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Ankara, Turkey

Khamis A.,National University of Malaysia | Khamis A.,University Technical Malaysia Melaka | Shareef H.,National University of Malaysia | Mohamed A.,National University of Malaysia | Bizkevelci E.,Tubitak Uzay

The high penetration level of distributed generation (DG) provides numerous potential environmental benefits, such as high reliability, efficiency, and low carbon emissions. However, the effective detection of islanding and rapid DG disconnection is essential to avoid safety problems and equipment damage caused by the island mode operations of DGs. The common islanding protection technology is based on passive techniques that do not perturb the system but have large non-detection zones. This study attempts to develop a simple and effective passive islanding detection method with reference to a probabilistic neural network-based classifier, as well as utilizes the features extracted from three phase voltages seen at the DG terminal. This approach enables initial features to be obtained using the phase-space technique. This technique analyzes the time series in a higher dimensional space, revealing several hidden features of the original signal. Intensive simulations were conducted using the DigSilent Power Factory® software. Results show that the proposed islanding detection method using probabilistic neural network and phase-space technique is robust and capable of sensing the difference between the islanding condition and other system disturbances. © 2014 Elsevier B.V. Source

Tor O.B.,Tubitak Uzay | Guven A.N.,Middle East Technical University | Shahidehpour M.,Illinois Institute of Technology
IEEE Transactions on Power Systems

This paper presents a transmission expansion planning (TEP) model which coordinates investment decisions in monopolistic transmission and decentralized generator sectors. The proposed planning approach gauges transmission congestion and security constraints with respect to transmission investments while promoting investments on independent power produces (IPPs) through incentive payments. The paper includes discussions on incentive mechanisms and prioritization among qualified IPPs for several planning scenarios. Such incentives might be necessary to trigger investments on IPPs earlier than those projected by the decentralized generation system, when the power system security is threatened. The proposed planning approach would optimize the sum of transmission investments, incentive payments to IPPs, and congestion costs along the planning horizon. The case studies illustrate how the proposed planning algorithm could be utilized in order to determine incentive payments to candidate generators when necessary, and prioritize such incentives among multiple IPP candidates. © 2010 IEEE. Source

Khamis A.,National University of Malaysia | Khamis A.,University Technical Malaysia Melaka | Shareef H.,National University of Malaysia | Bizkevelci E.,Tubitak Uzay | Khatib T.,National University of Malaysia
Renewable and Sustainable Energy Reviews

Islanding detection of distributed generations (DGs) is one of the most important aspects of interconnecting DGs to the distribution system. Islanding detection techniques can generally be classified as remote methods, which are associated with islanding detection on the utility sides, and local methods, which are associated with islanding detection on the DG side. This paper presents a survey of various islanding detection techniques and their advantages and disadvantages. The paper focused on islanding detection using a conventional and intelligent technique. A summary table that compares and contrasts the existing methods is also presented. © 2013 Elsevier Ltd. All rights reserved. Source

Atar O.,Tubitak Uzay | Sazli M.H.,Ankara University
Journal of the Faculty of Engineering and Architecture of Gazi University

The most difficult design issue for turbo codes, which is the most recent and successful channel coding method to approach the channel capacity limit, is the design of the iterative decoders which perform calculations for all possible states of the encoders. BCJR (MAP) algorithm, which is used for turbo decoders, embodies complex mathematical operations such as division, exponential and logarithm calculations. Therefore, BCJR algorithm was avoided and the sub-optimal derivatives of this algorithm such as Log-MAP and Max-Log-MAP were preferred for turbo decoder implementations. BCJR algorithm was reformulated and wrapped into a suitable structure for FPGA implementations at previous works [1]. Reformulated BCJR algorithm is implemented in this work. Complex mathematical operations which run slowly on hardware (division, exponential and logarithm calculations) are read from look-up-tables and high performance calculation structures are established. Implemented system is verified through simulations. It is observed that the BER performance obtained is better than the Log-MAP algorithm as expected. Source

Khamis A.,National University of Malaysia | Khamis A.,University Technical Malaysia Melaka | Shareef H.,National University of Malaysia | Mohamed A.,National University of Malaysia | Bizkevelci E.,Tubitak Uzay
Jurnal Teknologi (Sciences and Engineering)

Voltage stability is one of the major concerns in operational and planning of modern power system. Many strategies have been implemented to avoid voltage collapse, which the load shedding considered as the last option. However, optimization is needed to estimate the minimum amount to shed so as to prevent voltage instability. In this paper, an effective method is presented for estimating the optimal amount of load to be shed in a distribution system based on the gravitational search algorithm (GSA). The voltage stability margin (VSM) of the system has been considered in the objective function. The optimization problem is formulated to maximize the VSM of the system and at the same time satisfying the operation and security constraints. The optimum solution depends on the predefined constraints such as the number of load buses available to shed and the maximum amount of load permitted to shed. Simulation result conducted on the IEEE 33 bus radial distribution system shows that the system voltage stability can be improved by optimally shedding the loads at critical system buses. The results also indicate that the numbers of load buses available for load shedding does not have a significant impact on voltage stability margin, but it is highly dependent on the maximum amount of load permitted to shed. © 2014 Penerbit UTM Press. All rights reserved. Source

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