• Journal of Power Electronics
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• v.11 no.4
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• pp.561-567
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• 2011

This paper presents a high-efficiency power conditioning system (PCS) for grid-connected photovoltaic (PV) modules. The proposed PCS consists of a step-up DC-DC converter and a single-phase DC-AC inverter for the grid-connected PV modules. A soft-switching step-up DC-DC converter is proposed to generate a high DC-link voltage from the low PV module voltage with a high-efficiency. A DC-link voltage controller is presented for constant DC-link voltage regulation. A half-bridge inverter is used for the single-phase DC-AC inverter for grid connection. A grid current controller is suggested to supply PV electrical power to the power grid with a unity power factor. Experimental results are obtained from a 180 W grid-connected PV module system using the proposed PCS. The proposed PCS achieves a high power efficiency of 93.0 % with an unity power factor for a 60 Hz / 120 Vrms AC power grid.

• The Transactions of the Korean Institute of Power Electronics
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• v.22 no.4
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• pp.277-284
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• 2017

For passive power factor correction, the valley fill circuit approach is attractive for low power applications because of low cost, high efficiency, and simple circuit design. However, to vouch for the product quality, two dc-link capacitors in the valley fill circuit should be selected to withstand the peak rectified ac input voltage. The common mode (CM) and differential mode (DM) choke should be used to suppress the electromagnetic interference (EMI) noise, thereby resulting in large size volume product. This paper presents the practical design and implementation of a valley fill flyback converter with reduced dc link capacitors and EMI magnetic volumes. By using the proposed over voltage protection circuit, dc-link capacitors in the valley fill circuit can be selected to withstand half the peak rectified ac input voltage, and the proposed CM/DM choke can be successfully adopted. The proposed circuit effectiveness is shown by simulation and experimentally verified by a 78W prototype.

• 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 Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.5
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• pp.1240-1255
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• 1996

This paper suggests power optimization technique in multi-level SCPC system as a method for efficient utilization of limited satellite power. The power optimization is realized by optimal assignment of satellite input carrier powers considering interference and noise generated in up-link and down-link. The Fletcher-Powell algorithm searching minimum(or maximum) point using gradient information is used to detemine the optimal input carrier powers. To apply Flectcher-Powell algorithm mathematical descriptions and their partial derivatives to interference and nose are presented. Because a target, which should be optimized, is satellite input carrier power, amplitude of each carrier group will be assumed to be an independent variable. The performance criterion for optimal power assignmentis classified into 4 categories with respect to CNR of destination receiver earth station to meet the requirement for various satellite link environment. Simulation results for two-level, four-level and six-level SCPC system are presented.

• Journal of Power Electronics
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• v.7 no.2
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• pp.109-117
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• 2007

In this paper, a novel proposal for a utility-interactive three-phase soft commutation sinewave PWM power conditioner with an auxiliary active resonant DC-link snubber is developed for fuel cell and solar power generation systems. The prototype of this power conditioner consists of a PWM boost chopper cascaded three-phase power conditioner, a single two-switch auxiliary resonant DC-link snubber with two electrolytic capacitors incorporated into one leg of a three-phase V-connection inverter and a three-phase AC power source. The proposed cost-effective utility-interactive power conditioner implements a unique design and control system with a high-frequency soft switching sinewave PWM scheme for all system switches. The operating performance of the 10 kW experimental setup including waveform quality, EMI/RFI noises and actual efficiency characteristics of the proposed power conditioner are demonstrated on the basis of the measured data.

