Sharif Digital Repository

Advances in IC fabrication makes possible have systems on chips. In this thesis we have designed and fabricated a digitally controlled bias chip for a transceiver which can be programmed by its digital interface. In this thesis, briefly we review basics of voltage regulators and methods for controlling them. Then we introduce high voltage 0.18um CMOS technology. In this thesis, we describe the requirements of a specific transceiver and present a system to overcome these requirements. This system has positive, negative and internal regulators, a five-bit analog to digital converter, temperature sensors, power amplifier controller and digital serial interface. In this thesis, we present a... 

In this project the novel zero-voltage-switching topology for power factor correction bridgeless boost rectifier is proposed. By employing an improved ZVS pulse-width-modulation (PWM) switch cell, ZVS of all the main switches is achieved without additional current or voltage stress of main switches. Also for the auxiliary switch the zero-current-switching is provided. In all modes of opretion of this converter, the power path is provided by maximum two semiconductor so the conduction loss of converter is low as in conventional converter. With this features the efficiency of proposed converter is very high  

In this thesis, a power switch with a smart driver is designed. 4-ampere current can pass through the switch, and the driver is capable of switching the load with 50 kHz frequency. The smart driver consists of an internal oscillator, internal regulator, charge pump, current limit, a level shifter, overtemperature and over/under voltage circuit. All these circuits are designed and developed in high voltage BCD 0.18 um process and well discussed in the thesis. All four kinds of protections are designed and implemented; open load detection, short circuit detection, over temperature shut down, UV and OV detection. Charge pump idea is used instead of the bootstrap method, which makes it possible... 

High-power (108 – 109 W) RF pulses with a carrier frequency of C band and a duration of several oscillation periods can be produced through direct energy conversion of a travelling high-voltage pulse with the use of nonlinear elements.
Nonlinear transmission lines consist either of lumped nonlinear elements and provide spatial dispersion of excited oscillations or of elements uniformly distributed on a certain line segment. The first type of NLTL’s can be referred to NLTL’s with spatial dispersion. The second type of NLTL’s is ensemble of nonlinear oscillators with a characteristic natural frequency and temporal dispersion. In the first case, the duration of electromagnetic pulses is... 

In some high voltage applications it is necessary for high voltage power supply (HVPS) to operate over a wide load and gain range. For instance a HVPS may be used to supply various microwave tubes. Our goal in this thesis is to design a HVPS which can provide a DC voltage between 0-15 KV and 0-5 KW. In convetional approaches, operating over wide load and gain range necessitates the switching frequency or duty cycle to swing over a wide range. This approach may disturb soft switching, consequently switching loss will increase. The control process will be more complex too. the wide swing range of switching frequency means that the HVPS needs to operate with low switching frequency too.... 

Reduction of power converters’ cost is one of the most important efforts to improve machines control systems. In this way, some new topologies for power electronic converters have been proposed. Among various topologies, four switch three phase inverter (FSTPI) thanks to the simple circuit, low cost, minimized conduction and switching losses and high reliability has attracted much attention recently. In this thesis, direct torque control (DTC) method is utilized to control of four switch inverter fed induction motor. In this way, in order to decrease flux and torque ripple and achieving constant switching frequency, a new Discrete Space Vector Modulation (DSVM) method have been proposed in... 

High voltage power supplies (HVPS) are widely used to supply the vacuum tubes. The function of this power supply is disturbed by some internal and external faults. One of the external faults is the arc fault in the tube. The amount of delivered energy from the HVPS to the tube is an important issue during the arc fault in the tube. The conventional protection mechanism consists of a shunt crowbar device which divert the fault current from the tube arc. The crowbar circuit is usually built with thyristor in most cases. This type of crowbar cannot be turned off simply by protection command. It is a drawback since if the fault is transient such as arc in the load or false fault detection is... 

The amount of assigned computation to data centers, which generally process data streams in a parallel manner has grown in recent years. Switches are one of the most important components in such centers, and their appropriate design can reduce the power loss and increase the processing gain. Among such devices, holographic CDMA switches, which exploit the high storage capability of thin holograms to reduce the size of switches, are suitable alternatives to the traditional electronic switches. In this research, the fairly high power loss of such switches has significantly decreased by modifying the output filter. This modification includes two steps. In the first, the typical matched filter... 

There are a wide variety of light-triggered switches. Photoconductive semiconductor switches (PCSSs) have been investigated intensively for many applications owing to their unique advantages over other switches. The advantages of PCSSs make them a perfect choice for many important applications where high switching accuracy and high-power capability are required. Photoconductive switches are fabricated from a variety of semiconductors, including silicon carbide (SiC), gallium arsenide (GaAs) and gallium nitride (GaN). In Photoconductive semiconductor switches (PCSSs) the switching mechanism is initiated by optical illumination and laser source controls the flow of current. In the off or... 

Quantum interference and coherence are responsible for a novel set of physical phenomena, where Electromagnetically Induced Transparency is one of the most important of them. Each of these phenomena can make a new possibility for modifying the optical properties of a coherently prepared medium. Fast controllability of optical properties in one hand and flexibility of this control process in the other hand, are important factors that attract interests into coherent control of light .Coherent control of optical properties of the medium can be used in designing some advanced and challenging devices including All-Optical Switches. In this work , in a consistent picture, using a step by step... 

