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Linearized Optimal Power Flow Of Hierarchical Controlled Islanded Microgrids

Posted on:2018-04-17Degree:MasterType:Thesis
Country:ChinaCandidate:C GongFull Text:PDF
GTID:2322330518963710Subject:Electrical engineering
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Optimal power flow(OPF)is usually leveraged as tertiary control in hierarchical controlled microgrids to provide optimal operating point of the system.Nonlinear power flow constraints typically make AC OPF problems non-convex and NP-hard.Hence,linear approximation technique is often used in practice in order to conveniently utilize linear programming algorithms which are efficient and robust.Linearization of power flow equations mainly based on application scenarios.Therefore,modeling and analysis of linearized power flow equation for islanded microgrids and its OPF applications are of great importance for system operation.The main contribution of this thesis are as following:1.Considering islanded microgrids,a topology and line parameter independent,active-reactive linear lossless power flow is formulated under mild assumptions.Its approximation error is analyzed in finite-dimensional Banach space.2.Based on the linear power flow model formulated above,a linearized AC OPF is formulated.Its objective function is properly chosen to restrict approximation error when optimizing voltage quality.Furthermore,a posterior losses compensation method is developed to improve the accuracy of OPF solutions.3.Adjustable robust optimization approach is leveraged to solve the uncertainty of renewable energy resources output in OPF.The variables are divided by different time scales to derive the affine decision rule.Then,the affinely adjustable robust counterpart of OPF is formulated which could be reformulated by linear programming.To demonstrate the accuracy and efficiency of the models derived in this thesis,numerical simulations are computed on different test cases,which are modified from 33-,69-,135-and 874-node distribution network test systems.The results show that the proposed linearized power flow is accurate in regular operating test systems;the OPF based on proposed model provides substantial computational speed improvements with minimal errors compared to a typical AC OPF and has advantage of accuracy over the OPF based on linearized power flow for general distribution networks;the proposed affinely adjustable robust OPF can guarantee the robust feasibility for all possible realization of uncertain parameters in the specific uncertain set and optimize the worst-case objective function value.
Keywords/Search Tags:islanded microgrids, hierarchical control, optimal power flow, linear approximation, affine decision rule, adjustable robust optimization
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