Unit commitment by the lagrangian relaxation method

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Unit commitment by the lagrangian relaxation method


Author: Wong, Po-wah
Title: Unit commitment by the lagrangian relaxation method
Degree: M.Sc.
Year: 1994
Subject: Mathematical optimization -- Case studies
Multipliers (Mathematical analysis)
Lagrangian functions
Hong Kong Polytechnic -- Dissertations
Department: Multi-disciplinary Studies
Pages: v, 77 p. : ill. ; 30 cm
Language: English
OneSearch: https://www.lib.polyu.edu.hk/bib/b1161655
URI: http://theses.lib.polyu.edu.hk/handle/200/4857
Abstract: A new method based on the decomposition technique of Lagrangian Relaxation is developed in order to solve the unit commitment problem of a real system consisting of thermal, nuclear and pumped storage units. The system has large groups of identical units when compared with the system size, and has many operational constraints that are non-coupling and non-local in nature, including minimum plant on bar, forced pumping and generation, pumped storage operational flexibility requirement, crew constraints, minimum two-shifting of coal-fired units and unit grouping constraint. The major objective is to overcome the difficulty of the conventional Lagrangian Relaxation method in solving such a system, namely, simultaneous commitment of identical units and the inability to handle those non-coupling and non-local constraints. The proposed method consists of two phases of sequential commitment for the thermal units. The first phase produces a preliminary thermal unit commitment solution based on the assumption that there is no pumped storage operation. Then using the solution as the basis, the pumped storage units are scheduled optimally, taking into account the pumped storage related non-coupling and non-local constraints. On completion, the pumped storage capacity and generation contributions are deducted from the system requirements and the final solution is obtained after the second phase of sequential commitment. In each phase of sequential commitment, units are sequentially scheduled and system capacity requirement not yet met is considered whenever each unit is scheduled. This solves the problem of simultaneous commitment for identical units. The thermal unit related non-coupling and non-local constraints are handled through specially designed scheduling orders. The convergence rate of the solution process is improved by new updating algorithms for the Lagrange multipliers.

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