International Review on Modelling and Simulations - Papers (Part A)
Optimization of Augmented Rails in Augmented-Parallel Railgun by Augmented-LagrangianGenetic Algorithm
Vol. 4. n. 2, pp. 458-466
Abstract - Increase of inductance gradient is one of the most common methods for increasing applied force to projectile. Increase of inductance gradient is reachable by using augmented rails. Essentially, the inductance gradient is determined by current density in rails and projectile. If we change geometry and position of augmented rails, the current density and the inductance gradient will be changed. One of factors that limits variation domain of rails geometry and position is the tolerable current of rails. In this paper, we have obtained analytical formulas for the maximum current density and the inductance gradient in terms of augmented rails position and injection current using the results that have been obtained by 2-D finite-element method. By these formulas and augmented-lagrangian genetic algorithm(ALGA)optimization method, we determined the optimum position of augmented rails for the maximum inductance gradient. Tolerable current is bonded as an inequality constraint in ALGA.
Keywords: Augmented-lagrangian genetic algorithm(ALGA), optimization, railgun, 2-D finite-element method (FEM).
Input-State Feedback Linearization Control of Three-Phase Dual-Bridge Matrix Converters Operating Under Unbalanced Source Voltages
Vol. 4. n. 2, pp. 467-477
Abstract - This paper formulates for the first time a closed-loop current controller for matrix converters operating under generalized unbalanced source voltages. Under such conditions, the control strategy is developed with the aim to provide sinusoidal input/output waveforms free of low-order harmonics and perform an accurate regulation of the input displacement factor. First, the appropriate references of the dq-axis components of line currents are computed to Cancel out the low-frequency power ripple caused by unbalances and control the reactive power component at the input side of the converter. Second, by an applying input-state feedback linearization, the line current dynamics (active and reactive currents) are decoupled and linear control-laws are designed to achieve perfect and convergent tracking errors. Finally, numerical simulations carried out on a dual-bridge topology confirm the effectiveness of the proposed approach and theoretical development; the following attractive features are recorded:
- The line currents drawn by the converter are sinusoidal with low harmonic distortion and fast dynamic response.
- The output waveforms are balanced, sinusoidal, and free of low-order harmonics.
- The converter shows also a load-independent unity input displacement factor operation, as well as a leading reactive power operation capability.
Keywords: Matrix converters, Unbalanced source voltages, Feedback linearization, SVM, UIPF.
A New Switching Technique and Optimum Computation of DC Sources in Three-Phase Multilevel Inverter
Vol. 4. n. 2, pp. 478-484
Abstract - The purpose of this paper is to introduce a new switching technique to eliminate specific higher order harmonics of output voltage in three-phase multilevel inverter with unequal dc voltage sources. In ordinary switching techniques, switching times are selected as a way to produce the output voltage waveform which is close to the fundamental sine wave. In three-phase inverter, triple order harmonics will not appear in line to line voltage. The proposed switching technique is derived by adding a triple order harmonic to fundamental sine wave. Moreover, a concept is proposed to select the proper values of the dc voltage sources to control the output voltage by dc voltages regulation. Selections of proper DC voltage sources with proposed switching technique are exhibited for cascaded multilevel inverters, in general. Computation results show that the proposed method can eliminate the higher number of harmonics from output voltage. The proposed switching technique only can be used for three-phase inverters. Also, for applications that require a waveform containing triple order harmonics, like some operation states of Dynamic Voltage Restorer (DVR), this technique can't be used.
Keywords: Multilevel Inverter, Triple Order Harmonics, Switching Techniques, Harmonic Elimination.
Optimal Design of Passive Filters for Voltage Source Inverters
Vol. 4. n. 2, pp. 485-492
Abstract - One of the most important problems in the power systems are harmonics which have many. In the Voltage Source Inverters (VSI), the output voltage waveform is rectangular. That is the reason why there are many harmonics in the output voltage. Although in SPWM switching method, the harmonics can be transferred to higher frequencies, the output waveform is still rectangular. To eliminate harmonics and to convert the output voltage to be a sinusoidal waveform, a passive filter can be used. In this paper, how to design a LC passive filter for voltage source inverters and also the effective parameters on its operation is presented that among them load type, load power factor, output frequency and output current can be mentioned. There are some limitations to choose the filter parameters such as output voltage variations, input current increasing and the harmonics reduction of the output voltage. Filter parameters can be determined by equations considering these limitations. Two methods are introduced to obtain filter parameters values which are approximate and exact methods. Those values in approximate method can be obtained by plotting a number of curves and in exact method by definition an objective function and its optimization with GAMS software. Finally, to verify the designing results, a kind of filter for a single phase inverter is modeled and for two different types of load is simulated in PSPICE. The effects of mentioned parameters have been investigated in these simulations as well.
Keywords: Passive Filter, Voltage Source Inverter, Voltage Harmonics, Load Type and PSPICE.
Comparison Performances of Asymmetric Multilevel Inverters in the Maximum Voltage Rating of Power Electronic Devices
Vol. 4. n. 2, pp. 493-500
Abstract - The paper presents comparison performances of Asymmetric Cascaded Multilevel Inverter (ACMLI) in the maximum voltage rating of power electronic devices, to find which the DC voltage progression that has the best performance. The performances have been investigated based upon in amplitude, Total Harmonic Distortions (THD), and frequency spectrum in the binary (order-2) DC voltage progression, trinary (order-3), equal interval and sine quantization. A single phase ACMLI in the five H-bridges structures simulated by Matlab has been used to verify these performances. The comparisons show that the performance of sine quantization DC voltage progression have highest output voltage, low total harmonics distortions, amplitude of DC voltage realistically and good frequency spectrum, making it possible to overcome the limitation of maximum voltage rating of power electronic devices.
Keywords: Asymmetric Multilevel Inverter, Voltage Rating, Sine Quantization, Amplitude, Frequency Spectrum, Total Harmonic Distortion.
Computer Aided Design Tools in RF Power Amplifier Design
Vol. 4. n. 2, pp. 501-506
Abstract - Modeling, simulation and implementation of RF power amplifier system including driver, main power amplifier, electromagnetic models of resonating inductor, RF choke, output balun have been performed for industrial, scientific, and medical (ISM) applications at the high frequency (HF) range. Spice models of the components have been obtained using electromagnetic simulator and embedded in non-linear circuit simulator. The complete RF amplifier system simulation has been done using time domain non-linear circuit simulator in conjunction with electromagnetic simulator. RF power amplifier critical design parameters such as balancing between push-pull pair is analyzed with the electromagnetic simulator at the board level. The simulation results and measurement results have been compared against various load conditions. Agreement has been observed on all the values.
Keywords: Non-linear, circuit simulator, electromagnetic simulator, RF, amplifiers.
Detailed Analysis of Cascaded Multilevel Converter Based STATCOM
Vol. 4. n. 2, pp. 507-516
Abstract - In this paper an exact mathematical analysis of operating characteristics of static synchronous compensators (STATCOM) based on cascaded multilevel converters (CMC) is presented. A detailed analysis of voltages and currents is presented and equations describing the performance of circuit are derived. In a special case, the calculated results obtained from the analysis will be compared with the results obtained from the STATCOM simulation using MATLAB/SIMULINK software. Finally, active power interchange between the STATCOM and the power system will be considered. The results are used in the optimization of STATCOM behavior.
Keywords: STATCOM, CMC, reactive and active power compensation.
Steady-State Electromagnetic and Thermal Modelling of an Induction Motor Under Healthy Operation and Under Broken-Bar Fault
Vol. 4. n. 2, pp. 517-524
Abstract - The steady-state electromagnetic and thermal performance of an induction motor under healthy operation and under broken-bar fault are studied using the finite element method. The results are compared and therefore the effect of the fault on the electromagnetic and thermal behavior of the motor is determined. Two different electromagnetic finite element models, one for the healthy and the other one for the faulted operational state of the motor, are used. In both cases the copper and iron losses are calculated by means of two-dimensional time-stepping electromagnetic analysis, taking into consideration the high-order harmonics of the current and flux density respectively. The losses are imported into the respective thermal models as heat sources and the temperature distributions on the thermal models are eventually obtained and compared.
Keywords: Broken Bar, Copper Losses, Finite Element Method, Induction Motor, Iron Losses, Thermal Analysis.
