Abstract: This paper discusses coordinated reactive power -
voltage (Q-V) control in a multi machine steam power plant. The
drawbacks of manual Q-V control are briefly listed, and the design
requirements for coordinated Q-V controller are specified.
Theoretical background and mathematical model of the new
controller are presented next followed by validation of developed
Matlab/Simulink model through comparison with recorded
responses in real steam power plant and description of practical
realisation of the controller. Finally, the performance of
commissioned controller is illustrated on several examples of
coordinated Q-V control in real steam power plant and compared
with manual control.
Abstract: In the present work, we have developed a symmetric electrochemical capacitor based on the nanostructured iron oxide (Fe3O4)-activated carbon (AC) nanocomposite materials. The physical properties of the nanocomposites were characterized by Scanning Electron Microscopy (SEM) and Brunauer-Emmett-Teller (BET) analysis. The electrochemical performances of the composite electrode in 1.0 M Na2SO3 and 1.0 M Na2SO4 aqueous solutions were evaluated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The composite electrode with 4 wt% of iron oxide nanomaterials exhibits the highest capacitance of 86 F/g. The experimental results clearly indicate that the incorporation of iron oxide nanomaterials at low concentration to the composite can improve the capacitive performance, mainly attributed to the contribution of the pseudocapacitance charge storage mechanism and the enhancement on the effective surface area of the electrode. Nevertheless, there is an optimum threshold on the amount of iron oxide that needs to be incorporated into the composite system. When this optimum threshold is exceeded, the capacitive performance of the electrode starts to deteriorate, as a result of the undesired particle aggregation, which is clearly indicated in the SEM analysis. The electrochemical performance of the composite electrode is found to be superior when Na2SO3 is used as the electrolyte, if compared to the Na2SO4 solution. It is believed that Fe3O4 nanoparticles can provide favourable surface adsorption sites for sulphite (SO3 2-) anions which act as catalysts for subsequent redox and intercalation reactions.
Abstract: The scope of this paper is to describe a real electrical
installation of renewable energy using photovoltaic cells. The
displayed power grid connected network was established in 2007 at
area of Northern Greece. The photovoltaic park is composed of 6120
photovoltaic cells able to deliver a total power of 1.101.600 Wp. For
the transformation of DC voltage to AC voltage have been used 25
stand alone three phases inverters and for the connection at the
medium voltage network of Greek Power Authority have been
installed two oil immersed transformer of 630 kVA each one. Due to
the wide space area of installation a specific external lightning
protection system has been designed. Additionally, due to the
sensitive electronics of the control and protection systems of park,
surge protection, equipotent bonding and shielding were also of
major importance.
Abstract: Empirical force fields and density functional theory
(DFT) was used to study the binding energies and structures of
methylamine on the surface of activated carbons (ACs). This is a first
step in studying the adsorption of alkyl amines on the surface of
functionalized ACs. The force fields used were Dreiding (DFF),
Universal (UFF) and Compass (CFF) models. The generalized
gradient approximation with Perdew Wang 91 (PW91) functional
was used for DFT calculations. In addition to obtaining the aminecarboxylic
acid adsorption energies, the results were used to establish
reliability of the empirical models for these systems. CFF predicted a
binding energy of -9.227 (kcal/mol) which agreed with PW91 at -
13.17 (kcal/mol), compared to DFF 0 (kcal/mol) and UFF -0.72
(kcal/mol). However, the CFF binding energies for the amine to ester
and ketone disagreed with PW91 results. The structures obtained
from all models agreed with PW91 results.
Abstract: The present work deals with the calculation of
transport properties of Hg0.8Cd0.2Te (MCT) semiconductor in
degenerate case. Due to their energy-band structure, this material
becomes degenerate at moderate doping densities, which are around
1015 cm-3, so that the usual Maxwell-Boltzmann approximation is
inaccurate in the determination of transport parameters. This problem
is faced by using Fermi-Dirac (F-D) statistics, and the non-parabolic
behavior of the bands may be approximated by the Kane model. The
Monte Carlo (MC) simulation is used here to determinate transport
parameters: drift velocity, mean energy and drift mobility versus
electric field and the doped densities. The obtained results are in
good agreement with those extracted from literature.
