فهرست مطالب
Scientia Iranica
Volume:25 Issue: 3, May - June 2018
- Transactions on Computer Science & Engineering and Electrical Engineering (D)
- تاریخ انتشار: 1397/03/06
- تعداد عناوین: 15
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Pages 1441-1455Let G be a weighted digraph and s and t be two vertices of G. The reachability assurance (RA) problem is how to label the edges of G such that every path starting at s finally reaches t and the sum of the weights of the labeled edges, called the RA cost, is minimal. The common approach to the RA problem is pathfinding, in which a path is sought from s to t and then the edges of the path are labeled. This paper introduces a new approach, the marking problem (MP), to the RA problem. Compared to the common pathfinding approach, the proposed MP approach has a lower RA cost. It is shown that the MP is NP-complete, even when the underlying digraph is an unweighted directed acyclic graph (DAG) or a weighted DAG with an out-degree of two. An appropriate heuristic algorithm to solve the MP in polynomial time is provided. To mitigate the RA problem as a serious challenge in this area, application of the MP in software testing is also presented. By evaluating the datasets from various program flow graphs, it is shown that the MP is superior to the pathfinding in the context of test case generation.Keywords: Marking problem, Reachability assurance, Pathfinding, Software testing
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Pages 1456-1470Interval-valued intuitionistic fuzzy variables (IVIFVs) are powerful tools to denote the uncertain preferred and non-preferred degrees of decision makers. Considering the application of IVIFVs in decision making, this paper first gives some new operations that can address the shortages of previous ones. Then, an induced generalized symmetrical interval-valued intuitionistic fuzzy Choquet-Shapley (IG-SIVIFCS) operator is defined, which not only globally considers the importance of the elements but also overall reflects their interactions. After that, several desirable properties are briefly studied to provide assurance in application. In some situations, the weighting information of attributes is incompletely known. Considering this case, the Shapley function-based model for determining the optimal fuzzy measure on the attribute set is constructed. Furthermore, an approach to interval-valued intuitionistic fuzzy decision making with incomplete weighting information and interactive characteristics is developed to provide a completed theoretical framework. Finally, a practical example is provided to show the concrete practicality and validity of the proposed procedure.Keywords: decision making, interval-valued intuitionistic fuzzy value, generalized Shapley function, Choquet integral
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Pages 1471-1477In this paper using combination of two separated ideas the torque ripple of Interior Permanent Magnet Synchronous Motor (IPMSM) is reduced. These two ideas are rotor PM segmented and modifying the rotor structure based on pole-arc ratio of flux barrier optimization. In addition the torque ripple due to the reluctance torque component decreased too. Analysis and simulation results including saturation have been performed using analytical method and Finite Element Method (FEM). The rotor flux barrier configuration of the proposed design is carried out by Response Surface Method (RSM) as optimization technique which is verified by FEMKeywords: cogging torque, PM segmented, pole-arc ratio, saturation, response surface method
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Pages 1478-1491This paper presents a method to solve spatial network planning (SNP) in power systems expansion. SNP is an integration of transmission expansion planning (TEP) and optimal line routing problems. In fact, SNP considers the impacts of lines routing on the network power flow. Therefore, it can exploit such impacts to attain a signi cant techno-economic solution. In this work, a preprocess stage is employed to reduce the computational e ort demanded by line routing. Furthermore, a meta-heuristic algorithm is engaged to solve such a complicated problem. Applying these modi cations made it possible to solve SNP for large- scale systems with high-resolution rasterized maps. The proposed method is applied to a 3-bus system, an 18-bus test system as well as the original and modi ed versions of the IRAN southeast high-voltage transmission network to demonstrate the capability of the proposed methodology.Keywords: Geographical Information System (GIS), Spatial Network Planning, Transmission Expansion Planning, Transmission Line Routing
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Pages 1492-1506To increase transmitted power, series capacitors may be used in the transmission lines. A compensated transmission line together with a turbine-generator may cause sub-synchronous resonance (SSR) phenomena in a power system. In this paper, details of dynamic modeling of a single machine power system connected to the network through a transmission line, compensated with a series capacitor, has been presented. Static synchronous series compensator (SSSC) as one of series FACTS devices has been used for damping of the SSR oscillations. For this purpose, a linear damping SSSC-based stabilizer with lead-lag structure is included to SSSC controller. To determine parameters of SSSC stabilizer, a new multi-objective function has been proposed. In this function, in addition to improve stability of critical modes the gain of the stabilizer has been considered. To have stabilizer with minimum phase structure, suitable constraints have been determined and added to the objective function. To optimize the objective function, a recently developed optimization technique known as grey wolf optimization (GWO) algorithm has been applied. The eigenvalues analysis and nonlinear simulations on the IEEE first benchmark model (FBM) power system with a SSSC stabilizer illustrate the effectiveness of the proposed method to suppress SSR oscillations in the studied system.Keywords: Eigenvalues, Static Synchronous Series Compensator (SSSC), Sub- Synchronous Resonance (SSR), Gray Wolves Optimization (GWO) Algorithm
