水电机组引起的超低频振荡特性及抑制措施研究

Study on Characteristics and Suppressing Countermeasures of Ultra-low Frequency Oscillation Caused by Hydropower Units

近年来,直流孤岛送出系统中陆续出现了振荡频率低于0.1Hz的超低频振荡现象,严重危害电网的安全稳定运行。研究表明,由于水电机组中存在水锤效应,若调速器控制参数设置不合理,系统的阻尼和稳定性会恶化,水电机组比例过高会使得系统中出现超低频振荡。针对此问题,首先建立含PID型水电机组调速器的多机系统线性化状态空间模型,求解出超低频振荡模式。然后,采用阻尼转矩分析法分析调速器控制系统的阻尼特性,并提出一种基于相位补偿原理的调速器侧电力系统稳定器(governorpowersystem stabilizer,GPSS)设计方法,可以通过GPSS来增加调速器控制系统阻尼,从而抑制系统的超低频振荡。最后,在3机9节点系统中,采用特征分析法,根据参与因子和根轨迹对超低频振荡特性进行分析得出:调速器控制系统确实深度参与了超低频振荡现象,通过合理设置调速器控制参数可以增大超低频振荡模式的阻尼比。同时,在单机单负荷和4机2区域仿真系统中验证了该文所设计的GPSS抑制超低频振荡的有效性。

In recent years,ultra-low frequency oscillations with lower than 0.1 Hz have appeared in the islanded HVDC sending system successively,which seriously endangers the safety and stability of power grid.The research shows that the damping and stability of power system could be deteriorated due to the water hammer effect in the hydropower units and the unreasonable settings of governor control parameters.Moreover,the ultra-low frequency oscillation might be caused by the over-high proportion of hydropower units.Aiming at this problem,a linear state-space model of a multi-machine system with PID-type governor of hydropower units was firstly established in this paper to solve the ultra-low frequency oscillation mode.Then,the damping characteristics of governor control system were analyzed by using a damping torque method.Meanwhile,a novel design method of governor power system stabilizer(GPSS)by using phase compensation principle was also proposed,which can increase the damping of governor control system to suppress the ultra-low frequency oscillation.Finally,the characteristic analysis method was adopted in a 3-machine 9-bus system.According to the analysis of the ultra-low frequency oscillation characteristics based on the participation factor and the root trajectory,the governor control system has deeply participated in the ultra-low frequency oscillation,and the damping ratio of ultra-low frequency oscillation mode can be increased by setting the governor control parameters reasonably.And the effectiveness of GPSS designed for suppressing the ultra-low frequency oscillation is verified by simulation in a single-machine single-load system and a 4-machine 2-area system.