Economic Dispatch Considering N-k Security Constraint

Static security of power system has always been the important issues for system operation and dispatch.Many issues make the requirements for system security increasingly strict,such as the expansion of the system in recent years,the interconnection of regional power grids and the frequent occurrence of serious faults.How to further improve the system security has become a highly valued topic.A large number of economic dispatches are based on DC model and unable to consider reactive power flow and voltage magnitude.The security analysis is often deviated,which may cause the dispatch strategies violation of power flow or voltage,and even eventually lead to large blackout events.In this background,it is significant to propose a security dispatch scheme that takes into account reactive power flow and voltage magnitude for system security.This thesis firstly introduces the current researches about security-constrained economic dispatch at home and abroad,overviews the traditional dispatch model and other related researches,and points out the shortcomings and defects of these researches.For example,some researches lack consideration of reactive power flow and voltage magnitude,and some researches considering system security only stay at the N-1 security analysis.Then,due to the disadvantage of traditional model that cannot analyze the reactive power flow and voltage amplitude in failure scenario,this thesis proposes a security-constrained economic dispatch considering reactive power and voltage amplitude in N-k failure scenario.The model calculates the power flow and voltage under various N-k failure scenarios by proposing line outage distribution factor considering reactive power flow and voltage magnitude.It then screens the violation scenarios,and adds the corresponding security constraints to the dispatch model.Through continuous iterations,it ensures that the final dispatch scheme can still control the power flow and voltage within a reasonable range in the failure scenarios.The main research objectives of this thesis are as follows:（1）Based on the linearized AC（LAC）model,some sensitivity factors considering reactive power and voltage magnitude are derived,including the proposed shift factor LAC-SF,the proposed power transfer distribution factor LAC-PTDF,and the proposed line outage distribution factor LAC-LODF.The derivation process comprehensively considers the factors ignored in traditional models,such as bus type,ground capacitance,reactive power,and voltage magnitude.（2）By enlarging the application scenario of LAC-LODF from the original N-1 scenario to the N-k scenario,the line outage distribution factor considering reactive power flow and voltage magnitude is obtained,which is useful to fast calculation of power flow and voltage in N-k failure scenarios.（3）Security constrained economic dispatch based on the LAC model（LAC-SCED）and an iteration mechanism for adding security constraints considering N-k scenario and LAC-LODF are proposed.The solution obtained by LAC-SCED will be continuously corrected by security constraints.This model finally obtains a dispatch strategy that operates safely in a pre-defined failure scenario.At the same time,this thesis considers that it will greatly increase the solution difficulty to add a large number of security constraints at an iteration,and avoids this problem by the design of the iteration mechanism.（4）Simulation experiments are constructed in IEEE 30-bus and 118-bus systems to analyze the effectiveness of the sensitivity factor and dispatch model proposed in this thesis,such as testing the accuracy of LAC-LODF for calculating power flow and voltage in N-k scenarios,and proving the security of the proposed dispatch scheme.Then,by comparing proposed model with other power flow models and dispatch schemes,the effectiveness of the proposed model is verified.