The objective of this project is to design and control and optimize a single-stage three-phase three-switch unity power factor telecom rectifier. For this purpose, the topology of three-phase three-switch converter has been investigated for both isolated and un-isolated converters. Following a comprehensive investigation on the converter structure, the power dissipation factors have been detected and the quantity of the power dissipation has been calculated by analytical methods and it confirmed by simulation results. To avoid extra power losses some novel soft-switched structures for three-phase three-switched converters have been introduced. the proper operation of the soft-switched... 

In this thesis, marx pulsed power generators are investigated. Due to very large magnitude of its output voltage and very fast rise time, Marx generator is the first choice in lots of pulsed power applications. A significant barrier in the implementation of this generators are the switches with witch the structure is made. The short magnitude nominal voltage and current of the solid state switches lead to use of Spark Gaps in which the determinative parameter of the switch to turn on, is its breakdown voltage. These switches have some limitations in repetition rate and turn off ability. However due to very high range of nominal voltage and currents, they are an appropriate choice for marx... 

EEG Signal Processing has really important role in study of nerves system and nervous diseases. In most applications, signals occur in the frequency band ranging below 100 Hz are considered. In this study, the higher frequency components of the signal, especially in patients with epilepsy, reported which they are called high frequency oscillations (HFOs). Some sources considered that HFOs are up to 1000 Hz and some other considered up to 2500 Hz. In study of HFOs, the high frequencies between 100 and 200 Hz that are called ripple and seen in normal mode are separated from the faster frequencies from 200 to 500 Hz and these components can accurately help to detect epileptic foci generator (to... 

Nd:YAG laser is one of the most applicable lasers on laser researches where it’s basic wavelength and higher harmonics are used on different laser projects. It should be realized that it’s basic output has a wide pulse duration and lower peak power. Therefore, in order to increase the peak power the pulse duration is reduced by Q-switching.
In this project, in the first step, based on flash-lamp pump Nd:YAG laser a 600 mj energy per 60 µs pulse is constructed. Then a pulse duration is shorten by order of more than 3000 via electro-optics Q-switching system where we could reach up to 19 ns pulses and laser peak power is increased up to several megawatts  

Switched Reluctance Generator (SRG) has some unique features such as low cost, simple and rugged structure and high performance operation in wide range of speed. These features make the SRG one of the best candidates for optimum power generation. SRG has used as starter-alternator in Hybrid Electric Vehicles (HEV) and aircrafts. An SRG drive system operates by exciting the SRG phases with a DC voltage source and then discharging the stored and developed magnetic energy to the connected DC supply. Therefore, output power of a Switched Reluctance Generator directly depends on the excitation angles when operates in the Single Pulse Mode. In this dissertation the goal is to control a SRG in the... 

In this research, the numerical simulation of liquid jet ejecting for a series of elliptical orifices into gaseous phase with different aspect ratios, at Rayleigh flow regime and in a range of Weber numbers has been performed.
For simulations, the OpenFoam software was utilized, which its multiphase flow simulation solvers are based on volume of fluid (VOF) method. In order to achieve the most accurate results for axis-switching phenomenon and jet breakup length, the dynamic mesh refinement was used for all the examined cases. The results, which were validated with recent experimental and numerical works, indicate that jet breakup length raises by increasing Weber number from 20 to 300.... 

Through the last decades, due to environmental issues and to confine CO2 emission and also dependency to the fossil fuels, renewable energy resources has been developed. It’s been expected up to 2035, the renewable energy resources will be scaled three times and among those resources, the wind energy will stand prominently. Out of this king of renewable resource, the horizontal wind turbine has been subjected in this research.The focus of is to design the controller in third of a 2 MW turbine operation by which stable rotor speed and nominal output power to be attained. Besides, to enhance the accuracy of the windturbine profiles, the TURBSIM software (At the National Renewable Energy... 

Through the last decades, due to environmental issues and to confine CO2 emission and also dependency to the fossil fuels, renewable energy resources has been developed. It’s been expected up to 2035, the renewable energy resources will be scaled three times and among those resources, the wind energy will stand prominently. Out of this king of renewable resource, the horizontal wind turbine has been subjected in this research. The focus of is to design the controller in third of a 2 MW turbine operation by which stable rotor speed and nominal output power to be attained. Besides, to enhance the accuracy of the wind turbine profiles, the TURBSIM software (At the National Renewable Energy... 

This thesis deals with the theoretical and experimental investigation of quantum interference and coherence, and electromagnetic induced transparency (EIT) in multi-level atomic systems such as hot and cold Rb atoms, semiconductor quantum dots and wells. Optical properties of atomic media in presence of coherent laser fields and incoherent fields are studied.
Theoretical studies verify the crucial role of atomic coherence due to quantum interference in modifying optical properties of atomic media. Suitable and efficient models based on multi-level atomic systems to investigate the optical properties and, optical bistability and multistability are proposed. The most advantages of these... 

In recent years, multiport bidirectional converters have been a center of attention in renewable energy systems. This research focuses on three-port bidirectional converters. First, series resonant bidirectional converter is precisely analyzed. This analysis includes sinusoidal, exact state space and small signal analysis through phasor concept. This converter can work in higher switching frequencies and higher power ratings in comparison with common DAB bidirectional converter due to its inductor impedance cancellation. To increase power rating a three-phase version is proposed which has reduced output filter capacitance. Then, three-port bidirectional resonant converter is proposed and...