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Alternatives to Replace Rare-Earth Permanent Magnet Motors in Direct Drive Applications

Direct drive motors are spotlighted due to their advantage, which can deliver directly the torque coming from the motors without gearboxes, belts, and so on. Especially, since rare-earth permanent magnet (PM) helps the motors have higher performance and downsizing, the PM is applied for the motors. This paper investigates alternatives to replace rare-earth PM motors employed in direct drive applications. The proposed motors are a surfaced PM (SPM) motor with non rare-earth PM, ferrite PM (Fe-PM), a spoke type motor with Fe-PM, a synchronous reluctance motor (SynRM), and a PM assisted SynRM (PMaSynRM). The analyzed results of each motor are compared with the results of the reference motor. In particularly, the demagnetization phenomenon of the motors with Fe-PM is analyzed, since the Fe-PM is easily demagnetized by the reversed flux. Overall, this paper suggests the pros and cons of each alternative to substitute for rare-earth PM motors.