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International Review of Electrical Engineering  Vol. 5 N. 1-- Part A

International Review of Electrical Engineering  Vol. 5 N. 1-- Part B

 

International Review of Electrical Engineering - February 2010 - Papers Part A

 

 

go to top     International Review of Electrical Engineering - February 2010 - Papers Part B

 

 

 

International Review of Electrical Engineering - Papers- Part A

 

go to top   Analysis and Implementation of an Interleaved ZVS DC-DC Converter
         by Bor-Ren Lin, Huann-Keng Chiang, Chih-Yuan Cheng

         Vol. 5. n. 1, pp. 1-9

 

Abstract - An interleaved zero voltage switching (ZVS) converter with less component count and boost voltage conversion ratio is presented. The output voltage doubler is used on the output side to achieve the boost type of voltage conversion ratio. The proposed converter includes two active-clamping converters with common clamp capacitor to share load current. By the shared capacitor, the charge balance of two interleaved parts is automatically regulated under input voltage and load variations. The ZVS turn-on of all switching devices is achieved during the transition interval. The interleaved pulse-width modulation (PWM) operation will reduce the ripple current and the size of the output capacitor. The proposed circuit has no large output inductor such that the adopted circuit has simpler structure, lower cost and no effective duty loss. The voltage stresses on output diodes are clamped at the output voltage. The circuit configuration, operation principles and design consideration are presented. Finally experimental results based on a 425W (170V/2.5A) prototype are provided to verify the effectiveness of the proposed converter.

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Keywords: Voltage Step-Up, Power Conversion, Power Electronics.

 


 

go to top   A New Type-2 Fuzzy Logic Based Controller for Unbalance Problem of the DC-Link Voltages of Five-Level NPC Inverter
         by S. Boulkhrachef, S. Barkat, E. M. Berkouk

         Vol. 5. n. 1, pp. 10-18

 

Abstract - This paper describes a new dc-link voltages controller based on interval type-2 fuzzy systems for the cascade made up by two pulse width-modulation current source rectifiers and five-level inverter supplying an induction motor. The dc-link voltages balancing issue is addressed and a new balancing circuit with reduced number of power switches is proposed. Of particular interest, the used cascade guarantees balanced capacitors voltage and provides sinusoidal line currents having nearly unity input power factor. The power converters and the associated control algorithms based on the newly emerged type 2 fuzzy systems are presented and a set of simulations are carried out in order to highlight the good performances of the proposed control scheme. Moreover, a comparison between a type-2 fuzzy controller and a PI controller is made.

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Keywords: NPC Multilevel Inverter, PWM Rectifier, Type-2 Fuzzy Systems, Type Reduction, Input Dc Voltages Stabilisation, Induction Motor.

 


 

go to top   Analysis and Implementation of an Active-Clamping Quad-Flyback Converter
         by Bor-Ren Lin, Feng-Pin Tsao

         Vol. 5. n. 1, pp. 19-26

 

Abstract - An active-clamping quad-flyback converter is proposed to achieve zero voltage switching (ZVS) for all power switches. The secondary sides of quad-flyback converter are connected in parallel to share the load current. Thus, the transformer copper losses and the conduction losses on the output diodes are reduced. Active-clamping part including one auxiliary switch and one clamp capacitor can release the energy stored in the magnetizing and leakage inductances such that the voltage stress of main switch is clamped and main/auxiliary switches can be turned on at ZVS. In the proposed circuit, the constant switching frequency with asymmetrical PWM waveform is generated to realize the ZVS turn-on of switches at the transition interval between main and auxiliary switches. Thus, the switching losses and thermal stresses of the semiconductors are reduced. The operation principle, system analysis and design consideration of the proposed converter are discussed in detail. Finally, a prototype of the proposed converter is implemented by 200V input voltage, 48V output voltage, 480W output power and 90kHz switching frequency to verify the theoretical analysis and the effectiveness of the proposed converter.

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Keywords: Power Converters, ZVS, Power Electronics.

 


 

go to top   Implementation of a ZVS/ZCS Isolated Boost Converter
         by Bor-Ren Lin, Jyun-Ji Chen, Ming-Hung Yu

         Vol. 5. n. 1, pp. 27-36

 

Abstract -  An active clamp isolated boost circuit is presented in this paper. The active clamp circuit is employed in limiting voltage stress and create zero-voltage-switching (ZVS) turn-on feature for power switches. Moreover, the dual resonant tanks are composed of leakage inductors and resonant capacitors can achieve zero-current-switching (ZCS) turn-off mechanism for output diodes at the secondary side of transformer. Hence, the reverse-recovery problem of output diodes can be eliminated. The operational principles, design consideration and realization are discussed. Finally, experimental results from a 400W prototype are presented to confirm the effectiveness of the proposed converter.

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Keywords: Active Clamp, Zero Voltage Switching, Zero Current Switching.

 


 

go to top   Simulation and Implementation of a Novel Model-Based DPC for Three-Phase Power Converters
         by M. Monfared, H. Rastegar, H. M. Kojabadi

         Vol. 5. n. 1, pp. 37-46

 

Abstract - This paper presents theory, simulation and experimental verification of a new direct power control (DPC) method in comparison with the conventional switching table based method. In the presented strategy, hysteresis comparators and switching table are replaced by a PWM modulator. The required converter voltage in each sampling period is directly calculated based on measured currents and voltages and system parameters through simple equations. Then, a PWM generator synthesizes the switching pulses for the voltage source converter. Strong theoretical background besides simulation and experimental results has proven the excellent performance and verifies the validity of the proposed power control scheme.

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Keywords: Direct Power Control, PWM Converter.

