Research On Cascading Failures Prevention Strategy Of Power System With Regard To Voltage Stability

With the regional interconnection and marketisation of power systems,the scale of power grids is becoming larger and their architecture increasingly complex,leading to a wider spread of failures and an increased probability of triggering regional blackouts.Searching for key factors that trigger cascading failures at the source and developing effective prevention strategies to improve system operational safety are the keys to avoiding major outages.This paper focuses on power system interlocking failure defence,system safety assessment,voltage stability,vulnerable branches identification and interlocking failures prevention and control.The main work of the paper is as follows:For system safety assessment and voltage stability,this paper is based on the action characteristics of the line relay protection device,the distance between the electrical quantity and the boundary of the protection action zone to measure the safety level of the branch circuits,the construction of branch circuits safety index and system safety index,and give the cascading failures discriminatory formula;taking into account the impact of preventive control measures on the voltage stability level of the grid,this paper uses the Jacobi matrix minimum eigenvalue index to characterise the system In consideration of the influence of preventive control measures on the voltage stability level of the grid,this paper uses the Jacobi matrix minimum eigenvalue index to characterise the system voltage stability level.For the vulnerable branches identification,a vulnerable branches identification model that takes into account the difference in load rate is proposed.An expression for the degree of disturbance of the branches is obtained based on the deformation of the branches safety index to characterize the impact of the initial failures on the remaining branches of the system,and the Theil entropy index is introduced to analyse the impact of the difference in load rate of the branches on its vulnerability using its decomposability.The branches disturbance degree equilibrium is used to measure the impact distribution of the failure branches disconnection on the remaining system and to achieve the assessment of branches vulnerability.Finally,the rationality and effectiveness of the method in this paper are verified by simulation comparison.For the preventive control aspect,a cascading failures prevention strategy model for multiple initial failure scenarios with voltage stability in mind is proposed.The N-1 set of expected failures is established by screening several branches with high vulnerability from the vulnerable branches identification model,modelling the prevention strategy as an optimisation problem with the maximum system safety and voltage stability targets,and solving the model by non-dominated sorting genetic algorithms-II(NSGA-II).The model is solved and the Pareto compromise solution is selected from the solution set using the entropy weighting method to improve system operational safety and achieve preventive control of multiple initial failure scenarios by optimally adjusting the generator set output scheme.The effectiveness and superiority of the method in this paper is verified by simulation results of the IEEE-39 node system and the IEEE-118 node system.Finally,the full work is summarised and future research is envisaged.