Sharif Digital Repository

Contingency screening and ranking is one of the most important issues for security assessment in the field of power system operation. The objective of contingency screening and ranking is to quickly and accurately select a short list of critical contingencies from a large list of potential contingencies and rank them according to their severity. Then suitable preventive control actions can be implemented considering contingencies that are likely to affect the power system performance. In this paper a novel approach is presented for contingency ranking based on static security assessment (SSA). This method uses weighted performance index with the application of Analytical Hierarchy Process... 

In this paper, an analytical approach for the reliability modeling of large wind farms is presented. A systematic method based on frequency and duration approach is utilized to model a wind farm like a multistate conventional unit, where the probability, frequency of occurrence, and departure rate of each state can be obtained using the regional wind regime of wind farm and wind turbine characteristics. The proposed method is capable of finding both annual frequency and average time of load curtailment analytically in the presence of wind power. A wind farm in the northern region of Iran with the wind speed registration of one year is studied in this paper. To accommodate time-varying... 

In recent years, while energy consumption is still increasing, system peak load is decreasing due to deregulation in power systems, application of demand response programmes, microgrids and smart grids implementation, and so on. Thus, transmission system operators (TSOs), which are usually a public entity, must reinforce the transmission systems to maintain power system reliability. They are not interested in investing transmission network because of high investment costs. In this regard, this study presents a new bi-level model for co-planning of transmission system and merchant distributed energy resources (DERs). The upper level takes the TSOs perspective and aims to minimise the line... 

A new approach is presented in this paper to determine the degree of system well-being in the form of healthy, marginal and at risk state indices using the fuzzy logic concepts. Conventional well-being method uses a crisp deterministic criterion to divide power system comfort zone into the healthy and marginal states. In this regard, the main drawback is associated with categorising the system performance in the comfort zone into the healthy and marginal states. To overcome this problem, a new approach is developed that categorises the states as healthy or marginal using fuzzy logic. The technique together with the effects on the system risk and the system health and margin probabilities of... 

Operation of transmission lines are usually limited by stability limits rather than thermal capacity limits. Thermal limit of transmission lines is a physical limitation of their components and not related with the overall power system characteristics, but stability limits are strictly related with power system characteristics. This paper presents an approach for increasing stability limits using PSS. © 2008 IEEE  

Abstract- Benefits of PSS application for electromechanical oscillations damping is clarified. A major difficulty of PSS application is its tuning such that its damping characteristics do not fall into overcompensation facing continuously changing power systems. This paper presents an approach for wide area monitoring and control based PSS tuning. The presented approach originated from adaptive tuning based on real time power system state estimation. © 2008 IEEE  

One of the major problems in liberalized power markets is loss allocation. In this paper, a new method for allocating transmission losses to pool market participants is proposed. The proposed method is fundamentally based on Bialek's "Tracing the flow of electricity" method. The losses is allocated to market participants using the loss weight factors (LWFs) which are obtained from the square current magnitude and Z-bus matrix. The LWF method is based on a solved load flow and strongly emphasizes on current magnitude while considers network topology. The method has been implemented and tested on several networks and one sample summarized in the paper. The results show that the method has an... 

This paper presents a stochastic model for optimal generating units' restoration planning. Restoration plans will be performed based on different objectives i.e. total system risk, total served energy in the period of restoration, and total restoration time. The proposed model is a multi objective stochastic program in which generating units' restoration plan is assumed to optimize different kinds of objective function. The proposed approach to the optimal restoration of generating units can be used by vertically integrated utilities as well as the ISOs in electricity markets. The approach coordinates the optimal start up of generating units within the restoration period. Physical... 

this paper presents two new methods for power flow calculation of power systems in presence of Dynamic Flow Controller (DFC), which is a new member of FACTS controllers. In first method A new steady state model of DFC is introduced for the implementation of the device in the conventional Newton-Raphson power flow algorithm. The impact of DFC on power flow is accommodated by adding new entries and modifying some existing ones in the linearized Jacobian equations of the same system without DFC. The focus of second method is on the discrete nature of the DFC and including its effects on power flow. This method is based on Nabavi model for FACTS devices. A case study on a power system located in... 

This paper probes the impact of utilizing an IPFC on the reliability indices of interconnected power systems. First, a concise presentation of IPFC and its structure are provided and the reliability model of two unequally-rated parallel transmission lines equipped with IPFC is then extracted. The assumed IPFC is composed from two parallel converting bridges associated with each line. Afterwards, based-on equivalent assisting unit approach, different commonly-used adequacy indices including the loss of load expectation (LOLE), loss of energy expectation (LOEE) and system minutes (SM) are calculated. A set of numerical analyses are conducted to illustrate the sensitivity of these indices with... 

