Research On Analysing The Properties Of Power System Frequency Oscillation And The Suppression Method

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.