特高压直流换流站交流滤波器组对电网谐波的影响分析

特高压直流换流站配置的交流滤波器兼具特征谐波滤除和无功补偿功能，但其易与电网背景谐波阻抗相互作用导致低次谐波放大现象。交流电网谐波阻抗的获取是交直流系统谐波特性分析及交流滤波器设计配置的基础。文中根据电网谐波阻抗特性较为复杂，难以建模计算的特点，提出了一种基于换流站不同运行工况的500 kV交流电网背景谐波阻抗实用估算方法；定义了交流滤波器组谐波增益指标，通过该指标分析了特高压直流换流站交流滤波器组对电网低次谐波的放大机理；研究了交流滤波器参数与放大作用间的关系，提出了2种交流滤波器的改造方案。最后，以绍兴换流站测试数据为例，结合电网背景谐波阻抗估算结果，对其5次谐波放大问题进行了理论分析，并对交流滤波器改造方案进行了探讨。

Analysis on Impact of AC Filter Sets on Power Grid Harmonic in UHVDC Converter Station

The ultra-high voltage direct current(UHVDC)converter station is usually equipped with multiple sets of AC filters, which can filter the characteristic harmonics and compensate for the reactive power. However, the AC filters are easy to interact with the background harmonic impedance of power grid to cause low-order harmonic amplification. The background harmonic impedance of AC power grid is the foundation of harmonic characteristic analysis and AC filter design. According to the fact that the characteristics of background harmonic impedance of power grid are complex and it is hard to be calculated by modelling, this paper proposes an estimation method of background harmonic impedance of 500 kV AC power grid based on different operation conditions of the converter station. Then, the harmonic gain index of the AC filter sets is defined. Through this index, the amplification mechanism of the low-order harmonics by the AC filter sets in the UHVDC converter station is analyzed. The relationship between the amplification and the parameters of AC filter is studied, and two modification schemes for AC filters are proposed. Finally, taking the measured data of Shaoxing converter station as an example, and considering the estimation results of background harmonic impedance of power grid, the 5th harmonic amplification problem is theoretically analyzed, while the modification schemes for AC filters are discussed.