Switched reluctance motors (SRMs) are used in numerous applications due to their simple and robust structure. In addition to being mechanically and thermally robust, features such as high torque density, efficiency, and reliability, coupled with their fault tolerant structure and low manufacturing cost make SRMs quite attractive. SRMs are double salient pole motors. The stator has simple concentrated excitation windings, and there is no winding or magnet on the rotor. Although SRMs have many features and advantages, large torque ripple, vibration, and acoustic noise are the major disadvantages of these machines. The vibration and acoustic noise of SRMs are mainly generated by the radial forces. The radial forces cause deformation on the stator yoke, which results in vibrations and consequently, frame deformation. When these vibrations resonate with the motor body’s natural frequencies, the amplitude of the oscillations and the deformations are intensified. Hence, the acoustic noise increases significantly. The vibration and acoustic noise of SRMs have been deeply investigated throughout the years, and various methods are reported based on modifications on the motor structure and motor control for reducing them. Since this thesis is focused on the acoustic noise reduction techniques from the design perspective, the acoustic noise and vibration mitigation techniques based on the motor structure modifications are investigated. Existing methods are focused on the radial force reduction, motor natural frequency manipulation, and stator damping effect improvement. Although, improving one of these factors also improves the others, most previous studies focus on a single factor.
In this thesis, a new vibration and acoustic noise mitigation method is proposed. This method combines the radial force reduction and damping improvement on the stator. The radial force is reduced by introducing rectangular windows on the rotor and the stator poles, which result in a reduction on the stator deformation. In addition, damping elements that are diamond shaped air gaps are inserted into the stator back iron. The number, size, the distance between the elements, and the distance from the stator outer surface to the first air gap are adjusted to achieve the minimum stator deformation and consequently, the minimum acoustic noise. Analyses are performed with 2D/3D electromagnetic and mechanical finite element (FEAs) and vibration analyses tools, and the acoustic noise is reduced successfully.