Aerospace Electric Generator Specification and Selection - Opportunities and Challenges

The goal of this work is to specify and investigate suitability of a number of selected permanent magnet synchronous machine (PMSM) topologies to be mounted directly on a low pressure shaft (LPS) of a geared turbofan engine. The starting point of the work is to explore the status of electrical machines for more electric engine in order to study different design aspects when identifying and defining the designs. Even though the high flexibility and power density is anticipated from the system electrification the reliability is one of the most important aspects for the machine topology development and faultlessness can compromise desired performance. Large inner diameter of LPS and wide speed range are challenging the selection and specification of PMSM. The design initialisation is carried out by looking for more fault tolerant arrangements between machine windings and power converter topologies and appropriate rotor layouts that can provide excitation and constructional stability. Design space exploration is carried out on surface mounted Halbach array PMSM with distributed winding in the stator as one of the machine types that is best suited for high power density and high-speed application. Machine design aspects on modular design for faultlessness and cooling integration for enhanced thermal management and higher power density are the arguments behind the sensitivity study carried out on interior permanent magnet synchronous machine with non-overlapping concentrated winding. Six different magnetic core materials are compared to demonstrate that thin FeSi electromagnetic steel grades improve efficiency and FeCo materials mainly torque density but the machine may remain unsatisfactory in power and efficiency.