Robust Saliency-Based Speed Sensorless Control of Induction Machines under Overload Operation

The stable vector control at very low speeds and standstill is only possible using saliency extraction methods. There exist specific designs that lead to induction machines having a significant rotor slotting saliency. The slotting signal, in interaction with the magnetic saturation saliency signal, generates unavoidably a further harmonic, often referred as intermodulation harmonic. In this sense, some motors can show three main harmonics: saturation, slotting and intermodulation. In available literature, intermodulation has been treated as a distortion and thus compensated using filtering or feed-forward methods. Yet, this paper proposes to employ the intermodulation saliency harmonic itself as control signal. Applying a voltage step excitation strategy to an induction motor, an intermodulation saliency vector will be acquired using the resulting phase current derivatives and signal processing. Experimental results measured on an induction motor will show that the intermodulation saliency harmonic can deliver a robust and very accurate rotor position, especially when operated in the overload range.