• The Transactions of the Korean Institute of Electrical Engineers B
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• v.55 no.5
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• pp.280-286
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• 2006

The paper proposes a new protection algorithm for reliable operation of grid-interfaced PV system, which can flexibly interact with conventional protective schemes of power utility grid not only to prevent damages to utility or public persons and utility apparatus caused by malfunction or failure in distribution network protection system, but also to protect a PV system itself from faults or abnormal conditions of the network. The proposed algorithm is based on reclosing characteristics of the distribution system. As a network fault occurs, the new scheme determines whether it is momentary or permanent and responds in a pre-programmed way to the fault. For permanent outage, the proposed algorithm shuts down inverter's operations but monitoring system voltage and frequency at the point of common coupling with grid. When it comes to the momentary outage, Inverter starts stand-by operation mode so that it can be automatically connected to the grid without start-up procedures as soon as the system voltage and frequency returns into the normal operation range. In order to investigate' and evaluate the PV system operation, simulation study based on PSCAD/EMTDC has been carried out to verify the performance of the proposed protection scheme.

• The Transactions of the Korean Institute of Power Electronics
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• v.9 no.3
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• pp.231-239
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• 2004

A new scheme to estimate the moment of inertia in the motor drive system in very low speed is proposed in this paper. The simple estimation scheme, which is usually used in most servo system for low speed operation, is sensitive to the variation of the machine parameter, especially the moment of inertia. To estimate the motor inertia value, Reduced-Order Extended Luenberger Observer (ROELO) is applied. The effectiveness of the proposed inertia identification method using the RORLO is verified by simulation and experiment.

• International Journal of Precision Engineering and Manufacturing
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• v.8 no.1
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• pp.21-26
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• 2007

In industry, multihead automatic combination weighers are used to provide accurate weights at high speed. To minimize giveaway, greater accuracy is desired, especially for valuable products. This paper describes a combination algorithm based on bit operation. The combination method is simple and saves time, since only the elements to be considered for combination are generated. The total number of combinations from which the desired output weight is chosen can be increased by extending the combination from memory hoppers to include some weighing hoppers. For an eight-channel weigher, three or four combination elements are best. In addition to targeting approximately equal amounts of products in each channel, this study investigated other schemes. Simulation results show that schemes targeting combination elements with an unequal distribution of the output weight are more accurate. The most accurate scheme involves supplying products to all memory and weighing hoppers before commencing the combination operation. However, this scheme takes more time.

• Journal of Communications and Networks
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• v.12 no.5
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• pp.480-491
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• 2010

Along with the wide acceptance of IEEE 802.11 wireless local area network (WLAN), new applications such as Internet protocol (IP) telephony over WLAN are fast emerging today. For battery-powered IP phone devices, the life time extension is a key concern for the market acceptance while today's 802.11 is not optimized for snch an operation. In this paper, we propose a novel idle mode operation, which comprises paging, idle handoff, and delayed handoff. Under the idle mode operation, a mobile host(MH) without any active session does not need to perform handoff within a predefined paging area (PA). Only when it enters a new PA, an idle handoff is performed. The proposed idle mode allows an MH without traffic to extend its life time. We develop a new analytical model in order to comparatively evaluate our proposed scheme. The numerical resnlts demonstrate that the proposed scheme outperforms the existing schemes with respect to power consumption.

• Journal of Electrical Engineering and Technology
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• v.4 no.2
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• pp.194-200
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• 2009

In this paper, the cooperative control scheme of micro sources and an ESS (Energy Storage System) during islanded operation is presented and evaluated by a simulation study. The ESS handles the frequency and voltage as a primary control. Then, the secondary regulation control returns the cur-rent power output of ESS into a pre-planned value. The simulation's results show that the proposed co-operative control scheme can regulate the frequency and voltage and reduce the consumption of the stored energy of ESS.

