• Journal of Power Electronics
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• v.9 no.5
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• pp.691-699
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• 2009

This paper presents the analysis of series active power filter for reactive power compensation, load balancing, harmonic elimination, and neutral current eradication in three-phase four-wire power systems. Generally, the three-phase four-wire system is widely employed in distributing electric energy to several office building and manufacturing plants. In such systems, the third harmonic and its 3rd harmonics are termed as triple and zero sequence components that do not cancel each other in the system neutral. Consequently, the triple harmonics add together creating a primary source of excessive neutral current. Regarding this concern, this paper presents a new control algorithm for a series hybrid active system, whereas the control approach it adopts directly influence its compensation characteristics. Hence, the advantage of this control algorithm is the direct extraction of compensation voltage reference without phase transformations and multiplying harmonic current value by gain and the required rating of the series active filter is much smaller than that of a conventional shunt active power filter. In order to show the effectiveness of the proposed control algorithm, experiments have been carried out.

• Journal of Electrical Engineering and Technology
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• v.12 no.5
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• pp.1709-1718
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• 2017

This paper presents a hybrid stochastic deterministic multi-timescale scheduling (SDMS) approach for generation scheduling of a power grid. SDMS considers flexible resource options including conventional generation flexibility in a chance-constrained day-ahead scheduling optimization (DASO). The prime objective of the DASO is the minimization of the daily production cost in power systems with high penetration scenarios of variable generation. Furthermore, energy storage is scheduled in an hourly-ahead deterministic real-time scheduling optimization (RTSO). DASO simulation results are used as the base starting-point values in the hour-ahead online rolling RTSO with a 15-minute time interval. RTSO considers energy storage as another source of grid flexibility, to balance out the deviation between predicted and actual net load demand values. Numerical simulations, on the IEEE RTS test system with high wind penetration levels, indicate the effectiveness of the proposed SDMS framework for managing the grid flexibility to meet the net load demand, in both day-ahead and real-time timescales. Results also highlight the adequacy of the framework to adjust the scheduling, in real-time, to cope with large prediction errors of wind forecasting.

• International Journal of Contents
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• v.11 no.4
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• pp.38-43
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• 2015

Non-orthogonal multiple access (NOMA) where all users share the entire time and frequency resource has paid attention as one of the key technologies to enhance the spectral efficiency and the total throughput. Nevertheless, as the number of users and SIC error increase, the inter-user interference and the residual interference due to the SIC error also increase, resulting in performance degradation. In order to mitigate the performance degradation, we propose grouping-based NOMA system. In the proposed scheme, all users are divided into two groups based on the distance between the BS and each user, where one utilizes the first half of the bandwidth and the other utilizes the rest in the orthogonal manner. On the other hand, users in each group share the spectrum in the non-orthogonal manner. Grouping users can reduce both the inter-user interference and residual interference due to the SIC error, so it can outperform conventional NOMA system, especially in case that the number of users and the SIC error increase. Based on that, we also present the hybrid operation of the conventional and the proposed NOMA systems. In numerical results, the total throughput of the proposed NOMA systems is compared with that of the conventional NOMA systems with regard to the number of users and SIC error. It is confirmed that the proposed NOMA system outperforms the conventional NOMA system as the number of users and the SIC error increase.

• Journal of IKEEE
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• v.19 no.3
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• pp.327-334
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• 2015

Various types of middle-ware were created for integration between legacy systems and newly built systems. RPC(Remote Procedure Call), MOM(Message Oriented Middle-ware) and TM(Transaction processing Monitor) are the typical types of middle-ware. One of the most known MOM type middle-ware is PS(Publish/Subscribe). PS enables to create a system which has low coupling and high scalability. But PS based systems also have low cohesiveness. On the contrary, RPC has high cohesiveness but also has high coupling. This paper proposed design and implementation of hybrid model which offset disadvantages of RPC and PS.

• Journal of Institute of Control, Robotics and Systems
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• v.19 no.11
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• pp.960-967
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• 2013

Shape recognition of solder ball bumps in a BGA (Ball Grid Array) is an important issue in flip chip bonding technology. In particular, the semiconductor industry has required faster and more accurate inspection of micron-size solder bumps in flip chip bonding as the density of balls has increased dramatically. The difficulty of this issue comes from specular reflection on the metal ball. Shape recognition of a metal ball is a very realproblem for computer vision systems. Specular reflection of the metal ball appears, disappears, or changes its image abruptly due to tiny movementson behalf of the viewer. This paper presents a practical shape recognition method for three dimensional (3-D) inspection of a BGA using a 5-step ring illumination device. When the ring light illuminates the balls, distinctive specularity images of the balls, which are referred to as "iso-slope contours" in this paper, are shown. By using a mathematical reflectance model, we can drive the 3-D shape information of the ball in aquantitative manner. The experimental results show the usefulness of the method for industrial application in terms of time and accuracy.

