Search for: closed-loops
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    Direct controller order reduction by identification in closed loop

    , Article Automatica ; Volume 37, Issue 11 , 2001 , Pages 1689-1702 ; 00051098 (ISSN) Landau, I. D ; Karimi, A ; Constantinescu, A ; Sharif University of Technology
    The paper addresses the problem of directly estimating the parameters of a reduced order digital controller using a closed loop type identification algorithm. The algorithm minimizes the closed loop plant input error between the nominal closed loop system and the closed loop system using the reduced order controller. It is assumed that a plant model (if necessary validated in closed loop with the nominal controller) is available. One of the original features of this approach is that it can use either simulated or real data. The frequency bias distribution of the parameter estimates shows that the reduced order controller maintains the critical performance of the nominal closed loop system. A... 

    Effects of the design parameters of multimodel adaptive control on the performance of a flexible transmission system

    , Article International Journal of Adaptive Control and Signal Processing ; Volume 15, Issue 3 , 2001 , Pages 335-352 ; 08906327 (ISSN) Karimi, A ; Landau, I. D ; Motee, N ; Sharif University of Technology
    Design parameters selection in the multimodel adaptive control based on switching and tuning will be investigated. Some design parameters like number of fixed and adaptive models, forgetting factor and minimum time delay between switchings will be considered. A recently developed parameter adaptation algorithm based on closed-loop output error will be compared with the classical least-squares prediction error algorithm in the multimodel adaptive control. The effects of these parameters on the performance in tracking and in regulation of a flexible transmission system will be studied via several simulation examples  

    Experimental investigation on performance of a rotating closed loop pulsating heat pipe

    , Article International Communications in Heat and Mass Transfer ; Volume 45 , 2013 , Pages 137-145 ; 07351933 (ISSN) Aboutalebi, M ; Nikravan Moghaddam, A. M ; Mohammadi, N ; Shafii, M. B ; Sharif University of Technology
    Pulsating heat pipes (PHPs) are interesting heat transfer devices. Their simple, high maintaining, and cheap arrangement has made PHPs very efficient compared to conventional heat pipes. Rotating closed loop PHP (RCLPHP) is a novel kind of them, in which the thermodynamic principles of PHP are combined with rotation. In this paper, effect of rotational speed on thermal performance of a RCLPHP is investigated experimentally. The research was carried out by changing input power (from 25. W to 100. W, with 15. W steps) and filling ratio (25%, 50%, and 75%) for different rotational speeds (from 50. rpm to 800. rpm with an increment of 125. rpm). The results presented that at a fixed filling... 

    Sensitivity analysis of CRA based controllers in fractional order systems

    , Article Signal Processing ; Volume 92, Issue 9 , September , 2012 , Pages 2040-2055 ; 01651684 (ISSN) Tabatabaei, M ; Haeri, M ; Sharif University of Technology
    Elsevier  2012
    This paper focuses on robust performance analysis of a closed loop fractional order system through a sensitivity approach. The characteristic ratio assignment method is selected to attain a desired closed loop transient response. Then, we compute the sensitivity of such a desired transfer function with respect to its characteristic ratio and we explore its specifications. The relation between the coefficient diagram shape and the relative stability of the closed loop system is discussed. Also, the closed loop poles variations due to the changes in the characteristic ratios are investigated. Finally, we study a pseudo second order process to verify the robust performance of the characteristic... 

    Proportional stabilization and closed-loop identification of an unstable fractional order process

    , Article Journal of Process Control ; Vol. 24, Issue. 5 , 2014 , pp. 542-549 ; ISSN: 09591524 Tavakoli-Kakhki, M ; Tavazoei, M. S ; Sharif University of Technology
    This paper deals with proportional stabilization and closed-loop step response identification of the fractional order counterparts of the unstable first order plus dead time (FOPDT) processes. At first, the necessary and sufficient condition for stabilizability of such processes by proportional controllers is found. Then, by assuming that a process of this kind has been stabilized by a proportional controller and the step response data of the closed-loop system is available, an algorithm is proposed for estimating the order and the parameters of an unstable fractional order model by using the mentioned data  

    Development of a hybrid reference model for performance evaluation of resolvers

    , Article IEEE Transactions on Instrumentation and Measurement ; Volume 70 , 2021 ; 00189456 (ISSN) Khajueezadeh, M ; Saneie, H ; Nasiri Gheidari, Z ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2021
    Resolver is an electromagnetic position sensor typically used in the closed-loop control of permanent magnet synchronous motors (PMSMs). In terms of structure and principle of operation, resolvers are very similar to electrical machines. In this regard, different numerical and analytical models have been developed for the performance prediction of a resolver, with a compromise between computational burden and accuracy. Therefore, a fast and accurate hybrid model of the resolver is presented in this article, which can be used for resolvers with different structures. Additionally, this model can easily be implemented in software such as MATLAB/SIMULINK. The performance of different variable... 

