Reduction of Axial Magnetic Force and Starting Current in Single-Sided Axial-Flux Machine with Ring PM Unit and Flux-Weakening Control

This paper presents a novel single-sided axial-flux machine with a set of ring permanent magnet unit to reduce axial magnetic forces. The single-sided structure can be utilized in several applications of fans, blowers, pumps, and electric vehicles that have design constraints of short axial length. On the other hand, it generates extreme high axial force between the rotor permanent magnets and the stator core, and it causes serious vibrations of the rotor and damages to mechanical bearings. In this paper, the ring permanent magnet unit is proposed. It consists of two ring permanent magnets and a back yoke, and it is located on opposite side of the stator. Then, it can reduce the axial force because magnetic attraction force is generated in the opposite direction of the axial force. In addition, the flux-weakening control is applied to reduce the axial force. The reduction of the force contributes to reduce not only the rotor vibration but also starting currents. Furthermore, experimental results show the pump characteristics of flow rates and pressure, and rms currents and input power with and without the proposed ring permanent magnet unit.