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

2014年10月，英国冬季几个月的能源盈余降至产能过剩5%以下。未来，这种紧急过剩的产能可能会进一步减少，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国家两端的地区，否则能源供应将面临严重和有害的中断。解决这一供应问题的一个可行的解决方案是，除了与超级电网建立更多的国际连接外，还要建立新的国家高压直流(HVDC)能源网络连接。为了有效地实施高压直流输电，各公司正在考虑两种选择：1)实施成熟的硅300兆瓦高压直流输电技术(约2009年)，该技术需要较高的管理费用、土地需求、维护成本和冷却系统，可根据每条线路上的换流器数量进行扩展。或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，这样可以为2 GW MMC高压直流输电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输电和转换中的串联链条效应，3%的节省也相当于三个500兆瓦的燃煤发电站，而英国目前的用电量约为37GW。该奖学金旨在开发革命性的碳化硅(SIC)材料，用于额定电流高达150A的超高压(UHV)和GT；30千伏电力设备，目的是尽可能提高额定电流。特高压垂直器件的当前额定值取决于大表面积(&gt；1 cm2)的可用性，目前由于材料生长过程中晶片上形成的过量材料沉积造成的缺陷，目前的额定值是有限的。这是一个我认为将是此类技术的关键障碍的问题，而且很少受到关注，因为拟议的额定功率目前不在5-10年电力电子路线图的范围内。问题是，许多业内人士相信届时它将得到解决，然而，目前还没有进行重大研究来解决这一关键问题。化学气相沉积(CVD)是制造用于这些特高压设备的半导体材料的行业黄金标准技术，因为其出色的一致性、可扩展性和重复性，因此必须开发以快速采用任何功率设备技术。对于特高压器件，材料的选择和质量是关键，需要无缺陷、厚(~100微米)、具有大表面积的层。氯化化学是碳化硅化学气相沉积的最新发展，有助于将厚层的生长速度提高到100微米/小时，并可用于更好地实现高功率技术所需的低本底掺杂浓度。在这里，厚重的高质量材料将通过英国唯一的工业碳化硅CVD在沃里克进行最先进的外延生长来实现。随着材料的改进，其优势将通过制造垂直UHV器件：肖特基二极管、PIN二极管和MOSFET来展示，同时开发IGBT工艺，以展示它们在未来模块化多电平换流器(MMC)高压直流网络中的潜力。由于硅材料的高质量允许大电流额定，双极器件如硅晶闸管和硅PIN二极管将被用于轨道牵引和电网级高压直流输电应用。2014年，Yole预测这些行业将提振3.3千伏的碳化硅市场，2015年三菱展示了全碳化硅3.3千伏牵引逆变器系统。我进一步预测，只有当限制电流的表面缺陷最小化，以及更好地理解由于微小材料缺陷而导致的器件可靠性时，碳化硅器件才会在&gt；10kv范围内完全取代硅IGBT。只有到那时，才能实现大电流额定，这将使该技术超过目前的高压直流技术。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