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... 

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... 

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... 

Power system restoration is the procedure of restoring generators, transmission lines and loads in a minimum time without damaging power system elements. There are different strategies to restore a power system after a blackout. The one that we will introduce here is the build-upward or parallel restoration strategy. In this method power system will be divided into some independent islands firstly and then the restoration process will begin in each island separately and at the same time. The islands then will be connected together to have a complete restored network. The significant advantage of this strategy is minimizing duration of restoration. On the other hand, the use of Wide Area... 

The introduction of Wide Area Measurement Systems (WAMS) made it possible to monitor the stability online. This thesis presents a method for the optimal restoration planning based on Wide Area Measurement System (WAMS). In fact, the practical use of WAMS at the early stages of restoration provides precise determination of generators loading steps. Moreover, unification of phase angle references at different islands and presentation of tie line energizing priority list are significant benefits of WAMS at the last stages of restoration. The presented method uses observability analysis and Power Transfer Distribution Factor (PTDF) concept. The PTDF concept is applied to decrease the... 

In this thesis, the problem of placing a minimum number of phasor measurement units (PMUs) in a transmission system is considered so that faults on all lines of the network can be diagnosed and located irrespective of their locations. For this purpose, a PMU placement algorithm is proposed to calculate the required data for impedance-based fault-location of any fault line in the network, achieving the full potential of the circuit laws throughout the system. Another algorithm is then proposed to compute the voltage and current values of the fault line for fault-location purposes. Moreover, as many networks are already equipped with PMUs, the proposed algorithm makes it possible to locate... 

The traditional backup protection system of transmission lines are self-contained and only use from local measurements and generally, don’t use from wide area measurements. Hence, it can misoperate when the power system is extremely under stress conditions. So, the zone 3 of distance relays have been recognized as one of important participating causes of cascading phenomena that lead to major power system blackouts. In modern societies, power systems have become one of most important critical infrastructures, accordingly, blackouts can have catastrophic effects. Therefore, the novel backup protection schemes are required to improve security and dependability of protection system.
In... 

Transient stability as one of the power-angle stability parts is a phenomena which is threatening the security of power systems. Following the occurrence of a major disturbance such as a short circuit, each of the generators will be in risk of transient instability due to distance from the fault location. If a generator fails to maintain its stability with the network, it become out-of-step. Out-of-step caused rounding waste of generator rotor and zero average output power. Out-of-step on the one hand lead to severe mechanical and thermal damage to the generator and the other hand disrupt load providing in the power system. So, the instability of the generator must be detected in the... 

A power transmission system includes transmission lines that are interconnected for economic and security reasons. Power systems are often prone to faults at the transmission level, since transmission lines are spread over vast geographical areas. Being the most serious events in power systems, blackouts are often initiated by a fault and a sequence of events afterward leads to partial or complete power outage. In this condition, fault diagnosis is the first step for power system restoration. In this research work, a new approach utilizing impedance-based fault location is introduced for fault diagnosis. By developing wide-area measurements in the context of smart grids, accurate... 

As far as reliable supply and cost-effective methods of power delivery to end-users are concerned, new advancements in smart grids and, in particular, smart pricing are of high significance to grid operators. In the recent decade, there has been a considerable raise in penetration of renewable energy resources and also the number of hybrid electric vehicles which can act as a huge mobile storage in the network. Hence, finding a practical and cost-effective method of management of all these new resources and avoiding potential problems associated with them seems to be of high importance. In this study, first, the response of demand to pricing signals has been modeledAfterwards, the response... 

Nowadays, high reliability requirements for commercial and industrial loads, make it necessary to install microgrids for supplying the loads during power outages. Due to the fact that solar energy is clean, free of noise pullotion and also it benefits from the governmental obligations, it is a wealthy choice for supplying the load in microgrid. Designing and operation of the photovoltaic microgrid are the two important steps that should be considered. In this thesis, these two steps have been investigated by integrating a battery system into a solar PV plant and control of PV mictrorid in islanded mode. In the designing step, the optimum battery bank is calculated. For calculating the... 

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... 

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... 

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... 

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... 

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... 

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... 

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... 

In this research, the problem of bidding in the frequency regulation market, which is a subset of the ancillary services market , and equilibrium between multiple price maker participants has been studied.The Frequency Regulation Market system is considered to have a performance-based payment method, in which, in addition to the cost of the capacity provided by the energy producer, the cost of accuracy in following the signal generated by the network operator is paid.The details of the components of the frequency regulation market such as the AGC signal allocation mechanism and the dynamic model of energy production units have been investigated in this study.The effects of network and market...