Analysis of electro-mechanical interaction in aircraft generator systems

Abstract

Abstract-The supply of electrical power is usually achieved by a generator, driven from a prime mover, by some form of mechanical drivetrain. Such an electro-mechanical system will have natural resonant modes in both the electrical and mechanical subsystems. The electrical generator provides a coupling between the subsystems, transferring not only useful power but also disturbances between electrical and mechanical domains: these disturbances may excite resonances resulting in cross-domain (electro-mechanical) interaction. This can lead to lifetime reduction in the mechanical components and instability in the electrical network, resulting in poor reliability for the wider system, and potentially catastrophic component failure. Electro-mechanical interaction is particularly critical in power generation systems onboard aircraft, because the generator is driven by a gas turbine via an inherently low-stiffness drive train. It is then critical to identify electro-mechanical interaction at the design stage so that these issues can be avoided. However, predicting the occurrence of interaction, through simulation, is challenging, requiring multi-domain models, operating with different time scales. This paper analyses an aircraft auxiliary power offtake to produce a reduced-order mechanical drivetrain model, allowing the modal frequencies to be predicted and crossdomain interactions to be modelled. A purpose-built electromechanical test platform is used to validate the model and demonstrate how electrical disturbances are passed through the generator to the mechanical system and affect the electrical network. Future research will use the test bed to demonstrate strategies for avoiding or suppressing unwanted interactions.

The Doubly Fed Induction Machine as an Aero Generator

“…To validate the model, the control scheme is implemented on the laboratory machine using a commercial converter. An aero generator test platform [34], which represents the mechanical offtake of a GT, is used to drive the DFIG and is shown in Fig. 2.…”