Sharif Digital Repository

Switched systems as a subset of hybrid systems have both discrete and continuous behaviors and have attracted a lot of attention during the past decades. A set of subsystems or modes whose sequence is specified by a switching rule makes the switched system. Another category of systems is the fractional order system in which the order of derivatives is not limited to integers. This feature has provided a significant capacity for this type of system. On the other hand, every real system faces a set of limitations that neglecting them may reduce the quality of control or even lead to system instability. The purpose of this research is to model and control the switched system, whose subsystems... 

The objective of this research is designing a controller for the event-triggered control of multi-agent systems in the presence of common constraints. In this regard, an adaptive decentralized event-driven controller is designed for the agents of a multi-agent system. The dynamics of the agents are nonlinear and unknown and they are subject to external disturbances. This controller is capable of achieving the objective of consensus with the desired performance in the presence of sensor and actuator faults, input nonlinearity, input and output quantization, and unmeasured states. The stability of the closed-loop system has been established via Lyapuonov theory. The considered multi-agent... 

Due to the presence of a random variable in the process dynamics or due to the presence of measurement noise, many processes have stochastic in nature. Behaviors of these processes are different from the deterministic processes and therefore their controllers are also different. The aim of this research is to design adaptive controller for stochastic processes with a non-strict feedback structure and in the presence of input constraints. Also, the considered system has other limitations such as the unmeasured states, actuator failure, unknown dynamics and fixed time stability is desired. The input limitation can be caused by the limitation of the final control element, because the input... 

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... 

The objective of this research is to design an adaptive controller for a class of fractional-order nonlinear systems in the strict-feedback form with unmodeled dynamics. Actuator saturation and actuator fault are also considered. All of the system states are assumed to be measurable, and all the sensors can be faulty. Fractional-order systems are chosen because, in the modeling of physical systems, the fractional-order calculus is often preferable to the classical integer-order calculus. The controller is designed by using the backstepping design technique. The fuzzy logic systems are used to eliminate the problem of "explosion of complexity" in the conventional backstepping method and also... 

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... 

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... 

Since, presence of sulfur compounds in fuels leads to environmental pollution and deacrese of fuel quality, fuel desulfurization should be considered for enhancing the fuel charachteristics. Electrochemical desulfurization was recogonized as one of desulfurization techniques that uses anode and cathode in an electrolytic environment under mild temperature and pressure. In this research, electrochemical desulfurization of crude gas-oil has been studied over electrodes of copper and stainless steel in the presence of NaOH and sulfuric acid. In this research, the effects of operational prameters like stirring rate, temperature, applied potential, sodium hydroxide/sulfuric acid addition as... 

Due to the high cost and destructive effects of fossil fuels, the biogas production as a renewable and environmentally friendly fuel attracted much attention. In this regard, several targets are considered in this research. First, in order to increase of biogas production yield and accelerating the rate limiting steps in anaerobic digestion of wheat straw (lignocellulosic feedstock), the effect of additives containing trace elements (Fe and Ni) in form of nanoparticles and their salts was investigated through batch experiments. The results showed that addition of nanoparticles or salts resulted in the increase of methane production rate during the first 4 days of experiments. Then, a... 

The purpose of this study is to propose a stable treatment strategy for hepatitis C infection by considering several practical limitations of the treatment and using control theories. First, hepatitis C disease and its transmission, diagnosis, and treatment methods have been introduced. Then, the mathematical models of hepatitis C dynamics in the body have been presented, and their ability in predicting the observed clinical behaviors of the patients has been studied. Thereafter, the extended versions of these models by considering pharmacokinetics/dynamics equations of the drugs have been proposed to have a more realistic mathematical model. After that, the practical features of the disease... 

Considering input constraints is an essential task in the controller design. In this thesis, a controller has been designed for incommensurate fractional order nonlinear systems in the nonstrict feedback form subject to unknown dynamics, input nonlinearity and actuator failures. The Lyapunov direct method and the backstepping technique have been used to design the controller and stability analysis. The number of actuator faults can be infinite. In addition, the proposed control algorithm can cope with different types of input nonlinearities namely, saturation, dead zone, dead zone-saturation, backlash and hysteresis. To estimate the system uncertainties, neural networks have been employed... 

