多端柔直换流站高频谐振及传播机理分析与抑制

Analysis and Suppression of High-Frequency Resonance and Propagation Mechanism in Multiterminal Flexible Direct Converter Station

针对空载线路投入引起的多端柔性直流(modular multilevel converter multi-terminal direct current,MMCMTDC)输电系统高频谐振的问题,首先建立了MMC高频简化阻抗模型,基于阻抗分析法分析了空载线路投入引发单个MMC发生高频谐振的电气机理,分析发现由于空载线路投入使得MMC交流侧等效阻抗在高频段呈现负阻尼,继而引发高频谐振。而后针对不同控制方式下的受端换流站进行联合建模,通过对高频谐振能量在站间的传播路径及其对受端MMC运行影响的研究,发现MMC交流侧高频谐振能通过直流线路对其他MMC产生影响,其影响程度与外环控制方式有关。针对高频谐振问题,采用电压前馈增设带阻滤波器的抑制策略,消除了MMC在高频谐振点的负阻尼,完成了对起振MMC的阻抗重塑,有效抑制了MMC高频谐振,并降低了高频谐振能量传播对其余MMC的负面影响。最后利用RT-LAB5600实时在线仿真平台,验证了MMC高频谐振分析方法的正确性与相应抑制方法的有效性。

To address the issue of high-frequency resonance in multiterminal flexible direct current(DC)transmission systems caused by unloaded line input,a simplified impedance model is established for MMC in the high-frequency range.Based on the impedance analysis,the electrical mechanism of high-frequency resonance in a single MMC caused by an unloaded line input was analyzed.The analysis shows that owing to the unloaded line input,the MMC AC-side equivalent impedance exhibits negative damping in the high-frequency range,leading to high-frequency resonance.Joint modeling was then conducted for the receiving converter stations under different control methods.By analyzing the propagation path of high-frequency resonance energy between stations and its impact on the operation of receiving MMCs,research has shown that high-frequency resonance on the AC side of MMC can affect other MMCs through DC lines.The degree of the impact is related to the external control method.To solve the problem of high-frequency resonance,a suppression method involving the addition of a bandstop filter to the voltage feedforward was adopted to eliminate the negative damping of the MMC at the high-frequency resonance point,complete the impedance reshaping of the oscillating MMC,effectively suppress the highfrequency resonance of the MMC,and reduce the negative impact of high-frequency resonance energy propagation on other MMCs.Finally,the accuracy of the MMC high-frequency resonance analysis and the effectiveness of the corresponding suppression method were verified using the RT-LAB5600 real-time online simulation platform.