Research On Frequency Stability Strategy Of Power Grid Under High New Energy Proportion

At present,China is vigorously promoting the development and construction of new energy power generation.With the decrease of fossil energy and the increasingly serious environmental pollution,optimizing energy structure and gradually replacing traditional thermal power generation with new energy power generation will be the future development direction of power grid.Since the new energy power generation has the characteristics of random output and low inertia,the increase of the proportion of new energy power generation in the power grid will lead to the deterioration of the frequency modulation ability of the system and the decrease of the anti-disturbance ability of the power grid,which brings severe challenges to the frequency stability of the system.Therefore,it is of great significance to study the frequency stability strategy of new energy high proportion power grid.In this thesis,on the basis of summarizing and drawing on previous research results,the frequency characteristics of new energy high proportion power grid are analyzed,and the following aspects are studied to improve the frequency stability of new energy high proportion power grid :The influence of governor parameters,load frequency characteristics and different power characteristics on system frequency stability is analyzed,and the influence of new energy grid connection on system frequency characteristics is studied.On the basis of considering the overall rotational inertia of the system,a frequency response model is established to simulate the different proportions of new energy,and the change of system frequency characteristics after the grid connection of new energy is analyzed.With the increasing proportion of new energy output in power grid,the frequency characteristics of power system have changed.This thesis analyzes the influence of load frequency characteristics and generator frequency characteristics on frequency dynamic process,expounds the working principle of steam turbine and turbine,and analyzes the influence of steam volume and water hammer effect from the perspective of system frequency.The changes of system frequency modulation ability,system overall inertia and system anti-frequency fluctuation ability after the grid-connected of new energy are analyzed,and the changes of system frequency characteristics after the grid-connected of new energy are studied.Primary frequency regulation is an important means to deal with frequency fluctuation under normal operation of power grid,and it is also the basis for studying lowfrequency load shedding and frequency stability.The large-scale grid connection of new energy makes the system have higher requirements for the primary frequency regulation ability of conventional units.In this thesis,based on the traditional frequency response model,considering the difference between hydropower units and thermal power units in the process of frequency response,and the change of system rotation inertia after new energy grid connection,an improved frequency response model is established to simulate the different proportions of water,fire and new energy.The influencing factors of primary frequency regulation are analyzed.Based on the analysis of water hammer effect,an optimization method of primary frequency regulation is proposed.The method avoids the negative contribution of water hammer effect to system frequency recovery by changing the dead zone and delay settings of hydropower units.Simulation results show the effectiveness of the method.Under frequency load shedding is an important part of the third defense line,which plays an important role in preventing system frequency collapse.In this thesis,the under frequency load shedding feedback link is added in the improved frequency response model,and the adaptability of the traditional under frequency load shedding scheme in the new energy high proportion power grid is verified.Aiming at the frequency characteristics of the new energy high proportion power grid,an optimization method of multiple acceleration load shedding based on frequency change rate is proposed.This method can improve the speed and accuracy of load shedding at the same time.The simulation experiment is carried out by actual power grid data,and the results show the effectiveness of the method.