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    Oscillatory condition and invariant sets in fractional order relay feedback systems

    , Article 27th Iranian Conference on Electrical Engineering, ICEE 2019, 30 April 2019 through 2 May 2019 ; 2019 , Pages 1097-1101 ; 9781728115085 (ISBN) Rezaei, D ; Tavazoei, M. S ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    In this paper, an oscillatory condition is obtained for fractional order relay feedback systems. This condition is derived by time domain representation of the response of the fractional order relay feedback system on the basis of the Mittag-Leffler functions. Also, using an inequality, which has been recently proved for fractional derivative of convex Lyapunov functions, an invariant set is found for the under-study fractional order relay feedback system. The obtained results are validated by numerical examples  

    Analysis of oscillations in relay feedback systems with fractional-order integrating plants

    , Article Journal of Computational and Nonlinear Dynamics ; Volume 12, Issue 5 , 2017 ; 15551415 (ISSN) Rezaei, D ; Tavazoei, M. S ; Sharif University of Technology
    Oscillatory behavior and transfer properties of relay feedback systems with a linear plant including a fractional-order integrator are studied in this paper. An expression for system response in the time domain is obtained by means of short memory principle, Poincare return map, and Mittag-Leffler functions. On the basis of this expression, the frequency of self-excited oscillations is approximated. In addition, the locus of perturbed relay system (LPRS) is derived to analyze the input-output properties of the relay system. The presented analysis is supported by a numerical example. Copyright © 2017 by ASME  

    Identification of external power system linear dynamic equivalents as MIMO feedback blocks for the study system

    , Article International Journal of Emerging Electric Power Systems ; Volume 8, Issue 5 , 21 Nov. 2007 , 2007 ; 1553779X (ISSN) Hamed Shakouri, G ; Ranjbar, A. M ; Lesani, H ; Radmanesh, H ; Sharif University of Technology
    The necessity of dynamic equivalents for power system analysis has been well known since the expansion of large interconnected power networks, and has been discussed during the last decades. The present paper proposes a new method for constructing dynamic equivalents of power systems. In this method, at the first step the "study system" is modeled completely via a single machineinfinite bus modeling procedure. Then the "external system" is identified as a MIMO feedback block of this model in such a manner that can include dynamic effects of the latter on the behavior of the former. The method is successfully experimented on a part of the Iranian southern network. Copyright © 2007 The... 

    Reducing the Energy Overhead of Rollback/Recovery Mechanisms in Distributed Embedded Systems

    , M.Sc. Thesis Sharif University of Technology Khavari Tavanaو Mohammad (Author) ; Ejlali, Alireza (Supervisor)
    Hard real-time embedded systems often operate in harsh environmental conditions that necessitate fault tolerant computing techniques. These embedded systems are also energy-constrained, since energy consumption is one of the key objectives. Examples include satellites, surveillance systems, autonomous seaborne and airborne systems. Generally, fault tolerance is obtained by hardware or time redundancy in these systems. Checkpointing with rollback recovery which employs time redundancy is one of the common techniques for tolerating transient faults in real-time embedded systems. Using checkpointing in energy constrained hard real-time systems should be carefully employed. In this thesis, we... 

    Improvement of robot navigation using fuzzy method

    , Article 2013 3rd Joint Conference of AI and Robotics and 5th RoboCup Iran Open International Symposium: Learning, Glorious Future ; 2013 , pp.1-5 ; 9781467363150 (ISBN) Nazari, M ; Amiryan, J ; Nazemi, E ; Sharif University of Technology
    In this paper a technique for autonomous navigation of mobile robots is presented. The most important advantage of this method is to ignore the physical model of the robot and that the robot model is considered as an unknown but predictable system. This approach can be executed in environments which robot navigation is done using global sensors e.g. a camera installed in the environment to sense and control the robot and also every feedback system which is able to measure the velocity of the robot can be used for this technique. In this approach, the well-known fuzzy method, Takagi-Sugeno, has been applied to estimate the dynamic model of robot. Our technique has been applied successfully in... 

