Damping Technology Of Low Frequency Oscillation From Turbine Side

As the great development of electrical power industry, the power industry has been in a new stage of big-unit, ultra-high voltage, smart and large power network. The interconnection of grid is more and more strong; the distance of power transport is much longer. However, the operation condition of power system has also become more complicated and bad, the low frequency oscillations emerge oftentimes, become one of the most influential factors that restrict the line power transport, grid safety and stability.At present, the monitoring of low frequency oscillation is based mostly on WAMS, by a whole grid status monitoring and analysis, and to locate the oscillation source. But this method needs huge information and huge calculation, basically used for afterwards analysis, can hardly be used for real-time location. The damping method is mainly using PSS devices, which is an auxiliary for excitation system, to enhance the damping of the power system. But this method can only be used for damping a certain oscillation mode, can't damp all the modes of oscillation; it also can't deal the resonance oscillation.On these conditions, based on mechanic-electromagnetic torque coupling theory, this thesis brings forwards a new method of low frequency oscillation monitoring and damping from the turbine side. This method will realize the low frequency oscillation monitoring from power source side, and use the control system of steam turbine to damping the oscillation. To achieve this goal, this thesis builds a power system model including steam turbine and its control system, qualitatively and quantitatively analyzes the connection between each parameter of steam turbine, its control system and the power system stability, discussed the effect of nonlinearity of control valve flow output. Based on power system stability analysis, this thesis brings forward a new setting method of steam turbine control parameter, discusses the main ideas and key technologies of low frequency oscillation damping from the steam turbine side. In order to check the results of theory analysis, this thesis uses Matlab to build an analysis platform, including a multi-machine grid model, simulates the system damping changing caused by parameters, control modes and nonlinearity of control valves, and also checks the mechanism of resonance oscillation.This thesis introduces an oscillation distinguish method based on envelope curve shape. The energy function method can be used to realize the location of forced low frequency oscillation. The TLS-ESPRIT and damping torque method can be used to locate the negative damping low frequency oscillation, the simulation proved the validity. This thesis also discussed a new GPSS design method, which uses active power deviation as the input signal, phase makeup as the work principle. The parameter setting method has also been discussed. The simulation finds that this method can not only damping the negative damping oscillation but also the forced oscillation. This thesis also discussed the valid frequency range of this GPSS.Based on the researches above, this thesis designed a low frequency oscillation monitoring and damping system from steam turbine side, the simulation test finds that this system can realize the oscillation warning, mode analysis, source location, also damping the oscillation, can increase the maximum stability of the power system, guarantee the grid safe and stable running.