Showing 443 results for Ha
H. Shateri, S. Jamali,
Volume 2, Issue 3 (October 2006)
Abstract
This paper presents the effects of instrument transformers connection points on
the measured impedance by distance relays in the presence of Flexible Alternating Current
Transmission System (FACTS) devices with series connected branch. Distance relay
tripping characteristic itself depends on the power system structural conditions, pre-fault
operational conditions, and especially the ground fault resistance. The structural and
controlling parameters of FACTS devices as well as the connection points of instrument
transformers affect the ideal tripping characteristic of distance relay. This paper presents a
general set of equations to evaluate the measured impedance at the relaying point for a
general model of FACTS devices to consider different affecting parameters.
A. Badri, S. Jadid, M. Parsa-Moghaddam,
Volume 3, Issue 1 (April 2007)
Abstract
Unlike perfect competitive markets, in oligopoly electricity markets due to
strategic producers and transmission constraints GenCos may increase their own profit
through strategic biddings. This paper investigates the problem of developing optimal
bidding strategies of GenCos considering participants’ market power and transmission
constraints. The problem is modeled as a bi-level optimization that at the first level each
GenCo maximizes its payoff through strategic bidding and at the second level, in order to
consider transmission constraints a system dispatch is accomplished through an OPF
problem. The AC power flow model is used for proposed OPF. Here it is assumed that each
GenCo uses linear supply function model for its bidding and has information about initial
bidding of other competitors. The impact of optimal biddings on market characteristics as
well as GenCos’ payoffs are investigated and compared with perfect competitive markets
where all the participants bid with their marginal costs. Furthermore, effects of exercising
market power due to transmission constraints as well as different biddings of strategic
generators on GenCos’ optimal bidding strategies are presented. Finally IEEE-30 bus test
system is used for case study to demonstrate simulation results.
A. Hajizadeh, M. Aliakbar-Golkar,
Volume 3, Issue 1 (April 2007)
Abstract
The operation of Fuel Cell Distributed Generation (FCDG) systems in
distribution systems is introduced by modeling, controller design, and simulation study of a
Solid Oxide Fuel Cell (SOFC) distributed generation (DG) system. The physical model of
the fuel cell stack and dynamic models of power conditioning units are described. Then,
suitable control architecture based on fuzzy logic control for the overall system is presented
in order to active power control and power quality improvement. A MATLAB/Simulink
simulation model is developed for the SOFC DG system by combining the individual
component models and the controllers designed for the power conditioning units.
Simulation results are given to show the overall system performance including active power
control and voltage regulation capability of the distribution system.
D. Arab-Khaburi, F. Tootoonchian, Z. Nasiri-Gheidari,
Volume 3, Issue 1 (April 2007)
Abstract
Because of temperature independence, high resolution and noiseless outputs,
brushless resolvers are widely used in high precision control systems. In this paper, at first
dynamic performance characteristics of brushless resolver, considering parameters
identification are presented. Then a mathematical model based on d-q axis theory is given.
This model can be used for studying the dynamic behavior of the resolver and steady state
model is obtained by using dynamic model. The main object of this paper is to present an
approach to identify electrical and mechanical parameters of a brushless resolver based on
DC charge excitation and weight, pulley and belt method, respectively. Finally, the model
of resolver based on the obtained parameters is simulated. Experimental results approve the
validity of proposed method.
S. Olyaee, Sh. Mohammad-Nejad,
Volume 3, Issue 3 (October 2007)
Abstract
A new heterodyne nano-displacement with error reduction is presented. The
main errors affecting the displacement accuracy of the nano-displacement measurement
system including intermodulation distortion error, cross-talk error, cross-polarization error
and phase detection error are calculated. In the designed system, a He-Ne laser having
three-longitudinal-mode is considered as the stabilized source. The free spectral range of
the 35cm laser cavity is about 435-MHz at 632.8-nm wavelength, which a secondary beat
frequency equal to 300-kHz is produced by combining the reference and measurement
beams. The resolution of the displacement measurement resulting from intermodulation
distortion, cross-talk and cross-polarization errors is limited to 18-pm. Also, the phase
detection uncertainty causes an error of only 5.9-pm in the displacement measurement.
