Dual-rotor, radial-flux, toroidally-wound, permanent-magnet machines

A novel machine family - dual-rotor, Radial-Flux, Toroidally-wound, Permanent-Magnet (RFTPM) machines - is proposed in order to substantially improve machine torque density and efficiency. After the principles of operation, configurations, and features are discussed, the machine design and optimization guidelines are given. A prototype has been designed, built, and tested. The measured torque density of the prototype, which well matches the design value, is almost three times of that of the induction machine with the same power and speed. Meanwhile the efficiency is still kept high and the material cost is kept low by using ferrite magnets. Three novel approaches are proposed to reduce the cogging torque in RFTPM machines, whose validity is verified by FEA results and experimental measurements.