Power System Steady State Analysis And Optimal Operation Considering Uncertainty

With large-scale renewable energy systems integrated with existing power grid,prominent uncertainty arises in modern power system operation.Due to the randomness and intermittency of renewable energy,such as wind power and photovoltaic power,power system steady-state operation is significantly affected by uncertainty with wide usage and increasing penetration rate.Traditional methods based on deterministic theory are not fit for power system analysis considering uncertainty.In this context,the research of power system steady-state analysis and optimal operation under uncertainty is of theoretical and practical significance.From perspective of security and economy,this dissertation focuses on the influence of uncertainty of renewable generation on power system and presents research in three aspects including power flow analysis,steady state security analysis and economic dispatch.Firstly,power flow analysis based on interval model is studied in order to reduce the error of system state monitoring brings in by uncertainty.Secondary,research on steady state security analysis is conducted to improve the accuracy and efficiency of security evaluation method based on interval analysis theory.To make improvements on safety of economic dispatch scheme,robust optimal power flow considering contingencies in real-time economic dispatch is studied in the end.In the research of steady state power flow analysis based on interval model,current-injecting power flow algorithm based on interval theory and affine arithmetic is proposed in order to decrease the conservation of traditional iterative method.The proposed algorithm utilizes affine arithmetic in the problem solving procedure of current-injecting power flow model to decrease error cumulation.To increase accuracy and computation speed of existing optimal based interval power flow model,this dissertation proposes an improved affine arithmetic based optimization model and its solution method.Proposed two power flow algorithms were conducted in interval power flow calculation for several IEEE benchmark test systems.Test results show that the proposed interval current-injecting power flow algorithm is more accurate than traditional method,though conservation still exists.The improved affine arithmetic based optimization model is of high accuracy and its solution speed shows advantages in online application.In the research of interval steady state security analysis,an interval line flow calculation method based on power transfer distribution factor matrix is proposed in order to reduce the conservation of traditional interval DC power flow under line outage.In this research,interval AC power flow model under line outage based on sensitivity approach is also proposed to overcome the shortcoming of lacking interval bus voltage magnitude information in DC model.In contingency selection,a performance indices comparison and contingencies ranking approach based on Bayesian theory is proposed.Simulations on several IEEE benchmark test systems and two practical power grid show that the proposed method got the same results as Monte Carlo simulations.Computation costs show that proposed methods are suitable for online applications.In the research of robust optimal power flow considering contingency,a preventive security constrained optimal power flow method considering contingency is proposed.Comparing with existing model that takes no contingency into consideration,proposed model focuses on preventive security constraints in modeling.The model is based on affine adjustable robust optimization model and meets the requirements of system security under contingencies.In the proposed method,an effective constraints screening and selecting approach is utilized to overcome the computation burden brought in by numerous constraints.Multi-machine system under different operating conditions with various levels of uncertainty is selected as test system for preventive security constrained optimal power flow analysis.Test results show that proposed model with solution algorithm are able to acquire dispatch scheme which satisfies system security and economy.Computational cost illustrates the effectiveness of proposed method for real time economic dispatch.