Analysis On The Static Voltage Stability Of UHVDC Transmission Based On The Wind-thermal Bundled Power System

Hami grid's has the character of large wind farm site conditions but the local load demand is less,and the grid size is limited.These make the Hami grid's structure is weak.Thus,a large amount of wind power must be transported to the heavy load region of central China.Considering the randomness and volatility of wind power generation,thermal power plants at Hami Tianshan converter station are bundled with wind power to transmit power to the main land of china.In addition,the transmission system is carried out by dc transmission system,so a special kind of UHVDC transmission system called "wind-thermal-bundled power system" is constituted in the Hami area.The study of static voltage stability in Hami power grid can not be ignored for the transmission of high wind power penetration in the new system.Based on the Hami power grid's operation and DIgSILENT/Power Factory software,a wind-thermal-bundled power system based on UHVDC transmission system model was built.Besides,the analysis of the voltage collapse mechanism of traditional power system and the static voltage stability index system of the high-voltage dc transmission system was established.Static voltage stability analysis is performed under deterministic operating conditions.First of all,the weak region of Hami was judged by the active power margin and the active power margin.Based on the relations between the voltage and reactive power which are obtained by modal analysis,the weak bus in Hami area and the weak region composed of high branch participation factors were quickly judged.Secondly,sensitivity analysis was carried out to avoid the possibility of one sidedness by modal analysis and can make a further verification of the weak bus in Hami area.Finally,the V-Q curve method was used to judge the reactive margin of the key bus or central transformer bus in Hami power grid and determined the amount of compensation.The simulation results show that the built system can work well in the Hami area.In addition,this paper also analyzed the static voltage stability of the local wind farm in different regional wind farms in the area.At the last of this paper,two schemes to improve static voltage stability of power system are proposed in this paper.The first kind of scheme aims to improve the grid structure of weak wind farm.This method can not only improve the weak wind farm collection of bus bar voltage characteristics and the wind power grid active margin,but also can improve the collection point bus bar and static weak regional wind power grid reactive power margin of bus.The second scheme adopts the combination of the power generating set and the DC transmission system,which can improve the voltage characteristics of the power grid.The simulation results show that both methods can effectively improve the static voltage stability of the power grid.