交直流电网深度耦合场景下直流偏磁超标机理分析及协同治理理论研究

DC bias not only leads to abnormal operation of crucial power network equipment, but also may cause serious power system accidents. Along with the deeply coupling of AC-DC network and the emergence of subway and other high-power DC load, the control effect of traditional DC blocking devices usually deviates the expected objectives. In addition, redirecting the DC flow to the nearby transformers without BDs has led to frequent interest disputes between power grid department and other utilities. The aforementioned situation calls for new requirements for the DC bias treatment: it is needed to analyze the DC bias problem caused by various kinds of incentives, to introduce advanced theory of coordination control between equipment level and system level, and to propose new sequential theory concerning the DC bias sequent suppression treatment. This project aims at eliminating the adverse effects of DC bias on the power grid, taking into account the interests of other utilities, analyzing multi-scene DC bias over-limit mechanism, and studying the coordinated co-switching method among DC blocking devices, and multiple DC blocking/balancing device coordinated control strategy, and theory of AC-DC hybrid power grid initiative defense against DC bias. The achievement of this project will lay a theoretical foundation for the conversion of DC bias treatment from "passive control" to "initiative defense".

直流偏磁不仅导致主变等电网核心设备异常运行，还有可能引发严重的电力系统事件/事故，传统治理手段以隔直装置为主。随着交直流电网耦合加深、地铁等大功率直流负荷的不断涌现，隔直装置顾此失彼或一触即发的现象日趋突出，治理目标与效果大相径庭。另外，主要由电网自身诱发的直流偏磁及简单的驱赶式解决方法，频繁引发电网与其他部门的利益纠纷。上述局面对新形势下的直流偏磁治理提出了新的要求：需要针对性分析各种诱因导致的直流偏磁问题，引入设备级与系统级协同控制的先进理论，提出直流偏磁序贯治理新理论与新方法。本项目以根除直流偏磁对电网造成的不利影响、同时兼顾其他部门利益诉求为着眼点，分析多场景直流偏磁超标机理、研究隔直装置协同投切方法、隔直/均直装置协同运行策略、以及交直流混合电网主动防御直流偏磁的理论与方法。本项目成果将为直流偏磁治理从“治标”式的被动应对向“治本”式的主动防御转化奠定理论基础。

随着我国交直流电网协同运行格局的逐渐形成，交流输电系统与直流输电系统之间的耦合愈发紧密，以直流偏磁为代表的新型问题也逐渐凸显出来，其危害性引起了社会的广泛关注。针对上述问题，本研究深入分析了在交直流电网深度耦合场景下直流偏磁治理的困难及需要，首先对不同类型的直流偏磁特性进行归纳，研究计及土壤分层导电特性的直流偏磁电流分布仿真及其频发-偶发超标机理。基于上述超标机理，从设备级层面提出了一种基于隔直装置优化控制及隔直/均直装置协同投切的偏磁治理策略集，以及从系统级层面，提出了一种基于直流运行方式主动调整的直流偏磁治理策略集。最后，以提升电网总体直流偏磁的治理效果并兼顾多方主体利益为着眼点，提出计及多方利益的交直流混合电网直流偏磁系统级主动防御理论，为直流偏磁治理从“治标”式的被动应对向“治本”式的主动防御转化奠定理论基础。