系统阻抗对竞比型低励限制控制励磁系统的稳定性影响研究

Influence of system impedance on stability of excitation system controlled by comparative UEL

推导了单机-无穷大系统在竞比型低励限制(UEL)动作后的扩展菲利普斯模型,并基于阻尼转矩法分析了发电机励磁系统阻尼转矩系数及同步转矩系数随系统阻抗的变化特性;采用小干扰稳定性分析法,从特征根分布、阻尼比大小以及参与因子等方面研究了竞比型UEL动作后系统阻抗对系统稳定性的影响。研究结果表明:当竞比型UEL代替励磁主环控制励磁系统时,系统阻抗的增加能够提高系统阻尼,增强系统稳定性,但同时会对无功功率的稳定性产生不利的影响,增加无功功率的波动次数;基于某实际励磁调节器厂家UEL模型详细分析了其与励磁主环发生反复切换的机理,验证了无功功率波动的死区范围配合不当时会引发系统振荡的结论。

The extended Philips model of single-machine infinite-bus system after the action of comparative UEL（Under Excitation Limiter） is derived,and the variations of the damping and synchronizing torque coefficients of generator excitation system vs. system impedance are analyzed based on the damping torque analysis. The small signal stability analysis is applied to study the effect of system impedance on the system stability after the action of comparative UEL in the aspects of eigenvalue distribution,damping ratio and participation factor. Results show that,when the comparative UEL,instead of the excitation main loop,controls the excitation system,the increased system impedance improves the system torque and enhances system stability,while weakens the reactive power stability and increases the occurrence times of reactive power fluctuation. The mechanism of the repetitive switching between UEL and excitation main loop is analyzed based on the model of an actual UEL to verify the conclusion that the inappropriate dead zone of reactive power fluctuation may lead to system oscillation.