Comparative Study of Yokeless Dual-rotor and External-rotor Radial-Flux Fractional-Slot PM Machines

In this paper, electromagnetic performances of radial flux fractional-slot concentrated tooth-coil winding yokeless dual-rotor permanent magnet (YDRPM) machine and conventional external rotor surface-mounted PM (ERSPM) machine are compared. Both machines are optimized by genetic algorithm using finite element analysis under various optimization scenarios, i.e. with and without slot area restriction, different inner rotor bore diameter and pole number. It shows that the YDRPM machine has lower rated torque, but higher overload capability compared with the ERSPM machine, as also explained by the equivalent magnetic circuit.