Improved Simulation Strategy for DFIG in Wind Energy Applications
Vol. 4. n. 2, pp. 525-532
Abstract - A detailed computer simulation for interconnecting wind energy system to electric utility is presented. The proposed system consists of four high rating wind turbines each one uses double fed induction generator (DFIG). Two back to back bidirectional PWM inverters are used in the rotor circuit of each DFIG to be interfaced with electrical utility. This computer simulation incorporates a flexible independent control for the active and reactive powers by using field oriented control technique. Also it introduces an effective technique to track the maximum power point of the wind energy system by controlling the pitch angle and rotational speed. Active power is controlled through the direct axis current of the rotor side converter in outer control layer. Reactive power is controlled by the quadrature axis of the rotor side converter. The dc-link voltage of the PWM converter is maintained constant by controlling the direct axis current of the grid side converter. The system shows a stable operation under different operating conditions.
Keywords: DFIG, Induction Generator, Modeling, Wind Energy.
Vol. 4. n. 2, pp. 533-540
Abstract - This paper investigates the effect of linear and nonlinear core losses on the onset of chaotic ferroresonance and duration of transient chaos in an autotransformer and control of these phenomena by applying neutral earth resistance to the system grounding. The magnetization characteristic of the transformer is modeled by a single-value two-term polynomial. The nonlinear core loss is modeled by a third order power series in voltage with nonlinearities in core loss included, four effects are clear: (i) onset of chaos at larger values of open phase voltage, (ii) shorter duration of transient chaos,(iii) less susceptibility to ‘jump’ phenomena and (iv) effect of neutral resistance on controlling of ferroresonance phenomena. It is also shown that nonlinear core losses also can cause ferroresonance drop out.
Keywords: Linear and Nonlinear core losses, Chaos Control, Bifurcation Diagram, Ferroresonance Oscillation, Autotransformers, Neutral Earth Resistance.
Comparison of the Effect of Phase to Ground Faults and Three Phase Faults in a Micro-turbine Generation System
Vol. 4. n. 2, pp. 541-546
Abstract - This paper studies the effects of phase-to-ground faults and three phase faults on a microturbine generation system. The faults happened in the confluence of grid and microturbine generation system. We simulate the effects of these faults on the current and active and reactive powers of the system. Determining the magnitude of the fault current is the staple step to set the breakers properly and this is why we tried to study the effects of faults in this paper. The main parts of the system are: a microturbine, a permanents magnetic generator, three phase bridge rectifier and inverter. The model is developed in Matlab / Simulink.
Keywords: Distributed generation, Inverter, Microturbine, PM generator, Phase-to-ground faults, Rectifier, Three phase faults.
A Comparative Study on Optimal Design of LLC Resonant Converter by Intelligent Optimization Techniques
Vol. 4. n. 2, pp.547-554
Abstract - This paper presents a comparative study by three intelligent optimization techniques to accurately determine the optimal control parameters of a 1 MHz LLC resonant dc-dc converter aimed at minimizing the losses. Three evolutionary optimization techniques viz., Scatter Search (SS), Genetic Algorithm (GA) and Particle Swarm Optimization (PSO) are employed to derive the optimal control parameters of the resonant converter and the results obtained are compared in terms of efficiency. After deriving the optimal parameters, simulation studies are carried out using MATLAB /SIMULINK modeling approach to analyze the performance of the resonant converter.
Keywords: LLC resonant converter, Optimization techniques, Genetic Algorithm, Particle Swarm Optimization, Scatter Search.
Losses Minimization in DTC-DPWM Induction Motor Drives
Vol. 4. n. 2, pp. 555-561
Abstract - This paper presents a space vector based Discontinuous Pulse width Modulation (DPWM) algorithm applied to a direct torque control (DTC) for induction motor (IM) drives. The proposed work is a contribution to improve the efficiency and the robustness of the IM-DTC drives. The problem of variable switching frequency on the classic DTC is solved with the DPWM fed inverter control strategy. The undesirable torque ripple is reducing.
The efficiency of the IM is decreasing when it operates under weak loads with a constant reference stator flux. For this reasons, a method is proposed here to hold the optimal stator flux in order to minimize the total IM losses. In addition to that, Discontinuous modulation methods give lower (average 33%) switching inverter losses. Analysis, modelling and simulation results are presented to demonstrate the validity of the proposed overall IM drive scheme.
Keywords: Induction Motor, DTC DPWM, Losses minimization.
Doubly Fed Induction Generator Based a Novel Nine-Switch AC/AC Converter
Vol. 4. n. 2, pp. 562-567
Abstract - This paper proposes the use of a novel Nine-Switch AC/AC Converter topology for doubly fed induction generator (DFIG) applications. DFIG wind turbines use wound rotor induction generators, where the rotor winding is fed through a Nine-Switch AC/AC Converter variable frequency and amplitude PWM converter and regulates to zero the reactive power of stator. The proposed converter uses only nine IGBT devices for ac/ac conversion through a dc link. As compare to conventional back-to-back ac/ac converters, the numbers of power semiconductor switches are reduced in the suggested converter. The proposed topology results in reduction of installation area and cost. The operating principle, control strategy and characteristics of DFIG based proposed ac/ac converter is described in this paper. The performance of proposed DFIG is validated with simulation results using MATLAB/SIMULINK software.
Keywords: Doubly Fed Induction Generator (DFIG), Nine-Switch Converter, Switching Algorithm Wind Energy.
Suppression Chaotic Overvoltages in Potential Transformer including Nonlinear Core Losses Considering Neutral Earth Resistance
Vol. 4. n. 2, pp. 568-574
Abstract - Ferroresonance is a non-conventional electrical phenomenon which may cause overvoltages in the electrical power system endangers the system reliability. This paper studies the effect of circuit breaker shunt resistance, Metal Oxide Surge Arrester (MOSA) and neutral earth resistance on controlling chaotic ferroresonance in a potential transformer while transformer core losses is modeled as a nonlinear resistance which hysteresis and eddy current losses are included. It is expected that neutral earth resistance can control ferroresonance better than MOSA and circuit breaker air gap resistance. For confirmation this aspect, simulation has been done on a one phase potential transformer rated 100VA, 275kV. Simulation results show that considering shunt resistance on the circuit breaker and MOSA in parallel to the transformer, exhibits a great mitigating effect on ferroresonance oscillations, but these resistances cannot control these phenomena for wide variation of the power system parameters. By applying neutral earth resistance to the system grounding, ferroresonance is controlled and its amplitude has been damped for all parameters values.
Keywords: Circuit Breakers Shunt Resistance, Metal Oxide Surge Arreste, Chaos, Bifurcation Diagram, Ferroresonance, Potential Transformers, Neutral Earth Resistance, Nonlinear Core Losses Effect.
Direct Torque Controlled Induction Motor Drives Using Space Vector Based PWM Techniques for Reduced Common Mode Voltage
Vol. 4. n. 2, pp. 575-584
Abstract - This paper presents simple space vector based pulse width modulation techniques for the reduction of common mode voltage in direct torque controlled induction motor drives. In conventional space vector pulse width modulation (SVPWM) strategy, the desired reference voltage vector ( VREF ) is generated by time averaging the two nearby active voltage vectors and two zero voltage vectors in every sampling time (Ts) . Therefore the complexity involved in calculation of sector and angle information is more. The proposed PWM algorithms use the concept of imaginary switching times. The proposed algorithms avoid the requirement of reference voltage vector, sector and angle information. Moreover, to reduce the common mode voltage, the proposed algorithms avoid the use of zero voltage vectors. Instead of using zero voltage vectors two active opposite voltage vectors with equal time duration are utilized to compose required voltage vector. To validate the proposed PWM algorithms, numerical simulation studies have been carried out using MATLAB-Simulink and results are presented and compared.
Keywords: Direct Torque Control, Imaginary Switching Times, Induction Motor Drives, PWM Inverter, SVPWM.
