Static Voltage Stability Analysis And Control Considering Uncertainty From Renewables And Loads

Renewable technologies are vigorously developed in the new power systems.The characteristic of uncertainty and volatility of renewables result in significant challenges for the stable and safe operation of power systems.Coupled with the uncertainty of loads,the power systems are closer to the operating limits or stability boundary and even occurs voltage collapse.Thus,how to reduce the operational risk caused by the uncertainty and improve the static voltage stability of power systems are the urgent problems.In this thesis,static voltage stability analysis and preventive control methods of power systems with the uncertainty of renewables and loads are studied as follows.Firstly,the effects of uncertainties from both renewables and loads on two types of static bifurcation(i.e.,Saddle-Node Bifurcation and Structure-Induced Bifurcation)are studied.The nonlinear effects of renewables and load uncertainty on static voltage stability are illustrated by local bifurcation boundaries(or surfaces).Secondly,the dependence modeling method of renewables and the loads modeling method are investigated.A scenario-based scenario construction method is presented to model the uncertainty of both renewables and loads,respectively.The joint scenario sets generate by the Cartesian product of the renewable and load scenario sets.Considering the impacts of renewables and loads uncertainty on voltage stability,a scenario construction method is developed which is tailored for the static voltage stability problem.The method includes two parts: the scenario generation and scenario reduction,which can avoid the mis-elimination of the extreme scenarios and reduce the computational difficulties.Thirdly,the line switching problem with the uncertainty of renewables and loads is studied,and a three-stage solution method is proposed.The above scenario construction method is used to obtain representative scenarios.A weighted sensitivity-based method is used to quickly identify valid candidate lines,a more accurate look-ahead load margin estimation method is used to rank the valid lines,and finally uses the continuation power flow method to perform detailed evaluation calculations on the top-ranked lines.The results show that the method can ensure the maximum load margin of the look-ahead power system under the predicted value,as well as ensure the load margins of power system under all possible scenarios up to the desired value predefined by the operators,thus ensuring the static voltage stability of the power system.Finally,the effects and applications of line switching in AC/DC hybrid systems considering the uncertainty of renewables and loads are discussed.The effectiveness of the proposed method is illustrated by a modified IEEE 118-bus power system.The applicability of the proposed scenario construction method for voltage stability problems in AC/DC hybrid systems is discussed,and the validity of the proposed method is verified by the form of load margin interval.Secondly,the three-stage solution method is applied to the AC/DC hybrid system.The results show that line switching can improve the load margin of AC/DC hybrid system.