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Showing 56 results for Ev

A. Abadpour, S. Kasaei,
Volume 1, Issue 3 (7-2005)
Abstract

A robust skin detector is the primary need of many fields of computer vision, including face detection, gesture recognition, and pornography filtering. Less than 10 years ago, the first paper on automatic pornography filtering was published. Since then, different researchers claim different color spaces to be the best choice for skin detection in pornography filtering. Unfortunately, no comprehensive work is performed on evaluating different color spaces and their performance for detecting naked persons. As such, researchers usualy refer to the results of skin detection based on the work doen for face detection, which underlies different imaging conditions. In this paper, we examine 21 color spaces in all their possible representations for pixel-based skin detection in pornographic images. Consequently, this paper holds a large investigation in the field of skin detection, and a specific run on the pornographic images.
Shayegh, Mohammadi, Abdipour, Sedghi, Mirzavand,
Volume 2, Issue 1 (1-2006)
Abstract

A direct conversion modulator-demodulator with even harmonic mixers with emphasis on noise analysis is presented. The circuits consist of even harmonic mixers (EHMs) realized with antiparallel diode pairs (APDPs). We evaluate the different levels of I/Q imbalances and DC offsets and use signal space concepts to analyze the bit error rate (BER) of the proposed transceiver using M-ary QAM schemes. Moreover, the simultaneous analysis of the signal and noise has been presented.


H. Shateri, S. Jamali,
Volume 2, Issue 3 (7-2006)
Abstract

This paper presents the effects of instrument transformers connection points on the measured impedance by distance relays in the presence of Flexible Alternating Current Transmission System (FACTS) devices with series connected branch. Distance relay tripping characteristic itself depends on the power system structural conditions, pre-fault operational conditions, and especially the ground fault resistance. The structural and controlling parameters of FACTS devices as well as the connection points of instrument transformers affect the ideal tripping characteristic of distance relay. This paper presents a general set of equations to evaluate the measured impedance at the relaying point for a general model of FACTS devices to consider different affecting parameters.
R. Naderi, A. Rahmati,
Volume 4, Issue 4 (12-2008)
Abstract

Multilevel PWM waveforms can be decomposed into several multilevel PWM components. Phase-shifted carrier (PSC) is an efficient decomposition technique. In this paper, we have first demonstrated the equality of PSC and alternative phase opposition disposition techniques. Second, we have modified PSC to accommodate other disposition techniques. Third, we have investigated the effects of using asymmetrical carriers on the spectrum of the resulting PWM waveform. Fourth, we have proposed a logical algorithm for decomposing all types of multilevel PWM waveforms.
Gh. R. Karimi, and S. Mirzakuchaki,
Volume 4, Issue 4 (12-2008)
Abstract

During the past few years, a lot of work has been done on behavioral models and simulation tools. But a need for modeling strategy still remains. The VHDL-AMS language supports the description of analog electronic circuits using Ordinary Differential Algebraic Equations (ODAEs), in addition to its support for describing discrete-event systems. For VHDL-AMS to be useful to the analog design community, efficient semiconductor device models must be available. In this paper, potential merits of the new IEEE VHDL-AMS standard in the field of modeling semiconductor devices are discussed. The device models for diodes and the principles, techniques, and methodology used to achieve the design of an analytical third generation Spice transistor MOS model named EKV are presented. This is done by taking into account the thermoelectrical effect in VHDL-AMS, and with relevant parameters set to match a deep submicron technology developed in VHDL-AMS. The models were validated using System Vision from Mentor Graphics.
M. Gitizadeh, M. Kalantar,
Volume 4, Issue 4 (12-2008)
Abstract

This paper presents a novel optimization based methodology to allocate Flexible AC Transmission Systems (FACTS) devices in an attempt to improve the previously mentioned researches in this field. Static voltage stability enhancement, voltage profile improvement, line congestion alleviation, and FACTS devices investment cost reduction, have been considered, simultaneously, as objective functions. Therefore, multi-objective optimization without simplification has been used in this paper to find a logical solution to the allocation problem. The optimizations are carried out on the basis of location, size and type of FACTS devices. Thyristor Controlled Series Compensator (TCSC) and Static Var Compensator (SVC) are utilized to achieve the determined objectives. The problem is formulated according to Sequential Quadratic Programming (SQP) problem in the first stage. This formulation is used to accurately evaluate static security margin with congestion alleviation constraint incorporating voltage dependence of loads in the presence of FACTS devices and estimated annual load profile. The best trade-off between conflicting objectives has been obtained through Genetic Algorithm (GA) based fuzzy multi-objective optimization approach, in the next stage. The IEEE 14-bus test system is selected to validate the allocated devices for all load-voltage characteristics determined by the proposed approach.
M. Heydaripour, A. Akbari Foroud,
Volume 8, Issue 4 (12-2012)
Abstract

