Research On Analysis And Suppression Measures Of Power System Forced Oscillation

The security and stability of the power grid could be seriously affected by low frequency oscillation (LFO), power system stabilizer (PSS) designed according to the negative damping mechanism can effectively inhibit low frequency oscillation. With the continuous development of power system, power oscillation phenomenon still occurs even the PSS are installed. Traditional research mainly starts from the excitation system, studies show that the turbine valve control system will also lead to power system low frequency oscillation. Part of the low-frequency oscillation mechanism has not yet been clearly analyzed, because the complexity of the grid structure, and changing operation mode, on the other hand, the low frequency oscillation monitoring method and measured data are not comprehensive enough.In 2013, the system low frequency oscillation accident occurred in China Southern Power Grid Company ZDLX power plant Unit 1 during single-sequence valve switching operation, the oscillation frequency was 0.171Hz, seriously affected the stable operation of the power grid. In this paper, turbine valve flow characteristic is analyzed, and according to the actual operating conditions, the excitation system, governing system and PSS model are established. Particularly, turbine model considering the valve flow characteristics is designed. Simulation platform is set up in PSCAD/EMTDC according to the models, the effectiveness of the model is verified, and the low frequency oscillation event is reproduced by simulation and corresponding mechanism is analyzed.The oscillation signal time-frequency distribution is obtained by transforming oscillation signals using WVD. And thermal power plant large-scale steam turbine governing system low frequency oscillation online monitoring and early warning are achieved, in order to ensure oscillation suppression measures are input in time. By using the designed filter, governing system oscillation disturbing could be filtered out. So oscillation can be suppressed, the effectiveness is proven by simulation.