Field experiences have shown that sub-synchronous oscillations (SSOs) can occur in direct-drive wind farms with VSC-HVDC (DDWFV) systems. In light of this, a dynamic mathematical model of the DDWFV is established in this paper. The SSO characteristics are analyzed through the eigenvalue method. Considering the participation factor, the analysis reveals that the SSO is mainly affected by the grid-side converter controller of the wind turbine units, the rectifier controller of the VSC-HVDC and certain system parameters. The impact of system parameters on the damping performance and frequency characteristics of the SSO is further explored. By separating the VSC-HVDC into three parts, the impact of the control characteristics and the AC-side elements characteristics of the VSC-HVDC on the SSO is discussed. New insights into the SSO issue are also offered by analyzing the interaction among various state variables. The theoretical analysis is verified by extensive time-domain simulations.

中文翻译：

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带VSC-HVDC系统的直接驱动风电场的次同步振荡特性及分析

现场经验表明，在采用VSC-HVDC（DDWFV）系统的直驱风电场中，可能会发生次同步振荡（SSO）。有鉴于此，本文建立了DDWFV的动态数学模型。通过特征值方法分析SSO特性。考虑到参与因素，分析表明，SSO主要受风力发电机组的电网侧变流器控制器，VSC-HVDC的整流器控制器和某些系统参数的影响。进一步探讨了系统参数对SSO的阻尼性能和频率特性的影响。通过将VSC-HVDC分为三个部分，讨论了VSC-HVDC的控制特性和AC侧元件特性对SSO的影响。通过分析各种状态变量之间的交互作用，还可以提供有关SSO问题的新见解。通过大量的时域仿真验证了理论分析。