High Power Density Permanent Magnet Machines with Hollow Conductors

This thesis presents a study into the use of hollow copper conductors with an integral fluid cooling duct to achieve high power density in permanent magnet machines for aerospace. The drivers and challenges for aircraft electrification are discussed and the factors that influence the achievement of high-power density are reviewed. The thesis reviews literature on the use of hollow conductors in electrical machines and identifies that AC losses in the conductors are a major issue that needs to be taken into account.
The thesis presents the findings from two extensive design studies on concentrated and distributed winding machines of various slot-pole combinations and different winding configurations. Extensive use if made of transient finite element analysis to both predict torque capability and copper loss which include the effect of AC losses induced in the hollow copper conductors. These design studies demonstrate the key interaction between stator core geometry and AC losses. These chapter culminate in the selection of a preferred design based on a 30 slot-10 pole design which is then further optimised via a sensitivity study and analysed in terms of irreversible demagnetisation.
The results for a detailed and lengthy experimental investigation into the thermal performance of a commercial grade of hollow conductor are presented. This demonstrates both the ability of coolant flow within a conductor to provide very effective heat transfer but also the problems of dealing with coolant oil viscosity and the resulting pressure drop in very fine ducts.
The thesis concludes by drawing together the key findings and identifying topics for future research.