【作者】 谭平；

【导师】 竺炜；

【作者基本信息】 长沙理工大学 ， 电力系统及其自动化， 2011， 硕士

【摘要】 电力系统低频振荡主要是机电模式的振荡,其振荡频率多在0.2～2.5Hz之间。随着电力系统的互联规模的扩大,系统中还出现了频率低于0.2Hz的超低频振荡模式。这两种振荡都会严重降低系统的安全水平,甚至直接导致系统解列。本文通过分析电网侧扰动引起的机组强迫共振的原因,提出了共振抑制策略;并分析了电网侧扰动引起锅炉出力超低频振荡的原因。论文选题具有理论意义和实际应用价值。低频振荡常常发生在阻尼大于零的情况下,因此强迫阻尼共振往往是低频振荡发生的原因。介绍了振动力学中的单自由度弹簧系统及其强迫振动过程,阐述了与单自由度弹簧系统强迫振荡同原理的单机无穷大系统的强迫振荡过程。重点阐述分析了电网侧扰动引起汽轮发电机组机械功率共振的原因:当电网侧发生功率扰动时,实际的功频控制方式使机械功率阻尼降低,当扰动频率接近共振频率时,引发机械功率共振。现场运行证明,若汽轮发电机组发生低频振荡,可尝试改变调速系统控制方式以抑制振荡。只有通过对每种控制方式的阻尼特性和频率特性进行分析,才能在改变系统控制方式以抑制低频振荡时,做到有的放矢。因此,分析了汽轮机组调速系统在串级PI、单级PI1和单级PI2控制方式下的阻尼特性、频率特性和带宽;提出了控制方式的调整策略,以避开共振频率点。仿真表明,发生共振时,通过调整调速系统的控制方式,能有效地降低转子振幅。该方法依托调速系统的现有功能进行低频振荡抑制,便捷有效且能在线调整。发现了一种产生超低频振荡模式的物理原因。通过对火电单元机组的协调控制系统的原理分析,发现电网侧扰动可引起锅炉出力波动;分析了炉跟机和直接能量平衡两种机炉协调控制方式的动态特性,发现都存在0.1Hz左右的超低频共振点。仿真表明,若电网侧的超低频扰动与共振频率相同或接近,将引起锅炉汽轮机组输出功率的共振,功率的振荡幅值被放大。该发现对抑制电力系统超低频振荡方法研究具有现实意义。更多还原

【Abstract】 Power system low frequency oscillation mode is mainly mechanical and electrical oscillation, and the oscillation frequency between 0.2 ~ 2.5Hz. With the interconnected expansion of power system, it also appear ultra-low frequency oscillation mode in the frequency below 0.2Hz. The two oscillations would seriously reduce the level of system security, or even lead a direct result of system splitting. By analyzing the grid side disturbance to force unit resonance theory, we found the method to restrain the resonance; and analysis the reason why the grid side disturbance can cause the boiler output oscillation. The thesis topic has the Theoretical significance and practical application valueLow-frequency oscillations are often occurred in the case of damping greater than zero, so forced damped resonance often lead low-frequency oscillations. Firstly, the paper described the single degree of freedom vibration spring system and its forced vibration process in mechanics of vibration, and expounded the forced oscillation of single-machine infinite system which As profound as the mentioned theory. Secondly, it focuses on analyze the reasons of the mechanical power resonance of turbine units caused by disturbances in the grid side : When the grid-side power disturbance occurs, the actual power frequency control mode reduce the damping of mechanical power, when the disturbance frequency is close to the resonance frequency, it cause mechanical power resonance .Practical operation proved that if low-frequency oscillation occurs on turbines, that we can try to change the control mode of speed control system to suppress oscillations. Literature analysis shows that if the low-frequency power disturbance on grid side cause the mechanical power resonance, the rotor angle amplitude will be substantial increase. So, by analysis for the damping and frequency characteristics of the turbine control system in Serial PI、single stage PI1 and PI2 control mode, the adjustment strategy has been proposed, to avoid the resonance frequency. Simulation shows the amplitude of the rotor could be reduced effectively by turbine control mode adjustment when resonance occurs. This method inhibit low frequency oscillation based on the existing function of turbine regulating system, it is effective and can adjust on-line, and has the practical significance on system stable operation..This paper find a physical reason of what creates low frequency oscillation pattern. When we analysis Analyze the dynamic characteristics of the two kind of turbine and boiler Coordinated control system based on boiler follow and based on direct energy balance. The 0.1Hz Ultra-low frequency resonance point is in the system. Simulation results show that, if the ultra-low frequency perturbations of grid side close to or with the same resonant frequency, it will cause the resonance of boiler steam turbine output power, and the oscillation of the power is amplitude magnified. The discovery of suppressing power system’s ultra-low frequency oscillation method has practical significance.更多还原