Predicting the parameters and performance of brushless DC motor including saturation and slotting effects and magnetic circuit variations

In this paper, an analytical model is developed to predict brushless DC (BDC) motor performance. The program developed is based on an approximate 2-D solution of the magnetic field in the cross section of the motor using a Fourier series approximation. Having the field solution, one can predict the airgap flux density, coil flux linkage, inductances, and back emf of the motor. Using this information, other performance variables of the motor such as current and torque-speed characteristics can be calculated. Iron saturation, motor losses, armature effect, and slotting effect are included in the model. The model can also predict the back emf waveform. The back emf waveform shows the generated voltage ripple due to winding distribution which is one of the sources of electromagnetic torque ripple. The program is capable of predicting performance variation due to symmetric and unsymmetric variation in magnetic circuit variations