position of the PWM voltage harmonics cannot be controlled independently and are determined by the fundamental machine operation. However, they do form a high-frequency excitation and can provide information on saliencies within ac machines. This paper examines the feasibility of sensorless control based on extracting the rotor-bar slot position information for a cage induction machine using PWM harmonics. The position-signal demodulation and compensation schemes used are derived. Experimental results are provided for an off-the-shelf induction motor operating under sensorless current, speed, and position control, including zero excitation and zero speed.