Characteristics of a permanent-magnet synchronous motor with a dual-molding permanent-magnet rotor

A dual-molding magnet rotor was evaluated as a soft magnetic composite for the magnetic material of the rotor of a motor. Especially the possibility of using a dual-molding magnet rotor as means to improve motor efficiency was investigated. A dual-molding magnet rotor was a one-piece permanent magnet rotor made with bonded NdFeB magnet and soft magnetic composite core. A permanent-magnet synchronous motor was targeted for evaluation, and three types of dual-molding magnet rotors with different magnetic orientations were evaluated using the finite element method (FEM) and a trial model of test motor. It was confirmed that the cogging torque originated in the variation of the rotor element decreased because the pole-pitch accuracy and the outer-size accuracy were improved by utilizing a one-piece molding in the dual-molding magnet rotor. In spite a difference in the maximum energy products of the three magnets of about three times, the difference between maximum efficiency of the sintered rare-earth radial ring magnet and the isotropic-multi-pole oriented magnet and that between the former and the anisotropic-pole-concentrate oriented magnet are within 1%. The evaluation results show that the structure of dual-molding-magnet-rotor is superior to sintered rare-earth radial ring magnet rotor.