• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.8B
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• pp.1426-1437
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• 1999

The introduction of fast packet switching networks such as the ATM leads to the possibility of video services with constant quality. However, the fixed traffic descriptor(TD), which is defined by ATM Forum and ITU-T, can not simultaneously satisfy network efficiency and video quality. This paper presents fast resource reallocation protocol (FRRP) which can provide an effective compromise between network efficiency and video quality. This protocol reallocates the network resources and then adapts the traffic to the reallocated resources. In the proposed method, a video session is divided into several time-intervals according to its generated traffic and TD is calculated which well characterizes the traffic during the specific subdivided interval. In addition, a system model, where MPEG coding algorithm and network control are unified, is proposal and the performance of the FRRP in terms of cell loss rate(CLR) is evaluated though the simulation using real video traffic(Star Wars). Simulation results show that the FRRP has only 5 ~35% CLR of the fixed TD.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.12B
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• pp.1081-1090
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• 2003

NGI(Next Generation Internet) is characterized by QoS(Quality of Service) and high speed transmission. Recently, DiffServ and MPLS become most influential NGI architecture. To guarantee end-to-end QoS, it is essential for NGI to interwork MPLS with DiffServ. Here, MPLS WG(Working Group) in IETF(Internet Engineering Task Force) proposed the method of E-LSP(EXP inferred-PSC LSPs) and L-LSP(Label-Only-Inferred PSC LSPs), but both of them have serious problems to satisfy perfect interworking. In this paper, we proposed an extended E-LSP architecture that supports Perfect DiffServ class and experimental function in MPLS such as ECN(Explicit Congestion Notification) capability. We verify that the proposed E-LSP architecture improves QoS in NGI by using ns2 simulator.

• Journal of Power Electronics
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• v.16 no.1
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• pp.297-309
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• 2016

Grid-connected inverters (GCIs) with an LCL output filter have the ability of attenuating high-frequency (HF) switching ripples. However, by using only grid-current control, the system is prone to resonances if it is not properly damped, and the current distortion is amplified significantly under highly distorted grid conditions. This paper proposes a synchronous reference frame equivalent proportional-integral (SRF-EPI) controller in the αβ stationary frame using the parallel virtual resistance-based active damping (PVR-AD) strategy for grid-interfaced distributed generation (DG) systems to suppress LCL resonance. Although both a proportional-resonant (PR) controller in the αβ stationary frame and a PI controller in the dq synchronous frame achieve zero steady-state error, the amplitude- and phase-frequency characteristics differ greatly from each other except for the reference tracking at the fundamental frequency. Therefore, an accurate SRF-EPI controller in the αβ stationary frame is established to achieve precise tracking accuracy. Moreover, the robustness, the harmonic rejection capability, and the influence of the control delay are investigated by the Nyquist stability criterion when the PVR-based AD method is adopted. Furthermore, grid voltage feed-forward and multiple PR controllers are integrated into the current loop to mitigate the current distortion introduced by the grid background distortion. In addition, the parameters design guidelines are presented to show the effectiveness of the proposed strategy. Finally, simulation and experimental results are provided to validate the feasibility of the proposed control approach.

• The Transactions of the Korean Institute of Power Electronics
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• v.14 no.1
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• pp.72-81
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• 2009

This paper presents quasi-resonant type high power factor ac power supply for atmospheric pressure plasma cleaning system adopting three phase PFC boost converter and it's control method. The presented ac power supply consists of single phase H-bridge inverter, step-up transformer for generating high voltage and three phase PFC boost converter for high power factor on source utility. Unlikely to the traditional LC resonant converter, the propose one has an inductor inside only. A single resonant takes place through the inside inductor and the capacitor from the plasma load modeled into two series capacitor and one resistance. The quasi-resonant can be achieved by cutting the switching signal when the load current decrease to zero. To obtain power control ability, the propose converter controlled by two control schemes. One is the changing output pulse period scheme in the manner of PFM(Pulse Frequency Modulation) control. On the other, to provide more higher power to load, the DC rail voltage is directly controlled by the 3-phase PFC boost converter. The significant merits of the proposed converter are the uniform power providing capability for high quality plasma generation and low reactive power in AC and DC side. The proposed work is verified through digital simulation and experimental implementation.

• The Transactions of the Korean Institute of Power Electronics
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• v.14 no.1
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• pp.23-30
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• 2009

A new high performance and low cost unified power system is proposed through investigating conventional Power-Integrated Drive(PID) system and Power-Separated Drive(PSD) system applied to LCD TV. Since the proposed system consists of two stage, namely power and inverter stage it features high efficiency and cost effectiveness. To satisfy the safety standard of the High voltage transformer, 1:1 transformer is employed between inverter and high voltage transformer. Moreover, to ensure the Zero Voltage Switching(ZVS) of all power switches and the Pulse Count Modulation(PCM) method is employed, which controls the number of pulse at the fixed frequency and fixed duty cycle. Therefore, it features high efficiency, improved heat generation, cost effectiveness and good EMI performance including no additional current balancing coil. To confirm the validity of proposed system, comparison of conventional system, verification of experimental results are presented.

