Design of an Induction Machine with an Additional Asymmetrical Rotor Winding Providing a Rotor-Fixed Anisotropy for Self-Sensing Control

To operate an induction machine (IM) with self-sensing control at low speed, the IM's rotor position can be detected if its high frequency (HF) inductance provides a rotor-fixed anisotropy. IMs do not exhibit a significant rotor-fixed anisotropy by design and have a stator field-fixed anisotropy due to iron saturation, which disturb self-sensing control. Thus, rotor position estimation is usually not possible at low speed. In this paper, a rotor with an additional asymmetrical winding is investigated to provide a detectable rotor-fixed anisotropy. The additional winding leads to a reduction of the HF flux in one rotor axis, while the HF flux in the other rotor axis remains approximately unchanged. It is shown that the resulting rotor-fixed anisotropy is dominant over the saturation-dependent anisotropy and how the additional winding affects the operating behavior of the machine. The novel rotor design has been manufactured and the IM has been successfully operated in self-sensing control on a test bench.