Sharif Digital Repository

Since the power systems usually are being operated close to their nominal capacity due to economical reasons, the probability of wide blackouts in power grids have been increased. However by employing suitable strategies the probability of huge blackouts is still very small but if they occur may put the power system operators in trouble while restoring the system. Thus many studies have been conducted in recent years dealing with power system restoration planning to achieve fast and reliable restoration plans. The scope of this project is overvoltage assessment during system restoration. In this manner we can find the optimal strategy with the least overvoltage problems to prevent the... 

For many low-powered portable and wireless electronic applications the finite energy density of chemical batteries places limits on their functional lifetime. Through the use of energy harvesting techniques, ambient vibration energy can be captured and converted into usable electricity in order to create self-powering systems which are not limited by finite battery energy. Typical energy harvesting systems are composed of two components, a transducer that converts the mechanical vibrations into electrical energy and a power converter that efficiently delivers the harvested energy to the electronic load. The practical design of energy harvesting systems must include both components and... 

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... 

The aim of this thesis is investigating the approaches proposed for controlling switched systems and designing a controller for MIMO switched systems. The system under consideration is in strict feedback form with unknown dynamics, unmodeled dynamics, state-dependent delays and disturbances and input nonlinearity (saturation, backlash, dead-zone). In this work, the unknown dynamics are estimated by an intelligent approximator. The arbitrary switching law is assumed and for control purpose the switching instances are not required. The backstepping technique has been utilize for controller design and by using a nonnegative switching function and a common lyapunov function, the closed loop... 

Wireless power transfer provides many medical applications. Recently, power electronic devices are available with high power transmission capability at higher frequencies. This makes it possible to transfer wireless power with considerable amount of power. Due to the reductions of battery size and cost with using wireless power transfer system, this technology is introduced as one of the most interesting topics among researchers. There are obstacles in front of the progressing wireless power transfer applications. Lateral misalignment, load variations, component uncertainties in value are common in wireless power transfer applications. In order to bring this application in large scales, all... 

Time-Modulated Array is known as an electrical beamforming technique that has lower cost and complexity compared to the conventional beamforming techniques. In a Time-Modulated Array, the antennas are turned on and off periodically, so the harmonics of the switching appear in the spectrum of the signal. The radiation characteristics of the array such as Side Lobe Level and beam orientation can be controlled at these harmonics, also known as sidebands. The capability of the array in creating multiple simultaneous radiation patterns has paved the way toward employing this technique in wireless communication applications. In this thesis we explore the basic fundamentals and the characteristics... 

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... 

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... 

High voltage DC-DC converters are widely used in a variety industries. In these converters, the function of the step-up transformer is to provide a high voltage at the output. Increasing the power density in these converters has always been the researchers' focus. One of the most efficient ways to increase power density is to increase the switching frequency. In high-voltage step-up transformers, we can decrease transformer size by increasing switching frequency, but electric field strength and insulation issues put a lower limit on transformer dimension. Various winding methods address this issue and aid in achieving higher power densities at high operating frequencies. This thesis compares...