Improvement Of Static Voltage Security Evaluation Method Based On Security Region

In recent years,with the rapid economic growth in China,energy consumption is increasing day by day,and the power system is often under heavy load.Power outages can have a major impact on the national economy.This places higher demands on the static safety of the power system.Node voltage constraints as one of the most basic safety constraints of the power system must be given sufficient attention.Compared with the point-by-point analysis method,the security region method can evaluate the overall security margin of the system,and the evaluation results are intuitive and practical.It is easy to guide the operators to implement targeted measures and has been widely used in the static security analysis of power systems.The static voltage security region is a superpolyhedron composed of multiple hyperplanes.The operating personnel must determine the relative positional relationship between the current operation point and the security region boundary by taking its second and third-dimension sections,resulting in large information storage and inconvenient reading.It is not easy to implement online real-time applications.In fact,the relative positional relationship between the operating point and the security region boundary can be represented quantitatively by a series of directed distances.In this paper,the security region indicator of the boundary between the operating point and the security region is defined based on the security region boundary polynomial.The index calculates the coefficient of the hyperplane that consists of multiple critical points and obtains the directed distance d from the actual operating point to the hyperplane,the effects of various variables in the decision space on the safety distance of the operating point are fully taken into account.In practical applications,the safety of the system operating point can be judged by the positive and negative distances.The absolute value of the directed distance can further reflect the safety of the operating point.This index quantifies the assessment of node voltage safety in the static voltage security region.It can determine the safety of the system as a whole and completes the shortcomings of a section that can only determine the local safety of the system.It is more simple and practical,it is easy to guide operators to implement targeted measures.After the expected accident,point by point whether the system can only give a safe conclusion for an accident,the system can not provide a margin of safety information.In order to further extend the security region analysis method to the security analysis of N-1 network,on the basis of the basic operating state security region,a method based on the sensitivity method to modify the system parameters to rapidly obtain the N-1 static voltage security region is proposed.Firstly,the branch opening is considered as a kind of power disturbance.Based on the calculation of the power flow at the critical point,the power increment of the relevant node is obtained through the sensitivity equation,and the control variable at the critical point is corrected to obtain the value of the control variable at the critical point in the N-1 state.Then,the partial derivative of the Jacobian matrix element to the branch admittance was obtained.After the branch break occurred in the system,the relevant elements in the Jacobian matrix under the basic operating conditions were corrected by the sensitivity coefficient and the branch admittance to get the N-1 security region boundary to calculate the required row vector.Finally,replacing the corresponding variables in the security domain in the basic operating state,recalculating the security region polynomial,and quickly obtaining the N-1 static voltage security region.