design of a fractional slot concentrated winding double-speed afpm motor

In this paper, a new topology of fractional slot concentrated winding double rotor axial flux permanent magnet synchronous motor (fscw-drafpmsm) is introduced. the desired structure consists of a nonslotted stator core and two rotor discs. the pole number of the two rotors is different and these two rotors rotate at different speeds in opposite directions. a sample motor with an output power of 200 watts is designed with the proposed structure. the two rotors of this sample motor rotate with speeds of 1200 and 857 rpm. the finite element method (fem) is employed to evaluate the performance of the proposed structure. some performance characteristics of the case study machine, such as the back emf, input power, and electromagnetic torques of two rotors are presented to confirm the correctness of the operation of the proposed structure. in addition, the shifting technique is used to improve the back emf waveform of the machine. an analytical formula is proposed for calculating the fundamental component of the back emf waveform. the accuracy of the formula is approved by fem.