Abstract: This paper investigates the performance comparison of SVC (Static VAR Compensator) and DSTATCOM (Distribution Static Synchronous Compensator) to improve voltage stability in Radial Distribution System (RDS) which are efficient FACTS (Flexible AC Transmission System) devices that are capable of controlling the active and reactive power flows in a power system line by appropriately controlling parameters using ANFIS. Simulations are carried out in MATLAB/Simulink environment for the IEEE-4 bus system to test the ability of increasing load. It is found that these controllers significantly increase the margin of load in the power systems.
Abstract: There exist significant losses on transmission lines due to distance, as power generating stations could be located far from some isolated settlements. Standalone wind farms could be a good choice of alternative power generation for such settlements that are far from the grid due to factors of long distance or socio-economic problems. However, uncompensated wind farms consume reactive power since wind turbines are induction generators. Therefore, capacitor banks are used to compensate reactive power, which in turn improves the voltage profile of the network. Although capacitor banks help improving voltage profile, they also undergo switching actions due to its compensating response to the variation of various types of load at the consumer’s end. These switching activities could cause transient overvoltage on the network, jeopardizing the end-life of other equipment on the system. In this paper, the overvoltage caused by these switching activities is investigated using the IEEE bus 14-network to represent a standalone wind farm, and the simulation is done using ATP/EMTP software. Scenarios involving the use of pre-insertion resistor and pre-insertion inductor, as well as controlled switching was also carried out in order to decide the best mitigation option to reduce the overvoltage.
Abstract: Worldwide Interoperability for Microwave Access, is a broadband technology, which can effectively transmit a data across a group of users using Multicast and Broadcast Service. WiMAX belongs to a family of (IEEE 802.16) standards and is evolving as a fourth generation technology. WiMAX is the next generation technology that offers wireless access over long distances. MBS zone, which is a group of base stations that are broadcasting the same multicast packets which defines Multicast and Broadcast services. Handover is a process of transferring an ongoing call or data session from one channel connected to the core network to another channel. The handover causes authentication, delay, packet loss, jitter that mainly affects the communication. In this paper, we present a survey on handover security issues in WiMAX.
Abstract: The Flexible AC Transmission System (FACTS)
technology is a new advanced solution that increases the reliability
and provides more flexibility, controllability, and stability of a power
system. The Unified Power Flow Controller (UPFC), as the most
versatile FACTS device for regulating power flow, is able to control
respectively transmission line real power, reactive power, and node
voltage. The main purpose of this paper is to analyze the effect of the
UPFC on the load flow, the power losses, and the voltage stability
using NEPLAN software modules, Newton-Raphson load flow is
used for the power flow analysis and the modal analysis is used for
the study of the voltage stability. The simulation was carried out on
the IEEE 14-bus test system.
Abstract: In IEEE 802.11 networks, it is well known that the
traditional time-domain contention often leads to low channel
utilization. The first frequency-domain contention scheme, the time to
frequency (T2F), has recently been proposed to improve the channel
utilization and has attracted a great deal of attention. In this paper, we
present the latest research progress on the weighed frequency-domain
contention. We compare the basic ideas, work principles of these
related schemes and point out their differences. This paper is very
useful for further study on frequency-domain contention.
Abstract: This paper proposes an APPLE scheme that aims at providing absolute and proportional throughput guarantees, and maximizing system throughput simultaneously for wireless LANs with homogeneous and heterogenous traffic. We formulate our objectives as an optimization problem, present its exact and approximate solutions, and prove the existence and uniqueness of the approximate solution. Simulations validate that APPLE scheme is accurate, and the approximate solution can well achieve the desired objectives already.
Abstract: Weak damping of low frequency oscillations is a frequent phenomenon in electrical power systems. These frequencies can be damped by power system stabilizers. Unified power flow controller (UPFC), as one of the most important FACTS devices, can be applied to increase the damping of power system oscillations and the more effect of this controller on increasing the damping of oscillations depends on its proper placement in power systems. In this paper, a technique based on controllability is proposed to select proper location of UPFC and the best input control signal in order to enhance damping of power oscillations. The effectiveness of the proposed technique is demonstrated in IEEE 9 bus power system.
