Towards fault-tolerant, reliable, efficient, and economical DC-DC conversion for DC grid (FREE-DC)

英国在海上风能方面处于全球领先地位。根据政府的计划，到2030年，它的装机容量将增加近四倍，达到40千兆瓦。气候变化委员会(CCC)还预测，到2050年，海上风电总量可能会上升到100千兆瓦，以支持国家的净零目标。这种大规模的扩张，以及其他欧洲国家抗击气候危机的共同努力，将推动英国境内外海上高压直流基础设施的发展和互联，形成一个直流输电网络(而不是单独的点对点输电线路)，以确保能源安全并最大化经济收益。规划这样的直流电网的研究得到了英国的大量参与，并得到了几个大型欧盟和EPSRC项目的支持。虽然多端直流电网假定所有连接端子的标准电压水平(可能在一个规划阶段内)已经取得了相当大的进展，例如在控制和直流断路器方面，但将不同电压水平的直流系统互联在一起的DC-DC转换器面临着需要解决的严峻挑战。到目前为止，还没有安装这样的设备或试点规模的示范，不愿意安装的主要原因是现有的高压直流-直流转换概念成本高，功率损失大。这些基于拓扑级变化的方法往往会导致在关键性能指标(即成本、损耗和能力)之间出现典型的“WHAC-A-Mole”情况。拟议的研究将通过为高压直流-直流转换器补充使用混合功率开关来实现基本级创新，从而同时实现更低的成本、更低的损耗和更高的操作灵活性。为了充分发挥所提出的解决方案的潜力，该项目首先将对一种新型DC-DC转换架构进行系统的建模、设计、控制和仿真研究。然后，在所获得的知识的基础上，将建立一个大容量的混合开关换向试验台，以实验研究器件混合的优化。还将设计一个缩小到900 V至200 V、9.6 kW的DC-DC转换器原型，并将其与阿伯丁大学实验室的9转换器直流电网演示器集成，以测试其系统性能。在项目期间，通过与日立能源的专家密切合作，大学的研究和行业专业知识将有效地结合在一起。该项目的成功将为未来新的研究线路奠定坚实的基础，例如独特的直流电网拓扑和由新的DC-DC转换器实现的操作策略。

The UK is a global leader in offshore wind energy. Its installation will be nearly quadrupled to 40 GW by 2030 according to the government plan. The Climate Change Committee (CCC) also predicts that total offshore wind may rise to 100 GW by 2050 to back the nation's net-zero goal. Such large-scale expansion and the concerted effort of other European countries to battle the climate crisis will drive the development and interconnection of offshore HVDC infrastructures within and beyond the UK into a DC transmission grid (rather than separate point-to-point transmission links) to ensure energy security and maximise economic gains. Research on planning such a DC grid has significant participation from the UK, supported by several large EU and EPSRC projects. While the multi-terminal DC grid assuming a standard voltage level for all joining terminals (likely within one planning phase) has achieved considerable progress such as on the control and DC circuit breakers, the DC-DC converters interlinking DC systems at different voltage levels face serious challenges that need to be addressed. To date, no such equipment or pilot-scale demonstration has been installed, and the reluctance is mainly due to the high cost and power losses with the existing concepts for HVDC-DC conversion. These methods based on topology-level variations often lead to a typical "Whac-A-Mole" situation among key performance indicators (i.e., cost, losses, and capability).The above difficulty stems from the characteristics of the power transistors that are used to construct HVDC converters. The proposed research will enable fundamental-level innovation by complementary use of hybrid power switches for HVDC-DC converters, which will simultaneously achieve reduced cost, lower losses, and enhanced operational flexibility. To realise the full potential of the proposed solution, this project, at first, will systematically perform modelling, design, control, and simulation studies for a new breed of DC-DC conversion architectures. Then, based on the knowledge acquired, a high-capacity test bench for the hybrid switch commutation will be built to experimentally investigate the optimisation of device hybridisation. A downscaled 900 V to 200 V, 9.6 kW DC-DC converter prototype will also be designed and integrated with a 9-converter DC grid demonstrator in the Aberdeen University lab to test its system performance. During the project, the university research and industry expertise will be combined effectively by working closely with experts from Hitachi Energy. The success of this project will set a solid foundation for new research lines in the future such as unique DC grid topologies and operational strategies enabled by the new DC-DC converters.