    Design of fractional order proportional-integral-derivative controller based on moment matching and characteristic ratio assignment method

    , Article Proceedings of the Institution of Mechanical Engineers. Part I: Journal of Systems and Control Engineering ; Volume 225, Issue 8 , December , 2011 , Pages 1040-1053 ; 09596518 (ISSN) Tabatabaei, M ; Haeri, M ; Sharif University of Technology
    This paper presents a new analytical method to design fractional-order proportional- integral-derivative (PID) controllers. The control parameters are calculated so that the closedloop system approximates a desired transfer function with transient response requirements. This function is determined based on the characteristic ratio assignment method. The control parameters are calculated by matching the first three moments of the closed-loop transfer function with the corresponding values of the desired system. Furthermore, to ensure closed-loop stability the proposed method is improved by using the shifted moments around the crossover frequency. Illustrative examples are given to show the... 

    A novel voltage measurement technique for modular multilevel converter capacitors

    , Article 41st Annual Conference of the IEEE Industrial Electronics Society, 9 November 2015 through 12 November 2015 ; 2015 , Pages 238-243 ; 9781479917624 (ISBN) Haghnazari, S ; Zolghadri, M. R ; IEEE Industrial Electonics Society (IES) ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc 
    In this paper a new voltage measurement technique for modular multilevel converter (MMC) capacitors is proposed. While all the capacitors voltages should be known for closed loop control of MMCs, only the arms voltages are measured employing the proposed method. Therefore, the number of voltage sensors reduced dramatically to one per arm. The capacitors voltage quantities are updated continuously using the arms voltage and the switching signals. Although the proposed method precision is depended on the equality of the capacitors, presented investigations show that the steady state error and even transient error in capacitors voltage estimation is ignorable for the proper operation of the... 

    Design of a mechanically closed-loop test rig for testing aviation industry’s gearboxes

    , Article Aviation ; Volume 21, Issue 4 , 2017 , Pages 132-142 ; 16487788 (ISSN) Mozafari, S ; Rezazadeh Mohamadi, M ; Dolatkhah Takloo, S ; Mardani, M ; Sharif University of Technology
    Due to the wide usage of rotary equipment and the necessity of their testing for maintenance and repair, test rigs have become necessary. The mechanical closed-loop test rig developed in Sharif University of Technology branch of ACECR (Academic Centre of Education, Culture and Research) is a test rig with low energy losses that is suitable for testing high power gearboxes such as aerospace or wind turbine gearboxes. It can be loaded up to 489Hp at a maximum speed of 3000 rpm, and the test components can be tested in different testing conditions including a variety of torques and speeds. This paper describes the preliminary, conceptual, and detailed design, steps including frame work design,... 

    Inferential closed-loop control of particle size distribution for styrene emulsion polymerization

    , Article Chemical Engineering Science ; Volume 63, Issue 9 , 2008 , Pages 2378-2390 ; 00092509 (ISSN) Abedini, H ; Shahrokhi, M ; Sharif University of Technology
    In this work, a new control strategy for controlling the particle size distribution (PSD) in emulsion polymerization has been proposed. It is shown that the desired PSD can be achieved by controlling the free surfactant concentration which in turn can be done by manipulating the surfactant feed rate. Simulation results show that the closed-loop control of free surfactant concentration results in a better control of PSD compared to open-loop control strategy, in presence of model mismatch and disturbances. Since the on-line measuring of ionic free surfactant concentration is difficult, conductivity which is related to it is measured instead and used for control purposes. The closed-loop... 