• Proceedings of the KIEE Conference
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• 2004.11a
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• pp.212-214
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• 2004

In this study, we fabricated the organic thin film by self-assembly method by using nitro-group and methoxy-group organic molecule. Also, we selected the organic single molecule in organic thin film and measured current-voltage characteristics by using scanning tunneling microscopy. The Organic molecules that use in an experiment is 4,4'-(diethynylphenyl)-2'-nitro-1-benzen ethiol and 4-[2,5-dimethoxy-4-ph enylethynylphenyl]ethynylphenylethanthiol. 4,4'-(dimet hynylphenyl)-2'-nitro-1-benzenethiol is applied widely in molecular electronic device and 4-[2,5-dime thoxy-4-phenylethynylphenyl]ethynylphenylethanthiol composed in Korea Research Institute of Chemical Technology. To be confirmed the formation of the self-assembled monolayers, we observed the real time frequency shift of the QCM and investigated surface of the self-assembled monolayers the using STM. With this, we measured current to the organic single molecule, in condition of the air state. As a result, we confirmed in constant voltage that properties of negative differential resistance. Using properties of negative differential resistance to get from this study, application is expected to be molecular switching device, memory device and logic device.

• Clinics in Shoulder and Elbow
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• v.12 no.2
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• pp.221-225
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• 2009

Purpose: For an isolated tear of the subscapularis tendon, the presented technique using a subclavian portal provides both a good angle for anchor placement and sufficient space for managing the upper portion of a subscapularis tendon tear. Materials and Methods: The conventional method needs 2 additional portals for traction, debriding the footprint and anchor fixation for repair. The presented technique requires only an anterior portal for suture management and a subclavian portal without cannula for suture anchoring and placement of suture hooks. Results: The two suture limbs of the anchor can be placed on the subscapularis tendon by the switching technique and these limbs are repaired sequentially. Conclusion: This technique is simple and reproducible and it can be applied to partial tears and minimally retracted subscapularis tears.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.38-39
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• 2007

Recently, utility network is becoming more and more complicated and huge due to IT(Information Technology) and OA(Office Automation) devices. In addition to, demands of power conversion devices which have non-linear switching devices are getting more and more increased. Voltage sag from sudden increasing loads is also one of the major problems inside of the utility network. In order to compensate the voltage sag problem, power compensation devices systems could be a good solution method. In case of voltage sag, it needs an energy source to overcome the energy caused by voltage sag. Superconducting Magnet Energy Storage (SMES) is a very good promising source due to the high response time of charge and discharge. This paper presents a real-time simulation algorithm for the SMES by using Real Time Digital Simulator (RTDS). With this algorithm users can easily do the simulation of utility power network applied by SMES system with the SMES coil modeled in RTDS.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.2
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• pp.1020-1026
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• 2014

A problem of sliding mode control is chattering because of controle input signal included unknown disturbance and nonlinear input parameters. This paper presents a sliding mode controller design to inverted pendulum system. In this paper, a sliding mode control algorithm to reduce a chattering is proposed. The reduction of chattering is accomplished by smoothing function for nonlinear control input. In this method, the dynamic equations of the inverted pendulum is decoupled by considering nonlinear parameters and external disturbances. Therefore, this study is applied to obtain switching control inputs for sliding mode controller. The proposed technique is tested to the control of inverted pendulum through computer simulations. The result shown reduced chattering in control input.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.11
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• pp.1543-1550
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• 2015

Ferroresonance is a non-linear vibrational phenomenon that is generated by the electrical interaction of the inductance component with the capacitor component of a certain capacitance as the device of the inductance component such as a transformer is saturated due to the degradation, the waveform distortion of current and voltage, and the oscillation of overcurrent and overvoltage in a system. Recently, ferroresonance was generated from the waveform distortion of current and voltage, or the overvoltage or undervoltage phenomenon caused by the nature of an electrical power system and design technology of the transformer in the three phase transformer system. Hence, in general, ferroresonance analyzed by converting to the LC equivalent circuit. However, in general, the aforementioned analytical method only applies to the resonance phenomenon that is generated by the interaction of the capacitance of bussbar and grounding, and switching as the capacitor component with PT and the transformer as the inductance component in a system. Subsequently, the condition where ferroresonance was generated since overvoltage was supplied as line voltage to the phase voltage and thus the iron core is saturated due to the interconnection between grounded and ungrounded systems could not be analyzed when single phase PT was connected in a ${\Delta}$/Y connection system. In this study, voltage swell in the configuration of grounded circuit of a step-up transformer with the ${\Delta}-{\Delta}$ connection linked to PT for control power and the ferroresonance generated by overvoltage when the line voltage of the ${\Delta}-{\Delta}$ connection was connected to the phase voltage of the grounded Y-Y connection were analyzed using PSCAD / EMTDC through the failure case of the transformer caused by ferroresonance in the system with the ${\Delta}-{\Delta}$/Y-Y connection, and subsequently, the preventive measure of ferroresonance was proposed.