Abstract: This paper presents the development and application of an adaptive neuro fuzzy inference system (ANFIS) based intelligent hybrid neuro fuzzy controller for automatic generation control (AGC) of two-area interconnected thermal power system with reheat non linearity. The dynamic response of the system has been studied for 1% step load perturbation in area-1. The performance of the proposed neuro fuzzy controller is compared against conventional proportional-integral (PI) controller, state feedback linear quadratic regulator (LQR) controller and fuzzy gain scheduled proportionalintegral (FGSPI) controller. Comparative analysis demonstrates that the proposed intelligent neuro fuzzy controller is the most effective of all in improving the transients of frequency and tie-line power deviations against small step load disturbances. Simulations have been performed using Matlab®.
Abstract: This paper presents a procedure of forming the
mathematical model of radial electric power systems for simulation
of both transient and steady-state conditions. The research idea has
been based on nodal voltages technique and on differentiation of
Kirchhoff's current law (KCL) applied to each non-reference node of
the radial system, the result of which the nodal voltages has been
calculated by solving a system of algebraic equations. Currents of the
electric power system components have been determined by solving
their respective differential equations. Transforming the three-phase
coordinate system into Cartesian coordinate system in the model
decreased the overall number of equations by one third. The use of
Cartesian coordinate system does not ignore the DC component
during transient conditions, but restricts the model's implementation
for symmetrical modes of operation only. An example of the input
data for a four-bus radial electric power system has been calculated.
Abstract: Fractional Fourier Transform is a powerful tool,
which is a generalization of the classical Fourier Transform. This
paper provides a mathematical relation relating the span in Fractional
Fourier domain with the amplitude and phase functions of the signal,
which is further used to study the variation of quality factor with
different values of the transform order. It is seen that with the
increase in the number of transients in the signal, the deviation of
average Fractional Fourier span from the frequency bandwidth
increases. Also, with the increase in the transient nature of the signal,
the optimum value of transform order can be estimated based on the
quality factor variation, and this value is found to be very close to
that for which one can obtain the most compact representation. With
the entire mathematical analysis and experimentation, we consolidate
the fact that Fractional Fourier Transform gives more optimal
representations for a number of transform orders than Fourier
transform.
Abstract: Process control and energy conservation are the two
primary reasons for using an adjustable speed drive. However,
voltage sags are the most important power quality problems facing
many commercial and industrial customers. The development of
boost converters has raised much excitement and speculation
throughout the electric industry. Now utilities are looking to these
devices for performance improvement and reliability in a variety of
areas. Examples of these include sags, spikes, or transients in supply
voltage as well as unbalanced voltages, poor electrical system
grounding, and harmonics. In this paper, simulations results are
presented for the verification of the proposed boost converter
topology. Boost converter provides ride through capability during
sag and swell. Further, input currents are near sinusoidal. This
eliminates the need of braking resistor also.
Abstract: Monitoring lightning electromagnetic pulses (sferics)
and other terrestrial as well as extraterrestrial transient radiation signals
is of considerable interest for practical and theoretical purposes
in astro- and geophysics as well as meteorology. Managing a continuous
flow of data, automisation of the detection and classification
process is important. Features based on a combination of wavelet and
statistical methods proved efficient for analysis and characterisation
of transients and as input into a radial basis function network that is
trained to discriminate transients from pulse like to wave like.
Abstract: Iterative learning control aims to achieve zero tracking
error of a specific command. This is accomplished by iteratively
adjusting the command given to a feedback control system, based on
the tracking error observed in the previous iteration. One would like
the iterations to converge to zero tracking error in spite of any error
present in the model used to design the learning law. First, this need
for stability robustness is discussed, and then the need for robustness
of the property that the transients are well behaved. Methods of
producing the needed robustness to parameter variations and to
singular perturbations are presented. Then a method involving
reverse time runs is given that lets the world behavior produce the
ILC gains in such a way as to eliminate the need for a mathematical
model. Since the real world is producing the gains, there is no issue
of model error. Provided the world behaves linearly, the approach
gives an ILC law with both stability robustness and good transient
robustness, without the need to generate a model.
Abstract: This research proposes an algorithm for the simulation
of time-periodic unsteady problems via the solution unsteady Euler
and Navier-Stokes equations. This algorithm which is called Time
Spectral method uses a Fourier representation in time and hence
solve for the periodic state directly without resolving transients
(which consume most of the resources in a time-accurate scheme).
Mathematical tools used here are discrete Fourier transformations. It
has shown tremendous potential for reducing the computational cost
compared to conventional time-accurate methods, by enforcing
periodicity and using Fourier representation in time, leading to
spectral accuracy. The accuracy and efficiency of this technique is
verified by Euler and Navier-Stokes calculations for pitching airfoils.
