Summary of Engineering doctoral thesis: Study on stabilization and optimization of a large-scale system applying for power systems

The objectives of the thesis are to study on a method to analyze a large-scale system into a number of relatively independent subsystems (interconnected subsystems). Then, the dissertation will focus on designing a decentralized control method for the large-scale system which has been decomposed into the interconnected subsystems.
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Summary of Engineering doctoral thesis: Study on stabilization and optimization of a large-scale system applying for power systems MINISTRY OF VIETNAM ACADEMY OFEDUCATION AND SCIENCE AND TRAINING TECHNOLOGY GRADUATE UNIVERSITY SCIENCE AND TECHNOLOGY ……..….***………… VU DUY THUAN Study on stabilization and optimization of a large-scale system applying for power systems Major: Control theory and Optimization control Code: 62.52.60.05SUMMARY OF ENGINEERING DOCTORAL THESIS Hà Nội – 2018 INTRODUCTIONThe urgency of the thesis Study on large-scale systems have been facing a lot ofchallenges. One of the most difficulties is the increasing complexityof the mathematical models of the systems. This is due to a mutualinfluence of complex technology processes, environments andsociety on the system. In addition, calculation increase of eachsystem cannot be compared to the increase of its size. Thesedifficulties make the design of an efficient control strategy to dealwith the stability and reliability of a large-scale system, especiallyfor a multi-machine interconnected power network highlychallenging.2. The objectives, ranges, objects and research methods of thethesisa, The objectives The objectives of the thesis are to study on a method to analyze alarge-scale system into a number of relatively independentsubsystems (interconnected subsystems). Then, the dissertation willfocus on designing a decentralized control method for the large-scalesystem which has been decomposed into the interconnectedsubsystems. The proposed control strategy has been applied for amulti-machine electric power system, which is a typical example ofthe large-scale systems. With the above objectives, the dissertation consists of thefollowing contents: - Study on large-scale systems characterized by a number of nonlinearities and uncertainties. 1 - Design two control problems for a large-scale power system, including decentralized control for transient stability issue and hybrid control strategy for load-frequency control. - Design simulation model in MATLAB/Simulink package to demonstrate the accuracy and feasibility of the proposed control strategies. b, Range and object of research Relying on the previous studies about the large-scale systems,the author decided to design two control strategies to stabilize amulti-machine electric power grid which is considered to be a typicalexample of the large-scale systems under uncertainties andnonlinearities. The research range of this thesis is to build amathematical model for a large-scale electric power network consistsof more than three station areas under uncertainties as well asnonlinear constraints. The author applied analytical methods topropose a novel control strategy using modified Riccati equations indealing with the transient stability problem of the three-machineelectric power system. The author also suggested a hybrid controlscheme applying a PD-like fuzzy logic controller andsuperconducting magnetic energy storage devices to tackle the load-frequency control of a five-machine interconnected power network.Although the research results are obtained by numerical simulationdemonstrations, this study is completely significant in practicalapplications. c, Research methods - Theoretical research: Analyze the theory, build theoretical basisfor control problems under uncertainties with a number of given laws 2and constraints. The goal is to maintain the system frequency at thenominal value and bring the stability back to the power grid. - Tools: Lyapunov’s stability theory, Riccati equation, linearalgebra, fuzzy logic control, etc. - Based on the above tools, this thesis presented a controlstrategy applying modified Riccati equations to find an optimalfeedback control law with a state gain vector. The goal of this controlscheme is to damp instantaneous fluctuations caused by noises,thereby ensuring the stability of the system. The next part of thestudy focuses on designing an intelligent control strategy applying aPD-type fuzzy logic controller and superconducting magnetic energystorage (SMES) to maintain the network frequency at the nominalvalue. The control performances obtained in this study are verifiedthrough numerical simulations using MATLAB/Simulink package. Itis supposed that these research achievements are able to be afundamental study for the further studies of large-scale systemsunder uncertainties, then they can be applied for the reality.3. ...