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Risk Control Of Transmission Line Overload In Wind-integrated Power System Considering Branch Outages And Complex Variable Correlations

Posted on:2016-11-27Degree:MasterType:Thesis
Country:ChinaCandidate:P LuFull Text:PDF
GTID:2272330479495450Subject:Power system and its automation
Abstract/Summary:PDF Full Text Request
Risk control of transmission line overload in power system, reflecting the power system security by risk indices, can have a more scientific and careful assessment and control of system security in muiti-operating conditions. The risk indices of transmission line overload are quantified by combining the possibility and severity of transmission line overload. The static security level of the whole system is improved by risk control using optimal power flow(OPF) tool. It can provide more effective information for the decision-maker. With the rapid development of new energy, wind energy has been paid much attention due to its perfect prospect. However, wind energy has the characteristics of randomness, intermittence and fluctuation, which brings great challenge for the system operation. Therefore, it is necessary to control static security risk for wind-integrated power systems considering the uncertainties and correlation of random variables. The risk control of transmission line overload for wind-integrated power system, considering branch outages and complex variable correlations, is researched in this dissertation. The main contents of the dissertation are listed as follows.Firstly, considering the uncertainties of loads, generator outputs and wind powers, risk control of transmission line overload for wind-integrated power system is carried out by the OPF tool. The objective function of OPF aims at both the generation power cost and risk of line overload. The likelihood and the severity of line overload are modeled to show the impact and consequence of line flow fluctuations on overload. Then risk indices are computed. Inequality constraints of OPF include the reactive power compensation capacity constraints and unit climbing constraints and so on. The path following interior point(PFIP)method to solve the OPF problem is introduced explicitly. The simulation is made on the modified IEEE-30 bus system. Results show that the risk of line overload is effectively reduced through the optimization of control variables and the safety of the power system is improved to some extent.Secondly, Cholesky decomposition method is used to describe the correlation of loads.The likelihood and the severity models of line overload are proposed to compute risk index of line overload. The risk control model of line overload is proposed with a objective function including power generation cost and line overload risk. The risk indices and the generation power cost are obtained through the optimization of control variables. The proposed method is tested on the modified 14-bus system. Simulation results show that the correlation of load affects the system generation cost and the line overload risk, and load correlation should be considered for risk control of line overload.Thirdly, four schemes are presented for disposing the dependence of correlated random variables, including Nataf transformation / polynomial normal transformation(PNT)combined with orthogonal transformation(OT) / elementary transformation(ET).Combined with the PEM, the formulation is proposed and adopted for solving the PLF andassessing risks of the transmission line overload. The proposed approach is applied to the modified IEEE 30-bus system. Numerical results show the effectiveness of the proposed approach, as compared to those obtained from the MCS. Results also show that the scheme of combining Nataf transformation and elementary transformation with PEM provides the best performance.Finally, on the based of the uncertainties and correlation of loads, generator outputs and wind powers, the branch outages are considered. The model of branch outages is formulated by compensation method. The scheme of Nataf transformation and ET is provided to dispose the correlations between loads, generator outputs and wind powers. In order to achieve a reasonable tradeoff between economy and security, a multi-objective optimization model of risk control is presented. The method is tested on IEEE 30-bus system, and simulation results show that the branch outages have prominent influence on line flows and risk indices of line overload.
Keywords/Search Tags:Wind-integrated power system, Risk control, Correlation, Point estimate method, Line outages
PDF Full Text Request
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