Showing 12 results for Das
A. Dastfan, F. Behrangi,
Volume 5, Issue 1 (March 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. Dosaranian Moghadam, H. Bakhshi, G. Dadashzadeh,
Volume 6, Issue 3 (September 2010)
Abstract
In this paper, we propose smart step closed-loop power control (SSPC)
algorithm and base station assignment based on minimizing the transmitter power (BSAMTP)
technique in a direct sequence-code division multiple access (DS-CDMA) receiver in
the presence of frequency-selective Rayleigh fading. This receiver consists of three stages.
In the first stage, with conjugate gradient (CG) adaptive beamforming algorithm, the
desired users’ signal in an arbitrary path is passed and the inter-path interference is
canceled in other paths in each RAKE finger. Also in this stage, the multiple access
interference (MAI) from other users is reduced. Thus, the matched filter (MF) can be used
for the MAI reduction in each RAKE finger in the second stage. Also in the third stage, the
output signals from the matched filters are combined according to the conventional
maximal ratio combining (MRC) principle and then are fed into the decision circuit of the
desired user. The simulation results indicate that the SSPC algorithm and the BSA-MTP
technique can significantly improve the network bit error rate (BER) in comparison with
other algorithms. Also, we observe that significant savings in total transmit power (TTP)
are possible with our proposed methods.
Gh. Dastghaibyfard, N. Mansouri,
Volume 10, Issue 1 (March 2014)
Abstract
Abstract: A Data Grid connects a collection of geographically distributed computational and storage resources that enables users to share data and other resources. Data replication, a technique much discussed by Data Grid researchers in recent years creates multiple copies of file and places them in various locations to shorten file access times. In this paper, a dynamic data replication strategy, called Modified Dynamic Hierarchical Replication (MDHR) is proposed. This strategy is an enhanced version of Dynamic Hierarchical Replication (DHR). However, replication should be used wisely because the storage capacity of each Grid site is limited. Thus, it is important to design an effective strategy for the replication replacement task. MDHR replaces replicas based on the last time the replica was requested, number of access, and size of replica. It selects the best replica location from among the many replicas based on response time that can be determined by considering the data transfer time, the storage access latency, the replica requests that waiting in the storage queue, the distance between nodes and CPU process capability. Simulation results utilizing the OptorSim show MDHR achieves better performance overall than other strategies in terms of job execution time, effective network usage and storage usage.
S. M. Mousavi Gazafroodi, A. Dashti,
Volume 10, Issue 4 (December 2014)
Abstract
In this paper, a novel stator current based Model Reference Adaptive System (MRAS) estimator for speed estimation in the speed-sensorless vector controlled induction motor drives is presented. In the proposed MRAS estimator, measured stator current of the induction motor is considered as a reference model. The estimated stator current is produced in an adjustable model to compare with the measured stator current, where rotor flux identification is needed for stator current estimation. In the available stator current based MRAS estimator, rotor flux is estimated by the use of measured stator current, where the adjustable model and reference model depend on each other since measured stator current is employed in both of them. To improve the performance of the MRAS speed estimator, both the stator current and rotor flux are estimated in the adjustable model by using the state space equations of the induction motor, adjusted with the rotor speed calculated by an adaptation mechanism. The stability of the proposed MRAS estimator is studied through a small signal analysis. Senorless induction motor drive along with the proposed MRAS speed estimator is verified through computer simulations. In addition, performance of the proposed MRAS is compared with the available stator current based MRAS speed estimator
H. Hasanzadeh Fard, S. A. Bahreyni , R. Dashti , H. A. Shayanfar,
Volume 11, Issue 2 (June 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.
M Sedaghati, R Dashti,
Volume 11, Issue 4 (December 2015)
Abstract
In this paper, a new model has been presented to determine the number of spare transformers and their locations for distribution stations. The number of spare transformers must be so that they need minimum investment. Furthermore, they must be sufficient for replacing with transformers that have been damaged. For this reason, in this paper a new purpose function has been presented to maximize profit in distribution company’s budgeting and planning. For determining the number of spares that must be available in a stock room, this paper considers the number of spares and transformer’s fault at the same time. The number of spare transformers is determined so that at least one spare transformer will be available for replacing with the failed transformers. This paper considers time required for purchasing or repairing a failed transformer to determine the number of required spare transformers. Furthermore, whatever the number of spare equipment are increased, cost of maintenance will be increased, so an economic comparison must be done between reduced costs from reducing of outage time and increased costs from spare transformers existence.
M. Pashaian, M. R. Mosavi, M. S. Moghaddasi, M. J. Rezaei,
Volume 12, Issue 1 (March 2016)
Abstract
This paper proposes a new method for rejecting the Continuous Wave Interferences (CWI) in the Global Positioning System (GPS) receivers. The proposed filter is made by cascading an adaptive Finite Impulse Response (FIR) filter and a Wavelet Packet Transform (WPT) based filter. Although adaptive FIR filters are easy to implement and have a linear phase, they create self-noise in the rejection of strong interferences. Moreover, the WPT which provides detailed signal decomposition can be used for the excision of single-tone and multi-tone CWI and also for de-noising the retrieved GPS signal. By cascading these two filters, the self-noise imposed by FIR filter and the remaining jamming effects on GPS signal can be eliminated by the WPT based filter. The performance analysis of the proposed cascade filter is presented in this paper and it is compared with the FIR and the WPT based filters. Experimental results illustrate that the proposed method offers a better performance under the interference environments of interest in terms of the signal-to-noise ratio gain and mean square error factors compared to previous methods.
