Investigations On Voltage Security Risk Assessment Of Power System And Its Application

Voltage security assessment has been the most important part of the security assessment for power system and it is also one of the hot points in current power system research. With the great changes of China's power system in physical and economic characteristic, the method and standard for voltage assessment should been changed accordingly under such new operational environment. So the voltage assessment is also a challenge and meaningful task today.This thesis pays more attention to the model and algorithm improvement both in deterministic and risk assessment with steady state method in low voltage and voltage stability area, and then their applications and improvements on the power system with the integration of large wind farms are also presented.Firstly, in deterministic assessment, the provement for the linearity of second order loss sensitivity near PoC (Point of Collapse) and the improvement for determining PoC based on second order loss sensitivity are presented. These results will provide basic theory for the comprehensive methods. And then the comprehensive method based on the second order loss sensitivity with load parameter, predict/correct technical and dichotomy is proposed. This method can determine the load margin constrained by three restrictions such as SNB (saddle node bifurcation), LIB (limit induced bifurcation) and the operation limit. And the generation restrictions of active and reactive power are also considered. Moreover the comprehensive method is simplified to satisfy the quickness requirement.Secondly, in risk assessment, this thesis makes efforts to find a more suitable way to economize computational time for risk index and its sensitivity calculation with the techniques such as the quick comprehensive method, the CS&R (Contingency Screening and Ranking) method and analytical method of probability assessment.Thirdly, according to the different generator units with the different characteristic and control modle, the modifications for power flow as well as the comprehensive method is carried out. And voltage security risk assessment for power system integrating large wind farms is presented, which takes into account two uncertainties such as the load uncertainty with normal distribution and the wind speed with weilbull distribution. And the semi-invariant method and Edgeworth series expansion are adopted to find the voltage and load margin's density functions and distributions, and then their risk indices. Finally, the voltage security assessment for LiaoNin power system integrating large wind farms under normal and N-1 contigency is carried out to demonstrate the validity and efficiency of the former researches under new circumstance.