• Journal of the Korean Solar Energy Society
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• v.32 no.5
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• pp.1-10
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• 2012

This paper proposes a modeling and controller design approach for a wind-diesel hybrid system including dump load. Wind turbine depends on nature such as wind speed. It causes power fluctuations of wind turbine. Excessive power fluctuation at stand-alone power grid is even worse than large-scale power grid. The proposed control scheme for power quality is fuzzy PI controller. This controller has advantages of PI and fuzzy controller. The proposed model is carried out by using Matlab/Simulink simulation program. In the simulation study, the proposed controller is compared with a conventional PI controller. Simulation results show that the proposed controller is more effective against disturbances caused by wind speed and load variation than the PI controller, and thus it contributes to a better quality wind-diesel hybrid power system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37A no.12
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• pp.1133-1139
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• 2012

In this paper, hybrid mode beamforming (HMB) which allows simultaneous transmission of joint beamforming and disjoint beamforming is proposed. HMB is proven to be asymptotically optimal beamforming for sum rate growth. Extensive simulations show that HMB achieves nearly the same performance as joint encoding (JE) in symmetric interference channel. It is also shown that it outperforms JE in a more realistic asymmetric interference channel environment, though it still experiences some performance degradation due to power inefficiency of joint beamforming in asymmetric channel.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2009.10a
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• pp.37-41
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• 2009

In this paper, we propose to research the possibility of using a photovoltaic system and supercapacitor combined with a high speed microturbine. This hybrid energy system work as atand-alone mode or grid-connected mode as it will be a part of building micro-grid. Simple dynamic models of photovoltaic, microturbine systems and supercapacitor banks are proposed. their models are developed by Matlab/Simulink tool. Two important results are carried out to find power control effectiveness in case of with supercapacitor bank and without one. At least, simulation results show the effectiveness on the power control at AC busbar of hybrid energy system as building micro-grid system.

• Proceedings of the Korean Society of Computer Information Conference
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• 2016.01a
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• pp.253-255
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• 2016

본 논문에서는 H.264의 화면 내 예측 모드를 적용한 변형된 선택 보간법을 채택함으로써 고화질 DMB 시청시 사용자의 모바일 데이터 사용량과 전력사용량을 줄이는 것을 목적으로 하는 시스템을 제안한다. 스마트 DMB는 T-DMB망으로 전송되는 QVGA급 영상(기본영상)에 모바일 데이터망을 통해 전송되는 추가정보를 더하여 화질을 개선하는 방식이다. 제안 방법은 원본 고화질 영상과 T-DMB망으로 전송되는 기본영상의 오차를 효과적으로 줄이면 사용자 시스템의 부하와 데이터 사용량을 줄이면서 화질을 유지할 수 있다.

• The Transactions of the Korean Institute of Power Electronics
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• v.5 no.4
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• pp.352-357
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• 2000

The vector control scheme is usually applied to the high performance induction motor drives. The PI controller is adopted traditionally to control the motor speed and currents in the vector control scheme. In this case, the dynamic performance of the induction motor is dependent on the PI gains and the gain optimization is necessary in order to get a good dynamic performance. But, it is very hard to optimize the PI gains uniquely within the speed control range because the equivalent model of the motor control system should be known exactly. In this paper, we propose the hybrid control scheme to remove the defects of PI controller. The hybrid control scheme includes the simplified fuzzy controller which operates in the transient state and the PI controller which operates in the steady state. The proposed scheme is applied to the vector control for induction motor, and the digital simulation and the experimental results are given to verify the proposed scheme.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.4
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• pp.817-824
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• 2000

This paper presents circuit DQ modeling and analysis of operating characteristics of hybrid cascade multilevel PWM rectifier, especially five-level, without isolation transformers. The circuit DQ transformation changes the original three-phase time varying circuit to stationary equivalent one by employing the synchronously rotating transformation matrix. As a result of circuit DQ modeling, the operating characteristics and some useful design relationships for the system are obtained with ease. That is, the analytic equations for DC voltages and active/reactive power supplied by source with respect to control variables are Presented. Moreover, the DC voltages for the multilevel output generation may be directly built up from AC utility source and the important control equation ensuring 5-level output voltage is obtained. Finally, to confirm the validity of the analysis, MATLAB simulations are carried out and the simulation results show good agreements between analytic predictions and the simulated waveforms.

