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 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.... 

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... 

Plasma is a quasi-neutral gas consist of charged and neutral particles that manifest collective behavior. Plasma is an ionized gas in which all or a significant portion of its atoms have lost one or more electrons and become a set of positive ions and electrons. Plasma is one of the four primary states of matter. This project intends to generate plasma by a pulsed electric discharge in a gaseous environment. At first, in this project, the proper excitation circuits are collected and compared, then based on the feasibility of production, applicable methods are selected and constructed. The construction steps were such that the selected circuits were first simulated with the appropriate... 

Three-phase inverters as a UPS are very common in industry and non-linear loads such as rectifiers are growing in industry. Three phase inverter with non-linear load can lead to highly distorted output voltage which can make problem for sensitive loads such as servers etc. Parallel configuration of three-phase inverters, also have the same problem with non-linear loads. Droop control and Master/slave control methods are two major methods which investigated in this thesis. This paper proposes a method for reducing voltage THD in three phase inverters with non-linear load. The proposed method considers the load current as a disturbance and provide a control strategy to reject it using the... 

In order to adjust the electrons beam in microwave lamps, an accurate electromagnetic field that is produced by a solenoid is required. The precision of the magnetic field generated by this solenoid is very important, and in advanced systems this precision is less than 10 ppm. This system is used to adjust the radiation rate for producing a variety of radiopharmaceutical. The major problem of the system is that the electron beam changes by time due to a change in the magnetic field, and this event causes the operator's room to be radiated. Constant calibration of this system is also very demanding and impractical. An example of these highly accurate (several ppm) systems are used in the... 

In this thesis, pulsed power structures containing a step up high voltage transformer with large transformer ratio are investigated. In pulsed power applications, a step up pulse transformer is a proper choice in the cases in which a low primary voltage is available. The noticeable advantage of employing these transformers is the ability to use several modules in the primary side of the transformer. However, it should be noticed that the primary side current of the transformer is large. So to solve this problem, the number of primary windings could be increased and the primary large current can be shared between these windings. In this thesis, the sharing methods are investigated and the... 

Some microwave tubes can function as a narrowband power amplifier and their output power spectrum is an indicator of their amplification and efficiency. One of the factors affecting its power spectrum is the noise and ripple of its HVDC power supply. To reduce the negative effects of power supply, first there should be an exact measurement of ripple and noise in the output of the HVDC power supply. Destructive factors which affect voltage ripple measurement in the case of high DC voltage are follows as conductive interference, radiative interference, intrinsic noise of electrical elements, and nonideal frequency response of voltage divider. After identifying and suppressing the mentioned... 

In this thesis first of all the different approaches of control and parallel of multi-modular inverter system were investigated. These methods have been categorized and examined separately, and they were compared with each other in terms of quality and quantity. Afterwards, Active current sharing technique due to its high reliability was selected as the fundamental control approach. Among different ways for active current sharing, Avarage load sharing was chosen for its acceptable stability compared with other method. Approaching this goal, for the first time optimal control strategy and LQR method was proposed to parallel 3-phase inverters.At first, the problem was edited to be compatible... 

In creating a telecom battery charger there are three challenging factors which are high power density, high efficiency and modularity. A telecome battery charger consist of a rectifier with power factor correction capability and a DC-DC converter. The power stage of DC-DC converter with high output current and low output voltage has a vital role in the battery charger. The isolation transformer and magnetic component of LLC resonant tank are two huge and heavy parts of the DC-DC converter. With the emergence of GaN and SiC switches pushing frequency to to megahertz is possible which resulted in decreasing the volume of passive divices. But with increasing the frequency, designing of the... 

Station Blackout (SBO) involves Loss of Offsite Power (LOOP) concurrent with failure of the onsiteemergency ac power system. Although SBO is a beyond designbasis accident, in recent years this accident attracts a lot of attention. Fukushima nuclear accident which was initiated by earthquake followedby tsunami led to a SBO accident. In this thesis, Probabilistic Safety Assessment (PSA) is applied to analyze SBO in IR-360 nuclear power plant and to compute its frequency. Meanwhile, weak points of the plant are identified in order to minimize the SBOprobability of occurrence. Fault tree method is used to evaluate emergency power system and offsite power system reliabilities. Common Cause... 