 


 

go to top   Analysis of ZVS Series Resonant Converter with Two Transformers
         by Bor-Ren Lin, Po-Li Chen, Sin-Jhih Shen

         Vol. 5. n. 1, pp. 47-55

 

Abstract - Series resonant converter with two transformers and output voltage doubler is presented in this paper. Based on the resonant behavior of the resonant inductor and capacitor, the ZVS is achieved for all power switches and ZCS is realized for all rectifier diodes. For high power applications, the primary sides of two transformers are connected in series to reduce the voltage stress on primary windings. The secondary windings of two transformers are also connected in series to charge relative output capacitors. Since the voltage doubler rectifier is adopted in the secondary side, only one secondary winding per transformer is needed. Thus, the transformer secondary winding can be reduced. Compared with the conventional series resonant converter with center-tapped rectifier, the voltage stress of rectifier diodes is clamped to output voltage instead of two times of output voltage. The low voltage drop schottky diodes can be adopted in the output side to reduce the conduction loss. The principle of operation, steady state analysis and design example of the proposed converter are provided and discussed in detail. The proposed converter is suitable for high efficiency applications such as industrial power supply unit, all-in-one power supply and LCD-TV power unit. The laboratory experiments with a 480W (24V/20A) prototype are provided to verify the effectiveness of the proposed converter.

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Keywords: Series Resonant Converter, ZVS.

 


 

go to top   Dual Neutral-Point-Clamped Converters with Synchronized PWM for Photovoltaic Installations
         by Valentin Oleschuk, Giovanni Griva, Filippo Spertino

         Vol. 5. n. 1, pp. 56-63

 

Abstract - A novel method of synchronized pulsewidth modulation (PWM) has been modified and disseminated for control of dual (cascaded) neutral-point-clamped converters, supplied by two insulated strings of photovoltaic panels and connected to grid by a three-phase transformer with open-end windings on primary side. Specialized strategy and scheme of synchronized PWM, applied for control of dual converters, provide in this case: a) continuous phase voltage synchronization and required voltage regulation in the system by the corresponding control of modulation indices of the two converters; b) elimination of undesirable common-mode voltages both in each inverter and in the load, and c) an improvement of effectiveness of operation of the system due to flexible control of switching frequencies of inverters as function of DC voltages of photovoltaic panels. Simulations give a behavior of dual-converter-based photovoltaic system with three basic versions of synchronized PWM.

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Keywords: Cascaded Converters, Photovoltaic System, Phase Voltage Synchronization.

 


 

go to top   A Novel Control Strategy of Bidirectional DC-DC Converter for Interfacing Ultracapacitor to Fuel Cell Electric Vehicles System Based on Dynamic Evolution Control
         by A. S. Samosir, A. H. M. Yatim

         Vol. 5. n. 1, pp. 64-69

 

Abstract - Fuel cell electric vehicles gives far more promising performance. They have higher efficiency and lower emissions compared with the internal combustion engine vehicles. The fuel cell has a high energy storage capability, thus enhancing the range of operation for automobile and is a cleaner source of energy. However, the fuel cell has a slow dynamic response, so an auxiliary power source is needed during start up and transient conditions. Ultracapacitor usually used as secondary power source for improving the performance and efficiency of the overall system. Several methods have been devised to connect ultracapacitor to the fuel cell system. If the ultracapacitor is connected in parallel directly with the dc bus, its charge and discharge current cannot be controlled. Once the load changes significantly, the rush current would destroy the ultracapacitor. Therefore, a bidirectional converter needs to be inserted between the dc bus and the ultracapacitor to control the charge and discharge current. This paper proposes a novel control strategy of bidirectional dc-dc converter for interfacing ultracapacitor energy storage to fuel cell electric vehicles system. The controller of bidirectional dc-dc converter system was designed and implemented based on dynamic evolution control. Performance of the proposed dynamic evolution control is tested through simulation and experiment.

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Keywords: Fuel Cell, Ultracapacitor, Electric Vehicle, Dynamic Evolution Control, Bidirectional Dc-Dc Converter.

 


 

go to top   Direct Power Control of Doubly-Fed Induction Generators Using an Analytical Optimized Switching Table

         by Abdulrahim Kamalzadeh, Ahmad Radan

         Vol. 5. n. 1, pp. 70-82

 

Abstract - In this paper the role of the voltage vectors of a two-level converter on variations of active and reactive power of a Doubly Fed Induction Generator (DFIG) is studied more deeply. Previous approaches only have a qualitative look toward this issue that consequently, leads to extraction of an optimal switching table. With expanding accurate equations describing the variation of active and reactive power, this paper is going to inspect the role of the voltage vectors in active and reactive power control of a DFIG exactly, and to illuminate thoroughly the impression of terms like rotor velocity and load angle variation, neglected in the previous works. Expanding these equations provides the ability of scrutinizing the effect of the converter voltage vectors on active and reactive power of the machine at any operating point. This leads to achievement of a more accurate and optimal switching table. The distinction of this method accounts it as a good candidate for online methods to predict the effect of each voltage vector on active and reactive power variation.

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Keywords: Direct Power Control, Two-Level Converter, Doubly Fed Induction Generator, Induction Machine.

 


 

go to top   Air-Gap Eccentricity Effects on Harmonic Contents of Field Current in Synchronous Generators

         by Seyed Morteza Raziee, Homayoun Meshgin Kelk, Hamid-Reza Reza-Alikhani, Ali Omati
         Vol. 5. n. 1, pp. 83-89

 

Abstract - Mixed air gap eccentricity will produce extra harmonics in salient pole synchronous machines stator and field currents. It is determined that magnitudes of some harmonics will change with the variation of air gap eccentricity. In this paper, salient pole synchronous machines are modeled using winding function approach. Unsymmetrical machine are also simulated using the two dimensional finite element method. Analytical and simulation results are experimentally verified. It is shown that analysis of machine excitation current can be efficiently applied for condition monitoring of synchronous machines.

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Keywords: Salient Pole Synchronous Machine, Air Gap Eccentricity, Winding Function Approach, Finite Element Method .

