• Journal of the Korea Institute of Information Security & Cryptology
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• v.25 no.6
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• pp.1515-1523
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• 2015

It has been prevalent to be serviced through WLAN(Wireless Local Area Network) as a variety of mobile devices have been introduced. If the number of mobile devices increases rapidly for the network access in a limited range of ESS(Extended Service Set), a lengthy connection delays are induced due to the initial link setup process of the IEEE 802.11i which is WLAN security standard. In this paper, we propose a new initial link setup protocol which can be executed in the ESS area of WLAN.

• Proceedings of the Korean Reliability Society Conference
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• 2001.06a
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• pp.455-462
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• 2001

We propose a new method to evaluate the network reliability which greatly reduces the intermediate steps toward calculations of maximum capacity flow by excluding unnecessary simple paths contained in the set of failure simple paths. By using signed simple paths and signed flow, we show that our method is more efficient than that of Lee and Park (2001a) in the number of generated composite paths and in the procedure for obtaining minimal success composite paths. Numerical examples are given to illustrate the use and the efficiency of the method.

• Journal of the Korean Operations Research and Management Science Society
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• v.30 no.2
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• pp.1-11
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• 2005

The network structures of a hyperlinked environment can be a rich source of information about the contents of the environment and it provides effective means for understanding it. Recently, there have been a number of algorithms proposed analyzing hypertext link structure so as to determine the best authorities for a given topic or query. In this paper, we review the algorithm of mutual reinforcement relationship for finding hubs and authorities from World Wide Web, and suggest SHA, a new approach for link-structure analysis, which uses the relationships among a set of relative authoritative pages, a set of hub pages, and a set of super hub pages.

• Journal of Electrical Engineering and Technology
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• v.10 no.2
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• pp.529-538
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• 2015

Due to the high efficiency and compact mechanical structure, direct drive variable speed generators are used for power conversion in wind turbines. The wind energy conversion system (WECS) considered in this paper consists of a permanent magnet synchronous generator (PMSG), uncontrolled rectifier, dc-dc boost converter controlled with maximum power point tracking (MPPT) and adaptive hysteresis controlled voltage source inverter (VSI). For high utilization of the converter's power capability and stabilizing voltage and power flow, constant DC-link voltage is essential. Step and search MPPT algorithm which senses the rectified voltage ($V_{DC}$) alone and controls the same is used to effectively maximize the output power. The adaptive hysteresis band current control is characterized by fast dynamic response and constant switching frequency. With MPPT and adaptive hysteresis band current control in VSI, the DC link voltage is maintained constant under variable wind speeds and transient grid currents respectively.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.1
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• pp.81-87
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• 2007

This paper proposes a new capacitance estimation scheme for a DC-link capacitor in a three-phase AC/DC/AC PWM converter. A controlled AC voltage with a lower frequency than the line frequency is injected into the DC-link voltage, which then causes AC power ripples at the DC side. By extracting the AC voltage and power components on the DC output side using digital filters, the capacitance can then be calculated using the Support Vector Regression (SVR). By training of SVR, a function which relates a given input (capacitor's power) and its corresponding output (capacitance value) can be derived. This function is used to predict outputs for given inputs that are not included in the training set. The proposed method does not require the information of DC-link current and can be simply implemented with only software and no additional hardware. Experimental results confirm that the estimation error is less than 0.16%.

• Proceedings of the KIEE Conference
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• 2001.07b
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• pp.974-976
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• 2001

This paper presents a method to reduce commutation torque ripples occurred during commutation in brushless do motor drives using a single DC-link current sensor. In brushless dc motor drives with a single dc current sensor instead of 3-phase line current sensors, it is noted that dc-link current sensor cannot give any information corresponding to the motor currents during line current commutation intervals. A new technique to resolve such a problem is dealt with based on a deadbeat current control in which motor armature voltage command is computed from a dc-link current reference, an actual current and counter emf voltage. The simulation results show that the proposed method reduces the torque ripple significantly.

• Journal of information and communication convergence engineering
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• v.7 no.2
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• pp.185-192
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• 2009

In wireless mesh networks multi-rate technology environment, a mesh node can dynamically modify the data transmission rate on a particular link, in response to link distance, or more accurately, the perceived SNR ratio between neighbor nodes. In such networks, existing route selection schemes use a link quality metric. Thus, these schemes may easily result in the network being overloaded. In this paper, a new route metric is proposed; it considers both per-hop service delay and link quality at mesh nodes. In addition, the Load-Aware AODV (LA-AODV) protocol using the proposed metric is presented. The performance evaluation is performed by simulation using the OPNET simulator. It is demonstrated that the LA-AODV protocol outperforms the existing routing protocols using other existing route metrics in multi-rate WMN environment.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.795-800
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• 2000

In a parallel manipulator, there are three constraints that determine workspace: link length constraint, passive joint angle constraint, and interference among links. Generally, the link length constraint is the most dominant. The interference among links is, however, also an important parameter in designing a desired parallel manipulator. In this study, the interference among links is mathematically modeled by considering the links as a line and a cylinder of radius of twice the link radius, and a new algorithm is suggested to check if arbitrary two links interfere each other or not. The workspace of a cubic parallel manipulator is illustrated in a 2D space satisfying the three constraints.

• Proceedings of the KIPE Conference
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• 1998.10a
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• pp.524-528
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• 1998

The voltage-source inverters are normally equipped with an electrolytic capacitor in their DC link, however, the electrolytic capacitor has several disadvantages such as increasing size, limiting converter life and reliability. Therefore, several approaches for removing the DC link capacitor have been studied by the authors. This paper proposes a new voltage-source inverter without DC link components. To reduce waveform distortion of the AC source current, the current-controlled PWM-rectifier with di/dt feedback is introduced. The di/dt feedback gain and LC parameters are investigated by calculation for a 0.75kW induction motor driven by this inverter. The calculated AC source currents maintain nearly sinusoidal waveforms with a unity power factor.

• The Transactions of the Korean Institute of Power Electronics
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• v.5 no.2
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• pp.170-175
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• 2000

A new quasi-parallel resonant DC link inverter is proposed for three phase soft switching application. By i inserting only one additional switch, the proposed inverter excludes both voltage stresses and restricted PWM p problems, which are demerits of the conventional resonant inverter. In this paper, the circuit operations are e explained in detail using the operational mode analysis of the proposed inverter and design methods of the r resonant components are suggest('x:l. Lastly, the applicable possibility of the proposed inverter is vel예fied t through the experimental results.