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Controller Design for Nonlinear fractional Order Systems in the Presence of Input and Output Constraints
, M.Sc. Thesis Sharif University of Technology ; Shahrokhi, Mohammad (Supervisor)
Abstract
The purpose of this thesis is design of an adaptive tracking control for input-quantized strict-feedback fractional order nonlinear systems with unknown dynamics and asymmetric time-varying output constraints. The controller design is achieved by using a hysteretic quantizer to avoid chattering and not needing the quantization parameters. The fuzzy logic method has been used to solve the problem of unknown dynamics. Also, due to the asymmetric time-varying output constraints, the Barrier Lyapunov function has been used. In this thesis, less restrictive assumptions have been considered than the work performed in previous researches.By utilizing the adaptive backstepping approach and based on...
Design of Control for Fractional Order Systems with Output Constraints
, M.Sc. Thesis Sharif University of Technology ; Sharokhi, Mohammad (Supervisor)
Abstract
Identifying fractional systems and designing controllers for these systems is one of the leading challenges due to their limitations. Systems can have constraints on output, input, and states. These constraints make it difficult to design a controller. In this project, controller design methods for fractional-order systems with output constraints are investigated. A controller is designed for a strict feedback nonlinear system with unknown dynamics subject to asymmetric and variable output constraints, unknown direction of the controller, and unmeasurable states. To design the controller, the direct and backstepping technique is used and the Lyapunov barrier function is applied for the first...
Control Design for Nonlinear Stochastic Processes in the Presence of Output Constraint
, M.Sc. Thesis Sharif University of Technology ; Shahrokhi, Mohammad (Supervisor)
Abstract
This work addresses adaptive neural control for a class of stochastic nonlinear systems in the nonstrict-feedback form. By introducing a nonlinear mapping, the output-constrained stochastic system transformed into a new system without constraint. The systems under study is subject to state time delay, input nonlinearity, unavailable states, unknown dynamics and actuator failure. The appropriate Lyapunov-Krasovskii functionals is used to compensate the time-delay effects, the neural network is used to approximate the unknown nonlinearities, the linear state observer is constructed to estimate the unmeasured states, and a variable separation method is used to deal with the difficulty caused by...
Observer-based adaptive fuzzy controller for uncertain non-strict state-delayed nonlinear systems subject to input and output constraints
, Article Journal of the Franklin Institute ; Volume 357, Issue 12 , 2020 , Pages 7483-7514 ; Shahrokhi, M ; Khajeh Talkhoncheh, M ; Moradvandi, A ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
This paper addresses the design of an observer-based adaptive fuzzy controller for a class of uncertain non-strict nonlinear systems subject to time-delays, unknown direction, input saturation, and output constraint. The Barrier Lyapunov Function (BLF) has been utilized to keep the system output inside the desired bounds. The state and input delays have been handled by using the Lyapunov–Krasovskii function and including an integral compensator term in the controller, respectively. A state observer has been designed to estimate the unmeasured states. The Lipschitz condition for proving boundedness of the estimated states has been relaxed. The Nussbaum gain function has been exploited to deal...
Adaptive finite-time neural control of non-strict feedback systems subject to output constraint, unknown control direction, and input nonlinearities
, Article Information Sciences ; Volume 520 , 2020 , Pages 271-291 ; Shahrokhi, M ; Mohit, M ; Sharif University of Technology
Elsevier Inc
2020
Abstract
This paper addresses the finite-time controller design for a class of nonlinear systems in the non-strict feedback form subject to unknown system dynamics and disturbances, arbitrary asymmetric time-varying output constraints, four types of input nonlinearities, and unknown control direction. Utilizing the barrier Lyapunov function (BLF) and backstepping technique, an adaptive finite-time controller has been proposed. The difficulties associating with non-strict feedback systems have been handled using the variable separation approach. Furthermore, the unknown control direction problem has been tackled by using the Nussbaum gain function. A unified framework has been utilized for handling...
Adaptive finite-time fault-tolerant controller for a class of uncertain MIMO nonlinear switched systems subject to output constraints and unknown input nonlinearities
, Article Nonlinear Analysis: Hybrid Systems ; Volume 35 , February , 2020 ; Malek, S. A ; Shahrokhi, M ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
In this work, design of an adaptive finite-time fault-tolerant controller for a class of uncertain multi-input multi-output (MIMO) nonlinear switched systems with unmodeled dynamics subject to asymmetric time-varying output constraints and unknown faulty input nonlinearities has been addressed. The number of actuator faults can be infinite. In addition, the proposed control algorithm can cope with different unknown types of input nonlinearities namely, saturation, dead zone, backlash, and hysteresis. Actuator faults and input nonlinearities can be different in different modes. To estimate the system uncertainties, neural networks (NNs) have been employed and the unmodeled dynamics has been...
Control of Nonlinear Systems With Predefined Output Transient Performance
, M.Sc. Thesis Sharif University of Technology ; Shahrokhi, Mohammad (Supervisor)
Abstract
This project is aimed to design a controller for nonlinear systems that satisfy a prescribed performance while guaranteeing close-loop stability. To do this, the controller must be designed in such a way that the transient response of the system has had these performance indices and does not exceed them. These performance indices predefine some constraints for systems’ output.A comprehensive form for the model system, the unknown dynamics of the system, consideration of a variety of constraints on the system input, usage of the time-finite method for the residence time and consideration of just one tuning parameter to reduce the computation load, are among the other benefits for the proposed...
Multiple-horizon multiple-model predictive control of electromagnetic tethered satellite system
, Article Acta Astronautica ; Volume 157 , 2019 , Pages 250-262 ; 00945765 (ISSN) ; Assadian, N ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
This study aims to investigate the control of the electromagnetic tethered satellite system using a Model Predictive Control (MPC) scheme. The electromagnetic tethered satellite system is actuated by electromagnetic coils to generate controlling forces. The dynamical model of the system is described in high and low levels of accuracy, which are used to design the control framework. Multiple-Horizon Multiple-Model Predictive Control approach is employed to drive the formation to the desired state. Not only does the presented control law satisfy input and output constraints but also has appropriate characteristics in the sense of optimality. The main benefit of using Multiple-Horizon...
Fault-tolerant adaptive fractional controller design for incommensurate fractional-order nonlinear dynamic systems subject to input and output restrictions
, Article Chaos, Solitons and Fractals ; Volume 157 , 2022 ; 09600779 (ISSN) ; Shahrokhi, M ; Sadeghi, H ; Sharif University of Technology
Elsevier Ltd
2022
Abstract
In this article, a fault-tolerant adaptive neural network fractional controller has been proposed for a class of uncertain multi-input single-output (MISO) incommensurate fractional-order non-strict nonlinear systems subject to five different types of unknown input nonlinearities, infinite number of actuators failures and arbitrary independent time-varying output constraints. The barrier Lyapunov function (BLF)-based backstepping technique and fractional Lyapunov direct method (FLDM) have been used to design the controller and establish system stability. To tackle the incommensurate derivatives problem, in each step of the backstepping technique, an appropriate Lyapunov function has been...