多机系统锁相环振荡模式的数值域稳定判据

Numerical range stability criterion for PLL oscillation mode of multi-converter system

针对锁相环变流器多机系统的振荡问题,提出了面向多机系统锁相环振荡模式的数值域稳定判据,完善了广义Nyquist判据的可解释性。根据实际工程运行方式,通过保留变流器导纳矩阵中主导振荡的关键元素完成模型简化,进而利用矩阵数值域代替广义Nyquist判据,将多机系统的频域导纳矩阵等效为单机系统传递函数,以其Nyquist曲线不包围点(-1,0)作为多机系统稳定的充分条件。分析结果揭示了多机系统小干扰稳定性具有不同单机外特性相互折中的现象,为实用化的电网强度分析奠定了理论基础。通过特征值分析和时域仿真说明了所提方法的有效性。

For the oscillation of phase locked loop(PLL)multi-converter system,a numerical stability criterion for PLL oscillation mode of multi-converter system is proposed,and the poor interpretability of generalized Nyquist criterion is supplemented.Based on the actual operation modes in the engineering,the model is simplified by retaining the key elements dominating oscillation in the admittance matrix of the converter.With the numerical range of matrix instead of the generalized Nyquist criterion,the frequency-domain admit⁃tance matrix of the multi-converter system is equivalent to the transfer function of the single-converter system.Therefore,the Nyquist curve do not enclose the point(-1,0)serving as the sufficient condition for the sta⁃bility of multi-converter system.The analytical result reveals that the small disturbance stability of the multi-converter system has the rule that the external characteristics of single-converter compromise each other,which can provide a theoretical basis for the analysis of the practical grid strength.The validity of the pro⁃posed method is illustrated by eigenvalue analysis and time-domain simulation.