Thermal Analysis of Foil Wound Concentrated Coils for Use in Axial Flux Permanent Magnet Alternators

Axial flux permanent magnet (AFPM) generators for small-scale wind turbine applications have proven to be a useful design due to their reliability and ease of construction. Their stators have been realized using concentrate coils of enameled copper wires embedded in an epoxy-resin composite mixture. A static setting, opposed to a dynamic machine environment, is utilized to study the steady state thermal properties of five different variations of a single concentrated coil. This study was conducted to better understand the heat transfer properties, as well as verify other claims that foil windings have superior thermal characteristics over their round conductor counterpart. Although foil windings have been used in transformers and air core inductors, they have rarely been used in modern electric machines. There is an increasing demand for electric machines to play a larger role in a variety of industries. Electric machines boast a high efficiency and control sophistication which makes them an attractive alternative for many applications where mechanical power, in one form or another, is required. Notably in the aerospace industry there is a call for a more electric aircraft to reduce weight and improve reliability. Traditional pneumatic and hydraulic systems, however, offer power densities that remain difficult to match for electric machines. Axial flux machines have several advantages to their radial flux machine counterparts, especially in terms of power density. However, both radial and axial flux machines that exhibit high power densities are consequently subjected to a high temperature environment. As a result, high power density electric machines have many thermal related failures, particularly in the stator windings. Thermal issues for electric machines have been recognized both in industry and academia, but the investigations are typically application specific. This novel foil winding approach demands a more comprehensive study. In order to isolate the steady state thermal properties of a concentrated coil, a static setting, as opposed to a dynamic machine environment, is used. A variety of concentrated coils are constructed to create a comparative study between different coil winding designs. Specifically, a baseline design of a standard copper round conductor 4 magnet wire will be compared against different copper foil winding configurations. Two experiments are conducted to determine the temperature variation over an increasing DC current input. Additionally, an analytical lumped parameter (LP) model is developed to obtain a fast and accurate overview of the thermal behavior of the foil wound concentrated coils. Isolating the windings can help …