Dynamic characteristics of synchronous motors applying a plural sub-magnets scheme to the rotor

This paper treats the optimization of rotor construction in the permanent magnet synchronous motor (PMSM). While the field system of PMSM has generally one magnet per pole, we replace the magnet with plural sub-magnets. The dimensions of each sub-magnet are determined by the concept of pulse width modulation (PWM). By adopting the proposed rotor construction, we can not only reduce the spare harmonics of the air-gap field but also provide space for damper winding around the direct-axis. From the investigation by hybrid FE-BE (coupled finite element and boundary element) method combined with both electric circuit and motion equation, we verify that the proposed construction is effective for practical use in view of both the harmonics reduction and the damping effects.