• ETRI Journal
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• v.41 no.5
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• pp.648-657
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• 2019

A cluster topology was proposed with the assumption of zero noise to improve the performance of wireless body area networks (WBANs). However, in WBANs, the transmission power should be reduced as low as possible to avoid the effect of electromagnetic waves on the human body and to extend the lifetime of a battery. Therefore, in this work, we consider a bit error rate for a cluster-based WBAN and analyze the performance of the system while the transmission of sensors and cluster headers (CHs) is controlled. Moreover, a hierarchical topology is proposed for the cluster-based WBAN to further improve the throughput of the system; this proposed system is called as the hierarchical cluster WBAN. The hierarchical cluster WBAN is combined with a transmission control scheme, that is, complete control, spatial reuse superframe, to increase the throughput. The proposed system is analyzed and evaluated based on several factors of the system model, such as signal-to-noise ratio, number of clusters, and number of sensors. The calculation result indicates that the proposed hierarchical cluster WBAN outperforms the cluster-based WBAN in all analyzed scenarios.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.6
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• pp.105-113
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• 2013

In this paper a micro solar energy harvesting system with MPPT(Maximum Power Point Tracking) control using a miniature PV(photovoltaic) cell of which the output is less than 0.5V is proposed. The MPPT control is implemented using linear relationship between the open-circuit voltage of a PV cell and its MPP(Maximum Power Point) voltage such that a pilot PV cell can track the MPP of the main PV cell in real time. The proposed circuit is designed in 0.18um CMOS process. The designed chip area is $900um{\times}1370um$ including a load charge pump and pads. Measured results show that the designed system can track the MPP voltage changes with variations of light intensity. The designed circuit with MPPT control delivers MPP voltages to load even though the load is heavy such that it can supply more power when the MPPT control is applied. The proposed circuit does not require any precharged battery resulting in more suitability for miniaturized self-powered systems compared to the existing works.

• Journal of Internet of Things and Convergence
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• v.6 no.2
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• pp.11-18
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• 2020

Since the end devices of the Internet of Things (IoT) are battery operated products, careful consideration for ultra-low power (ULP) is required. The Micro Controller Unit (MCU) industry has developed very effective functions to save energy, but developers have difficulty in selecting the MCU because various operating modes are applied to reduce energy consumption by manufacturers. Therefore, this paper introduces ULPMark benchmark, a standardized benchmark method that can compare MCUs of various vendors and feature sets, and provides hardware functions for ultra-low-power operation of the two platforms that received the high evaluation scores from ULPMark. In addition, we investigated and analyzed how developers can utilize the functions for ultra low power consumption through driver APIs and detailed register control.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.25 no.11
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• pp.1596-1602
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• 2021

Battery-operated IoT devices in IoT systems require low power consumption. In general, IoT devices enter a sleep state synchronously to reduce power consumption. A problem arises when an IoT device has to handle asynchronous user requests, as the duty cycle must be reduced to enhance response time. In this paper, we propose a new low-power-consumption scheme, called Repetitive Wake-up scheme for IoT systems of asynchronous environments such as indoor lights control. The proposed scheme can reduce power consumption by sending wake-up signals from the smartphone repetitively and by retaining the IoT device in sleep state to the smallest possible duty cycle. In the various environments with IoT devices at home or office space, we showed that the proposed scheme can reduce power consumption by up to five times compared to the existing synchronous interlocking technique.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.16 no.2
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• pp.81-89
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• 2002

The Battery Energy Storage System (BESS) has lots of advantages such as load leveling, quick response emergency power (spinning reserve), frequency and voltage control, improvement of reliability, and deferred generation and transmission construction. However, it is very critical that economic feasibility requires justification from the customer side of meter to promoting the dissemination of BESS in nation widely. In this paper, we proposed the economic assessment model of customer owned BESS which is complemented and improved the existing model. The proposed model is applied to the typical customer types, i.e. light industrial, commercial, and residential, which are taken from the statistical analysis on the load profile survey of Korea Electric Power COmpany (KEPCO). The economic viability performed for each customer load type to justifying their economic feasibility of BESS installation from the economic measures such as payback period, Net Present Worth (NPW), Rate Of Return (ROR). The results show that the BESS has economic benefits to the specific customer type, i.e. residential customer. Therefore, the government and the energy agency should be committing the support program, such as tax incentive, financial support, to disseminate the BESS nation widely. The results of this paper are useful to the customer investment decision-making and the national energy policy & strategy in Korea.

