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E. Montero, M Vogelsberger, T. Wolbank:
"Offset Estimation Strategies and Influence on Slotting Signal Resolution in Angular Voltage Step Excitation for Speed Sensorless Control of Induction Machines";
Poster: EPE 2019, Genova / Italy; 2019-09-03 - 2019-09-05; in: "Signal Resolution in Angular Voltage Step Excitation for Speed Sensorless Control of Induction Machines," XXI European Conference on Power Electronics and Applications", (2019), 1 - 9.

The stable operation around zero electrical frequency of sensorless AC drives requires the utilization of external injection techniques (as high frequency or as voltage step) in order to obtain a leakage inductance modulated by the machine inherent saliencies. During the last two decades, numerous attempts have been done in order to reduce the impact of the external injection in terms of current ripple. In this sense, strategies have calculated the machine position from the saliency-offset vector using the actual SVPWM switching states. The saliency-offset vector obtained from one active SVPWM switching state delivers, in induction machines, a huge load and sector dependent offset. Its elimination is critical to obtain the machine saliency (in this work, slotting), as a poor offset amplitude estimation distorts the saliency signal and may lead to an untraceable sensorless rotor angle. This paper will analyze the effect that offset estimation errors produce in the desired saliency vector, and will compare the accuracy of two estimation strategies based on mean and circle-fit functions.

Angular Voltage, Slotting Signal