基于系统开环频率特性的自动发电控制振荡分析

频率振荡中与自动发电控制(AGC)过程强相关的振荡被称为AGC振荡.基于单机单负荷系统,利用开环传递函数对AGC振荡进行分析,并通过分析不同参数或环节对开环传递函数频率特性的影响,研究其对AGC振荡的影响,结果表明:AGC参数中频差系数及积分系数过大、AGC传输延时过大、机组环节频率特性的幅值过大或相位滞后过大,都会导致系统开环传递函数的稳定裕度过小甚至为负,从而降低系统稳定性甚至引发AGC振荡.分析了机组特性对于AGC振荡的影响:一次调频起作用时,机组环节的幅值将会降低,从而提高AGC模式的稳定性;不同的水火电机组,其原动机环节的相位滞后不同,这会影响开环传递函数的相位裕度,进而影响AGC模式稳定性;机组的开度模式一般比功率模式拥有更快的一次调频调节速度,此时采用开度模式,机组在振荡频率处的幅值更低,系统AGC模式更稳定.特征值分析验证了理论分析的结果,且在多机多负荷系统算例中,验证了基于单机单负荷系统分析得到的结论.

Analysis of Automatic Generation Control Oscillation Based on Open-loop Frequency Characteristic of System

In the categories of frequency oscillation, the oscillation strongly related to the process of automatic generation control (AGC) is called AGC oscillation. Based on the single-unit single-load system, the AGC oscillation is analyzed using open-loop transfer function. And the influences of various parameters or elements on AGC oscillation are studied by analyzing their influences on frequency characteristics of the open-loop transfer function. The results show that the stability margin of the open-loop transfer function of the system will be too small or even negative, thus reducing the stability of the system and even causing AGC oscillation if the frequency response coefficient and integral coefficient of AGC parameters are too large, the transmission delay of AGC is too long, and the amplitude or phase lag of the frequency characteristic in the generation unit is too large. The influences of the unit characteristics on AGC oscillation are also studied. When primary frequency regulation works, the amplitude of the unit will be smaller, thus improving the stability of AGC mode. The phase lags of prime movers for different hydropower or thermal units are different, which will affect the phase margin of the open-loop transfer function, and then affect the stability of AGC mode. The opening regulation mode tends to have faster primary frequency regulation speed than power regulation mode. Therefore, when adopting opening regulation mode, the unit will have lower amplitude at the oscillation frequency to make the AGC mode more stable. The results of theoretical analysis are all verified by eigenvalue analysis. Moreover, in the example of a multi-unit multi-load system, the conclusions based on the single-machine single-load system are verified.