风火打捆系统次同步模式相互作用特性

风电和与其打捆的火电机组的模式相互作用存在诱发次同步振荡的风险。研究了风火打捆系统的模式准强相互作用的规律：随着参数的改变，直驱风机(permanent magnetic synchronous generator, PMSG)锁相环(phase-locked loop, PLL)模式靠近火电轴系模式并发生模式准强相互作用，两个模式的运动方向发生改变，其中的弱阻尼模式穿越虚轴快速变为负阻尼模式，引发次同步振荡，模式相互远离后系统振荡消失。研究表明，火电厂汽轮发电机轴系模式和PLL模式都可能穿越虚轴导致次同步振荡，而系统主要振荡的部分由负阻尼的模式决定。增强发生耦合的模式的阻尼有利于抑制相互作用，增大并网风机数量与线路阻抗都会加剧系统次同步振荡风险和振荡程度。最后基于PSCAD/EMTDC搭建风火打捆系统模型验证了理论分析的正确性，并提出应对措施避免振荡的发生。

Interaction characteristics of subsynchronous modes of a wind-thermal bundled system

There is a risk of inducing subsynchronous oscillations in the mode interactions between wind power and the thermal units that are bundled with it. In this paper, the law of mode quasi-strong interaction of a wind-thermal bundled system is studied: with a change of parameters, the permanent magnetic synchronous generator (PMSG) phase-locked loop (PLL) mode is close to that of the thermal power shaft system and a mode quasi-strong interaction occurs. The motion direction of two modes changes, whereby the weakly damped mode crosses the imaginary axis and quickly becomes the negatively damped mode, triggering subsynchronous oscillation, and the system oscillation disappears after the modes move away from each other. It is shown that both the turbine shaft mode of thermal power plants and the PLL mode may cross the imaginary axis leading to subsynchronous oscillations, while the main part of the system oscillations is determined by the negatively damped modes. Enhancing the damping of the modes where coupling occurs helps to suppress the interaction, and increasing the number of grid-connected turbines and line impedance both enhance the risk of system subsynchronous oscillations and exacerbate the degree of oscillations. Finally, the correctness of the theoretical analysis is verified by building a model of a wind-thermal bundled system based on PSCAD/EMTDC, and countermeasures are proposed to avoid the occurrence of oscillations.