Because of flow turbulence nature, Baldwin-Lomax turbulence
model has been used at viscous flow analysis. The results presented
by the Time Spectral method are compared with experimental data. It
has shown tremendous potential for reducing the computational cost
compared to the conventional time-accurate methods, by enforcing
periodicity and using Fourier representation in time, leading to
spectral accuracy, because results verify the small number of time
intervals per pitching cycle required to capture the flow physics.
Abstract: In this paper, the authors take a look at advantages of
multiphase induction motors comparing them with three phase ones
and present the applications where six-phase induction motors are
used. They elaborate the mathematical model of six-phase induction
motor with two similar stator three phase winding, shifted by 30
degrees in space and three phase winding in rotor, in synchronous
reference frame for soft starting and scalar control. The authors
simulate and discuss results of speed and torque starting transients.
Abstract: This paper presents features that characterize power
quality disturbances from recorded voltage waveforms using wavelet
transform. The discrete wavelet transform has been used to detect
and analyze power quality disturbances. The disturbances of interest
include sag, swell, outage and transient. A power system network has
been simulated by Electromagnetic Transients Program. Voltage
waveforms at strategic points have been obtained for analysis, which
includes different power quality disturbances. Then wavelet has been
chosen to perform feature extraction. The outputs of the feature
extraction are the wavelet coefficients representing the power quality
disturbance signal. Wavelet coefficients at different levels reveal the
time localizing information about the variation of the signal.
Abstract: Worldwide many electrical equipment insulation
failures have been reported caused by switching operations, while
those equipments had previously passed all the standard tests and
complied with all quality requirements. The problem is mostly
associated with high-frequency overvoltages generated during
opening or closing of a switching device. The transients generated
during switching operations in a Gas Insulated Substation (GIS) are
associated with high frequency components in the order of few tens
of MHz.
The frequency spectrum of the VFTO generated in the 220/66 kV
Wadi-Hoff GIS is analyzed using Fast Fourier Transform technique.
The main frequency with high voltage amplitude due to the operation
of disconnector (DS5) is 5 to 10 MHz, with the highest amplitude at 9
MHz. The main frequency with high voltage amplitude due to the
operation of circuit breaker (CB5) is 1 to 25 MHz, with the highest
amplitude at 2 MHz.
Mitigating techniques damped the oscillating frequencies
effectively. The using of cable terminal reduced the frequency
oscillation effectively than that of OHTL terminal. The using of a
shunt capacitance results in vanishing the high frequency
components. Ferrite rings reduces the high frequency components
effectively especially in the range 2 to 7 MHz. The using of RC and
RL filters results in vanishing the high frequency components.
Abstract: This paper describes the development of a control
system model using a graphical software tool. This control system is
part of an operator training simulator developed for the National
Training Center for Operators of Ixtapantongo (CNCAOI, acronym
according to its name in Spanish language) of the Mexico-s Federal
Commission of Electricity, CFE). The Department of Simulation of
the Electrical Research Institute (IIE) developed this simulator using
as reference the Unit I of the Combined Cycle Power Plant El Sauz,
located at the centre of Mexico. The first step in the project was the
developing of the Gas Turbine System and its control system
simulator. The Turbo Gas simulator was finished and delivered to
CNCAOI in March 2007 for commercial operation. This simulator is
a high-fidelity real time dynamic simulator built and tested for
accurate operation over the entire load range. The simulator was used
primarily for operator training although it has been used for
procedure development and evaluation of plant transients.
Abstract: The paper shows that in the analysis of a queuing system with fixed-size batch arrivals, there emerges a set of polynomials which are a generalization of Chebyshev polynomials of the second kind. The paper uses these polynomials in assessing the transient behaviour of the overflow (equivalently call blocking) probability in the system. A key figure to note is the proportion of the overflow (or blocking) probability resident in the transient component, which is shown in the results to be more significant at the beginning of the transient and naturally decays to zero in the limit of large t. The results also show that the significance of transients is more pronounced in cases of lighter loads, but lasts longer for heavier loads.
Abstract: Happening of Ferroresonance phenomenon is one of the reasons of consuming and ruining transformers, so recognition of Ferroresonance phenomenon has a special importance. A novel method for classification of Ferroresonance presented in this paper. Using this method Ferroresonance can be discriminate from other transients such as capacitor switching, load switching, transformer switching. Wavelet transform is used for decomposition of signals and Competitive Neural Network used for classification. Ferroresonance data and other transients was obtained by simulation using EMTP program. Using Daubechies wavelet transform signals has been decomposed till six levels. The energy of six detailed signals that obtained by wavelet transform are used for training and trailing Competitive Neural Network. Results show that the proposed procedure is efficient in identifying Ferroresonance from other events.
