渝鄂柔性直流输电系统中高频振荡影响因素及抑制策略

针对柔性直流输电工程中出现的中高频振荡问题，现有解决方法是在电压前馈通道中增设滤波器以抑制高频振荡，但增加了中频振荡的风险。以渝鄂柔直工程南通道单元为研究对象，提出了一种通过调整控制链路延时以避免中、高频振荡的方法。首先，基于多谐波线性化原理建立了MMC换流站阻抗模型，详细分析控制链路延时、电网电压前馈策略对MMC换流站阻抗特性以及对系统稳定性的影响；然后，探讨通过调整控制链路延时以避免中高频振荡的可行性，并给出了控制链路延时的选择方法；最后，通过PSCAD/EMTDC电磁暂态仿真验证了所提方法可实现渝侧、鄂侧系统中高频振荡抑制，同时对系统动态特性影响较小。

Key Factors of Medium-High Frequency Oscillation in Chongqing-Hubei HVDC System and Suppression Strategies

For the problem of medium and high frequency oscillations in flexible HVDC projects, the existing solution is to add a filter in the voltage feedforward path to suppress high frequency oscillations, which, however, increases the risk of medium frequency oscillations. For this reason, a method is proposed to avoid medium-high frequency oscillations by adjusting the control link delay based on the south channel of the Chongqing-Hubei flexible HVDC transmission project. Firstly, a impedance model of MMC converter station is established based on the principle of multi-harmonic linearization, and a comprehensive analysis is made on the influence of control link delay and grid voltage feedforward strategy on the impedance characteristics of MMC converter station and system stability. And then, the feasibility of adjusting the delay of the control link to avoid the medium-high frequency oscillation is discussed, and the method for selecting the time delay of the control link is given. Finally, based on PSCAD/EMTDC electromagnetic transient simulation, it is verified that the proposed method can achieve the suppression of the medium-high frequency oscillations in both the Hubei-side and Chongqing-side systems. Meanwhile, the proposed method has minor effect on the dynamic characteristics of the system.