Improved design for minimizing torque ripples at BLDC motors used in washers

In this paper, a Brushless Direct Current (BLDC) motor is analyzed and redesigned for torque ripple reduction. This motor is produced and used for home appliances, specifically washers. Electromagnetic torque ripples are produced by two different effects in BLDC motors: first by reluctance discontinuities in the magnetic circuit (cogging), second by stator and rotor magneto motive force (MMF) harmonic interactions. A simple decrease in cogging torque can be achieved by changing some physical parameters such as magnet arc, slot openings, skewing etc. Similarly changing the winding type helps to decrease some harmonic component in the MMF. In this work, a systematic approach to identify and reduce the vibration sources is presented. Some torque ripple minimization techniques are proposed and simulation results are provided for the 24 slots, interior type BLDC motor used in washers. After various comparisons, the optimized solution is chosen for prototyping. The simulation and experimental results for the prototype is also presented. These results also supported with vibration and acoustic level measurement tests.