Electromagnetic Analysis of the Effects of Static Eccentricity Fault on the Radial Force Variations in Switched Reluctance Motors
Vol. 4. n. 2, pp. 585-590
The real performance of the Switched Reluctance Machines (SRMs) in industrial applications has widely been investigated by variety of studies during the recent decades. Thus the effects of the some abnormalities of their physical structures have also applied significant orientations on new research areas. One of the most important problems seen in the industrial applications of SRMs which has concerned users is the rotor eccentricity of this type of electric machine which may conclude the unbalanced distribution of flux linkage as well as acoustic noise and vibration due to the radial forces produced during the rotation of machine’s rotor. In this paper, it is attempted to firstly introduce the radial force and secondly to analyze and obtain this type of force resulted from different values of static eccentricity faults based on a conventional model of 6/4 SRM via electromagnetic analysis done by three dimensional finite element method (3D FEM). Finally, it will be tried to detect the eccentricity faults via Fast Fourier Transform (FFT) of radial force component's pattern.
Keywords: Switched Reluctance Motor, Radial Force Analysis, Eccentricity Fault, 3D Finite Element Method.
Reduced Common Mode Voltage PWM Algorithms for Vector Controlled Induction Motor Drives
Vol. 4. n. 2, pp. 591-600
Abstract - This paper presents few space vector based reduced common mode voltage pulsewidth modulation (RCMVPWM) algorithms for vector controlled induction motor drives to reduce common mode voltage variations. The existing RCMVPWM algorithms use conventional space vector approach, which requires angle and sector information for the calculation of gating times of the inverter. Hence, to reduce the complexity, the proposed algorithms have been developed by using the concept of imaginary switching times. The proposed algorithms use active voltage vectors only in order to reduce the common mode voltage. To validate the proposed RCMVPWM algorithms based vector controlled induction motor drive, numerical simulation studies have been carried out and results are presented and compared.
Keywords: AZSPWM, Common Mode Voltage, Induction Motor, NSPWM, SVPWM, Vector Control.
Sympathetic Inrush Phenomenon Analysis and Solution for a Power Transformer
Vol. 4. n. 2, pp. 601-607
Abstract - This paper present the sympathetic inrush phenomenon analysis and the solution for a Power Transformer. The objectives are to investigate the sympathetic inrush phenomenon and then propose a solution to overcome the unnecessary tripping phenomena due to mal-operation of the relay. When the transformer is close without load, it led to the mal-operation of the protection relay. It occurs because when the transformer is being closed, it will produce excitation current that will pass the system resistance, resulting in saturations that generate a phenomenon called sympathetic inrush current. This phenomenon has been pointed out as one of the reasons for false operation of transformer differential relays. Based on the simulation of the simplified basic network of two parallel 3phase, 100MVA, 132kV/11kV power transformers, the phenomenon and characteristics are analyzed. PSCAD software is used for system execution. The sympathetic current and the inrush magnetizing current reach the peak value alternately, on alternate half cycle which sharing transient current of two transformers is almost symmetrical. As to come out with a solution, two options are being investigated, which are to reduce the 2nd harmonics setting from 20% to 15% and to implement a cross blocking feature to block a tripping when one of the phases experiences higher 2nd harmonics. The simulations show both of the options can solve the problem. By dwelling into the implications, the second option which to implement a cross blocking is accepted since it is safer, cheaper and does not require hassle job to the practitioners to being implemented. Since this cross blocking feature is only incorporated with high- set Transformer Differential, it is proposed that TDR type 7UT613 (Siemens) or SEL587 (Schweitzer) is being used.
Keywords: Sympathetic Inrush, Power Transformer, Transformer Differential Relay Mal-Operation, Harmonics Setting, Cross Blocking.
Low-Impedance Restricted Earth Fault Numerical Algorithms Operation in Power-Transformer Protection
Vol. 4. n. 2, pp. 608-615
Abstract - Low impedance restricted earth fault protection is one of the protection function to protect the transformer winding with earthed star point. This paper presents a critical comparison of restricted earth fault algorithms among four restricted earth fault (REF) numerical relay algorithms: ABB’s, AREVA T&D’s, SIEMENS’s, and GENERAL ELECTRIC’s. Advantages and disadvantages of these algorithms are investigated based on speed, sensitivity and selectivity. Also, magnetizing inrush current, over excitation and CT saturation impression on the restricted earth fault operation is presented. After the algorithms assessment, to confirm the results they are simulated by using MATLAB SIMULINK. The relay operation characteristic curves and restraint currents for each of algorithms are then investigated.
Keywords: Low Impedance Restricted Earth Fault, REF, Numerical Relay, Transformer Protection.
A Series DC Motor Time-Varying Observer Based on Flatness and Genetic Algorithm
Vol. 4. n. 2, pp. 616-623
Abstract - This paper focuses on a fundamental problem related to the parameters adjustment of a time-varying observer, when the observer design for a series DC motor is considered. Based on the flatness inversion and genetic algorithm, a recursive nonlinear controller is proposed to improve the transient response. This algorithm is conducted to substitute the conventional control structure of a nonlinear system into a linear nonstationary one. This work deals with two major concerns in the series DC motor control. First, we start by linearizing the nonlinear system along its nominal trajectory and we deduce the controller canonical form, which is used in the control law design. Second, we investigate the observer canonical form in order to design the time-varying observer and we perform the genetic algorithm to guarantee the adjustment of the observer parameters.
Keywords: Time-Varying Observer; Genetic Algorithm; Flatness; DC Motor; Inversion Problem; Trajectory Tracking.
TORUS and AFIR Axial-Flux Permanent-Magnet Machines: A Comparison via Finite Element Analysis
Vol. 4. n. 2, pp. 624-631
Abstract - Presented here is a comparison between TORUS and AFIR, the two topologies for double-sided axial-flux permanent-magnet machines. Investigated and compared were their slotted and non-slotted topologies, in terms of power density and torque quality. Field analysis of the topologies was by finite element method. Results show TORUS topology’s high power-density in high current-density and low electrical-loading. AFIR topology has high power in low current-density and high electrical-loading. Non-slotted TORUS and AFIR AFPM machines have negligible cogging torque and lower ripple torque than their slotted counterparts.
Keywords: Axial-Flux; Permanent-Magnet; Slotted; Non-Slotted.
Analysis and Robust Controller Design for a Hybrid Electrical Vehicle with PMSM
Vol. 4. n. 2, pp. 632-639
Increasing the growing need of using combustion vehicles and consequently increasing of air pollution lead to further studies and experiments. For this purpose, in this article, the structure and how to design a hybrid electrical vehicle (HEV) with permanent magnet synchronous motor has been discussed. Advantages of hybrid electrical vehicle design are using two sources of energy, one of them is fossil fuel (gasoline) and the other is the electrical battery and its energy converter is internal combustion motor and electrical motor. Existence of electrical motor reduces the motive system pollution and also improves the overall system efficiency. Permanent magnetic synchronous motor because of special features is considered a suitable candidate beside those motors like inductive motor and direct flow motor. In this paper, by dynamic modeling of a permanent magnetic synchronous motor with other components of vehicle, dynamic performance of motor is evaluated. The following describes the benefits of magnetic synchronous motor than other motors and history of them is described. Finally, we explain the hybrid electrical vehicle simulation of series type by Matlab and adviser software.
Keywords: Hybrid Electrical Vehicle (HEV), Dynamic, Static, Air Pollution.
Modelling of an electro-hydraulic forklift in Matlab Simulink
Vol. 4. n. 2, pp. 640-647
Abstract - Evaluation of an electro-hydraulic system of a working machine is carried out by a Matlab Simulink model. Modelling of the total forklift system is presented. Analysis and verification of the Simulink model with practical results are also performed for an internal gear and axial piston hydraulic machine drive. Practical results are presented to demonstrate the energy efficiency of the proposed electro-hydraulic forklift arrangement with potential energy recovery feature.
Keywords: Drives, Pumps, Permanent Magnet Machines, Energy Efficiency, Energy Recovery, Model.
The Use of SOM and MLP Neural Networks in the Classification of Pulse-Echo Ultra-Sonic Signals
Vol. 4. n. 2, pp. 648-652
Abstract - The present work evaluates the application of artificial neural networks to pattern recognition of ultrasonic signals reflected from weld beads. Classifiers are Self Organizing Map (SOM) and Multi-layer Perceptron (MLP). The ultrasonic signals acquired from pulse-echo are introduced to the artificial neural network classifiers with and without preprocessing. The preprocessing is aimed to smoothen the signal that improves the classification.
Five conditions of weld bead are evaluated: lack of fusion (LOF), lack of penetration (LOP), excess penetration (EX.P), slag inclusion (SL) and non-defect (ND). The defects have been intentionally inserted in a weld bead of AISI 1020 steel plates of 20 mm thickness and confirmed using radiographic tests. The results obtained show that it is possible to classify ultrasonic signals of weld joints by the pulse-echo techniques using artificial neural networks. Classification error rate as low as 6% has been the outcome of the best test set up.
