Yazar "Nwankpa, Chika O." seçeneğine göre listele
Listeleniyor 1 - 5 / 5
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe A sensitivity approach for computation of the probability density function of critical clearing time and probability of stability in power system transient stability analysis(ELSEVIER SCIENCE INC, 2006) Ayasun, Saffet; Liang, Yiqiao; Nwankpa, Chika O.This paper presents a linear approximation method to determine the probability density function (PDF) of the critical clearing time (CCT) and probability of stability for a given disturbance in power system transient stability analysis. The CCT is the maximum time interval by which the fault must be cleared in order to preserve the system stability. The CCT depends on the system load level and thus, is modeled as a random variable due to the probabilistic nature of system load demand. The proposed method first determines the sensitivity of the CCT with respect to the system load, and using these sensitivities it computes the PDF of the CCT based on the PDF of the system load. The probability of system being transiently stable for a particular disturbance and for a given fault clearing time is calculated using the PDF of CCT. This approach is verified to be accurate under the condition of small load deviation by Monte Carlo simulations method. Moreover, the proposed method reduces the computational effort significantly in Monte Carlo simulations indicating that it could be used in real-time on-line applications. (c) 2005 Elsevier Inc. All rights reserved.Öğe An Exact Method for Computing Delay Margin for Stability of Load Frequency Control Systems With Constant Communication Delays(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2016) Sonmez, Sahin; Ayasun, Saffet; Nwankpa, Chika O.The extensive usage of open communication networks in power system control causes inevitable time delays. This paper studies impacts of such delays on the stability of one-area and two-area load frequency control (LFC) systems and proposes an analytical method to determine delay margins, the upper bound on the delay for stability. The proposed method first eliminates transcendental terms in characteristic equation of LFC systems without making any approximation and transforms the transcendental characteristic equation into a regular polynomial. The key result of the elimination process is that real roots of the new polynomial correspond to imaginary roots of the transcendental characteristic equation. With the help of new polynomial, it is also possible to determine the delay-dependency of system stability and root tendency with respect to the time delay. An analytical formula is then developed to compute delay margins in terms of system parameters. For a large set of controller gains, delay margins of LFC systems are computed to investigate the qualitative effect of controller gains on the delay margin. Finally, simulations studies are carried out to verify the effectiveness of the proposed method.Öğe Probabilistic Evaluation of Small-Signal Stability of Power Systems with Time Delays(PRAISE WORTHY PRIZE SRL, 2010) Ayasun, Saffet; Nwankpa, Chika O.This paper presents a probabilistic approach to evaluate the small-signal stability of power systems in the presence of time delays. An exact method is proposed to determine the functional relationship between delay margin for stability and system parameters. The delay margin is modeled as a random variable and its probability density function (PDF) is estimated based on the PDF of the load using a Monte Carlo simulation approach. The probability of stability for a given time delay is determined using the estimated PDF of the delay margin. For illustration purposes, the method is applied to a single-machine-infinite bus (SMIB) power system with an exciter. The probability of stability for a given time delay is computed and their sensitivity with respect to various system parameters is investigated. It is found that the probability of stability values reduce with increasing the load uncertainty resulting in a less stable system while the stability performance could be improved by increasing the generator transient reactance. Moreover, the effect of generating damping on the probability of stability is relatively complex and larger damping may not result in a more stable operation. Copyright (C) 2010 Praise Worthy Prize S.r.l. - All rights reserved.Öğe Transformer tests using MATLAB/Simulink and their integration into undergraduate electric machinery courses(JOHN WILEY & SONS INC, 2006) Ayasun, Saffet; Nwankpa, Chika O.This article describes MATLAB/Simulink realization of open-circuit and short-circuit tests of transformers that are performed to identify equivalent circuit parameters. These simulation models are developed to support and enhance electric machinery education at the undergraduate level. The proposed tests have been successfully integrated into electric machinery courses at Drexel University, Philadelphia, PA and Nigde University, Nigde, Turkey. (C) 2006 Wiley Periodicals, Inc.Öğe Voltage stability toolbox for power system education and research(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2006) Ayasun, Saffet; Nwankpa, Chika O.; Kwatny, Harry G.This paper presents a Matlab-based voltage stability toolbox (VST) designed to analyze bifurcation and voltage stability problems in electric power systems. VST combines proven computational and analytical capabilities of bifurcation theory, and symbolic implementation and graphical representation capabilities of Matlab and its toolboxes. The motivation for developing the package is to provide a flexible simutlation environment for an ongoing research conducted at the Center for Electric Power Engineering (CEPE) of Drexel University, Philadelphia, PA, and to enhance undergraduate/graduate power engineering courses. VST is a very flexible tool for load flow, small-signal and transient stability, and bifurcation analysis. After a brief summary of power system model and local bifurcations, the paper illustrates the capabilities of VST using the IEEE 14-bus system as an example and describes its successful integration into power engineering courses at Nigde University, Nigde, Turkey.
