Investigation of electromagnetic force components in SR machines: design and control issues

This paper presents the results of an investigation on components of the electromagnetic force in the airgap of an 8/6 switched reluctance machine (SRM). Using Maxwell stress method variations of radial and tangential force components with respect to saliency of the machine and saturation effects have been studied. Access to distribution of the force components acting on the rotor and stator enables us to provide a more accurate picture of the torque generation and vibration in this family of electric machines. Furthermore, distribution of magnetic forces under multiphase excitation has been studied in details. Our findings show that bipolar excitation of SRM phases, resulting in a short flux path magnetic circuit, favors its efficiency and power quality while generating slightly higher torque with less pulsation. This is a significant improvement especially for automotive current intensive applications where the difference in price of power electronics components can be justified. An experimental, 2 kW, 42 Volts, 8/6 SRM drive which has been designed and manufactured in our energy system laboratory was targeted for this study. In addition to our extensive finite element (FE) analysis, experimental work is being carried out on our motor to validate some of the findings of this investigation.