Prediction of Rotor Slotting Harmonics in Induction Machines in the Presence of Air-gap Eccentricity

The paper analyses the influence of induction machine (IM) design on rotor slotting harmonics used for sensorless control strategies. These harmonics have a direct impact on flux and rotor position estimation accuracy. Therefore prediction of their magnitude helps in selecting suitable machine designs with regard to stator/rotor slotting and winding configuration. The paper at hand focuses on the effects that lead to the formation of the rotor slotting harmonic, by analyzing them with a simplified inductance phasor model, finite element (FE) simulations and measurement results. These three means are used to prove the existence of certain machine slotting and winding configurations that result in rotor slotting harmonic mitigation, or even complete cancelation. As will be shown, the magnitude of this mitigation effect is directly linked to a fault induced asymmetry originating from mixed (static and dynamic) rotor eccentricity within the machine.