Static Security Analysis And Multi-objective Optimal Research Under N-1 In Wind Power Integrated System

In recent years,several blackouts that result from instability of power systems caused great losses to the country and local people.Grid interconnection of wind farms has large energy-saving emission reduction benefits.Meanwhile,large-scale wind power onlinein power systemhas brought new risksto secure and stable operation,and pose fresh challenges to dispatch and operation.Therefore,Multi-objective operation research of system energy conservation and emission reductionbased onassessment of wind powerfluctuation to the powersystem is very important.For this purpose,this thesis in allusion to the problem of power flow transfer and multi-objective optimizationunder N-1 in wind power integrated system,the specific contents are as follows:Firstly,in allusion to transmission lines overload caused by uncertain power flow transition due to grid-connection of wind farms,a method to analyze out-of-limit line flow,which describes system state variation by state transition theory,is proposed,and a system state transition model is established;The uncertain description of the injected wind power at grid-connected node is described by Weibull distribution,and state transition theory is adopted to determine the influence of the injected wind power on the variation of branch power flow and a state transition decision model under grid-connected wind farms is put forward;Utilizing fuzzy comprehensive evaluation and combining with the proposed indices the operational risks of transmission lines after the grid-connection of wind farms are effectively identified and the transmission line,where the out-of-limit power flow most likely occurs,is found;The highest capacity of grid-connected wind power,by which the secure and stable operation of power grid can be ensured,is given.Simulation results of IEEE 30-bus system show that the proposed theory and method are correct and effective.Secondly,in allusion to the problem of line overloadcaused byuncertaintypower flow transferin wind power integrated system,a method of N-1 security verification with wind farm is researched.This method firstly find severely affected lines by wind power through applying severity lines analysis method under wind power integrated system in the above chapter.This method then construct a new model of ground state current transfer factor combined with the theory of power flow transfer factor and the model of state transition with wind farm,which descript the proportional relationship between transferred trend and ground state power(no wind power integrated)under N-1 in wind power integrated system,and identify the power flow transfer path effectively.Finally,this paper introduced the fuzzy comprehensive evaluation method,built the severity evaluation model system,and quantified the running state of other lines after N-1 with wind power system.Simulation resuhs of IEEE 30-bus system show that the proposed theory and method are correct and effective.Lastly,in allusion to the problem of multi-objective optimization of energy-saving emission reductionunder N-1 in wind power integrated system,NSGA-H based multi-objective optimal power flowmodel under N-1 state in wind power integrated system is constructed.Under premise of guaranteeing the system operating safely,a multi-objective model with minimum generation cost and minimum emissions as objectives is built to find the Pareto set of optimal adjustable output in wind power integrated system under N-1 state.Fuzzy satisfaction-maximizing method is applied to choose compromise solution in Pareto solution set.At the end,the detail solving approach and process of multi-objective optimal power flow model is given in this chapter.Through the analysis of the example of IEEE-30,the rationality and the validity of the model is verified.This paper provides a theoretical analysis foundation to system power flow transfer identification,N-1 static security assessment and multi-objective optimization of energy-saving emission reductionin wind power integrated system.Thus provide guiding significance and reference value to security assessmentand multi-objective optimization analysisin wind power integrated system.