Showing 81 results for Cr
A. Abdolali, M. M Salary,
Volume 10, Issue 3 (9-2014)
Abstract
The proposed theorem in this paper is indicative of a kind of duality in the propagation of waves in the dual media of and in the spherical structures. Independent of wave frequency, the number of layers, their thickness, and the type of polarization, this theorem holds true in case of any change in any of these conditions.
Theorem: Consider a plane wave incident on a multilayered spherical structure. The core of structure may be PEC, metamaterial or dielectric. If we apply the interchange or for the constituting materials of the spherical structure and the surrounding medium the radar cross section of the structure will not change in any direction.
A. Halvaei Niasar, E. Boloor Kashani,
Volume 10, Issue 3 (9-2014)
Abstract
In this paper, one-cycle control (OCC), as a constant-frequency PWM control strategy for current control of a six-switch brushless dc (BLDC) motor drive is investigated. Developed current regulator is a unified controller and PWM modulator. Employing the one-cycle control strategy, decreases the torque ripple resulted from the conventional hysteresis current controllers and therefore, the vibration and acoustic noise of the drive are reduced. Total operations of the system control and OCC strategy are realized by a low-cost general-purpose AVR microcontroller (Atmega8) that leads to a low-cost, high performance BLDC motor drive. Computer simulations using Matlab simulator, have been presented to show the good characteristics of this solution. Furthermore, experimental works show the excellent behavior of developed BLDC drive and agreement with simulation results.
S. M. Marvasti Zadeh, H. Ghanei Yakhdan, Sh. Kasaei,
Volume 10, Issue 3 (9-2014)
Abstract
Sending compressed video data in error-prone environments (like the Internet and wireless networks) might cause data degradation. Error concealment techniques try to conceal the received data in the decoder side. In this paper, an adaptive boundary matching algorithm is presented for recovering the damaged motion vectors (MVs). This algorithm uses an outer boundary matching or directional temporal boundary matching method to compare every boundary of candidate macroblocks (MBs), adaptively. It gives a specific weight according to the accuracy of each boundary of the damaged MB. Moreover, if each of the adjacent MBs is already concealed, different weights are given to the boundaries. Finally, the MV with minimum adaptive boundary distortion is selected as the MV of the damaged MB. Experimental results show that the proposed algorithm can improve both objective and subjective quality of reconstructed frames without any considerable computational complexity The average PSNR in some frames of test sequences increases about 4.59, 4.44, 3.57, and 2.98 dB compared to classic boundary matching, directional boundary matching, directional temporal boundary matching, and outer boundary matching algorithm, respectively.
A. Vahedi, A. Baktash,
Volume 11, Issue 1 (3-2015)
Abstract
Recently, tape wound cores due to their excellent magnetic properties, are widely used in different types of transformers. Performance prediction of these transformers needs an accurate model with ability to determine flux distribution within the core and magnetic loss. Spiral structure of tape wound cores affects the flux distribution and always cause complication of analysis. In this paper, a model based on reluctance networks method is presented for analysis of magnetic flux in wound cores. Using this model, distribution of longitudinal and transverse fluxes within the core can be determined. To consider the nonlinearity of the core, a dynamic hysteresis model is included in the presented model. Having flux density in different points of the core, magnetic losses can be calculated. To evaluate the validity of the model, results are compared with 2-D FEM simulations. In addition, a transformer designed for series-resonant converter and simulation results are compared with experimental measurements. Comparisons show accuracy of the model besides simplicity and fast convergence
H. Rahmanian, S. H Sedighy, M. Khalaj Amirhosseini,
Volume 11, Issue 1 (3-2015)
Abstract
A method for design and implementation of a compact via-less Composite
Right/Left-Handed Transmission Line (CRLH TL) is presented. By introducing a new
circuit model, the CRLH transmission line behavior is studied versus the parameters
variations to achieve the desired characteristic impedance and electrical length. Then a
compact quarter wavelength CRLH transmission line with 70 Ω characteristic impedance is
designed as an example. Finally a very compact four way Wilkinson power divider and a
rat-race coupler are designed and fabricated by using this type of CRLH TL which exhibit
about 75% and 80% compactness, respectively.
M. Pourmahyabadi,
Volume 11, Issue 1 (3-2015)
Abstract
In this article, Hill Climbing (HC) and Estimation of Distribution Algorithm (EDA) are integrated to produce a hybrid intelligent algorithm for design of endlessly Single Mode Photonic Crystal Fibers (SMPCFs) structure with desired properties over the C communication band. In order to analyzing the fiber components, Finite Difference Frequency Domain (FDFD) solver is applied. In addition, a special cost function which simultaneously includes the confinement loss, dispersion and its slope is considered in the proposed optimization algorithm. The results revealed that the proposed method is a powerful tool for solving this optimization problem. The optimized PCF exhibits an ultra-low confinement loss and low dispersion at 1.55 µm wavelength with a nearly zero dispersion slope over the C communication band.
