Design of a Brushless PM Starter Generator for Low-Cost Manufacture and a High-Aspect-Ratio Mechanical Space Envelope

This paper presents the results of a brushless permanent magnet (PM) starter-generator design, which caters for low-cost manufacture and a highly constrained mechanical space envelope. The starter-generator design addresses the low-cost requirement through the use of aluminium winding conductors and ferrite PM. This presents several challenges which include, but are not limited to, the selection of an appropriate machine topology to realise a high specific output with the lower performance materials, minimizing the power losses associated with the higher resistivity of aluminium, and the enhancement of thermal performance. The problem is further exacerbated by the demanding space envelope, operating requirements, and the necessity of “design for manufacture.” The selection of an appropriate machine topology is paramount in the present application as the limited mechanical space-envelope results in a “pancake” like geometry in which the aspect ratio of the stator outer diameter to the machine active length is high. To provide a solution satisfying all these challenging design requirements, an approach combining the theoretical electromagnetic and thermal analyses together with tests on machine subassemblies has been employed here. Such a method allows for a more informed design process, where the manufacture and assembly nuances affecting the starter-generator's performance are identified and accounted for prior to prototyping of the complete machine assembly. This paper discusses the employed design methodology in detail. A number of machine designs with alternative winding constructions have been considered providing an insight into challenges and limitations for the cost-effective winding construction utilizing aluminium conductors. The results from analysis of the starter generator suggest that the proposed machine design is capable of achieving the design requirements for both continuous and transient operating modes.