Sharif Digital Repository

Islanding detection methods are divided into three main groups as remote, active and passive. Although passive schemes have larger Non Detection Zones (NDZ) relative to other schemes, they are more used in utilities due to their low costs and less PQ problems than in other schemes. Passive Schemes are based on the measurements of passive system parameters. These parameters are measured at the point of common coupling (PCC). A new approach in passive techniques is the use of data-mining to classify the system parameters which affect the islanding detection. Therefore, by finding an efficient and robust data-mining algorithm, the inherent problem of passive schemes, which is their relatively... 

The wide-area damping controller (WADC) has been proposed to enhance the damping of inter-area oscillations. The most challenging deficiencies to make this controller practical are the power system operating condition changes and the inherent time delay of remote signals. They can deteriorate the controller performance and the whole system stability if not properly accounted for in the design procedure. This thesis presents an adaptive delay compensator (ADC) on the basis of the latest development in the wide-area measurement system (WAMS) to cater to varying latencies. The proposed compensator can effectively reciprocate the phase deviation resulting from varying delays to improve the... 

Power system frequency regulation entitled load frequency control (LFC) has been one of the important control problems in electric power system design and operation. Off-normal frequency can directly impact on power system operation and system reliability. A large frequency deviation can damage equipment, degrade load performance, cause the transmission lines to be overloaded and can interfere with system protection schemes, ultimately leading to an unstable condition for the power system . On the other hand, the increasing need for electrical energy in the 21st century, as well as limited fossil fuel reserves and the increasing concerns with environmental issues for the reduction of carbon... 

Synthetic inertial frequency response has attracted increasing attention due to the paradigm shift in power generation from synchronous generators toward wind turbines. Due to application of back-to-back converters in the structure of variable speed wind turbines (VSWTs), their shaft speeds become decoupled from the system frequency and thus, they cannot provide intrinsic inertial response. However, this type of response can be emulated via an extra auxiliary frequency controller or by modifying the conventional control system of the VSWTs. To achieve this goal, a frequency model of VSWT is developed in this dissertation. The power system's load-generation mismatch model is integrated into... 

Flying has fascinated mankind for ages. Nowadays, planar actuators are performing the same task as that, once a dream, of a flying magic carpet found in Persian mythology. Magnetically levitated planar actuators (MLPAs) consist of two parts; a moving part, and a stationary part. In most applications the moving part which is an array of permanent magnets (PMs) produces a magnetic flux density in the air-gap, and the stationary part, an array of current carrying coils, produces force and torque when it is exposed to the magnetic flux of the PM array. These actuators have been utilized in industry in applications where precise positioning is important. In recent years however, they have found... 

One of the most important problems in using wind energy is the estimation of wind energy potential of a region with acceptable accuracy. To use wind energy and convert it to electrical energy it is necessary to study the economical aspects of wind farm installation, and to choose an appropriate wind turbine to be installed in a region. To do such a study and to choose approperiate wind turbine, annual energy output of different wind turbines should be estimated in that region. The porpuse of this thesis is to develop new methods to estimate annual energy production of a wind turbine by using some of the parameters of wind speed pattern of a region such as wind speed average, wind speed... 

The problem of restoring power systems after a complete or partial blackout is as old as the power industry itself. In recent years, due to economic competition and deregulation, power systems are operated closer and closer to their limits. At the same time, power systems have increased in size and complexity. Both factors increase the risk of major power outages. After a blackout, power needs to be restored as quickly and reliably as possible, and consequently, detailed restoration plants are necessary. This thesis concentrates on the initial stages of restoration where load pickup and frequency control problem is identified. The best sequence of load pickup for power plants during power... 

Load frequency control (LFC) is one of the important control problems in interconnected power system design and operation, and is becoming more significant today because of the increasing size, changing structure, emerging new uncertainties, environmental constraints and the omplexity of power systems. Therefore, load frequency function requires increased performance and flexibility to ensure that it is capable of maintaining a generation-load balance, following serious disturbances.Real power systems are often large-scale systems which are composed of many interacting subsystems. Therefore, it is difficult to control such systems due to the required inherent computational complexities and... 

Increasing energy demand and at the same time, considering exhaustible fossil fuel resources has led to increase distributed generation for reducing energy loss and increasing efficiency of energy systems specially due to technical development on generation systems that meet environmental and energy policy concerns. One of the most important distributed energy technologies is Combined Heat and Power (CHP). CHP is small, high efficiency, low installation time and self-contained electric generation plant that can provide power for household applications, commercial or industrial facilities and hence its applications are overtly increasing. It can reduce power loss and enhance service... 

Nowadays the growing demand for energy, and, on the other hand, the limited resources of fossil consuming energy in the world have caused the energy operation and consumption management to be taken into consideration much more than the past. Based on this background, improving the efficiency of feed conversion technologies in supplying the energy demanded by the consumers is the foremost and the most crucial solution to preventing energy loss. Another approach to reducing the losses through energy generation and transmission is the use of distributed energy generation systems in small scale. The advantages of applying this type of technology are the possibility of installing near the load... 