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Pages 1507-1522In this paper, the power quality in a wind power generation system is studied. It is shown that adding a Series Grid-Side Converter (SGSC) to the Doubly Fed Induction Generator (DFIG) structure and applying a suitable control algorithm will make the system be able to compensate the adverse effects of the voltage unbalance and consequently can improve the power quality. In order to decrease design complexity and implement the control algorithms in the stationary reference frame, a Sliding-Mode Control (SMC) method for controlling of the DFIG system with SGSC is proposed. One of the advantages of the proposed method in this paper is its robustness to parameter variations both in the DFIG and the connected network. Moreover, the designed controller leads to a fast dynamic response. It should be mentioned that, a coordinated control carries out between SGSC with the other DFIG converters. The simulation results approve the validity of the mentioned advantages and the effectiveness of the proposed method.Keywords: Doubly Fed Induction Generator (DFIG), Unbalanced grid voltage, Rotor-Side Converter (RSC), Grid-Side Converter (GSC), Series Grid-Side Converter (SGSC), Sliding-Mode Control (SMC)
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Pages 1523-1532This paper is concerned with the stability of nonlinear Lipschitz systems subject to bounded process and measurement noises when transmission from sensor to controller is subject to distortion due to quantization. A stabilizing technique and a sufficient condition relating transmission rate to Lipschitz coefficients are presented for almost sure asymptotic bounded stability of nonlinear uncertain Lipschitz systems. In the absence of process and measurement noises, it is shown that the proposed stabilizing technique results in almost sure asymptotic stability. Computer simulations illustrate the satisfactory performance of the proposed technique for almost sure asymptotic bounded stability and asymptotic stability.Keywords: Networked control system, Lipschitz nonlinear system, uncertain dynamic system, the digital noiseless channel
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Pages 1533-1544This paper proposes the optimized design of the permanent magnet synchronous motor (PMSM) based on the analysis of radial-flux permanent magnet motor with minimum weight, maximum efficiency and an increased torque. The rotor of the PMSM uses segmented permanent magnets mounted on the surface. The achievement of the method involves four steps. Firstly, the simplified motor model is presented in a manner which yields symbolic solution for optimal motor parameters as a function of mass. Secondly, Monte Carlo method is employed to compute optimal motor dimensions giving efficiency, torque and optimal motor active mass. Then, the steady state characteristics of the optimized primary optimized design obtained in the last step are calculated and compared to satisfy the flux condition. Finally, the performance of the optimized machine has been calculated by using 2D transient finite-element analysis (FEA). Subsequently, the model mesh and the boundary conditions were handled and presented. According to the obtained results, the essential purpose of the work has been reached, the weight has been reduced by 24%, the efficiency was improved by 8% and the rated torque by 40%. The proposed design approach has also the advantage for its significant time reduction of the design cycle.Keywords: Permanent magnet machine, design methodology, Optimization, Monte Carlo method, performance, Finite-Element Analysis (FEA)
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Pages 1545-1560A full automatic technique and a user friendly toolbox developed to assist physicians in early clinical detection of breast cancer. Database contains different degrees of thermal images obtained from normal or cancerous mammary tissues of patients with mean age of 42.3 years (SD: ±10.50) which their sympathetic nervous system activated with a cold stimulus on hands. First ROI was determined using full automatic operation and the quality of image improved. Then, some features, including statistical, morphological, frequency domain, histogram and GLCM features were extracted from segmented right and left breast. Subsequently, to achieve the best feature space decreasing complexity and increasing accuracy, feature selectors such as mRMR, SFS, SBS, SFFS, SFBS and GA have been used. Finally to classify and TH labeling, supervised learning techniques such as AdaBoost, SVM, kNN, NB and PNN were applied and compared with each other to find the best suitable one. The experimental results obtained on native database showed the mean accuracy of 88.03% for 0 degree images using combination of mRMR and AdaBoost and for combined 3 degrees using combination of GA and AdaBoost. The maximum accuracy obtained from all degrees and their combinations in before and after ice test is nearly to 100%.Keywords: Breast Cancer Detection, Thermography, Classification, Clinical Applications, Ice Test, Feature Selection, Supervised Classifiers
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Pages 1561-1570Cascaded H-Bridge converter has recently been utilized in different high-power applications due to its modular and simple structure. In order to have a balanced operation after a fault occurrence in this converter, it is necessary to detect the switch fault and its location. In this paper, a fast power switch fault detection method is presented to identify the fault and its location. Only one voltage measurement per phase is required by this method, and the fault detection is faster compared to the existing methods. Moreover, it is suitable for implementation on an FPGA device, due to the use of simple math, relational and state machine blocks. The proposed method is verified by computer simulations and FPGA-based experimental testsKeywords: Power switch fault detection, open-switch fault, multilevel converter, cascaded H-bridge converter Insulated Gate Bipolar Transistor (IGBT)