H. Hasanzadeh Fard, S. A. Bahreyni , R. Dashti , H. A. Shayanfar,
Volume 11, Issue 2 (6-2015)
Abstract
Evaluation of the reliability parameters in micro-grids based on renewable energy sources is one of the main problems that are investigated in this paper. Renewable energy sources such as solar and wind energy, battery as an energy storage system and fuel cell as a backup system are used to provide power to the electrical loads of the micro-grid. Loads in the micro-grid consist of interruptible and uninterruptible loads. In addition to the reliability parameters, Forced Outage Rate of each component and also uncertainty of wind power, PV power and demand are considered for micro-grid. In this paper, the problem is formulated as a nonlinear integer minimization problem which minimizes the sum of the total capital, operational, maintenance and replacement cost of DERs. This paper proposes PSO for solving this minimization problem.
F. Namdari, M. Parvizi, E. Rokrok,
Volume 12, Issue 1 (3-2016)
Abstract
Integration of distributed generations (DGs) in power grids is expected to play an essential role in the infrastructure and market of electrical power systems. Microgrids are small energy systems, capable of balancing captive supply and requesting resources to retain stable service within a specific boundary. Microgrids can operate in grid-connected or islanding modes. Effective islanding detection methods are essential for realizing the optimal operation of microgrids. In this paper, a new passive islanding detection method is presented according to the change rate of DG’s voltage over active power index. This technique has been applied on inverter-based and synchronous-based microgrids. The efficiency of the proposed method is verified through a comprehensive set of simulation studies carried out in Matlab/Simulink.
R. Sanjari, M. Pourmahyabadi,
Volume 12, Issue 1 (3-2016)
Abstract
In this article, a novel structure of photonic crystal fiber with nearly zero ultra-flattened chromatic dispersion and ultra-low confinement loss is presented. By replacing the circular air-holes of two first rings with the elliptical air-holes, a fiber with outstanding features of chromatic dispersion and confinement loss is designed. The proposed structure is optimized for operating in a wide wavelength range covering S, C, and L communications bands. Finite Difference Frequency Domain (FDFD) solver is applied to analyze the proposed fiber components. The designed fiber exhibits a chromatic dispersion of -0.12 ps/nm/km at 1.55 µm along with a slope of 0.002 ps/nm2 /km. Also, the other remarkable feature of this fiber is ultra-low confinement loss in order of 10-5 dB/km around λ = 1.55 µm.
E. Alizadeh, A. M. Birjandi, M. Hamzeh,
Volume 12, Issue 4 (12-2016)
Abstract
This paper proposes an autonomous and economic droop control scheme for DC microgrid application. In this method, a cost-effective power sharing technique among various types of DG units is properly adopted. The droop settings are determined based on an algorithm to individually manage the power management without any complicated optimization methods commonly applied in the centralized control method. In the proposed scheme, the system retains all the advantages of the traditional droop method while minimizes the generation costs of the DC microgrid. In the proposed method, all DGs are classified in a sorting rule based on their total generation cost and the reference voltage of their droop equations is then determined. The proposed scheme is applied to a typical DC microgrid consisting of four different types of DGs and a controllable load. The simulation results are presented to verify the effectiveness of the proposed method using MATLAB/SIMULINK software.
H. Shayeghi, A. Ghasemi,
Volume 12, Issue 4 (12-2016)
Abstract
Microgrids is an new opportunity to reduce the total costs of power generation and supply the energy demands through small-scale power plants such as wind sources, photo voltaic panels, battery banks, fuel cells, etc. Like any power system in micro grid (MG), an unexpected faults or load shifting leads to frequency oscillations. Hence, this paper employs an adaptive fuzzy P-PID controller for frequency control of microgrid and a modified multi objective Chaotic Gravitational Search Algorithm (CGSA) in order to find out the optimal setting parameters of the proposed controller. To provide a robust controller design, two non-commensurable objective functions are formulated based on eigenvalues-domain and time-domain and multi objective CGSA algorithm is used to solve them. Moreover, a fuzzy decision method is applied to extract the best and optimal Pareto fronts. The proposed controller is carried out on a MG system under different loading conditions with wind turbine generators, photovoltaic system, flywheel energy, battery storages, diesel generator and electrolyzer. The simulation results revealed that the proposed controller is more stable in comparison with the classical and other types of fuzzy controller.