J. Fallah Ardashir, M. Sabahi, S. H. Hosseini, E. Babaei, G. B. Gharehpetian,
Volume 13, Issue 2 (June 2017)
Abstract
This paper proposes a new single phase transformerless Photovoltaic (PV) inverter for grid connected systems. It consists of six power switches, two diodes, one capacitor and filter at the output stage. The neutral of the grid is directly connected to the negative terminal of the source. This results in constant common mode voltage and zero leakage current. Model Predictive Controller (MPC) technique is used to modulate the converter to reduce the output current ripple and filter requirements. The main advantages of this inverter are compact size, low cost, flexible grounding configuration. Due to brevity, the operating principle and analysis of the proposed circuit are presented in brief. Simulation and experimental results of 200W prototype are shown at the end to validate the proposed topology and concept. The results obtained clearly verifies the performance of the proposed inverter and its practical application for grid connected PV systems.
G. Das, R. Panda, L. Samantaray , S. Agrawal,
Volume 18, Issue 2 (June 2022)
Abstract
Multilevel optimal threshold selection is important and comprehensively used in the area of image processing. Mostly, entropic information-based threshold selection techniques are used. These methods make use of the entropy of the distribution of the grey levels of an image. However, entropy functions largely depend on spatial distribution of the image. This makes the methods inefficient when the distribution of the grey information of an image is not uniform. To solve this problem, a novel non-entropic method for multilevel optimal threshold selection is proposed. In this contribution, simple numbers (pixel counts), explicitly free from the spatial distribution, are used. A novel non-entropic objective function is proposed. It is used for multilevel threshold selection by maximizing the partition score using the adaptive equilibrium method. A new theoretical derivation for the fitness function is highlighted. The key to the achievement is the exploitation of the score among classes, reinforcing an improvised threshold selection process. Standard test images are considered for the experiment. The performances are compared with state-of-the-art entropic value-based methods used for multilevel threshold assortment and are found better. It is revealed that the results obtained using the suggested technique are encouraging both qualitatively and quantitatively. The newly proposed method would be very useful for solving different real-world engineering optimization problems.
Amir Gallaj, Jaber Fallah Ardashir, Mojtaba Beiraghi,
Volume 18, Issue 4 (December 2022)
Abstract
This work proposes a high step-up interleaved dc/dc topology utilizing a VM (voltage multiplier) cell suitable for PV applications. The VM cells D/C (Diode/Cap.) are cascaded among the phases to approach a high voltage gain. Besides, the voltage converting ratio of the presented structure can be improved by extending the VM cells and it also leads to drop in the normalized voltage stress throughout the switches and some diodes. Therefore, by utilizing a semiconductor (Switch/Diode) with a lower rating leads to a decline in system losses. Also, the efficiency of the suggested topology will be considerable and the overall cost can be decreased. To elaborate on the main benefits of the proposed topology, a comparison has been made across other literature regarding the efficiency, peak voltage throughout the semiconductors and voltage ratio of the converter. To prove the accuracy principle of operation of the suggested converter, two prototypes (for n=1, 2 stages) were built and tested at 350 W and 453 W with an operating frequency of about 40 kHz performed.
Das P. Chennamsetty, Sravana K. Bali,
Volume 19, Issue 2 (June 2023)
Abstract
Symmetrical nature of mean of electrical signals during normal operating conditions is used in the fault detection task for dependable, robust, and simple fault detector implementation is presented in this work. Every fourth cycle of the instantaneous current signal, the mean is computed and carried into the next cycle to discover nonlinearities in the signal. A fault detection task is completed using a comparison of two sub cycle means, and the same concept is extended to faulty phase classification. Under various fault and system operating situations, the suggested technique is assessed for regular faults, remote end faults, high resistive faults, and high impedance arcing faults. This paper's extensive case studies illustrate the suggested scheme's simplicity, computational flexibility, speed, and reliability. The suggested approach yields 100% consistent results in 4-8 msec detection time.
Atefeh Sohrabi, Hamideh Dashti, Javad Ahmadi-Shokouh,
Volume 19, Issue 4 (December 2023)
Abstract
In this article, an active electrically small Horn antenna for very high frequency (VHF) and ultra-high frequency (UHF) frequencies is presented. The proposed horn antenna has a height of 5 cm and a diameter of 4.28 cm which can cover 6-12 GHz without a special active circuit with the VSWR of less than 2. A Non-foster Active Adaptation Circuit is used to reduce the antenna input frequency from 164 MHz to 880 MHz. Good matching is visible between the simulation results and the measurement of the antenna reflection coefficient with the active matching circuit. The proposed structure has more than 137 % bandwidth. With the proposed active antenna, the problem of non-portability of VHF and UHF Horn antenna antennas has been solved. Finally, by analyzing the time domain, the stability of the circuit is examined, and the results of the stability test show that the system, including the antenna and the circuit, is stable. The antenna and the matching circuits are simulated by CST microwave studio and advanced design system, respectively.
