Abstract：In unmanned aerial vehicle (UAV) noise fields, extensive research on propeller noise generation mechanisms and suppression methods has achieved remarkable results. The noise radiated by UAV motors has become a new research focus. The study addresses a 17 kW UAV with a surface-mounted external rotor permanent magnet synchronous motor. The existing methods reduce the motor output torque but increase manufacturing complexity. Therefore, the paper proposes an optimization method for pole and stator slotting parameters to improve the motor vibration noise without reducing the output torque. Since radial air-gap flux density and radial electromagnetic force cause motor vibration noises, the space harmonic characteristics of the radial air-gap flux density are analyzed according to the effects of the magnetic pole and stator slotting parameters on the amplitude of low-order radial air-gap flux density. Rotor modal simulation is carried out to investigate the mechanism of the radial electromagnetic force and the motor space modes. Then, the characteristics of electromagnetic vibration noises at multiple speeds are analyzed, focusing on the vibration noise at a cruising speed of 1 880 r/min. A multi-objective optimization mathematical model is established using a hybrid particle swarm optimization algorithm, taking the average torque, torque pulsation, and flux density fundamental wave amplitude as the constraints. After comparing three alternatives, Scheme 1 is selected as the optimization scheme. The simulation shows that the amplitude of the 3rd and 5th-order components of the radial air gap magnetization is decreased by 45.57% and 60.92% compared with the original scheme. The magnitude of the radial electromagnetic force decreases by 5.88% in the fundamental component, 33.03% in the 2nd component, and 6.81% in the 4th component. The torque fluctuation of Scheme 1 decreases by 32% when the average torque is almost unchanged. Experimental results show that after structure optimization, the electromagnetic vibration tip noise at the cruising speed is reduced by 6.36 dB from the initial 71.61 dB to 65.25 dB, and the overall performance of the motor vibration noise is improved at multiple speeds. The optimized structure significantly suppresses the UAV motor tip vibration noise at the cruising speed. In addition, the average torque is 87.44 N·m for the original scheme and 87.56 N·m for the optimized scheme, and the average torque is almost constant. The torque pulsation is 3.30%, and the torque fluctuation of the optimized scheme is 2.16%. The overall decrease in torque fluctuation is 34.5%. The optimized structure reduces the tip noise of the motor and optimizes the torque pulsation.
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2024, Vol. 39 
