Chapter 1 presents the classification , causes , and harmful subsequences of low - frequency electromechanical oscillations in power systems . some typical accidents resulting from this kind of oscillations are presented 分析了低频振荡的分类，危害，成因以及典型故障事例，比较了多种能够抑制低频振荡的措施。
According to these theories we know the reason of the emergence of low frequency oscillation is lacking positive damping even appearing negative damping . this problem can be classified as dynamic stability 从而得出，电力系统低频振荡是由于系统正阻尼不足甚至产生负阻尼而引起的，可以将其归类为动态稳定问题。
On the basis of long - term mean summer rainfall in china , the onset , progression and withdraw of rainy season in china are analyzed , as well as the lfo climatology of summer rainfall over china is discussed 并且利用气候的中国夏季降水资料，分析了中国雨季的爆发、推进和结束，讨论了中国夏季降水低频振荡特征的气候学。
Low frequency oscillations among interconnected synchronous generators are phenomena inherent to power systems . the stability of these oscillations is of vital concern , and is a prerequisite for secure operation of power system 低频振荡是互联电力系统固有的现象，其振荡的稳定性是保障系统安全运行的先决条件，因此得到极大关注。
With high practicability , a set of novel analysis methods and control strategies on low frequency oscillations in interconnected power grids is established by the research results of this dissertation 对测试系统和实际电网的分析结果表明，论文的研究成果具有良好的工程实用性，从而为互联系统低频振荡研究提供了新的分析方法和控制策略。
Then residues associated with the oscillation of interest are used as the effective index and their relative magnitude under several operation conditions are used as the robust index of damping controllers 在此基础上，提出了用低频振荡模态对应的留数大小来衡量控制器输入信号的有效性，用多个运行方式下留数的相对大小来衡量输入信号的鲁棒性。
Compared with non - slung - load flight , additional aerodynamic load , gravity load should be considered in the slung - load system . so the moment to the gravity center , flight mode and the natural frequency will change 直升机吊挂飞行,与直升机非吊挂飞行状态相比,增加了新的气动载荷、重力载荷,和因此产生的对直升机重心的力矩,其飞行运动模式、低频振荡固有频率均发生改变。
The theoretical background of the test signal method is the theory of mechanical admittance and mode identification , which is based on the frequency scanning of the test signal and has already been used widely in mechanical engineering 提出了一种基于测试信号的小扰动稳定性分析方法?测试信号法，用于分析电力系统低频振荡问题。其理论基础是机械导纳理论和模态辨识理论。
The power spectral analysis is performed for daily 500hpa height field data in the mid - high latitudes of the northern hemisphere from 1950 to 1996 . the results show that : ( 1 ) intensity of low - frequency oscillation in winter is stronger than that in summer 应用1950 - 1996年北半球中高纬逐日500hpa高度场资料进行功率谱分析，得出： ( 1 )夏季低频振荡较弱，冬季低频振荡较强。
The driver adopted the technique of automatic power changing between high and low voltage and the driving mode of constant current cutting wave , so that the low - frequency vibration of the stepping motor was reduced and the high - frequency torque was increased 该驱动器采用高、低压电源自动切换供电技术和恒流斩波驱动方式，降低了步进电动机的低频振荡，提高了步进电动机的高频力矩。
