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    Properties of the stability boundary in linear distributed-order systems

    , Article International Journal of Systems Science ; Volume 51, Issue 10 , June , 2020 , Pages 1733-1743 Majma, E ; Tavazoei, M. S ; Sharif University of Technology
    Taylor and Francis Ltd  2020
    Abstract
    This paper mainly focuses on some behaviours of the bounded input-bounded output (BIBO) stability boundary in the linear distributed-order system (LDOS). Finding an association between changes of weight functions of LDOS and variation of its BIBO stability boundary is the other aim of this paper. To achieve these goals, the tangential lines of the BIBO stability boundary for the extremely high and low frequencies are founded in the first step. Then, the additive identity and the multiplicative identity for the weight function maintaining the stability boundary intact are determined. In addition, it is proved that multiplying a set of multiplication factors in the form of polynomials to the... 

    Extended phase compensation design of power system stabilizer for Bisotoun power plant

    , Article Power Plants and Power Systems Control 2006 ; Volume 39, Issue 7 , 2006 , Pages 279-284 ; 9780080466200 (ISBN) Zafarabadi, G ; Parniani, M ; Rasouli, M ; Ansarimehr, P ; Sharif University of Technology
    Elsevier Ltd  2006
    Abstract
    This chapter describes performance of the power system stabilizer (PSS) of a large thermal power plant as tuned by the manufacturer. The stabilizer was redesigned based on extended phase compensation of the exciter input-the electrical torque transfer function and root locus analysis; and its effect on local, interplant, and interarea electromechanical oscillations was thoroughly analyzed. Participation factors and mode shapes were effectively employed to identify local, interplant, and interarea modes, as well as their characteristics. The PSS designed with extended phase compensation improves the damping of local and interplant oscillation modes considerably, and has some positive damping... 

    Transient stability improvement by using Advanced Static Var Compensator

    , Article 2003 IEEE Bologna PowerTech Conference, Bologna, 23 June 2003 through 26 June 2003 ; Volume 2 , 2003 , Pages 7-13 ; 0780379675 (ISBN); 9780780379671 (ISBN) Abazari, S ; Mahdavi, J ; Ehsan, M ; Zolghadri, M ; Sharif University of Technology
    IEEE Computer Society  2003
    Abstract
    Advanced Static Var Compensators (ASVCs) are used to improve transient stability of power systems. Transient stability enhancement is one of such applications which employs Flexible AC Transmission System (FACTS). This paper proposes a new method for calculating the current references for an ASVC. These current references are calculated based on Transient Energy Function (TEF). The simulations have been carried out using C++ and Matlab Sirnulink, and the corresponding results are provided. © 2003 IEEE  

    Convective stability of carbon sequestration in anisotropic porous media

    , Article Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences ; Vol. 470, Issue. 2170 , 2014 ; ISSN: 13645021 Hill, A. A ; Morad, M. R ; Sharif University of Technology
    Abstract
    The stability of convection in an anisotropic porous medium, where the solute concentration is assumed to decay via a first-order chemical reaction, is studied. This is a simplified model for the interactions between carbon dioxide and brine in underground aquifers; the instability of which is essential in reducing reservoir mixing times. The key purpose of this paper is to explore the role porous media anisotropy plays in convective instabilities. It is shown that varying the ratio of horizontal to vertical solutal diffusivites does not significantly affect the behaviour of the instability. This is also the case for changes of permeability when the diffusion rate dominates the solute... 

    Constrained tuning of two-parameter controllers: A centroid approach

    , Article Proceedings of the Institution of Mechanical Engineers. Part I: Journal of Systems and Control Engineering ; Volume 226, Issue 5 , 2012 , Pages 685-698 ; 09596518 (ISSN) Rahimian, M. A ; Tavazoei, M. S ; Sharif University of Technology
    2012
    Abstract
    The problem of tuning a two-parameter controller has been formulated as finding the centroid of the admissible region specified by the set of constraints that the controller should satisfy. The constraints can be as general as the closed-loop system stability or they may include several requirements on various stability, sensitivity, or performance measures. The design of stabilizing proportional-derivative (PD) controllers using the centroid of the stability region in the controller parameter space is considered as a case study. To this end, analytical formulas are derived to describe the stability boundaries of a class of integrating time delay systems, the stability region of which has a... 