• ETRI Journal
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• v.22 no.1
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• pp.1-11
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• 2000

The Satellite Operation System (SOS) has been developed for a low earth orbiting remote sensing satellite, Korea Multipurpose Satellite-I, to monitor and control the spacecraft as well as to perform the mission operation. SOS was designed to operate on UNIX in the HP workstations. In the design of SOS, flexibility, reliability, expandability and interoperability were the main objectives. In order to achieve these objectives, a CASE tool, a database management system, consultative committee for space data systems recommendation, and a real-time distributed processing middle-ware have been integrated into the system. A database driven structure was adopted as the baseline architecture for a generic machine-independent, mission specific database. Also a logical address based inter-process communication scheme was introduced for a distributed allocation of the network resources. Specifically, a hotstandby redundancy scheme was highlighted in the design seeking for higher system reliability and uninterrupted service required in a real-time fashion during the satellite passes. Through various tests, SOS had been verified its functional, performance, and inter-face requirements. Design, implementation, and testing of the SOS for KOMPSAT-I is presented in this paper.

• Journal of the Korean Society for Precision Engineering
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• v.9 no.4
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• pp.36-43
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• 1992

This paper presents a hierarchical real-time operation control and monitoring scheme of the FMS/CIM center which has been implemented at the Automation and Systems Research Institute of Seoul National University. The hierarchical structure of the whole scheme consists of three lavers. The upper layer is in charge of on-line scheduling, computer network control, shop-floor monitoring and command generation for AGV dispatching, machining, assembly, inspection, set-up, etc. The middle layer has six modules, which are installed in the FMS host computer with the upper layer and run on the multi-tasking basis. Each module is connected to one of six cell controllers distributed in the FMS model plant and transfers operation command down to each cell controller through the Ethernet/TCP-IP local area network. The lower layer is comprised of six cell control software modules for machining cell, assembly cell, inspection cell, set-up stations. AS/RS and AGV. Each cell controller reports the status of the manufacturing facilites to the middle layer as well as ecxecuting the appropriate sequence control of the manufacturing processes.

• Journal of Power Electronics
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• v.7 no.2
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• pp.118-123
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• 2007

This paper presents a new ZCS-PWM high frequency inverter. Zero current switching operation is achieved in the whole load range by using a simple auxiliary reverse blocking switch in parallel with series resonant capacitor. Dual duty cycle control scheme is used to provide a wide range of high frequency AC output power regulation that is important in many high frequency inverter applications. It found that a complete soft switching operation can be achieved even for low power setting ranges by introducing high-frequency dual duty cycle control scheme. The proposed high frequency inverter is more suitable for consumer induction heating(IH) applications. The operation and control principle of the proposed high frequency inverter are described and verified through simulated results.

• ETRI Journal
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• v.37 no.2
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• pp.380-386
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• 2015

Guaranteeing quality of service over a multihop wireless network is difficult because end-to-end (ETE) delay is accumulated at each hop in a multihop flow. Recently, research has been conducted on network coding (NC) schemes as an alternative mechanism to significantly increase the utilization of valuable resources in multihop wireless networks. This paper proposes a new section-based joint NC and scheduling scheme that can reduce ETE delay and enhance resource efficiency in a multihop wireless network. Next, this paper derives the average ETE delay of the proposed scheme and simulates a TDMA network where the proposed scheme is deployed. Finally, this paper compares the performance of the proposed scheme with that of the conventional sequential scheduling scheme. From the performance analysis and simulation results, the proposed scheme gives more delay-and energy-efficient slot assignments even if the NC operation is applied, resulting in a use of fewer network resources and a reduction in ETE delay.

• Proceedings of the KSR Conference
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• 2006.11b
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• pp.1442-1447
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• 2006

Recently, According to rapid advancements in railway system and IT have enabled manless operation in urban transit system. Futhermore, development countries have been tried to develop unmaned operation system for reliability, safety, efficiency, and some ones already adopted. In this paper, we define system requirements and functionalities, and establish the system scenarios to handle the various accidents/faults in manless operation environment.