面向直流短路故障全过程的架空柔性直流电网自适应控制技术研究

The overhead modular multilevel converter (MMC) based DC grid technology is a promising approach for integration of bulk renewable energy and power supply for multiple receiving ends. However, the fault rate of overhead lines is high, leading to the problem of DC short circuit faults. In order to isolate the DC faults and restore the power supply quickly, this project fully exploits the controllability of hybrid MMC. The adaptive current limiting control and adaptive re-closing control based on fault prediction during DC fault isolation and post-fault recovery are designed respectively. By the adaptive control of hybrid MMC during the entire DC fault process, the breaking current and capacity requirement of DC circuit breaker (DCCB) will be significantly decreased, resulting in a significant reduce of the cost and difficulty of DCCB manufacturing. In addition, the second fault strike on the system caused by the unscheduled re-closing is avoided. The fast recovery of instantaneous DC faults is achieved. Finally, a novel adaptive control scheme to handle with the DC line faults is obtained. In this way, this project provides a new method to control and protection design of MMC based DC grids and gives an impetus to development and industrial application of DC grids.

架空柔性直流电网技术是进行远距离大规模新能源并网、实现多电源供电和多落点受电的优选方案。但架空线路故障率高，直流短路故障是不能忽视的问题。为快速隔离直流故障并重恢复供电，本项目充分利用混合型MMC的控制能力，设计故障隔离期间的自适应动态限流控制和重恢复期间面向故障性质预判的自适应重合闸控制。基于故障全过程的自适应控制设计，降低对直流断路器开断电流和容量的要求，从而大幅降低直流断路器的技术难度和制造成本；避免盲目重合闸对系统造成的二次冲击，解决大概率瞬时性故障的快速重合问题。最终形成一套应对直流线路短路故障的自适应控制方案，为架空线柔性直流电网控制与保护的研究提供新思路，推动直流电网技术的发展与工程实践。

架空柔性直流电网是大规模新能源并网消纳的优选技术。针对柔性直流输电系统应对直流短路故障的问题，本项目圆满完成了项目计划书的研究任务，取得以下创新性成果：1. 突破柔性直流换流器在直流短路故障期间只能被动闭锁的常规认知，提出了柔性直流换流器自适应限流控制策略，利用换流器主动控制能力限制故障电流，大大降低直流断路器开断容量需求。2. 发明了一种交流侧级联混合型MMC拓扑，利用半桥子模块作为主桥臂承担直流侧高压、利用全桥子模块作为辅助桥臂进行波形“整形”，仅比半桥型MMC增加23%的IGBT数目即具备交、直流故障主动限流能力。3. 提出了一种基于换流器主动信号注入的柔性直流输电系统自适应重合闸控制，利用换流器主动控制注入信号至故障线路，实现了故障性质预判，降低了直流断路器二次开断容量，避免柔直系统遭受二次冲击。.基于项目研究成果，形成了一套应对直流线路短路故障的自适应控制（自适应限流+自适应重合闸）方案，为架空线柔性直流电网控制与保护的研究提供了新的思路。本项目在国际学术期刊及国内核心期刊上发表论文4篇，其中，SCI收录3篇、EI收录1篇；授权国家发明专利2项；培养硕士1名、博士1名；获得2020年第六届直流输电与电力电子创新杯大赛优秀奖。