Design of Low Rating Axial Flux Permanent Magnet Brushless DC Motor

Abstract

The drop in prices of rare-earth permanent magnet (PM) materials and progress in power electronics have played an important role in the development of PM brushless machines in the last three decade. These machines have recently become mature and their high efficiency, power density and reliability has led to PM brushless machines successfully replacing D.C commutator machines and cage induction machines in many areas. The axial flux P (AFPM) brushless machine, also called the disctype machine, is an attractive alternative to its cylindrical radial flux counter part due to the pancake shape, compact construction and high torque density. Axial flux machines have undergone a tremendous development in the past decade and are widely used in Pump, Fan, Wheel, Floppy disc drives, wind power generation and high performance direct drive servo applications. With the advent of modern high-energy magnets (like Neodymium Iron Boron (NdFeB)), slotless and coreles structures are possible resulting in small overall size, weight and less torque ripple (low cogging torque). The power range of AFPM brushless machine is now from a fraction of a watt to sub-MW. The main objective of this work is to develop a design methodology for axial flux machine from the basic sizing and force equation.