Analysis And Control Method Of Short-term Voltage Stability For Large-scale Grid Integration Of Photovoltaic Stations

With the increasing grid-connected penetration of photovoltaic power generation system,the impact of high photovoltaic penetration on the stability of power system,especially the short-term voltage stability caused by three-phase short-circuit fault is also increasingly significant.In order to improve the short-term voltage stability of gridconnected photovoltaic power generation system caused by three-phase short-circuit fault,this paper studies and explores three aspects: the modeling of photovoltaic power generation system suitable for fault-crossing,the analysis of the dominant factors of gridconnected voltage instability,and the formulation of control strategies to improve shortterm voltage stability.Firstly,a grid-connected photovoltaic power generation system model suitable for the whole process analysis of fault ride-through is established.Aiming at the whole fault ride-through process including the steady state before the fault,the fault period and the fault recovery period,based on the decoupling of active and reactive power,and according to China's grid-connected standard "Technical Regulations for Accessing Photovoltaic Power Stations to Power Systems",the reference values of active and reactive current in photovoltaic system during the whole process of fault ride-through are analyzed and formalized,and a photovoltaic power generation system model consistent with the response characteristics of actual units is established.The dynamic response characteristics of the whole fault ride-through process of the photovoltaic power generation system are analyzed under different voltage sags and stable output conditions,and the accuracy and reliability of the model are verified.Then,the different factors affecting the short-term voltage stability of large-scale photovoltaic grid-connected are analyzed and compared comprehensively.In order to simulate the actual grid structure,the influence of photovoltaic permeability,load composition(including load capacity and dynamic load proportion),control strategy(including active power recovery rate,reactive power support coefficient,control voltage switching threshold and starting point of active recovery)and power grid strength of photovoltaic power station on steady-state and dynamic voltage response characteristics are compared and summarized in detail,with typical systems including synchronous generation system,which provides a basis for analyzing voltage instability mechanism of photovoltaic grid-connected and proposing voltage-friendly control strategy.Finally,voltage-friendly control strategies are proposed to improve the short-term voltage stability of large-scale photovoltaic grid-connected.Based on the time domain simulation and dynamic bifurcation theory and according to the trajectory of typical operation points in the whole process of fault ride-through of voltage stability examples,it is found that the voltage instability at grid-connected points is strongly related to the power control strategy and control voltage switching threshold of photovoltaic system during and after fault clearance.For typical voltage instability cases,this paper comprehensively compares and analyses the influence of different parameters on the typical operating point trajectory in the process of fault ride-through.Voltage-friendly control strategies such as increasing the reactive power support coefficient,reducing the control voltage switching threshold,delaying the reactive power withdrawal and optimizing the active and reactive current,are proposed.The simulation results show that the proposed control strategies can effectively support the voltage sags caused by faults and improve the voltage recovery characteristics after fault clearance.