• Proceedings of the IEEK Conference
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• 2004.06a
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• pp.249-252
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• 2004

Recently, wireless repeater with interference rejection has been considered for the next generation repeater. In this paper, adaptive interference rejection module suppressing interference in the 3G band is proposed. A novel adaptive rejection scheme is proposed and it is partially implemented by FPGA devices.

• Proceedings of the KIPE Conference
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• 2016.07a
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• pp.491-492
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• 2016

This paper presents a robust feedback control design to mitigate the effect of grid voltage disturbances for three-phase grid-connected inverters in distributed generation systems. The proposed strategy consists of two major design steps. First, the controller is synthesized using the internal model principle to achieve a good reference tracking and disturbance rejection performance. Then, the feedback gain is systematically obtained by solving the linear matrix inequality conditions which are directly derived from the stability criteria. The main contribution of this paper is that the complexity of control structure can be substantially reduced and transient response is improved as compared with the existing robust control design methods. The simulation results are given to prove the validity of the proposed control scheme.

• Journal of Electrical Engineering and Technology
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• v.13 no.1
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• pp.105-113
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• 2018

This paper proposes pre-analysis on planning of high-voltage direct current (HVDC) transmission system applied to Korea electric power grid. HVDC transmission system for interface lines has been considered as alternative solution for high-voltage AC transmission line in South Korea since constructing new high-voltage AC transmission lines is challenging due to political, environmental and social acceptance problems. However, the installation of HVDC transmission system as interface line in AC grid must be examined carefully. Thus, this paper suggests three scenarios to examine the influences of the installation of HVDC transmission system in AC grid. The power flow and contingency analyses are carried out for the proposed scenarios. Power reserves in metro area are also evaluated. And then the transient stability analysis focusing on special protection scheme (SPS) operations is analyzed when critical lines, which are HVDC lines or high voltage AC lines, are tripped. The latest generic model of HVDC system is considered for evaluating the impacts of the SPS operations for introducing HVDC system in the AC grid. The analyses of proposed scenarios are evaluated by electromechanical simulation.

• Journal of Communications and Networks
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• v.9 no.4
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• pp.368-376
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• 2007

The large potential bandwidth available in wavelength-division multiplexed optical networks makes this technology of crucial importance for satisfying the ever increasing capacity requirements of the next-generation Internet. In this scenario, the routing and wavelength assignment(RWA) problem that concerns determining the optical paths and wavelengths to be used for connection establishment in a wavelength-routed network, is still one of the most important open issues. In this paper we propose a new online dynamic grooming-capable RWA heuristic scheme working on wavelength division multiplexing(WDM) networks as a multistage selection process. The proposed algorithm is transparent with respect to the presence of wavelength converters, achieves very low connection rejection ratios with minimal computational complexity and is appropriate for the modern multilayer optical circuit and wavelength switched networks with sparse wavelength conversion capability.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37C no.11
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• pp.1138-1147
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• 2012

In this paper, an efficient power control based MF-TDMA resource allocation scheme is proposed for next generation military satellite communication systems. The proposed scheme has the flexibility is used to support heterogeneous terminals with differ in transmission capabilities. The method can be divided into two parts : burst size calculation and burst structure determination. At first, we estimate the link budget taken into account a dynamic satellite link state variation. Then, applicable ACM level and burst size is chosen. In burst structure determination phase, we reorganize the burst structure in time-frequency domain by controlling limited power, bandwidth, time resources. In particular, we compensate the power spectral density among different terminals to integrate them in same transponder, Furthermore, we increase the packing efficiency by controlling the ACM level of the burst in applicable power spectral density range. Simulation results show that the method increase the spectral efficiency and burst packing efficiency. In addition, slot allocation rejection ratio is successfully reduced.

• 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.