Design and Analysis of a Two-phase BLDC Motor with Hybrid Permanent Magnet Material for Only-pull Drive Technique

Permanent magnets with high energy density are widely used for high performance permanent magnet (PM) machines. However, the cost increase of rare-earth magnets demand the effective utilization or the use of relatively thin magnets in PM machines. To reduce the consumption of rare-earth magnets, hybrid permanent magnets arrangements (combined with ferrite) have been used in various PM motors, and the demagnetization endurance has been investigated [1], [2]. The surface type and the spoke type magnets forming the parallel and serial magnetic circuits have been employed for the purpose of torque improvement. However, spoke type magnets and the thin surface magnets suffer the greater risk of irreversible demagnetization. Traditionally, the thick magnets are utilized to ensure the healthy operation of PM machines without irreversible demagnetization [3]. Recently, an only-pull drive technique have been developed in [4] to protect the thin magnets from irreversible demagnetization and discussed a surface mounted PM (SPM) motor to validate the effectiveness. This paper proposed a two-phase radial flux brushless DC (BLDC) motor comprising of hybrid permanent magnet material on the rotor; NdFeB in SPM type and ferrite in spoke type configuration. The purpose of this hybrid topology is to improve the output torque and to save both types of magnets from irreversible demagnetization at a time. The electromagnetic performance of the proposed motor has been compared with that of a basic two-phase SPM type motor driven by the only-pull drive technique. Further, the operating point of the both magnet types has been analyzed to confirm the safe operation of the proposed motor without irreversible demagnetization. The merits and demerits of the proposed operation are also discussed.