 


 

go to top   On-Line Synchronous Generator Stability Limit Determination
         by N. Bulić, D. Sumina, M. Mišković

        Vol. 5. n. 1, pp. 90-98

 

Abstract - This paper presents the method for on-line determining the dynamic stability limit of a synchronous generator connected to power system. Presented method is implemented in digital control system and a series of experiments have been carried out on a synchronous generator. In order to determine damping of electromechanical oscillation the following methodology was applied. In real time a third order system matrix is identified from the measurements. The algorithm for identifying the system matrix is a recursive last squares algorithm in real time. For the current operating point from system matrix are determined eigenvalues, the damping coefficient and oscillations frequency. The character of electromechanical oscillations changes when the operating point of the synchronous generator is changed. With that the system's eigenvalues change as well, leading to a change in the damping coefficient of electromechanical oscillations. In the synchronous generator capacitive operating area, with the electromechanical oscillations mode dominant, the dynamic stability limit will be characterized by the occurrence of undamped electromechanical oscillations, i.e Hopf bifurcation. The proposed method is intended for implementation in excitation systems of synchronous generators in power plants so as to determine the dynamic stability of the synchronous generator in real time.

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Keywords: Synchronous Generator, Dynamic Stability, Stability Limit.
 


 

go to top   Speed Control by Internal Model with Load Observer of a Permanent Magnet Synchronous Motor
         by M. Larbi, S. Hassaine, B. Mazari

         Vol. 5. n. 1, pp. 99-105

 

Abstract - This paper presents an experimental study of the Internal Model Control (IMC) method applied to control the speed of a Permanent Magnets Synchronous Motor (PMSM) supplied with a vectorial PWM (Pulse Width Modulation) inverter. The IMC is used together with a predictive state observer in order to estimate the load torque. The experimental results prove that the presence of this observer allows a better control of the actuator behavior while guaranteeing robustness characterized by a good insensitivity with respect the parametric variations.

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Keywords: PMSM, Vector Control, IMC, Predictive Observer, Numeric Implementation.

 


 

go to top   Profit-Based Reconfiguration Methodology for Multi-Feeder Multi-Substation Distribution Network
         by M. Mashhour, M. A. Golkar, S. M. Moghaddas-Tafreshi

         Vol. 5. n. 1, pp. 106-119

 

Abstract - With the liberalization in the electrical energy market and the increase in the capacity level of Distributed Generation (DG), new economic opportunities for Distribution Companies (DISCO) are being created. This paper develops an extended profit model for DSICO's activities in energy and reserve markets. Through this model DISCO can effectively split its generation capacity, produced by the aggregation of DGs' capacities, between the markets so as to maximize its benefits. For a DISCO with some multi-feeder substations, this paper uses a profit-based network reconfiguration for shuffling the loads and DGs among substations and feeders to improve the DISCO's ability to earn from the market environment by affecting the characteristics of DISCO's equivalent units (introduced and extracted by the proposed method in [1]) at the connecting points to upstream network. It also proposes two new algorithms for rejecting unfeasible topologies created during reconfiguration processes. The method is implemented and tested on the IEEE 18-bus primary distribution network. Simulation results show that rational changes in the network topology can promote the DISCO's earnings from the new market activities.

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Keywords: Distributed Generation, Distribution System, Reconfiguration.

 


 

go to top   Modulation Error Observation and Regulation in Use of GA-Based Optimized PWM Fed High Power Synchronous Motors

         by Alireza Rezazadeh, Arash Sayyah

         Vol. 5. n. 1, pp. 120-129

 

Abstract - Off-line optimal PWM is preferred to use in synchronous motors, in the range of several mega watts which operated at low switching frequencies, to reduce the switching losses and undesired frequency harmonic components. But produced transients in such PWM commands, restricts the use of such pulses. In this paper, considering the feed-forward structure of PWM modulators, it is attempted to compensate the undesired transients due to modulation-error that may cause high over-currents. A laboratory 80kW setup is used to emulate the experiments. Two-point voltage source IGBT based inverter is used, and operated at low switching frequencies to emulate GTO-based inverters that are generally used to supply motors in this power range.

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Keywords: Optimal PWM, Genetic Algorithm, Modulation Error, Model Identification, Synchronous Motor.

 


 

go to top   FDTD Simulation of Voltage Distribution in Transformer Winding under VFTO Phenomena
         by J. Shakeri, A. H.Abbasi, A. A. Shayegani, H. Mohseni

         Vol. 5. n. 1, pp. 130-137

 

Abstract - In this paper, the authors investigate the evaluation of FOC, DTC and DPC strategies applied to a Variable Speed Wind System (VSWS) based on a DFIG. A comparative analysis of the three controls is performed, in healthy and faulty grid conditions: balanced and unbalanced small voltage dips and grid frequency disturbances. The study emphasizes the limitations introduced by the approximations usually assumed to simplify the design of these control strategies. The influence of these hypotheses is analysed through of the specific wind turbine quantities like generated active and reactive power, electromagnetic torque and currents. Simulation results are provided to illustrate the effectiveness of the approach.

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Keywords: VFTO Phenomenon, MTL Model, Transformer Winding, FDTD Method, Voltage Distribution.

 


 

go to top   Overvoltages Study During Three-Phase Transformer Energization Using Artificial Neural Network
         by A. Ketabi, I. Sadeghkhani, R. Feuillet

         Vol. 5. n. 1, pp. 138-147

 

Abstract - In a small power system that appears in an early stage of a black ‎start of a power system, an overvoltage could be caused by core ‎saturation on the energization of a three-phase transformer with residual flux. ‎Such an overvoltage might damage some equipment and delay ‎power system restoration. A new approach based on worst case determination is proposed to reduce time-domain simulations. Also, an artificial neural network (ANN) is addressed in this work, in order to estimate the temporary overvoltages (TOVs) due to three-phase transformer ‎energization. In proposed methodology, Levenberg–Marquardt ‎second order method is used to train the multilayer perceptron. ANN Training is performed based on equivalent circuit parameters of the network; thus trained ANN is applicable to every studied system. The ‎developed ANN is trained with the worst case of the switching condition and remanent flux, and ‎tested for typical cases. The simulated results for a partial of 39-bus New England test system, ‎show that the proposed technique can estimate the peak values and ‎durations of switching overvoltages with good accuracy.

