Design and analysis of dual-rotor, radial-flux, toroidally-wound, surface-mounted-PM machines

A novel machine family—dual-rotor, Radial-Flux, Toroidally-wound, Permanent-Magnet (RFTPM) machines—is proposed in order to improve electrical machine torque density and efficiency. Two concentric surface-mounted-PM steel rotors are located inside and outside of a torus shaped stator with back-to-back windings, respectively.; General purpose sizing equations, a direct analytical design approach including a set of equations, and several optimization processes have been developed. More accurate models of the air gap and zigzag leakage fluxes have been developed and proven by FEM analyses. Design guidelines have been developed and FEM analyses have been made as well.; The study has shown that the dual-rotor RFTPM machines can substantially improve the machine efficiency due to the greatly shortened end windings and boost the torque density by doubling the air gap and optimizing the machine aspect ratio. The ratio of the torque densities between dual-rotor RFTPM and conventional induction machines increases as the rated power increases. Even ferrite magnets can be employed in the slotted structure. The output torque can be as high as that achieved in axial flux machines using rare earth magnets. In addition, the cogging torque and associated noise can be reduced to a very low level at no additional cost or penalty by using three proposed unique techniques for the RFTPM machine: Varying Slot Opening Angular Width, Varying PM Angular Width, and Slot Opening Shifting.; A 3-HP prototype has been designed and built using ferrite magnets. The designed torque and efficiency have been experimentally verified at the steady state operation. The prototype torque density is as high as 2.9 times of that of the induction machine with the same rated power and speed.; This machine could be a potential candidate in many cases, especially suitable for the case where an outside rotor is preferred, such as fans and electric automobiles. Especially, it could be a good competitor with the strong potential in the aerospace industry due to its very high torque density and high efficiency.