Keywords: Non-Destructive Testing (NDT), Artificial Neural Network (ANN), Angle-Beam Probe, Ultrasonic Wave.
Effects of Oil Palm Shell Filler on Inception and Propagation of Electrical Treeing in Silicone Rubber Composite Material Under AC Voltage
Vol. 4. n. 2, pp. 653-660
Abstract - There are many inhibitors of electrical treeing being used in polymeric insulation but none have studied on the use of low-cost organic filler to act as inhibitor to the growth of electrical trees. Therefore, this paper presents the study on the investigation of effect of filler on the initiation and propagation of electrical treeing in silicone rubber-oil palm shell composite material via leaf-like specimen being experimented in High Voltage Engineering Laboratory. The tree inception voltage and tree inception time for two types test samples; “with filler” and “without filler” were measured. The study shows that the average tree inception voltage for sample “with filler” and “without filler” was 8 kV and 7.5 kV respectively, whereas for the average tree inception time was 182 seconds and 137 seconds for sample “with filler” and sample “without filler” respectively. It was found that the tree propagation in the sample “with filler” was kind of retarded. More tree branches were observed in the sample with filler than its counterpart. Organic filler has great potentiality to be used as electrical tree inhibition. However, more studies are required to investigate the organic fillers’ long term performance and comparative studies with inorganic fillers.
Keywords: Electrical Treeing, Silicone Rubber, Filler, Oil Palm Shell.
Noise Smoothing for GPS Receivers Positioning Data Using Wavelet Transform
Vol. 4. n. 2, pp. 661-667
Abstract - The use of GPS receivers has become widespread over recent years. The GPS data are subject to numerous sources of error, including satellite orbit errors, satellite clock errors, receiver errors, tropospheric and ionospheric errors, multi-path errors, and Selective Availability (SA). The accuracies of these receivers range from centimeter to several meters, making it necessary to evaluate how accuracy and precision can affect individual applications. In this paper, a new method based on wavelet analysis is applied to smooth noise for GPS receiver positioning data. Wavelet transform is a useful tool for the time-frequency analysis of signals. From the viewpoint of signal processing, wavelet analysis represents a signal by its components in a series of independent frequency scales. By analyzing the behavior of the signal in each scales, we can find the features of the signal or discriminate different parts, such as the noise and the useful signal, of the combined signal. A single-frequency and low cost commercial GPS receiver manufactured by Rockwell Company is used. The experimental results on measurement data demonstrate the effectiveness of the proposed method; so that the total RMS error reduces to less than 0.38 metre with SA on and 0.21 metre with SA off using Daubechie wavelet.
Keywords: GPS, Noise Smoothing, Position, Wavelet Transform.
Vol. 4. n. 2, pp. 668-673
Abstract - Electromagnetic force is one of the main feature in designing large-capacity and small-sized high power circuit breakers, disconnectors or isolated switches. This paper presents an analytical approach from which active forces at electromagnetic devices basis on axial forces can be computed. The established formula for some particular cases are useful in order to develop new drive systems for electrical apparatus basis on electromagnetic devices with axial forces.
Keywords: Electromagnetic Force, Coils, Electromagnetic Device.
Modeling of Distribution of PD Pulses within Micro-Cavities
Vol. 4. n. 2, pp. 674-682
Abstract - In this paper, a two dimensional kinetic model has been used to investigate the filamentary distribution of spark-type partial discharges (PD’s) inside a micro-cavity. The model is based on Particle-in-Cell methods with Monte Carlo Collision techniques for modeling of collision processes (PIC-MCC). The gas considered is air at atmospheric pressure and secondary processes like photo-emission and cathode-emission are considered. The micro-cavity may be sandwiched between two dielectrics. The discharge within the void is studied in conjunction with the external circuit. The phase-space scatter plots for electrons, positive, negative ions are obtained in order to analyze the filamentary distribution of PD pulse within micro-cavity and to understand the manner in which microdischarges form and their shapes change over a wide range of variations in micro-cavity width (5-4000µm). The rise-time and the magnitude of the PD pulse are obtained and are seen to be affected by micro-cavity width. The results have been compared with existing experimental, theoretical and computational results, wherever possible.
Keywords: Partial Discharges, PIC-MCC Simulation, Electric Field.
Analysis Natural Frequencies a Functionally Graded Cylindrical Shell with Effects Symmetrical boundary conditions
Vol. 4. n. 2, pp. 683-690
Abstract - Cylindrical shells made of a functionally gradient material (FGM) composed of stainless steel and nickel is very important. The objective is to study the natural frequencies and the effects simply support-simply support boundary conditions on the natural frequencies of the functionally graded cylindrical shell. The study is carried out using third order shear deformation shell theory. The analysis is carried out using Hamilton’s principle. The governing equations of motion of functionally graded cylindrical shells are derived based on third order shear deformation shell theory. Results are presented on the frequencies characteristics and the effects of simply support-simply support boundary conditions on edge end functionally graded cylindrical shell.
Keywords: Vibration, Cylindrical Shell, Hamilton’s Principle, Simply Support.
A New Module Design for 3D Graphic Transformations Using Generated Floating-Point Core Units
Vol. 4. n. 2, pp. 691-698
Abstract - A typical animation scene of a computer animation may include hundreds of mathematically defined objects. Applying Three Dimensional (3D) affine transformations to such scenes requires huge amount of CPU time. In this study, an improved hardware module was designed to speed-up 3D graphic transformations using FPGA (Field Programmable Gate Array) chips. In the module design, for multiplication and addition operations, 32-bit multipliers and adders formed on FPGA fabric by IP CORE Generator tool were utilized. The module was tested and functionally verified. Module’s data processing speed was compared to various PCs and to our previous module design. Results showed that, 3D graphic transformations can be speeded-up by factor of up to 40 times using the designed module compared to the PCs. Employing multipliers and adders formed with Xilinx’s IP CORE Generator in the module design provided 1.4 times performance gain over our previous module design.
Keywords: FPGA, Computer Graphics, 3D Transformation, Hardware Module, Core Generator.
Study on Post Arc Current and Transient Recovery Voltage in Vacuum Circuit Breaker
Vol. 4. n. 2, pp. 699-709
Abstract - The post arc phenomenon in Vacuum Circuit Breaker (VCB) is investigated in this paper. The describing equations of Post Arc Current (PAC) are solved together with network equations. Two methods are proposed here to compute Transient Recovery Voltage (TRV) and PAC; the sequential TRV and PAC calculation method, which is a combined numerical and analytical method and the simultaneous TRV and PAC calculation method, which is a totally numerical method where applied numerical techniques like averaging in first and second derivative are used to get the fast convergence of solutions by avoiding sharp numerical oscillations in results. In addition, the numerical part of both methods is based on Gauss-Seidel method. The impact of PAC on TRV for different cases like interruption of inductive and capacitive currents is studied. The results indicate that in the case of inductive load and Short Circuit current interruption, there is no remarkable influence of PAC and TRV on each other. But in the case of capacitive current interruption, the TRV waveform in the first microseconds is determined by the PAC of the VCB. The simulation results show that the impact of physical parameters of VCB like diffusion time constant (τ) and initial PAC (I0) is much more significant than that of network parameters like capacitance of VCB and equivalent network inductance.
Keywords: Current Interruption, Post Arc Current, Transient Recovery Voltage, Vacuum Circuit Breaker.
Static and Dynamic Behaviors of an Electrostatically Actuated Micro Beam
Vol. 4. n. 2, pp. 710-717
Abstract - This paper presents the static and dynamic behaviors of a doubly clamped micro beam under electrostatic actuation. Responses to direct and alternating currents and the pull-in phenomena of the mentioned micro beam are presented in detail. The effects of dimensional variations on pull-in phenomena are investigated and also the effects of applied voltages on the fundamental natural frequency of the micro beam are presented.
Keywords: Micro Beam, Direct and Alternating Currents, Statics and Dynamics, Pull-In.
