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电压源型变流器(VSC)接入弱同步电网后与电网交互作用显著,易引发系统次同步频带的稳定性问题.为研究这一现象的机理和特性,建立包含锁相环、电压前馈等环节的VSC变流器小信号数学模型.采用特征值分析方法进行系统振荡模态、阻尼比、相关因子计算,分析得出影响系统次同步频带稳定性的关键因素及变化规律.结果显示,增强电网网架结构,优化VSC变流器中的锁相环和电压前馈滤波参数可以减小系统振荡风险.最后通过电磁暂态仿真对上述分析结论进行了验证.“,”Voltage-source Converters (VSC) have significant interaction with the power grid after being connected to the weak synchronous grid, which easily leads to the stability problem of sub-synchronous frequency band. In order to study the mechanism and characteristics of this phenomenon, a small signal model of VSC grid connected converter containing PLL and voltage feedforward control loop is constructed. The eigenvalue analysis method is used to calculate the system oscillation modes, damping ratios, and related factors. The key factors affecting the stability and changing rules are analyzed. The results show that the system oscillation risk can be reduced by enhancing the grid structure and optimizing the phase lock loop and voltage forward feed filter parameters in the VSC converter. Finally, the analysis results are verified by electromagnetic transient simulation.