Convergence problems in fast decoupled load flow type methods

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Convergence problems in fast decoupled load flow type methods


Author: Hui, Hoi-chau
Title: Convergence problems in fast decoupled load flow type methods
Degree: M.Sc.
Year: 1995
Subject: Electric power systems -- Load dispatching
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Pages: 1 v. (various pagings) : ill. ; 30 cm
Language: English
InnoPac Record:
Abstract: The FDLF type methods developed by Stott and Alsac have been widely used in power system load flow studies to expedite the speed of computation. However, under certain conditions, FDLF does have convergence difficulties. In the dissertation, the convergence condition for the general non-linear iteration scheme is first determined and this is applied to the FDLF to get the theoretical convergence criteria. The convergence of FDLF is shown to be dependent on the network parameters (the maximum R/X ratio, the susceptances) and the region of interest for the solution. To overcome the convergence problem, several approaches have been suggested, namely: 1. The series compensation scheme by Dy Liacco and Ramarao, 2. The parallel compensation scheme by Deckmann et al, 3. The MFDLF by Fang, Song and Chung, 4. The reverse Stott model by Nanda et al, 5. Rajicic and Bose's Method, and 6. Super decoupled load flow with distributed slack bus by Haley and Ayres. The various methods have been surveyed, this is followed by critical evaluation and comparison of the efficiency and effectiveness of them. None of the methods seems to offer a perfect solution. The FDLF and MFDLF have been successfully implemented on a personal computer, using the standardised FORTRAN language, and applied to a 5 bus sample and the IEEE 14 bus. No computer storage problem was encountered, acceptable accuracy was achieved, and the time of execution was generally within seconds. Only a modest amount of modifications on the FDLF program is necessary to accomplish the MFDLF. The MFDLF method has been further amended here with the following novel features: a. Use the mean argument of Yii's as the angle of rotation, b. Employ a multiplier p, which is empirically determined, to the angle of rotation, c. Adjustment of the P vector for PV buses. The amendments will enhance convergence, preserve the symmetry of the [Y] matrix, simplify calculations and improve accuracy.

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