大扰动后正阻尼单机水电系统频率振荡的近似及适应性分析

Approximation and adaptability analysis of frequency oscillation in single hydromachine power system with positive damping after large disturbance

实际电网中发生了多次与调速器的死区和限幅非线性切换环节相关的复杂频率振荡事故。针对相关近似分析仅考虑单一的死区问题,构建了同时考虑死区和限幅的分段描述函数,基于此分析了含死区和限幅的非光滑单机水电系统在大扰动后正阻尼时出现的频率振荡现象及其特性,并分析了描述函数法的适应性。结果表明,近似光滑系统中同时存在不稳定和稳定极限环,其中稳定极限环可近似对应大扰动后正阻尼的非光滑系统出现的死区和限幅起作用的切换型频率振荡,并进一步解释了不同限幅参数下,振荡幅值变化而振荡频率基本不变的现象。适应性分析表明,系统参数变化可能使得低通滤波特性变差,导致描述函数法近似非光滑切换型振荡的分析精度变差。

Complex frequency oscillation accidents related to the dead zone and limitation nonlinear switching link of the governor have occurred in the actual power grid.In view of the problem that only dead zone is considered in the correlation approximate analysis,a piecewise description function considering both dead zone and limitation is constructed.Based on this,the oscillation phenomenon and characteristics of non-smooth single hydro-machine power system with dead zone and limitation when it has positive damping after large disturbance are analyzed,and the adaptability of the description function method is analyzed.The results show that there are both the stable and unstable limit cycles in the approximately smooth system,and the stable limit cycle can approximately correspond to the switching-type frequency oscillation engaged with dead zone and limitation in the non-smooth system with positive damping after large disturbances.It could also explain the phenomenon that the oscillation amplitude varies according to the limitation value,while the oscillation frequency remains unchanged.The adaptability analysis shows that the change of system parameters will deteriorate the low-pass filtering characteristics,resulting in the deterioration of the accuracy of description function method in approximating non-smooth switching-type oscillation analysis.