Sharif Digital Repository

In this study, control and protection of low voltage microgrids have been analyzed. Studied microgrid takes the advantages of inverter based distributed generation. One of the most important issues in inverter based microgrids is the control of its distributed generation. Since, the low voltage networks have single phase loads and many imbalances, these imbalances can affect the control of IBDGs (inverter based distributed generations). This issue in the islanded mode of operation is the most important, because in this mode of operation, IBDGs control the network voltage and frequency.
In this thesis, the different control strategies of IBDGs are reviewed, and then modified to address... 

In recent years, climate change due to greenhouse gases caused an increase in frequency and intensity of the natural disasters such as hurricanes, blizzards and floods. Moreover, it is anticipated that such events will increase in the future. As a result, power system decision makers are looking for methods to improve power system resiliency against such natural disasters with low occurrence probability and high impact. In this report, the distribution system resiliency has improved via placing remote control sectionalizing switches and micro grids formation during natural disasters. In this regard, the concept of resiliency and its characteristics along with the effect of remote control... 

According to uncertainty of retailer's customers electricity load and energy price in day-ahead and real-time markets, different scenarios are faced to an electricity retailer. As a result, due to possibility of different scenarios accurance, profit and financial loss of retailer has uncertainty and significant financial risk is imposed to retailer. Electricity retailers for earning the expected profit, reduction ofpossibility of scenarios with little profit (or much loss) and reduction of their risks, use different sources. bilateral contracts, like forward and call option,local wind turbines, distributed generaion, demand response, like load shift and curtailment can be named. This... 

This thesis presents a stochastic framework to properly involve the uncertainties associated with demand in distribution system restoration (DSR) problem. The restoration process returns the system back to normal operation after any combination of system components have been lost due to an outage. During restoration, the system operator executes a set of actions that progressively mitigate the outage. These actions aim at minimizing the impact of the outage on the final user without compromising the security and operability of the system. In this framework, dynamic programming (DP) is used to solve DSR problem for a distribution system that accommodates various technologies of DG units and... 

Design and parametric study of a coupled thermoacoustic refrigerator system has been carried out based on thermoacoustic theories. The purpose of coupled thermoacoustic refrigerator design is to cool a container with small dimensions for use in cold storage above zero. The application of this refrigerator is where the waste heat of piston engines of distributed generation (DG) plants can be used as energy input. The design is based on the simplicity and low cost of the refrigerator. Therefore, the engine and refrigerator part of the coupled thermoacoustic refrigerator is enclosed in a resonator with a fixed diameter, which is closed on both sides of the resonator. Two standing-wave... 

In this dissertation, the value of distribution network reconfiguration in presence of distributed generation is investigated. In the first step, a mathematical optimization model is devised to minimize daily network losses via applying hourly reconfigurations. The results show that the hourly reconfiguration reduces the losses. Then, sensitivity analyses on the renewable penetration, wind and load correlation, switching cost and wind power prediction are conducted and discussed. The switching cost analysis revealed that a great amount of loss reduction could be attained with a small number of switching operations. The worthiness of reconfiguration becomes more in systems with high... 

Electricity is one of the most important kinds of energy and also one of essential needs of humans for maintaining their life. Due to growth of costumer’s load and In order for delivering high reliable power to the consumers, the structure of the power grid must be expanded and/or demand side management policies like demand response programs must be taken into consideration. One of the most important and less-focused aspects of power grid expansion planning is, distribution system expansion planning. Distribution system expansion planning (DSEP) is an important task of electric distribution companies and operators in order to appropriately supply their customers load with the minimum cost... 

Due to the increasing influence of distribution generation , their effect in planning can't be ignord , especially solar panels ,which are incresing rapidly. The main purpose of this thesis is to an active distribution network that annually load bus and the amount of photovoltaic production in it increases and plan dynamically. In the planning that is done , uncertanty in the amount comsumption load and uncertanty in the pattern of sunlight and also annual innterest rates in the classical system we have planned by optimizing the network expansion costs , in addition to supplying the load bus, we can keep the voltage drop bus and line filling within the allowable . To do this , we considered... 

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... 

Reward-penalty schemes are known as the most effective tools to regulate the service quality. This thesis tries to design a comprehensive reward-penalty scheme to properly motivate electricity distribution companies (DisCos) to improve the reliability and reduce the energy losses in their networks using Distributed Generation (DG) Resources. So, as the first step, the designing methods of reward-penalty scheme (RPS) and their advantage and disadvantages are introduced, and also a method based on concept of the Yaredestic theory is proposed. The proposed method uses the Fuzzy clustering and is able to set the parameters of RPS in a fair and efficient way. The proposed RPS is implemented on... 

