基于虚拟同步机控制的新能源发电并网系统小干扰稳定临界短路比

近年来的研究表明,电压控制型虚拟同步机(virtual synchronous generator,VSG)除具备为交流系统提供频率和电压支撑的能力外,对弱电网运行条件也具有良好的适应性。为提升电压控制型虚拟同步机并网系统运行稳定性,充分发挥其优势,探讨了电压控制型虚拟同步机并网系统小干扰稳定临界短路比(critical short circuit ratio,CSCR)的确定方法及相关稳定判据。为此,首先建立了虚拟同步机并网系统小信号模型,并将其整理为两输入两输出单位负反馈系统的表示形式。然后,基于广义奈奎斯特判据,探讨了考虑电网强度作用的系统小干扰稳定判据,定义了系统小干扰稳定临界短路比,可为未来虚拟同步机并网系统规划提供指导和借鉴。最后,通过仿真算例,验证了所提方法的有效性。

Critical Short-Circuit Ratio of Small-Signal Stability for a Grid-Connected Renewable Power Generation System Based on Virtual Synchronous Generator Control

Studies in recent years have shown that in addition to the ability to provide frequency and voltage support for AC system, the voltage-controlled virtual synchronous generators (VSG) are also of good adaptability to the operation conditions of weak grid. To improve the stability of a grid-connected VSG and exploit its advantages to the full, in this paper, a method to determine the critical short-circuit ratio (SCR) of the gird-connected VSG system and related stability criteria are explored considering small-signal stability (SSS). To do so, the small-signal model of a grid-connected VSG system is established and sorted into a form of negative feedback system with two-input and two-output units at first. Secondly, according to the generalized Nyquist criterion, a SSS criterion for the system considering impact of grid strength is proposed and a critical SCR is defined, which can provide guidance and reference for planning of gird-connected VSG systems in the future. Finally, methods proposed in the paper are validated through study cases.