Ultra-high voltage (>30KV) power devices through superior materials for HVDC transmission

2014年10月，英国冬季能源过剩降至5%以下。在未来，这种紧急过剩的能力可能会进一步减少，实际上变得严重不足，迫使国家电网将大量电力需求转移到该国两端的地区，否则将面临严重和有害的能源供应中断。解决这一供应问题的一个可行方案是建立新的国家高压直流（HVDC）能源网络连接，以及与超级电网的更多国际连接。为了有效地实施HVDC，公司正在考虑两种选择：1）实施成熟的Si 300 MW HVDC技术（大约2009年），需要通过按每条线路的换流器数量进行缩放来增加开销、土地要求、维护成本和冷却系统。或者2）投资于提高换流器中单个功率设备的阻断电压和电流容量的技术，其中对于2 GW MMC HVDC可以实现更少的线路换流器和更高的效率。即使通过减少整个英国电力传输和转换中的串联链效应，3%的节省也相当于从目前英国约37 GW的电力使用量中节省三个500 MW的燃煤发电站。该奖学金旨在开发革命性的碳化硅（SiC）材料，用于超高压（UHV）>30 kV的大电流额定值，高达150 A，目的是尽可能地提高当前的评级。UHV垂直器件的额定电流取决于大表面积（> 1cm 2）的可用性，并且目前由于在材料生长期间在晶片上形成的过量材料沉积物的缺陷而受到限制。这是一个问题，我相信这将是一个关键的路障，这种技术，并得到很少的关注，因为拟议的额定功率目前是5-10年的电力电子路线图。问题是，该领域的许多人相信到那时它会得到解决，然而，目前还没有重大的研究驱动来解决这个关键问题。化学气相沉积（CVD）是制造这些UHV器件中使用的半导体材料的行业黄金标准技术，因为它具有出色的均匀性，可扩展性和可重复性，因此必须开发用于快速吸收任何功率器件技术的技术。对于UHV器件，材料选择和质量是关键，其中需要具有大表面积的无缺陷厚（~100 μ m）层。氯化化学是SiC CVD中的最新发展，有助于将厚层的生长速率推高至100 μ m/hr，并且可以用于更好地实现高功率技术所需的低背景掺杂密度。在这里，厚的高质量材料将通过最先进的外延生长在英国唯一的工业SiC CVD在沃里克的状态。在改进材料的同时，其优越性将通过制造垂直UHV器件来展示：肖特基二极管、PiN二极管和MOSFET，同时开发IGBT工艺，展示其在未来模块化多电平变流器（MMC）中的潜力由于Si材料的高质量，诸如Si晶闸管和Si PiN二极管的双极器件将用于铁路牵引和电网级HVDC应用，这允许在高压直流输电（HVDC）网络中使用Si材料。大电流额定值。2014年，Yole预测这些行业将推动>3.3 kV SiC市场的发展，2015年三菱展示了全SiC 3.3 kV牵引逆变器系统。我进一步预测，只有当限流表面缺陷被最小化，并且由于微小的材料缺陷而导致的器件可靠性被更好地理解时，SiC器件才会在> 10 kV范围内完全取代Si IGBT。只有这样才能实现大电流额定值，这将使该技术超过目前的HVDC技术。该奖学金直接研究这些限制机制，并将开发材料和相关技术，以支持电力技术的这一步变化

In October 2014 the UK energy surplus during winter months dropped to below 5% overcapacity. In the future, this emergency overcapacity may be further diminished and actually become devastatingly insufficient, necessitating the national grid to divert large power demands to areas at opposite ends of the country or face serious and harmful disruption to energy supply. A viable solution to this supply problem is to build new national high voltage DC (HVDC) energy network connections in addition to more international connections to the super grid. To implement HVDC effectively, companies are considering two options: 1) to implement mature Si 300 MW HVDC technologies (circa 2009) requiring large overhead, land requirements, maintenance costs and cooling systems by scaling with the number of converters per line. Or 2) to invest in technologies which upscale the blocking voltage and the current capacity of individual power devices in a converter where fewer line converters and greater efficiency can be achieved for 2 GW MMC HVDC. Even by reducing the series chain effect in power transmission across the UK and conversion a 3% saving can equate to three 500 MW coal power stations from the current UK power usage of approximately 37 GW.This fellowship seeks to develop revolutionary Silicon Carbide (SiC) material for ultra-high voltage (UHV) >30 kV power devices with large current ratings, up to 150A, with the intention of pushing the current rating as far as possible. The current rating of UHV vertical devices depends on availability of large surface areas (> 1 cm2) and is presently limited due to defects from excess material deposits forming on the wafer during the material growth. This is a problem which I believe will be a critical roadblock to such technology and receives little attention as the proposed power ratings are currently off the 5-10 year power electronics roadmap. Problematically, many in the field trust it will be solved at that point, however, no major research drive is currently underway to solve this essential problem.Chemical vapour deposition (CVD) is the industry gold-standard technique for creating the semiconductor materials used in these UHV devices due to its excellent uniformity, scalability and reproducibility and so must be developed for quick uptake of any power device technology. For UHV devices the material choice and quality is key, where a defect free, thick (~100 um) layer with a large surface area is needed. Chlorinated chemistry is a recent development in SiC CVD and helps push growth rates up to 100 um/hr for thick layers and can be used to better achieve low background doping densities which are both required for high power technology. Here, thick high quality material will be achieved by state of the art epitaxial growth in the UK's only industrial SiC CVD at Warwick. In tandem to improving the material, its superiority will be shown by fabrication of vertical UHV devices: Schottky Diodes, PiN Diodes and MOSFETS, whilst developing IGBT processing, to show their potential for future modular multi-level converter (MMC) HVDC networks.Bipolar devices such as Si thyristors and Si PiN diodes will be used in rail traction and grid level HVDC applications due to the high quality of Si material which allows large current ratings. In 2014, Yole predicted that these sectors would boost the >3.3 kV SiC market and in 2015 Mitsubishi showed an all SiC 3.3 kV traction inverter system. I further predict that SiC devices will only completely replace Si IGBTs in the > 10 kV range when the current-limiting surface defects are minimised and device reliability due to minor material defects is better understood. Only then will large current ratings be achieved, which will allow the technology to surpass current HVDC technology. This fellowship directly studies these limiting mechanisms and will develop the material and associated technology to underpin this step change in power technology