    Fractional order model reduction approach based on retention of the dominant dynamics: Application in IMC based tuning of FOPI and FOPID controllers

    , Article ISA Transactions ; Volume 50, Issue 3 , July , 2011 , Pages 432-442 ; 00190578 (ISSN) Tavakoli Kakhki, M ; Haeri, M ; Sharif University of Technology
    Fractional order PI and PID controllers are the most common fractional order controllers used in practice. In this paper, a simple analytical method is proposed for tuning the parameters of these controllers. The proposed method is useful in designing fractional order PI and PID controllers for control of complicated fractional order systems. To achieve the goal, at first a reduction technique is presented for approximating complicated fractional order models. Then, based on the obtained reduced models some analytical rules are suggested to determine the parameters of fractional order PI and PID controllers. Finally, numerical results are given to show the efficiency of the proposed tuning... 

    Fuzzy control of a hand rehabilitation robot to optimize the exercise speed in passive working mode

    , Article Studies in Health Technology and Informatics ; Vol. 163 , 2011 , pp. 39-43 ; 09269630 (ISSN) ; 9781607507055 (ISBN) Baniasad, M. A ; Akbar, M ; Alasty, A ; Farahmand, F ; Sharif University of Technology
    The robotic rehabilitation devices can undertake the difficult physical therapy tasks and provide improved treatment procedures for post stroke patients. During passive working mode, the speed of the exercise needs to be controlled continuously by the robot to avoid excessive injurious torques. We designed a fuzzy controller for a hand rehabilitation robot to adjust the exercise speed by considering the wrist angle and joint resistive torque, measured continuously, and the patient's general condition, determined by the therapist. With a set of rules based on an expert therapist experience, the fuzzy system could adapt effectively to the neuromuscular conditions of the patient's paretic hand.... 

    Predictive directional compensator for systems with input constraints

    , Article ISA Transactions ; Volume 45, Issue 3 , 2006 , Pages 393-405 ; 00190578 (ISSN) Haeri, M ; Aalam, N ; Sharif University of Technology
    ISA - Instrumentation, Systems, and Automation Society  2006
    Nonlinearity caused by actuator constraint plays a destructive role in the overall performance of a control system. A model predictive controller can handle the problem by implementing a constrained optimization algorithm. Due to the iterative nature of the solution, however, this requires high computation power. In the present work we propose a new method to approach the problem by separating the constraint handling from the predictive control job. The input constraint effects are dealt with in a newly defined component called a predictive directional compensator, which works based on the directionality and predictive concepts. Through implementation of the proposed method, the... 

    Observer-Based Controller Design for Nonlinear Fractional Order Systems

    , M.Sc. Thesis Sharif University of Technology Rahmani Nooshabadi, Ali (Author) ; Shahrokhi, Mohammad (Supervisor)
    In this study, an adaptive controller design for nonlinear fractional order systems in the strict-feedback form has been investigated. The system is subject to unknown dynamics, unmeasured state variables, quantized input and output, and input nonlinearity. A linear observer is used to solve the problem of unmeasured state variables. The fuzzy logic system is used to estimate the unknown functions, and instead of updating all the regressor weights, only the upper bound of their norms is updated, which significantly reduces the computational load. In the controller design, limitations due to the bandwidth of data transmission have been considered by applying quantizers in the input and output... 

    All-optical controlled switching in centrally coupled circular array of nonlinear optical fibers

    , Article Applied Optics ; Volume 52, Issue 25 , Sep , 2013 , Pages 6131-6137 ; 1559128X (ISSN) Tofighi, S ; Bahrampour, A. R ; Sharif University of Technology
    Optical Society of American (OSA)  2013
    We show that, in a nonlinear centrally coupled circular array of evanescently coupled fibers, the coupling dynamics of a weak signal beam can be efficiently influenced by a high-power control beam that induces nonlinear defects. When the intense control beam is launched into the central core and one core in the periphery, then localized solitons are formed and cause the fibers with induced defects (defected fibers) to decouple from the other array elements. In the presence of a high-intensity control beam, the propagation of weak signal is restricted to the defected optical fibers. The weak signal periodically couples between the induced defects. This oscillatory behavior depends on the sign... 

