• KSII Transactions on Internet and Information Systems (TIIS)
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• v.17 no.7
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• pp.1823-1840
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• 2023

In order to improve spectral efficiency and reduce power consumption for reconfigurable intelligent surface (RIS) assisted wireless communication systems, a joint design considering irregular RIS topology, RIS on-off switch, power allocation and phase adjustment is investigated in this paper. Firstly, a multi-dimensional variable joint optimization problem is established under multiple constraints, such as the minimum data requirement and power constraints, with the goal of maximizing the system energy efficiency. However, the proposed optimization problem is hard to be resolved due to its property of nonlinear nonconvex integer programming. Then, to tackle this issue, the problem is decomposed into four sub-problems: topology design, phase shift adjustment, power allocation and switch selection. In terms of topology design, Tabu search algorithm is introduced to select the components that play the main role. For RIS switch selection, greedy algorithm is used to turn off the RISs that play the secondary role. Finally, an iterative optimization algorithm with high data-rate and low power consumption is proposed. The simulation results show that the performance of the irregular RIS aided system with topology design and RIS selection is better than that of the fixed topology and the fix number of RISs. In addition, the proposed joint optimization algorithm can effectively improve the data rate and energy efficiency by changing the propagation environment.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.5
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• pp.69-76
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• 2016

Current driving capability of MCT (MOS Controlled Thyristor) is determined by turn-off capability of conducting current, that is off-FET performance of MCT. On the other hand, having a good turn-on characteristics, including high peak anode current ($I_{peak}$) and rate of change of current (di/dt), is essential for pulsed power system which is one of major application field of MCTs. To satisfy above two requirements, careful control of on/off-FET performance is required. However, triple diffusion and several oxidation processes change surface doping profile and make it hard to control threshold voltage ($V_{th}$) of on/off-FET. In this paper, we have demonstrated the effect of $V_{th}$ adjustment ion implantation on the performance of MCT. The fabricated MCTs (active area = $0.465mm^2$) show forward voltage drop ($V_F$) of 1.25 V at $100A/cm^2$ and Ipeak of 290 A and di/dt of $5.8kA/{\mu}s$ at $V_A=800V$. While these characteristics are unaltered by $V_{th}$ adjustment ion implantation, the turn-off gate voltage is reduced from -3.5 V to -1.6 V for conducting current of $100A/cm^2$ when the $V_{th}$ adjustment ion implantation is carried out. This demonstrates that the current driving capability is enhanced without degradation of forward conduction and turn-on switching characteristics.

• Proceedings of the KIEE Conference
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• 1998.07b
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• pp.725-727
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• 1998

It is difficult to determine the controller parameters that we can get optimum response of the controlled process variable. In this paper we investigate the effects of various elements of which a gas turbine MW control loop is consists. And we describe the result of actual adjustment on the parameters of these elements to improve the speed regulation of a gas turbine.

• Proceedings of the KIPE Conference
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• 2015.11a
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• pp.133-134
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• 2015

본 논문은 배터리 시뮬레이터용 양방향 DC-DC 컨버터에서 스위칭 주파수를 조절하여 넓은 출력 전압 범위에서 출력을 향상시킴을 보였다. 전 부하 영역에서 ZVS를 구현하였고, Psim 시뮬레이션을 통해 검증하였다.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2005.05a
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• pp.795-797
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• 2005

During the past few years, various traffic-flow forecasting models, i.e. an ARIMA, an ANN, and so on, have been developed to predict more accurate traffic flow. However, these models analyze historical data in an attempt to predict future value of a variable of interest. They make use of the following basic strategy. Past data are analyzed in order to identify a pattern that can be used to describe them. Then this pattern is extrapolated, or extended, into the future in order to make forecasts. This strategy rests on the assumption that the pattern that has been identified will continue into the future. So ARIMA or ANN models with its traditional architecture cannot be expected to give good predictions unless this assumption is valid; The statistical models in particular, the time series models are deficient in the sense that they merely extrapolate past patterns in the data without reflecting the expected irregular and infrequent future events Also forecasting power of a single model is limited to its accurate. In this paper, we compared with an ANN model and ARIMA model and tried to combine an ARIMA model and ANN model for obtaining a better forecasting performance. In addition to combining two models, we also introduced judgmental adjustment technique. Our approach can improve the forecasting power in traffic flow. To validate our model, we have compared the performance with other models. Finally we prove that the proposed model, i.e. ARIMA + ANN + Judgmental Adjustment, is superior to the other model.

