Sensorless Position and Torque Control of Induction Motors Based on Transient Signal Injection and Advanced Signal Processing

Sensorless control of ac machines which is able to work even at zero speed can be realized using high frequency excitation. Different schemes have been presented recently, which use transient excitation caused by the switching of the voltage source inverter. Transient excitations of only one pair of test vectors are applied for each measurement in this paper. The signals resulting from transient excitation based sensorless control methods are composed of components caused by saturation, slotting, or anisotropy saliencies, as well as inter-modulation effects and an offset in the mean excitation direction. An accurate and reliable separation of the different signal components is possible even at high load levels using neural network technique and Fourier transform. Experimental results for sensorless control showing the tracking of rotor/flux position under rated flux, high torque levels at low as well as zero and high speed levels enabling torque and even position control.