No abstract

We use first-principles density functional theory based calculations to determine the stability and properties of silicene, a graphene-like structure made from silicon, and explore the possibilities of modifying its structure and properties through incorporation of transition metal ions (M: Ti, Nb, Ta, Cr, Mo and W) in its lattice, forming MSi(2). While pure silicene is stable in a distorted honeycomb lattice structure obtained by opposite out-of-plane displacements of the two Si sub-lattices, its electronic structure still exhibits linear dispersion with the Dirac conical feature similar to graphene. We show that incorporation of transition metal ions in its lattice results in a rich set of properties with a clear dependence on the structural changes, and that CrSi(2) forms a two-dimensional magnet exhibiting a strong piezomagnetic coupling.

Abstract-This paper investigates the effect of two soft magnetic materials on a high speed machine design, namely 6.5% Silicon Steel and Cobalt-Iron alloy. The effect of design parameters on the machine performance as an aircraft starter-generator is analysed. The material properties which include B-H characteristics and the losses are obtained at different frequencies under an experiment and used to predict the machine performance accurately. In the investigation presented in this paper, it is shown that machines designed with 6.5% Silicon Steel at a high core flux density has lower weight and lower losses than the Cobalt-Iron alloy designs. This is mainly due to the extra weight contributed by the copper content especially in the end-windings. Due to the high operating frequencies, the core-losses in the Cobalt-Iron machine designs are found to outweigh the copper-losses incurred in the Silicon Steel machines. It is also shown that change in stack length/number of turns has a considerable effect on the copper losses at starting, however has no significant advantage on rated efficiency which happens to be in a field-weakening operating point. It is also shown that the performance of the machine designs depend significantly on material selection and the operating point of the core. The implications of the variation of design parameters on the machine performance is discussed and provides insight into the influence of parameters that effect overall power density.Index Terms-Aircraft, cobalt steel, flux density, high speed, machine design, soft magnetic material, silicon steel

A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription.For more information, please contact eprints@nottingham.ac.uk

No abstract

The ever increasing electric power demand and the advent of renewable energy sources have revived the interest in high-voltage direct current (HVDC) multi-terminal networks. However, the absence of a suitable circuit breaker or fault tolerant VSC station topologies with the required characteristics (such as operating speed) have, until recently, been an obstacle in the development of large scale multi-terminal networks for HVDC. This paper presents a hybrid HVDC circuit breaker concept which is capable of meeting the requirements of HVDC networks. Simulation results are presented which are validated by experimental results taken from a 2.5kV, 700A rated laboratory prototype.

. (2015) Impact of slot/pole combination on inter-turn short-circuit current in faulttolerant permanent magnet machines. IEEE Transactions on Magnetics, 52 (4). ISSN 0018-9464Access from the University of Nottingham repository: http://eprints.nottingham.ac.uk/33837/1/Impact%20of%20Slot%20Pole%20Combination %20on%20Inter-Turn%20Short-Circuit%20Current%20in%20Fault-Tolerant%20Permanent %20Magnet%20Machines.pdf Copyright and reuse:The Nottingham ePrints service makes this work by researchers of the University of Nottingham available open access under the following conditions. This article is made available under the University of Nottingham End User licence and may be reused according to the conditions of the licence. For more details see: http://eprints.nottingham.ac.uk/end_user_agreement.pdf A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription.For more information, please contact eprints@nottingham.ac.uk I E E E P r o o f IEEE TRANSACTIONS ON MAGNETICS XXX

This paper discusses a small scale laboratory model constructed to validate the operation of a recently proposed parallel hybrid modular multilevel voltage source converter which is intended for HVDC applications. The converter is characterized by a 'chainlink' arrangement composed of a number of half bridge cells capable of operating with bidirectional current and an associated full bridge converter for each converter phase arrangement. Each half bridge cell is made up of two bidirectional switches and a local storage capacitor. The voltages on the local storage capacitors of the 'chainlink' cells need to be controlled within a tolerance band to ensure sustainable operation of the converter. The paper also presents a capacitor voltage balancing scheme for this converter and further demonstrates black start capability using a lower rated auxiliary DC source. Four quadrant operation of the converter is also demonstrated as would be expected of a grid connected voltage source converter. Simulation and experimental results are presented to support the converter operation.