Research On Ultra-low Frequency Oscillation Suppression Model And Control Strategy Of Hydropower Unit

To achieve the " double carbon target " proposed by China,hydropower,wind power and solar energy will gradually occupy the proportion of fossil energy generation.For example,the hydropower share of the Southwest Power Grid is 70 %.The high proportion of hydropower has brought new control problems to the hydropower-dominated power grid.Studies have shown that the water hammer effect of the prime mover part of the hydrogenerator unit has a power reverse regulation characteristic,which will greatly affect the dynamic performance of the hydro-generator unit.In addition,unreasonable governor parameters will eventually lead to ultra-low frequency oscillation.Aiming at the problem of ultra-low frequency oscillation in hydropower-dominated power grid,this paper first analyzes the mechanism of ultra-low frequency oscillation based on damping torque method.Based on the analysis and construction of the transfer function model of the main components of the hydropower governor system,a four-machine twonode power grid simulation system is constructed,and the main source of negative damping in the governor system is analyzed.For each variable in the governor transfer function model,the influence of the system damping in the 0.01 ～ 0.1 Hz frequency band is analyzed in detail,and several variables that are artificially adjustable and have a greater impact on the damping are found.Then the paper uses the idea of power system stabilizer for reference,and designs an additional damping controller for suppressing ultra-low frequency oscillation.After analyzing the amplitude-frequency characteristic curve and phase-frequency characteristic curve of the governor system,it is found that the phase angle difference between the input speed change and the output torque change of the governor system is more than 90 ° in the ultra-low frequency range of 0.01～0.1Hz.Therefore,based on the phase compensation idea,an additional damping controller using a central filter is designed.The paper builds a simulation model of a four machine two node power grid system to verify the theoretical research results,uses the matrix constraint method to analyze the dynamic curve of the governor system,and combines the root locus method to verify that the designed additional damping controller can effectively improve the damping of the system and suppress the ultra-low frequency oscillation phenomenon.Finally,aiming at the practical application of the additional damping controller,the paper analyzes the main factor that affects the parameters of the additional damping controller-the time-varying water hammer coefficient,discusses the adaptive tuning method of the controller parameters and designs the on-site tuning steps.Taking the DSP hydraulic turbine speed controller as an example,a semi-physical simulation system for the on-site tuning of the controller parameters is designed.