光伏场经柔直并网振荡稳定性分析与抑制方法研究

大容量远距离的光伏场经柔直送出将是未来电力系统发展的一个重要趋势,然而,光伏场经柔直送出互联系统存在建模复杂、阶数过高、难以直观解释失稳机理等问题。为此,本文建立了光伏场经柔直接入交流系统的开环、闭环模型,在此基础上基于开环模式谐振理论,提出了一种光伏场经柔直并网引发振荡失稳的分析方法,并且进一步地针对光伏场与柔直之间的动态交互展开了研究。研究表明：当光伏场主导开环振荡模式与换流站开环振荡模式在复平面接近时,二者将会发生强交互作用,降低闭环系统的稳定性,甚至失稳；基于残差理论可以对强交互作用下闭环振荡模式的数值进行预测。为了抑制光伏场与柔直之间的强交互作用,可以通过调整主导环节的参数抑制。若参数不可调整时,通过在发电单元主导环节装设阻尼控制器,使得其开环振荡模式远离换流站的开环振荡模式,从而破坏开环模式谐振导致的强交互作用,消除由强交互产生的振荡失稳风险。文中通过算例系统,验证了上述理论分析的正确性以及所提阻尼控制器的合理性。

Research on oscillation stability analysis and mitigation method of photovoltaic field connected to the grid via VSC-HVDC

Large-capacity long-distance photovoltaic field direct transmission will be an important trend in the development of power system in the future, however, photovoltaic field direct transmission interconnection system has problems such as complex modeling, high order, and difficult to intuitively explain the instability mechanism. Based on the open-loop mode resonance theory, an analysis method for oscillation instability caused by flexible grid connection of photovoltaic field is proposed, and the dynamic interaction between photovoltaic field and flexible straight is further studied. The results show that when the open-loop oscillation mode dominated by the photovoltaic field and the oscillation mode of the converter station are close in the complex plane, the two will have strong interaction, reducing the stability of the closed-loop system or even instability. Based on the residual theory, the numerical value of the closed-loop oscillation mode under strong interaction can be predicted. In order to suppress the strong interaction between the photovoltaic field and the flexible straight, the parameter suppression of the dominant link can be adjusted. If the parameters cannot be adjusted, the damping controller is installed in the leading link of the power generation unit to make its open-loop oscillation mode away from the open-loop oscillation mode of the converter station, thereby destroying the strong interaction caused by the resonance of the open-loop mode and eliminating the risk of oscillation instability caused by strong interaction. In this paper, the correctness of the above theoretical analysis and the rationality of the proposed damping controller are verified by the example system.