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Online ISSN 2042-9746 Print ISSN 2042-9738

IET Electrical Systems in Transportation

Volume 1, Issue 4, December 2011

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Volume 1, Issue 4

December 2011

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    • Determination of protection system requirements for DC unmanned aerial vehicle electrical power networks for enhanced capability and survivability
      • Author(s): S.D.A. Fletcher ; P.J. Norman ; S.J. Galloway ; G.M. Burt
      • Source: IET Electrical Systems in Transportation, Volume 1, Issue 4, p. 137 –147
      • DOI:  10.1049/iet-est.2010.0070
      • Type: Article
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      • p. 137 –147 (11)
        A growing number of designs of future unmanned aerial vehicle (UAV) applications utilise DC for the primary power distribution method. Such systems typically employ large numbers of power electronic converters as interfaces for novel loads and generators. The characteristic behaviour of these systems under electrical fault conditions, and in particular their natural response, can produce particularly demanding protection requirements. Although a number of protection methods for multi-terminal DC networks have been proposed in the literature, these are not universally applicable and will not meet the specific protection challenges associated with the aerospace domain. Through extensive analysis, this study seeks to determine the operating requirements of protection systems for compact DC networks proposed for future UAV applications, with particular emphasis on dealing with the issues of capacitive discharge in these compact networks. The capability of existing multi-terminal DC network protection methods and technologies are then assessed against these criteria in order to determine their suitability for UAV applications. Recommendations for best protection practice are proposed and key inhibiting research challenges are discussed.
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      Hybrid power generation system for aircraft electrical emergency network
      • Author(s): X. Roboam ; O. Langlois ; H. Piquet ; B. Morin ; C. Turpin
      • Source: IET Electrical Systems in Transportation, Volume 1, Issue 4, p. 148 –155
      • DOI:  10.1049/iet-est.2010.0045
      • Type: Article
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      • p. 148 –155 (8)
        A whole structure and two management strategies are proposed here for hybridisation of a Ram air turbine (RAT) by means of supercapacitors. Such hybrid structure is dedicated to an aircraft emergency network. The structure consists in coupling, through a 270 V DC bus, a controlled source (RAT) with a storage device interfaced through a bidirectional DC–DC converter. Both the energy-management strategies are described and analysed: the first one is to assign the ‘high-frequency harmonics’ of the load power to the storage which is current controlled, whereas the RAT controls the bus voltage and then only feeds the average power, losses and low-frequency harmonics of the load. The second one proposes an energy optimised operation of the system: the RAT, being current controlled, is able to maximise the supplied power (maximum power point tracking), as for classical wind turbines. For such a strategy, the bus voltage is regulated from the storage device. The RAT sizing and its mass can then be strongly reduced by means of this hybrid structure controlled with optimised management strategies. Experiments on a lab test-bench confirm analyses presented.
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      Active fault protection for an AC zonal marine power system
      • Author(s): J. Wang ; M. Sumner ; D.W.P. Thomas ; R.D. Geertsma
      • Source: IET Electrical Systems in Transportation, Volume 1, Issue 4, p. 156 –166
      • DOI:  10.1049/iet-est.2010.0082
      • Type: Article
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      • p. 156 –166 (11)
        This study presents a method to protect the zonal distribution system proposed for future ships when fault occurs. By utilising a bus interface unit, the energy storage and grid interface within it provide one benefit that an independent fault protection scheme can be achieved. The new protection scheme is based on active impedance estimation. This technique actively imposes small transient disturbances onto the system at a point of measurement to excite the system in real time and estimate the system impedance at that point. The continuous wavelet transform is employed to achieve accurate impedance estimation over a broad frequency range from a small amount and very noisy data. The performance of this proposed technique is investigated both by simulation and experiment. The scheme exploits the increased use of power electronic devices to provide a useful complement to traditional protection strategies, which can also provide the necessary back up protection during extreme protection failure, without the need for communication channels.
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