Sharif Digital Repository

In this research, a new step-by-step and comprehensive method for the design of back-to-back converters in the presence of nonlinear and constant power loads is proposed. Common methods for the design and control of back-to-back converters consider the design procedure independent of the linearity and dynamic of the load, also, the control system design and performance of the load-side and grid-side inverters of back-to-back converters are assumed to be independent of each other which is shown in this thesis that this assumption is not valid in the presence of nonlinear loads. These methods result in challenges and problems regarding stability and power quality indices of back-to-back... 

The matrix converter is an array of controlled bidirectional semi-conductor switches that allows direct ac–ac conversion without an intermediate dc link. This converter has several attractive features that have been investigated in the last two decades. Multilevel converter technology has become increasingly popular in recent years due to high power quality,high-voltage capability, low switching losses and low EMI issues.This paper is concerned with applying multilevel techniques to direct ac–ac power converters and concentrates on developing the concepts of space vector modulation for a multilevel matrix converter. The common-mode voltage produced by a modern power converter has been... 

Regarding increasing rate of electrical energy demand, paucity of fossil fuels and the pollution stemmed from burning them, using renewable energy is inevitable. For transmitting the generated electrical energy to grid, power electronics converters are used. Inverters and back-to-back converters are some of these converters. Inverters and back-to-back converters are used in connecting photovoltaic power plants and wind systems to grid respectively. Because of technological limitation, converters are paralleled with others at high power transmitting. Paralleling converters has other merits such as increasing system reliability through redundancy and repairing defective converter without... 

Generally, virtual loads is used to test all AC power and energy meters and are usually passive. To prevent possible damage of this heat and to control the temperature, cooling blowers are used which increases the volume and weight. So, recycling the power delivered from the grid causes a small amount of power to be converted to heat in proportion to the load efficiency. The purpose of this study is design, predictive controller model for programmable electronic regenerative AC load. The structure used is a back-to-back converter consisting of an AC-DC converter and a DC-AC converter, which according to existence of capacitance between these two structures, two converters can be controlled... 

Condition monitoring of a system refers to the process of measuring and analyzing the aging indicators of critical components of a system that can be harnessed to estimate the system’s health. One of the main interests in condition monitoring is to performing the scheduled maintenance activities for the system. Monitoring the status of the system reduces maintenance costs and prevents unwanted contingencies and outages in the system.
In power electronics, the capacitors are the most critical components of the system from the point of reliability. Capacitors are the leading cause of failure in the power electronic converters so, this essay attempts to attain a solution to monitor the... 

In this research a special Three-Phase to Single-Phase converter has been proposed to connect a three-phase Permanent Magnet Synchronous Generator (PMSG) of a wind turbine to a single-phase network. Common back-to-back converter used for this application employs a bulk capacitor in its DC link to generate the pulsating component of the single-phase side instantaneous power. This capacitor is costly and reduces system overall reliability. This problem is alleviated in this work by providing the single-phase load pulsating power using the PMSG large inductances. The proposed system leaves the PMSG torque ripple-free while providing the single-phase load power. With the help of this method,... 

Permanent-magnet synchronous generators have attracted more attention in recent years due to their special advantages which make them a suitable option for variable-speed wind turbines.Low-voltage ride through capability is one of the main concerns in widespread use of wind turbines in electric grids. Nowadays wind turbines are expected to remain connected to the grid during voltage dips and support the voltage recovery process by supplying reactive power.This thesis aims at behavior analysis and performance improvement of permanent-magnet synchronous generator-based wind turbines during grid faults. A simple method is presented to overcome the over current problem of the grid-side converter... 

A microgrid system consists of some distributed generators (DGs) and local loads which can operate in both grid-connected and islanded modes of operation. An islanded mode of operation is required when the grid voltage deteriorates and its power quality drops. This islanding operation can be attained by opening grid-side switches or by using back-to-back (b-to-b) converters. Due to the increase of highly sensitive loads and to have better power control and higher power quality, the use of back-to-back converters has recently attracted interests among researchers. However, the major drawback of this solution is the cost of a b-to-b converter. Therefore the aim of this project is to gain some... 

Three-phase electronic loads are used to test the performance of various electrical devices such as power supplies, generators, and transformers. Conventional electronic loads are composed of passive components that consume the energy, so have low power density and efficiency and to manage the produced heat, massive cooling systems are required. Nowadays, to increase efficiency and power density, three-phase regenerative electronic AC loads have been developed. To return energy to the grid and control the input power factor, the structure of these loads is based on back-to-back converters. In this project, a 35 kVA three-phase regenerative electronic AC load is designed. To control the power... 

This thesis aims at developing control system of a full converter wind turbine with modular and parallel back-to-back converters. Modular structures and paralleling of power electronic converters are the state-of-the-art methods for increasing their transferable power to the grid. Technological advances in high power wind turbines, especially for the offshore installations, which contain permanent magnet synchronous generators with back-to-back full converters, promote the use of modular structures.
In addition to developing the regular control systems of wind turbines for modular structures, selection of appropriate structures, power sharing between parallel converters and mitigation of...