M. Khalilzadeh, A. Fereidunian,
Volume 12, Issue 4 (12-2016)
Abstract
In this paper, a stochastic approach is proposed for reliability assessment of bidirectional DC-DC converters, including the fault-tolerant ones. This type of converters can be used in a smart DC grid, feeding DC loads such as home appliances and plug-in hybrid electric vehicles (PHEVs). The reliability of bidirectional DC-DC converters is of such an importance, due to the key role of the expected increasingly utilization of DC grids in modern Smart Grid. Markov processes are suggested for reliability modeling and consequently calculating the expected effective lifetime of bidirectional converters. A three-leg bidirectional interleaved converter using data of Toyota Prius 2012 hybrid electric vehicle is used as a case study. Besides, the influence of environment and ambient temperature on converter lifetime is studied. The impact of modeling the reliability of the converter and adding reliability constraints on the technical design procedure of the converter is also investigated. In order to investigate the effect of leg increase on the lifetime of the converter, single leg to five-leg interleave DC-DC converters are studied considering economical aspect and the results are extrapolated for six and seven-leg converters. The proposed method could be generalized so that the number of legs and input and output capacitors could be an arbitrary number.
A. A. Khodadoost Arani, B. Zaker, G. B. Gharehpetian,
Volume 13, Issue 1 (3-2017)
Abstract
The Micro-Grid (MG) stability is a significant issue that must be maintained in all operational modes. Usually, two control strategies can be applied to MG; V/f control and PQ control strategies. MGs with V/f control strategy should have some Distributed Generators (DGs) which have fast responses versus load changes. The Flywheel Energy Storage System (FESS) has this characteristic. The FESS, which converts the mechanical energy to electrical form, can generate electrical power or absorb the additional power in power systems or MGs. In this paper, the FESS structure modeled in detail and two control strategies (V/f and PQ control) are applied for this application. In addition, in order to improve the MG frequency and voltage stability, two complementary controllers are proposed for the V/f control strategy; conventional PI and Fuzzy Controllers. A typical low voltage network, including FESS is simulated for four distinct scenarios in the MATLAB/ Simulink environment. It is shown that fuzzy controller has better performance than conventional PI controller in islanded microgrid.
N. Okati, M. R. Mosavi, H. Behroozi,
Volume 13, Issue 4 (12-2017)
Abstract
Node cooperation can protect wireless networks from eavesdropping by using the physical characteristics of wireless channels rather than cryptographic methods. Allocating the proper amount of power to cooperative nodes is a challenging task. In this paper, we use three cooperative nodes, one as relay to increase throughput at the destination and two friendly jammers to degrade eavesdropper’s link. For this scenario, the secrecy rate function is a non-linear non-convex problem. So, in this case, exact optimization methods can only achieve suboptimal solution. In this paper, we applied different meta-heuristic optimization techniques, like Genetic Algorithm (GA), Partial Swarm Optimization (PSO), Bee Algorithm (BA), Tabu Search (TS), Simulated Annealing (SA) and Teaching-Learning-Based Optimization (TLBO). They are compared with each other to obtain solution for power allocation in a wiretap wireless network. Although all these techniques find suboptimal solutions, but they appear superlative to exact optimization methods. Finally, we define a Figure of Merit (FOM) as a rule of thumb to determine the best meta-heuristic algorithm. This FOM considers quality of solution, number of required iterations to converge, and CPU time.
E. Alizadeh, A. Motie Birjandi, M. Hamzeh,
Volume 13, Issue 4 (12-2017)
Abstract
This paper proposes a decentralized control technique to minimize the total operation cost of a DC microgrid in both grid-connected and islanded modes. In this study, a cost-based droop control scheme based on the hourly bids of all participant distributed generators (DGs) and the hourly energy price of the utility is presented. An economic power sharing technique among various types of DG units is adopted to appropriately minimize the daily total operation cost of DC microgrid without a microgrid central controller. The DC microgrid may include non-dispatchable DG units (such as photovoltaic systems) and dispatchable generation units. Unlike other energy management techniques, the proposed method suffers neither from forecasting errors for both load demand and renewable energy power prediction modules, nor from complicated optimization techniques. In the proposed method, all DGs and the utility are classified in a sorting rule based on their hourly bids and open market price, and then the droop parameters are determined. The simulation results are presented to verify the effectiveness of the proposed method using MATLAB/SIMULINK software. The results show that the proposed strategy is able to be implemented in various operation conditions of DC microgrid with resistance to uncertainties.