Electricity distribution systems are dynamically expanded in anticipation of new demands. Cost and reliability are the most important factors in finding the optimal plans for network expansion. Recently, implementation of incentive reliability regulations has accentuated the role of reliability considerations in distribution systems studies. This is because such incentive schemes create a direct link between distribution companies' revenues and their service reliability. Thus, these schemes have changed the role of reliability from a technical constraint to an economic factor. In this occasion, distribution companies require new techniques to incorporate the effects of incentive reliability... 

In the near future, it is expected that the microgrids become widespreed due to issues such as reliability, increased penetration of renewable energy sources and distributed generation, environmental concerns and shortage of fossil fuels. Different control methods have been suggested to regulate the frequency and voltage of the system so that these quantities remain in their permissible range upon islanding and in the islanded operation mode. However, in emergency conditions, such as shortage of generated power compared to the load of microgrid, frequency or voltage reduction occures due to imbalance. In this situation, it is invitable to shed extra load to maintain the stability and... 

Environmental problems and limitation in fossil fuels have increased the application of renewable energy sources (RES) and distributed generations (DG). Due to the DC nature of most loads and DGs, DC microgrids provide a suitable structure to integrate different kinds of DGs and loads. Undesirable voltage regulation and poor power sharing among the sources in conventional voltage-based control methods are solved by the superimposed droop frequency method. However, the superimposed droop frequency scheme suffers from three major problems which are (i) instability in terms of load variation, (ii) limitation in the system maximum loading which is due to the limitation in the transferred... 

Nowadays, concerns about the reduction of fossil fuels and environmental issues, have made renewable resources more important. Among these resources, photovoltaic (PV) systems are more popular than others, due to their environmental compatibility and unlimited availability of sunlight. Increasing the penetration level of PV systems in electricity networks presents various technical and control challenges such as voltage and frequency variations; and protection and harmonics issues. In this thesis, voltage rise problem due to reverse power flow in distribution feeders is discussed. This is one of the main obstacles to the expansion of these resources in distribution networks.Various solutions... 

In recent years, due to restructuring in the electric power industry, distributed generation has become one of the most important subjects and DGs and renewable energy sources have been increasingly expected as a supplement and an alternative to a conventional large scale central power system. their success depends not only on the distribution of the available renewable energy sources in a region but also on the power grids connectable capacity in the area. Photovoltaic system is one of the best RESs for residential electricity supply because it is noiseless and solar power is widely available and households can use it via photovoltaic cells in their homes. There are two major problems... 

Todays, thanks to the positive effects of electric vehicles, (against the vehicles which use patrol as their fuel), reduction of the Earth temperature and its climate change; the manufacturing, sale and use of electric vehicles experience a sharp increase. In addition to decreasing the air pollution, due to their abundant smart implications, they have been dramatically propagated. Massive use of these devices has raised the concern about the loss of the security which is indispensable part of the infrastructure. None of the past publications and works have taken the cyber-attack on the charging price rate and other data into account. In this thesis, charging methods of electric vehicles are... 

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... 

The design and operation of energy systems infrastructure is typically based on key reliability criteria such as system security and adequacy. Nowaday, with the rise of unexpected events and events such as floods, earthquakes, storms, and other natural phenomena can affect the performance of energy infrastructure. Given the low probability of these events, reliability studies and relevant criteria cannot guarantee that an energy infrastructure can respond well to these events. Investigating the ability of energy infrastructures to deal with these phenomena is divided into resilience studies. To overcome these challenges, this thesis has attempted to detail some of these natural events.... 

The centralized and decentralized control approaches are the most effective control approaches to be applied in micro grids. However, practically to rerduce the cost and improve the reliability, decentralized control is usually employed. Initially, this thesis discusses the components and dynamic model of the micro grid in order to evaluate the stability. Then, it introduces the decentralized control methods which can be used in a micro grid. In the next step, a sample micro gird is studied (with high ratio of lines R/X). This microgrid has three DG plants having DC voltage sources, inverter, and LCL filter. The performance of AVR controls is evaluated by combining the PQ and droop control... 

Nowadays, classic energy supply systems are rapidly shifting towards more efficient, with less pollution, and more economic energy systems. In the meantime, the growing dependence of human activities on energy sources and the reduction of fossil fuels resources as the main source of energy supply at present time, has led to fundamental changes in the energy policy of communities. The use of distributed power generation systems utilizing renewable energy sources is one of the solutions that have been proposed in this regard. This research aims to develop a local energy supply network for a specific rural district using energy sources in place, so that the area is energy self-sufficient and...