Cascading Failure Analysis And Emer-Gency Control Of Power System

In recent years,a number of large-scale blackouts caused by cascading failures have oc-curred worldwide,resulting in huge economic losses and adverse social impact.Cascading fail-ures usually originate from simple faults,and their evolution is affected by various uncertainties,accompanied by overload,transient instability and other phenomena.With the large-scale inter-gration of new energy and the continuous expansion of the system scale,the disturbance of the power grid has a wider scope,and the consequences of cascading failures are more serious.In this paper,the analysis and control of cascading failures and emergency control of transient sta-bility are studied.The main research contents are as follows:1)In the analysis of cascading failures,a path searching method for cascading failures con-sidering the uncertainties of wind power output and load power is proposed.The error distribu-tion model of wind power output and load power is established.Based on cumulants and series expansion,the probabilistic power flow is calculated.The power flow distribution and power flow over-limit probability are obtained,which can reveal the operation state of the system more comprehensively.Considering the uncertainties of line power,the outage probability model is established.The cascading failure simulation is carried out according to the outage probability,and the potential cascading failure paths are found.2)Aiming at the prevention and control of load-dominated cascading faults,an emergency control model of power system cascading failures is proposed considering the probability of transmission line outages.Based on the operational reliability model,the spread path of over-load-dominated cascading failure is searched,and the high risk paths are selected according to the risk index.On this basis,taking the means of adjusting the output of generators and shedding load,an emergency control model is proposed for a high-risk cascading failure path.In this con-trol model,operational reliability model is approximated by the Sigmoid function and consi-dered as a constraint.Test case shows that the proposed model can coordinate security and economy while blocking the development of cascading failures.3)In the aspect of transient stability emergency control,the transient stability emergency control of power system is modeled as a large scale optimal control problem with the objective of minimizing generator trippig and load shedding,and the constraints of maintaining the tran-sient stability of power system.A sequential optimization algorithm based on finite element or-thogonal collocation is proposed,which transformes the original dynamic optimization problem into an alternating iteration of simulation layer and optimization layer.In simulation layer,dif-ferential-algebraic equations and sensitivity are solved based on finite element orthogonal collo-cation method combined with parallel computing technology.In optimization layer,the predic-tion-correction interior point method is used to solve the small-scale nonlinear programming problems,which improves the efficiency of the algorithm.4)For large-scale power system transient stability emergency control,a parallel sequential optimization algorithm based on network partition is proposed,including preprocessing layer,simulation layer and optimization layer.By controlling variable selection and initialization strat-egy in the preprocessing layer,the optimization space is greatly reduced and the convergence of the algorithm is improved.Through network partitioning,the block characteristics of Jacobian matrix is adopted in the simulation layer.The multi-core processor platform is applied to solve differential-algebraic equations and sensitivity in parallel,which further improves the computa-tional efficiency of the emergency control algorithm in large-scale systems.