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Keywords: Artificial Neural Networks, Harmonic Index, Power System Restoration, Temporary Overvoltages, Three-Phase Transformers Switching‎.

 


 

go to top   A Practical Bearing Fault Diagnosing System Based on Vibration Power Signal Autocorrelation
         by Alireza Sadoughi, Mehrdad Jafarboland, Soheil Tashakkor

          Vol. 5. n. 1, pp. 148-154

 

Abstract - Bearings are important parts of rotating machines. To avoid unscheduled outputs due to bearing defect, it is important to detect an upcoming fault as soon as possible. Fault in a great number of bearings commences from a single point defect. Therefore; research on this category of faults has shared a great deal in predictive diagnosis literature. Single point defects cause certain frequencies, which appear in vibration spectrum. Traditionally, data extracted from frequency spectrum are used to identify damaged part. Because of impulsive nature of fault strikes, and complex modulations present in vibration signal, a simple spectrum analysis may result in erroneous conclusions. When a shaft rotates at constant speed, strikes due to a single point defect repeat at constant intervals. Each strike shows a high energy distribution around it. This paper considers the time intervals between successive impulses in auto-correlated vibration power signals. The most frequent interval between successive impulses determines the period of defective part. This period is related to fault frequency. According to the proposed method, an apparatus is designed. Introducing the structure of this apparatus, the circuits, hardware, and software is one of the objectives of this paper. The apparatus has shown its effectiveness in laboratory and field tests.

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Keywords: Apparatus, Autocorrelation, Bearing, Fault Diagnosis, Intelligent, Vibration.

 


 

go to top   Investigation on Dynamic and Steady State Performance of Axial Flux Hysteresis Motors Considering Rotor Configuration
         by M. Modarres, A. Vahedi, M. R. Ghazanchaei

          Vol. 5. n. 1, pp. 155-159

 

Abstract - Axial flux hysteresis motor (AFHM) is self-starting synchronous motor that uses the hysteresis characteristics of magnetic materials. It is known that the magnetic characteristics of hysteresis motor could be easily affected by variation of airgap length and structure dimensions. In conventional AFHM the hysteresis ring holder is placed between the hysteresis ring and stator. In this configuration holder is the major source of dynamic torque but on synchronous speed that induction torque reduce to zero is such as airgap. So, effective airgap length is increased in this Topology and the steady state output torque, efficiency and power factor is decreased. Regarding this issue, in this study effect of holder and hysteresis ring displacement on dynamic and steady state quantities of AFHM is investigated. Meanwhile, simulation of AFHM in both configurations is done in order to extract the output values of motors using 3D Finite Element Model. Finally, an experimental set up is provided and the output values of AFHM in both configurations are measured. There is a reasonably agreement between experimental and simulation results.

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Keywords: Axial Flux Hysteresis Motor, Finite Element Model, Complex Permeability.

 


 

go to top   Development and Implementation of High-Performance Variable Structure Tracking for Induction Motor Using Fuzzy-Logic Controller
         by M. Zerikat, S. Chekroun, A. Mechernene

         Vol. 5. n. 1, pp. 160-166

 

Abstract - The paper deals with the design and the implementation of fuzzy control system for robust tracking of induction motor drive operating in a high-performance drives environment. The introducing of fuzzy logic in control system helps to achieve good dynamic response, disturbance rejection and low sensibility to plant parameter variation the AC motor drive. It also assures precise trajectory tracking with the prescribed dynamics. In the proposed approach of this paper, by using a simple and flexible structure of a fuzzy controller, the FLC controller is implemented using the field oriented control technique as it provides better control of motor torque with dynamic performance. In order to verify the performances of the proposed observers and control algorithms and to test behavior of the controlled system, numerical and real experiments are achieved. Simulation and experimental results have shown excellent tracking performance of the proposed control system and achieve convincingly demonstrated the usefulness of fuzzy-logic controller in high-performance drives with uncertainties.

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Keywords: Induction Motor, Field Oriented Control, Fuzzy Logic Controller, Speed Observer, Variable Structure, Robustness.

 


 

go to top   A Dummy Load for Tester Stand-alone Photovoltaic 5 kWp with the Maximum Power Tracking System
         by Narin Watanakul, Sing thong Pattanasethanon

         Vol. 5. n. 1, pp. 167-172

 

Abstract - Power generation system with solar cell according to Phra Ratchadamri (Royal) project has been implemented at border patrol schools and government health stations covering approximately a total of 730 stations throughout Thailand. The work has designed and built a dummy load Prototype. Dummy load can adjust the load current when excess energy dumped to dummy load, the maximum power tracking load change according to sun irradiation. The test is with size 5 kWp panel type amorphous system. The analysis is made to assess system performance produced by the cell referenced with the International Agency Photovoltaic Power Systems TASK 2 - Performance, Reliability and Analysis of Photovoltaic Systems (IEA PVPS Task 2). Dummy load can be used as a tool to test performance with the PV system produces electricity for the full range of stations to be installed before the new use. PV Cell system helps to ensure that electric power can pay for full range. This study can be used as reference values to the design and development of solar energy systems equipment in the future.

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Keywords: Dummy load , AC Chopper, PV Stand-alone system(SAS) , Performance Ratio(PR).

 


 

 

International Review of Electrical Engineering - Papers- Part B

 

go to top   The Application of Voltage Sags Pattern to Locate a Faulted Section in Distribution Network
         by H. Mokhlis, H. Y. Li, A. R. Khalid

         Vol. 5. n. 1, pp. 173-179

 

Abstract - This paper proposes an alternative automated fault location algorithm to locate a faulted section in distribution network using only voltage sag data monitored at the primary substation. A pattern matching approach between simulated voltage sag and measurement is proposed to identify the faulted section. The degree of matching between the actual and simulated one is then used to rank the possible faulted sections. The algorithm has been tested on an actual urban underground distribution network feeder. The results show that most faulted sections can be located by the first attempt. All remaining faulted sections can be found by the second attempt.

