Yazar "Atherton, Derek P." seçeneğine göre listele

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    Computation of Limit Cycles in Nonlinear Feedback Loops with Fractional Order Plants
    (Ieee, 2014) Atherton, Derek P.; Tan, Nusret; Yeroglu, Celaleddin; Kavuran, Gurkan; Yuce, Ali
    The paper deals with an aspect of the analysis of nonlinear feedback control systems with a fractional order transfer function. A review of the classical describing function (DF) method is given and its application to a control system with a fractional order plant is demonstrated. Unlike the DF method the frequency domain approach of Tsypkin is known to give exact results for limit cycles in relay systems and it is shown that this approach extends to systems with fractional order transfer functions. The formulation is done in terms of A loci which are related to and more general than the Tsypkin loci. Programs have been developed in MATLAB to compute the limit cycle frequency and also to show the results graphically. Examples are provided to illustrate the approach for a relay with no dead zone.
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    Design of stabilizing PI and PID controllers
    (Taylor & Francis Ltd, 2006) Tan, Nusret; Atherton, Derek P.
    In this paper, a new method for the calculation of all stabilizing PI controllers is given. The proposed method is based on plotting the stability boundary locus in the (k(p), k(i))-plane and then computing the stabilizing values of the parameters of a PI controller for a given control system. The technique presented does not require sweeping over the parameters and also does not need linear programming to solve a set of inequalities. Thus, it offers several important advantages over existing results obtained in this direction. The proposed method is also applied for computation of all stabilizing PI controllers for multi-input multi-output ( MIMO) control systems with consideration given to two-input two-output (TITO) systems using decoupling technique. Beyond stabilization, the method is used to compute all stabilizing PI controllers which achieve user-specified gain and phase margins. Furthermore, the method is extended to tackle 3-parameters PID controllers. The limiting values of PID controller parameters which stabilize a given system are obtained in the (k(p), k(i))-plane for fixed values of k(d) and (k(p), k(d))-plane for fixed values of k(i). However, for the case of PID controller, a grid on the derivative gain or integral gain is needed for computation of all stabilizing PID controllers. Examples are given to show the benefits of the method presented.
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    Estimating the Time Response of Control Systems with Fractional Order PI from Frequency Response
    (Ieee, 2015) Tan, Nusret; Yuce, Ali; Atherton, Derek P.; Deniz, Furkan Nur
    This paper deals with the time response computation of closed loop control systems with fractional order PI controllers using the frequency response data of the closed loop system. The time response of fractional order transfer functions from frequency response data was first obtained by the authors using Fourier Series Method(FSM) and Inverse Fourier Transform Method(IFTM). In this paper, these methods are further extended for estimating unit step and unit impulse responses of control systems with fractional order PI controllers from the frequency response information of the closed loop system.
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    Fractional Order PI Controller Design for Time Delay Systems
    (Elsevier Science Bv, 2016) Yuce, Ali; Tan, Nusret; Atherton, Derek P.
    This paper aims to look into the fractional PI controller design for a closed loop system having a plant with time-delay. The ultimate frequency of the system is found using a relay auto tuning test and then the parameters of a PI controller are estimated using this frequency in the Ziegler-Nichols (Z-N) tuning formula. These parameters are then used for a fractional order PI controller and the effect of varying the fractional integrator order (2) of the PI controller on the closed loop step response is examined. Finally, for a given example, the table that includes specifications of the control system for different A. values has been obtained and according to the desired specifications, optimum fractional order PI controller is designed. The presented results are illustrated with some examples. (C) 2016. IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.
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    An integer order approximation method based on stability boundary locus for fractional order derivative/integrator operators
    (Elsevier Science Inc, 2016) Deniz, Furkan Nur; Alagoz, Baris Baykant; Tan, Nusret; Atherton, Derek P.
    This paper introduces an integer order approximation method for numerical implementation of fractional order derivative/integrator operators in control systems. The proposed method is based on fitting the stability boundary locus (SBL) of fractional order derivative/integrator operators and SBL of integer order transfer functions. SBL defines a boundary in the parametric design plane of controller, which separates stable and unstable regions of a feedback control system and SBL analysis is mainly employed to graphically indicate the choice of controller parameters which result in stable operation of the feedback systems. This study reveals that the SBL curves of fractional order operators can be matched with integer order models in a limited frequency range. SBL fitting method provides straightforward solutions to obtain an integer order model approximation of fractional order operators and systems according to matching points from SBL of fractional order systems in desired frequency ranges. Thus, the proposed method can effectively deal with stability preservation problems of approximate models. Illustrative examples are given to show performance of the proposed method and results are compared with the well-known approximation methods developed for fractional order systems. The integer-order approximate modeling of fractional order PID controllers is also illustrated for control applications. (C) 2016 ISA. Published by Elsevier Ltd. All rights reserved.
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    An interactive design strategy for fractional order PI controllers in LabVIEW
    (Inderscience Enterprises Ltd, 2018) Yuce, Ali; Deniz, Furkan Nur; Tan, Nusret; Atherton, Derek P.
