Power Conversion Group

School of Electrical and Electronic Engineering

The University of Manchester

Electro-Mechanical Interaction in

Aero Gas Turbines

For details contact: Tom Feehally;

E-Mail: tom.feehally@postgrad.manchester.ac.uk

Supervisor: Dr J Apsley; Tel.: +44 (0)161 306 4732;

E-Mail: j.apsley@manchester.ac.uk

Acknowledgements: University of Manchester Alumni Fund,

EPSRC, Rolls-Royce Plc

• Develop methods for predicting electro-mechanical interaction in

aero gas turbines

• Assess functionality of DFIGs for aero applications

• Develop schemes to reduce the impact of interaction between

electrical and mechanical domains

Today’s aircraft require high levels of electrical power. Typical loads

can include: flight control systems, wing anti-icing, actuation and air-

conditioning.

Electrical generators are mounted on the outer casing of the gas

turbine alongside other auxiliary loads such as hydraulic pumps, fuel

pumps and oil scavengers. These are driven from a common, parallel

axis, gearbox which is coupled mechanically to a rotating spool of the

engine via a complex transmission system. This electro-mechanical

network is shown in Figure 1.

Project Background

Project Objectives

Electro-Mechanical Interaction

Double Fed Induction Generator

Electrical loading is transferred through the generator as torque

loading on the mechanical drivetrain. Hence, variable electrical loads

can excite resonances within the mechanical network, increasing the

likelihood of mechanical component failure.

Extensive MATLAB/Simulink simulation has been carried out which

includes the mechanical transmission and electrical generator. This is

used to demonstrate the ability of pulsed electrical loads to induce

sustained mechanical oscillation within the gearbox, see Figure 2.

Electro-Mechanical Test Rig

The electrical generator and its control dictates the extent to which

mechanical resonances can be excited by electrical systems. The fast

dynamics of a Double Fed Induction Generator (DFIG) offer the

potential for a control system to partially decouple the electrical and

mechanical domains.

The DFIG is also able to provide a constant frequency electrical

output across the mechanical speed range of the gas turbine. This

offers the benefit of a constant frequency system without the

traditional requirement for a Constant Speed Drive hydraulic coupling,

The test rig, shown in Figure 3, provides a scaled representation of an aero gas turbine electro-mechanical system. A DC drive machine and high

inertia flywheel are controlled to replicate spool behaviour. The transmission system is represented by a long driveshaft, with low torsional

stiffness, which powers the gearbox. Three loads are driven from the gearbox, two flywheel loads and a DFIG with coupled electrical load bank.

Generator control is implemented to produce constant frequency electrical supply and to develop active damping between electrical and

mechanical networks.

Figure 3: Electro-mechanical test rig (CAD)

Figure 1: Gas turbine cross section showing mechanical drivetrain (CAD)

[image courtesy of Rolls-Royce plc]

Key features of the test rig:

• Based on Trent1000 architecture

(matching frequency response)

• Variable gearbox drive configuration

• Software based emulation of gas turbine

spool behaviour

• Adaptable architecture (e.g. alternate

generator configurations, use of hydraulic

loads)

• Control scheme to reproduce aircraft

mission profile

• High bandwidth torque and position

sensing

Figure 2: Simulated pulsed electrical loading and resultant gearbox torque