• Journal of Environmental Impact Assessment
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• v.26 no.4
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• pp.217-226
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• 2017

Although the effects of climate change are universal, Small Island Developing States (SIDS) are considered to be most vulnerable. SIDS heavily rely on imported oil and fossil fuels for electricity generation and transportation, which makes them economically vulnerable and exposed to fluctuating oil price. Among the reasons SIDS highly depend on diesel fuel is due to the dispersed population living in remote islands which means, providing electricity through on on-grid system is difficult. Fiji as one of the SIDS, has actively promoted renewable sourced energy through a national plan to mitigate the impacts of climate change. In order to determine how feasible implementing a renewable energy (RE) system will be in Fiji, this study chose a remote island called Mavuva Island to test application of a hybrid RE system using HOMER. A combination of energy storage system (ESS), solar photovoltaic (PV) and diesel generator turns out to be the most cost effective and optimal configuration, resulting in effective greenhouse gas reduction for the given region.

• The Journal of the Korea institute of electronic communication sciences
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• v.10 no.11
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• pp.1271-1276
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• 2015

The recent trend is that diesel power generation on islands where its prime cost for power generation is high is replaced by new and renewable energy. Therefore, south Jeolla province is progressing the construction project of self-sufficient islands for the areas where power is supplied by depending on diesel generators, which is the project that power is supplied through eco-friendly energy source using sunlight, wind power and energy storage device etc. However, it is difficult to construct new and renewable energy source with the capacity to respond to the load perfectly due to its environmental and geographical conditions regarding capacity design of new and renewable energy. Besides, Microgrid design considering appropriate capacity design of the system components and efficient operation is required through the analysis of climate conditions and load patterns from the design stage for optimal composition of a hybrid system with economic feasibility. Therefore, this study is aimed to conduct a research on optimal combination, capacity calculation and economic feasibility by comprising a hybrid power generation system which will replace 40% of power generation by diesel as new and renewable energy source for Geomun Island where has more than 300 households and requires expansion of the facility among islands located in southwest coast.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.12
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• pp.2489-2497
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• 1994

This paper presents the development of a 10 W solid-state hybrid power amplifier(SSPA). operating over $7.7\sim8.5GHz$. The fabrication and measurement of this amplifier are performed with 3 sections, such as the front one for high gain, the middle one for driving, and high power one, to minimize the risk of failure and to increase the easiness of development. and then the final amplifier is realized by connecting 3 sections above mentioned, DC bias circuit, and temperature compensation circuit on one housing. Total small signal gain obtained is about $45\pm1dB$, the input and output return losses are 25 and 27 dB respectively. The output power measured at 1 dB gain compression point for 3 frequencies at 7.7, 8.1, and 8.5 GHz are $39.8\sim40.4dBm$, which is about 10 W. and the 3rd-order harmonic powers of 2 tones test are 13.34 dBc at output power 37.5 dBm. These obtained results satisfies the initially required specification. and the realized SSPA can be installed as a subsystem of the microwave transponder for telecommunication.

• Journal of KIISE
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• v.42 no.11
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• pp.1314-1321
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• 2015

Mobile devices employ buffer cache mechanisms, just as in computer systems such as desktops or servers, to mitigate the performance gap between main memory and secondary storage. However, DRAM has a problem in that it accelerates battery consumption by performing refresh operations periodically to maintain the stored data. In this paper, we propose a novel buffer cache scheme to increase the battery lifecycle in mobile devices based on a hybrid main memory architecture consisting of DRAM and non-volatile PCM. We also suggest a new buffer cache policy that allocates buffers based on process states to optimize the performance and endurance of PCM. In particular, our algorithm allocates each page to the appropriate position corresponding to the state of the application that owns the page, and tries to ensure a rapid response of foreground applications even with a small amount of DRAM memory. The experimental results indicate that the proposed scheme reduces the elapsed time of foreground applications by 58% on average and power consumption by 23% on average without negatively impacting the performance of background applications.