    Feedback-based energy management in a standby-sparing scheme for hard real-time systems

    , Article Proceedings - Real-Time Systems Symposium, 29 November 2011 through 2 December 2011 ; December , 2011 , Pages 349-356 ; 10528725 (ISSN) ; 9780769545912 (ISBN) Tavana, M. K ; Salehi, M ; Ejlali, A ; Sharif University of Technology
    The interaction between fault tolerance and energy consumption is an interesting avenue in the realm of designing embedded systems. In this paper, a scheme for reducing energy consumption in conventional standby-sparing systems is introduced. In the proposed method, the primary unit exploits dynamic voltage scaling (DVS) and dynamic power management (DPM) is employed for the spare unit. The framework which is used in the primary unit is composed of a feedback system to follow up workload along with a three-layer yet light-weight energy manager which guarantees hard real-time constraints of the system. Moreover, an optimal approach (but not practical) as a margin for the minimum energy... 

    On the stability issues for fuzzy large-scale systems

    , Article Fuzzy Sets and Systems ; Volume 174, Issue 1 , July , 2011 , Pages 31-49 ; 01650114 (ISSN) Zamani, I ; Sadati, N ; Zarif, M. H ; Sharif University of Technology
    The main objective of this paper is to investigate the stability and stabilization problem of fuzzy large-scale systems in which the system is composed of a number of Takagi-Sugeno fuzzy subsystems with interconnection. Instead of fuzzy parallel distributed compensation (PDC) design, nonlinear state feedback controllers are used in stabilization of the overall large-scale system. Based on Lyapunov stability theory, linear matrix inequalities (LMIs) conditions are derived for asymptotic and exponential stability. Two numerical examples are given to confirm the analytical results and illustrate the effectiveness of the proposed strategy  

    Integrated guidance and control of elastic flight vehicle based on robust MPC

    , Article International Journal of Robust and Nonlinear Control ; Volume 25, Issue 15 , 2015 , Pages 2608-2630 ; 10498923 (ISSN) Shamaghdari, S ; Nikravesh, S. K. Y ; Haeri, M ; Sharif University of Technology
    John Wiley and Sons Ltd  2015
    Integrated guidance and control of an elastic flight vehicle based on constrained robust model predictive control is proposed. The design is based on a partial state feedback control law that minimizes a cost function within the framework of linear matrix inequalities. It is shown that the solution of the defined optimization problem stabilizes the nonlinear plant. Nonlinear kinematics and dynamics are taken into account, and internal stability of the closed-loop nonlinear system is guaranteed. The performance and effectiveness of the proposed integrated guidance and control against non-maneuvering and weaving targets are evaluated using computer simulations  

    Asymptotic stability of linear descriptor systems with time-delay by designing delay margin

    , Article 5th International Conference on Control, Instrumentation, and Automation, ICCIA 2017 ; Volume 2018-January , 2018 , Pages 23-29 ; 9781538621349 (ISBN) Zahedi, F ; Haeri, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2018
    In this paper a new approach is developed to stabilize descriptor systems with time-delay, while time-delay can belong to a given interval. This approach takes the advantages of system's singularity to simplify the model and uses the so-called Rekasius substitution to compute the controller parameters in a way that the asymptotic stability of the closed-loop system in the given interval of the delay can be guaranteed. Finally, a numerical example is provided to evaluate the proposed method's effectiveness. © 2017 IEEE  

    Global stabilization of Lotka-Volterra systems with interval uncertainty

    , Article IEEE Transactions on Automatic Control ; Volume 64, Issue 3 , 2019 , Pages 1209-1213 ; 00189286 (ISSN) Badri, V ; Yazdanpanah, M. J ; Tavazoei, M. S ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    This paper deals with the stabilization of the feasible equilibrium point of a special class of nonlinear quadratic systems known as Lotka-Volterra (LV) systems, in the presence of interval uncertainty via a fixed linear state feedback (FLSF). It is well known that for a linear time-invariant system with interval uncertainty, stability at the vertices of a polytope implies stability in the interior of the whole polytope. It has been shown that this idea can be extended to examine the stability of LV systems in the presence of interval uncertainty, recently. In fact, it has been proved that in spite of nonlinear nature of the system, stability at a special vertex guarantees stability at all... 