Modified Spectrum Sensing and Awareness in Wireless Radio Networks
Vol. 4. n. 2, pp. 718-722
Abstract - The spectrum sensing is a quite important part in cognitive radio. This paper discusses energy sensing, the common spectrum sensing algorithm in cognitive radio, as well as some cooperative algorithms such as AND, OR rule. Also some modified periodogram methods have been investigated and simulated, moreover these various methods of detection of signal simulated by specifying their advantages and their drawbacks. Our simulations shows that the energy detector is so easy to implement and is good when there is no knowledge of secondary users. Besides simulation about modified periodogram shows that there are differences in detection of signals by using different types of filtering and windowing. Finally, sensing features of these current methods are described.
Keywords: Modified Periodogram, Spectrum Sensing, Radiometry, Power Spectral Density.
Simulation of High Operating Temperature InSb/In1-xAlxSb Infrared Photodetector
Vol. 4. n. 2, pp. 723-726
Abstract - High operating temperatures infrared photodetectors are needed for improving the performance of these systems. To obtain high device performance at higher temperatures, the thermally generated noise required to be reduced. Minority-carrier extraction and exclusion techniques are the approaches for decreasing the thermal noise of infrared systems. In this paper, an InSb extraction and an InSb/In1-xAlxSb extraction/exclusion diode were studied and simulated for operation in the MWIR region. The simulation was performed using ATLAS software from SILVACO. The device was characterized in respect of energy band diagram, carrier concentration, dark current and zero bias resistance–area products .The simulation results were compared with those of other authors and found to be in a better agreement with actual measurement.
Keywords: InSb, Infrared, Photodetector, Simulation.
Optimization of Organic Solar Cells Using the New Unified Model of Electric Field at the Active Layer
Vol. 4. n. 2, pp. 727-731
Abstract - In this paper, we report our results on the electro-optical modelling of a multi-layer organic photovoltaic device, in which the incident light of sun is absorbed in the active layer. The influence of the optical parameters and thicknesses of different layers had been taken into account to improve the device performance. A composite of poly(2-methoxy-5-(20-ethylhexyloxy)-1,4phenylenevinylene) (MEH-PPV)/6,6-phenyl C61-butyric acid methyl ester (PCBM) blends are used as photo-active materials, sandwiched between a transparent Indium Tin Oxide (ITO)-electrode and metallic backside contact (Ag) . This study aims to show optical effects of the equivalent point of electric field at the active layer to be a future promising substitution for the two conventional models used in the literature .
Our objective is the study of the methods which make it possible the description of the electric field inside the organic solar cells described previously with different deposited layers to make a rigorous modelling of these devices. The basic criterion for optical optimization is to maximize the generation rate and the quantum effiency at a first hand and minimizing the recombination rate at a second hand in the active layer according to the distribution of electrical field on the device. The theoretical results are in good agreement with the experimental observations.
Keywords: Organic Solar Cell, Bulk Heterojunction, Equivalent Point, Modelling, Simulation.
Modeling and Simulation of Discharges Propagating over Discontinuously Polluted Insulator Surfaces under Impulse Voltages
Vol. 4. n. 2, pp. 732-738
Abstract - This paper is aimed at the determination of the characteristics of discharge propagating over discontinuously polluted insulators under bi-exponential waves simulating switching impulse voltages, using a predictive dynamic model based on an equivalent electrical network. This model enables to compute the current, electrical charge, instantaneous propagation velocity and channel radius of the discharge, and the flashover voltage for different distributions and conductivities of deposits. The simulated results are first validated with experimental data obtained with an electrolytic model representing a surface with a deposit uniformly distributed and then extended to discontinuously polluted surface.
Keywords: Outdoor insulation, Modeling, Simulation, Discontinuous pollution layer, Flashover.
International Review on Modelling and Simulations - Papers (Part B)
Damping Power System Oscillations Using Superconducting Magnetic Energy Storage for Single Machine Infinite Bus
Vol. 4. n. 2, pp. 739-744
Abstract - This paper presents an application of superconducting magnetic energy storage (SMES) in damping power systems oscillations subject to disturbances. The effectiveness of SMES is validated by using frequency and time domain approach. Faults are simulated and applied to evaluate the capabilities of SMES. Results show that SMES successfully damped out power system oscillations.
Keywords: Small signal and Transient Analysis, Power System Damping, Superconducting Magnetic Energy Storage.
Vol. 4. n. 2, pp. 745-752
Abstract - In this study, an instantaneous reactive power calculation method that is based on wavelet system was recommended by taking generalized instantaneous reactive power theory as basis. Validity of calculation method was indicated in a sample power system. For that purpose, generalized instantaneous reactive power theory and wavelet based instantaneous reactive power calculation method were compared for same load, instantaneous active, reactive powers and currents. It was observed that the difference between result values were as small as to be ignored. For the study, firstly instantaneous current and phase-ground voltage values were acquired at the sampling rate of 0.000625 seconds, and then voltages and currents were decomposed into approximation and detail coefficients with three-level multiresolution analysis. Instantaneous active and reactive power values and instantaneous active and reactive current values were determined on various frequency resolutions with scalar and vector products of these decompositions. Thus, instantaneous active and reactive power values that were directly drawn from the source by main harmonic and add number harmonic currents were calculated without applying an additional frequency analysis.
Keywords: Current Transform, Power Distribution Harmonics, Power Measurement, Reactive Power, Wavelet Transform.
Designing a Hybrid Compensator to Eliminate Harmonics and Control Reactive Power in Distributed Generation Systems
Vol. 4. n. 2, pp. 753-758
Abstract - In this paper operation of a hybrid active filter consist of a shunt active filter and distributed passive filters in a simple distribution system is investigated. The test system contains nonlinear loads among with passive filters to eliminate certain harmonics of the load current and also to supply reactive power. A micro turbine unit is also considered as a DG in the test system. The active filter is utilized and controlled to eliminate the remaining harmonics of the supply current and to correct the current unbalance. In order to examine the operation of the compensation system, simulations are carried out using Matlab/Simulink software. Simulations are conducted under different cases including the operation of passive, active and hybrid filters individually and in combination. Simulation results demonstrated the effectiveness of the described hybrid structure to improve the power quality indices of the system under study.
Keywords: Active Filter, Passive Filter, Hybrid Filter, Current Unbalance, DG Unit, Power Quality.
A New Modeling Approach for the Arcing Fault in Power Distribution Networks Using Lab Results
Vol. 4. n. 2, pp. 759-765
Abstract - The energy wasted due to faults or interruption in servicing consumers, causing a lack of reliability of power system in the electric market. Therefore, locating and diagnosing faults in power distribution networks enhance system reliability and prevent potential risks for people and system. Faults in 20-kv power distribution network are associated with the arc, due to low voltage conductors and poor connections with the ground or grounded object. Such arc creates large impedance so arc faults are known as high impedance faults that make it difficult to detect and locate. To calculate the arc characteristics and their impact on the waveforms , voltage and electric current have been simulated in the laboratory and practical results have been utilized in EMTP program to model faults. Unlike such results mentioned in some paper, the model precisely shows that the arcing fault doesn’t include pure ohm or Induction properties, but its nature is same as a capacitor. Then comparing the frequency content of such model with the real arc is carried out through wavelet transform, to examine the validity of the fault model. This model can be used to design and test protective relays, as well as design of fault detection and location algorithms.
Keywords: Power Distribution Network, Arc, Capacitor, Model Fault, EMTP, Wavelet.
Vol. 4. n. 2, pp. 766-771
In the emerging scenario of restructuring of power system networks, the transmission lines are prone to be operated under heavily stressed conditions and there is a risk of line outage due to voltage instability. This necessitates voltage stability improvement under probable line outage conditions to keep the system under voltage secured conditions. A line voltage stability index is used to assess the stability of the lines during contingency. Voltage stability improvement is achieved by installation of Static VAR Compensator (SVC) at an optimal location. The optimal location and sizing of SVC is identified through Particle Swarm Optimization (PSO) algorithm. The proposed method is tested in IEEE 30 bus test system and results obtained are proving the validity of the work.
Keywords: SVC, FVSI, PSO, Contingency.