Furthermore, frequency-path models of two- and three-longitudinal-mode laser
interferometers are modeled as the ac interference, ac reference, dc interference and optical
power terms. A comparison study between two- and three-longitudinal-mode laser
interferometers confirms that the performance of the designed system is considerably
improved.
A. Hajiaboli, Hodjat-Kashani, M. Omidi,
Volume 3, Issue 3 (October 2007)
Abstract
This paper presents a novel implementation of an electromagnetically coupled
patch antenna using air gap filled substrates to achieve the maximum bandwidth. We also
propose an efficient modeling technique using the FDTD method which can substantially
reduce the simulation cost for modeling the structure. The simulated results have been
compared with measurement to show the broadband behavior of the antenna and the
accuracy of the proposed modeling technique. The measured results show a 16% of
VSWR<2 bandwidth which is considerable considering the inherent bandwidth limitations
in microstrip antenna technology.
F. Bagheri, H. Khaloozadeh, K. Abbaszadeh,
Volume 3, Issue 3 (October 2007)
Abstract
This paper presents a parametric low differential order model, suitable for
mathematically analysis for Induction Machines with faulty stator. An adaptive Kalman
filter is proposed for recursively estimating the states and parameters of continuous–time
model with discrete measurements for fault detection ends. Typical motor faults as interturn
short circuit and increased winding resistance are taken into account. The models are
validated against winding function induction motor modeling which is well known in
machine modeling field. The validation shows very good agreement between proposed
method simulations and winding function method, for short-turn stator fault detection.
A. Halvaei-Niasar, A. Vahedi, H. Moghbelli,
Volume 3, Issue 3 (October 2007)
Abstract
This paper presents an original study on the generated torque ripples of phase
commutation in the Four-Switch, Three-Phase Inverter (FSTPI) Brushless DC (BLDC)
motor drive which is suitable for low cost applications. Analytic values of torque ripple and
commutation duration are obtained for different operation conditions. Moreover, limitation
on the speed range operation caused from splitting of the DC-link voltage is shown exactly.
Then a novel current control technique is developed to minimize the commutation torque
ripple for a wide speed range. The technique proposed here is based on a strategy that the
current slopes of the rising and the decaying phases during the commutation intervals can
be equalized by proper duty-ratios at commutations. Finally, the validity of the proposed
analysis and developed torque ripple reduction technique are verified via simulation.
R. Noroozian, M. Abedi, G. B. Gharehpetian, S. H. Hosseini,
Volume 3, Issue 3 (October 2007)
Abstract
This paper describes a DC isolated network which is fed with Distributed
Generation (DG) from photovoltaic (PV) renewable sources for supplying unbalanced AC
loads. The battery energy storage bank has been connected to the DC network via DC/DC
converter to control the voltage of the network and optimize the operation of the PV
generation units. The PV arrays are connected to the DC network via its own DC/DC
converter to ensure the required power flow. The unbalanced AC loads are connected to the
DC network via its own DC/AC converter. This paper proposes a novel control strategy for
storage converter which has a DC voltage droop regulator. Also a novel control system
based on Park rotating frame has been proposed for DC/AC converters. In this paper, the
proposed operation method is demonstrated by simulation of power transfer between PV
arrays, unbalanced AC loads and battery unit. The simulation results based on
PSCAD/EMTDC software show that DC isolated distribution system including PV
generation systems can provide the high power quality to supplying unbalanced AC loads.
M. Eghtedari, M.-H. Kahaei,
Volume 4, Issue 1 (April 2008)
Abstract
In this paper, the nonlinear lattice-Hammerstein filter and its properties are
derived. It is shown that the error signals are orthogonal to the input signal and also
backward errors of different stages are orthogonal to each other. Numerical results confirm
all the theoretical properties of the lattice-Hammerstein structure.
A. Falahati, M.-R. Ardestani,
Volume 4, Issue 1 (April 2008)
Abstract
A low complexity dynamic subcarrier and power allocation methodology for
downlink communication in an OFDM-based multiuser environment is developed. The
problem of maximizing overall capacity with constraints on total power consumption, bit
error rate and data rate proportionality among users requiring different QOS specifications
is formulated. Assuming perfect knowledge of the instantaneous channel gains for all users,
a new simple algorithm is developed to solve the mentioned problem. We compare the sum
capacity, proportionality, and computational complexity of the proposed algorithm with the
one presented by Wong et al. Numerical results demonstrate that the proposed algorithm
offers a performance comparable with Wong’s algorithm, yet complexity remains low and
proportionality constraint will be tightly satisfied. As well, the proposed algorithm can
provide a flexible trade-off between complexity, capacity and proportionality constraint.
