Reduction of noise and vibration in switched reluctance motors: new aspects

This paper describes recent work of the authors on an active noise cancellation techniques for switched reluctance drives. This work goes beyond the research previously published in the literature, in that vibration cancellation can now be equally effective at any motor speed. The proposed method focuses on the reduction of acoustic noise by inducing two minor stator vibrations that oppose each other. In order to achieve a significant reduction in acoustic noise, the magnitude of the two opposing vibrations must be approximately equal. This is achieved by adopting a two stage commutation method with an average negative voltage, V_n. At the commutation instant, a step change from the average chopping voltage, V_c, to V_n is initiated and a resulting vibration is induced. Half a mechanical resonant cycle of the stator later, a second step change in voltage from V_n to the negative supply voltage, -V_s, is induced. The resulting second vibration is 180° out of phase with the first vibration. The two opposing vibrations of equal magnitude almost completely cancel each other out. The level of the average negative voltage, V_n, must be continuously monitored and adjusted, depending on the motor running and base speeds in order to keep the magnitude of the two opposing vibrations equal. Experimental results demonstrate the effectiveness of the proposed method