Axial Flux PMG

PM machines are increasingly becoming dominant machines with the cost competitiveness of high energy permanent magnets. These machines offer many unique features. They are usually more efficient because of the fact that field excitation losses are eliminated resulting in significant rotor loss reduction.

Axial flux machines are classified based on the rotor structure. It is termed an axial flux induction machine if the rotor structure is a squirrel cage; an axial flux surface mounted permanent magnet machine if the rotor is formed by surface mounted permanent magnets; and an axial flux interior PM machine if the rotor has an interior magnet structure. In this paper, the focus will be on axial flux surface mounted PM machines with different rotor configurations but there will be a short review of some other type of AFMs and applications as well.

The basic and simplest axial flux structure is the singlerotor- single-stator structure. The stator consists of a ring type winding embedded in epoxylike material and an iron disc which is manufactured from a simple tape wound iron core. The rotor is formed from a solid steel disc on which the magnets are embedded.

An axial-flux permanent-magnet machine with one-rotor-two-stators configuration has generally a weaker efficiency than a radial-flux permanent-magnet machine if for all designs the same electric loading, air-gap flux density and current density have been applied. On the other hand, axial-flux machines are usually smaller in volume, especially when compared to radial-flux machines for which the length ratio (axial length of stator stack vs. air-gap diameter) is below 0.5.

History of the Axial Flux Electrical Machine

The first electrical machine was a primitive axial flux machine constructed by Michael Faraday. Since then, continuous development of electrical machines resulted in the prevalence of the radial flux machine technology which already early in the 1900's held the market of electric machines. At that time, development trends were pushed by the materials and manufacturing methods available.