Analysis of Electromechanical Interaction in Aircraft Generator Systems

The supply of electrical power is usually achieved by a generator driven from a prime mover by some form of mechanical drivetrain. Such an electromechanical 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 the electrical and mechanical domains. These disturbances may excite resonances resulting in cross-domain (electromechanical) 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. Electromechanical 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 electromechanical interaction at the design stage so that these issues can be avoided. However, predicting the occurrence of interaction through simulation is challenging, requiring multidomain models operating with different time scales. This paper analyzes an aircraft auxiliary power offtake to produce a reduced-order mechanical drivetrain model, allowing the modal frequencies to be predicted and cross-domain interactions to be modeled. 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.