Research On Fault Impact Feature And Stability Control Of Power Grid With High Penetration Of Photovoltaic

In recent years,low-carbon industry and new energy technology have become research hotspots.The development of photovoltaic is rapid,the scale of power generation has been continuously expanded,and the penetration rate has gradually increased.The photovoltaic is connected to the power grid by the inverter and does not have the characteristics of conventional units.The inertia and equivalent scale of the power grid are both reduced,and the stability of the power grid is threatened.Therefore,the research on the impact of large-scaled photovoltaic grid-connection on the stability of the system becomes particularly important.In this paper,the photovoltaic electromechanical transient model has been established,and the large disturbance excitation method has been used to analyze the transient characteristics of photovoltaic grid-connected system.The optimization measures to improve the stability of the system have been proposed,and the actual large power grid have been simulated and verified.The main research contents and results are as follows.Firstly,the electromechanical transient model of photovoltaic grid-connected system considering LVRT has been built.The structure and characteristics of the photovoltaic power generation system have been described.The low voltage ride through control link has been added to the traditional photovoltaic electromechanical transient model.The four components of the model have been introduced in detail,especially LVRT and its recovery control system.Secondly,the impact of the gradual increase of photovoltaic grid-connected capacity on the transient power characteristics of the system has been analyzed by using the large disturbance excitation method,and the optimization schemes to improve the low-frequency problem of the system have been proposed.For the large-scaled photovoltaic grid-connected test system,the influence of strong related factors such as control mode and control parameters has been studied.Taking photovoltaic high-permeability Tibetan power grid as an example,the impact of LVRT of photovoltaic power generation on the frequency characteristics under the impact of short-circuit faults on the power connection line has been simulated and the corresponding optimization schemes have been proposed to improve the low-frequency problem that threatens the stable operation of the system.Then,the problem of voltage fluctuation has been studied after large-scaled photovoltaic grid-connected system is disturbed,and voltage control strategies for photovoltaic grid-connected system that takes into account HVRT have been proposed.The voltage characteristics and the principle of voltage rise of the AC grid after photovoltaic grid-connection have been analyzed.Based on the photovoltaic electromechanical transient model taking into account LVRT,different control parameters have been changed to solve the problem of voltage rise,and short circuit fault simulation has been performed for the Xinjiang PV power grid with high photovoltaic permeability,which verifies the effectiveness of the control strategies.At the same time,a photovoltaic electromechanical transient model that takes into account high voltage ride through has been established,and the feasibility of the control strategies has been illustrated by a photovoltaic grid-connected test system.Finally,the impact of large-scaled photovoltaic access on the dynamic frequency characteristics of the system has been analyzed from the perspective of three stages of frequency response,and measures to improve the frequency stability of the system using additional frequency controller have been given.By explaining the frequency response analysis model and the typical trajectory of the frequency response,the changes in the three phases of the grid frequency after photovoltaic grid-connection have been revealed.For the photovoltaic high-permeability Tibetan power grid,the changes in system frequency,mechanical power,and electromagnetic power under different photovoltaic penetration rates have been analyzed in delivery and receiving modes.By adding an AC frequency controller or a DC frequency controller and a combination of the two,the frequency stability of the system has been improved.