• IEMEK Journal of Embedded Systems and Applications
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• v.12 no.4
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• pp.193-204
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• 2017

Various 3D-stacked DRAMs have been proposed to overcome the memory wall problem. Hybrid Memory Cube (HMC) is a true 3D-stacked DRAM with stacked DRAM layers on top of a logic layer. The logic die is mainly used to implement a memory controller for HMC, and it is connected through a high speed serial link called SerDes with a host that is either a processor or another HMC. In HMC, the serial link is crucial for both performance and power consumption. Therefore, it is important that the link is configured properly so that the required performance should be satisfied while the power consumption is minimized. In this paper, we propose a HMC system model included the high speed serial link to estimate performance accurately. Since the link modeling strictly follows the link flow control mechanism defined in the HMC spec, the actual HMC performance can be estimated accurately with respect to each link configuration. Various simulations are conducted in order to deduce the correlation between the HMC performance and the link configuration with regard to memory utilization. It is confirmed that there is a strong correlation between the achievable maximum performance of HMC and the link configuration in terms of both bandwidth and latency. Therefore, it is possible to find the best link configuration when the required HMC performance is known in advance, and finding the best configuration will lead to significant power saving while the performance requirement is satisfied.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.8A
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• pp.868-878
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• 2004

In this paper, we analyse feasibility of Zone-based Power Control (ZPC) scheme introduced for CDMA forward link(1) in the reverse link. To operate ZPC scheme in the CDMA systems the maximum power level that can be allocated to each traffic channel should be determined. Because all the service channels share the whole power resource in the forward lint a specific mechanism that determines Maximum power resource to each traffic channel is required to operate ZPC scheme in the forward link. However, ZPC scheme can be easily adopted to the reverse link, because of the fact that the whole power resource of service terminal is only confined to its traffic channel. In other words, we need not to determine the maximum power resource to be allocated in the reverse traffic channel. Simulation results show that ZPC scheme adopted to the reverse link yields a significant performance improvement compared with the conventional TPC(IS-95 TPC) scheme in terms of the power consumption and the traffic capacity of Portables, especially with the increasing number of high-rate data traffics. With the proposed scheme, not only be extended the service coverage of high-rate data traffic to the entire cell service coverage, but also the QoS of low-rate traffic can keep going through the service time, especially, in the situation that the incoming interference is much larger.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.8
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• pp.607-614
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• 2013

In this work we investigate the power of power law in the VoD service over IP network. Especially, we show that the power of power law is strong in the location of the contents storage for the VoD service and its impact on the link dimensioning. This work first shows the instance of the power law in the popularity of the video contents from the real data for the IPTV service. After that we propose an analytic model that characterizes the behavior of customers in accessing the video servers as well as the power law in the viewing pattern. Finally, we show the impact of the power law by proposing a model for the cost as well as link dimensioning. Via numerical experiment we show the implication of the proposition.

• Proceedings of the KSRS Conference
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• 2005.10a
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• pp.98-100
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• 2005

This paper describes link analysis on the processed data, HRIT (High Rate Information Transmission) and LRIT (Low Rate Information Transmission), for the preliminary design of interface between COMS (Communication, Ocean and Meteorological Satellite) and ground station. At the MODAC (MeteorologicaVOcean Data Application Center), the processed data are transmitted to user station via COMS with normalization and calibration by pre-processing of MI (Meteorological Imager) data. Due to consider satellite as radio relay, overall analysis containing uplink and downlink is needed. Specific link parameters can be obtained with using the outcomes of SRR (System Requirement Review) which was held on 13-14 June 2005, in Toulouse. From the relation between overall link margin and output power of HPA (High Power Amplifier) of MODAC, it is shown that even though the minimum power related with COMS receiving power range is transmitted at MODAC, the obtained link margin of HRIT could be above 3 dB at user station which antenna elevation angle is 10 degree.

• The Transactions of the Korean Institute of Power Electronics
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• v.23 no.2
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• pp.94-100
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• 2018

Generally, in a single-phase energy storage system (ESS) for households, AC ripple component with twice the fundamental frequency exists inevitably in the DC link voltage of single-phase PCS. In the grid-connected mode of a single-phase inverter, the AC ripple component in the DC link voltage causes low-order harmonics on grid-side current that deteriorates power quality on an AC grid. In this work, a control system adopting a feedforward controller is established to eliminate the AC ripple interference on the DC link side. Optimal battery nominal voltage design method is also proposed by considering the voltage loss and AC ripple voltage on DC link side in a single-phase ESS. Finally, the control system and battery nominal voltage design method are verified through simulations and experiments.