Abstract: The use of wireless technology in industrial networks
has gained vast attraction in recent years. In this paper, we have
thoroughly analyzed the effect of contention window (CW) size on
the performance of IEEE 802.11-based industrial wireless networks
(IWN), from delay and reliability perspective. Results show that the
default values of CWmin, CWmax, and retry limit (RL) are far from
the optimum performance due to the industrial application
characteristics, including short packet and noisy environment. In this
paper, an adaptive CW algorithm (payload-dependent) has been
proposed to minimize the average delay. Finally a simple, but
effective CW and RL setting has been proposed for industrial
applications which outperforms the minimum-average-delay solution
from maximum delay and jitter perspective, at the cost of a little
higher average delay. Simulation results show an improvement of up
to 20%, 25%, and 30% in average delay, maximum delay and jitter
respectively.
Abstract: In this paper, various methods of providing restricted
earth fault protection are discussed. The proper operation of high and
low impedance Restricted Earth Fault (REF) protection for various
applications has been discussed. The maloperation of a relay due to
improper placement of CTs has been identified and a simple/unique
solution has been proposed in this work with a case study. Moreover,
it is found that the proper placement of CT in high impedance method
will provide the same result with reduced CT. This methodology has
been successfully implemented in Al Takreer refinery for a 2000
KVA transformer. The outcome of the paper may be included in
IEEEC37.91 standard to give the proper guidance for protection
engineers to sort out the issues related to mal functioning of REF
relays.
Abstract: This paper proposes a novel heuristic algorithm that aims to determine the best size and location of distributed generators in unbalanced distribution networks. The proposed heuristic algorithm can deal with the planning cases where power loss is to be optimized without violating the system practical constraints. The distributed generation units in the proposed algorithm is modeled as voltage controlled node with the flexibility to be converted to constant power factor node in case of reactive power limit violation. The proposed algorithm is implemented in MATLAB and tested on the IEEE 37 -node feeder. The results obtained show the effectiveness of the proposed algorithm.
Abstract: This paper presents an analytical approach for
evaluating distribution system reliability indices in the presence of
distributed generation. Modeling distributed generation and
evaluation of distribution system reliability indices using the
frequency duration technique. Using model implements and case
studies are discussed. Results showed that location of DG and its
effect in distribution reliability indices. In this respect, impact of DG
on distribution system is investigated using the IEEE Roy Billinton
test system (RBTS2) included feeder 1. Therefore, it will help to the
distribution system planners in the DG resource placement.
Abstract: The use of Flexible AC Transmission System
(FACTS) devices in a power system can potentially overcome
limitations of the present mechanically controlled transmission
system. Also, the advance of technology makes possible to include
new energy storage devices in the electrical power system. The
integration of Superconducting Magnetic Energy Storage (SMES)
into Static Synchronous Compensator (STATCOM) can lead to
increase their flexibility in improvement of power system dynamic
behaviour by exchanging both active and reactive powers with power
grids. This paper describes structure and behaviour of SMES,
specifications and performance principles of the STATCOM/SMES
compensator. Moreover, the benefits and effectiveness of integrated
SMES with STATCOM in power systems is presented. Also, the
performance of the STATCOM/SMES compensator is evaluated
using an IEEE 3-bus system through the dynamic simulation by
PSCAD/EMTDC software.
Abstract: The recent interest in alternative and renewable
energy systems results in increased installed capacity ratio of such
systems in total energy production of the world. Specifically, Wind
Energy Conversion Systems (WECS) draw significant attention
among possible alternative energy options, recently. On the contrary
of the positive points of penetrating WECS in all over the world in
terms of environment protection, energy independence of the
countries, etc., there are significant problems to be solved for the grid
connection of large scale WECS. The reactive power regulation,
voltage variation suppression, etc. can be presented as major issues to
be considered in this regard. Thus, this paper evaluates the
application of a Static VAr Compensator (SVC) unit for the reactive
power regulation and operation continuity of WECS during a fault
condition. The system is modeled employing the IEEE 13 node test
system. Thus, it is possible to evaluate the system performance with
an overall grid simulation model close to real grid systems. The
overall simulation model is developed in
MATLAB/Simulink/SimPowerSystems® environments and the
obtained results effectively match the target of the provided study.
Abstract: To tackle the air pollution issues, Plug-in Hybrid
Electric Vehicles (PHEVs) are proposed as an appropriate solution.
Charging a large amount of PHEV batteries, if not controlled, would
have negative impacts on the distribution system. The control process
of charging of these vehicles can be centralized in parking lots that
may provide a chance for better coordination than the individual
charging in houses. In this paper, an optimization-based approach is
proposed to determine the optimum PHEV parking capacities in
candidate nodes of the distribution system. In so doing, a profile for
charging and discharging of PHEVs is developed in order to flatten
the network load profile. Then, this profile is used in solving an
optimization problem to minimize the distribution system losses. The
outputs of the proposed method are the proper place for PHEV
parking lots and optimum capacity for each parking. The application
of the proposed method on the IEEE-34 node test feeder verifies the
effectiveness of the method.