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Pages 1571-1581In this paper differential evolution with wavelet mutation (DEWM) is applied for the radiation pattern synthesis for circular geometry of antenna array. Two circular geometries have been considered namely; (a) time modulated half symmetric circular array (TMHSCAA) and (b) 9-ring time modulated concentric circular antenna array (TMCCAA). DEWM algorithm is applied to show the performance improvement for the optimal design of TMHSCAA and TMCCAA. While doing so various other stochastic algorithms like real coded genetic algorithm (RGA), particle swarm optimization (PSO), and differential evolution (DE) are also used for the sake of comparison to establish the superiority of DEWM. For TMHSCAA, elements are symmetrical around to the vertical axis, so the number of parameters to be optimized is reduced, with two control parameters like switching excitation phase of each element. For TMCCAA, two proportional case studies as Case-1 and Case-2 are carried out with different variable parameters. The simulation outcomes show the supremacy of DEWM to be a plausible claimant for scheming the best TMHSCAA and TMCCAA. The simulation tests have also been performed with 20- and 36- element TMHSCAA and 9 rings TMCCAA.Keywords: Side Lobe Level (SLL), TMHSCAA, TMCCAA, RF Switch, DEWM, First Null Beamwidth (FNBW)
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Pages 1582-1592An educational robot is described, which is designed and constructed for use in the laboratory of Principles of Electrical Engineering. The discrete nature of design, conforming to a simple block strategy, allows fairly easy introduction of basic and fundamental concepts of Electrical Engineering to the freshman students, including control, actuation, wireless signal transmission, and analogue/digital conversions. Each block or module represents one or few engineering ideas, and helps the students to understand the interplay and connection between system divisions, and enhance their creative thinking. Circuits are designed and implemented that both the structure and functionality of each module are clearly presented. Inputs and outputs as well as major signals can be traced and measured through several test pointsKeywords: Electrical Engineering Education, Educational Robot, Principles of Electrical Engineering, Laboratory-Based Education
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Pages 1593-1607This paper first deals with the analytical controller design in wind turbines with variable rotor-resistance control. Wind turbines with variable rotor-resistance control, known as limited variable speed wind turbine (LVS-WT), provide a limited variation of the generator speed. In the LVS-WT, the rotor current and consequently the output power can be controlled by varying the rotor resistance. Then modal and small signal analysis of the wind turbine is examined. It is found that for certain value of shaft stiffness, frequency of the mechanical modes coincides with the triple oscillation frequency appeared due to tower shadow effects. This in turn results in resonance phenomena magnifying the fluctuation of the generator power and electromagnetic torque. The paper next evaluates the impact of aerodynamic torque fluctuations on the dynamic response of the LVS-WT. In this way, analytical expressions for the fluctuations of the stator voltage and current, electromagnetic torque, and generator active power are proposed. These fluctuations arise as a consequence of the aerodynamic torque and rotor speed perturbations. The paper also investigates the effects of shaft stiffness, slope of power-slip curve and rotor resistance on the wind turbine response. At the end, results of theoretical analyses are verified by time domain simulations.Keywords: Aerodynamic torque fluctuations, Limited variable speed wind turbine, Power-slip curve, Shaft stiffness, Wind turbine with variable rotor resistance
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Pages 1608-1615In this paper we investigate the effect of uniaxial and torsional strains on the Density of States (DOS) of single walled Carbon nanotubes (SWCNTs). We employ the nearest neighbor and the third nearest neighbor π-TB (Tight Binding) models for our investigation. It is shown that uniaxial and torsional strains in some cases of metallic SWCNTs not only open a band gap but also effectively increase the DOS of SWCNT. It is also shown that, the mentioned types of strain have different effects on the DOS of chiral SWCNTs; in some types, they increase the DOS at the band edges while in other types they decrease it at the band edges.Keywords: Tight Binding, Carbon Nanotubes, Density of States, Electronic Band Structure, Uniaxial strain, Torsional strain
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Pages 1616-1628Mathematical modeling of complex electrical systems, has led us to linear mathematical models of higher order. Consequently, it is difficult to analyse and to design a control strategy of these systems. The order reduction is an important and effective tool to facilitate the handling and designing of a control strategy. In this paper we present, firstly, a reduction method which is based on the Krylov subspace and Lyapunov techniques, that we call Lyapunov-Global-Lanczos. This method minimizes the H1 norm error, absolute error and preserves the stability of the reduced system. It also provides a better reduced system of order 1, with closer behaviour to the original system. This first order system is used to design PI (Proportional-Integral) controller. Secondly, we implement an adaptive digital PI controller in a microcontroller. It calculates the PI parameters in real time, referring to the error between the desired and measured outputs and the initial values of PI controller, that were determined from the first order system. Two simulation examples and a real time experimentation are presented to show the effectiveness of the proposed algorithms.Keywords: Lanczos, Lyapunov, Model order reduction, Adaptive PI, Global Lanczos, ARDUIN