Electromagnetic Vibration-Prediction Process in Interior Permanent Magnet Synchronous Motors Using an Air Gap Relative Permeance Formula

Interior permanent magnet synchronous motors have the advantage of being applicable to various fields owing to their high torque density and wide operating range but have the disadvantage of large electromagnetic vibrations. To calculate the electromagnetic vibration, analysis of the magnetic flux density of the air gap using the finite element method (FEM) is essential. This process requires a significant amount of time because of the use of many analysis models. The radial force, which is the source of vibration, is expressed as the square of the air gap magnetic flux density, the vibration can be predicted in advance by calculating the waveform of the air gap magnetic flux density using a formula. In this paper, a new air gap relative permeance formula is proposed when an offset is applied to the outer diameter of the rotor to reduce electromagnetic vibration. By calculating the waveform of the air gap magnetic flux density using the proposed air gap relative permeance formula, a model with a minimum total harmonic distortion is selected. The validity of the formula was confirmed by comparing the FEM result with the waveform of the air gap magnetic flux density calculated using the proposed formula. The proposed model minimized the vibration and was confirmed using FEM. Using the proposed formula, vibration can be easily and quickly predicted in analytic way. The prototype of the final model was developed and compared using FEM, and the validity of the analysis result was confirmed.