A Novel Structure for Exterior-Rotor Switched Reluctance Machines

This paper proposes a novel structure for exterior- rotor switched reluctance machines (SRM). The proposed SRM possesses radial saliency and axial saliency such that a very high volumetric torque density can be achieved. Since reluctance torque originates from changes in reluctance within the magnetic circuit, introducing magnetic saliency in both radial and axial directions will contribute to development of higher torque within a given space. In the literature, radial flux and axial flux configurations of SRM have been studied separately. Significance of pole depth, pole arc, pole shoes, and yoke to increase torque are explored in the past for each configuration. The scope of optimization, however, can be further extended by a question - whether available space in a motor can be better utilized for space restricted applications. From this vantage point a hybrid configuration housing both radial and axial saliency will increase the effective area of airgap within which electromechanical energy conversion takes place. To accommodate the above goal an inner stator housing multi-phase toroidal winding on the yoke has been proposed and current excitation for each phase has been optimized. Using the proposed structure, the end windings have been kept to a minimum. Besides introducing this novel magnetic configuration, the corresponding magnetic field distribution, optimization schemes, impacts of different stator pole/rotor pole configurations have been discussed.