    Global stabilization of uncertain lotka-volterra systems via positive nonlinear state feedback

    , Article IEEE Transactions on Automatic Control ; Volume 65, Issue 12 , 2020 , Pages 5450-5455 Badri, V ; Tavazoei, M. S ; Yazdanpanah, M. J ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2020
    This article deals with stabilization of Lotka-Volterra (LV) systems in the presence of interval uncertainty and a physical limitation on the control input, which restricts this input to be strictly positive. Considering the positiveness property of LV systems, a quasi-monomial structure for the state feedback based control input is proposed. Considering this structure, stability of the closed-loop system with no uncertainty is analyzed. This analysis leads to an algebraic inequality, whose satisfaction guarantees stability of the closed-loop system. To extend this result to uncertain LV systems with interval parameter uncertainty, a new approach, by which stability of the positive... 

    Backlash nonlinearity modeling and adaptive controller design for an electromechanical power transmission system

    , Article Scientia Iranica ; Volume 16, Issue 6 B , 2009 , Pages 463-469 ; 10263098 (ISSN) Kalantari, R ; Saadat Foomani, M ; Sharif University of Technology
    Nonlinearity characteristics, such as backlash, in various mechanisms, limit the performance of feedback systems by causing delays, undesired oscillations and inaccuracy. Backlash influence analysis and modeling is necessary to design a precision controller for this nonlinearity. Backlash between meshing gears in an electromechanical system is modeled by the use of differential equations and a nonlinear spring-damper. According to this model, the paper shows that oscillations and delays cannot be compensated by a state feedback controller. Therefore, an adaptive algorithm is designed, based on different regions of the system angular position error. Since this controller needs an estimation... 

    An interactive cbir system based on anfis learning scheme for human brain magnetic resonance images retrieval

    , Article Biomedical Engineering - Applications, Basis and Communications ; Volume 24, Issue 1 , 2012 , Pages 27-36 ; 10162372 (ISSN) Tarjoman, M ; Fatemizadeh, E ; Badie, K ; Sharif University of Technology
    Content-based image retrieval (CBIR) has turned into an important and active potential research field with the advance of multimedia and imaging technology. It makes use of image features, such as color, texture and shape, to index images with minimal human intervention. A CBIR system can be used to locate medical images in large databases. In this paper we propose a CBIR system which describes the methodology for retrieving digital human brain magnetic resonance images (MRI) based on textural features and the Adaptive neuro-fuzzy inference system (ANFIS) learning to retrieve similar images from database in two categories: normal and tumoral. A fuzzy classifier has been used, because of the... 

    Feedback control of the neuromusculoskeletal system in a forward dynamics simulation of stair locomotion

    , Article Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine ; Volume 223, Issue 6 , 2009 , Pages 663-675 ; 09544119 (ISSN) Selk Ghafari, A ; Meghdari, A ; Vossoughi, G ; Sharif University of Technology
    The aim of this study is to employ feedback control loops to provide a stable forward dynamics simulation of human movement under repeated position constraint conditions in the environment, particularly during stair climbing. A ten-degrees-of-freedom skeletal model containing 18 Hill-type musculotendon actuators per leg was employed to simulate the model in the sagittal plane. The postural tracking and obstacle avoidance were provided by the proportional-integral-derivative controller according to the modulation of the time rate change of the joint kinematics. The stability of the model was maintained by controlling the velocity of the body's centre of mass according to the desired centre of... 

    Improvement of upper limb motor control and function after competitive and noncompetitive volleyball exercises in chronic stroke survivors: a randomized clinical trial

    , Article Archives of Physical Medicine and Rehabilitation ; Volume 100, Issue 3 , 2019 , Pages 401-411 ; 00039993 (ISSN) Mandehgary Najafabadi, M ; Azad, A ; Mehdizadeh, H ; Behzadipour, S ; Fakhar, M ; Taghavi Azar Sharabiani, P ; Parnianpour, M ; Taghizadeh, G ; Khalaf, K ; Sharif University of Technology
    W.B. Saunders  2019
    Objectives: To investigate the effects of competitive and noncompetitive volleyball exercises on the functional performance and motor control of the upper limbs in chronic stroke survivors. Design: Randomized clinical trial. Setting: Outpatient rehabilitation center. Participants: Chronic stroke survivors (N=48). Interventions: Participants were randomly assigned to competitive (n=16) or noncompetitive (n=16) volleyball exercise groups (60min/d volleyball exercise+30min/d traditional rehabilitation, 3d/wk for 7wk) and control group (n=16). Main Outcome Measures: Reach and grasp motor control measures were evaluated through kinematic analysis. Functional outcomes were assessed via Motor...