S. Dolatabadi, S. Tohidi, S. Ghasemzadeh,
Volume 14, Issue 4 (12-2018)
Abstract
In this paper, a new active method based on traveling wave theory for islanding detection is presented. A standard power grid that combines a distributed generation source and local loads is used to test the proposed method. Simulations are carried out in MATLAB/Simulink and EMTP/rv which demonstrate fast response and zero non-detection zone (NDZ) of the method along with low perturbation.
M. Tahmasebipour, M. Modarres,
Volume 14, Issue 4 (12-2018)
Abstract
In this paper, a highly sensitive piezoresistive differential pressure microsensor is proposed. This microsensor is consisted of a silicon microcantilever (Length=145 µm; Width=100 µm; Thickness=0.29 µm) and two piezoresistors were mounted (via proper connections) on the microsensor for measuring the created pressure difference. Applying pressure to the microcantilever induces longitudinal and transverse stresses in the piezoresistors, changing their electric resistance and, consequently, the output voltage in the reading circuit of the microsensor. Longitudinal and transverse stresses, different relative sensor resistances resulting from different pressures, voltage variations along the piezoresistors, and microcantilever deflection resulting from different pressures were investigated. To improve the sensor sensitivity, effect of doping concentration, piezoresistors width, and the width of the structure placed under the piezoresistors were studied. In addition, we studied how increasing the width and length of the beam influenced the sensitivity of the sensor. Based on analysis results, the sensor sensitivity was increased from 0.26 W/Pa to 15.78 W/Pa (~60 times). To evaluate the behavior and performance of the proposed microsensor, the following characteristics were analyzed: maximum microcantilever displacement, von Mises stress distribution along the beam and microsensor resistance variations.
S. Mirzakuchaki, Z. Paydar,
Volume 14, Issue 4 (12-2018)
Abstract
In this study a method has been introduced to map the features extracted from the recorded electromyogram signals from the forearm and the force generated by the fingers. In order to simultaneously record of sEMG signals and the force produced by fingers, 9 requested movements of fingers conducted by 10 healthy people. Estimation was done for 6 degrees of freedom (DoF) and generalized regression neural network (GRNN) was selected for system training. The optimal parameters, including the length of the time windows, the parameters of the neural network, and the characteristics of the sEMG signal were calculated to improve the performance of the estimate. The performance was obtained based on R2 criterion. The Total value of R2 for 6 DoF was 92.8±5.2% that obtained by greedy looking system parameters in all the subjects. The result shows that proposed method can be significant in simultaneous myoelectric control.
F. Khamin Hamedani, Gh. Karimi,
Volume 14, Issue 4 (12-2018)
Abstract
A novel dual-band bandpass filter (DB-BPF) with controllable parameters in design process and a compact structure is introduced in this paper. The total structure includes open-circuited and short circuited coupled-lines, leading to a compact circuit. The resonance frequencies, insertion loss and quality factor can be independently controlled by adjusting the coupled lines. In order to eliminate the magnetic and electric coupling effects, the virtual grounds are placed in coupled complementary hairpin resonator. To verify the validity of the design approach, a DB-BPF centring, at 3.5 and 5 GHz with respective insertion losses of 0.7 and 0.58dB for WIMAX (IEEE 802.16 band) and WLAN (IEEE 802.11 band) applications has been designed and fabricated, whose the measured results confirm the electromagnetic simulation.
A. Younesi, H. Shayeghi,
Volume 15, Issue 1 (3-2019)
Abstract
The purpose of this paper is to design a supplementary controller for traditional PID controller in order to damp the frequency oscillations in a micro-grid. Q-learning, which is used for supervise a classical PID controller in this paper, is a model free and a simple solution method of reinforcement learning (RL). RL is one of the branches of the machine learning, which is the main solution method of Markov decision process (MDPs). The proposed control mechanism is consisting of two main parts. The first part is a classical PID controller which is fixed tuned using Salp swarm algorithm. The second part is a Q‑learning based control strategy which is consistent and updates its characteristics according to the changes in the system continuously. Eventually, a hybrid micro-grid is considered to evaluate the performance of the suggested control method compared to classical PID and fractional order fuzzy PID (FOFPID) controllers. The considered hybrid system is consisting of renewable energy resources such as solar-thermal power station (STPS) and wind turbine generation (WTG), along with several energy storage devices such as batteries, flywheel and ultra-capacitor with physical constraints and time delays. Simulations are carried out in various realistic scenarios considering system parameter variations along with changing in operating conditions. Results indicate that the proposed control strategy has an excellent dynamic response compared to the traditional PID and FOFPID controllers for damping the frequency oscillations in different operating conditions.