    Design of a nonlinear power system stabilizer

    , Article IEEE International Symposium on Industrial Electronics, 4 July 2010 through 7 July 2010 ; July , 2010 , Pages 143-147 ; 9781424463916 (ISBN) Yasaei, Y ; Karimi Ghartemani, M ; Bakhshai, A ; Parniani, M ; Sharif University of Technology
    2010
    Abstract
    This paper presents a new controller for power system stabilizer (PSS) that, unlike the conventional linear controllers, consists of both a linear and a nonlinear part. The linear part is properly designed to improve the small-signal stability margin and the damping of the local electromechanical modes. The nonlinear part is then designed to improve transient stability margin of the system without violating the features offered by the linear controller. Both parts are designed based on a perspective which attributes the system oscillations to a Hopf bifurcation (HB) phenomenon. More specifically, the design of the nonlinear part is done through the definition of a nonlinear index that... 

    Stability analysis in graphene nanoribbon interconnects

    , Article IEEE Electron Device Letters ; Volume 31, Issue 12 , 2010 , Pages 1458-1460 ; 07413106 (ISSN) Haji Nasiri, S ; Moravvej Farshi, M. K ; Faez, R ; Sharif University of Technology
    Abstract
    We present a Nyquist stability criterion based on transmission line modeling for graphene nanoribbon (GNR) interconnects. This is the first instance that such an analysis has been presented for GNR, so far. In this analysis, the dependence of the degree of relative stability for multilayer GNR (MLGNR) interconnects on the geometry of each ribbon has been acquired. It is shown that, increasing the length and width, MLGNR interconnects become more stable  

    Robust stability analysis of uncertain multiorder fractional systems: young and Jensen inequalities approach

    , Article International Journal of Robust and Nonlinear Control ; Volume 28, Issue 4 , March , 2018 , Pages 1127-1144 ; 10498923 (ISSN) Taghavian, H ; Tavazoei, M. S ; Sharif University of Technology
    John Wiley and Sons Ltd  2018
    Abstract
    Robust stability analysis of multiorder fractional linear time-invariant systems is studied in this paper. In the present study, first, conservative stability boundaries with respect to the eigenvalues of a dynamic matrix for this kind of systems are found by using Young and Jensen inequalities. Then, considering uncertainty on the dynamic matrix, fractional orders, and fractional derivative coefficients, some sufficient conditions are derived for the stability analysis of uncertain multiorder fractional systems. Numerical examples are presented to confirm the obtained analytical results. Copyright © 2017 John Wiley & Sons, Ltd  

    Stability criteria for a class of fractional order systems

    , Article Nonlinear Dynamics ; Volume 61, Issue 1-2 , 2010 , Pages 153-161 ; 0924090X (ISSN) Kheirizad, I ; Tavazoei, M. S ; Jalali, A. A ; Sharif University of Technology
    2010
    Abstract
    This paper deals with the stability problem in LTI fractional order systems having fractional orders between 1 and 1.5. Some sufficient algebraic conditions to guarantee the BIBO stability in such systems are obtained. The obtained conditions directly depend on the coefficients of the system equations, and consequently using them is easier than the use of conditions constructed based on solving the characteristic equation of the system. Some illustrations are presented to show the applicability of the obtained conditions. For example, it is shown that these conditions may be useful in stabilization of unstable fractional order systems or in taming fractional order chaotic systems  

    A note on the stability of fractional order systems

    , Article Mathematics and Computers in Simulation ; Volume 79, Issue 5 , January , 2009 , Pages 1566-1576 ; 03784754 (ISSN) Tavazoei, M. S ; Haeri, M ; Sharif University of Technology
    2009
    Abstract
    In this paper, a new approach is suggested to investigate stability in a family of fractional order linear time invariant systems with order between 1 and 2. The proposed method relies on finding a linear ordinary system that possesses the same stability property as the fractional order system. In this way, instead of performing the stability analysis on the fractional order systems, the analysis is converted into the domain of ordinary systems which is well established and well understood. As a useful consequence, we have extended two general tests for robust stability check of ordinary systems to fractional order systems. © 2008 IMACS  

