• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.1
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• pp.142-147
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• 2018

Private electrical facilities are judged whether it is suitable for the insulation aging condition of their incoming underground cables using DC leakage current test method. In the case where the service point of utility is the secondary side of cut out switch installed in the electric pole, there is a problem that it is difficult to separate the lightning arresters(LA) because of their high position of the pole. Therefore, the field test voltage is applied at value lower than DC 30 kV, which are stated in the inspection guideline. However, this test could reduced the insulation performance of the LA by accelerating the electrical stress of the metal oxide varistor element in the pre-breakdown region. In this study, we analyzed the relationship between the DC test voltage and the leakage current using the non-destructive DC high voltage equipment with leakage current measurement function. The results show that the leakage current increases sharply above the specified test voltage. As a consequence, it could be contributed to improve insulation aging inspection method by selecting the possible test area on the VI characteristic curve of the pre-breakdown area of the LA.

• Journal of Institute of Control, Robotics and Systems
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• v.15 no.10
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• pp.1029-1038
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• 2009

This paper proposes a gain switching algorithm for joint position control of a hydraulic humanoid robot. Accurate position control of the lower body is one of the basic requirements for robust balance and walking control. Joint position control is more difficult for hydraulic robots than it is for electric robots because of an absence of reduction gear and better back-drivability of hydraulic joints. Backdrivability causes external forces and torques to have a large effect on the position of the joints. External ground reaction forces therefore prevent a simple proportional-derivative (PD) controller from realizing accurate and fast joint position control. We propose a state feedback controller for joint position control of the lower body, define three modes of state feedback gains, and switch the gains according to the Zero Moment Point (ZMP) and linear interpolation. Dynamic equations of hydraulic actuators were experimentally derived and applied to a robot simulator. Finally, the performance of the algorithm is evaluated with dynamic simulations.

• JSTS:Journal of Semiconductor Technology and Science
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• v.16 no.5
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• pp.595-604
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• 2016

Utilizing a standard 130-nm CMOS process, a RF frontend is designed at 24 GHz for automotive collision avoidance radar application. Single IF direct conversion receiver (DCR) architecture is adopted to achieve high integration level and to alleviate the DCR problem. The proposed frontend is composed of a two-stage LNA and downconversion mixers. To save power consumption, and to enhance gain and linearity, stacked NMOS-PMOS $g_m$-boosting technique is employed in the design of LNA as the first stage. The switch transistors in the mixing stage are biased in subthreshold region to achieve low power consumption. The single balanced mixer is designed in PMOS transistors and is also realized based on the well-known folded architecture to increase voltage headroom. This frontend circuit features enhancement in gain, linearity, and power dissipation. The proposed circuit showed a maximum conversion gain of 19.6 dB and noise figure of 3 dB at the operation frequency. It also showed input and output return losses of less than -10 dB within bandwidth. Furthermore, the port-to-port isolation illustrated excellent characteristic between two ports. This frontend showed the third-order input intercept point (IIP3) of 3 dBm for the whole circuit with power dissipation of 6.5 mW from a 1.5 V supply.

• The Transactions of the Korean Institute of Power Electronics
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• v.17 no.6
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• pp.471-477
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• 2012

In this paper, in order to use module integrated converter using cascaded buck-boost converter for a low battery charger in stand-alone system, a charging algorithm which considers photovoltaic and battery status and PWM controllers which are changed according to charging modes are proposed. The proposed algorithm consists of constant current mode, constant voltage mode and maximum power point tracking mode which enables the battery to charge with maximum power rate. This paper also presents design of cascaded buck-boost converter that is the photovoltaic charger system. A 150W prototype system is built according to verify proposed the charger system and the algorithm.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.48 no.10
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• pp.1190-1197
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• 1999

The management of power factor(PF) in the distribution line is treated according to the measurement a month about the feeder unit at the substation. In Korea, we have not researched into power factor in distribution system due to it's less weight. The reactive power in advanced countries is controlled automatically by the compensative condenser switch on/off under the monitoring. This paper first presents the optimal condenser position and proper capacity by lagrangue factor ${\lambda}_{Q}$ which is the line loss index about reactive power unit. Therefore, the largest ${\lambda}_{Q}$ node is the condenser injection point and we find out the best condenser capacity when the line loss is saturated by the moderation of condenser volume. By this method, we suggest 0.6% uprising PF by injection of 15 kVA condenser. Additionally, PF is analysed into 5 areas; large city, middle city, small city, farm village, fishing village by the use of Power Platform which is classified the same concept of the low load management in KEPCO. Two feeders of each area are selected by the worst results of PF in specified areas.