Steady-State Wind Turbine Generation Model for Three-Phase Distribution Load Flow Analysis
Vol. 4. n. 2, pp. 772-777
Abstract - The paper presents Wind Turbine Generation (WTG) models as three-phase resource and analyses their effect when they are connected in distribution networks using three-phase distribution load flow. The WTGs can be modelled as a voltage-controlled node (PV node) or as a complex power injection (PQ node). The three-phase distribution load flow has been developed based on the theory of symmetrical components. The Newton Raphson method has been chosen for well known excellent convergence characteristics. The three-phase load flow program has been tested using the IEEE 13 node feeder. The solution of the base case is compared with the radial distribution analysis package (RDAP). Then, the three-phase load flow method is used to analyze distribution networks with WTGs. The analysis is carried out with various WTG mathematical models. The simulation results show that the integration of WTG into an existing distribution network can improve the voltage profile as well as reduces the total system losses.
Keywords: Three Phase Load Flow, Wind Turbine Generation (WTG), Sequence Decoupled Newton Raphson Method.
Modeling and Simulation of Isolated Wind/Diesel Hybrid power System Connected to Estimated Variable Load
Vol. 4. n. 2, pp. 778-783
Abstract - Variable speed Wind turbines coupled with squirrel cage induction generators are vastly used in wind power plants. But, they suffer from some fundamental problems. If this type of wind turbines were is applied to remote areas, they cannot stabilize frequency and voltage of the grid in acceptable limits. Changes in load during one day also make this problem harder to deal with. In this paper, a system consist of three wind turbines integrated with one diesel generator connected to a variable load is analyzed, and a new model for this kind of load is presented. This model is implemented a changing power demand based on load curve. A new management method is also developed for commitment of power sources. Simulation with "PSCAD/EMTDC" software shows the ability of the proposed method to provide high quality power for this type of load.
Keywords: Wind Turbine, Diesel, Load Curve, PSCAD, Isolated Power System.
Benefits, Barriers and Challenges of Demand Side Management: A Review of Electrical Systems in Oman
Vol. 4. n. 2, pp. 784-794
Abstract - Paper presents the review of key benefits, barriers and challenges of demand side management in context of electrical system in Oman. The main interconnected system which feeding more than 85% of electricity demand across the country, has analyzed to find out the potential application of demand side management. The wide range of demand variation on power plants, lower utilization of transmission system and significant influence of temperature sensitive load provide the scopes to improve the operating efficiency of electrical system using demand side management techniques. The prospective benefits are then discussed in the framework of generation, transmission, distribution and utilization. Analysis shows that spinning reserves can be limited and transmission efficiency may be improved by shifting the load from peak to off-peak hours using strategic load growth, higher plant use factor and dynamic tariff like real time pricing techniques of demand side management. Paper has reviewed the major demand side management techniques and identified a number of barriers like inadequate permitted tariffs, less competitive energy cost in market and lack of information and communication technology infrastructure etc. The appropriate policies to overcome these barriers and to develop the sustainable energy efficient environment are also reviewed.
Keywords: Benefits, Barrier, Challenges, Demand Side Management, Renewable Energy, Tariffs.
HVAC, Hybrid and HVDC links: Stability Analysis and Comparison
Vol. 4. n. 2, pp. 795-802
Abstract - High Voltage Direct Current (HVDC) technology has important characteristics which makes it attractive to connect two or more weak power systems, increasing the power transmission; or when the power systems are separated by long distances, in order to reduce electromechanical oscillations. However, CSC-HVDC technology has disadvantages related to the elevated power reactive losses and low voltage stability, compared to VSC-HVDC technology. In this paper, a brief HVDC characteristics description is presented, followed by an analysis and comparison between a power system that uses a HVAC, Hybrid, or HVDC link. The NETS and NYPS power system of 68 nodes is simulated in order to show differences and similarities of the power system’s behavior when different links are used; and a small signal stability analysis and voltage stability analysis are carried out, in order to identify advantages and disadvantages related to the different links, and their impact on the stability of system. All simulations and results are obtained with PSAT.
Keywords: Small Signal Stability Analysis, Voltage Stability Analysis, HVAC link, Hybrid (AC/DC) link, HVDC link, SVC.
Design of a Continuously Controlled Linear Static Var Compensator for Load Balancing and Power Factor Correction Purposes
Vol. 4. n. 2, pp. 803-812
Abstract - In this paper a new configuration of static Var compensator is presented. The configuration is a parallel combination of a binary thyristor switched-capacitor bank (BTSCB), a binary thyristor switched-reactor bank (BTSRB), and a thyristor controlled reactor (TCR). This compensator is capable of responding equally to both capacitive and inductive reactive current or reactive power demands for load balancing and power factor correction purposes. The harmonic contents of this configuration are almost ineffective, since the TCR which is the main source of them is only representing one seventh the compensator rating. Even though the BTSCB and BTSRB are offering stepping responses, the overall compensator response is linear since the TCR functions as a linearizer between adjacent steps in both capacitive and inductive modes of operation. This compensator is characterized by the possibility of operation at higher voltage and current ratings, low no load operating losses, and no need to harmonic filtering,. A complete system was designed and tested on the computer program PSpice.
Keywords: Load balancing, Power factor, Reactive Power Control, Static Var, Voltage Control.
An Efficient Clustering Method in Evaluation of the Electric Energy Consumption from Water Hydrophore Stations
Vol. 4. n. 2, pp. 813-818
Abstract - Each amount of water insured for the consumption includes a huge quantity of electrical energy necessary for the transportation, treatment, distribution, different internal technological processes of water supply systems. The electrical energy consumption depends on the specific character of the area, the specific character of the water supply source, the treatment technology used, the means by which the water is transported and distribution, the types and numbers of consumers. Starting from these issues, in the paper is presented an approach to determine the electrical energy consumption levels using the K-means clustering method. The methodology is applied to an urban water supply system with a total of 74 hydrophore stations.
Keywords: Electrical Energy Consumption, Hydrophore Stations, K-Means Clustering Method.
Determination of Wind Plant Output Capacity Using Discrete Markov Chains and PSO Methods in Comparison with FCM
Vol. 4. n. 2, pp. 819-823
Abstract - Wind power generation is noteworthy as the fastest-growing of all renewable energy sources to meet the global commitment to climate change. However, due to fluctuating and intermittent behavior of wind power, it is difficult to estimate its suitable penetration level into the electricity grid. The power output from wind depends on a number of factors that one of them is the wind speed. Thus, clustering of speed data, considering the steady changing of wind speed in different times is of great importance. The novelty of this paper is proposing two estimation scheme for clustering of speed data namely fuzzy c-means (FCM) and particle swarm optimization (PSO) algorithms. Then, the amount of probable output power is determined by means of discrete Markov chains apiece. Finally, in order to illustrate the proposed methods efficiency and ability, they are experimentally compared to each other.
Keywords: Clustering, Discrete Markov Chains, Fuzzy C-Means (FCM), Particle Swarm Optimization (PSO), Output Power, Wind Speed.
Voltage Sag Mitigation with Dynamic Voltage Restorer (DVR) In Distribution Systems
Vol. 4. n. 2, pp. 824-828
Abstract - This paper presents the application of Dynamic Voltage Restorer (DVR) on power distribution systems for mitigation of voltage sag at critical loads. DVR is one of the compensating types of custom power devices. The DVR, which is based on forced-commutated voltage source converter (VSC) has been proved suitable for the task of compensating voltage sags/swells. Simulation results are presented to illustrate and understand the performances of DVR in supporting load voltages under voltage sags/swells conditions.
Keywords: Power Quality, Voltage Sags, Dynamic Voltage Restorer (DVR).
ICA-Based Distributed Generation Location in Radial Distribution Systems
Vol. 4. n. 2, pp. 829-836
Abstract - Heuristic Search and PSO optimization methods and Imperialist Competitive Algorithm(ICA) to optimally determine distributed generation location and size are compared in a distribution network. Objective function consists of power losses and improvement in voltage profile and applied methods are tested on the IEEE 69-bus system. This study demonstrates comparson results of proposed approaches. It includes determination of required DG being installed in an appropriate location. This study also demonstrates that system losses may increase if DG units are connected at non-optimal locations or have non-optimal size.Results indicate that by ICA method, better results are obtained in comparison to PSO and the simple heuristic search method on the 69-bus radial distribution systems. By ICA, maximum loss reduction for each of three types of optimally placed multi-DGs is determined. furthermore, voltage profile improvement and branch current reduction are achieved.
Keywords: Distributed Generation; DG types; Optimal DG size; Imperialist Competitive Algorithm(ICA); Particle Swarm Optimization (PSO), Heuristic Search (HS).
