Voltage Characteristics Analysis And Optimal Control Of Weak Transmission System With Large-scale Wind Power Photovoltaic

The continuous growth of the grid-connected scale of new energy power sources has significantly changed the dynamic behavior characteristics of the power system after large disturbances,and the system stability control is facing new requirements and challenges.Large-capacity wind power and photovoltaic power generation systems developed on a large scale are usually located in remote areas far from the main grid,and the short-circuit capacity is small and the AC grid is weak.With the large-scale application of conventional DC,flexible DC and flexible AC transmission FACTS devices in the power grid,a large number of new loads such as load-side variable-frequency loads and electric vehicles are connected.Affected by this,the power system has shown an obvious "double high"-high proportion can be Renewable energy and high proportion of power electronic equipment characteristics.The deep adjustment and change of the source,grid,and load structure have significantly changed the safety and stability characteristics of the power system.Therefore,it is necessary to deeply study the safety and stability problems that may exist in the power grid at the weak sending end under the large disturbance short-circuit fault of the branch circuit breaking.Based on the typical data of the northwest and southwest UHV AC and DC large power grids of scientific research projects,this paper uses the PSD simulation software to study the safety,stability and suppression measures of the weak sending end power grid under the large disturbance short-circuit fault of the branch breaking.The establishment of the AC/DC hybrid system model connected to the w ind farm and the simulation model of the photovoltaic power generation system is studied.The wind power generation model considering LVRT is studied,and the model composition of HVDC transmission system is studied.A photovoltaic power generation system simulation model considering the low voltage ride-through function is established.Its main components include photovoltaic cell arrays for photoelectric conversion,Voltage Source Converter(VSC)and its control system,and AC side reactance.The voltage characteristics and optimal control measures of wind power grid-connected systems based on different simulation scales are analyzed.This paper analyzes the key factors of the commutation failure of the HVDC system after the short-circuit fault occurs on the inverter side of the receiving-end power grid,which leads to the transient overvoltage of the transmitting-end busbar,and analyzes the AC-DC interaction mechanism.The difference between the simulation results of transient overvoltage at the sending end and the sending end under different fault locations verifies the accuracy difference of the simulation results of different simulation models and the use of electromechanical-electromagnetic transient hybrid simulation to take into account the simulation speed and accuracy in the AC-DC hybrid power grid.sex,with better usability Finally,a solution is proposed for the transient overvoltage problem of the sending bus caused by the short-circuit fault.The purpose of suppressing the voltage fluctuation caused by the large-scale wind power connection to the power grid is achieved,and it has certain engineering practical value.The voltage characteristics and optimal control measures of the photovoltaic grid-connected system are analyzed.The influence of the dynamic changes of active and reactive power on the grid-connected voltage of the weak AC system under the large disturbance short-circuit fault is analyzed,and the mechanism of the voltage oscillation of the weak AC system caused by the periodic entry and exit of photovoltaics is revealed.On the basis of the impact of low wear recovery speed on oscillation,mitigation countermeasures are proposed.For the central Tibet power grid with high photovoltaic penetration,for the photovoltaic weak AC grid-connected system after large disturbance,the correctness of the analysis of the periodic oscillation generation mechanism and the effectiveness of the countermeasures are verified.