Security Region And Sensitivity Based Optimal Power Flow

As the fundamental industry, the security and economic operation of the electricpower system is quite significant to the economic development and society stability ofthe whole nation. In the recent years, on the contribution to the grid scale enlargement,rapid electricity marketing progress, interconnection of regional power grid as well asthe fast growing load, the operation state becomes closer to the stability boundary.Besides, the large-scale cascade blackouts take place in high frequency all around theworld, which makes it even urgent to efficiently and sufficiently consider thecomprehensive security constraints in the optimal power flow. The methodology ofsecurity region provides new views and powerful means to solve such problems; inthe meantime the application of sensitivity method is proved to be effective to dealwith complicate nonlinear constraints and power space transformation.First of all, a general optimization model of real and reactive power based onsecurity region and sensitivity method is established in this paper, and thecorresponding algorithm is developed. Their characteristics are as follows:a) The research is based on non-decoupled AC power flow model, and aims atthe total active and reactive power generation cost optimization;b) For the first time, the thermal security region in the decision-making space isadopted to describe the thermal security constraints, in addition to the practicaldynamic security region in the decision-making space ensuring transient stability andthe static voltage stability region in the cut set power space ensuring voltage stability.Since the power flow is not decoupled in the optimization, and the description ofthermal security constraints takes both the effects of real and reactive power in thetransmission line, the result in this paper is quite precise. This research not onlyconquers the problem of taking both voltage stability and transient stability intoaccount in the traditional method, but also improves the consideration of thermalconstraints in the previous study of security based optimal power flow.In this paper, the computing speed of optimal power flow is improved byapplying sensitivity method to concerting the static voltage stability region in the cutset power space into linear constraints in the decision space. Furthermore, the researchuses a dual iterative method to timely correct the coefficients of linear constraintsexpression in the optimization process, in order that the accuracy of static voltagestability constraints is ensured along with fast convergence speed.