Sharif Digital Repository

The three dimensional resonant interaction between a surface wave and harmonic interfacial waves in a horizontally infinite two-layer fluid was investigated theoretically and experimentally. Initially, both layers assumed to be inviscid, but after obtaining the final equations of the interfacial wave's amplitude, with perturbation, the viscous damping effect, was incorporated in to the interaction equations. It is shown that, surface wave can trigger four opposite- traveling interfacial waves whose amplitudes grow with time. But because of viscosity damping effect, these amplitudes will become constant and won't change with time. The frequencies of the interfacial waves are approximately... 

This research presents a new harmonic model for compact fluorescent lamps and other nonlinear loads. In recent years, nonlinear loads have gained widespread acceptance due to their characteristics. Although CFLs consume less energy, they draw extremely distorted current waveforms resulting in harmonic losses in distribution networks. The presented harmonic Norton models in this work are simple and accurate models which can consider the impact of supply voltage harmonics as well. The parameters of non linear appliances model are determined based on measurements. The characteristics of the proposed models make it suitable for analyzing the impacts of large number of CFLs or other non-linear... 

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... 

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... 

Long lasting portable power is an ultimate desire for electronic devices. The limited capacity of the batteries in addition to the heavy weight and extra costs are the main challenges of the batteries for energy storage in large electrical devices like electric vehicles. Wireless Power Transmission (WPT) technology can address these issues by providing online electric power for these portable devices. Furthermore, this technology can supply electric devices especially portable ones by eliminating cables and connectors with more reliability.The current research is focused on optimum design of the wireless power transfer system for electric vehicle charging applications. The optimization of... 

In this thesis, we exploit N-path architecture in multi-standard transmitter in order to reduce the number of power amplifiers and matching networks. First, a new model of this transmitter is developed and simplified to improve its performance in operating frequency,power consumption and power efficiency . The model is then used for computer simulations of the proposed system for a variety of different modulations. Eight clock signals with consecutive phase difference of 2π/8 are generated by a divider and are applied to the power amplifier. The power amplifier is fullydigital. This removes the need for analog mixers and converts the transmitter to a fully digital transmitter. The proposed... 

A grid simulator is a system for testing various types of grid-connected devices, such as inverters of renewable energy sources, chargers, power supplies, etc. In this project, the design and implementation of a 3 KVA three-phase regenerative programmable AC current source is presented. In the future, this structure can be used as a grid simulator. The topology used for the current source is a two-level three-phase AC to DC converter. The current source can operate in constant current (CC), constant power (CP), constant impedance (CI), and constant voltage (CV) modes. In the constant current operating mode, the user sets the amplitude and phase of the 1st, 5th, 7th, 11th, and 13th harmonics... 

Considering the increasing development of renewable power plants including solar and wind power plants in the country, the need to investigate the effects of these power plants on the power grid is more needed and attention than before. Since these power plants are connected to the distribution network by means of power electronics, this problem has caused the injection of harmonics into the network, which can be transferred to higher voltage levels (upper distribution and transmission network). Harmonics in networks cause increased losses and reduced efficiency, false operation of protective relays, and damage to equipment due to the creation of harmonic intensifications. The purpose of...