Real-time dynamic substructure testing applied to a weight optimised synchronous power conversion system

As the relevant technologies develop, energy efficient electric power systems are replacing equivalent hydraulic, pneumatic and mechanical systems. This is most apparent in the transportation sector in which energy efficiency is of primary importance, leading to increased range and reduced vehicle emissions and fuel consumption, essential if the UK is to meet EC emissions targets by 2020. Working towards these targets, the current generation of electric technologies are already providing the back-up and auxiliary systems on the newest civil aircraft and motive power on the very latest hybrid and electric vehicles. Looking to the future, the next generation of civil airliners are expected to use electric power as the primary source (except for propulsion) meaning that they will have an on-board electrical generation capacity of around 1MW. Efficient generation, distribution and consumption of this amount of energy in the face of continuously changing power demands of an aircraft during flight requires complex power conversion systems which add mass to the aircraft, reducing the overall system benefits. This has more impact on smaller aircraft such as helicopters as the mass of the extra equipment needed forms a greater proportion of the total vehicle mass. To truly viable in smaller aircraft, the power conversion systems must be lighter, occupy less space and still be capable of delivering the required power safely, operating much closer to the limit of their capabilities.Broadly, this research programme proposes in will investigate two concepts;1. A low mass power conversion system that could be used to drive electric systems in which require a supply frequency that is at a fixed ratio to that of the primary generation system is proposed and analysed in terms of its stability. The resulting converter would be extremely efficient and would increase the likelihood that large electric power technologies (e.g. for propulsion) could be used on helicopters safely.2. A testing method that will allow the critical pieces of equipment (be they software or hardware) to be dynamically loaded and tested in the lab as if they were present in the complete, real system for which they were designed.Specifically the research will take the form of an in-depth analytical study that will determine theoretically and demonstrate experimentally using real-time dynamic substructuring methods, the dynamic stability and control of the proposed power conversion topology. As the topology does not require an intermediate fully rated power electronics stage, it has many benefits including low mass, very high efficiency and little electro-magnetic interference (EMI) which also means heavy EMI filters will not be required.For validation and a reliable assessment of the true stability of the system under loading, a phase of laboratory-based testing will be conducted that will use and assess state-of-the-art control, real-time numerical modelling coupled with load and source emulation techniques (which combine to form a real-time dynamic substructured test) to accurately reproduce the controlled output of a field-wound aircraft generator, and the fan loading of a propeller, with a view to replicating the dynamic conditions observed under true operating conditions.Finally a phase of full laboratory tests will be conduction to demonstrate the accuracy and validity of the implementation of the real-time dynamically substructured test facility.

Using the state-of-the-art material, maximum machine efficiencies of 95% can be achieve over a wide range of operating conditions at reasonable cost. To realise the full benefits offered by these machines a sequence of power electronics systems are commonly adopted, reducing the system efficiency to 80% and increasing the mass of the total system. Hence novel methods of driving these machines will be required to accelerate their use in transportation systems where power densities are a critical design factor for their selection. The proposed topology drives down the mass of active (and hence heat producing) components required in a conversion scheme (also improving reliability of that systems) making the use of an electric machine for use in a primary system for a manned mainstream aerospace application closer to a realisable technology for the first time. Early demonstration of stability, control and reliability will be essential to the uptake of this technology. The main beneficiaries of the proposed power conversion topology will be the aerospace sector (and specifically the industrial collaborators) where reduction of mass of components is of primary concern. Given its strong industrial portfolio and links in the relevant industrial sector, the EEMG at the University of Bristol is ideally placed to ensure that this sector is exposed and adopts the relevant developments as they mature, as part of industry-led research collaborations funded jointly by that industry and technology development grant bodies such as EC, BERR and EPSRC. Impacts of the real-time dynamic substructuring testing method applied to electrical systems are considered to be widespread and could be felt anywhere that large pieces or systems of equipment need testing as a single unit. The cost of testing large systems in the proposed manner is much less than if all pieces of equipment where needed in the lab with the main need in the area being confidence that the substructured systems truly represents the real system. The research proposal aims to improve the capability of the technology to improve confidence in it within industry, promoting its uptake as a mainstream testing methodology with the techniques having the potential to impact and simplify certification of systems in the longer term. As well as strong links inside the aerospace sector with Agusta-Westland and Goodrich, the EEMG also has a considerable portfolio of past and current industrially focused projects in the automotive and renewable energy industries (Ford, Zytek, Ricardo, Smiths Electric Vehicles, QinetiQ, Intec Power Systems). With the EEMG performing significant amounts of machine testing for all of these partners, the potential for the substructuring methods to accelerate understanding of dynamic behaviour of systems and therefore produce efficient control systems design is significant. Through links formed as a member of the EPSRC Network, HybTestNet, relationships exist that will be used to both contribute to and draw upon the outcomes of the research programme. The most immediate route to forwarding the work specifically in the proposed programme will be to prepare an EPSRC Follow-On proposal that will transfer directly the knowledge gained through the research to the industrial collaborator, an identified deliverable of the work. Given that the proposal is for a First Grant Application a critical aspect of its impact is its ability to provide the applicant with a framework for development of independent research career. The expertise, industrial participation, equipment and current relevance contained within the proposed work indeed provides this and maximises the return of the requested sum to the academic community and as a result to the competitiveness of the associated UK industries.