Research On Security Constrained Optimal Power Flow Based On Power Transfer Relations

With the expansion of power system,the development of the national economy relies increasingly on electric power industry,and at the same time also put forward higher requirements to the power quality and power supply reliability,so that security constrained optimal power flow has become an important research direction of ensuring the safety and stability of power system operation and rapid response to a variety of contingencies.At present,the computational scale of SCOPF becomes larger with the anticipated fault set,and there are great difficulties in numerical solution.Therefore,how to optimize the complex SCOPF model and improve the accuracy and speed of the optimization algorithm has become a research hotspot.With the development of fully controlled power electronic devices,more and more SCOPF problems are taken into account Voltage Source Converter Based High Voltage Direct Current,VSC-HVDC.Based on the power flow transition relation,the preventive security constrained optimal power flow and the corrective security constrained optimal power flow with VSC-HVDC are studied in this dissertation.Specifically,the main focuses of this dissertation can be summarized as follows:First of all,the optimal power flow model of power system is described with mathematical language,and the objective function and the pre-contingency state constraints are introduced.On the basis of OPF,based on the power flow transfer relations established by contingency analysis,the active power flows on branches in the post-contingency state can be described as linear functions of those in the pre-contingency state,so that the active power flow constraints of the branches in the post-contingency state are modeled as reformed linear inequality constraints of the branch flows in the pre-contingency state.The post-contingency state constraints are established only including the pre-contingency state of active power flow which makes the PSCOPF model simplified.Secondly,the research on SCOPF model reduction methods is discussed.By grouping parallel lines and parallel transformers,the number of monitored branches is reduced according to the distribution of active power flow in grouped branches.Additionally,since the short-term capacity of power equipment is usually much greater than the long-term capacity,the flow constraints of the branches in the post-contingency state are screened accordingly to further reduce the scale of SCOPF problem.According to the simulation of test system and actual power system,the superiority of the proposed model in terms of speed is verified,compared to the traditional SCOPF model,and calculation accuracy is guaranteed under the premise.The application of the primal-dual interior point method to solve the SCOPF practical model has a good calculation efficiency,which can meet the application requirements of the actual large power grids.Finally,based on the OPF model of the AC system,the VSC equivalent model is established,which increases new constraints brought by the introduction of VSC-HVDC,and improves the OPF model considering VSC.In order to exert the rapid regulation ability of the converter station,We update the post-contingency state constraints with sensitivity coefficient so that the correction of the power flow after the contingency reflects in the constraints.Based on the basic theory and simulation of the test system,the feasibility of the method considering the correction of the VSC-HVDC control is validated.