多直流馈入受端电网主变充电对直流输电及受端电网运行影响研究

It is the significant strategy for power system development of China by transmitting clean energy like hydro- and wind-energy from northwest of China to the load centre at southeast of China. However, with multiple HVDC fed in, the safety and stability operation of the power system would be imperiled by commutation failure or block caused by transformer charging. Taking commutation failure caused by transformer charging as the target of the study, this project would research the impact of the transformer charging on the operation of the receiving end power system and multi-infeed HVDCs. The main work are as follows: the voltage distortion of the converter station bus caused by harmonic current injection at different position would be studied, the method of risk assessment for commutation failure caused by different transformer charging would be proposed, the buses where transformer charging would most probably cause commutation failure would be identified, and consequently the impact of the transformer charging on the operation of the receiving end power system and multi-infeed HVDCs would be researched. Aimed at establishing the method of fast assessing the risk of commutation failure caused by different transformer charging, this project could supply theoretical basis to cope with the problem of commutation failure caused by transformer charging.

利用特高压直流输电将我国西北部地区水电和风电等清洁能源大规模、远距离输送至中东部地区负荷中心消纳，是我国电网发展的重要战略。然而，多回特高压直流馈入电网后，网内主变充电等造成直流换相失败甚至闭锁，严重威胁着多直流馈入电网安全稳定运行。本项目以主变充电造成直流换相失败为研究对象，对多直流馈入受端电网主变充电对直流输电及受端电网运行影响进行研究。主要研究内容为：研究电网不同位置谐波注入电流引起换流站母线电压畸变的情况，建立电网不同位置主变充电引起直流换相失败风险评估方法，揭示系统内引发直流换相失败风险较高的主变充电位置，并进一步分析研究多直流馈入受端电网主变充电对直流输电及受端电网运行影响。上述研究旨在建立主变充电引起直流换相失败风险的快速评价方法，为应对主变充电造成的直流换相失败和闭锁问题提供理论基础。

直流输电是我国电网“西电东送、北电南送”战略的重要输电手段，华东等负荷中心电网均已形成多回特高压直流馈入的大型受端电网；运行经验表明，受端电网主变充电等谐波电流注入可能造成直流输电换相失败甚至闭锁，严重威胁多直流馈入受端电网的安全稳定运行；而采用电磁暂态仿真的方法，逐个节点的详细研究主变充电是否会造成直流换相失败工作量巨大，难以实现。针对上述问题，项目组首先综合利用系统宽频导纳模型和频率扫描法，建立了不同位置谐波电流注入引起换流站母线电压畸变的快速评价方法；基于换相电压-时间面积分析，项目组提出了一种分析谐波电压对换相过程影响程度的方法，建立了换流母线谐波电压畸变诱发直流输电换相失败评估指标，并进一步建立了谐波电流注入诱发系统内直流输电换相失败的评估方法，所提方法避免了繁杂的电磁暂态仿真，且具有易于编程实现等优势。项目组基于RTDS实时数字仿真系统和锦苏特高压直流实际控保系统，研究了锦苏直流近区1000/500kV主变充电励磁涌流对锦苏直流运行的影响，为特高压东吴站主变扩建等工程的启动调试提供了重要参考和指导；并以我国实际电网系统为例，分析了特高压直流换相失败甚至是闭锁对受端电网潮流、电压、频率的影响，明晰“大直流、弱受端”的特高压直流多馈入受端电网运行特性。此外，项目组还提出了一种基于谐波附加控制抑制直流输电连续换相失败的方法，该方法通过附加控制来改进低压限流环节（VDCOL）在换相失败恢复过程中的性能，可有效抑制直流输电连续换相失败的发生；所提控制方法不会对直流输电系统的正常运行产生不利影响，且仅需对直流输电VDCOL控制器进行适当的改造，无需一次设备投资、易于实现且成本较低，为直流输电连续换相失败抑制提供了一种新的思路和参考。