Abstract: This paper proposes a Fuzzy Sliding Mode Control (FSMC) as a control strategy for Buck-Boost DC-DC converter. The proposed fuzzy controller specifies changes in the control signal based on the knowledge of the surface and the surface change to satisfy the sliding mode stability and attraction conditions. The performances of the proposed fuzzy sliding controller are compared to those obtained by a classical sliding mode controller. The satisfactory simulation results show the efficiency of the proposed control law which reduces the chattering phenomenon. Moreover, the obtained results prove the robustness of the proposed control law against variation of the load resistance and the input voltage of the studied converter.
Abstract: Custom power is a technology driven product and
service solution which embraces a family devices such as Dynamic
Voltage Restorer (DVR), Distributed Shunt Compensator
(DSTATCOM), Solid State Breaker (SSB) etc which will provide
power quality functions at distribution voltages. The rapid response
of these devices enables them to operate in real time, providing
continuous and dynamic control of the supply including voltage and
reactive power regulation, harmonic reduction and elimination of
voltage dips. This paper presents the benefits of multilevel inverters
when they are used for DPC based custom power devices. Power
flow control mechanism, salient features, advantages and
disadvantages of direct power control (DPC) using lookup table,
SVM, predictive voltage vector and hybrid DPC strategies are
discussed in this paper. Simulation results of three level inverter
based STATCOM, harmonic analysis of multi level inverters are
presented at the end.
Abstract: Self-sensing estimates the air gap within an electro
magnetic path by analyzing the bearing coil current and/or voltage
waveform. The self-sensing concept presented in this paper has been
developed within the research project “Active Magnetic Bearings
with Supreme Reliability" and is used for position sensor fault
detection.
Within this new concept gap calculation is carried out by an alldigital
analysis of the digitized coil current and voltage waveform.
For analysis those time periods within the PWM period are used,
which give the best results. Additionally, the concept allows the
digital compensation of nonlinearities, for example magnetic
saturation, without degrading signal quality. This increases the
accuracy and robustness of the air gap estimation and additionally
reduces phase delays.
Beneath an overview about the developed concept first
measurement results are presented which show the potential of this
all-digital self-sensing concept.
Abstract: Composite steel shear wall is a lateral load resisting system which consists of a steel plate with concrete wall attached to one or both sides to prevent it from elastic buckling. The composite behavior is ensured by utilizing high-strength bolts. This paper investigates the effect of distance between bolts, and for this purpose 14 one-story one-bay specimens with various bolts spacing were modeled by finite element code which is developed by the authors. To verify the model, numerical results were compared with a valid experiment which illustrate proper agreement. Results depict increasing the distance between bolts would improve the seismic ever, this increase must be limited, because of large distances will cause widespread buckling of the steel plate in free subpanels between bolts and would result in no improvement. By comparing the results in elastic region, it was observed initial stiffness is not affected by changing the distance.
Abstract: The usual method of river flow diversion involves construction of tunnels and cofferdams. Given the fact that the cost of diversion works could be as high as 10-20% of the total dam construction cost, due attention should be paid to optimum design of the diversion works. The cost of diversion works depends, on factors, such as: the tunnel dimensions and the intended tunneling support measures during and after excavation; quality and characterizes of the rock through which the tunnel should be excavated; the dimensions of the upstream (and downstream) cofferdams; and the magnitude of river flood the system is designed to divert. In this paper by use of the cost of unit prices for tunnel excavation, tunnel lining, tunnel support (rock bolt + shotcrete) and cofferdam fill the cost function was determined. The function is then minimized by the aid of PSO Algorithm (particle swarm optimization). It is found that the optimum diameter and the total diversion cost are directly related to the river flood discharge (Q). It has also shown that in addition to optimum diameter design discharge (Q), river length, tunnel length, is mainly a function of the ratios (not the absolute values) of the unit prices and does not depend on the overall price levels in the respective country. The results of optimization use in some of the case study lead us to significant changes in the cost.
