Curvature Effects on Permanent Magnet Harmonic Losses of Surface-Mounted Permanent Magnet Machines

Permanent magnets mounted on the rotor (or mover) of surface-mounted permanent magnet (SPM) rotating (or linear) synchronous machines are exposed to armature reaction field magneto-motive force (MMF) space harmonics, which cause eddy currents and losses. Magnet losses in rotating machines are sometimes studied through simplified models where the air-gap geometry is linearized. This may lead to suppose that curvature plays a minor role. In order to verify the extent to which such assumption holds, explicit formulas are derived and assessed in this paper for magnet loss estimation in case of both linear and circular air-gap geometry. Then, magnet losses in rotating and linear machines having equal MMF harmonics, air-gap width and magnet height and material are compared and conclusions about curvature effects on permanent magnet losses are drawn.