Search for: system-frequency
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    Modeling, simulation and frequency-response identification of a quadrotor

    , Article Proceedings of the IASTED International Conference on Modelling, Identification and Control ; 2013 , Pages 476-483 ; 10258973 (ISSN) ; 9780889869431 (ISBN) Shadram, Z ; Bassam, S. S ; Sharif University of Technology
    Due to their agile manoeuvrability and simplicity of construction, quadrotor are employed in a variety of applications. Most of their expenses are due to complex control systems, since, to reduce these expenses, low cost control methods which are based on linear models should be used to achieve an autonomous flight. First, the process of accurate dynamic modeling of a sample quad rotor which is simulated by MATLAB SIMULINK is presented. Then, a frequency sweep input stimulates the virtual model in order to identify a linear model based on frequency response analysis. Consequently, the desired linear model is obtained in both hover and yaw mode of motion. However, pitch and roll mode were too... 

    The effect of fractional order on oscillatory behavior of scalar fractional delay systems of neutral type

    , Article IFAC Proceedings Volumes (IFAC-PapersOnline) ; February , 2013 , Pages 480-485 ; 14746670 (ISSN); 9783902823274 (ISBN) Mesbahi, A ; Haeri, M ; Sharif University of Technology
    The undamped oscillations of a scalar fractional neutral system are studied in this paper. For this purpose, it is proved that this kind of systems can have the oscillatory behavior. The necessary and sufficient condition is proposed to determine that there exists a delay value for which the system oscillates. The frequency, amplitude and required delay for the undamped oscillations depend on the fractional order. However, the behavior of dependencies is not specified. Indeed, when the system has oscillatory behavior, it is bounded-input bounded-output stable for delay less than the required delay. Moreover, when the order is approaching to an integer value, the necessary and sufficient... 

    Capacity of a class of symmetric relay networks with orthogonal components

    , Article IET Communications ; Volume 4, Issue 18 , 2010 , Pages 2181-2186 ; 17518628 (ISSN) Ghabeli, L ; Aref, M. R ; Sharif University of Technology
    In this study, the authors extend the concept of relay channel with orthogonal components to define a class of symmetric relay networks with orthogonal components named symmetric orthogonal relay network. In the defined network, the channels diverge from each node sender use different frequency bands whereas the channels converge to each node receiver use the same frequency band. This structure is very well understood in half-duplex transmission systems where the relays cannot send and receive at the same time or over the same frequency band. The authors show that the unicast capacity of the defined network is equal to the cut-set bound. In the achievability proof, the authors take advantage... 

    On a generalized fractional-order LTI compensator: Exact formulas for compensation at two different frequencies

    , Article JVC/Journal of Vibration and Control ; Volume 22, Issue 19 , 2016 , Pages 4074-4086 ; 10775463 (ISSN) Sayyaf, N ; Tavazoei, M. S ; Sharif University of Technology
    SAGE Publications Inc 
    Nowadays, design and tuning of controllers with predefined structures are among the most popular topics in control system theory. During the last decade, many studies have focused on designing fixed-structure fractional-order compensators. This paper presents a generalized version of fractional-order compensators to achieve the required magnitudes and phases at two given frequencies (for example, to achieve desired phase and gain margins with adjustable cross frequencies). In this generalization, at first some basic analysis of the phase behaviour of this introduced type of fractional-order compensators is presented. Also, exact formulas are found for designing this family of compensators in... 

    Fractional order control of thermal systems: achievability of frequency-domain requirements

    , Article Nonlinear Dynamics ; Volume 80, Issue 4 , 2015 , Pages 1773-1783 ; 0924090X (ISSN) Badri, V ; Tavazoei, M. S ; Sharif University of Technology
    Fractional order models have been widely used in modeling and identification of thermal systems. General model in this category is considered as the model of thermal systems in this paper, and a fractional order controller is proposed for controlling such systems. The proposed controller is a generalization for the traditional PI controllers. The parameters of this controller can be obtained by using a recently introduced tuning method which can simultaneously ensure the following three requirements: desired phase margin, desired gain crossover frequency, and flatness of the phase Bode plot at this frequency. In this paper, it is found whether simultaneously achieving the mentioned... 

