Sharif Digital Repository

This thesis proposes a new method for estimation of parameters of a multi-component signal. The signal is composed of several sinusoidal components whose frequencies and magnitudes are unknown. Moreover, the signal is polluted with white noise. The estimated parameters are frequency, amplitude, and phase-angle of each component. The proposed method is able to adaptively decompose the multi-component signal into its constituting sinusoidal components. The core unit of the proposed method comprises an adaptive band-pass and an adaptive notch filter. The proposed method consists of parallel connection of several core units. The band pass filter rejects all components except the one whose... 

Design of optimal controllers for nonlinear systems and even for linear systems is one of the most important parts of the control science. In optimal controller design, our aim is to maximize or minimize some kind of cost function associated with that particular problem. Such cost functions are usually combining the overall control effort, system’s energy, or some other important specifications of the system. Explicit solution for linear quadratic controllers exists under some mild conditions such as stabilizability of the system. The solution is in the form of a full state-feedback law. But in practical problems, we may not have access to all of the system state variables. The problem can... 

A robust decentralized control strategy for the islanded operation of a microgrid is proposed in this thesis. The microgrid consists of the parallel connection of several electronically-coupled distributed generation (DG) units. All DG units are connected to a point of common coupling (PCC) where a passive load is also connected. It is shown that the islanded microgrid can be modeled by an interconnected composite system comprising equal number of subsystems (to the DGs). Moreover, it is shown that the overall islanded microgrid can be controlled by only the local controllers about the individual subsystems. In this case, one of the DGs, referred to as the Master DG, is responsible for... 

A control strategy for islanded (autonomous) operation of a microgrid consisting of two Distributed Generation (DG) units is proposed in this thesis. The DG units are connected together in a radial configuration. Each DG unit utilizes a voltage-sourced converter (VSC) to interface to its dedicated load. The DG units and the loads are to operate in the islanded mode of operation. To provide autonomous operation for the microgrid, voltage and frequency of the loads should be regulated. The proposed control strategy utilizes (i) an internal oscillator for frequency control in an open loop manner and (ii) a decentralized servomechanism controller to regulate the load voltage. The microgrid is... 

Nowadays, the use of distributed generation (DG) units and microgrid systems is mainly limited to their operation in the grid-connected mode. In the grid-connected mode, a microgrid including its loads and DG units is connected to the main grid at the point of common coupling (PCC). In this case, the main grid provides fixed voltage and frequency for the microgird and each DG unit regulates its power components based on the conventional dq-current control strategy. Autonomous (islanded) operation of a microgrid, however, is not as straightforward as its operation in the grid-connected mode, i.e., control and power management of an islanded microgrid is very difficult due to the stochastic... 

With the increasing expansion of modern DC loads and utilizing energy storage systems along with distributed renewable energy resources, grid-following bidirectional voltage-sourced converters (GFBVSCs) with fast dynamic performance are required. Due to the presence of single-phase loads and asymmetrical short circuit faults, unbalanced grid voltage conditions are available in the distribution system. Under unbalanced conditions, an oscillating component with a frequency of twice the grid angular frequency appears on the DC side. Removing double-frequency ripple in the DC link voltage without third harmonic current injection and reactive power injection to the grid based on the grid codes to... 

The use of distributed generation (DG) units provides several advantages for the utility distribution grid. Mostly power electronics converter is used as an interface to connect a DG unit to a utility grid. A DG unit normally operates in a grid-connected mode. In this mode, the host grid dominantly dictates the voltage amplitude and frequency of the local load at the point of common coupling (PCC) and the DG unit controls its real/reactive power components. Separation of the DG unit and its dedicated load from the host grid is called islanding. Subsequent to the formation of an island, due to the lack of control over the voltage magnitude and frequency, the islanded DG system becomes... 

On account of the exhausting nature and increasing daily cost of the fossil fuels, it seems that replacing the fossil fuels by an alternative source of energy is inevitable. Moreover, in the remote areas that the electricity network is not accessible, the use of distributed sources (DSs) such as solar energy and wind energy is advantageous. Continuity of the supply and voltage control of the load in spite of the stochastic nature of the generated power of the renewable energy resources are the main concerns in the distributed generation (DG) systems. In this thesis, stand-alone operation of a DG unit comprising a solar unit and wind turbine as primary sources of energy is considered. A... 

The level of current and voltage harmonics in power networks has been increased due to the widespread use of power electronic equipment. This increase may, in turn, result in damage to power system equipment in addition to extra power losses in the network. In order to assess the level of harmonics, it is required to monitor power networks using power quality analyzers. However, due to the high costs, only limited number of measurements can be used in practice. The task of harmonic state estimation is to identify the location and magnitude of harmonic sources and to estimate the harmonic voltage and current by partial measurements. Due to the high price of measurement instruments and... 

The microstructures of stainless steels consist of an austenitic matrix with almost continuous network of primery carbides.This class of steel had replaced the traditional super alloys with a reduction in costs and has similar properties under conditions of creep, which is one of the principal degradation mechanisms leading to failure in service at elevated temperaturs , therefore, their mechanical properties such as tensile strength and creep resistance are particularly important in hot deformation. Recently the effects of temperature and aging time on static strain aging in worked stainless steel have been investigated. In this study the deformation behavior of HP-series austenitic... 

Possessing second place among gas reserve owner countries worldwide, Iran enjoys a very particular position in energy supply field. The crude oil is about to be replaced by natural gas in fuel sector because of growing demand for natural gas along with depletion of crude oil reserves. Some other drivers to this change are the increase in the known reserves of natural gas, the need to monetize stranded gas reserves and the environmental pressure to minimize the flaring of associated gas and carbon dioxide emissions. In such conditions the optimum consumption of these national abundant resources results in obtaining considerable revenues and strong presence of Iran in world consumption... 

When organizations prefer to outsource their data, security protection of data will be more important. Using cryptography in addition to access control techniques is a natural way for saving confidentiality of data against untrusted server. However, encryption and decryption of data result in database performance degradation. In such a situation all the information stored in encrypted form, one cannot make the selection on the database content any more. Data should be decrypted first, so an unwilling tradeoff between the security and performance is normally forced. The appropriate approaches to increase the performance are methods to deal directly with the encrypted data without firstly... 

Analysis and design of power systems are challenging due to ever increasing dimension of the system and also the nonlinearities involved in the system. The conventional approach is to use linear analysis tools and then investigate the nonlinear impacts by the means of computer simulations. This requires great deal of trial and error and it is not always a timely approach. In this project, we initiate a comprehensive nonlinear analysis for a single-machine infinite-bus system by studying a Hopf bifurcation in its dynamics. We use results of our nonlinear analysis to study how a capacitive compensation such as TCSC works. Subsequently, we design a nonlinear controller for a PSS to have...