With the increasing share of distributed generation in electrical energy supply, the proper planning procedure for using these units, has become more vital for power system planners. In this paper, the application of multi-objective optimization techniques for siting, sizing and determination of the proper technology to be used, has been investigated in such a way that, the load demand during the planning horizon is met and the technical and environmental constraints are satisfied. Unlike the traditional optimization methods used in power system optimization, NSGA-II multi-objective optimization algorithm does not consider techno-economical and environmental parameters in the constraints of... 

This paper presents a new approach for unit commitment (UC); where a large scale wind power exists and the wind speed has a fuzzy characteristic; by using particle swarm optimization method (PSO). In this approach, the system reserve requirements, the requirement of having a load balance, and the wind power availability constraints are realized. A proper modeling of these constraints is an important issue in power system scheduling. Since these constraints are "fuzzy" in nature, any crisp treatment of them in this problem may lead to over conservative solutions. In this paper, a fuzzy optimization-based method is developed to solve power system UC problem with a fuzzy objective function and... 

Ancillary services are generally referred as those services other than energy that are essential for ensuring reliable operation of electric power systems. This paper discuses different approaches for procuring required ancillary services for power system security. Furthermore, various design options for ancillary service markets are studied. Such markets are typically operated by an independent system operator (ISO). Different characteristics of each design option are also explained in this paper. The two most important factors which will be discussed for each design option are the price reversal phenomenon and total procurement cost. © 2007 IEEE  

In this paper a strategic planning framework is proposed for generation expansion planning of grid-connected micro-power systems. The proposed framework is composed of two different decision making techniques that results a robust planning approach compared to previous techniques to identify the feasible and efficient plans according to attributes and uncertain parameters considered in planning environment. The framework considers the robustness and risk exposure of different configurations according to uncertain parameters in the planning environment to select the plans which meet the objectives more efficiently with least risk exposure. The proposed methodology is implemented for... 

Reliability assessment of power systems is very vital particularly in the market-driven environment. As the power systems are nonlinear and large-scale systems, extracting their reliability indices involves much uncertainty. Calculation of power system reliability using stochastic methods is a complex and relatively difficult procedure. However, using fuzzy logic methods it would be possible to calculate the reliability in accordance with the existing uncertainties. In this paper, a new fuzzy logic based method is proposed to calculate the reliability indices of composite power systems. Then, the suggested method is examined on a sample network as a case study. © 2007 IEEE  

This paper proposes a method for unit commitment in restructured power systems with high penetration of wind farms. As wind is an intermittent source of energy and can not be predicted with high accuracy, reliability of wind farms compare to conventional power plants is lower. By increasing penetration of wind farms in generation system, reliability of power system will decrease. Therefore, reliability constraint should be added to unit commitment (UC) formulation. On the other hand, wind is a green source of energy; additionally environmental crisis is very important issue in the 21st century. By adding emission constraint to UC, wind energy will be valued. Both reliability and emission... 

This paper presents the application of a fuzzy logic controlled Static Compensator (STATCOM) to improve stability of power system. The nonlinear fuzzy logic controller is used to overcome the problems generated by different uncertainties exist in power systems. Different input variables are used to design the controller. Parameters of the proposed controller are adjusted by means of Neural Network techniques to improve performance of the system. Proposed controller is implemented on a single machine infinite bus system to confirm the performance of the controller through simulation results  

To make the energy market reliable and transactions deliverable, transmission owners must provide required ancillary services that are critical to ensure transmission open access, and to maintain an acceptable level of power system security. Spinning reserve is one of the most important ancillary services required to maintain system reliability in case of occurring a contingency. By definition, spinning reserve is the unloaded section of synchronized generation that is able to respond immediately to serve load. Studies indicate that spinning reserve requirements have significant impacts on the energy market. A new spinning reserve market structure is proposed in this paper to best utilize... 

An important issue in power system planning is maintenance scheduling of generating units. In a traditional power system, the problem of maintenance scheduling is of high importance and has various technical and economical constraints. Different methods have been used to solve the problem. On the other hand, changes in legal environment of electricity industry poses new bound and requirements on the maintenance scheduling problem. This paper presents a new approach on maintenance scheduling of generating units in a generating company (GENCO). The proposed approach uses Markov Decision Process (MDP) to minimize total costs of unserved energy and reserve. The impacts on maintenance scheduling... 

Energy storage systems (ESSs) play a vital role in dealing with uncertainties originated from the intermittent power generation of renewable energy sources (RESs) leading to improvement of flexibility and reliability of power systems. Needless to say, a key factor is selecting the best technology of ESSs which yields to maximum leverage of ESSs presence in power systems. On this basis, in this paper, a mixed integer linear programming (MILP) direct-optimization model is proposed to effectively mitigate the impacts of insufficient transmission lines capacities by installation of different ESS technologies using a DC optimal power flow model. Firstly, a precise model for the technical...