Structural analysis of the interior PM rotor considering both static and fatigue loading

Interior permanent magnet synchronous machines result to be a valid motor topology in case of both high efficiency and high flux-weakening range. These interesting peculiarities can be profitably achieved adopting a salient rotor structure. However, the design of an anisotropic rotor equipped with a multi flux-barrier structure is a very challenging task due to two conflicting requirements: (i) torque performance and (ii) structural integrity. The necessary iron bridges between the multiple rotor cavities, in which the permanent magnets are inset, represent a magnetic short circuit reducing the overall air gap flux. The structural strength assessments under static and fatigue loading of a radially laminated interior permanent magnet rotor are presented. The static resistance is assessed by using a classical approach in mechanical structural design, while the fatigue assessment required careful considerations due to the reduced values of the tip radius of the cavities, which induce severe stress concentration effects. Then the fatigue assessments are carried out using both the classical notch sensitivity theory and a more recent approach based on a non-conventional extension of the Fracture Mechanics discipline. As a result, both static and fatigue strengths are assessed successfully.