Sharif Digital Repository

converters, the different configurations for matrix converters are proposed. In this thesis, a one-phase to three-phase matrix converter is used to control in three-phase induction motor. Different control methods are proposed to control the induction motor. The novel control methods include close loop speed and converter output current controls of induction motor are proposed based on SPWM. The structure of indirect matrix converter for the mentioned application also investigated. Moreover, three usual method of control of induction motor: DTC (Direct Torque Control), FOC (Field Oriented Control) and Space Vector Modulation are applied to the single to three- phase matrix converter. Each of... 

In recent years, there has been an increasing concern about harmonic distortion and the effects of harmonics on power systems. Nonlinear loads such as electronic power supplies, battery chargers, motor drives, UPS systems and … are the primary source of harmonic currents. Harmonic currents generated by nonlinear loads flow from the load into the power system due to the network low path of impedance Harmonic currents cause additional heat and losses in power system components and results in voltage distortion as well.To deal with the problems associated with harmonics and to reduce their effects on power networks, study of the effects of non-linear loads on distribution networks is essential.... 

Harmonics are of the most important issues associated with electric power quality. Non-linear loads such as power electronic converters are harmonic-producing devices in a network. Due to negative impacts of harmonics such as increased losses and reduced life of network equipment, harmonic analysis of a polluted network, is an essential task. Furthermore, harmonic source identification in order to trace harmonics in a network and adequate implementation of harmonic mitigation techniques is also important. Harmonic contribution determination of a customer at a point of common coupling (PCC) is subjected to difficulties such as harmonic voltage and current interactions, unknown customer and... 

Increase of nonlinear loads has led rise of harmonic currents, voltage distortion and imbalance in power system. Those polluted nonsinusuidal environments have made electrical engineer and researchers to define new and more compelet definition of electrical power quantities such as power factor, apparent power, THD and … . The new definitions have resulted in new methods of power quality enhancement technique. IEEE-1459 Std. proposes definitions for electric power in sinusoidal, nonsinusoidal, balanced and unbalanced conditions which can be used for compensation of nonsinusoidal and unbalanced systems. This reaserch introduces a new method to obtain shunt active filter reference signal. This... 

Nowdays, distributed generation (DG) systems based on renewable energy sources have significantly increased around the world as an alternative solution to enhance the power quality and reliability and reduce the need for extensive transmission system as well. An evolved recent concept called microgrid is developed by grouping a cluster of loads and DG units in a common local area which increases the integaration of sustainable energy generation systems. This thesis presents control of a medium voltage (MV) microgrid considering multi-hybrid distributed generation systems (MHGS) and renewable energy resources in island mode. The first part is focused on the development a control strategy for... 

Modeling and control of power electronic converters, due to their non-linear nature, are from important research subjects in power electronics. Power electronic systems contain both continuous-time dynamics and discrete-time inputs, and therefore, are categorized as hybrid systems. Conventionally, modeling and control of hybrid systems is done by linearizing and state-space averaging. However, these methods do not guaranty well operation of the system over a wide range of load or input variation. In this project, by employingMLD modeling method, a model for an inverter which is connected to a three-phase RL load through an LC filter, is derived. Then, this model is used in an optimization... 

This dissertation studies the operation of the power sharing system in a micro-grid (MG) which includes a synchronous generator and the converter based distributed generation (DG) units. Increasing advent of MGs and the huge penetration of DGs to the existing power systems require comprehensive studies on the interactions between synchronous generators and converter based DGs for the sharing of power during and after the occurrence of different disturbances such as load changing. Thus, this project discusses existing control methods which can be used to share the power between a synchronous generator and converter based DGs. Then, a new control strategy is proposed in order to enhance the... 

The extensive use of nonlinear loads such as motor drives and new generation of home appliances has caused a deterioration of power quality in power systems. The use of active power filters due to the fast variation of the loads has been recommended by power engineering. In this method, the harmonic profiles are controlled by applying active filters in a distribution feeder. Optimal placement of active filters in a distribution system due to the increase of harmonic generation loads has attracted researchers. However placement of each filter is the major concern that researchers face. In this paper, a new objective function is introduced to determine the optimal number and location of active... 

The need for independent power generation has been increased in recent years with the growing demand in micro grid systems. Losses in power systems are unavoidable. These losses occur in transmission to distributionnetworks from the generation sites to the end-user loads. Reduction of power losses has been one of the reasons for engineers to be attracted by micro grid systems which include small size independent power generation units. However, in a micro grid with several DGs of different types and with all kinds of loads of variable nature, an optimal power balance in the system has to be achieved. This optimal objective, which results in minimal energy losses over a specific period of... 

