特高压直流工程在极端工况严重故障下功率振荡及抑制策略优化研究

The UHVDC Power Oscillation Under Severe Faults in Extreme Conditions and Its Suppression Optimization Strategy

基于华东电网经典夏低极限方式搭建全电磁暂态模型,开展交直流电网交互影响的仿真研究时,发现在锦苏直流落点区域发生交流严重故障时,锦苏直流功率会大幅度持续振荡的隐患。研究分析确定,受苏州地区电网强度、负荷特性的影响,在极端工况下,锦苏直流过快的直流调节速度、缓慢恢复的交流电压交互影响,使得电流指令反复进出VDCOL环节,引起直流功率持续振荡。构建了采用典型交直流模型的小型算例,发现在特殊系统条件下,不同控制特性的直流输电系统均有可能出现上述问题。针对此种极端情况,提出了抑制振荡的优化控制策略,通过仿真试验,对优化策略的有效性和实用性进行了验证,保证故障恢复期间有效抑制直流功率振荡,使直流工况快速稳定恢复。目前该策略已应用于锦苏直流实际工程中。

Based on the classic summer low limit mode of East China power grid, an all electromagnetic transient simulation model of East China power grid is built to carry out the simulation study of the operating characteristics of UHV AC/DC hybrid power grids and to research the interaction between the AC and DC power grids. A hidden danger,the Jinsu DC power would oscillate and lasted for a while, was exposed when severe AC faults occurred nearby Suzhou Converter Station. Research and analysis show that affected by Suzhou power grid strength and load characteristics, under extreme conditions, the contradiction between the slow recovery speed of AC voltage of invertor station and the rapid adjustment speed of DC control system causes current command to enter and exit the VDCOL repeatedly, thereby causing DC power oscillation. By doing research in typical AC/DC models,it is found that the same problem may occur in HVDC systems with different control characteristics under special grid conditions. In response to these,we analyzed the oscillation causes and formulated optimizing strategies to suppress oscillation. A method of optimizing the VDCOL control strategy is proposed to ensure the effective suppression of DC power oscillation during fault recovery and to recover the DC operating conditions rapidly and stably without affecting the original DC control strategy. Through a series of simulation experiments, the effectiveness and practicability of the optimization strategy were verified. At present, this strategy has been applied to Jinsu DC project in real.