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Keywords: Distribution Network, Faulted Section, Voltage Sags, Pattern Matching.

 


 

go to top   A Simple Approach to Construct the Bayesian Network Associated with Electric Transmission Systems
         by A. Ebrahimi, T. Daemi

        Vol. 5. n. 1, pp. 180-184

 

Abstract - In this paper a simple approach to construct the Bayesian Network (BN) associated with an electric transmission system is presented. The proposed approach for constructing the BN, that is applicable in large systems, is based on the capability of the BN to learn from data. The required training data is provided by the state sampling method of Monte Carlo (MC) simulation where Importance Sampling (IS) scheme is employed for a more accurate impact analysis of transmission system components that have relatively low failure probabilities.
In this study, assuming independent outage events, a general structure is considered for BN which is then modified by using the Mutual Information (MI) of variables. Therefore the BN associated with the system is constructed easily and it is not required to use the common structure learning algorithms or use from the physical topology or cause-effect relations that for complex and large systems are intractable. The derived BN is used for a detailed reliability assessment of the transmission system based on the loss of load and component outage probabilities. The proposed method is applied to IEEE Reliability Test System (IEEE-RTS) that its results show the validity and efficiency of the approach.

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Keywords: Bayesian Network, Importance Sampling, Reliability, Transmission System.

 


 

go to top   Controlling Unscheduled Flows Using Fuzzy Set Theory and Genetic Algorithms
         by Gulcihan O. Dag, Mustafa Bagriyanik

         Vol. 5. n. 1, pp. 185-193

 

Abstract - Controlling of undesired circulation of power flows in the de-regulated power systems is one of the most important problems for a power system operator. Although he/she may have some tools such as phase-shifting transformers to take remedial actions they may not be sufficient for system-wide actions. The problem gains more importance when an interconnected power transmission system is operated at or close to its power-carrying limits. Thus, the problem of the prevention and/or control of loop flows (also called unscheduled power flow) need be solved efficiently and fast. In this paper, a fuzzy set theory based procedure using genetic algorithm is proposed for the solution of this problem. The constraints and objectives are handled in a fuzzy environment and the resulting optimization problem is solved using genetic algorithm. The proposed method is applied to the IEEE 30 and 118 bus test systems and the results are presented.

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Keywords: Fuzzy Set, Fuzzy Decision-Making, Genetic Algorithms (Gas), Interconnected Power Systems, Loop Flows, Unscheduled Flows, Power Flow.

 


 

go to top   Comparison and Combination of Shuffled Frog-Leaping Algorithm and K-Means for Clustering of VCAs in Power System
         by F. Rameshkhah, M. Abedi, S. H. Hosseinian

          Vol. 5. n. 1, pp. 194-204

 

Abstract - Voltage Control Areas, is one of the main concepts in both voltage stability assessment and control. Employing an artificial intelligent system, for detecting VCAs and identifying the prone buses is an important part of a reasonable response to the need for real time monitoring and control of power system in emergency cases of voltage instability appearance. For this purpose the database of training data, contains the simulation results due to wide range of various emergency cases. A clustering process which provide finite clusters belong to VCAs, in addition of a classification function based on the provided clusters, are the main stages to prepare AIS for automatic VCA identification. In this paper a novel data clustering method based on Shuffled Frog Leaping Algorithm is presented to cluster the VCAs in excessive emergency cases in electric power system. In present study the application of SFLA in data clustering is also compared with the most popular analytic algorithm of clustering, K-means, and also the hybrid SFLA and K-means method are used for better clustering performance. The advantage of using the data points from the same under clustering database as initial positions for some frogs is illustrated too. Numerical results are presented for IEEE 14-bus test system and two standard test data sets. The comparative results show the effectiveness of proposed algorithms.

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Keywords: Voltage Control Area, Participation Factors, Data Clustering, Evolutionary Algorithms, Shuffled Frog Leaping Algorithm.

 


 

go to top   Probabilistic Evaluation of Small-Signal Stability of Power Systems with Time Delays
         by Saffet Ayasun, Chika O. Nwankpa

         Vol. 5. n. 1, pp. 205-216

 

Abstract - This paper presents a probabilistic approach to evaluate the small-signal stability of power systems in the presence of time delays. An exact method is proposed to determine the functional relationship between delay margin for stability and system parameters. The delay margin is modeled as a random variable and its probability density function (PDF) is estimated based on the PDF of the load using a Monte Carlo simulation approach. The probability of stability for a given time delay is determined using the estimated PDF of the delay margin. For illustration purposes, the method is applied to a single-machine-infinite bus (SMIB) power system with an exciter. The probability of stability for a given time delay is computed and their sensitivity with respect to various system parameters is investigated. It is found that the probability of stability values reduce with increasing the load uncertainty resulting in a less stable system while the stability performance could be improved by increasing the generator transient reactance. Moreover, the effect of generating damping on the probability of stability is relatively complex and larger damping may not result in a more stable operation.

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Keywords: Power System, Small-Signal Stability, Time Delay, Delay Margin, Probability of Stability.

 


 

go to top   Optimal Voltage/Reactive Control By an Improve Harmony Search Algorithm
         by A. H. Khazali, A. Parizad, M. Kalantar

         Vol. 5. n. 1, pp. 217-224

 

Abstract - This paper presents an improved harmony search algorithm for the optimal reactive/voltage control problem. Optimal reactive/voltage control is a mixed integer, nonlinear optimization problem which includes both continuous and discrete control variables. The proposed algorithm is used to find the settings of control variables such as generator voltages, tap positions of tap changing transformers and the amount of reactive compensation devices to optimize a certain objective. The objectives are power transmission loss, voltage stability and voltage profile which are optimized separately. In the presented method, the inequality constraints are handled by penalty coefficients. The study is implemented on the IEEE 30 Bus system and the results are compared with other algorithms such as harmony search algorithm (HSA) and particle swarm optimization (PSO).