Researchers have paid more attention to greenhouse cultivation, due to the exacerbation of food and water crisis. Higher production with lower cost could be achieved through greenhouse climate control (temperature, humidity, carbon dioxide concentration). However, greenhouse climate control is a challenging task, because greenhouses have highly interactive nonlinear dynamics and model uncertainties and are subject to input saturation. In light of the fact that Iran is a country with a warm and arid climate, tunnel greenhouses equipped with evaporative cooling system are very common in Iran. Accordingly, this type of greenhouse is considered for modelling, simulation and control in this... 

Because of lower energy consumption and lower capital cost, divided wall columns attracted wide attention. The main challenge of these units is their controllability. In this thesis dynamic simulation and control of a divided wall column is investigated and an adaptive model predictive controller has been used for control purpose. For dynamic simulation the Aspen Dynamics software and for applying control strategy the MATLAB software have been utilized. The model used for model predictive controller has been obtained by using open loop responses of the system. The main advantage of presented work over the existing ones is using the input-output transfer function of the system model instead... 

The diesel fuel produced from vegetable oils or animal fats is called biodoesel. Biodiesel has desired fuel property as an alternative for diesel engines. Moreover, It is biodegerable, non-toxic, environmental friendly and has lesser undesirable exhaust. Due to biodiesel advantages, production of biodiesel and control of the biodiesel production reactor is noteworthy. The objective of this work is to control the mass fraction of the produced ester and the reactor temperature by manipulating methanol feed flow rate and the heat duty of the reactor. For this purpose, an adaptive multivariable generalized model predictive control (GPC) has been applied to the reactor. The results indicate that... 

This thesis addresses design of an adaptive tracking control of input-quantized strict-feedback fractional-order nonlinear systems with unknown control directions. The control design is achieved by using a hysteretic quantizer to avoid chattering. The main advantages of the proposed controller are: the fractional order is available for both commensurate and non-commensurate cases, the¬¬ controller design does not depend on the quantization parameters and some restrictive assumptions are relaxed. Additionally only one adaptive law has been used for the unknown control directions which leads to reduction of computational load. By utilizing the backstepping approach and based on the frequency... 

Anaerobic digestion of waste and wastewater has attracted researchers’ attention due to its important effect on reducing greenhouse gas emissions and reducing the level of environmental pollution and production of methane as a renewable energy source. This process is highly sensitive and can become unstable due to the presence of complex biochemical reactions and containing various types of chemical in it. In order to understand and improve the performance of this process, modeling and design of an appropriate control strategy is needed. ADM1 is the most accurate model for this process which is used in this study to describe and simulate the anaerobic reactor. Constrained and unconstrained... 

Anaerobic digestion of waste and wastewater has attracted researchers’ attention due to its important effect on reducing greenhouse gas emissions and reducing the level of environmental pollution and production of methane as a renewable energy source. This process is highly sensitive and can become unstable due to the presence of complex biochemical reactions and containing various types of chemical in it. In order to understand and improve the performance of this process, modeling and design of an appropriate control strategy is needed. ADM1 is the most accurate model for this process which is used in this study to describe and simulate the anaerobic reactor. Constrained and unconstrained... 

Due to the successful experience gained in the process intensification and implementation of Reactive Distillation and Divided Wall Column in industry, Reactive Divided Wall Column have also been considered as a further step in process intensification. One important research area in implementation of RDWCs is their control issue. In the present study, the dynamic simulation of reactive divided wall columns and their control were studied and the adaptive model predictive control was used for the control objectives. Aspen Dynamics software was used for simulation and MATLAB software was utilized for applying the control strategy. The advantage of the applied control method is the use of... 

In this research work, to enhance the performance of the conventional spinning disk reactors, a novel type of spinning disk reactor has been proposed and tested successfully through the synthesis of barium sulfate nanoparticles by means of the reactive precipitation. This reactor consists of two coaxial rotating disks placed horizontally in a cylindrical chamber. The experimental results clearly indicate the capability of the proposed reactor in the synthesis of nanoparticles with the smaller mean particle size and the narrower particle size distribution compared to those obtained in various process intensification devices such that barium sulfate nanoparticles with a mean particle size of... 

Due to the importance of hepatitis disease, especially hepatitis C, from public health view point, this research aims to investigate and suggest an efficient medical therapy for this disease. First, available models are analyzed and the suitable one is chosen. Three controllers namely, fixed PI, adaptive PI and exact linearization control (GLC) are designed to control the hepatitis C disease using the drug efficacy as the manipulated variabel. Controller parameters are determined by the Genetic Algorithm (GA) and their performances are evaluated using the selected model. Uncertainties have been considerd in both model structure and parameters and controllers performances are investigated in...