Design and Experimental Performance Assessment of an Outer Rotor PM-Assisted SynRM for the Electric Bike Propulsion

Brushless dc motor (BLDCM) is a conventional machine type used in the electric bike (e-bike) industry due to its simple controllability and drive system. However, the fluctuating price and scarcity of NdFeB magnets used in BLDCMs, lower power density compared to ac machines, and high torque ripple have pushed researchers in industry and academia to investigate technology alternatives to BLDCMs in e-bike applications. Permanent magnet-assisted synchronous reluctance motor (PMaSynRM) is an attractive option to this end because of its adjustable reluctance torque component and the recent advancements in finite-element (FE)-based design algorithms and implementation. Not yet covered in the existing literature and industry reports for e-bike applications, an in-hub outer rotor PMaSynRM is designed in this article to improve the power density and reduce the torque ripple characteristics for replacing a 500-W commercial BLDCM. The designed PMaSynRM is fabricated and tested to validate the power density and torque ripple improvements compared to an existing Golden Motor MP2 BLDCM counterpart.