    Robust control of smart beam with pizoelectric actuators

    , Article Eight IASTED International Conference on Control and Applications, Montreal, QC, 24 May 2006 through 26 May 2006 ; Volume 2006 , 2006 , Pages 41-47 ; 0889865531 (ISBN); 9780889865532 (ISBN) Khanmirza, E ; Yousefi Koma, A ; Akbari, S ; Zadeh, B. T ; Sharif University of Technology
    In this paper, a robust control system is developed for a flexible beam with piezoelectric actuators (called Smart Beam). The active control system of smart beam satisfied desired properties for all admissible measurement and plant noises, disturbances and model uncertainties. Thus it is the best candidate for sensitive industrial, medical and etc. robot arms and bases a new concept in the use of smart structures in robotics. The Frequency Response Function (FRF) of the smart beam was obtained from a Finite Element (FE) model. The corresponding transfer function was derived from the □ synthesis and several control schemes were then designed to suppress the vibration. Results showed the... 

    Dynamic participation of wind farms in system frequency control

    , Article IEEE PES Innovative Smart Grid Technologies Conference Europe, 14 October 2012 through 17 October 2012 ; October , 2012 ; 9781467325974 (ISBN) Toulabi, M ; Ranjbar, A. M ; Karimi, H ; Shiroie, M ; Sharif University of Technology
    In this paper, the participation of wind farms in load frequency control (LFC) is studied. A previously proposed macromodel for the wind farm is employed to regulate its output power. The wind farm including its proposed control strategy is incorporated into the conventional LFC model. The proposed LFC structure is able to dynamically maintain the system frequency at the nominal value against the power imbalances. To achieve proper transient response, the integral control parameter of the LFC controller is optimized using the genetic algorithm (GA). To verify the effectiveness of the proposed method, several simulation case studies are carried out. The results show that the wind farm can... 

    Modified power reserve management solution in power system considering frequency constraints

    , Article IEEE Systems Journal ; Volume 14, Issue 1 , 2020 , Pages 1125-1134 Hosseini, S. A ; Toulabi, M ; Ashouri Zadeh, A ; Ranjbar, A. M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2020
    In this paper, security constrained reserve management (SCRM) problem is formulated. In this trend, security constrained economic dispatch as well as operating reserve in both normal and {N-1} contingency condition are considered. To address the computational complexity associated with the SCRM problem, the distributed-SCRM (D-SCRM) is proposed. In the suggested method, the power system is decomposed to several subsystems called zone. These zones are interconnected via some tie-lines. By defining two virtual generation units at the middle of each tie-line, all neighbor zones become isolated. This causes the main SCRM problem to be converted to some subproblems. To solve these subproblems,... 

    Integer frequency offset recovery in OFDM systems

    , Article 18th Asia-Pacific Conference on Communications: "Green and Smart Communications for IT Innovation", APCC 2012, Jeju Island, 15 October 2012 through 17 October 2012 ; 2012 , Pages 641-646 Abdzadeh Ziabari, H ; Shayesteh, M. G ; Sharif University of Technology
    This paper addresses the estimation of the integer part of the carrier frequency offset (CFO) in orthogonal frequency division multiplexing (OFDM) systems. A novel method is presented based on the maximum likelihood (ML) approach that jointly estimates the channel impulse response (CIR) and the integer CFO. The new scheme estimates the CIR by using pilots and obtains the estimate of the integer CFO by taking advantage of the effect of the CFO on the CIR and data symbols. The performance of the new method is evaluated in Rayleigh fading channels. The results demonstrate that the proposed scheme significantly outperforms the previous methods  

    Distributed subband, rate and power allocation in OFDMA based two-tier femtocell networks using fractional frequency reuse

    , Article IEEE Wireless Communications and Networking Conference, WCNC, 1 April 2012 through 4 ; 2012 , Pages 2626-2630 ; 15253511 (ISSN) ; 9781467304375 (ISBN) Salati, A. H ; Nasiri Kenari, M ; Sadeghi, P ; Sharif University of Technology
    IEEE  2012
    Femtocell has appeared as a solution to increase both coverage and capacity of cellular networks. However, interference problem between the macrocell and the femtocell must be solved before any deployment. In this paper, we deal with the problem of joint subband, rate, and power allocation in OFDMA based two-tier femtocell networks. It is assumed that for macrocell users, spectrum allocation is accomplished through Fractional Frequency Reuse (FFR). Our objective is to maximize the femtocell user's throughput while maintaining as little as possible reduction in the macrocell users' performance. Our proposed algorithm is decentralized, and needs to be done only when femtocell access point is... 

