Abstract
This paper deals with the possibility to replace rare-earth permanent magnet (PM) motors in direct drive applications. According to previous researches, there are alternatives such as surface-mounted PM motors and spoke-type motors adopting Ferrite PMs, synchronous reluctance motors, with or without the assistance of low-energy PMs. Few studies have been carried out to compare all models at once, thus it is hard to choose which type motor is to be preferred as a valid alternative of rare-earth PM motors in direct drive applications. In this paper, the representative candidates listed above are analyzed and the results are compared with that of a rare-earth PM motor, which is considered as a reference motor. Additionally, the demagnetization phenomenon of the motors with Ferrite PMs is deeply analyzed because this kind of PM may be easily demagnetized by the stator flux. Finally, both strengths and weaknesses of each alternative motors are highlighted.
Highlights
This paper considers some alternative motors to substitute for rare-earth permanent magnet (PM) motors in direct drive applications
According to the analysis presented above the spoke-type Ferrite PM motor has been chosen as a small-size prototype
This paper considers some alternatives to the NdFeB surface-mounted PM (SPM) motor for direct drive applications
Summary
Direct drive motors are spotlighted due to their advantages, among the others the higher efficiency and the lower cost of the system, because the electric motor is able to deliver directly the torque without mechanical transmission elements such as gearboxes, chains or belts [1,2,3]. PM [9,10], the residual flux density of the motor with ferrite PM is lower than that of the rare-earth PM motor by at least two to three times [11,12] Another candidate is the motors without PM, such as switched reluctance motor and synchronous reluctance motor (SynREL) [13,14]. The torque ripple of the PMaREL is still higher than that of the PM motor, such as the surface-mounted PM (SPM) or interior PM (IPM) motor All candidates have their advantages and disadvantages, but it is difficult to choose which one is the best from these pros and cons. This paper considers some alternative motors to substitute for rare-earth PM motors in direct drive applications These motors are analyzed and their performance is compared under the one criteria. The strengths and weaknesses of such alternative motors are found out through the comparison of their capability to meet specific requirements
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