Comparative study of self-cooling PM machines with different winding structures

This paper compares several self-cooled permanent magnet machines having different winding configurations, including concentrated single-layer and double-layer windings as well as distributed winding. The self-cooling capability is achieved by integrating fan blades into the rotor hub, specifically, the space between the rotor core and the shaft. As rotor rotates, the fan blades draw air in through the inlets and expel it through the outlets, thereby facilitating the removal of heat generated in the windings and rotor-mounted permanent magnets. The study focuses on evaluating the maximum temperatures at key machine components, such as the magnets and end windings, under varying rotational speeds. Two scenarios have been considered in this study. One assumes that all the machines have the same copper loss density while with the core losses and magnet eddy current loss being neglected, and the other uses real losses obtained by finite element models. By conducting thermal analyses under these conditions, the self-cooling capability of permanent magnet machines with different winding structures can be comprehensively assessed. Thermal analyses based on computational fluid dynamics modelling are performed under these conditions to comprehensively assess the self-cooling capability of permanent magnet machines with different winding structures. The results demonstrate that concentrated windings gain greater benefit from the proposed self-cooling scheme than distributed windings, with the double-layer configuration showing the best overall performance. The computational fluid dynamics models were subsequently validated through a series of experiments.