Comprehensive Approach for Locating and Determining the number of HV/MV Substations and Service Area based on Particle Swarm Algorithm
Vol. 4. n. 2, pp. 837-842
Abstract - This paper presents a comprehensive approach for locating and determining the number of feeding points and feeding areas of HV/MV substations using particle swarm algorithm. In this paper, only the HV/MV substations have been studied. Determining the proper (or improper) placement of these substations could affect on designing other parts of distribution networks such as distribution substation placement and medium voltage distribution feeder s. In other words, if positioning the HV/MV substations is not done appropriately enough, designing medium voltage feeders and other parts of distribution system will be encountered with the technical and economical problems. The proposed method was carried out on a test system with 50 load points using MATLAB7 software to determine the number, location and feeding areas of HV/MV system. Finally, obtained simulation results will be studied.
Keywords: Designing distribution systems, Locating and determining the number of feeding points and feeding areas of the HV/MV /transmission substations.
Generation Simulation in Energy and Reserve Market and Their Economic Analysis in Iran
Vol. 4. n. 2, pp. 843-850
Abstract - In this paper, economic analysis of gas-fired generator, biomass unit and wind turbine is carried out in different scenarios based on gas price, energy selling price, and load factor in Iran and the payback period and rate of return are determined. Then, the participation of the Distributed Generations (DGs) in a day-ahead energy and reserve market is simulated for scheduling from the view point of ISO. The ISO target in this model is minimizing total system producing cost considering system security constraints and technical limitation of all units. Finally, the simulation results demonstrate the reserve market as an apt place for DGs.
Keywords: Distributed Generation, Economic Analysis, Energy Market, Reserve Market, Security Constraint Unit Commitment.
Three Techniques Based On Artificial Neural Networks for the Identification of Power System Harmonics - A comparative Study
Vol. 4. n. 2, pp. 851-857
Abstract - A new strategy to estimate harmonic distortion from an AC line is presented for power electronic converters. An Adaptive linear neural network (ADALINE) allows the estimation of the necessary currents in order to cancel harmonics. The comparative study is carried out for three different techniques, with all of them giving the same result. The first technique is based on a Matlab implementation of the Adaline algorithm without using the toolbox. On the contrary, the Matlab toolbox is used in the second technique, and finally Simulink is used for the implementation of the third. The speed and accuracy of the ADALINE results in improved performances of the active power line filter. Thus, according to the application it is possible to choose the adequate technique for the harmonics identification.
Keywords: Harmonics, ADALINE, Artificial Neural Networks, Training, Real-Time learning, Power System.
Using Simulator with Learning Capability to Determine Bidding Strategy in a Multi-Agent Wholesale Power Market
Vol. 4. n. 2, pp. 858-864
Abstract - During recent years, most of the modern countries have changed their power market system from traditional to competitive. So, different components of power market (i.e. production, transmission, and distribution) have been partitioned. In new markets, generator companies (Gencos) bid their price to Independent System Operator (ISO). ISO tries to minimize the power purchasing cost due to various constraints, such as maximum capacity of Genco, and transmission line capacity. One of the main challenges in these markets is determining the optimum bidding strategy for each Genco. In this paper bidding strategy is being explored by means of a simulator with learning capability. Using this simulator, purchasing price of power from Gencos, rewards and capacities of Gencos will be obtained. A numerical example has been discussed by detail to show the application and capabilities of this method.
Keywords: Bidding strategies, Power pool, Simulator with learning capability, Wholesale power market.
A New Index for Voltage Stability Monitoring and Enhancement Using UPFC and Optimization through PSO
Vol. 4. n. 2, pp. 865-873
Abstract - This paper presents a novel proximity index based on the cosØ for the static voltage stability analysis to determine the voltage profiles at all the load buses & thus, the identification of the weak buses on the basis of their corresponding voltage profile. Static voltage stability enhancement is performed with the incorporation of UPFC in order to improve the voltage profile at all the weak load buses along with the system stability. For the enhancement, UPFC is placed in between the most weak load buses to improve the proximity index as well as reactive margin of the system. The proximity index is used for the real time voltage stability enhancement using the PSO technique, involving the minimization of the fitness function under the constraints of reactive power generation at the generation side, control efforts, voltage stability limits & the proximity limit of the network. The voltage stability enhancement through optimization using PSO is proposed along with incorporation of UPFC for improving the reactive margin & the corresponding voltage profiles are obtained for the two test cases, viz. IEEE 14 Bus Test System & Indian Utility 75 Bus Test System. MATLAB 7.0 software is involved in the evaluation of various parameters for the above test cases.
Keywords: Proximity Index, Reactive Power, UPFC, Voltage Stability.
Vol. 4. n. 2, pp. 874-879
Abstract - Power system stability is a growing concern due to ongoing deregulations in power markets, which result new interconnections among the individual power pools. Here, we propose a new method for identification of coherent generators in multi-machine power systems. Our method is based on the minimum-distance solution of Travelling Salesman Problem (TSP). This method develops an electrical distance definition from the reduced admittance matrix. This definition aims at taking into account the effects of inertias on the coherency behaviour of generators. We treat these terms as the ordinary distances in TSP. The shortest route from the TSP solution and the distance terms on this route are processed to determine the mostly coupled generators. This information is also the starting point deriving a tolerance value for grouping process. We adopted a hierarchical additive clustering technique to identify the mostly coupled units. Since our coherency measure develops from the stationary parameters, the formed groups are of structural type and constitute a base for further clustering at a variety of loading conditions and disturbances. We tested the method on the IEEE 50 Machine Test System and Turkish Interconnected System. Results are promising.
Keywords: Travelling Salesman Problem, Coherency, Clustering, Power System Reduction.
Tuning of Over and Under Excitation System Limiters of Synchronous Generator and Studying of its Effects on Power System Voltage Stability
Vol. 4. n. 2, pp. 880-887
Abstract - Excitation system of synchronous generator can help to an effective voltage control and power system stability support. In fact, for the stability improvement, this excitation system should be able to apply proper input voltage to the generator field winding. In this paper limiters and protective circuits of generator excitation system are explained. Two important types of these limiters are over and under excitation ones. The over-excitation limiter protects the generator a-gainst over-temperature caused by high field current for long time. Under-excitation limiter prevents the decrease of generator field current to the values lower than the stability margin or the thermal limit of end side of the stator core. Various models of the over and under excitation limiters have been presented in the literature. Tuning these limiters can be performed in different ways by considering the generator’s capability curves. The limiter models and their parameters tuning affect voltage stability straightly. In this research, after implementation the proper model for our case study, the tuning of limiters is obtained by analyzing well known voltage stability methods. Some simulations have been done in Matlab/Simulink to analyze the effect of the selected model and tuned limiters on voltage stability both in single and multi-machines system. Also the dynamic parameters of a real system (Bistun power plant) are used as the case study. The results issued from this study are also discussed and validate the simulations.
Keywords: Excitation System, Voltage Stability, Synchronous Generator, Over Excitation Limiter, Under Excitation Limiter.
Crack Growth Modelling without Remeshing: DQPE and LSM Coupling
Vol. 4. n. 2, pp. 888-890
Abstract - In this paper, we present a new numerical schema to model the crack growth without remeshing. We proposed an algorithm that couples the level set method with the double degenerated finite element DQPE to solve the elastic-static fatigue crack problem: The LSM is used to represent the crack location, including the location of crack tips. The DQ-FEM is used to compute the stress and displacement fields necessary for determining the rate of crack growth. The results obtained are compared to reference solutions and show excellent agreement.
Keywords: Singularity, Crack, Level Set Method, DQPE Element.
Vol. 4. n. 2, pp. 891-895
Abstract - The problem of electromagnetic wave scattering by nihility circular or elliptical cylinders coated by lossy Metamaterials is analyzed by solving the problem of scattering by two dielectric layered elliptic cylinders using the separation of variables method. The incident, scattered and transmitted fields are expressed in term of complex Mathieu functions. Numerical results are obtained for the scattered fields by nihility circular or elliptical cylinders coated by lossy and lossless Metamaterials to show the effect of the loss on the backscattering width. Numerical results show a significant change in the backscattering width, i.e. reduced at some geometrical parameters.
Keywords: Elliptic cylinder, Nihility, Mathieu functions, Lossy Metamaterials, backscattering width.
