调速系统频率模态对电网低频振荡的影响

Influence of Governor System and Its Frequency Mode on Low Frequency Oscillations of Power Grid

随着调速系统技术的不断发展,调速系统对电网低频振荡(low frequency oscillation,LFO)的影响越来越引起人们的关注。现有理论研究表明,调速系统不仅会影响电网LFO阻尼特性,还会向电网引入一个独特的比LFO频率更低的振荡模态,该文称为频率模态,该模态会在调速系统动作时出现。该文首先采用转矩分析理论研究了调速系统对电网LFO阻尼特性的影响。然后以4机2区域系统为例,重点分析了频率模态的特点及其对LFO的影响,分析结果表明:频率模态是调速系统自身的一种控制模态,其阻尼比主要受调速比例–积分–微分控制器的参数影响;考虑到调速系统动作死区影响,在系统发生LFO且调速系统使该LFO阻尼为负的情况下,当频率模态阻尼较强时,电网功率LFO发散后会逐渐变为等幅振荡;而当频率模态阻尼较弱,电网功率LFO将会呈现出类似"拍频"的特性。最后,通过某实际互联电力系统仿真验证了上述分析结果的有效性。

With the technique development of the governor system, the influence of governor system on low frequency oscillations（LFOs） has attracted more and more attention. The current research shows that the governor system not only can influence the damping characteristics of LFOs, but also will introduce a special very low frequency mode into the power system. This mode, called by frequency mode, has lower frequency than LFOs and would appear when the governor system is performed. In this paper, the influence of governor system on the damping characteristics of LFOs was investigated by using the torque analysis theory. Then the feature of the frequency mode and its influence on LFOs were mainly analyzed base on a 4-machine 2-area system. The analysis results show that frequency mode is a control mode of governor system and its damping ratio is significantly influenced by the parameters of the governor proportional integral derivative（PID） controller. When the governor system makes the damping ratios of LFOs become negative and the dead band is taken into account, the system LFO will gradually become equispacing oscillation if the damping ratio of the frequency mode is relatively strong, while the power LFO will appear like a beat frequency oscillation if the damping ratio of the frequency mode is relatively weak. Finally, simulation results of a practical inter-connected power system validate the effectiveness of the analysis results above.