    Nonlinear oscillation analysis of a pendulum wrapping on a cylinder

    , Article Scientia Iranica ; Volume 19, Issue 2 , 2012 , Pages 335-340 ; 10263098 (ISSN) Mazaheri, H ; Hosseinzadeh, A ; Ahmadian, M. T ; Sharif University of Technology
    In this paper, the nonlinear oscillation of a pendulum wrapping and unwrapping on two cylindrical bases is studied, and an analytical solution is obtained using the multiple scales method. The equation of motion is derived based on an energy conservation technique. By applying the perturbation method to the differential equation, the nonlinear natural frequency of the system is calculated, along with its time response. Analytical results are compared with numerical findings and good agreement is found. The effect of large amplitude and radius of cylinders on system frequency is evaluated. The results indicate that as the radius of the cylinder increases, the system frequency is increased.... 

    Analytical approach to vibration analysis of a pendulum wrapping on a cylinder

    , Article ASME 2011 International Mechanical Engineering Congress and Exposition, IMECE 2011, 11 November 2011 through 17 November 2011 ; Volume 7, Issue PARTS A AND B , November , 2011 , Pages 761-765 ; 9780791854938 (ISBN) Mazaheri, H ; Hosseinzadeh, A ; Ahmadian, M. T ; Barari, A ; Sharif University of Technology
    In this paper, nonlinear oscillation of a pendulum wrapping and unwrapping around two cylindrical bases is studied and an analytical solution is obtained using multiple scales method. Equations of motion are derived based on energy conservation technique. Applying perturbation method on the equations, nonlinear natural frequency of the system is calculated along with its time response. Analytical results are compared with numerical findings and good agreement is found. Effect of nonlinearity due to large amplitude and radius of cylinders on the system frequency is evaluated. Results indicate that as the radius of cylinder is increased, nonlinear frequency is enhanced. Initial amplitude plays... 

    Different approaches for estimation of dampings and frequencies of electromechanical modes from PMU ambient data

    , Article 2015 IEEE 15th International Conference on Environment and Electrical Engineering, EEEIC 2015 - Conference Proceedings, 10 June 2015 through 13 June 2015 ; June , 2015 , Pages 1748-1753 ; 9781479979936 (ISBN) Farrokhifard, M ; Hatami, M ; Parniani, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2015
    Small signal stability of power systems is one of the most crucially important issues, since the electrical demand is increasing at a galloping rate and power systems are expanding day by day. In this regard, estimation of dampings and frequencies of electromechanical modes through the analysis of field measurements has become a heated study topic for electrical power system researchers in recent years. There have been several methods to analyze different types of Phasor Measurement Units (PMUs) signals i.e., transient, ambient, and probing. Among the proposed techniques, those which are capable of analyzing ambient data seems to be more practical, since this type of data can be achieved... 

    Maximum number of frequencies in oscillations generated by fractional order LTI systems

    , Article IEEE Transactions on Signal Processing ; Volume 58, Issue 8 , May , 2010 , Pages 4003-4012 ; 1053587X (ISSN) Tavazoei, M. S ; Haeri, M ; Siami, M ; Bolouki, S ; Sharif University of Technology
    In this paper, relation between the inner dimension of a fractional order LTI system and the maximum number of frequencies which exist in oscillations generated by the system is investigated. The considered system is defined in pseudo state space form and the orders of its involved fractional derivatives are rational numbers between zero and one. First, an upper bound is derived for the maximum number of frequencies. Then, using the restricted difference bases concept, a new method is introduced to design a multifrequency oscillatory fractional order system. Finally, based on the proposed method some lower bounds are derived for the maximum number of frequencies obtainable in solutions of a... 

    Dynamic stability of a Hexaglide machine tool for milling processes

    , Article International Journal of Advanced Manufacturing Technology ; Volume 86, Issue 5-8 , 2016 , Pages 1753-1762 ; 02683768 (ISSN) Najafi, A ; Movahhedy, M. R ; Zohoor, H ; Alasty, A ; Sharif University of Technology
    Springer-Verlag London Ltd 
    One of the major issues related to parallel kinematic machine tools (PKMs) is their structural dependency on their configuration. In this paper, the machine configuration effect on its stability is investigated for the case of a Hexaglide machine tool. An FEM model of the Hexaglide machine tool is developed. The frequency response function (FRF) at the tool tip is obtained by a modal analysis. The numerical results are validated through comparison with those of an experimental modal test. The pose dependency of the PKM stability over its workspace is investigated. It is shown that the machine stability over the workspace is dependent on the spindle/tool/holder system characteristic. For... 

