Modulation of the transient reactances of inverter fed induction motors by rotor fixed saliencies

To realise position control of an induction machine without a mechanical sensor it is necessary to exploit the slotting of the rotor and its influence on the terminal voltage and current respectively. Different rotor designs have already been proposed to generate a spatial influence of the rotor position on the transient terminal quantities. However, in this paper only conventionally designed machines are considered. The influence of rotor skewing, slot opening and saturation on the scope for sensorless position estimation is shown. The investigation of the transient electrical behaviour of the induction machine is done by two different measurement methods. First by applying the INFORM-method (indirect flux detection by on-line reactance measurement). It detects local differences in the stator impedance of the machine by evaluating the transient current change due to voltage pulses applied to the terminals of the machine. Usually the INFORM method is used to detect the saliencies caused by main flux saturation. However it can as well be utilised for position estimation. The second method is the determination of the transient flux-change by measurements made with special measurement coils at different spots in the machine. It is shown that sensorless position control with standard machines in the whole operating range is a very challenging task due to saturation