The purpose of this paper is to characterize electromagnetic excitation forces in Interior Permanent Magnet (IPM) Brushless Direct Current (BLDC) motors and to investigate into their effects on noise and vibration.
Analysis of electromagnetic excitation sources in the IPM motors is far more difficult than in the SPM motors because magnetic saturations in the rotor core are more likely to occur in the former. In this paper, such sources were classified into three types and efficient methods were presented to characterize each source, and then contribution of the sources to the noise and vibration was investigated for an IPM motor.
One is so called cogging torque, for which an efficient technique of computation with saturation effects taken into account is proposed as a function of rotor position. In this technique, magnetic saturations in the rotor can be taken into account by employing the FEM just once for the slotless stator and effects of the stator slot are reflected by the concept of relative permeance.
Another is fluctuation of attractive forces in the radial direction between the stator and rotor. The distribution of radial attractive forces due to the magnetic flux by the permanent magnets in the rotor and electric currents in the stator is computed by an efficient technique, where significance of the magnetic flux due to the electric current that is often neglected in the SPM motors is pointed out.
The third is called ripples of mutual and reluctance torque, for which an equation is developed to characterize the combination of space harmonics of inductances and flux linkages related to permanent magnets and time harmonics of current. It is shown that the space and time harmonics are responsible for the torque ripples at three times the source frequency and their integer multiples.
Then, influences of structural dynamic characteristics such as natural frequencies and mode shapes as well as electromagnetic excitation forces on the noise and vibration are experimentally investigated for an IPM motor used in washing machines.