A.-R. Zirak, M. Khademi, M.-S. Mahloji,
Volume 4, Issue 1 (April 2008)
Abstract
We present an efficient method for the reduction of model equations in the
linearized diffuse optical tomography (DOT) problem. We first implement the maximum a
posteriori (MAP) estimator and Tikhonov regularization, which are based on applying
preconditioners to linear perturbation equations. For model reduction, the precondition is
split into two parts: the principal components are considered as reduced size
preconditioners applied to linear perturbation equations while the less important
components are marginalized as noise. Simulation results illustrate that the new proposed
method improves the image reconstruction performance and localizes the abnormal section
well with a better computational efficiency.
S. Jamali , A. Parham,
Volume 4, Issue 3 (July 2008)
Abstract
This paper presents an algorithm for adaptive determination of the dead time
during transient arcing faults and blocking automatic reclosing during permanent faults on
overhead transmission lines. The discrimination between transient and permanent faults is
made by the zero sequence voltage measured at the relay point. If the fault is recognised as
an arcing one, then the third harmonic of the zero sequence voltage is used to evaluate the
extinction time of the secondary arc and to initiate reclosing signal. The significant
advantage of this algorithm is that it uses an adaptive threshold level and therefore its
performance is independent of fault location, line parameters and the system operating
conditions. The proposed algorithm has been successfully tested under a variety of fault
locations and load angles on a 400KV overhead line using Electro-Magnetic Transient
Program (EMTP). The test results validate the algorithm ability in determining the
secondary arc extinction time during transient faults as well as blocking unsuccessful
automatic reclosing during permanent faults.
M. Hariri, S. B. Shokouhi, N. Mozayani,
Volume 4, Issue 3 (July 2008)
Abstract
Dealing with uncertainty is one of the most critical problems in complicated
pattern recognition subjects. In this paper, we modify the structure of a useful Unsupervised
Fuzzy Neural Network (UFNN) of Kwan and Cai, and compose a new FNN with 6 types of
fuzzy neurons and its associated self organizing supervised learning algorithm. This
improved five-layer feed forward Supervised Fuzzy Neural Network (SFNN) is used for
classification and identification of shifted and distorted training patterns. It is generally
useful for those flexible patterns which are not certainly identifiable upon their features. To
show the identification capability of our proposed network, we used fingerprint, as the most
flexible and varied pattern. After feature extraction of different shapes of fingerprints, the
pattern of these features, “feature-map”, is applied to the network. The network first
fuzzifies the pattern and then computes its similarities to all of the learned pattern classes.
The network eventually selects the learned pattern of highest similarity and returns its
specific class as a non fuzzy output. To test our FNN, we applied the standard (NIST
database) and our databases (with 176×224 dimensions). The feature-maps of these
fingerprints contain two types of minutiae and three types of singular points, each of them
is represented by 22×28 pixels, which is less than real size and suitable for real time
applications. The feature maps are applied to the FNN as training patterns. Upon its setting
parameters, the network discriminates 3 to 7 subclasses for each main classes assigned to
one of the subjects.
D. Arab-Khaburi, F. Tootoonchian, Z. Nasiri-Gheidari,
Volume 4, Issue 3 (July 2008)
Abstract
A mathematical model based on d-q axis theory and dynamic performance
characteristic of brushless resolvers is discussed in this paper. The impact of rotor
eccentricity on the accuracy of position in precise applications is investigated. In particular,
the model takes the stator currents of brushless resolver into account. The proposed model
is used to compute the dynamic and steady state equivalent circuit of resolvers. Finally,
simulation results are presented. The validity and usefulness of the proposed method are
thoroughly verified with experiments.