    This paper presents an interactive design for fractional order PI (FOPI) controller based on inverse Fourier transform method (IFTM) in accordance with stability region of a closed-loop control system in LabVIEW, which is a powerful graphical program. Stability boundary locus (SBL) method is used to obtain the stability region including all stabilising FOPI controller parameters in (K-p, K-i) plane. The time response of the closed-loop control system with FOPI controller is then obtained by IFTM using the stabilising controller parameters selected from stability region. Changing the selected fractional order controller parameters in stability region, users can observe the step response of the system interactively.
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    Limit Cycles in Nonlinear Systems with Fractional Order Plants
    (Mdpi, 2014) Atherton, Derek P.; Tan, Nusret; Yeroglu, Celaleddin; Kavuran, Gurkan; Yuce, Ali
    In recent years, there has been considerable interest in the study of feedback systems containing processes whose dynamics are best described by fractional order derivatives. Various situations have been cited for describing heat flow and aspects of bioengineering, where such models are believed to be superior. In many situations these feedback systems are not linear and information on their stability and the possibility of the existence of limit cycles is required. This paper presents new results for determining limit cycles using the approximate describing function method and an exact method when the nonlinearity is a relay characteristic.
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    Limit cycles in relay systems with fractional order plants
    (Sage Publications Ltd, 2019) Yuce, Ali; Tan, Nusret; Atherton, Derek P.
    In this paper, limit cycle frequency, pulse width and stability analysis are examined using different methods for relay feedback nonlinear control systems with integer or fractional order plant transfer functions. The describing function (DF), A loci, a time domain method formulated in state space notation and Matlab/Simulink simulations are used for the analysis. Comparisons of the results of using these methods are given in several examples. In addition, the work has been extended to fractional order systems with time delay. Programs have been developed in the Matlab environment for all the theoretical methods. In particular, Matlab programs have been written to obtain a graphical solution for the A loci method, which can precisely calculate the limit cycle frequency. The developed solution methods are shown in various examples. The major contribution is to look at finding limit cycles for relay feedback systems having plants with a fractional order transfer function (FOTF). However, en route to this goal new assessments of limit cycle stability have been done for a rational plant transfer function plus a time delay.
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    Methods for computing the time response of fractional-order systems
    (Inst Engineering Technology-Iet, 2015) Atherton, Derek P.; Tan, Nusret; Yuce, Ali
    There is considerable interest in the study of fractional-order systems but obtaining accurate time domain responses is a difficult problem. This is because all methods reported on to date use approximations for the fractional derivative both for analytical-based computations and more relevantly in simulation studies. This means unlike in integer systems exact simulations are not available and thus for considering non-linear problems and comparisons with measured data no exact solution reference exists. In this study, the authors provide a major breakthrough for this situation by developing methods which allow the exact computation of the time responses of fractional-order systems.
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    Obtaining the Time Response of Control Systems with Fractional Order PID from Frequency Responses
    (Ieee, 2015) Yuce, Ali; Deniz, Furkan Nur; Tan, Nusret; Atherton, Derek P.
    The paper deals with obtaining the time response of closed loop control system with fractional order PID controller using frequency response data. For this aim, a feedback control system with an integer order plant and a fractional order PID controller are studied. The real and imaginary parts of the closed loop transfer function are obtained which depend on the parameters K-p, K-i, K-d, lambda and mu of fractional order PID controller and real and imaginary parts of the plant. Then the time domain responses of the closed loop control system with fractional order PID controller are plotted by using Inverse Fourier Transform Method (IFTM) or Fourier Series Method (FSM). The presented idea is supported by some numerical examples.
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    Time Response Computation of Control systems with Fractional Order Lag or Lead Controller
    (Ieee, 2015) Tan, Nusret; Yuce, Ali; Atherton, Derek P.; Deniz, Furkan Nur
    In recent years, there have been many studies in the field of fractional order control systems. Many results have been published related with the frequency and time domains analysis of closed loop fractional order control systems. However, obtaining exact time response of a fractional order system is a difficult problem since it is not possible to derive analytical inverse Laplace transform of a fractional order transfer function. In this paper, an exact method is presented for computation of the time response of a closed loop control system with a fractional order lag or lead controller using frequency response data of the closed loop system. The presented method is based on the results, which use Fourier series of a square wave and inverse Fourier transform of frequency response information, previously derived by the authors. Numerical examples are provided to show the success of the presented method.
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    Tuning of Fractional Order PID Controllers Based on Integral Performance Criteria Using Fourier Series Method
    (Elsevier, 2017) Deniz, F. Nur; Yuce, Ali; Tan, Nusret; Atherton, Derek P.
    This paper presents a time domain tuning technique for a fractional order PID controller based on optimizing an integral performance criterion. A Fourier series based method (FSM) is used to calculate accurately the step response of the closed loop control systems so as to determine the exact value of the error function performance criterion. The initial guesses for the FOPID controller parameters to be optimized are found using the analytical solution for integral squared error optimization for an integer order PID controller. The proposed method is used for two test plant transfer functions by comparing different optimal FOPID controllers. The results show that the design technique based on optimization of different integral performance criteria give good step responses for FOPID controller. (C) 2017, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.