• Proceedings of the KIPE Conference
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• 2016.07a
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• pp.459-460
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• 2016

본 논문은 분산전원과 베터리에너지저장장치로 구성된 독립형 DC 마이크로그리드에서 배터리 에너지저장장치의 SoC변동에 따른 새로운 출력 전압 제어 방식을 제안하고 동작과 성능을 분석한 내용에 대하여 기술하고 있다. 제안하는 제어 방식은 SoC를 검출하여 일정한 게인 값을 곱하고 그 결과를 기저전압에 더해 DC Grid전압을 산출하는 방식이다. 제안하는 시스템의 동작타당성을 체계적으로 비교 분석하기 위해 PSCAD/EMTDC 소프트웨어를 이용하여 검증하였다. 이를 기반으로 하드웨어 시뮬레이터를 제작하고 실험을 실시하여 실제 독립형 DC 마이크로그리드에 적용 가능성을 확인하였다.

• Proceedings of the KIPE Conference
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• 2011.11a
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• pp.307-308
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• 2011

본 논문에서는 2차전지의 필수적인 충 방전 데이터의 수집 및 분석을 쉽게 할 수 있는 배터리 충 방전 데이터 수집 장치를 개발하였다. 개발된 장치는 데이터 샘플링 시간 설정(0.1~10초)과 충 방전 사이클 중 대기시간 설정이 가능하도록 설계하였다. 또한 충 방전 사이클 횟수를 배터리의 활성화와 전압 평균화를 위하여 최대 10회까지의 수행할 수 있도록 개발하였다. 개발된 장치의 성능을 검증하기 위해 LabVIEW로 측정된 데이터와 비교 분석하여 타당성을 검증하였다.

• Proceedings of the KIPE Conference
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• 2011.11a
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• pp.311-312
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• 2011

본 논문에서는 납축전지의 충전 초기 전압변화를 이용한 축전지의 상태와 충전상태를 비교 평가하는 방법을 연구하였다. 12V/1.2Ah의 납축전지를 대상으로 NI사의 DAQ 장치로 충방전 실험 장치를 구축하고 LabVIEW로 프로그램을 작성하여 축전지의 전압과 전류를 측정하였다. 축전지가 노화된 경우 충전 초기 전압이 급격히 상승하였고, 충전 전류는 정상적인 축전지에 비해 상대적으로 적게 나타났다. 실험 결과를 바탕으로 축전지의 충전상태를 평가하였다.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.52 no.6
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• pp.291-297
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• 2003

This paper presents a current-source-inverter based on a buck-boost configuration and its application for residential photovoltaic system. The proposed circuit has five switches. Among them, only one switch acts as chopping, and the other determine the polarity of output; therefore, it can reduce the switching loss. Because the input inductor current is operated on the discontinuous conduction mode, high power factor can be achieved without additional input current controller. So the overall system shows a simple structure. The operational modes are analysed in depth, and then it was verified through the experimental results using a 150 [W] prototype equipped with digital signal processor TMS320F241.

• Proceedings of the KIPE Conference
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• 2007.11a
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• pp.21-23
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• 2007

In this paper a high efficiency bi-directional DC-DC converter for hybrid vehicles is proposed. The proposed converter a three-phase half-bridge interleaved ZVS converter, is designed to have high efficiency in the main operation range. The component ratings are calculated, the actual devices are selected, and the efficiency analysis has been performed to determine optimal ZVS range. The input and output current ripples are significantly reduced due to the interleaved operation. The dual loop control for the interleaved three-phase converter is also presented. To confirm the proposed convert ter, The simulation and experimental results are presented.