    Robust stability testing function and Kharitonov-like theorem for fractional order interval systems

    , Article IET Control Theory and Applications ; Volume 4, Issue 10 , 2010 , Pages 2097-2108 ; 17518644 (ISSN) Akbari Moornani, K ; Haeri, M ; Sharif University of Technology
    Abstract
    This study deals with the subject of robust bounded-input bounded-output (BIBO)-stability of a family of fractional order interval systems. Employing the idea of'robust stability testing function'and extending it to the case of intended systems, a simple graphical procedure for checking the robust BIBO-stability applicable to both commensurate and incommensurate orders is developed. Moreover, a Kharitonov-like theorem is provided that presents necessary and sufficient conditions for checking the mentioned stability of the fractional order interval systems with commensurate order α belonging to [1,2), but only sufficient conditions for commensurate order α in interval (0,1). Besides, lower... 

    A fast local index for online estimation of closeness to loadability limit

    , Article IEEE Transactions on Power Systems ; Volume 25, Issue 1 , December , 2010 , Pages 584-585 ; 08858950 (ISSN) Parniani, M ; Vanouni, M ; Sharif University of Technology
    2010
    Abstract
    Closeness to the nose point of P-V curve, or loadability limit (LL), and voltage instability is one of the main concerns of modern power systems. Hence, online evaluation of LL has attracted the interest of researchers in recent years. This letter introduces a simple local index for online estimation of closeness to LL, using two consecutive scalar local measurements. This index is achieved based on the fact that variation of the load apparent power is zero at LL. The index is suitable for implementation in numerical relays to stimulate local control actions to prevent voltage instability, and in the system control center for system-wide coordinated analysis and control measures. Simulation... 

    Game theoretic analysis of self-stabilizing systems on arrays

    , Article Journal of Computer and Systems Sciences International ; Volume 60, Issue 2 , 2021 , Pages 227-238 ; 10642307 (ISSN) Shoja, E ; Izadi, M ; Sharif University of Technology
    Pleiades journals  2021
    Abstract
    Abstract: In 1973 E.W. Dijkstra introduced the notion of self-stabilization in the context of mutual exclusion. Considering the same problem on an array, we present a game theoretic analysis of self-stabilizing systems with three- or four-state machines. We give a formalized definition of the problem as a game where each player’s strategy represents the state of its corresponding machine. For the three-state case, we prove the impossibility of any infinite self-stabilizing systems on an array. For the four-state case we consider two algorithms. For Ghosh’s solution [1] we prove the upper bound of (n – 1)(n – 3) steps and that this bound is tight. Also we present another four-state... 

    The Stability Analysis of Distributed Amplifier

    , M.Sc. Thesis Sharif University of Technology Pasdar, Abbas (Author) ; Medi, Ali (Supervisor)
    Abstract
    Advancement in the field of electronics can often be observed from the improvement in performance of active circuits and systems. The amplifier, because it is a highly versatile functional circuit, has always been one of the first to benefit from new developments. Of the many characteristic of an amplifier, perhaps the most notable are the gain and the frequency response. In many applications, both the gain and the bandwidth need to be optimized. One of the most significant structures which have proper gain and bandwidth, are distributed amplifiers. But these structures are nonsymmetrical and have many active loops. As a result, the stability analysis of distributed amplifier is quite... 

    Electronic and Structural Properties of Neutral, Anionic, and Cationic RhxCu4-x (x = 0-4) Small Clusters: A DFT Study

    , Article Journal of Cluster Science ; Volume 24, Issue 1 , 2013 , Pages 273-287 ; 10407278 (ISSN) Arab, A ; Gobal, F ; Nahali, N ; Nahali, M ; Sharif University of Technology
    2013
    Abstract
    In this study, electronic structure, stability, and tendency to exchange electron of neutral, anionic, and cationic RhxCu4-x (x = 0-4) small clusters were investigated by density functional theory calculations. For neutral small clusters, it was found that the most stable structures of Rh4, Rh3Cu and Rh2Cu2 have distorted tetrahedral shape while the most stable structures of RhCu3 and Cu4 have quasi-planer shape. Adding charges to the clusters, caused shapes of the most stable structures undergo variations. Stabilities of the neutral, anionic, and cationic clusters decrease linearly with increasing the copper content. In addition, calculated chemical harnesses indicated that the small... 

