Showing 19 results for Ber
A. Dastfan, F. Behrangi,
Volume 5, Issue 1 (3-2009)
Abstract
A conventional high power DC power supply systems consist of a three-phase
diode rectifier followed by a high frequency converter to supply loads at regulated DC
voltage. These rectifiers draw significant harmonic currents from the utility, resulting in
poor input power factor. In this paper, a DC power supply based on dual-bridge matrix
converter (DBMC) with reduced number of switches is proposed. In the proposed circuit,
three switches convert the low frequency AC input to a DC link. A single-phase bridge
inverter converts the DC-link to a high frequency AC output. The output of the matrix
converter is then processed via a high frequency isolation transformer and rectified to the
regulated DC voltage. In the proposed topology only a simple voltage control loop ensures
that the output voltage is regulated against load changes as well as input supply variations
and the current control loop is not used to correct the input currents. Theory analysis and
simulation are made to investigate performance of the proposed circuit. Simulation results
show that in the proposed power supply with 7-switch, the input currents are of a high
quality under varying load conditions and input voltage.
M. Pourmahyabadi, Sh. Mohammad Nejad,
Volume 5, Issue 3 (9-2009)
Abstract
In this article, perfectly matched layer (PML) for the boundary treatment and an efficient compact two dimensional finite-difference frequency-domain (2-D FDFD) method were combined to model photonic crystal fibers (PCF). For photonic crystal fibers, if we assume that the propagation constant along the propagation direction is fixed, three-dimensional hybrid guided modes can be calculated by using only a two-dimensional mesh. An index-guiding PCF with an array of air-holes surrounding the silica core region has special characteristics compared with conventional single-mode fibers (SMFs). Using this model, the fundamental characteristics of single mode photonic crystal fibers (SMPCFs) such as confinement loss, bending loss, effective mode area and chromatic dispersion are numerically investigated. The results revealed that low confinement loss and zero-flattened chromatic dispersion can be obtained by varying the air-holes diameter of each ring along the PCF radius. In this work, an especial PCF with nearly zero-flattened dispersion (1.3 ps/nm/km) over a wide wavelength range which covers O, E, S, C, L and U telecommunication wavelength bands and low confinement loss (0.06 dB/km at 1.55μm) is designed. Macro-bending loss performance of the designed PCF is also studied and it is found that the fiber shows low bending losses for the smallest feasible bending radius of 5 mm. Also, it is revealed that the temperature sensitivity of PCFs is very low in compared with the conventional fibers.
Vahid Abbasi, Ahmad Gholami,
Volume 6, Issue 1 (3-2010)
Abstract
Abstract: The application of electric field theory to widely different aspects of electrical
insulation has led to more understanding the phenomena. Electric fields may be considered
as the main reason for insulation failure. The purpose of this paper is to modify importance
of analyzing electric field in insulation design. The SF6 circuit breaker is chosen as case
study that encounters critical situations during its application. The other phenomena affects
insulation is the presence of polar species in a non-polar molecular material locally
modifies the polarization energy, thus creating local states (traps) on neighboring
molecules. Results of calculations carried out for arrays of spatially connected dipoles
indicating that local states of a considerable density may be created, modifying the densityof-
states function, and therefore influencing the effective mobility of charge carriers. The
main result of polarization during application in circuit breaker is loss of life. In this paper
the reduction of negative effects of electric field and polarization by choosing a suitable
insulation structure in a 33 kV SF6 circuit breaker according to calculation in critical areas
is investigated that can also be studied in other types of circuit breakers.
M. R. Homaeinezhad, A. Ghaffari, H. Najjaran Toosi, M. Tahmasebi, M. M. Daevaeiha,
Volume 7, Issue 1 (3-2011)
Abstract
In this study, a new long-duration holter electrocardiogram (ECG) major events detection-delineation algorithm is described which operates based on the false-alarm error bounded segmentation of a decision statistic with simple mathematical origin. To meet this end, first three-lead holter data is pre-processed by implementation of an appropriate bandpass finite-duration impulse response (FIR) filter and also by calculation of the Euclidean norm between corresponding samples of three leads. Then, a trous discrete wavelet transform (DWT) is applied to the resulted norm and an unscented synthetic measure is calculated between some obtained dyadic scales to magnify the effects of low-power waves such as P or T-waves during occurrence of arrhythmia(s). Afterwards, a uniform length window is slid sample to sample on the synthetic scale and in each slid, six features namely as summation of the nonlinearly amplified Hilbert transform, summation of absolute first order differentiation, summation of absolute second order differentiation, curve length, area and variance of the excerpted segment are calculated. Then all feature trends are normalized and superimposed to yield the newly defined multiple-order derivative wavelet based measure (MDWM) for the detection and delineation of ECG events. In the next step, a α-level Neyman-Pearson classifier (which is a false-alarm probability-FAP controlled tester) is implemented to detect and delineate QRS complexes. To show advantages of the presented method, it is applied to MIT-BIH Arrhythmia Database, QT Database, and T-Wave Alternans Database and as a result, the average values of sensitivity and positive predictivity Se = 99.96% and P+ = 99.96% are obtained for the detection of QRS complexes, with the average maximum delineation error of 5.7 msec, 3.8 msec and 6.1 msec for P-wave, QRS complex and T-wave, respectively showing marginal improvement of detection-delineation performance. In the next step, the proposed method is applied to DAY hospital high resolution holter data (more than 1,500,000 beats including Bundle Branch Blocks-BBB, Premature Ventricular Complex-PVC and Premature Atrial Complex-PAC) and average values of Se=99.98% and P+=99.97% are obtained for QRS detection. In summary, marginal performance improvement of ECG events detection-delineation process in a widespread values of signal to noise ratio (SNR), reliable robustness against strong noise, artifacts and probable severe arrhythmia(s) of high resolution holter data and the processing speed 163,000 samples/sec can be mentioned as important merits and capabilities of the proposed algorithm.
