This thesis describes a systematic investigation into the sources of acoustic noise and vibration in switched reluctance machines, and encompasses the vibrational behaviour ofudthe stator, the influence of control parameters, and an evaluation of the effectiveness ofudactive vibration cancellation.udThe influence of leading design parameters, such as the width and number of poles andudthe yoke thickness, and geometric asymmetries, such as lamination notches in the statorudcore, and the effect of the stator windings, the frame, the end-caps and the mountingudassembly, on the natural frequencies and modes of vibration are investigated, Chapter 3.udBoth two-dimensional and three-dimensional finite element analyses are employed, theudpredicted results being validated by measurements on various experimental models,udwhich consequently highlights the limitation of the finite element technique for highlyudcomplex structures with discontinuities in their fabrication. The influence of the massudand stiffness of the laminated stator core and the stator windings on the naturaludfrequencies and vibration modes is investigated, and effective material properties areuddeduced for the analyses. It is found that the number of poles and lamination notches onudthe stator influence the number of vibrational modes which occur in the audibleudfrequency range due to the introduction of dual natural frequencies, viz. symmetrical andudanti-symmetrical modes, which are shown to separate further in value as the asymmetriesudbecome more profound. As the diameter of the stator yoke is reduced the naturaludfrequencies increase, whereas increasing the thickness of the yoke and the adding of audframe and end-caps significantly increase the natural frequencies. The effect of the statorudpoles is to significantly reduce the stator natural frequencies, which are irrespective to audvariation to the width of the poles, a variation in their mass being annulled by theudresulting change in stiffness. Similarly, it is shown that the winding mass and stiffnessudoffset each other so that their influence is also relatively small, whereas, althoughudquantification of the damping is not within the aims of this thesis, it is apparent that theudwindings introduce a high level of damping which consequently limits the magnitude ofudthe vibrations and hence acoustic noise. Finally, the laminated nature of the core isudquantified and is shown to affect the effective material properties compared to anudequivalent solid core, and to increase the effective damping.udPrevious investigations have studied the influence of the drive control parameters, butudgenerally limit the analysis to either the frequency or time domain or to measurements of udthe sound pressure level, and are generally carried out in isolation. Therefore. theudinfluence of alternative operating modes and their associated control parameters on theudacoustic noise and vibration of an SR machine is thoroughly investigated. the resultsudbeing analysed in both the frequency and time domains, and compared withudmeasurements of the sound pressure level, Chapter 4. The noise and vibration whichudresults when the SR machine is operated under both voltage and current control. withudboth hard and soft chopping techniques, and various switching angles, and for variousudsampling and switching frequencies, is measured. The influence of speed and load is alsoudinvestigated, and the vibration and noise are also investigated under single pulse modeudoperation. It is found that hard chopping results in a noisier operation than with softudchopping due to increased current ripple, especially under current control. The noise andudvibration is clearly shown to differ under current control compared to voltage control andudsingle pulse mode, due to the random switching of the phase voltages resulting in widebandudharmonic spectra, thereby increasing the levels of all the mechanical resonances.udFurther, it is found that the noise and vibration increase with both speed and load. Inudgeneral, the increases in noise and vibration are attributed to an increase in the rate ofuddecay of current at phase turn-off, regardless of the control parameter underudinvestigation.udFinally, the effectiveness of active vibration cancellation for nOIse reduction isudinvestigated under typical operating modes in Chapter 5, which, for the first time, isudanalysed in both the frequency and time domains, and validated by measurements of theudsound pressure level. It is found that active vibration cancellation is less effective forudmachine stators which have more than one dominant vibration mode within the audibleudfrequency range, since the technique is only capable of applying active cancellation for audsingle vibration mode, thus any further resonances remain unaffected. Further, duringudchopping control, especially current control which results in random switching, it hasudbeen shown, for the first time, that the effective time-delay varies to that applied, thusudrendering the technique less effective. This is found to be attributed to the asynchronismudof the final chopping edge and point of phase turn-off, therefore preventing theudvibrations from being excited in anti-phase, as explained in section 5.6.
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