    Fractional calculus based stabilization technique applied to suppress chaos in chaotic circuits

    , Article International Journal of Modern Physics B ; Volume 24, Issue 24 , September , 2010 , Pages 4861-4879 ; 02179792 (ISSN) Tavazoei, M. S ; Haeri, M ; Jafari, S ; Sharif University of Technology
    2010
    Abstract
    This paper deals with a new fractional calculus based method to stabilize fixed points of single-input 3D systems. In the proposed method, the control signal is determined by fractional order integration of a linear combination of the system linearized model states. The tuning rule for this method is based on the stability theorems in the incommensurate fractional order systems. The introduced technique can be used in suppression of chaotic oscillations. To evaluate the performance of the proposed technique in practical applications, it has been experimentally applied to control chaos in two chaotic circuits  

    Boundary stabilization of a cosserat elastic body

    , Article Asian Journal of Control ; Volume 19, Issue 6 , 2017 , Pages 2219-2225 ; 15618625 (ISSN) Najafi, A ; Alasty, A ; Vatankhah, R ; Eghtesad, M ; Daneshmand, F ; Sharif University of Technology
    Abstract
    Boundary stabilization of vibrating three-dimensional Cosserat elastic solids are studied using mathematical tools, such as operator theory and semigroup techniques. The advantages of the boundary control laws for both boundary stabilization problems are investigated. The boundary stabilization problems are studied using a Lyapunov stability method and LaSalle's invariant set theorem. Numerical simulations are provided to illustrate the effectiveness and performance of the designed control scheme. © 2017 Chinese Automatic Control Society and John Wiley & Sons Australia, Ltd  

    An integrated performance and robust stability based multi-model control of nonlinear systems: a PH neutralization reactor

    , Article 2017 25th Iranian Conference on Electrical Engineering, ICEE 2017, 2 May 2017 through 4 May 2017 ; 2017 , Pages 679-684 ; 9781509059638 (ISBN) Ahmadi, M ; Haeri, M ; Sharif University of Technology
    Abstract
    This paper presents a new multi-model control scheme which integrates the stability and performance requirements to determine the nominal local models. Gap metric and stability margin concepts are applied to measure the distance between the local models and to grid the operation range of nonlinear system, respectively. The minimization of the integral of time absolute error is included as performance criterion. Furthermore, the multi-model decomposition and local controllers design are integrated in an optimization problem which provides avoidance of the redundancy issue. A fixed PI structure is considered as the local controllers to simplify the global multi-model controller structure.... 

    Algebraic conditions for stability analysis of linear time-invariant distributed order dynamic systems: a lagrange inversion theorem approach

    , Article Asian Journal of Control ; 2018 ; 15618625 (ISSN) Taghavian, H ; Tavazoei, M. S ; Sharif University of Technology
    Wiley-Blackwell  2018
    Abstract
    BIBO stability of linear time-invariant (LTI) distributed order dynamic systems with non-negative weight functions is investigated in this paper by using Lagrange inversion theorem. New sufficient conditions of stability/instability are presented for these systems accordingly. These algebraically simple conditions are relatively tight and their conservatism is adjustable. © 2018 Chinese Automatic Control Society and John Wiley & Sons Australia, Ltd  

    Algebraic conditions for stability analysis of linear time-invariant distributed order dynamic systems: a lagrange inversion theorem approach

    , Article Asian Journal of Control ; Volume 21, Issue 2 , 2019 , Pages 879-890 ; 15618625 (ISSN) Taghavian, H ; Tavazoei, M. S ; Sharif University of Technology
    Wiley-Blackwell  2019
    Abstract
    BIBO stability of linear time-invariant (LTI) distributed order dynamic systems with non-negative weight functions is investigated in this paper by using Lagrange inversion theorem. New sufficient conditions of stability/instability are presented for these systems accordingly. These algebraically simple conditions are relatively tight and their conservatism is adjustable. © 2018 Chinese Automatic Control Society and John Wiley & Sons Australia, Ltd