Modeling of the influence of coil winding pattern on tooth forces in brushless DC motors

The use of neodymium and other rare earth magnets in brushless DC motors increases their torque, but also magnetically induced vibration due to rotating stator tooth force. This paper investigates the influence of the stator coil winding pattern on stator tooth force and torque from three common winding patterns, e.g., center-tapped-wye (CTY), wye (Y) and delta (Δ), with equivalent torque output. Stator tooth forces and torque in a 6-pole, 9-tooth, 3-phase motor were calculated from the flux density using finite element analysis and the Maxwell stress tensor. Their frequency spectra were analyzed through multi-dimensional spectral analysis. The analyses show that the driving frequencies of tooth forces appear at the integer multiple of rotor speed multiplied by the number of pole. The driving frequencies of forces have larger amplitudes at the leading edge than at the trailing edge of the tooth. At low frequencies, CTY and Δ windings produce larger amplitudes at the leading edge and smaller amplitudes at the trailing edge than those of Y winding. Y windings may produce higher torque ripple than the other winding patterns