Investigating the dependence of induction machines transient reactances on stator teeth saturation reference to sensorless control

Control of induction machines without mechanical sensors has gained more and more interest in the past years. Different methods for zero-speed sensorless control have been proposed in literature. Most of them use parasitic effects which can be exploited with a transient or high frequency excitation of the machine, what is often denoted as saliency tracking, in order to extract the rotor or flux position. The most prominent inherent saliencies of a standard induction machine are induced by saturation and slotting and strongly depend on the machine design parameters. It is thus of high importance to know these dependencies before designing a machine for application in a sensorless control scheme. In this paper the influence of stator tooth saturation on the transient electrical behaviour of the machine is investigated with reference to the use in sensorless control. The measurements were made on induction machines with different stator design. The sensorless control scheme used is based on a transient excitation of the machine with voltage pulses. While the first machine is of standard design, the second machine has a considerably reduced tooth width leaving other geometric parameters as far as possible unchanged. The sensorless control signal consists of different harmonic components. Measurement results of the load and flux dependence of the harmonics caused by saturation and slotting are used to explain the mentioned influence