Abstract: The operating control parameters of injection
flushing type of electrical discharge machining process on stainless
steel 304 workpiece using copper tools are being optimized
according to its individual machining characteristic i.e. Electrode
Wear Ratio (EWR). Higher EWR would give bad dimensional
precision for the EDM machined workpiece because of high
electrode wear. Hence, the quality characteristic for EWR is set to
lower-the-better to achieve the optimum dimensional precision for
the machined workpiece. Taguchi method has been used for the
construction, layout and analysis of the experiment for EWR
machining characteristic. The use of Taguchi method in the
experiment saves a lot of time and cost of preparing and machining
the experiment samples. Therefore, an L18 Orthogonal array
which was the fundamental component in the statistical design of
experiments has been used to plan the experiments and Analysis of
Variance (ANOVA) is used to determine the optimum machining
parameters for this machining characteristic. The control
parameters selected for this optimization experiments are polarity,
pulse on duration, discharge current, discharge voltage, machining
depth, machining diameter and dielectric liquid pressure. The
result had shown that negative polarity machining parameter
setting will decreases EWR.
Abstract: In this paper, an attempt has been made to obtain nonsensitive
solutions in the multi-objective optimization of a
photovoltaic/thermal (PV/T) air collector. The selected objective
functions are overall energy efficiency and exergy efficiency.
Improved thermal, electrical and exergy models are used to calculate
the thermal and electrical parameters, overall energy efficiency,
exergy components and exergy efficiency of a typical PV/T air
collector. A computer simulation program is also developed. The
results of numerical simulation are in good agreement with the
experimental measurements noted in the previous literature. Finally,
multi-objective optimization has been carried out under given
climatic, operating and design parameters. The optimized ranges of
inlet air velocity, duct depth and the objective functions in optimal
Pareto front have been obtained. Furthermore, non-sensitive solutions
from energy or exergy point of view in the results of multi-objective
optimization have been shown.
Abstract: In this paper the authors propose a flexible electronic solution, to improve the energetic efficiency of a thermo plant. This is achieved by replacing the mechanical gear box, placed traditionally between a gas turbine and a synchronous generator; by a power electronic converter. After reminding problematic of gear boxes and interest of a proposed electronic solution in high power plants, the authors describe a new control strategy for an indirect frequency converter, which is characterized by its high efficiency due to the use of SWM: Square Wave Modulation. The main advantage of this mode is the quasi absence of switching losses. A control method is also proposed to resolve some problems incurred by using square wave modulation, in particular to reduce the harmonics distortion of the output inverter voltage and current. Simulation examples as well as experimental results are included.
Abstract: Adjacent Hall microsensors, comprising a silicon
substrate and four contacts, providing simultaneously two supply inputs and two differential outputs, are characterized. The voltage
related sensitivity is in the order of 0.11T-1, and a cancellation method for offset compensation is used, achieving residual offset in
the micro scale which is also compared to a single Hall plate.
Abstract: Preliminary studies on Kuwait high voltage
transmission system show significant increase in the short circuit
level at some of the grid substations and some generating stations.
This increase results from the growth in the power transmission
systems in size and complexity. New generating stations are expected
to be added to the system within the next few years. This paper
describes the study analysis performed to evaluate the available and
potential solutions to control SC levels in Kuwait power system. It
also presents a modified planning of the transmission network in
order to fulfill this task.
Abstract: This paper presents the mathematical model and
control strategy on DQ frame of shunt active power filter. The
structure of the shunt active power filter is the voltage source inverter
(VSI). The pulse width modulation (PWM) with PI controller is used
in the paper. The concept of DQ frame to apply with the shunt active
power filter is described. Moreover, the detail of the PI controller
design for two current loops and one voltage loop are fully explained.
