Torque Improvement of Dual-Rotor Coreless Stator AFPM Machine With Non-Overlapping Concentrated Winding for Counter-Rotating Ducted Fan Application

Due to structural attributes such as shorter axial dimensions, lighter stator weight, and easier rotor-fan integration, dual-rotor coreless stator axial flux permanent magnet (AFPM) machines with non-overlapping concentrated winding are more suitable as drive machines for counter-rotating ducted fans. However, although the elimination of the stator core reduces the weight of the machine, it also limits the torque output capability of the machine. To address the issue, first, the improvement method for the torque output capability of the machine is analyzed. Specifically, the influence of pole number on torque output capability from the perspectives of magnetomotive force (MMF) and rotor equivalent magnetic circuit is quantitatively analyzed to obtain design guideline for the pole number of the machine. Additionally, the design concept of Halbach permanent magnet (PM) array pattern based on maximum air gap flux density is investigated. To further augment the torque output capacity, an optimized PM array pattern is proposed. Subsequent to the design improvements, the torque output capability and loss characteristics of the machine are studied and compared. The torque output capability of the optimized 12-slot-14-pole (12s14p) dual-rotor coreless stator AFPM machine with non-overlapping concentrated winding has significantly increased. Finally, a coreless stator AFPM prototype is fabricated and tested for verification.