• 한국태양에너지학회:학술대회논문집
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• 2012.03a
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• pp.427-432
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• 2012

This paper proposes efficient operation method of PV system consisted of multi-central which is suitable for large scale system. The multi-central system used switch at a DC-link and applied proposed algorithm can improve the efficiency and the reliability on the existing system. This algorithm, with advantage of Multi-Central system can minimize the effect of different characteristic of each PV array due to a shadow or damaged PV cell. Each system is analysed and maximum power point tracking control, DC-link voltage control and output current control is used commonly. The validity is verified after comparing of the existing system and proposed system by simulation.

• Journal of the Korean Solar Energy Society
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• v.29 no.6
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• pp.1-13
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• 2009

Photovoltaic conditioning systems normally use a maximum power point tracking (MPPT) technique to deliver the highest possible power to the load continuously when variations occur in the insolation and temperature. A unique method of tracking the maximum power points (MPPs) and forcing the boost converter system to operate close to these points is presented through deriving small-signal model and transfer function of boost converter considering input capacitor. This paper aims at modeling boost converter including fairly large equivalent series resistance(ESR) of input reservoir capacitor by state-space-averaging method and PWM switch model and compares both methods using Bode plots. In the future, properly designed controller for compensation will be constructed in 3kw real system for maximum photovoltaic power tracking control.

• Journal of Navigation and Port Research
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• v.31 no.10
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• pp.839-844
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• 2007

This paper describes the performance of DC-DC converters for buoy such as buck, boost, and buck-boost. The operating characteristic and charging efficiency with battery, which has a considerable properties about converters with PV(photovoltaic) system, is analyzed in this paper. It is performed by using the MPPT(Maximum Power Point Tracker) algorithm The basic equations of switching operation for converter are described, and the equations are analyzed with according to switch state. Whereas this analysis is directed toward the selection of converter for buoy, it also provides the insight into the behaviour of converter and performance of the proposed algorithm Finally, the suitable DC-DC converter is proposed for buoy, and the characteristic experiment is performed with the buck converter.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2006.05a
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• pp.391-394
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• 2006

This paper presents soft switching zero voltage switching high frequency inverter for rare gas fluorescent lamp using dielectric-barrier discharge phenomenon. The simple high-frequency inverter can completely achieve stable zero voltage soft switching (ZVS) commutation for wide its output power regulation ranges and load variations under its constant high frequency pulse density modulation (PDM) scheme. Its transient and steady state operating principle is originally described and discussed for a constant high-frequency PDM control strategy under a stable ZVS operation commutation, together with its output effective power regulation characteristics-based on the high frequency PDM strategy. The experimental operating performances of this high frequency Inverter are illustrated as compared with computer simulation results and experimental ones. Its light dimming characteristics due to power regulation scheme are evaluated and discussed on the basis of simulation and experimental results. The feasible effectiveness of this high frequency inverter appliance implemented here is proven from the practical point of view.

• Proceedings of the Korean Information Science Society Conference
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• 2003.04d
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• pp.515-517
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• 2003

In this paper we examine the effects of the required portions of guard timing spaces in a MAC frame of ETSI BRAN HIPERLAN/2 system such as inter-mobile guard timing space in UL(Up Link) duration, inter-RCH(Random CHannel) guard timing space, sector switch guard timing space. In particular, we calculate the number of OFDM(Orthogonal Frequency Division Multiplexing) symbols required for these guard timing spaces in a MAC frame. We them evaluate the throughput of HIPERLAN/2 system as we vary parameter such as the guard time values defined in [2], the number of DLCCs(Data Link Control Connections), and the number of RCHs. Finally we show by numerical results that the portions for the 새심 summation of required guard timing spaces in a MAC frame are not negligible, and that they should be properly considered when trying to evaluate the performance of MAC protocol of HIPERLAN/2 system and also when determining the number of RCHs as well as the number of DLCCs in UL PDU trains at an AP/CC(Access Point/Central Controller).