The DQ axis with Fourier (DQF) method is applied to calculate the
reference currents on DQ frame. The simulation results show that the
control strategy and the design method presented in the paper can
provide the good performance of the shunt active power filter.
Moreover, the %THD of the source currents after compensation can
follow the IEEE Std.519-1992.
Abstract: Distributed Power generation has gained a lot of
attention in recent times due to constraints associated with
conventional power generation and new advancements in DG
technologies .The need to operate the power system economically
and with optimum levels of reliability has further led to an increase
in interest in Distributed Generation. However it is important to place
Distributed Generator on an optimum location so that the purpose of
loss minimization and voltage regulation is dully served on the
feeder. This paper investigates the impact of DG units installation on
electric losses, reliability and voltage profile of distribution networks.
In this paper, our aim would be to find optimal distributed
generation allocation for loss reduction subjected to constraint of
voltage regulation in distribution network. The system is further
analyzed for increased levels of Reliability. Distributed Generator
offers the additional advantage of increase in reliability levels as
suggested by the improvements in various reliability indices such as
SAIDI, CAIDI and AENS. Comparative studies are performed and
related results are addressed. An analytical technique is used in order
to find the optimal location of Distributed Generator. The suggested
technique is programmed under MATLAB software. The results
clearly indicate that DG can reduce the electrical line loss while
simultaneously improving the reliability of the system.
Abstract: To maximise furnace production it-s necessary to
optimise furnace control, with the objectives of achieving maximum
power input into the melting process, minimum network distortion
and power-off time, without compromise on quality and safety. This
can be achieved with on the one hand by an appropriate electrode
control and on the other hand by a minimum of AC transformer
switching.
Electrical arc is a stochastic process; witch is the principal cause
of power quality problems, including voltages dips, harmonic
distortion, unbalance loads and flicker. So it is difficult to make an
appropriate model for an Electrical Arc Furnace (EAF). The factors
that effect EAF operation are the melting or refining materials,
melting stage, electrode position (arc length), electrode arm control
and short circuit power of the feeder. So arc voltages, current and
power are defined as a nonlinear function of the arc length. In this
article we propose our own empirical function of the EAF and model,
for the mean stages of the melting process, thanks to the
measurements in the steel factory.
Abstract: This paper proposes a three-phase four-wire currentcontrolled
Voltage Source Inverter (CC-VSI) for both power quality
improvement and PV energy extraction. For power quality
improvement, the CC-VSI works as a grid current-controlling shunt
active power filter to compensate for harmonic and reactive power of
loads. Then, the PV array is coupled to the DC bus of the CC-VSI
and supplies active power to the grid. The MPPT controller employs
the particle swarm optimization technique. The output of the MPPT
controller is a DC voltage that determines the DC-bus voltage
according to PV maximum power. The PSO method is simple and
effective especially for a partially shaded PV array. From computer
simulation results, it proves that grid currents are sinusoidal and inphase
with grid voltages, while the PV maximum active power is
delivered to loads.
Abstract: Added stresses due to adjacent structure should be
considered in foundation design and stress control in soil under the structure. This case is considered less than other cases in design and
calculation whereas stresses in implementation are greater than analytical stress.
Structure load are transmitted to earth by foundation and role of foundation is propagation of load on the continuous and half extreme
soil. This act cause that, present stresses lessen to allowable strength
of soil. Some researchers such as Boussinesq and westergaurd by
using of some assumption studied on this issue, theorically. Target of
this paper is study and evaluation of added stresses under structure
due to adjacent structure. For this purpose, by using of assumption, theoric relation and numeral methods, effects of adjacent structure
with 4 to 10 storeys on the main structure with 4 storeys are studied
and effect of parameters and sensitivity of them are evaluated.