Sharif Digital Repository

The application of Stochastic Differential Equations in branches like nonlinear control,robatic systems, financial mathematics and etc. has grown impressively nowadays. In this thesis, we are going to introduce this equations and study their stability. First, we will present methods to check the stability of nonlinear systems dx(t) = f(x(t); t)dt using Lyapunov’s theorem.Then we will study stability of autonomous systems using it’s results. In the case of instability, we will study the possibility of stabilizing the stochastic equations dx(t) = Ax(t)dt + Σn i=1 Bix(t)dWi(t) by using Brownian motions and these methods. In the end, we will study the stabilizablity conditions of instable... 

In this thesis, a new general state space form for uncertain LTI-fractional order system subjected to interval and polytopic uncertainties is introduced. Robust stability analysis and robust stabilization of presented system are investigated. Fractional derivative order assumed to be a known constant. Sufficient conditions in terms linear matrix inequalities (LMIs) are concluded to check the robust stability of the presented system. Then, these results are extended to derive some sufficient LMI conditions to design a state feedback controller in order to stabilize the mentioned uncertain system robustly. Effectiveness and correctness of presented sufficient conditions and application of... 

The following thesis is concerned with the effect of channel feedback in tracking and stability of linear Gaussian systems over Additive White Gaussian Noise (AWGN) channel when the decoder is the Kalman filter and encoder is the innovation encoder. When the feedback channel is described by a noisy link or a random switch, it is shown that stability is not possible for unstable systems. But for stable systems, an innovation encoder, Kalman filter decoder and a certainly equivalent controller for tracking and stability are presented. When the feedback channel is described by a deterministic switch, for both stable and unstable systems, an innovation encoder, Kalman filter decoder and a... 

Advancement in the field of electronics can often be observed from the improvement in performance of active circuits and systems. The amplifier, because it is a highly versatile functional circuit, has always been one of the first to benefit from new developments. Of the many characteristic of an amplifier, perhaps the most notable are the gain and the frequency response. In many applications, both the gain and the bandwidth need to be optimized. One of the most significant structures which have proper gain and bandwidth, are distributed amplifiers. But these structures are nonsymmetrical and have many active loops. As a result, the stability analysis of distributed amplifier is quite... 

Chlorinated hydrocarbons such as trichloroethylene form a kind of dense non-aqueous phase liquid contaminants in groundwater and soil that are so difficult to remediate. In recent years, many field research has been demonstrated application of nano scale zero valent iron can degrade these contaminants.
In this research, nZVI particle synthesized by liquid phase reduction method. Nickel (25%wt ) has been added to increase the reduction rate and also reduce intermediate pollutions. However, the combination of a noble metal to nZVI, leads to more rapid oxidation and tendency to agglomeration. So nZVI particles coated by applying a water soluble-starch solution (0.4%wt) as a stabilizer. The... 

This thesis is concerned with stability and tracking of nonlinear noisy Lipschitz systems over the packet erasure channel with feedback acknowledgment when system and measurement are due to bounded noises. The desired stability and tracking criteria is bounded stability and tracking in probability. Two approaches are adopted to address the desired stability and tracking performance, one is based on the Chebyshev inequality and the other is based on the Binomial distribution. It is illustrated that when the erasure probability is large, the approach based on the Chebyshev inequality provides a better bound for stability and tracking in probability; while, when the erasure probability is... 

In this thesis, stability and stabilization of fractional-order linear time invariant swarm systems are studied. In recent years it has been proved that the exact model of dynamic agents in most of the swarm systems can be modeled more accurate by fractional order differential equations. Stating the motivation of choosing this subject, the achievements of the thesis can be divided into two general parts: Investigating the stability of fractional-order swarm systems and how to stabilize such systems. After introducing the fractional-order systems and fractional-order model of swarm systems in the introduction part, the literature review is presented in Chapter 2. In Chapter 3 the results... 

