| With the development of electricity markets and the scale of the power grid in China,the number of accidents caused by power oscillations(or low-frequency oscillations)has increased a lot.It is generally believed that low-frequency oscillations are caused by the negative damping effect produced by the generator's fast excitation when the power system works at the states nearing to the stability boundary due to the limitation from economy,environmental protection,etc.However,as the capacity of steam turbines has increased and the performance of control systems has improved,the interaction between turbine-generators and the power system is much susceptible,and the governor system is led to play a more important role in low-frequency oscillations.The impacts of the turbine governor system on power system oscillations are investigated in this thesis by using MATLAB/SIMULINK.The main conclusions are shown as follow:(1)The electro-mechanical system of the interaction between turbine governors and power oscillations is modelled firstly.The models of the turbine and its digital electro-hydraulic(DEH)governor system as well as the electrical system are studies especially.The presented models are validated by simulation.(2)The impacts of the pure speed-loop DEH governor system as well as the combined power-frequency-loop DEH governor system on the power oscillations are studied through eigenvalue analysis and dynamic torque analysis method.And a mitigation strategy of power oscillations is provided by the means of lead-lag compensation.(3)The impacts of the turbine governor system with jam faults on power oscillations are studied by simulation analysis.The impacts of degree of jam faults,type of governor system and parameters of governor system on the low-frequency oscillation are simulated an analyzed.And a mitigation strategy to suppress the low-frequency oscillation caused by jam faults is proposed and validated through simulation study. |
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