Electro-Mechanical Interaction in Aircraft Generator Drivetrains

Modern aircraft require substantial electrical power to supply a wide range of flight critical and ancillary systems, and this requirement is set to grow given the industry desire to replace hydraulic and pneumatic systems with electrical equivalents. Electrical generators are driven via a complex drivetrain, from the rotating spools of the gas turbine. The drivetrain is flight critical, however, given its structure and light weight design, it is prone to resonance. Furthermore, electrical loads are non-constant and so variations in electrical power demand are transferred through the generator to produce torque variation on the drivetrain. This electro-mechanical interaction may trigger system resonances and result in reduced component lifespan and poor electrical regulation. A further issue for large aircraft is the desire to deliver a constant frequency electrical supply from a variable speed gas turbine.

This paper investigates the full electro-mechanical system of an aero gas turbine. Modelling and analysis of the drivetrain is carried out to identify key resonances. A doubly-fed induction generator is considered as it offers a means of decoupling the generator drivespeed and electrical frequency, and also high bandwidth control - potentially to mitigate electro-mechanical interaction. A test platform is developed which incorporates realistic driveshafts, gearbox, generators, and electrical load, scaled with respect to power and speed. Generator control is implemented to provide constant electrical frequency over a speed range. Results from the test platform are presented which demonstrate electro-mechanical interaction at predicted frequencies, and discussion is made of ways to mitigate electro-mechanical interaction, to make electrical generation of future aircraft more robust.