Sharif Digital Repository

When there are transmission service requests for a specific sink/source pair in a transmission system, the ISO must allocate the ATC of that pair to the requests. Since the requests could have different types, tariffs and time frame, the allocation must be accomplished in a sound and fair manner that considers various aspects of the requests. This paper proposes an approach to allocate the ATC to transmission service requests in both operating and planning horizons. The proposed method considers types and tariffs of requests in a nonlinear optimization which maximizes the expected net revenue of ATC allocation. The solution to the optimization problem gives the amount of accepted requests.... 

In this paper, a system wide scheme is proposed to arrest voltage instability. This scheme consists of two stabilizing and securing parts. For post- contingency situations, where there are no equilibrium solutions, first, the stabilizing scheme finds the closest solvable operating point, and then passes this point to the securing scheme. The securing scheme brings the solvable, but insecure operating point, back to a secure and stable one. Also, a voltage stability indicator is proposed to monitor the available margin to the collapse point. The proposed stabilizing and securing model are solved using the sequential quadratic programming technique. ©2009 IEEE  

The objective of this research is geometrical and kinematical optimization of full-toroidal continuously variable transmission (CVT) in order to achieve high power transmission efficiency and low mass. At first, a dynamic analysis is performed for the system. A computer model is developed to simulate elastohydrodynamic (EHL) contact between disks and roller and consequently, calculate CVT efficiency. The validity of EHL model is investigated by comparing output of this model and experimental data. Geometrical parameters are obtained by means of Particle Swarm Optimization algorithm, while the optimization objective is to maximize CVT efficiency and minimize its mass. The algorithm is run for... 

Wind power generation is increasing fast as a clean renewable energy resource. Offshore wind farms are popular due to advantages such as higher and smoother wind speeds, less farm site limitations, etc. High capacitive currents and need to expensive compensations, make use of high-voltage-direct-current (HVDC) power transmission indispensable for longdistance wind farm power generations. Steady-state and transient performance improvements of HVDC systems have always been an interesting industrial and academic research area. In this paper, a novel control method is proposed to improve the steady-state operation of HVDC system. Moreover, a new fault detection scheme is proposed to improve the... 

This paper establishes a simple and topological approach to track real and reactive power flow in electric transmission systems. The presented method utilizes the well-known Proportional Sharing Theorem in order to evaluate the contribution of each power source to grid elements' supplied input power. We have also put forward an approximate power tracing method for upgraded grids, using its own previously surveyed results. The main advantages of the proposed procedure, compared with conventional methods, are discussed extensively. The effectiveness of this approach has been studied and ascertained for small-scale power systems, showing prominent speed and accuracy  

The present context of the electric industry, characterized by competitive markets, privatization, and regulatory of technical requirements forces the power utilities to optimize their asset management practices and develop the requisite decision plans techno-economically. Practically approaching, this paper devises a new support tool based on a multiattribute decision making (MADM) framework in combination with analytical hierarchical process (AHP) to determine the most critical components of power transmission systems. Measure of system-wide reliability performance, outage cost, marginal clearing prices demonstrative of market fairness, and network losses are among the attributes... 

The increasing variability of renewables and volatile chronological net-load in power grids engenders significant risks of an uncertain sufficiency of flexible capacity. Although considerable advances in power grid flexibility assessment have been made, modeling the effect of temporal correlations associated with wind generations on the system flexibility provision capability has remained a challenge. This paper proposes a novel UC-time-scale security-constrained affinely robust formulation for wind-originated uncertainty sets in order to evaluate the system flexibility capacity over time. An efficient model based on duality theorem and affine policy is proposed to assess a secure region in... 

In this paper, we discuss the optimum random and deterministic power selection algorithms in Aloha networks, where nodes run Exponential Backoff (EB) for contention resolution. In random case, the transmission power of a packet is selected from the available power levels, based on a predetermined probability mass function, while with the deterministic algorithms the transmission power of a packet is a deterministic function of the number of collisions the packet has experienced. Most of the related works in the literature have not addressed the power-throughput characteristics of the power selection algorithms for use in practical system designs and, therefore, this subject has been the... 

An array of N weakly coupled oscillators is investigated in two major configurations. The locking bandwidth for linear and circular arrays is assessed through an array coupling matrix, in a worst-case free-running frequency distribution of oscillators. The superior locking bandwidth for circular arrays is demonstrated  

In this paper we investigated the structural properties of the ultra high voltage power transmission network of Iran. We modeled the power grid as a network with 105 nodes and 142 connection links. We found that the Iranian power grid displays a relatively moderate clustering coefficient-much larger than that of corresponding random networks-and small characteristics path length comparable to that of corresponding random networks; i.e. the power grid is a small-world network with exponential degree distribution. Global efficiency was considered as an indicator of grid's performance and the influence of random and intentional nodal failures on the efficiency was investigated. We also studied... 