M. Shams Esfand Abadi, S. Nikbakht,
Volume 7, Issue 2 (6-2011)
Abstract
Two-dimensional (TD) adaptive filtering is a technique that can be applied to many image, and signal processing applications. This paper extends the one-dimensional adaptive filter algorithms to TD structures and the novel TD adaptive filters are established. Based on this extension, the TD variable step-size normalized least mean squares (TD-VSS-NLMS), the TD-VSS affine projection algorithms (TD-VSS-APA), the TD set-membership NLMS (TD-SM-NLMS), the TD-SM-APA, the TD selective partial update NLMS (TD-SPU-NLMS), and the TD-SPU-APA are presented. In TD-VSS adaptive filters, the step-size changes during the adaptation which leads to improve the performance of the algorithms. In TD-SM adaptive filter algorithms, the filter coefficients are not updated at each iteration. Therefore, the computational complexity is reduced. In TD-SPU adaptive algorithms, the filter coefficients are partially updated which reduce the computational complexity. We demonstrate the good performance of the proposed algorithms thorough several simulation results in TD adaptive noise cancellation (TD-ANC) for image restoration. The results are compared with the classical TD adaptive filters such as TD-LMS, TD-NLMS, and TD-APA
M. Aliramezani, Sh. Mohammad Nejad,
Volume 8, Issue 2 (6-2012)
Abstract
In this paper, a novel design of all-solid photonic bandgap fiber with ultra-low
confinement loss is proposed. The confinement loss is reduced remarkably by managing the
number of rods rings, up-doping level, pitch value, and rods diameters. Moreover, the
designed PCF shows ultra-flattened dispersion in L- and U-band. Furthermore, a new
design, based on introducing of an extra ring of air holes on the outside of the all-solid
bandgap structure, is then proposed and characterized. We demonstrate that it significantly
reduces the fiber diameter to achieve negligible confinement loss. The validation of the
proposed design is carried out by employing a two dimensional finite difference frequency
domain with perfectly matched layers.
B. Ghafary, F.d. Kashani, E. Kazemian,
Volume 9, Issue 1 (3-2013)
Abstract
The effects of aberration on the Bit-Error-Rate (BER) and reliability of free- space optical (FSO) communication links are investigated. Based on aberrated divergent rectangular partially coherent flat-topped beam formula on the receiver plane and considering the atmosphere losses due to absorption and scattering, numerical values for Power In Bucket (PIB), Signal to Noise Ratio (SNR) and BER are calculated. Using above mentioned values, the effects of source parameters on link reliability is described. The results are illustrated by graphs obtained by calculation and simulation.
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.
M. Rezaei, A. Falahati,
Volume 12, Issue 1 (3-2016)
Abstract
In this paper, a cooperative algorithm to improve the orthogonal space-timefrequency block codes (OSTFBC) in frequency selective channels for 2*1, 2*2, 4*1, 4*2 MIMO-OFDM systems, is presented. The algorithm of three node, a source node, a relay node and a destination node is formed, and is implemented in two stages. During the first stage, the destination and the relay antennas receive the symbols sent by the source antennas. The destination node and the relay node obtain the decision variables employing time-space-frequency decoding process by the received signals. During the second stage, the relay node transmits decision variables to the destination node. Due to the increasing diversity in the proposed algorithm, decision variables in the destination node are increased to improve system performance. The bit error rate of the proposed algorithm at high SNR is estimated by considering the BPSK modulation. The simulation results show that cooperative orthogonal space-time-frequency block coding, improves system performance and reduces the BER in a frequency selective channel.
