The project aims for an innovative solution for an aircraft electrical starter-generation system. The driver behind the project is the move towards green more-efficient aircraft technology by employing electric power to eventually replace conventional hydraulic and pneumatic power.
Increased weight of green aircraft systems based on existing electrical aircraft components may offset savings due to higher efficiency. The electrical generation system incurs the largest weight increase when moving towards more-electric aircraft and this is a major challenge.
Within the project this challenge will be addressed by the development of a novel generation system comprising the electrical machine, the power electronic converter, the associated cooling system, and the control with health monitoring functions that enable the system to function safely and reliably as a starter/generator system for a small aircraft. An integrated design and modelling approach will provide an overall optimised solution that will reduce component count and maintenance cost, improve system reliability and save weight, thus improving the environmental impact of aircraft operations.
The AEGART project has developed and demonstrated a novel, beyond state-of-the-art type of starter-generator system for more-electric business jet.
The most popular state-of-the-art starter/generator technology employs a three-stage wound field synchronous generator with rotating rectifier. This machine has been extensively adopted in fixed wing and rotor craft applications and has proved to be highly reliable, inherently safe with voltage control achieved by varying the excitation current. However, the wound rotor technology with rotating diodes limits the machine speed hence the achievable power density, passive rectification to achieve dc output requires large and heavy filters and extra winding is required to perform starter function. Hence, the design cannot be regarded as optimal and has an obvious limitation if considering a move to new, more-electric aircraft platforms.
Recent advances in areas of power electronics, electric machines and control methods made it possible to consider new starter-generator system topologies aiming for the improved performance, reduced fuel consumption and environmental impact, improved safety and reliability, as well as increased aircraft availability by implementing enhanced prognostic, diagnostic and health monitoring. The AEGART project has developed a starter-generator system proposing a radical, beyond state-of-the-art solution based on permanent magnet machine controlled by active front-end rectifier. Combination of unique properties of permanent magnet machine such as high power/torque density with fully controlled bi-directional power electronic converter in the main path of energy flow, thorough addressing the thermal management of both the machine and the converter, and development of advanced control and health monitoring strategies has led to the substantial improvement of overall system mass (about 20% reduction) and system efficiency (about 10% improvement) compared to most advanced existing solutions. In addition, the AEGART system introduces new functionalities not employed in existing starter-generators, including:
- Controlled acceleration start making the starting duration independent on environmental conditions
- Capability of paralleled operation with other sources in future aircraft electric power systems architectures controlling the share of total load power taken by the system
- Capability to regenerate the excess of power in the DC grid
- Limitation of the torque slew rate seen by the engine
- Advanced machine fault diagnostic and fault prediction mechanisms to improve availability of the aircraft and to reduce unscheduled maintenance.
The developed AEGART system has been successfully tested in both University of Nottingham laboratories and at Labinal Power Systems’ ETB where all the key performance requirements/indicators set at the beginning of the project have been clearly demonstrated in the context of evaluation at TRL5.
Success of AEGART project means the development of a novel aircraft starter-generator system that allows saving weight (up to 20% compare to existing state-of-the-art systems) and reducing the environmental impact of next-generation aircrafts (by improving efficiency of electromechanical power conversion up to 10%), as well as improving their safety, reliability and reducing maintenance costs.