Ni-based bulk metallic glasses and composites with high absolute densities exceeding 11 g/cm3 were synthesized via spark plasma sintering of Ni45Co10Ta25Nb20 powders produced from pulverized, melt-spun amorphous ribbons. Optimizing the synthesis via selection of sintering temperature, uniaxial load pressure, and powder mechanical screening yielded samples with relative densities of nearly 100% and hardness values in excess of 12.5 GPa without cracking. Mechanical testing included Weibull modulus determination for hardness and compression testing at 10-3 s-1 and 103 s-1 strain rates. The capability of using spark plasma sintering to fabricate high hardness, high density, large scale metallic glasses is demonstrated. The mechanical properties of these compacted comminuted melt-spun glass ribbons are presented.

Abstract-Multilevel converters are an emerging industrial technology and are the subject of a substantial amount of research. However, they are yet to find their way into many mainstream engineering applications. This paper presents a method of quantifying the benefits and disadvantages of multilevel converters of increasing order. The analysis focuses on the cascaded H-bride topology for grid-tie battery inverter applications. The analysis includes both semiconductors losses and semiconductor driver losses. It is shown that multilevel converters can have significant benefits over their conventional counterparts, but that more levels is not necessarily better. This paper's important result is to create a quantitative measure of the pros and cons of multilevel architecture.

. orcid.org/0000-0002-5770-3917 and Foster, M.P. (2017) On the impact of current generation commercial gallium nitride power transistors on power converter loss. Electronics Letters, 53 (22 ReuseUnless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request.On the impact of current generation commercial gallium nitride power transistors on power converter loss The enormous potential benefits of gallium nitride based power switching devices, only commercially available very recently, in terms of power switching device loss are highlighted. This is first demonstrated through a simulated prediction of loss in multilevel converters, followed by experimental validation. While the simulations focus on losses in multilevel converters, the observations made are relevant in a broad range of applications.Introduction: Currently, power switching devices are predominantly silicon (Si) based, with the notable exception of silicon carbide based power switching devices which already find somewhat widespread use, especially in high-voltage switching applications.

Focusing on cascaded H-bridge converters for grid-tie battery energy storage, a practical, analytical method is derived to evaluate the switching-associated power loss in multilevel converters, evaluated from a number of sources of loss. This new method is then used to find performance trends in the use of converters of increasing order over a range of switching frequencies. This includes an experimental analysis into predicting the performance of MOSFET body diodes. Authors' analysis with this model shows that a multilevel converter can have lower losses than the equivalent single-bridge, three-level converter, particularly at higher switching frequencies, due to the availability of suitable switching devices. It also has interesting implications for enabling the use of cutting-edge non-silicon power switching devices to further improve potential efficiencies.

This paper investigates the benefits of distributing thermal load across multiple devices on a single heatsink, with a focus on how this might be a benefit in the use of multilevel converters. The analysis uses finite element modelling to derive trends in performance, which combined with real world data permits for a bulk analysis in to whether multilevel converters have thermal benefits, and if so, to how great an extent. The paper concludes that there are significant and quantifiable benefits to distributing the thermal load, but high order multilevel converters may yield little benefit over lower order systems.