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. Babaei, Z. Saadatizadeh, S. Laali,
Volume 12, Issue 2 (6-2016)
Abstract
In this paper, a new bidirectional buck-boost dc-dc converter with capability of soft switching and zero input current ripple is proposed. The coupled inductor is used in the proposed converter to eliminate the input current ripple. In the proposed converter, zero voltage switching (ZVS) and zero current switching (ZCS) can be obtained for the main and auxiliary switches, respectively. In addition, the proposed topology is analyzed in all operating modes and all equations of voltage and current for components are obtained. Moreover, the required conditions for soft switching operation and also achieving zero input current ripple are calculated. Finally, the acuracy performance of the proposed converter is reconfirmed through simulation results in EMTDC/PSCAD software program.
S. Mohammad Nejad, H. Arab, N. Ronagh Sheshkelani,
Volume 14, Issue 3 (9-2018)
Abstract
In this paper, after a brief overview on laser warning system (LWS), a new structure for an optical array that is used in its optical subsystem is introduced. According to the laser threats’ wavelengths (0.5 – 1.6 µm) and our desirable field of view (FOV), we used 6 lenses for gathering the incident radiation and then optimized the optical array. Lenses’ radius, their semi diameter, their distance from each other, their thickness and the kind of glass used in them was chosen in which we access a very high transmission coefficient. Also the optical reflection and absorption of the array decreases at the same time. After optimization, the obtained optical transmission in our desirable FOV is up to 82% and the obtained optical reflection and absorption is less than 15%. Total aberration of the incident ray decreased notably and the results showed that this parameter is less than 2µm. The laser spot diameter which is focused on the detector is smaller than 400 µm in the worst case which is the laser radiation with 1.54 µm wavelength and field of 10 degrees. Total track of the array is 66.819 mm and effective focal length and F/# parameter are as small as possible which leads to high quality of the light’s focus on the detector and smaller dimension and lighter weight for the receiver. Using optical devices with such appropriate arrangement and very good optical transmission coefficient, the offered structure has a remarkable signal to noise ratio (SNR) which is up to 160 dB. The receiver’s operation in far distances from laser sources (beyond 15 km) and in hazy conditions and low temperatures is quite suitable as well.
S. Hajiaghasi, Z. Rafiee, A. Salemnia, T. Soleymani Aghdam,
Volume 15, Issue 3 (9-2019)
Abstract
Since the insulators of transmission lines are exposed to different environmental conditions, it is important task to study insulators performance under different conditions. In this paper, silicone rubber insulators performance under different environmental conditions including rainy, icy, salt and cement are proposed and exactly is studied. Electric fields (E-fields) and voltage distributions along the insulator under various conditions have been evaluated. Moreover, the corona rings effects on insulator performance under these conditions have been presented. A 230 kV silicone rubber insulator is selected, modeled and simulated with finite element method (FEM) using the COMSOL software. The simulation is repeated for different environmental conditions and efficiency of corona ring for each scenario is evaluated. The results indicate that environmental conditions have a significant effect on the insulator performance and the corona ring somewhat alleviate the adverse effect of environmental conditions on the insulator performance.
Z. Kazemi, A. A. Safavi,
Volume 16, Issue 3 (9-2020)
Abstract
Kalman filtering has been widely considered for dynamic state estimation in smart grids. Despite its unique merits, the Kalman Filter (KF)-based dynamic state estimation can be undesirably influenced by cyber adversarial attacks that can potentially be launched against the communication links in the Cyber-Physical System (CPS). To enhance the security of KF-based state estimation, in this paper, the basic KF-based method is enhanced by incorporating the dynamics of the attack vector into the system state-space model using an observer-based preprocessing stage. The proposed technique not only immunizes the state estimation against cyber-attacks but also effectively handles the issues relevant to the modeling uncertainties and measurement noises/errors. The effectiveness of the proposed approach is demonstrated by detailed mathematical analysis and testing it on two well-known IEEE cyber-physical test systems.
G. Morankar,
Volume 17, Issue 3 (9-2021)
Abstract
Tremendous developments in integrated circuit technology, wireless communication systems, and personal assistant devices have fuelled growth of Internet of Things (IoT) applications and smart cards. The security of these devices completely depends upon the generation of random and unpredictable digital data streams through random number generator. Low quality, low throughput, and high processing time are observed in software-based pseudo-random number generator due to interrelated data or programs and serial execution of codes respectively. In this paper, FPGA implementation of low power true random number generator through ring oscillator for IoT applications and smart cards is presented. Ring oscillators based on higher jitter and sampling techniques were exploited to present true random number generator. Further statistical parameters of the generated data streams are enhanced through feedback mechanism and post-processing technique. The presented true random number generator technique does not depend on the characteristics of a particular FPGA. The presented technique consumes low power, requires low hardware footprints and passes the entire National Institute of Standards & Technology (NIST) 800-22 statistical test suite. The presented low power and area true random number generator with enhanced security through post-processing unit may be applied for encryption/decryption of data in IoT and smart cards.