Abstract: The impact of fixed speed squirrel cage type as well as
variable speed doubly fed induction generators (DFIG) on dynamic
performance of a multimachine power system has been investigated.
Detailed models of the various components have been presented and
the integration of asynchronous and synchronous generators has been
carried out through a rotor angle based transform. Simulation studies
carried out considering the conventional dynamic model of squirrel
cage asynchronous generators show that integration, as such, could
degrade to the AC system performance transiently. This article
proposes a frequency or power controller which can effectively
control the transients and restore normal operation of fixed speed
induction generator quickly. Comparison of simulation results
between classical cage and doubly-fed induction generators indicate
that the doubly fed induction machine is more adaptable to
multimachine AC system. Frequency controller installed in the DFIG
system can also improve its transient profile.
Abstract: This paper presents the development of adaptive
distance relay for protection of parallel transmission line with mutual
coupling. The proposed adaptive relay, automatically adjusts its
operation based on the acquisition of the data from distance relay of
adjacent line and status of adjacent line from line circuit breaker IED
(Intelligent Electronic Device). The zero sequence current of the
adjacent parallel transmission line is used to compute zero sequence
current ratio and the mutual coupling effect is fully compensated.
The relay adapts to changing circumstances, like failure in
communication from other relays and non - availability of adjacent
transmission line. The performance of the proposed adaptive relay is
tested using steady state and dynamic test procedures. The fault
transients are obtained by simulating a realistic parallel transmission
line system with mutual coupling effect in PSCAD. The evaluation
test results show the efficacy of adaptive distance relay over the
conventional distance relay.
Abstract: This paper focuses on PSS/E modeling of wind farms
of Doubly-fed Induction Generator (DFIG) type and their impact on
issues of power system operation. Since Wind Turbine Generators
(WTG) don-t have the same characteristics as synchronous
generators, the appropriate modeling of wind farms is essential for
transmission system operators to analyze the best options of
transmission grid reinforcements as well as to evaluate the wind
power impact on reliability and security of supply. With the high
excepted penetration of wind power into the power system a
simultaneous loss of Wind Farm generation will put at risk power
system security and reliability. Therefore, the main wind grid code
requirements concern the fault ride through capability and frequency
operation range of wind turbines. In case of grid faults wind turbines
have to supply a definite reactive power depending on the
instantaneous voltage and to return quickly to normal operation.
Abstract: Monitoring lightning electromagnetic pulses (sferics) and other terrestrial as well as extraterrestrial transient radiation signals is of considerable interest for practical and theoretical purposes in astro- and geophysics as well as meteorology. Managing a continuous flow of data, automation of the analysis and classification process is important. Features based on a combination of wavelet and statistical methods proved efficient for this task and serve as input into a radial basis function network that is trained to discriminate transient shapes from pulse like to wave like. We concentrate on signals in the Very Low Frequency (VLF, 3 -30 kHz) range in this paper, but the developed methods are independent of this specific choice.
Abstract: A novel approach to speech coding using the hybrid architecture is presented. Advantages of parametric and perceptual coding methods are utilized together in order to create a speech coding algorithm assuring better signal quality than in traditional CELP parametric codec. Two approaches are discussed. One is based on selection of voiced signal components that are encoded using parametric algorithm, unvoiced components that are encoded perceptually and transients that remain unencoded. The second approach uses perceptual encoding of the residual signal in CELP codec. The algorithm applied for precise transient selection is described. Signal quality achieved using the proposed hybrid codec is compared to quality of some standard speech codecs.
Abstract: We introduce an adaptive technique for the joint mitigation of transients and continuous-wave radio-frequency co-channel interference (CW RFI) in high-frequency (HF) over-the-horizon radars (OTHRs). The performance of this technique is illustrated using data from an operational surface-wave radar (SECAR) and from recent experimental trials with sky-wave (SW) and sky-wave–line-of-sight (SKYLOS) HF OTHRs.
Abstract: Computerized alarm systems have been applied
increasingly to nuclear power plants. For existing plants, an add-on
computer alarm system is often installed to the control rooms. Alarm
avalanches during the plant transients are major problems with the
alarm systems in nuclear power plants. Computerized alarm systems
can process alarms to reduce the number of alarms during the plant
transients. This paper describes various alarm processing methods, an
alarm cause tracking function, and various alarm presentation schemes
to show alarm information to the operators effectively which are
considered during the development of several computerized alarm
systems for Korean nuclear power plants and are found to be helpful to
the operators.