Coping with through life fast jet upgrades, towards a decentralised electrical system

Student thesis: Doctoral Thesis


Fast jet aircraft go through continuous upgrades throughout their life cycle to keep them operationally relevant until the next replacement fast jet is available. Such lifecycles can stretch over timescales of a few decades for the same fast jet aircraft (e.g. the Panavia Tornado iterations). Overall, these upgrades for typical legacy fast jet aircraft are likely to be "electronic" in nature where specific upgrades examples include additional or replacement (more powerful) sensors, mission computing, electronic warfare, communication and pilot interface equipment to increase mission effectiveness. Apart from some self-powering pod based equipment, the end result of through life upgrades is a continuously increasing power demand. This becomes problematic when the increase is against an unchanged main electrical system within a spatially unchanging compact and limited weight allowance environment within the airframe. Under normal conditions, the generic fast jet system is powered by a centralised source of power generation: being the engine mechanical off-take driven generator/s. The generator and off-take are installed at the manufacturing stage of the aircraft and at the start of the fast jet service life where the capacity of the generator is greater than the initial loading. However with the through life upgrades, past trends have shown that such built in growth is not enough. Hence to cope with such power increases one can change the main generators during the operational life of the fast jet.However, this requires cumbersome and expensive rework of the associated mechanical off take and the more powerful replacement generator will still need to fit into the same space as the original generator with the same space constraints. Hence the replacement generator needs to be more power dense. Load shedding can also be considered but due to the lack of hotel or non-critical loads on a fast jet aircraft minimises the scope to load shed (when compared to civil aircraft such as in-flight entertainment). As such, the aim of the thesis seeks to explore the novel and alternative move towards a decentralised electrical system whereby supplementary generation sources are inserted around the aircraft. In essence, this is additional generation sources distributed around the aircraft to conform to remaining space for the compact airframe i.e. "filling the gaps". The reasoning of this work is that such distributed generation can work in parallel to the existing main generation leaving it intact with limited rework.;The upgrades themselves can be added in conjunction with the equipment upgrades to minimise the downtime of the aircraft. Such an approach has not been widely seen on contemporary fast jet to date which the novelty of such is presented in this thesis. Such distributed integration of supplementary generation also requires loose coupling for retrofit/modification purposes.Hence the thesis looks at the novel application of paralleling techniques taken from other domains with similar paralleling needs: such as Electric Vehicles (EVs), microgrids, distributed generation and renewables research for the fast jet domain. In line with this, the thesis firstly reviews different types of sources that are potentially suitable for such application and provides "weight" to the argument of having distributed generation for fast jet. From the literature review of the paralleling techniques from other domains, the thesis then presents the down selected and novel adaption of three possible integration methods to integrate supplementary power generation into the fast jet network in a distributed manner. These include 1. Using passive links of existing rectifiers around the fast jet electrical system as distributed DC integration points.2. Use of Shunt Active Filtering to inject power into the fast jet system in parallel to the main generation (additional to the base power quality improvement functionality). This is achieved by placing additional sources onto the DC link of the Shunt Active Filter.3. Converting passive rectifiers around the fast jet electrical system into active rectifiers/inverters to feed power back into the system.Underpinning these techniques is the proposed use of a common voltage master current slave scheme at the separate DC links which is used to control power flow into the fast jet electrical system. Illustration of the operation and benefits of these are presented against generic fast jet electrical system simulations.In summary the novelty of the work comes from firstly, the proposal to move towards a more decentralised system for coping with the unique upgrade problem on fast jet where there is limited space to accommodate additional bulk generation upgrades. Addition to this, additional novelty of the work comes from the exploration of the three integration methods stated above which represents a "first pass" attempt to increase the penetration of such distributed generation.
Date of Award28 Sept 2016
Original languageEnglish
Awarding Institution
  • University Of Strathclyde

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