    Supplier selection and order allocation in CLSC configuration with various supply strategies under disruption risk

    , Article OPSEARCH ; Volume 57, Issue 3 , 2020 , Pages 908-934 Rezaei, S ; Ghalehkhondabi, I ; Rafiee, M ; Namdar Zanganeh, S ; Sharif University of Technology
    Springer  2020
    Supplier selection and order allocation are important keys for reverse logistics and closed-loop supply chain networks especially with the presence of demand–supply imbalance risks. If such uncertainties and risks are not foreseen in the chain, and corresponding appropriate measures are not taken to handle them, irreparable damages would be expected consequently. The importance of this issue in closed-loop supply chains is more appreciated due to the importance and the effect of this chain on the environment. In this research, the disruption risk and the uncertainties related to the demand, market price, and the number of returned products are simultaneously considered. Purchasing from the... 

    A green closed-loop supply chain network: A bi-objective mixed integer linear programming model

    , Article International Journal of Operational Research ; Volume 41, Issue 4 , 2021 , Pages 492-513 ; 17457645 (ISSN) Gholipour, S ; Salehian, F ; Lamouchi, H ; Mina, H ; Sharif University of Technology
    Inderscience Publishers  2021
    The increasing level of customer awareness and application of environmental laws by governments, on the one hand, and the increasing number of competitors, on the other hand, has obliged industry owners to include green activities in the design of the supply chain network. Green activities include any type of action that reduces environmental degradation. Hence, this study seeks to develop a bi-objective, mixed integer linear programming (MILP) model for designing a green supply chain network. In the proposed model, the minimisation of costs and detrimental environmental effects are discussed. LP metric method is used to solve the bi-objective model and the proposed model is run by using... 

    Robust optimization of risk-aware, resilient and sustainable closed-loop supply chain network design with Lagrange relaxation and fix-and-optimize

    , Article International Journal of Logistics Research and Applications ; 2021 ; 13675567 (ISSN) Lotfi, R ; Sheikhi, Z ; Amra, M ; AliBakhshi, M ; Weber, G. W ; Sharif University of Technology
    Taylor and Francis Ltd  2021
    This study explores a Robust, Risk-aware, Resilient, and Sustainable Closed-Loop Supply Chain Network Design (3RSCLSCND) to tackle demand fluctuation like COVID-19 pandemic. A two-stage robust stochastic multiobjective programming model serves to express the proposed problems in formulae. The objective functions include minimising costs, CO2 emissions, energy consumption, and maximising employment by applying Conditional Value at Risk (CVaR) to achieve reliability through risk reduction. The Entropic Value at Risk (EVaR) and Minimax method are used to compare with the proposed model. We utilise the Lp-Metric method to solve the multiobjective problem. Since this model is complex, the... 

    Design of an stable GPC for nonminimum phase LTI systems

    , Article Wec 05: Fourth World Enformatika Conference, Istanbul, 24 June 2005 through 26 June 2005 ; Volume 6 , 2005 , Pages 88-91 ; 9759845857 (ISBN); 9789759845858 (ISBN) Yaghobi, M ; Haeri, M ; Sharif University of Technology
    The current methods of predictive controllers are utilized for those processes in which the rate of output variations is not high. For such processes, therefore, stability can be achieved by implementing the constrained predictive controller or applying infinite prediction horizon. When the rate of the output growth is high (e.g. for unstable nonminimum phase process) the stabilization seems to be problematic. In order to avoid this, it is suggested to change the method in the way that: first, the prediction error growth should be decreased at the early stage of the prediction horizon, and second, the rate of the error variation should be penalized. The growth of the error is decreased... 

    Characteristic ratio assignment in fractional order systems (case 0 < v ≤ 0.5)

    , Article Transactions of the Institute of Measurement and Control ; Volume 35, Issue 3 , 2013 , Pages 360-374 ; 01423312 (ISSN) Tabatabaei, M ; Haeri, M ; Sharif University of Technology
    Five different approaches are presented to assign characteristic ratios for commensurate fractional order systems having order in (0,0.5]. Through the indirect methods, a closed-loop or plant transfer function is converted to a commensurate order one with an order greater than 0.5 so that the previously designed CRA method by the authors is applicable. The first method among the proposed direct ones is based on increasing the order of the desired closed-loop transfer function that allows the employment of positive characteristic ratios. In the second method the closed-loop response is sped up by augmenting an appropriate zero. The final method uses negative characteristic ratios to reach the... 