Congestion in the transmission lines is one of the technical problems that appear particularly in the deregulated environment. The voltage stability issue gets more important because of heavy loading in this environment. The main factor causing instability is the inability of the power system to meet the demand for reactive power. This paper presents a new approach for alleviation congestion relieving cost by feeding required reactive power of system in addition to re-dispatching active power of generators and load shedding. Furthermore with considering different static load models in congestion management problem with both thermal and voltage instability criteria, tries to the evaluated congestion management cost become more real, accurate and acceptable. The voltage stability is a dynamic phenomenon but often static tools are used for investigating the stability conditions, so this work offers new method that considers two snapshots after contingency to consider voltage stability phenomena more accurate. This algorithm uses different preventive and corrective actions to improve unsuitable voltage stability margin after contingency. The proposed method is tested on IEEE 24-bus Reliability test system, the simulation results shows the effectiveness of the method.
R. Ghazi, N. Pariz, R. Zeinali,
Volume 9, Issue 2 (6-2013)
Abstract

In this paper, the effect of Static VAr Compensator (SVC) parameters on the nonlinear interaction of steam power plant turbine-generator set is studied using the Modal Series (MS) method. A second order representation of a power system equipped with SVC is developed and then by MS method the nonlinear interaction of torsional modes is assessed under various conditions and the most influencing factors are determined. The results show that the stress conditions and some SVC control parameters will adversely affect the dynamic performance of a power system by increasing the nonlinear interaction of torsional modes. In this situation, the MS method can precisely provide a reliable prediction of the torsional oscillations amplitudes and the frequency content of the output system response. As the angle and speed of turbine-generator segments are used as input signals in several controllers, the frequency content of these signals are quite important in designing such controllers. This analysis is performed on a 4-areas WSCC system, which is equipped with a SVC. The obtained results can provide some important guidelines for coordinate operation and design of FACTS controllers to reduce the risk of shaft failure arising from torsional interaction in long term.
M. R. Mosavi, A. Akhyani,
Volume 9, Issue 2 (6-2013)
Abstract

In this paper, optimal placement of Phasor Measurement Unit (PMU) using Global Positioning System (GPS) is discussed. Ant Colony Optimization (ACO), Simulated Annealing (SA), Particle Swarm Optimization (PSO) and Genetic Algorithm (GA) are used for this problem. Pheromone evaporation coefficient and the probability of moving from state x to state y by ant are introduced into the ACO. The modified algorithm overcomes the ACO in obtaining global optimal solution and convergence speed, when applied to optimizing the PMU placement problem. We also compare this simulink with SA, PSO and GA that to find capability of ACO in the search of optimal solution. The fitness function includes observability, redundancy and number of PMU. Logarithmic Least Square Method (LLSM) is used to calculate the weights of fitness function. The suggested optimization method is applied in 30-bus IEEE system and the simulation results show modified ACO find results better than PSO and SA, but same result with GA.
M. Piry, M. Khanjani Moaf, P. Amiri,
Volume 10, Issue 1 (3-2014)
Abstract

Class-AB circuits, which are able to deal with currents several orders of magnitude larger than their quiescent current, are good candidates for low-power and high slew-rate analog design. This paper presents a novel topology of a class AB flipped voltage follower (FVF) that has better slew rate and the same power consumption as the conventional class-AB FVF buffer previously presented in literature. It is thus suitable for low-voltage and low-power stages requiring low bias currents. These buffers have been simulated using 0.5µm CMOS Technology models provided by IBM. The buffer consumes 20µA from a 0.9V supply and has a bandwidth of 50MHz with a 18pF load. It has a slew rate of 9.8V/µs and power consumption of 42µw
R. Samadi, S. A. Seyedin,
Volume 10, Issue 2 (6-2014)
Abstract

Unintentional attacks on watermarking schemes lead to degrade the watermarking channel, while intentional attacks try to access the watermarking channel. Therefore, watermarking schemes should be robust and secure against unintentional and intentional attacks respectively. Usual security attack on watermarking schemes is the Known Message Attack (KMA). Most popular watermarking scheme with structured codebook is the Scalar Costa Scheme (SCS). The main goal of this paper is to increase security and robustness of SCS in the KMA scenario. To do this, SCS model is extended to more general case. In this case, the usual assumption of an infinite Document to Watermark Ratio (DWR) is not applied. Moreover watermark is assumed to be an arbitrary function of the quantization noise without transgressing orthogonality as in the Costa’s construction. Also, this case is restricted to the structured codebooks. The fundamental trade-off is proved between security and robustness of Generalized SCS (GSCS) in the KMA scenario. Based on this trade-off and practical security attack on SCS, a new extension of SCS is proposed which is called Surjective-SCS (SSCS). In the absence of robustness attack, the SSCS has more security than SCS in the same DWR. However, the SSCS achieves more security and robustness than SCS only in low Watermark to Noise Ratio (WNR) regime or low rate communications.
H. Rajabi Mashhadi, H. Safari Farmad,
Volume 11, Issue 1 (3-2015)
Abstract