In this thesis, the general form of descriptor linear systems with time-delay is studied. First, an approach is presented to analyze the stability of descriptor linear systems with commensurate time-delay. Through this approach, not only stable and unstable regions of the system can be determined, but also the number of unstable roots in each unstable region can be calculated. Additionally, a decomposition approach is proposed, which transforms the descriptor systems with time-delay to normal time-delay systems with a lower order. As a result, a large number of methods which are only available for normal systems with time-delay can be utilized for descriptor systems with time-delay. Also,... 

Ilam refinery has three synchronous generator units each with a capacity of 26.5 MVA and two six-phase LCI-fed synchronous compressors, each with a capacity of 8 MW. Generators of Ilam gas refinery have instability issue in case of island operation. With launching one generator unit and then connecting two compressors the instability problem and tripping of the generators appear. Given the importance of this issue, various tests and corresponding measurements in both electrical and mechanical aspects were carried out at the plant in on-grid and island operations to analyze the cause of instability phenomena. The mechanical part of tests analyses the frequency of oscillations and vibration in... 

Collapsible soils, a kind of which is Loess, are mainly in silt size in the nature, and are present in many part of Iran, such as Golestan, Semnan, Khorasan, Yazd, Kerman, Hormozgan, Sistan and Balouchestan provinces. when the water content of the soil is lower than a critical water content, the soil shows high shear strength. However, increase in water content due to leakage of water, wastewater or heavy rains in the presence of enough induced pressure, when a certain coupled hydro-mechanical condition is reached, will result in a sudden collapse or excessive deformation. Hence, improvement or stabilization of this kind of soil is of high importance. In this research, specimens are prepared... 

Abstract: In this dissertation, the problem of tracking and stabilization of nonlinear dynamic systems over the packet erasure channel is addressed. Using the idea of linearization of nonlinear system around current working point, and by the design of an encoder, decoder, and controller for the linearized system, state tracking and reference tracking of the nonlinear system are addressed. To prove the traking and stability of the system, the strong law of large numbers and the dwell time approach are used. By computer simulations, the theoretical development is applied on the nonlinear dynamic of the unicycle model, which is a suitable model for autonomous vehicles, such as drones, unmanned... 

In this research, a new step-by-step and comprehensive method for the design of back-to-back converters in the presence of nonlinear and constant power loads is proposed. Common methods for the design and control of back-to-back converters consider the design procedure independent of the linearity and dynamic of the load, also, the control system design and performance of the load-side and grid-side inverters of back-to-back converters are assumed to be independent of each other which is shown in this thesis that this assumption is not valid in the presence of nonlinear loads. These methods result in challenges and problems regarding stability and power quality indices of back-to-back... 

Video stabilization is one of the main quality enhance- ment techniques for the data captured by a moving/shaking video recorder. In this work, we focus on video stabilization in smartphones equipped with inertial measurement units (IMU). Specifically, we present a fully differentiable dynamic computational graph to compensate for simple pinhole camera model deficiencies, using the suggested model and estimated angular rotation changes inferred from IMU data, We try to improve and stabilize shaky videos. Further using qualitative and quantitative approaches we show our method’s supremacy against current state of the art stabilization methods. This work accompanied with software and necessary... 

This thesis presents a new approach to design structural output feedback controllers with stabilization and pole-placement at desired points on the S plane. It is assumed that the linear time-invariant system has no fixed mode corresponding to the specified control structure, outside the desired region of the closed-loop poles, such that the structural controller design problem is theoretically feasible. To this end, the structural output controller design problem is first transformed into a structurally equivalent problem based on the solution of a set of discrete linear programs. Then, by using the resultant structure, a new method is proposed for designing static and dynamic control loops... 

The purpose of this thesis is sliding mode control of a roll-pitch seeker by considering the zenith pass problem. This problem takes place when the target appears in front of the seeker’s head. First, the mathematical model of the roll and pitch frames is obtained by the Newton-Euler equations of motion. Then, a MIMO sliding mode controller is designed. The performance of the controller is investigated in the presence of model uncertainties and seeker disturbances. The results indicate that the designed controller is robust enough and provides a suitable performance in the stabilization, tracking and guidance loops.