Design and development of permanent magnet synchronous machines shaft-line embedded in aeronautic engines

Technological advances in the aerospace industry have improved aircraft efficiency and reduced the cost of air transport, leading since 1960 to a continuous growth of the worldwide air traffic. Today it is postulated that also into the foreseeable future both the passenger and cargo air traffic will continue to growth, increasing the CO2 air transport emissions. In this contest, there are many environmental as well as commercial pressures on aircraft manufacturers to improve performances of future aircraft in terms of safety, air pollution, noise and climate change. To achieve these goals, it is necessary revisiting the whole aircraft architecture system, with the introduction of new technologies for performing key functions on aircraft. Today the conventional civil aircraft are characterized by four different secondary power distribution systems: mechanical, hydraulic, pneumatic and electrical. This implies a complex power distribution nets aboard, and the necessity of an appropriate redundancy of each of them. In order to reduce this complexity, with the aim to improve efficiency and reliability, the aerospace designer community trend is towards the `More Electric Aircraft (MEA)' concept, that is the wider adoption of electrical systems in preference to the others. This solution involves an increase of the aircraft electrical loads and, as a consequence, heavy implications for the on-board electrical generation systems are predictable. The resulting increase of the electrical power requirements encourage the research of alternative solutions rather than simply scaling up existing technologies such as generators driven by gearboxes. To address these challenges, many studies are in the direction of the so called `More Electric Engine (MEE)', in which the electrical machines are integrated inside the main gas turbine engine to generate electrical power, start the engine and guarantee safety generation in case of a critical on-flight failure. In this way the mechanical gearbox which connects the actual generators to the aeroengine shaft can be eliminated. The MEA and the MEE concept can be considered as an evolutionary implementation of the `All Electric Aircraft (AEA)', in which all the aircraft on-board systems are supplied in an electrical form. The MEE concept will involve important mechanical and thermodynamic implications in the aeroengine design, making necessary a preliminary system analysis on today conventional aeroengine, in order to evaluate the integration feasibility with the actual mechanical and environmental constraints. The electrical machines can be integrated inside the engine in some different positions, either in the front part before the combustion chamber, in particular in the low-pressure or in the high-pressure compressor stages, or in the rear part of the engine, in the tail-cone zone. In the frame of the GREAT2020 (GReen Engine for Air Transport in 2020) project co-founded by Regione Piemonte, aimed to the development of new eco-compatible aircraft engines for the entry into service in 2020, the MEE concept focus is on the evaluation of the most suitable solution between four possible integration positions in the front part of the today conventional two-shaft GEnx turbofan engine. The rotational speeds and the maximum available volumes are respectively imposed by the shaft connection and by the available spaces inside the aeroengine. In the purpose of the MEE concept on which the work presented in this dissertations is based, in order to evaluate the less critical solution between the proposed, a trade-off study conducted on preliminary electromagnetic design has been performed considering both radial and axial flux surface mounted permanent magnet synchronous machines. The comparison of the different solutions have been done on the base of same sizing indexes. Due to the particular application in which the electrical machine integration is involved, in order to evaluate impact on the whole system performance, a wider trade-off study concerning the overall aeroengine system has been done by the aerospace company Avio, partner of the GREAT2020 project. The focus of the work presented in this dissertation, is the development of appropriate tools to perform a preliminary electromagnetic design of radial and axial flux, surface mounted, permanent magnet synchronous machines with three-phase distributed and single-layer fractional-slot non-overlapping concentrated windings. In particular, this latter winding topology has been considered for its specific application for its shorter end-winding connections respect to the distributed layout, and for their high fault tolerant capability due to the electrical and physical separation between the phases which reduces the possibility of a fault propagation. Regarding the radial flux topologies, both inner and outer rotor machine structures have been considered; for the axial flux machines the single-stage (one stator and one rotor) as well as the multi-stage structures, obtained connecting on the same axis more than one single-stage structure, have been considered. The developed general purpose tools are based on simple geometrical approach using conventional design equations. The geometrical dimensions are computed starting from the design specifications and material utilization indexes imposed by the designer. The implemented codes would be a useful tool for the electrical machine designer in order to quickly define a preliminary electromagnetic design starting from a fresh sheet of paper. The conducted comparisons with commercial software have proved the validity of the tools for the conducted MEE trade-off study; however, in a prototype design aimed to the construction, detailed analysis using commercial software available on the market and Finite Element Method analysis have to be done in order to verify and improve in details the preliminary electromagnetic design obtained by the implemented codes.