The design and implementation of a control system to introduce randomizationinto the control of a variable reluctance motor (VRM) is presented. The goal is to reduce noise generated by radial vibrations of the stator. Motor phase commutationangles are dithered by 1 or 2 mechanical degrees to investigate the effect ofrandomization on acoustic noise. VRM commutation points are varied using a uniform probability density function and a 4 state Markov chain among other methods.The theory of VRM and inverter operation and a derivation of the major source ofacoustic noise are developed.The experimental results show the effects of randomization. Uniform ditheringand Markov chain dithering both tend to spread the noise spectrum, reducing peaknoise components. No clear evidence is found to determine which is the optimumrandomization scheme. The benefit of commutation angle randomization in reducingVRM loudness as perceived by humans is found to be questionable.
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