The series structure of semiconductor devices has a wide application in the industry and research field. The most critical issue in the series structure of series switches is the safe operating condition provision. Hence many kinds of research have been intensively focused on this topic to overcome this necessity. However, many existing aspects relevant to the series stacking of the semiconductor switches have not been pointed out. These include, the power loss must be accepted for the series devices and recovery of this power, providing balanced voltage for the series devices through a simple and easy implementing structure and providing a safe voltage condition for the series devices under... 

Advancements in solar powered systems bring about the possibility for today’s transportation systems to be operated and driven by such a clean and renewable source of energy. The challenging point of this combination is to draw high power levels from such a low power density source of energy. As a result, employing an efficient power storage and management system becomes inventible. The subjects of this research are to design a grid connected system and evaluate its performance and feasibility in a real application (Tehran- Mehrshahr surface train – Tehran 5th Metro Line). The task includes sixteen pairs of DC transmission lines which are powered by CIGS solar module technology and four... 

Programmable AC Power Supply is a part of any Grid Simulator. Grid simulator is a system that, as a voltage source, can produce various power grid voltage waveforms in the output, and as a load, can draw different currents of ordinary loads from the power grid. The application of Grid Simulators is testing many grid connected systems, such as chargers, power supplies, PV inverters and etc. The purpose of this thesis is to design and build a 3 kW Programmable AC power supply, which can be used as a part of a grid simulator in future works. In this thesis, back to back converter topology is used for implementation of the programmable AC power supply. This back to back converter consists of an... 

DC-DC switching convertors are power electronic circuits that have various applications nowadays. Quasi-resonant convertors are a kind of these convertors that are of great interest due to their simple structure and soft switching. The goal of controlling these convertors is to achieve constant output voltage while varying the input voltage and the load by choosing a proper switching frequency. Classic controllers show drawbacks in the case of high input voltage and load tolerance, and this nonlinear behavior of the systems results in some practical challenges. In this thesis, nonlinear predictive controller for quasi-resonant Buck convertors is designed. Having designed the linear... 

In recent years, and with the development of information technology in various aspects of life, the growth of energy consumption in this sector has accelerated. With the advent of cloud computing and the development of its users, data centers have become one of the largest consumers of energy in the world. Adverse effects of fossil fuel consumption on the one hand and the global energy crisis as a limiting factor for development, on the other hand, have doubled the importance of managing the issue and reducing energy consumption in this sector. The two main energy-related concerns in data center construction are clean energy and energy management. The use of new energy and natural facilities... 

The TWT is highly sensitive to the ripple amplitude of its power supply output voltage. If the amplitude of the output voltage's ripple exceeds a certain limit, the amplitude of the undesired harmonics in the power spectrum of the TWT is greatly increased. Increasing the amplitude of undesired harmonics in the TWT output power spectrum reduces the accuracy and performance of the TWT. Therefore, for optimum TWT performance, a low-ripple power supply is essential. Typically, a low-frequency rectifier or high-frequency switching structure is used to build a high-voltage DC power supply. In this thesis, the different structures of high voltage DC power supplies are studied. Next, by focusing on... 

High voltage power supplies have a wide range of applications, and due to their high cost, it is essential to monitor their condition to predict potential failures and prevent significant losses. The most common cause of power supply failure is the wear and tear of its components. However, these components can be replaced before they wear out completely to prevent the failure of the power supply and, consequently, avoid damaging the load. Estimating the lifetime of power supplies is crucial because it allows for scheduled maintenance and helps prevent significant problems in power supplies. By estimating the lifespan of a power supply, one can anticipate when it may fail, allowing for the... 

Nowadays, non-linear loads comprise an important part of electrical grids. One of the most essential sources of nonlinear loads is switching power supplies, which mainly include power electronic rectifiers. When power outage occurs, Uninterruptible Power Supplies (UPS) must be able to supply these loads. The nonlinearity of the load has a significant effect on the Total Harmonic Distortion (THD) of the output voltage, which may not be easily reduced, especially in three-phase inverters. Furthermore, the presence of isolating transformers in these power supplies limits the control of harmonics and intensifies the nonlinear effects of the system.In this Master Thesis, a disturbance observer is... 

In this research, we have presented a method to delay the propagation of fault current in high voltage power supplies. Common protection methods usually protect the load and do not protect the power supply itself well. In this research, our goal was to propose a method to prevent the short circuit fault current from reaching the power supply elements. At first, the available methods to limit the fault current and protect the high voltage power sources were studied and investigated. Then, using the transmission line theory, a ladder filter was designed as an alternative to the normal filter at the output of the power supply. In the next step, using software simulation, the performance of the...