External-Rotor Switched Reluctance Motor for an Electric Bicycle

As a cost-effective, healthy, and environmental friendly personal mode of transportation, electric bicycles (E-bikes) are gaining an increasing market share from conventional bicycles and automobiles. Considering the legal rules in Ontario, Canada, a 500-W electric motor providing power assist makes the E-bike more attractive to urban commuters. The simple structure, high torque, and power density, as well as the potential for low cost make the switched reluctance machine (SRM) a strong candidate for E-bike traction. In this paper, a three-phase, external-rotor SRM with 6 stator poles and 10 rotor poles is designed for a representative E-bike. The design of an external rotor arrangement of the 6-10 SRM topology has not previously been reported, this brings the challenge of sizing the geometry of this topology, but the solution offers a new contribution to published works. The external-rotor arrangement is chosen to facilitate ease of integration into the wheel hub structure of a typical pedal bicycle. The increased rotor poles yield improved torque ripple reduction than more conventional (i.e., 6-4 and 12-8) SRM design, which is an essential feature for low-speed rider comfort. The final machine design is experimentally validated via a full system prototype and dynamometer test facility. Results highlight some limitation of the 2-D finite element analysis (FEA) study in terms of the winding inductance calculation, more accurate 3-D FEA model is implemented.