Nowadays, demands increment is one of the greatest concerns of energy systems operators. Consequently, enhancing the efficiency of consumption is an inevitable goal, which leads us to a concept named as energy hub (EH). In a simple definition, an EH is a multi-generation system where different energy carriers are converted and stored by various devices such as combined cooling, heating and power (CCHP), battery, and boiler to meet the load demands. In addition, with advent of smart grids (SG), demand side management (DSM) becomes one of the effective techniques with significant role in optimizing energy systems performance. DSM commonly refers to methods implemented by utility companies to... 

Low-frequency oscillation damping in power system is main determinants of the stability of the system. According to increasing of wind farms with high penetration levels in the power system, participation and control of wind farms for increase damping inter area oscillations seems important. In this study a damping controller suggested for Doubly Fed Induction Generator (DFIG). Using this controller and only available local signal as input controller and combination of both active and reactive power modulation, can greatly increase damping inter area oscillations and stability of uncertainty and different working points. Using linear analysis system, identified modes oscillating system and... 

One of the important tasks of operation manager is keeping system in safe and reliable situation. There are many tools that supply safety in the power system. One of them is operation reserve. Operation reserve is any type of capacity being used to support active power balance. In this thesis, an approach for optimal determining reserve capacity with considering dynamic constraint is presented. This thesis describes a method for setting the optimum value of reserve capacity based on the cost of its provision, the benefit derived from its availability and Frequency stability. The method that used is D-SCRM algorithm. However, as the size of power systems increases, the current centralized... 

Wind energy, as a type of renewable energy resource, is clean and is rapidly growing globally. The intermittency in the production of wind energy is the most major obstacle for these producers in a competitive electricity market, to compete with thermal units. Most existing models in the literature mitigate the risk of wind power, by coordinating them with energy storages such as pumped storages power plant. Here, in this thesis, another risk mitigation approach is introduced which combines wind energy and natural gas power plant in an electricity market. In addition, as the penetration level of wind power grows, the wind power producers must be considered as a price-maker player which their... 

The development of technologies such as micro turbines and gas furnaces has been the major driving force towards integration of electricity and natural gas networks in the energy hubs (EH). Besides, the existing power grids are getting smarter by implementing the new generation of information technologies and communication systems. In smart grid, the electricity suppliers can modify the customers’ electrical load consumption by employing appropriate scheduling schemes such as DR (demand response) programs. In this thesis, I consider the S. E. Hubs (smartenergy hubs) framework, in which the customers can use EMS (energy management system) to access to the electricity and natural gas prices... 

As long as the wind power penetration is low, overall dynamic behavior of a power system is determined by the interactions of system synchronous generators, but introduction of large amounts of new wind generation can affect the power system behavior. In this research, the impact of large wind farms on the small signal stability of power systems is studied. Because constant wind turbines are not very conventional in today’s wind industry and the dynamics of full converter wind turbines are isolated from power system, in this study only the doubly fed wind turbines are considered. In this order, a novel index is introduced to analyze the impact of doubly fed wind farms on the damping of... 

Controlled islanding, also known as system splitting, can effectively prevent blackouts of power system by separating it into two or more islands. To make each island reach steady state point by available measures, each island must be observable. This paper proposes a new modified three phase method to find proper splitting strategy, considering observability as a new constraint, to minimize effect of system splitting on network observability. Some techniques about strategy searching are introduced to increase its speediness and related algorithms are described in detail in this thesis. The simulation results presented show efficiency of method in finding proper splitting strategies. In the... 

Because of deregulation and economic issues, power systems operate closer to their stability limits than before. So, security assessment of power system has gained a lot of attention in power system studies. Transient stability and its real time assessment is a great concern in power system security. Among all different methods for transient stability assessment, Automatic Learning methods are used the most in real time assessment problems. These methods can provide fast assessment of transient stability, sensitivity analysis and means of control of the transient stability phenomena. In this paper Adaboost algorithm is used as a brand new method in transient stability assessment of a medium... 

global warming and air pollution due to the excessive consumption of fossil fuels have led to the proliferation of renewable energy sources (RESs). RESs are connected to the grid through power electronic converters and therefore, provide insignificant inertia and damping property for the system. As a result, the system overall inertia and damping is decreased and therefore, the system stability is jeopardized. This thesis presents a comprehensive small signal model for a virtual synchronous generator (VSG) integrated into a microgrid. In the developed state space, active and reactive power control loops of the VSG as well as resistances and reactances of the lines are considered. Based on... 

In this thesis, optimal offering strategy problem of a virtual power plant (VPP) as a price-maker player in day-ahead frequency constrained electricity market is presented. The optimal offering strategy problem is modeled as a bi-level optimization problem. In the upper level, the total profit of VPP is maximized. In the lower level, the clearing conditions of frequency constrained electricity market is modeled. The proposed bi-level optimization problem is reformulated as a mathematical programming with equilibrium constraints (MPEC) problem by using Karush-Kuhn-Tucker (KKT) conditions. Then, the proposed MPEC problem, which is nonlinear and hard to solve by commercial solvers, is...