Copyright © 2010 Praise Worthy Prize S.r.l. - All rights reserved

 

Keywords: Optimal Reactive/Voltage, Harmony Search Algorithm, Optimization, Loss minimization.

 


 

go to top   Fuzzy-Statistical Assessment of a Global Power Quality Index for Competitive Electricity Market
         by Ali Salarvand, Behzad Mirzaeian Dehkordi, Mehdi Moallem

         Vol. 5. n. 1, pp. 225-233

 

Abstract - Restructuring and deregulation in power system market result in growing attention to power quality (PQ) issues. Along with the increment of disturbing loads in the power system, the effect on network that is brought by the power quality problems, become increasingly serious. Existing PQ indices are usually isolated and lack the cost impact of bad power quality. This paper presents a method based on mathematical statistics and fuzzy logic to obtain a quantitative global index for PQ evaluation and pricing in competitive electricity market. Taking into account the cost of PQ phenomena with their relative weights in this index, it can be used as a PQ measure in electricity tariffs by utility companies. The method provides some basis for contract’s subscribing in the future. Advantage of the method is its consistency which gives a useful and unique measure of quality of electricity for both supply side and customer side. The proposed algorithm has been implemented on real measured data of a distribution network. Results show the capability of this method to obtain an accurate measure for PQ evaluation and pricing.

Copyright © 2010 Praise Worthy Prize S.r.l. - All rights reserved

 

Keywords:  Electricity Market, Fuzzy Logic, Global Power Quality Index.

 


 

go to top   A New Method for Assessment of Voltage Stability in Transmission and Distribution Networks
         by M. Eidiani

         Vol. 5. n. 1, pp. 234-240

 

Abstract - Voltage instability and collapse has been the subject of an increasing body of research over the past few years. In this paper, we proposed a new method of assessing static voltage stability in transmission and distribution networks. The proposed method (PM) is fast, accurate and robust. The expanded Newton-Raphson-Seydel (NRS) and Down-Hill (DH) algorithms are used in PM. Moreover, the elimination of the trigonometric terms in power flow equations and Jacobian matrix, will improve the convergence of PM algorithm. Standard CPF, CPF-GMRES and expanded NRS methods are compared to PM. These algorithms are tested on 350 bus transmission and 1316 bus distribution networks.

Copyright © 2010 Praise Worthy Prize S.r.l. - All rights reserved

 

Keywords: Voltage Stability, CPF, GMRES, NRS.

 


 

go to top   An Efficient Unified Methodology for Steady-State Security Assessment of Electric Power Interconnection
         by D. P. Popović

        Vol. 5. n. 1, pp. 241-249

 

Abstract - This paper presents the relevant aspects of an efficient unified methodology for steady-state security assessment of electric power interconnection, in conditions of deregulation of electric power market. Its characteristics are enabled the unification of corresponding computer program, autonomy and uniformity of security analysis, as well as their fast and successive realization, which have a great practical importance. The main characteristics and possibilities of proposed methodology, especially in context of transfer capability evaluation, are demonstrated on the example of the existing electric power interconnection in the Balkan area.

Copyright © 2010 Praise Worthy Prize S.r.l. - All rights reserved

 

Keywords: Efficient Unified Methodology, Steady-State Security Assessment, Deregulated Environment, Balkan Interconnection.

 


 

go to top   Experimental Studies of a Scaled-Down TSC Prototype for Voltage Regulation and Compensation
         by Ayetül Gelen,Tankut Yalcinoz

         Vol. 5. n. 1, pp. 250-256

 

Abstract - In this paper, a prototype of Thyristor Switched Capacitor (TSC), which is one of shunt Flexible AC Transmission Systems (FACTS) devices, has been developed. The design and testing of TSC are verified in the Power Systems Research Laboratory at Nigde University. The TSC device is studied at two-bus, three-bus and single machine infinite bus (SMIB) systems for three-phase static load conditions. The effects of the TSC device on load voltages are also analyzed. The experiment results show that significant improvement on reactive power compensation and voltage regulation is achieved by using TSC.

Copyright © 2010 Praise Worthy Prize S.r.l. - All rights reserved

 

Keywords: Compensation, Flexible AC Transmission Systems (FACTS), Thyristor Switched Capacitors (TSC), Voltage Regulation.

 


 

go to top   Study of Lead-Acid Battery Charging by Using Sinusoidal Current
         by Liang-Rui Chen, Shing-Lih Wu, Tsair-Rong Chen, Wen-Ren Yang

         Vol. 5. n. 1, pp. 257-263

 

Abstract - This paper aims to explore the Lead-acid battery charging performance by the analysis of the AC impedance. The experiments show that the optimal charging frequency is within the range from the resonant frequency to the minimum AC impedance frequency. In such a condition, the Lead-acid battery charging time and charging efficiency are improved about 13.8% and 27.5%, respectively.

Copyright © 2010 Praise Worthy Prize S.r.l. - All rights reserved

 

Keywords: Minimum AC Impedance, Lead-Acid Battery.

 


 

go to top   Reliability Study of Supercapacitor Based on the Activated Carbons by Fault Tree Analysis
         by Kais Brik, Faouzi Ben Ammar

        Vol. 5. n. 1, pp. 264-271

 

Abstract - In this paper the authors propose a reliability approach analyzing the degradation of supercapacitor based on the activated carbons and organic electrolyte technology. This approach uses the experimental measurements to develop an electric equivalent circuit model and uses the reliability analysis tools to evaluate the lifetime of the supercapacitor. The causal tree analysis is adopted to present the different possible combinations of the events involving the supercapacitor degradation. Then, the experimental identification of the circuit parameters variation intervals according to each degradation mode is presented. Therefore a diagnosis system allowing the description of failure modes and degradation states of the supercapacitor is developed.

