The Diagnostics of the rotor misalignment of a permanent magnet motor

Abstract

A mathematical model of the magnetic field in the working gap of a brushless motor is considered in a case of rotor misalignment arising during manufacture, for example, due to defects in end shields, or in operation due to bearing wear. a gap in a uniform (circular ring). The stator gearing is taken into account on average using the Carter coefficient, the magnetic field in the inhomogeneous air gap, created by the rotor magnets and the stator winding current, is assumed to be plane-parallel, having a two-dimensional character. It was found that the rotor misalignment associated with the rotational movement of the eccentricity causes nonsinusoidality of the idle EMF and pulsation of the electromagnetic moment with a frequency 3p times higher than the rotor speed. When the eccentricity is stationary, a variable EMF is induced along the rotor shaft, causing an alternating current in the circuit: shaft-bearings-bearing shields-stator housing. To clarify the nature of the defect in order to identify the actual misalignment of the rotor, it is recommended to control currents and voltages using specialized software and hardware complexes for spectrum analysis.