Using CFD Simulation to Study Mechanical Agitation of Yield Stress Fluid Induced by a Gate Impeller
Vol. 4. n. 2, pp.896-902
Abstract - Great number of operations of the chemical, biochemical or petrochemical industry is very dependent on the rheological nature of the fluids. The present work studies the viscoplastic case of fluids in a classical system of agitation: a flat-bottomed cylindrical tank, not baffled provided by a gate impeller. We focus on the incompressible laminar flows, by using a numerical approach based on CFD Fluent code which uses as a resolution technique the finite volume method for the Navier-Stokes equations formulated in (U.V.P) variables. The yield stress of flow related to the viscoplastic behavior is modelled by a theoretical law of Bingham. We examine the influence of inertia, crossed effect between inertia and viscoplasticity, the yield of flow on the hydrodynamic and power consumption by the variation of the Reynolds and generalized Reynolds, Bingham and Hedström numbers respectively. The findings show that the existence of a yield stress of flow can lead to a quasi-immobilization zone inside the simulated system of agitation.
Keywords: Agitated Vessel, Gate Impeller, Yield Stress Fluids, CFD.
Investigation of the Using Stainless Steel and Nickel for Vibration Two Type Functionally Graded Cylindrical Shell
Vol. 4. n. 2, pp. 903-910
Study on the vibration of cylindrical shell made of a functionally gradient material (FGM) composed of stainless steel and nickel is presented. The effects of the FGM configuration are studied by studying the frequencies of two FGM cylindrical shells. Type I FGM cylindrical shell has Nickel on its inner surface and stainless steel on its outer surface and Type II FGM cylindrical shell has stainless steel on its inner surface and nickel on its outer surface. The study is carried out based on third order shear deformation shell theory. The objective is to study the natural frequencies, the influence of constituent volume fractions and the effects of configurations of the constituent materials on the frequencies. The properties are graded in the thickness direction according to the volume fraction power-law distribution. The governing equations are obtained using energy functional with the Rayleigh-Ritz method. Results are presented on the frequency characteristics, the influence of the constituent various volume fractions on the frequencies for a Type I, II FGM cylindrical shell.
Keywords: Stainless Steel, Nickel, FGM.
Application of Genetic Algorithm in Optimization of Composite Laminates
Vol. 4. n. 2, pp. 911-917
Abstract - In this paper, application of genetic algorithm (GA) to optimize composite laminates from weight and resistance against buckling point of views is presented. A rectangular composite laminate under axial, bending and general loadings is considered to minimize its weight. Furthermore, a cylindrical shell under compressive loading is considered to optimize its resistance against buckling. Number of plies, stacking sequences and thickness of each layer are design variables. Tsai-Wu failure criterion is the constraint of the optimization problems.
Keywords: Composite Materials, Optimization, Genetic Algorithm.
Feasibility Study on Increasing the Power of the Turbine Driver of Compressor Using an Absorption Refrigeration Cycle on Cooling Circuit of Condenser
Vol. 4. n. 2, pp. 918-928
Abstract - One of the methods of increasing the power of the steam turbines is decreasing the exhaust pressure. In this method, the exhaust section is connected to a surface condenser which operates in vacuum condition. Consequently, the lower saturating pressure of condensed vapor leads to the higher power of turbine. Steam turbine studied here consists of two high- and low-pressure cylinders that, a portion of steam should be extracted between them. Saturation pressure of this temperature is about 24 kPa that is higher than exhaust pressure of similar turbines in this region of Iran. Therefore, in this research, feasibility of utilization of absorption refrigeration in lowering the cooling water temperature and its effect on increasing the power of the turbine was studied. In order to this, firstly, mathematical model of the system was defined, then this model was simulated by EES software, then, the variation of exhaust pressure and power of the turbine were obtained. Results show that, 75.31% decrease in the temperature of cooling water causes 13.94% decrease in the exhaust pressure and 0.93% increase in the power of the turbine. Regarding the water velocity in the condenser pipes, effect of increasing this velocity on power of the turbine was studied. Results show that increasing the velocity to 8 ft/sec, using first method causes 3.93% decrease in the exhaust pressure and 0.205% raise in the power. Finally, specification of a suitable condenser that should be replaced with the present one was estimated.
Keywords: Cooling Water, Absorption Refrigeration, Condenser Pressure, Simulation, Improvement.
A New Approach for Annoyances Assessment of the Urban Building Sites
Vol. 4. n. 2, pp. 929-934
Abstract - In this paper, we focus our study on the modelling of the annoyances generated by the urban building sites. Specifically, we present a new approach that allows evaluating the annoyances caused by some nuisances of the building sites. This approach will be used in a decision support system to help managers of public spaces to reduce annoyances and improve the life quality of the townsmen. However, in this paper, we limit our study to the modelling of annoyance caused by a single nuisance, namely, noise.
Keywords: Annoyance, Decision-Making, Noise, Nuisance, Urban Building Sites.
Vol. 4. n. 2, pp. 935-941
Abstract - In this paper, the laser beam welding is studied and copper temperature field is gained in this process. The thermal effect of laser beam that specially depends on the laser type and temperature field of it in workpiece, is the main key of analysis and optimization of this process, from which the main goal of this paper has been defined. Utilizing laser as a method to join plastic components is growing in popularity. The ability to create clean, strong and consistent hermetic seals is very attractive for manufacturers. Numerical simulation of welding process in SIMPELC method and by ANSYS software for gaining the temperature field of copper, the effect of parameter variation on temperature field and process optimization for different cases of laser are done. Conditions were determined for consistent coupling of a laser beam to weld copperalloy sheet. Process conditions examined included beam mode, spot size and irradiance, shielding gas flow, and edge quality and fit up.
Keywords: Copper, Laser beam welding, Numerical Simulation, ANSYS-FSI.
Modelling of Residence Time Distribution in Static Mixer: A Ricker Approach
Vol. 4. n. 2, pp. 942-950
Abstract - To improve the understanding of how static mixers work and how to better utilize them in environmental engineering (or, specifically, drinking water treatment), a numerical model for simulating RTD of turbulent flows in helical static mixers is developed. Ricker model are carried out for a static mixer, and the computed results are analyzed to elucidate the complex, three-dimensional features of the flow. The experimental unit is an annulus in which helical elements are brazed on the outer surface of inner tube. The helical elements are arranged alternatively in right and left-handed format. RTD studies were performed by injecting a pulse (NaCl solution) and the response at the outlet was measured. Even at low flow rates, the exit age distribution curves for the unit with mixing elements were highly skewed in nature and the variance was in the range of 0.27 to 0.12. The proposed model is found to fit the RTD with a high degree of correlation.
Keywords: Mathematical simulations, Residence Time Distribution, Ricker Model, Tubular Reactor, Standard Error Estimation, Static Mixer.
Vol. 4. n. 2, pp. 951-960
Abstract - The problem addressed in this work concerns a new heuristic based on a shifting method used to solve an integrated production and preventive maintenance strategy for a job shop scheduling problem. This shifting new method aims to reduce the Makespan Cmax and the maintenance total cost caused by the advances or the delays of preventive maintenance tasks. In general, delayed maintenance tasks have a higher cost because they increase the risk of the breakdowns and generate a stop of production. This proposed method is based on a set of rules taking into account the job shop scheduling problem constraints and the maintenance tasks ranges. To underline the effectiveness of the method, some illustrative benchmarks are provided. The performances of the new algorithm concerns the Makespan Cmax, the free time rate and some other statistics related to the production cost.
Keywords: Assignment, Availability, constraints, Maintenance, Optimization, Methods, Scheduling.
Interactive Fuzzy Programming for the Production Planning: the Case of Textile Firm
Vol. 4. n. 2, pp. 961-970
Abstract - The main goal of this paper is to investigate an application problem of fuzzy linear programming model in a textile firm. A new recursive iteration method has been proposed in this research work to solve an uncertain resource variables problem under fuzzy environments. A realistic modified logistic membership function has been utilized in order to capture the fuzziness in the resource variables. The proposed method successfully solves the fuzzy optimization problem in obtaining the optimal solution of the profit function. A comparative study reveals the significant contribution of the proposed techniques in solving the fuzzy optimization problem. The computational results obtained in this paper will be very useful for the analyst and the implementers in the process of satisfactory decision making under turbulent environment.
Keywords: Fuzziness, recursive, resource variables, logistic membership function, degree of satisfaction, optimal profit.
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