Copyright © 2010 Praise Worthy Prize S.r.l. - All rights reserved

 

Keywords: Supercapacitor, Reliability, Degradation, Causal Tree Analysis, Fault Tree Analysis.

 


 

go to top   Activated Carbon Based Electrodes in Commercial Supercapacitors and their Performance
         by Vasile V. N. Obreja, Adrian Dinescu, Alexandru C. Obreja

         Vol. 5. n. 1, pp. 272-280

 

Abstract - Investigation of commercial supercapacitor cell samples indicates a specific capacitance of maximum 25 -30 F/g whereas in the literature more than 100 F/g has been reported for experimental cells. Activated (nanoporou carbon based electrodes on aluminum foil substrate extracted from the assembled coil of a typical supercapacitor cell of high performance at this time have been analyzed. The electrode thickness can reach 200 m and the metallic foil substrate 30 m. SEM images have indicated carbon particles with a size in the range of 0.1 – 10 m as the main constituent. At higher magnification, thin fibers attributed to polymer binder have been distinguished. The binder material may cover part of the particle surface and lower exposed area at the interface with the electrolyte (or lower specific capacitance) is available for the electrode. Mesopores of 10 - 20 nm and higher size are not exhibited in large number at the particle’s surface and most of the surface is free of such pores. Existing micropores (size up to 2 nm) have not been revealed with the available magnifications and their contribution to the specific capacitance depends on the penetration of electrolyte ions. Activated carbon of high specific capacitance demonstrated in experimental cell electrodes, reported in the literature may be not yet cost effective for its use in commercial supercapacitors.

Copyright © 2010 Praise Worthy Prize S.r.l. - All rights reserved

 

Keywords: Ultracapacitor, Specific Capacitance, Specific Stored Energy, Activated Carbon, Supercapacitor Cell.

 


 

go to top   A New Readout Circuit Structure for SAR Satellite Imaging Sensors

         by Gholam Ali Rezai-Rad, Gholamreza Akbarizadeh

         Vol. 5. n. 1, pp. 281-290

 

Abstract - In this paper we propose and design a new CMOS readout circuit for high-resolution Synthetic Aperture Radar imaging system. This CMOS readout circuit is designed for Gallium Nitride detector with PV type and it is simulated in transistor level and its physical layout is also drawn. The detector of this circuit works in Microwave-Radar length. This structure can simultaneously provide high (azimuth) resolution and wide coverage (swath) and it has Smart Multi Aperture Radar technology. Substance of material in this circuit is GaN. Recent development in semiconductor technology, specifically Gallium Nitride, allows handling significantly higher amount of peak power and be this prove to be an attractive solution to increase the echo window length without sacrificing average transmit power and SNR. To provide stable bias voltage across the photo detector diode, we use a feedback structure with current mirrors in our scheme, while mirroring the diode current to an integration capacitor. In this circuit, the integration capacitor is placed outside of the unit pixel. This technique used in the circuit structure, reduces the pixel area and allows integrating the current on larger capacitance for larger charge storage capacity and dynamic range. One of the greater properties of current feedback in this structure is that, very low (ideally zero) input impedance is achieved. The unit-cell which we designed and proposed contains just nine MOS transistors and occupies 30 micro meters by 30 micro meters area in a 0.35 micro-meter CMOS process. This circuit has 10 MHz maximum readout speed, a linearity of 99.55%, a power dissipation of 150nW for 1 cell and 50mW for test chip, a voltage swing of 2.8v, an injection efficiency of 100% and provides a maximum charge storage capacity of 1×107 electrons. This readout circuit has 1pF off-pixel integration capacitor for a 3.3 V power supply. The chip layout of this circuit was designed in a 0.35 µm standard N-well CMOS process which shows that each Pixel of this circuit occupies 1.95mm2 of silicon area. This portable chip is very useful to use on SAR satellites.

Copyright © 2010 Praise Worthy Prize S.r.l. - All rights reserved

 

Keywords: Synthetic Aperture Radar, Readout Circuit, Readout Electronics, SAR Imaging Systems, Satellite.

 


 

go to top   Improve RADAR Waveform Metrics Using Lorenz Based Method

         by J. Pourahmadazar, H. Shirzad, Ch. Ghobadi , J. Nourinia

         Vol. 5. n. 1, pp. 291-303

 

Abstract - The problem of insulation damage due to partial discharges of low magnitudes has not yet attracted much attention. Indications of possible damage and long term effects of accumulated partial discharges of low magnitudes are evident from published literature. In this paper, the possibility of existence of such phenomena is investigated with different insulation systems namely small air gaps under point-plane electrode arrangement, gas-gap in a coaxial geometry consisting of a 10:90 gas mixture of SF6 and N2 gases and paper-oil insulation of a power transformer. It is observed that random discharges below inception voltage do exist. Such discharges are studied and their impact on insulation is discussed. Experimental evidence is offered to substantiate that discharges change from the pulse-type to a pulse less-type as the gap becomes larger in case of air. Phenomena of PD below or in the vicinity of inception voltages may help in better understanding of the mechanism of small current flow at relatively low voltages and may help in development of better dielectric materials and insulation systems for high voltage applications.

Copyright © 2010 Praise Worthy Prize S.r.l. - All rights reserved

 

Keywords: Chaos, Radar, Lorenz, Waveform.

