Reduction of low-frequency noise and vibration for low-speed high-torque permanent magnet synchronous machines

This paper deals with the improvement of lowfrequency noise and vibration (NV) performance for low-speed high-torque permanent magnet synchronous machines (PMSMs). The low-frequency NV refers to that induced by the PM field harmonics and the low-frequency current harmonics, as well as their interactions. In the paper, it is proposed to weaken the effect of local force by choosing suitable pole-slot combinations firstly, and then suppress the effect of global force, i.e., torque ripple and cogging torque, by reducing the torque harmonics for further optimization. The configurations of 12-pole/18-slot and 6-pole/36-slot are finally selected. It is found a better configuration to suppress the effect of local force is usually at expense of worse torque characteristic, if the number of slots is fixed. PM shaping and step skewing are used to further reduce the torque ripple and cogging torque for both machines. In the end, the vibrations of the machines have been successfully largely suppressed, and the total sound power levels are distinctly cut down by at least 30 dBA for both machines, whether under no-load condition or rated-load condition.