• International Journal of Advanced Culture Technology
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• v.4 no.1
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• pp.37-50
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• 2016

In recent years, the development and application of green energy resources have attracted more and more /$^*$ 'tention of people. The training room presented here is focused on the terminal applications of a photovoltaic power generation system (PPGS). Through introducing the composition and the general design principles, we aimed at leading the students to master the fundamental skills required for its design, installation and construction. The training room consists of numerous platforms, such as: PPGS, Wind and Photovoltaic Hybrid Power Generation Systems, Wind Power Generation Equipments, Simulative Grid-Connected Power Generation System, Electronic Technology Application of New Energy, etc. This enables the students to obtain their project and professional skills training via assembling, adjusting, maintaining and inspecting, etc., various component parts of the photovoltaic and new energy power generation systems, to further grasp the fundamental and related theoretical knowledge, and to further reinforce their practical and operational skills, so as to improve their problem-analyzing and problem-solving abilities.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.7
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• pp.744-749
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• 2005

This paper describes the performance improvement of power control system of magnetron (MGT) for microwave oven. The MGT is used extensively in household microwave oven and industrial microwave heating devices, and is operated by 3.0[kV] $\∼$5.0[kV] dc high voltage. The proposed power supply is consisted of a bridge rectifier, step-up converter(SUC) and its controller, half bridge inverter(HBI) and its controller, and full wave double voltage rectifier(DVR). In the proposed system, a good power factor can be obtained by the SUC' switching method that the inductor current waveforms follows that of the rectified voltage, and a line input power can be controlled to a range of 17.5[$\%$] by duty ratio (DR) adjustment of the HBI.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.3-32
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• 2016

High power impulse magnetron sputtering (HiPIMS) technique has been developed for more than 15 years. It is characterized by its ultra-high peak current and peak power density to obtain unique thin film properties, such as high hardness, good adhesion and tribological performance. However, its low deposition rate makes it hard to be applied in industries. In this work, the development of HiPIMS system and integration of radio frequency (RF) or mid-frequency (MF) power supplies were introduced. Effects of duty cycle and repetition frequency on the microstructure, mechanical property, optical and electrical properties of some binary, ternary and quarternary nitride coatings and oxide thin films were discussed. It can be observed that the deposition rate was effectively increased by the superimposed HiPIMS with RF or MF power. High hardness, good adhesion and sufficient wear resistance can be obtained through a proper adjustment of processing parameters of HiPIMS power system.

• Journal of information and communication convergence engineering
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• v.6 no.3
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• pp.343-347
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• 2008

Wakeup schemes that turn off sensors' radio when communication is not necessary have great potential in energy saving. At the start of each beacon interval in the IEEE 802.11 power saving mode specified for DCF, each node periodically wakes up for duration called the ATIM Window. However, in the power saving mechanism specified in IEEE 802.11, all nodes use the same ATIM window size. Since the ATIM window size critically affects throughput and energy consumption, a fixed ATIM window does not perform well in all situations. This paper proposes an adaptive mechanism to dynamically choose an ATIM window size according to network condition. Simulation results show that the proposed scheme outperforms the IEEE 802.11 power saving mechanism in terms of the amount of power consumed and the packet delivery ratio.

• Proceedings of the KIEE Conference
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• 2006.05a
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• pp.66-70
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• 2006

Frequency is an important operating parameter of a power system. Electric power systems sustain transient frequency swings whenever the balance between generation and load does not no longer hold. To cope with this Constraints, il requires an accurate and high speedy frequency deviation estimation technique and suitable adjustment to obtain the power system energy balance. This paper describes the design, computational aspects and implementation of an iterative technique for measuring power system. The rate change of the phase angle is used for estimation. To confirm the validity of the proposed algorithm, the simulation studies carried out on a typical 154[KV] double T/L system by using EMTP software. Some test results are presented in the paper.