The main goal of this paper is to present a new day-ahead energy acquisition model for a distribution company (Disco) in a competitive electricity market environment with Interruptible Load (IL). The work formulates the Disco energy acquisition model as a bi-level optimization problem with some of real issues, and then studies and designs a Genetic Algorithm (GA) of this optimization problem too. To achieve this goal, a novel two-step procedure is proposed. At the first step, a realistic model for an industrial interruptible load is introduced, and it is shown that Interruptible load model may affect the problem modeling and solving. At the second step, Disco energy acquisition program is formulated and solved with this realistic model. As a result, this paper shows energy acquisition programming model with ILs, by considering real assumptions. The introduced method shows a good performance of problem modeling and solving algorithm both in terms of solution quality and computational results. In addition, a case study is carried out considering a test system with some assumptions. Subsequently results show the general applicability of the proposed model with potential cost saving for the Disco
A. R. Soofiabadi, Dr. A. Akbari Foroud,
Volume 11, Issue 2 (6-2015)
Abstract

This paper develops a method for nodal pricing and market clearing mechanism considering reliability of the system. The effects of components reliability on electricity price, market participants’ profit and system social welfare is considered. This paper considers reliability both for evaluation of market participant’s optimality as well as for fair pricing and market clearing mechanism. To achieve fair pricing, nodal price has been obtained through a two stage optimization problem and to achieve fair market clearing mechanism, comprehensive criteria has been introduced for optimality evaluation of market participant. Social welfare of the system and system efficiency are increased under proposed modified nodal pricing method.
I. Ehsani, A. Akbari Foroud, A. R. Soofiabadi,
Volume 11, Issue 3 (9-2015)
Abstract

Locational Marginal Pricing (LMP) is a method for energy pricing in deregulated power systems. Loss and congestion cause different prices for energy at load or generation buses. In this pricing method there is a different between payments of customers and revenue of generators which is called Merchandizing Surplus (MS). Independent System Operator (ISO) receives MS and generally renders it to Transmission Company (Transco). It is rational that the MS be allocated among power market participants fairly instead of granting whole MS to Transco. In this paper a novel method is proposed to allocate MS among market participant according to their role in the congestion of system. In the presented method by decomposing LMP and identifying congestion part of LMP, the part of generators’ revenue and customers’ payments which caused by congestion are calculated. Then MS is allocated among market participants as the payment of customers to be equal to revenue of generators. The proposed method has been tested on five bus test system. Results indicate the effectiveness of the proposed method to allocate MS between power market participants.

AWT IMAGE


N. Tabrizi, E. Babaei, M. Mehdinejad,
Volume 12, Issue 1 (3-2016)
Abstract

Reactive power plays an important role in supporting real power transmission, maintaining system voltages within proper limits and overall system reliability. In this paper, the production cost of reactive power, cost of the system transmission loss, investment cost of capacitor banks and absolute value of total voltage deviation (TVD) are included into the objective function of the power flow problem. Then, by using particle swarm optimization algorithm (PSO), the problem is solved. The proposed PSO algorithm is implemented on standard IEEE 14-bus and IEEE 57-bus test systems and with using fuzzy satisfying method the optimal solutions are determined. The fuzzy goals are quantified by defining their corresponding membership functions and the decision maker is then asked to specify the desirable membership values. The obtained results show that solving this problem by using the proposed method gives much better results than all the other algorithms.


A. A. Khodadoost Arani, J. S. Moghani, A. Khoshsaadat, G. B. Gharehpetian,
Volume 12, Issue 2 (6-2016)
Abstract

Multilevel voltage source inverters have several advantages compare to traditional voltage source inverter. These inverters reduce cost, get better voltage waveform and decrease Total Harmonic Distortion (THD) by increasing the levels of output voltage. In this paper Genetic Algorithm (GA) and Particle Swarm Optimization (PSO) methods are used to find the switching angles for achieving to the minimum THD for output voltage waveform of the Cascaded H-bridge Multi-Level Inverters (MLI). These methods are used for a 27-level inverter for different modulation indices. Result of two methods is identical and in comparison to other methods have the smallest THD. To verify results of two mentioned methods, a simulation using MATLAB/Simulink software is presented.