    Norm-bounded integrity conditions of uncertain multivariable linear time-invariant systems under decentralized control with integral action

    , Article Journal of Process Control ; Volume 22, Issue 2 , 2012 , Pages 463-469 ; 09591524 (ISSN) Firouzbahrami, M ; Nobakhti, A ; Sharif University of Technology
    Decentralized controllers with integral action represent a large portion of multivariable controllers currently employed in the process industry. The integrity of these systems with respect to loop failures has been relatively well researched. In particular, important results have been found with respect to the relative gain array (RGA). However, less has been done on the treatment of the integrity of uncertain systems. This paper considers the integrity conditions of uncertain systems with norm-bounded uncertainties, and extends four existing integrity conditions to these uncertain systems. These are: integral stabilizable (IS), integral controllable (IC), integral controllable with... 

    CDM-based closed-loop transfer function design for ramp input

    , Article Transactions of the Institute of Measurement and Control ; Volume 33, Issue 5 , 2011 , Pages 558-572 ; 01423312 (ISSN) Haeri, M ; Tavazoei, M. S ; Sharif University of Technology
    This paper presents a method to determine the denominator and numerator polynomials of a closed-loop transfer function in order to obtain desired transient and steady-state responses in terms of the overshoot, speed (time needed for the relative error to become less than a specific amount) and the steady-state error when the desired output is a ramp signal. Meanwhile, a controller is designed with the same characteristic equation for the closed-loop system to eliminate step and ramp disturbances  

    Adaptive prescribed performance control of switched MIMO uncertain nonlinear systems subject to unmodeled dynamics and input nonlinearities

    , Article International Journal of Robust and Nonlinear Control ; Volume 28, Issue 18 , 2018 , Pages 5981-5996 ; 10498923 (ISSN) Malek, S. A ; Shahrokhi, M ; Vafa, E ; Moradvandi, A ; Sharif University of Technology
    In this paper, the design of an adaptive tracking control for a class of switched uncertain multiple-input–multiple-output nonlinear systems in the strict-feedback form with unmodeled dynamics in the presence of three types of input nonlinearity under arbitrary switching has been addressed. By means of an intelligent approximator like a fuzzy logic system or a neural network, the unknown dynamics are estimated. The unmodeled dynamics have been tackled with a dynamic signal. A universal framework for describing different types of input nonlinearity including saturation, backlash, and dead zone has been utilized. By applying the backstepping approach and the common Lyapunov function method,... 

    Stability and performance preserving controller order reduction via Youla parameterization and lmis

    , Article 2003 10th IEEE International Conference on Electronics, Circuits and Systems, ICECS2003, Sharjah, 14 December 2003 through 17 December 2003 ; Volume 2 , 2003 , Pages 663-666 ; 0780381637 (ISBN); 9780780381636 (ISBN) Amirgar, R ; Sadati, N ; Sharif University of Technology
    This paper develops a stability and performance preserving controller order reduction method for linear time-invariant continuous-time single-input, single-output systems. In this method, the error between the complementary sensitivity functions of the nominal closed-loop system and closed-loop system using the reduced-order controller is converted to a frequency-weighted error between the Youla parameters of the full-order and reduced-order controllers and then the H∞norm of this error, subject to a set of linear matrix inequality constraints, is minimized. The main ideas of order reduction and stability preservation are contained in the constraints of the optimization problem. However,... 

    Robust adaptive backstepping control of uncertain lorenz system [electronic resource]

    , Article Journal of American Institute of Physics ; 2010, Vol. 20, pp. 1-5 Nejat Pishkenari, H. (Hossein) ; Jalili, Nader ; Mahboobi, Seyed Hanif ; Alasty, Aria ; Meghdari, Ali ; Sharif University of Technology
    In this paper, a novel robust adaptive control method is proposed for controlling the Lorenz chaotic attractor. A new backstepping controller for the Lorenz system based on the Lyapunov stability theorem is proposed to overcome the singularity problem that appeared in using the typical backstepping control method. By exploiting the property of the system, the resulting controller is shown to be singularity free and the closed loop system is globally stable. Due to unavailability of system states measurement in practice, the controller is selected such that only one system state is needed. To overcome the problem of parameter uncertainty, an additional term to Lyapunov function is added and...