Reza Behnam, Gevork Gharehpetian,
Volume 18, Issue 4 (12-2022)
Abstract
State estimation is used in power systems to estimate grid variables based on meter measurements. Unfortunately, power grids are vulnerable to cyber-attacks. Reducing cyber-attacks against state estimation is necessary to ensure power system safe and reliable operation. False data injection (FDI) is a type of cyber-attack that tampers with measurements. This paper proposes network reconfiguration as a strategy to decrease FDI attacks on distribution system state estimation. It is well-known that network reconfiguration is a common approach in distribution systems to improve the system’s operation. In this paper, a modified switch opening and exchange (MSOE) method is used to reconfigure the network. The proposed method is tested on the IEEE 33-bus system. It is shown that network reconfiguration decreases the power measurements manipulation under false data injection attacks. Also, the resilient configuration of the distribution system is achieved, and the best particular configuration for reducing FDI attacks on each bus is obtained.
Makan Torabi, Yousef Alinejad-Beromi,
Volume 19, Issue 4 (12-2023)
Abstract
A double-sided axial flux Permanent Magnet (PM) generator which can be directly driven by small-scale low-speed turbines is highly suitable for use in renewable energy generation systems. Partial demagnetization is a failure occurring under the high thermal operation of a Permanent Magnet machine. This paper focuses on partial demagnetization fault diagnosis in a double-rotor double-sided axial flux PM generator using stator currents analysis under time-varying conditions. One of the most important problems in any fault diagnosis approach is the investigation of load and speed variation on the proposed indices. To overcome the aforementioned problems, this paper adopts a novelty detection algorithm based on the Hilbert–Huang transform for fault diagnosis. This approach relies on two steps: estimating the intrinsic mode functions (IMFs) by the empirical mode decomposition (EMD) and computing the instantaneous amplitude (IA) and Instantaneous Frequency (IF) of IMFs using the Hilbert transform. The more significant IMFs are determined using the Hilbert spectrum, which is applied for accurate fault diagnosis. The Partial demagnetization severity can be evaluated based on the IMF’s energy value. The theoretical basis of the proposed method is presented. The effectiveness of the proposed method is verified by a series of simulation and experimental tests under different conditions.
Aboubakeur Hadjaissa, Mohammed Benmiloud, Khaled Ameur, Halima Bouchenak, Maria Dimeh,
Volume 20, Issue 4 (11-2024)
Abstract
As solar photovoltaic power generation becomes increasingly widespread, the need for photovoltaic emulators (PVEs) for testing and comparing control strategies, such as Maximum Power Point Tracking (MPPT), is growing. PVEs allow for consistent testing by accurately simulating the behavior of PV panels, free from external influences like irradiance and temperature variations. This study focuses on developing a PVE model using deep learning techniques, specifically a Multi-Layer Perceptron (MLP) Artificial Neural Network (ANN) with backpropagation as the learning algorithm. The ANN is integrated with a DC-DC push-pull converter controlled via a Linear Quadratic Regulator (LQR) strategy. The ANN emulates the nonlinear characteristics of PV panels, generating precise reference currents. Additionally, the use of a single voltage sensor paired with a current observer enhances control signal accuracy and reduces the PVE system's hardware requirements. Comparative analysis demonstrates that the proposed LQR-based controller significantly outperforms conventional PID controllers in both steady-state error and response time.
Srinivas Babu N, Shashikiran S, M Jayanthi, Rajani N, K M Palaniswamy, M R Kushalatha,
Volume 20, Issue 4 (11-2024)
Abstract
Tuberculosis (TB) is a dangerous disease caused by mycobacterium leads to mortality. Early detection and identification of tuberculosis is crucial for managing tuberculosis infections. Recent technological improvements use a machine learning-based SVM and Modified CNN to identify specific diseases more accurately, as demonstrated in this research. The modified CNN's improved feature extraction and classification accuracy are maintained throughout construction. To obtain good performance a TBX11K publicly accessible dataset is used it consists of 11000 images of which 4600 chest x-ray (CXR) images are considered in this research, and the suggested model is verified. This approach significantly increases the accuracy of categorizing TB symptoms. The PCA in this system locates the elements and extracts a large amount of variance technique applied to the full chest radiograph for pulmonary tuberculosis identification accuracy using SVM is 93.14% and modified CNN 96.72% respectively. When it comes to helping radiologists diagnose patients and public health professionals screen for tuberculosis in places where the disease is endemic, the proposed system SVM and modified CNN perform better than existing methods.
