Performance Comparison of Dual-Rotor Radial-Flux and Axial-Flux Permanent-Magnet BLDC Machines

A novel machine family – dual-rotor, Radial-Flux, Permanent-Magnet (RFPM) machines -has demonstrated that it can substantially improve machine torque density and efficiency. The objective of this paper is to provide a performance comparison between two major alternatives of this technology: Surface-mounted dual-rotor RFPM machines and Axial-Flux Permanent-Magnet (AFPM) machines. The comparison is accomplished at four power levels ranging from 3 to 50 HP at a constant speed of 1800 RPM. The comparison includes material weights and costs, copper and iron losses, torque and power per unit active volume, torque per unit active material weight, magnet material effect, losses per unit airgap area, and machine efficiency. Pole number effects on both machine types are investigated as well. The results reveal an indication of the machine best suited with respect to performance criterion for a particular design requirement.