M. R. Aghamohammadi,
Volume 4, Issue 3 (July 2008)
Abstract
This paper proposes a novel approach for generation scheduling using sensitivity
characteristic of a Security Analyzer Neural Network (SANN) for improving static security
of power system. In this paper, the potential overloading at the post contingency steadystate
associated with each line outage is proposed as a security index which is used for
evaluation and enhancement of system static security. A multilayer feed forward neural
network is trained as SANN for both evaluation and enhancement of system security. The
input of SANN is load/generation pattern. By using sensitivity characteristic of SANN,
sensitivity of security indices with respect to generation pattern is used as a guide line for
generation rescheduling aimed to enhance security. Economic characteristic of generation
pattern is also considered in the process of rescheduling to find an optimum generation
pattern satisfying both security and economic aspects of power system. One interesting
feature of the proposed approach is its ability for flexible handling of system security into
generation rescheduling and compromising with the economic feature with any degree of
coordination. By using SANN, several generation patterns with different level of security
and cost could be evaluated which constitute the Pareto solution of the multi-objective
problem. A compromised generation pattern could be found from Pareto solution with any
degree of coordination between security and cost. The effectiveness of the proposed
approach is studied on the IEEE 30 bus system with promising results.
A. Moharampour, J. Poshtan, A. Khaki-Sedigh,
Volume 4, Issue 3 (July 2008)
Abstract
In this paper, after defining pure proportional navigation guidance in the 3-
dimensional state from a new point of view, range estimation for passive homing missiles is
explained. Modeling has been performed by using line of sight coordinates with a particular
definition. To obtain convergent estimates of those state variables involved particularly in
range channel and unavailable from IR trackers, nonlinear filters such as sequential U-D
extended Kalman filter and Unscented Kalman filter in modified spherical coordinate
combined with a modified proportional navigation guidance law are proposed. Simulation
results indicate that the proposed tracking filters in conjunction with the dual guidance law
are able to provide the convergence of the range estimate for both maneuvering and nonmaneuvering
targets.
M. Mahdavi, Sh. Samavi, N. Zaker, M. Modarres-Hashemi,
Volume 4, Issue 3 (July 2008)
Abstract
In this paper we present a new accurate steganalysis method for the LSB
replacement steganography. The suggested method is based on the changes that occur in the
histogram of an image after the embedding of data. Every pair of neighboring bins of a
histogram are either inter-related or unrelated depending on whether embedding of a bit of
data in the image could affect both bins or not. We show that the overall behavior of all
inter-related bins, when compared with that of the unrelated ones, could give an accurate
measure for the amount of the embedded data. Both analytical analysis and simulation
results show the accuracy of the proposed method. The suggested method has been
implemented and tested for over 2000 samples and compared with the RS Steganalysis
method. Mean and variance of error were 0.0025 and 0.0037 for the suggested method
where these quantities were 0.0070 and 0.0182 for the RS Steganalysis. Using 4800
samples, we showed that the performance of the suggested method is comparable with
those of the RS steganalysis for JPEG filtered images. The new approach is applicable for
the detection of both random and sequential LSB embedding.
R. Kharel, K. Busawon, Z. Ghassemlooy,
Volume 4, Issue 4 (October 2008)
Abstract
In this paper, we propose a new chaos-based communication scheme using the observers. The novelty lies in the masking procedure that is employed to hide the confidential information using the chaotic oscillator. We use a combination of the addition and inclusion methods to mask the information. The performance of two observers, the proportional observer (P-observer) and the proportional integral observer (PI-observer) is compared that are employed as receivers for the proposed communication scheme. We show that the P-observer is not suitable scheme since it imposes unpractical constraints on the messages to be transmitted. On the other hand, we show that the PI-observer is the better solution because it allows greater flexibility in choosing the gains of the observer and does not impose any unpractical restrictions on the message.
Gh. R. Karimi, and S. Mirzakuchaki,
Volume 4, Issue 4 (October 2008)
Abstract
During the past few years, a lot of work has been done on behavioral models and
simulation tools. But a need for modeling strategy still remains. The VHDL-AMS language
supports the description of analog electronic circuits using Ordinary Differential Algebraic
Equations (ODAEs), in addition to its support for describing discrete-event systems. For
VHDL-AMS to be useful to the analog design community, efficient semiconductor device
models must be available. In this paper, potential merits of the new IEEE VHDL-AMS
standard in the field of modeling semiconductor devices are discussed. The device models
for diodes and the principles, techniques, and methodology used to achieve the design of an
analytical third generation Spice transistor MOS model named EKV are presented. This is
done by taking into account the thermoelectrical effect in VHDL-AMS, and with relevant
parameters set to match a deep submicron technology developed in VHDL-AMS. The
models were validated using System Vision from Mentor Graphics.
