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T. Wolbank, R. Wöhrnschimmel:
"A study on the Transient Behaviour of Induction Machines with the help of Measurement Coils";
Talk: IEEE International Symposium on Industrial Electronics ISIE, Pusan, Korea; 2001-06-12 - 2001-06-16; in: "Proceedings", Vol.2 (2001), ISBN: 0-7803-7090-2; 1135 - 1140.

Abstract - Sensorless field oriented control of induction machines has been of high interest in recent years since the mechanical sensor increases the cost of a drive and decreases its reliability considerably. Methods which do not fail at zero fundamental frequency have to rely on non-fundamental effects of the motor. These effects are caused by saliencies which are mainly due to slotting and saturation of the iron core and become visible if the machine is excited with high frequency. From the machines response the desired information about flux- or rotorposition can be evaluated.
In this paper, voltage pulses applied by the inverter serve as the high frequency excitation. The change of the armature currents during these pulses is modulated with the machines saliencies and therefore a control signal can be extracted.
The magnitude of this modulation depends on the interaction of the stator coils with the saliencies and furthermore on the machine design. The scope of this paper is to describe these interactions with the help of measurement coils placed in standard induction machines. They allow to measure the flux change during the voltage pulses and after signal processing to interpret the transient behaviour.
Measurements were made with 3 different induction machines and the analysis of the measured signals will focus on the effect of stator and rotor slotting. One machine will be the reference machine while the second one has a distinct number of stator and rotor slots and the third machine differs in the stator winding scheme.
It will be seen that these two design parameters influence the signal component related to rotor slotting to a high extend. Maximizing this signal component is advantageous for sensorless position control. If the flux position wants to be detected, the machine design should be chosen to minimize the appropriate signal component.