Research On Situation Awareness And Optimal Control Of Power System Operation Security

The implement of global energy interconnection promotes the interconnection of transnational power grid and development of clean power generation.However,it raises a great challenge to power system security and defense.Due to the increasing complexity of large-scale power systems,successive failures make operation states worse.These failures can propagate and lead to large blackouts.Operation security analysis is the core part of defense architecture for power system security.It includes assessing the security margin of system operation states,capturing the trend features of changing states as well as providing control strategies to optimize operation states.Therefore,it is important to find effecive methods to enhance the situation awareness of operation security and take preventative or corrective controls when a worsening trend is detected,so that the risk of cascading failures can be reduced and the defense capability can be improved.Under the framework of defense architecture for power system security,this thesis studies several related issues,including synthetic evaluation of power system operation states,situation awareness in operation security,and security control.Main work of this thesis is summarized as follows:1.An intuitionistic fuzzy analytic hierarchy process(IFAHP)based method for evaluating power system operation states is proposed.The hierarchy model for assessing operation states is established,incorporating topology characteristics of network and operation security.According to the limitless of fuzzy set theory,intuitionistic fuzzy set(IFS)theory is employed to take into account the degree of membership,nonmembership and indeterminacy.Then,the judgment matrix is built using intuitionistic fuzzy numbers,and the weight coefficients are calculated by IFAHP.Furthermore,a dynamic adjustment strategy for the degree of indeterminacy is proposed,which improves the differentiation degree of evaluation.Compared with traditional methods,the proposed IFAHP model can effectively and flexibly identify the operation state of power systems.2.A framework of situation awareness in power system security is proposed.This framework consists of three levels:the perception of operation data,the security assessment of the current state,as well as the prediction of future system states and their trends.Firstly,the security distance model incorporating dynamic line ratings is established to measure the security margin of current and future system states.Then,the trend analysis method is developed to capture and identify trend features of the changing security margin.Furthermore,a homogeneous dispatch strategy with optimal transmission switching is proposed for power systems in worse situation.The proposed framework of situation awareness in operation security is important to improve smart monitoring for power systems.Besides,the proposed dispatch strategy can effectively improve the homogeneity of power flow distribution,so that the operation state of power systems can be optimized flexibly.3.A corrective control method is proposed from the perspective of power system security region.According to the limitless of traditional sensitivity method for active power security correction,the theory of security region is employed and the sensitivity of security distance is proposed.Based on the strategy of opposite and equal quantities,generators are ranked by their sensitivities of security distance and actual adjustable abilities.Then,a linear optimization model for active power security correction is established.The objective function is minimizing total adjustments,and the constraints incorporate power limits of all transmission lines.Generators are selected in pairs and the linear programming problem is solved.The proposed corrective strategy integrates security assessment and control.Besides,it is more intuitive and efficient than traditional methods when dealing with multi-overload cases,so that the problem of repeated adjustments can be avoided.4.A corrective control method for wind-integrated power systems is proposed.In order to connect with wind power forecasting,the range and mean values of wind power outputs are used to reflect uncertainties.With the objective of minimizing economic costs,a corrective control model is established.Based on distributionally robust optimization method,this model is transformed into a peer model that can be solved by linear programming.The proposed control strategy can deal with all possible fluctuations of wind power as well as ensure system security.In addition,the transition between economy and robustness can be realized by adjusting the constrained variables,and the evaluation of corresponding possibility can also be obtained.The proposed corrective control method can provide strategies with more flexiblity for system operators.