A microgrid is a collection of loads, sources, and power storage units that operates as a single controllable system and can operate in grid-connected or islanded mode. From the generating side, renewable energy resources such as photovoltaic system, fuel cell and power storage units are inherently DC. From the load side, electronic loads such as computers, data centers and most of the variable speed motor drives require a DC supply. Therefore, DC Microgrids have gained widespread attention in recent years. On the other hand, since existing distribution systems are mostly AC, a hybrid microgrid is more likely. The hybrid microgrid is composed of two AC and DC subgrids interlinked by power... 

Iran's electrical grid is connected to the Eastern Turkey grid via Khoy-Basqale 400KV transmission line. Harmonic mesurements indicate high level of the 5th harmonic voltage in Azarbayjan grid which is magnified in Van substation. According to Iran international obligations and economic losses caused by the high level of harmonics in Azerbaijan regional electricity grid, a comprehensive study is required. Early studies showed that this unprecedented increase in the 5th harmonic voltage is due to the small harmonic loads scattered throughout the network. The aim of this thesis is to perform a comprehensive harmonic analysis of Azerbaijan network due to scattered harmonic loads. In this... 

The demand for independent power generation has been increased in recent years due to the growing demand in distributed networks, losses and power qaulity in power systems. These losses occur in transmission to distribution networks from the generation sites to the end-user loads which have harmonic losses besides fundamental losses.. The non-linear load makes the harmonics flow in the line and create the harmonic losses. However, in a distributed network with several DGs of different types and with all kinds of variable nature loads, an optimal power balance in the system has to be achieved. This optimal objective, which results in minimal energy losses over a specific period of time,... 

Power Quality can be simply defined as the quality of voltage at electrical loads. Detection and classification of voltage and current disturbances is of high importance in power system protection and monitoring. This procedure cannot be implemented by operators because of the high volume of the data which must be processed. So, it is needed to automate this procedure. Systems designed for this purpose usually contain three main parts: feature generation, feature selection and classifier design. The algorithms used for feature generation for power quality disturbances are mainly based on discrete Fourier transformation or discrete wavelet transformation. These approaches have shown some... 

Ilam refinery has three synchronous generator units each with a capacity of 26.5 MVA and two six-phase LCI-fed synchronous compressors, each with a capacity of 8 MW. Generators of Ilam gas refinery have instability issue in case of island operation. With launching one generator unit and then connecting two compressors the instability problem and tripping of the generators appear. Given the importance of this issue, various tests and corresponding measurements in both electrical and mechanical aspects were carried out at the plant in on-grid and island operations to analyze the cause of instability phenomena. The mechanical part of tests analyses the frequency of oscillations and vibration in... 

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... 

The growing usage of nonlinear loads has resulted in increasing voltage and current harmonic levels in distribution systems. Additionally the faults occurring in the distribution system cause voltage sag at the point of customer supply. These two power quality disturbances impose considerable costs on consumers through disrupting the correct performance of sensitive loads, causing unintended outages and decreasing the devices’ useful lifetime. Besides the aforementioned power quality issues, the electric power loss has a determining role in operational costs. In this thesis, based on feeder reconfiguration and shunt passive filters, a strategy is proposed in order to reduce the average... 

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... 

Electric motors used in electrical vehicles are varied, but in light electric vehicles such as electric motors and electric bikes, with limited space, permanent magnet motors due to their high power density and efficiency are very useful. These motors are divided into two types: trapezoidal and sinusoidal due to the waveform of the Back EMF voltage. The trapezoidal type, also known as the brushless DC motor , is more commonly used in light electric vehicles due to the simplicity of the control system and the lower cost. The control system of the BLDC motor is very important in its performance. Providing a controller for these engines that at low cost improves their performance is considered... 

In this thesis, a model is presented to detect and monitor the rotor bar's condition of large motors. This proposed model uses two diagnostic methods MCSA and ZCT, to extract the fault components. The input of the proposed model is only the motor current at two levels of 80% and 100% of the nominal motor load, which by using the two methods MCSA and ZCT and making changes in how to use them can be the disadvantages of other methods such as incorrect detection of rotor bars in Large motors with variable load, the harmonical stator voltage (or the presence of the drives) and asymmetric conditions. The extracted components are classified using two learnable algorithms, the k-NN algorithm and... 

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...