    Reliability assessment of protective relays in harmonic-polluted power systems

    , Article IEEE Transactions on Power Delivery ; Volume 32, Issue 1 , 2017 , Pages 556-564 ; 08858977 (ISSN) Jedrzejczak, J ; Anders, G. J ; Fotuhi Firuzabad, M ; Farzin, H ; Aminifar, F ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2017
    Proliferation of distributed generations (DGs) and power-electronics-based loads is bringing about more harmonic-polluted power signals. While some failures may occur as a consequence of nonsinusoidal current or voltage waveforms, existing reliability models of protection relays have not taken the harmonic-related failures into consideration. This paper develops a comprehensive Markov reliability model to categorize the possible functional states of a component, say a transmission line, protected by a relay, operating in a harmonic-polluted environment. In order to make the proposed model practically tractable, it is further simplified in two ways, through merging the states of the same... 

    Optimal robust first-order frequency controller design for DFIG-based wind farm utilising 16-plant theorem

    , Article IET Renewable Power Generation ; Volume 12, Issue 3 , 2018 , Pages 298-310 ; 17521416 (ISSN) Toulabi, M. R ; Salehi Dobakhshari, A ; Ranjbar, A. M ; Sharif University of Technology
    Institution of Engineering and Technology  2018
    With increasing the share of wind farms in generation profile, their contribution to frequency regulation has become crucial. This study presents an optimal robust first-order frequency controller in the wind farms, which collectively emulates the inertial response as well as governor droop of synchronous generators. To account for various uncertainties associated with system inertia, damping, and doubly-fed induction generator (DFIG)-based wind turbine's parameters, the robustness of controller is verified through the 16-plant theorem. An analytic method based on the small-signal model of the system is utilised to determine the stability region of the first-order controller. To evaluate the... 

    Frequency stability improvement in windthermal dominated power grids

    , Article IET Generation, Transmission and Distribution ; Volume 14, Issue 4 , 2020 , Pages 619-627 Ashouri Zadeh, A ; Toulabi, M ; Dobakhshari, A. S ; Ranjbar, A. M ; Sharif University of Technology
    Institution of Engineering and Technology  2020
    With the proliferation of intermittent renewable energy sources, power systems need to withstand an increasing number of disturbances that may affect system frequency. In this paper, we focus on the effects of high penetration level of wind turbine-generators (WTG) on the power system operational planning from the frequency point of view. Specifically, an exact formulation for the minimum frequency calculation is presented to increase accuracy and speed of analyses. Then, the effect of WTG's frequency response on the power system frequency stability is investigated to compute the maximum acceptable generation outage as a function of penetration level. Finally, as an application to power... 

    Temporal super resolution imaging inspired by structured illumination microscopy

    , Article Optics Communications ; Volume 467 , 2020 Shateri, F ; Alizadeh, M. H ; Kavehvash, Z ; Sharif University of Technology
    Elsevier B.V  2020
    In this paper, a method for increasing the temporal resolution of a temporal imaging system has been developed. Analogously to the conventional spatial imaging systems in which resolution limit is due to the finite aperture of the lens, in a temporal imaging system, the finite temporal aperture of the time lens is responsible for limited temporal resolution. Based on the method used in spatial structured illumination super-resolution microscopy in spatial optics, we have utilized frequency converters (time prisms), to shift the elusive frequency components of the input signal to become captured by the time lens. This method proved numerically to enhance the temporal resolution by a factor of... 

    Limitations of frequency domain approximation for detecting chaos in fractional order systems

    , Article Nonlinear Analysis, Theory, Methods and Applications ; Volume 69, Issue 4 , 15 August , 2008 , Pages 1299-1320 ; 0362546X (ISSN) Tavazoei, M. S ; Haeri, M ; Sharif University of Technology
    In this paper, we analytically study the influences of using frequency domain approximation in numerical simulations of fractional order systems. The number and location of equilibria, and also the stability of these points, are compared between the original system and its frequency based approximated counterpart. It is shown that the original system and its approximation are not necessarily equivalent according to the number, location and stability of the fixed points. This problem can cause erroneous results in special cases. For instance, to prove the existence of chaos in fractional order systems, numerical simulations have been largely based on frequency domain approximations, but in...