Separation of different saliencies modulations for zero speed sensorless control of induction machines using Discrete Fourier Transform and on-line window length adaptation

Controlled operation of ac machines without mechanical sensor at the motor shaft at zero speed so far is only possible using signal injection methods and exploiting non-fundamental wave effects. By establishing a transient excitation of the machine with voltage pulses imposed by the inverter and evaluate the change of the machine line currents due to these pulses. This transient current change is influenced by the transient phase reactances and these in turn are modulated with the flux-and rotor position, which is the desired information for sensorless control. In this paper a special algorithm is proposed using DFT (discrete fourier transform) method for tracking the saturation and slotting components from the measured saliency signal. The proposed algorithm depends on adaptive window length changing. For tracking of one distinct saliency, its modulation is fixed to a specific harmonic order by changing the window length inversely with the speed of the machine.