The aim of this research is the optimisation of full-toroidal continuously variable transmission (CVT) in conjunction with the fixed ratio (FR) mechanism, while the optimisation objective is to minimise fuel consumption (FC) of the vehicle in the new European driving cycle. After the dynamic analysis of the power train, a computer model is developed to simulate contact between CVT elements and consequently calculate its efficiency. Then an algorithm is presented to calculate FC of the vehicle in the driving cycle. Then, an optimisation using particle swarm optimisation on the CVT geometry and FR mechanism (which is embedded between CVT and final drive) is carried out to minimise FC. It is... 

This paper presents a practical scheme that can be used for allocating the transmission loss to generators and loads. In this scheme first the share of a generator or load on the current through a branch is determined using Z-bus modified matrix. Then the current components are decomposed and the branch loss allocation is obtained. A motivation of proposed scheme is to improve the results of Z-bus method and to reach more fair allocation. The proposed scheme has been implemented and tested on several networks. To achieve practical and applicable results, the proposed scheme is simulated and compared on the transmission network (400kv) of Khorasan region in Iran and the 14-bus standard IEEE... 

Reliability evaluation of a large composite generation and transmission system involves extensive and time-consuming calculations. Application of reliability equivalent networks therefore seems necessary in the reliability evaluation of large power systems. An approach is presented to develop an adequacy equivalent of a composite system using network screening. In the proposed method, a power system is divided into two portions designated as the study area and the external area. The goal is to find the adequacy equivalent of the external area in order to facilitate extensive reliability studies in the study area. The elements in the external area are ranked or screened based on their impacts... 

The overall system status calculated by pflower flow analysis is the most basic information used for all decisions taken by power system operators and planners. While conventional AC pflower flow solutions are computationally tractable, approximate DC models are employed in many applications, such as optimal power flow studies and unit commitment problems, mainly due to the linear nature of DC models. These models do not provide any information on the reactive power and voltage magnitude quantities and occasionally inaccurate results of the active power values. This paper presents an efficient power flow approach compromising both the con icting aspects of speed and accuracy. The proposed... 

Increasing redundant paths in transmission grids has always been thought to be a tool to enhance service reliability. However, network equations by intertwining power flows through redundant paths impose more limits on systems with more redundancy. Accordingly, autonomous removing of a few lines may relief capacity limit violations in some contingency events thereby enhancing service reliability. This paper aims to study impacts of manual removing of transmission lines on composite system reliability. For doing so, the existing model is extended to consider optimal transmission switching (OTS) as a remedial action. The model minimizes total damage cost imposed by load curtailments. The... 

Power sharing control among grid forming dc sources employing a conventional voltage droop approach meets inaccurate load sharing and unacceptable voltage regulation performance. Thereby, communication-based secondary and supervisory controllers have been presented to overcome the aforementioned issues. Furthermore, with the aim of eliminating communication system, frequency-based droop approaches have been introduced for low-voltage dc grids where the frequency of the superimposed ac signal onto the dc voltage is proportional to the output power. However, in reality, dc grid structures can be applied to medium and high voltage applications with different X/R ratios. This paper generalizes... 

Reliability assessment is of primary importance in designing and planning distribution systems that operate in an economical manner with minimal interruption of customer loads. Distributed generation (DG) is expected to play an increasing role in emerging power systems because they use different type of resources and technologies to serve energy to power systems. DG is expected to improve the system reliability as its backup generation. Since DG units are subject to failures as all other generation units, the random behavior of these units must be taken into account in the analysis. Existence of DG units in a distribution system will effect on restoration time of load points. In this paper,... 

Developing an accurate network equivalent to reduce the computational time of an electromagnetic transient study has been the major task of many researches in the past two decades. However, still no accurate wide band equivalent for an asymmetrical network is addressed in the literature. This paper presents a Hybrid equivalent for the external system, assuming that it contains an asymmetrical transmission system at the terminal of this external system. The proposed method is based on the introduction of an asymmetrical transmission system in the model through application of a real constant transformation matrix in the subsystem and dealing with its asymmetrical effects in the external... 

This paper presents several techniques for the processing of power system signals in a power system setup. The techniques exhibit a desirable performance against signal pollutions such as noise and distortions, signal unbalance (in three-phase applications), and Variations in the signal attributes (mainly its frequency). These features render them a promising set of options for modern power systems in which all or some of these undesired factors may be amplified depending on the case. Single-phase and three-phase applications are both examined and appropriate techniques are suggested for different scenarios. © 2007 IEEE  

The concept of energy hub has been used recently to study multi-carrier energy systems. A model has been proposed in this paper for planning multi-hub energy system considering the competition between the hubs. The energy hubs are interconnected by a power grid. Hubs supply the demands for heat and electricity using various technologies and access to several energy carriers. To this aim, load zones were used to incorporate demand profiles for both heat and electricity in the different seasons of the year. Supplying the demand most cost-effectively is the objective function of each hub. These hubs select the optimum strategy separately in a competitive space. The power grid is owned by...