Abstract: This paper presents an application of Artificial Neural
Network (ANN) algorithm for improving power system voltage
stability. The training data is obtained by solving several normal and
abnormal conditions using the Linear Programming technique. The
selected objective function gives minimum deviation of the reactive
power control variables, which leads to the maximization of
minimum Eigen value of load flow Jacobian. The considered reactive
power control variables are switchable VAR compensators, OLTC
transformers and excitation of generators. The method has been
implemented on a modified IEEE 30-bus test system. The results
obtain from the test clearly show that the trained neural network is
capable of improving the voltage stability in power system with a
high level of precision and speed.
Abstract: This paper proposes a novel heuristic algorithm that aims to determine the best size and location of distributed generators in unbalanced distribution networks. The proposed heuristic algorithm can deal with the planning cases where power loss is to be optimized without violating the system practical constraints. The distributed generation units in the proposed algorithm is modeled as voltage controlled node with the flexibility to be converted to constant power factor node in case of reactive power limit violation. The proposed algorithm is implemented in MATLAB and tested on the IEEE 37 -node feeder. The results obtained show the effectiveness of the proposed algorithm.
Abstract: Due to the continuous increment of the load demand,
identification of weaker buses, improvement of voltage profile and
power losses in the context of the voltage stability problems has
become one of the major concerns for the larger, complex,
interconnected power systems. The objective of this paper is to
review the impact of Flexible AC Transmission System (FACTS)
controller in Wind generators connected electrical network for
maintaining voltage stability. Wind energy could be the growing
renewable energy due to several advantages. The influence of wind
generators on power quality is a significant issue; non uniform power
production causes variations in system voltage and frequency.
Therefore, wind farm requires high reactive power compensation; the
advances in high power semiconducting devices have led to the
development of FACTS. The FACTS devices such as for example
SVC inject reactive power into the system which helps in maintaining
a better voltage profile. The performance is evaluated on an IEEE 14
bus system, two wind generators are connected at low voltage buses
to meet the increased load demand and SVC devices are integrated at
the buses with wind generators to keep voltage stability. Power
flows, nodal voltage magnitudes and angles of the power network are
obtained by iterative solutions using MIPOWER.
Abstract: IEEE 802.11a/b/g standards provide multiple
transmission rates, which can be changed dynamically according to the
channel condition. Cooperative communications were introduced to
improve the overall performance of wireless LANs with the help of
relay nodes with higher transmission rates. The cooperative
communications are based on the fact that the transmission is much
faster when sending data packets to a destination node through a relay
node with higher transmission rate, rather than sending data directly to
the destination node at low transmission rate. To apply the cooperative
communications in wireless LAN, several MAC protocols have been
proposed. Some of them can result in collisions among relay nodes in a
dense network. In order to solve this problem, we propose a new
protocol. Relay nodes are grouped based on their transmission rates.
And then, relay nodes only in the highest group try to get channel
access. Performance evaluation is conducted using simulation, and
shows that the proposed protocol significantly outperforms the
previous protocol in terms of throughput and collision probability.
Abstract: IEEE 802.16 (WiMAX) aims to present high speed
wireless access to cover wide range coverage. The base station (BS)
and the subscriber station (SS) are the main parts of WiMAX.
WiMAX uses either Point-to-Multipoint (PMP) or mesh topologies.
In the PMP mode, the SSs connect to the BS to gain access to the
network. However, in the mesh mode, the SSs connect to each other
to gain access to the BS.
The main components of QoS management in the 802.16 standard
are the admission control, buffer management and packet scheduling.
In this paper, we use QualNet 5.0.2 to study the performance of
different scheduling schemes, such as WFQ, SCFQ, RR and SP when
the numbers of SSs increase. We find that when the number of SSs
increases, the average jitter and average end-to-end delay is increased
and the throughput is reduced.
Abstract: This paper presents a methodology using
Gravitational Search Algorithm for optimal placement of Phasor
Measurement Units (PMUs) in order to achieve complete
observability of the power system. The objective of proposed
algorithm is to minimize the total number of PMUs at the power
system buses, which in turn minimize installation cost of the PMUs.
In this algorithm, the searcher agents are collection of masses which
interact with each other using Newton’s laws of gravity and motion.
This new Gravitational Search Algorithm based method has been
applied to the IEEE 14-bus, IEEE 30-bus and IEEE 118-bus test
systems. Case studies reveal optimal number of PMUs with better
observability by proposed method.