Jet Engine Integrated Generator

The paper presented discusses the design of a permanent magnet (PM) excited synchronous generator to be integrated into a modern jet engine. The electrical machine is to replace the mechanical accessory power drive system; thus all secondary power supplied from the engine to the aircraft is supplied by the electrical generator. The generator is also to double as starter motor for the engine, a job which can easily be handled at the required total secondary power level. It has been found that an integrated generator is technically feasible. It is heavier than its conventional counterpart, but offers significant reliability and maintenance benefits. This paper describes part of the work done for a study to investigate the feasibility of integrating a PM generator into a jet engine. IR Force and industry have recognized the potential value of integrating secondary-power-generation devices and engine accessory components into the basic engine structure. The objective of this design approach is to minimize the propulsion system envelope. Provided that a suitable configuration can be defined, the propulsion system should then provide improved installed performance, in two respects: drag will be reduced, and reliability will be improved by eliminating the complex mechanical secondary-power- generating equipment and accessory drive system. A program was undertaken to study the practicality of an integrated jet engine generator and its potential benefits. Experience with conventional aircraft alternators had proven that only solid rotor type electrical machines such as a per- manent magnet (PM) machine would meet the stringent reliability and maintainability requirements which would allow the integration of the alternator into an engine. The program encompassed a detailed study and design effort to determine applicability, location, and configuration of the engine structure. This paper describes the tradeoff and design studies un- dertaken to obtain an electrical machine design suitable for the application. The major goals were to achieve high reliability, low maintenance, and low life cycle costs for the electrical system. These goals can best be served by PM ex- cited electrical machines, since their rotors have a reliability potential which is higher than that for industrial induction motors and only surpassed by solid rotor machines. The PM generator is part of a variable speed constant- frequency-generating system which consists of the high frequency generator and a cycloconverter. The cycloconverter allows power flow in both directions. Thus the cycloconverter generator system is also capable of operating as an elec- tronically commutated motor-drive to start the engine. The cycloconverter will provide for all electrical controls, in- cluding frequency and voltage control, since an ac-PM machine does not allow for a simple reliable voltage control within the machine itself.