 


 

go to top   Optimal Feedback Control Approach to Pattern Signal Generation with Chua-Matsumoto’s Chaotic Oscillator
         by K. Bousson, Sandra C. R. Antunes

         Vol. 5. n. 1, pp. 304-310

 

Abstract - The present paper deals with the active control of chaotic systems. The main contribution is the use of a simple linear optimal robust control method to drive chaotic systems to generate specified pattern signals intended to be used as carriers for communication matters, contrarily to existing methods that use complex and not necessarily robust nonlinear control laws. The robustness of the control law stems, on one hand, from an extended version of the linear quadratic regulator (LQR) method, and on the other by resorting to an optimal linear approximation of the chaotic oscillator model. Chua-Matsumoto’s chaotic oscillator is used for that purpose because of the simplicity of its underlying electronic circuit. Simulation results show that the method enable us to stabilize the chaotic system and to track explicit signals in a very short time. The interest of these results is that the method may be used for effective generation of carrier signals of various kinds of patterns and frequencies with only one oscillator which has to be controlled by means of the method presented in the paper.

Copyright © 2010 Praise Worthy Prize S.r.l. - All rights reserved

 

Keywords: Chua-Matsumoto’s Chaotic Oscillator, Optimal Control, Active Control of Chaotic Oscillators, Carrier Signal Generation.

 


 

go to top   Modeling of Protective System Failures to Operate for Reliability Studies at the Power System Level using Stochastic Point Processes
         by Carlos J. Zapata, Daniel S. Kirschen, Mario A. Rios, Alvaro Torres

         Vol. 5. n. 1, pp. 311-316

 

Abstract - This paper present a method for representing protective systems in reliability studies of the power system which condenses at the circuit breakers of the protection zone the effect of protective component failures, protective scheme configuration and preventive maintenance strategies. It combines the modeling of failure and repair processes using stochastic point process theory and a procedure of sequential Monte Carlo to artificially generate the operating sequence of the protective system and for computing the probabilities of failure to operate seen at the circuit breakers. Its main advantage is that it supports the use of time varying failure rates, a feature not offered by the other methods that have been traditionally applied for this task. On the other hand, its main disadvantage is the long computational time required by the simulation.

Copyright © 2010 Praise Worthy Prize S.r.l. - All rights reserved

 

Keywords: Aging, Monte Carlo Simulation, Power System Reliability, Protective Relaying, Stochastic Point Processes.

 


 

go to top   Protection of Lightning Disturbances on MV Underground Cable
         by Michael A. Omidiora, Matti Lehtonen

         Vol. 5. n. 1, pp. 317-326

 

Abstract - This paper studies the performance of an MV underground cable due to a nearby lightning discharge. The effects of lightning stroke location, resistivity of the soil and underground cable configurations are considered. The results of the numerical computation show how electric field intensity and potential distribution vary with the factors mentioned above. Lightning protection of medium voltage underground cables is examined. Simulation of an underground cable with a shield wire is made to investigate protection against lightning discharges around the cable. The performance of the protection scheme is investigated with the Finite Element Method (FEM) considering different soil structures and resistivities. Finally, the failure rates of the underground cable with and without a shield wire are compared based on the real lightning statistics in Finland. It is expected that the results will further understanding of the need for lightning protection on medium voltage underground cables.

Copyright © 2010 Praise Worthy Prize S.r.l. - All rights reserved

 

Keywords: FEM (Finite Element Method), Lightning Discharge, Ground Flash Density (GFD), Electric Field Intensity, Underground Cable (UC), Overvoltage, Soil Resistivity, Shield Wire (SW).

 


 

go to top   Tele-Reading Device of an Analogical Meters Index for Energy
         by I. Jabri, T. Battikh, Y. Abdellaoui

         Vol. 5. n. 1, pp. 327-334

 

Abstract - After presenting the global energetic context and the need to develop a measure device of energy consumption exploiting the ICT environment, we present a remote reading device of analogical meter index using image processing techniques. The tele-reading device of meter index is composed of an acquisition system, digitization and images pre-processing. The extraction and recognition of figures caught a particular attention and was realized by exploiting various techniques including the recognition that we have developed and which is based on the characterization notion by the associated cavities. Development and exploitation prospects of the device are presented within a framework of an industrial partnership.

Copyright © 2010 Praise Worthy Prize S.r.l. - All rights reserved

 

Keywords:  Index Tele-Reading, Remote Reading, Meter, Image Processing, Pattern Recognition.

 


 

go to top   Inductance Measurement and Magnetic Flux Density Analysis of Modular Toroidal Coil Using FEM Approach Applicable to Tokamak Reactors
         by M. R. Alizadeh Pahlavani, A. Shiri, H. A. Mohammadpour, A. Shoulaie

         Vol. 5. n. 1, pp. 335-345

 

Abstract - In this paper, equations for calculation of the self and mutual inductances of the Modular Toroidal Coil (MTC) applicable to Tokamak reactors are presented. The MTC is composed of several solenoidal coils (SCs) connected in series and distributed in the toroidal and the symmetrical form. These equations are based on the Biot-Savart and Neumann’s equations, respectively. The numerical analysis of the integrations resulting from these equations is solved using the extended three-point Gaussian algorithm. Comparing the results obtained from the numerical simulation with the experimental and the empirical results confirms the presented equations. Furthermore, the comparison of the behavior of these inductances, when the geometrical parameters of the MTC are changed, with the experimental results shows an error of less than 0.5%. The behavior of the inductance of the coil indicates that the optimum structure of this coil with the stored magnetic energy as the optimization function is obtained when the SCs are located on the toroidal planes. At the end, the Finite Element Method (FEM) approach is employed to present an algorithm to study the three dimensional leakage flux distribution pattern of the coil and to draw the magnetic flux density lines of the MTC. The presented algorithm, due to its simplicity in analysis and ease of implementation of the non-symmetrical and three dimensional objects, is advantageous to the commercial software such as ANSYS, MAXWELL, and FLUX.

Copyright © 2010 Praise Worthy Prize S.r.l. - All rights reserved

 

Keywords:  Modular Toroidal Coil (MTC), Finite Element Method (FEM), Self And Mutual Inductances, Biot-Savart And Neumann’s Equations, Extended Three-Point Gaussian Algorithm, Tokamak Reactors.

 



 
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