S. Laali, E. Babaei, Z. Saadatizadeh,
Volume 12, Issue 3 (9-2016)
Abstract

In this paper, several optimum structures of a cascaded multilevel inverter is proposed. This optimization is based on generation a constant number of output voltage levels by using minimum number of power switches or dc voltage sources or minimum amount of blocked voltage by power switches. In addition, the optimum structure for a constant number of dc voltage sources by using minimum number of power switches is obtained. In these optimizations, all of the presented algorithms to generate a desired sinosuidal waveform of the cascaded multilevel inverter are considered. Then, the proposed optimum topologies are compared with several conventional cascaded multilevel invereters that have been presented in literature. These comparisons are from the number of required power switches, dc voltag sources, variabilty the magnitude of dc voltage source and the value of blocked voltage by switches points of view. The conduction and switching losses of the proposed topologies are calculated. In addition, a 49-level cascaded inverter based on the proposed optimum topologies is designed. Moreover, the designed topologies are compared to each other from the amount of blocked voltage by swithes, the maximum magnitude of output voltage levels and the number of required power electronic devices such as power switches, driver circuits and diodes points of view. Finally, the ability of the optimium topology in generation all voltage levels (even and odd) by using minimum number of power switches is reconfirmed thruogh PSCAD/EMTDC simulation and experimental results on a 49-level inverter.


M. Khalilzadeh, A. Fereidunian,
Volume 12, Issue 4 (12-2016)
Abstract

In this paper, a stochastic approach is proposed for reliability assessment of bidirectional DC-DC converters, including the fault-tolerant ones. This type of converters can be used in a smart DC grid, feeding DC loads such as home appliances and plug-in hybrid electric vehicles (PHEVs). The reliability of bidirectional DC-DC converters is of such an importance, due to the key role of the expected increasingly utilization of DC grids in modern Smart Grid. Markov processes are suggested for reliability modeling and consequently calculating the expected effective lifetime of bidirectional converters. A three-leg bidirectional interleaved converter using data of Toyota Prius 2012 hybrid electric vehicle is used as a case study. Besides, the influence of environment and ambient temperature on converter lifetime is studied. The impact of modeling the reliability of the converter and adding reliability constraints on the technical design procedure of the converter is also investigated. In order to investigate the effect of leg increase on the lifetime of the converter, single leg to five-leg interleave DC-DC converters are studied considering economical aspect and the results are extrapolated for six and seven-leg converters. The proposed method could be generalized so that the number of legs and input and output capacitors could be an arbitrary number.


A. R. Moradi, Y. Alinejad-Beromi, K. Kiani,
Volume 13, Issue 1 (3-2017)
Abstract

Congestion and overloading for lines are the main problems in the exploitation of power grids. The consequences of these problems in deregulated systems can be mentioned as sudden jumps in prices in some parts of the power system, lead to an increase in market power and reduction of competition in it. FACTS devices are efficient, powerful and economical tools in controlling power flows through transmission lines that play a fundamental role in congestion management. However, after removing congestion, power systems due to targeting security restrictions may be managed with a lower voltage or transient stability rather than before removing. Thus, power system stability should be considered within the construction of congestion management. In this paper, a multi-objective structure is presented for congestion management that simultaneously optimizes goals such as total operating cost, voltage and transient security. In order to achieve the desired goals, locating and sizing of series FACTS devices are done with using components of nodal prices and the newly developed grey wolf optimizer (GWO) algorithm, respectively. In order to evaluate reliability of mentioned approaches, a simulation is done on the 39-bus New England network.


F. Nazari, A. Zangeneh, A. Shayegan-Rad,
Volume 13, Issue 1 (3-2017)
Abstract

By increasing the use of distributed generation (DG) in the distribution network operation, an entity called virtual power plant (VPP) has been introduced to control, dispatch and aggregate the generation of DGs, enabling them to participate either in the electricity market or the distribution network operation. The participation of VPPs in the electricity market has made challenges to fairly allocate payments and benefits between VPPs and distribution network operator (DNO). This paper presents a bilevel scheduling approach to model the energy transaction between VPPs and DNO.  The upper level corresponds to the decision making of VPPs which bid their long- term contract prices so that their own profits are maximized and the lower level represents the DNO decision making to supply electricity demand of the network by minimizing its overall cost. The proposed bilevel scheduling approach is transformed to a single level optimizing problem using its Karush-Kuhn-Tucker (KKT) optimality conditions. Several scenarios are applied to scrutinize the effectiveness and usefulness of the proposed model. 



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© 2022 by the authors. Licensee IUST, Tehran, Iran. This is an open access journal distributed under the terms and conditions of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) license.