Multipolar Rotor with Loaf-Shaped Permanent Magnets

The patent applies curvature principle by designing the permanent magnets with a convex curvature that deviates from the rotor's circumferential curvature. Specifically, the magnet's outer surface has a radius of curvature that is larger than the rotor's circumferential radius, creating a deliberate mismatch. This curvature difference modifies the magnetic field distribution in the air gap, effectively reducing cogging torque while maintaining manufacturing feasibility through standardized magnet shapes.

The patent applies asymmetry principle by configuring the magnetization directions of adjacent permanent magnets at different angles relative to the radial direction. Instead of uniform radial magnetization, the magnets are magnetized at specific asymmetric angles (e.g., alternating angles such as 15° and -15° from radial). This asymmetric magnetization pattern creates a magnetic field distribution that suppresses specific harmonics, particularly the third harmonic in delta-connected motors, while maintaining acceptable structural simplicity.

The patent applies parameter changes principle by optimizing multiple parameters simultaneously: the convex curvature radius of the permanent magnets, the magnetization angles, the magnet arc spacing, and the magnet height. By carefully selecting these parameters, the patent achieves a balance where magnets can be closely spaced to maintain high power density while the specific curvature and angle configurations reduce magnetic interactions that cause cogging torque. The key parameter is the magnet's outer radius of curvature being deliberately larger than the rotor circumferential radius.