On The Accuracy Of The Online Static Security Analysis Under Power Flow Model: Research And Improvement

Static security assessment(SSA)has been conducted on the power flow(PF)model for decades and plays an important role in on-line security analysis.Its postcontingency solutions well approximate the post-contingency steady states of the corresponding time-domain(TD)model when the loading conditions are not high.However,with the rapid development of national economy and the constant expansion of power grid,the maintenance of the aging facilities and the speed of new facilities construction cannot meet the increasing demand of people,which makes the power grid operating in heavy loading condition or overload state for most of the time and gradually pushes the system closer to its operating limits and security boundaries.The security and reliability of modern power system is facing more and more arduous challenge.Thus,this thesis aims to examine the accuracy of PF model-based SSA for whether there are misclassifications in evaluation or not under heavy loading conditions.According to the results of numerical study,taking the steady-state of the timedomain(TD)model as the benchmark,this thesis shows that the results of PF modelbased SSA approximates the benchmark and the accuracy of PF model-based SSA is satisfactory.However,as the loading condition increases,there are considerable increasing differences between the PF solutions and the benchmark,making PF modelbased SSA inaccurate which may misclassify insecure contingencies as secure ones(miss alarm)and secure contingencies as being insecure(false alarm),etc.what's more,it is worth mentioning that this observation persists both in different size cases when load variations and generation re-dispatch patterns are taken into account and in different load models.Physical explanations for misclassifications made by the PF modelbased SSA are provided.At last,this thesis suggests using the quasi steady-state(QSS)model in performing SSA and presents a theoretical foundation for the QSS model-based SSA to show that the QSS model offers an accurate approximation of the TD model in terms of the ?-limit set.Also,numerical study shows that the QSS model is about one magnitude faster than the TD model.Recent progress in high-performance computing infrastructures and commercial availability of GPU parallel computing enable the applicability of QSS model-based SSA in the online environment.Thus,we propose a remedy scheme to add a re-screening process to the existing on-line SSA,and use QSS model-based SSA to accurately analysis all possibly misclassified contingencies.It's remarkable that the re-screening index is derived from the physical explanations presented above.The feasibility and validity of this index and the remedy scheme are proved by numerical study.