• IEMEK Journal of Embedded Systems and Applications
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• v.11 no.2
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• pp.87-95
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• 2016

Nonvolatile memory (NVM) is being considered as an alternative of traditional memory devices such as SRAM and DRAM, which suffer from various limitations due to the technology scaling of modern integrated circuits. Although NVMs have advantages including nonvolatility, low leakage current, and high density, their inferior write performance in terms of energy and endurance becomes a major challenge to the successful design of NVM-based memory systems. In order to overcome the aforementioned drawback of the NVM, extensive research is required to develop energy- and endurance-aware optimization techniques for NVM-based memory systems. However, researchers have experienced difficulty in finding a suitable simulation tool to prototype and evaluate new NVM optimization schemes because existing simulation tools do not consider the feature of NVM devices. In this article, we introduce a NVM-based cache simulator to support rapid prototyping and evaluation of NVM-based caches, as well as energy- and endurance-aware NVM cache optimization schemes. We demonstrate that the proposed NVM cache simulator can easily prototype PRAM cache and PRAM+STT-RAM hybrid cache as well as evaluate various write traffic reduction schemes and wear leveling schemes.

• Journal of Korea Multimedia Society
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• v.16 no.5
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• pp.601-609
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• 2013

One of the most serious factors constraining the next generation cellular mobile consumer communication systems will be the severe co-channel interference experienced at the cell edge. Such a capacity-degrading impairment combined with the limited available spectrum resource makes it essential to develop more spectrally efficient solutions to enhance the system performance and enrich the mobile user's application services. This paper proposes a unique hybrid method of frequency hopping (FH) and subcarrier-reuse-partitioning that can maximize the system capacity by efficiently utilizing the available spectrum while at the same time reduce the co-channel interference effect. The main feature of the proposed method is that it applies an optimal combination of different frequency reuse factors (FRF) and FH-subcarrier allocation patterns into the partitioned cell regions. From the simulation results, it is shown that the proposed method can achieve the optimum number of subcarrier subsets according to the frequency-reuse distance and results in better performance than the fixed FRF methods, for a given partitioning arrangement. The results are presented in the context of both blocking probability and BER performances. It will also be shown how the proposed scheme is well suited to FH-OFDMA based cellular systems aiming at low co-channel interference performance and optimized number of subcarriers.

• Journal of Power Electronics
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• v.13 no.4
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• pp.569-583
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• 2013

In this study, the simultaneous use of a multi-level converter (MLC) as a DC-motor drive and as an active battery cell balancer is investigated. MLCs allow each battery cell in a battery pack to be independently switched on and off, thereby enabling the potential non-uniform use of battery cells. By exploiting this property and the brake regeneration phases in the drive cycle, MLCs can balance both the state of charge (SoC) and temperature differences between cells, which are two known causes of battery wear, even without reciprocating the coolant flow inside the pack. The optimal control policy (OP) that considers both battery pack temperature and SoC dynamics is studied in detail based on the assumption that information on the state of each cell, the schedule of reciprocating air flow and the future driving profile are perfectly known. Results show that OP provides significant reductions in temperature and in SoC deviations compared with the uniform use of all cells even with uni-directional coolant flow. Thus, reciprocating coolant flow is a redundant function for a MLC-based cell balancer. A specific contribution of this paper is the derivation of a state-space electro-thermal model of a battery submodule for both uni-directional and reciprocating coolant flows under the switching action of MLC, resulting in OP being derived by the solution of a convex optimization problem.

• Journal of Power Electronics
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• v.17 no.5
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• pp.1327-1337
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• 2017

Photovoltaic (PV) systems are influenced by disproportionate impacts on energy production caused by frequent mismatch cases. The occurrence of multiple maximum power points (MPPs) adds complexity to the tracking process in various PV systems. However, current maximum-power point tracking (MPPT) techniques exhibit limited performance. This paper introduces an enhanced simulated annealing (ESA)-based GMPPT technique against multiple MPP issues in P-V curve with different PV system structures. The proposed technique not only distinguishes global and local MPPs but also performs rapid convergence speed and high tracking accuracy of irradiance changing and restart capability detection. Moreover, the proposed global maximum power tracking algorithm can be applied in the central converter of DMPPT and hybrid PV system to meet various application scenarios. Its effectiveness is verified by simulation and test results.

• Journal of Information Management
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• v.26 no.2
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• pp.61-79
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• 1995

The purpose of this paper is to investigate search efficiency of controlled vocabulary versus uncontrolled vocabulary subject access in online catalog systems. The question of the effectiveness of controlled versus uncontrolled vocabulary in information retrieval has been raised in many literatures. A debate continues in the Library and Information Science Professions over the relative merit, appropriateness, and efficiency of uncontrolled vocabulary subject access in online catalog systems. Actually users used to combine uncontrolled vocabulary subject searching with controlled vocabulary subject searching. But the success of user's subject search depends on his choice of search terms. Also the technical developments that facilitate cooperation among information services in general make it increasingly possible for such cooperation to take place on an international level. In this study, several common types of vocabularies on online catalog systems are described and compared, especially usages of vocabularies in multilingual environment are analyzed.