Jo Nov 12, 2024
Wind power generation system mainly consists of a wind power generator, a battery group to store generated electricity, a controller unit to transmit maximum power to load and an inverter system to supply power to AC load.
Generally, small wind power system is controlled by maximum power point tracking method, whereby the output current is controlled so that the wind power generation system can be operated at the maximum power point of the wind turbine regardless of the changing wind speed when the wind power generation system is operated independently. This method is suitable for systems where the rotational speed of the wind turbine varies sensitively with the change of wind speed due to the small inertia moment.
Hence, present papers introduce a method for maximum power output without a control circuit in a small wind power generation system. It is a driving method that approximates the active power curve of load to the maximum power curve of the wind turbine for maximum power operation by changing the generator’s electromotive force coefficient and the inductance of the two-winding generator. In wind power generation systems with two-winding generators of great inductance, however, the load power characteristics have saturation characteristics with respect to the number of turns. Therefore, the inductance alone is not enough to approximate the load power characteristics to the maximum power curve of wind turbines.
Kim Yong San, a researcher at the Faculty of Electrical Engineering, has solved scientific and technological problems arising in providing maximum power point operation of wind turbines using the two-winding generator and electromotive force coefficients in permanent magnet generators connected with wind turbines.
He theoretically analyzed how the power output of load depends on the generator’s electromotive force coefficient and the inductance of a two-winding generator, and proposed a method for determining the reasonable inductance and electromotive force coefficient that brings the generator’s effective power characteristics depending on the rotational speed closest to approach the maximum power curve of wind turbines.
Through the simulation analysis using MATLAB, he confirmed that the power characteristics of load could be operated near the maximum power curve of wind turbines.
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Jo Nov 8, 2024
Nowadays, according to constant changes in the manufacturing style of products, there arises a requirement for rearrangement of facilities. The way how facilities are laid out might cause bottleneck or not in production processes, and decides production efficiency. Therefore, reasonable layout of facilities is a very important problem in factories to be newly built or already built.
Generally, layout of facilities is based on mathematical modeling and optimized planning. However, its complexity fails to meet the requirements of developing modern production modes.
Paek Chol Yong, a researcher at the Faculty of Automation Engineering, has proposed a reasonable layout of facilities. Deciding that the layout of facilities in the machining workshop is a typical discrete event system, he conducted a simulation of the layout of existing facilities by using FlexSim to find its disadvantages and eliminate bottleneck phenomena.
Then, he applied the proposed layout method to a workshop. As a result, the productivity increased by 1.15 times and the production time decreased by 1.21 times as much as the original layout of facilities.
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Jo Nov 5, 2024
In order to realize automated and unmanned production processes, it is necessary to supervise and control the production process in real time, and check and evaluate the quality of products. Image processing units such as digital cameras are usually used to implement it. Recently, high-resolution cameras are used to improve the accuracy of data. The higher the resolution is, the bigger the amount of data is. Therefore, data transmission rate between computers and peripherals should be increased.
USB3.0 is a computer interface protocol that makes possible up to 5Gbps of data transmission by means of advanced techniques such as full-duplex transmission mode by multi channels, burst function using integrated packets and high-speed encoding technique by 8b/10b encoding, and its application technology has been widely studied for its good hardware connectivity and ease of use.
Ri Pyong Chol, a researcher at the Faculty of Information Science and Technology, has proposed a configuration and design of a USB high-speed transmission system that can achieve a USB3.0 data transmission rate of up to 3.2Gbps.
First, he combined a USB3.0 chip and Cyclone II FPGA to configure a high-speed data transmission system. Then, he programmed a firmware to set the data packet size and buffer size for maximum data transmission rate of the USB port. He also designed FPGA internal logic to increase the data transmission efficiency through the synchronous SlaveFIFO controller, the internal buffer, and the external I/O controller.
Finally, he measured the data transmission performance from the development system to the computer with a test program, and evaluated the efficiency of the proposed system design method.
He confirmed that the proposed method could ensure the data transmission rate of up to 3.2Gbps.
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Jo Oct 31, 2024
There are two main schemes of charging scheduling of a mobile charger (MC): periodic and on-demand. The latter schedules on-demand charging of a BS or MS, whose order is determined by temporal and spatial factors of request nodes. Recently, several intelligent on-demand charging scheduling schemes combined with multi-criteria have been proposed. Multi-criteria that conflict with each other, such as residual energy, distance to the MC, energy consumption rate, traffic relay load of charging request nodes, etc., play a key role in determining the charging priority of charging request nodes. However, which theory should be applied to determining the most suitable charging order of request nodes with such contradictory criteria is still a challenge that needs urgent solution.
Among the various multi-criteria decision making (MCDM) methods, the FAHP-TOPSIS method combined with fuzzy analytical hierarchy process (FAHP) and the technique for order preference by similarity to ideal solution (TOPSIS) are most widely used.
From the inspiration that an integrated MCDM in charging scheduling using multi-criteria could be effectively available throughout the whole charging scheduling process, Ri Man Gun, an institute head at the Faculty of Communication, has proposed a novel charging scheduling scheme based on an integrated FAHP-VWA-TOPSIS (iFVT).
Using an iFVT, he has also proposed a method of accurately calculating the relative weights of multi-criteria and determining the most suitable next-to-be-charged node by combinatorial evaluation of multi-criteria of request nodes
You can find the details in his paper published in “The 14th international Conference on Computing, Communication and Networking Technology (ICCCNT 2023)”.
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Jo Oct 29, 2024
Subcooled flow boiling is widely used in many cooling systems due to its high cooling effect. In such systems, it is very important to accurately analyze the boiling heat transfer behavior of working fluid. Therefore, there have been several researches on accurately analyzing the behavior of subcooled flow boiling heat transfer by using commercial Computational Fluid Dynamics (CFD) codes. Most of the researchers have used the RPI (Rensseler Polytechnic Institute) model within Eulerian multi-phase framework in their CFD simulations of subcooled flow boiling heat transfer.
In a word, there have been many studies on the CFD analysis of subcooled flow boiling and a lot of progress has been made in terms of accuracy. However, most of the previous works for CFD simulations considered water as the working fluid, and the works for the CFD simulations with CO2 as the working fluid are rare.
Ma Kuk Chol, a researcher at the Faculty of Heat Engineering, has developed a mathematical model to simulate the subcooled flow boiling of CO2 by utilizing the Eulerian multi-phase model combined with the RPI and IAC models, and solved the model by means of the CFD solver, ANSYS FLUENT 19.3.
Thus, he proved that the coefficient of heat transfer is greatly affected by bubble waiting time coefficient (CWT) and critical Weber number (Wecri) and determined reasonable CWT and Wecri.
The details are found in his paper “Determining of bubble waiting time coefficient, critical Webber number and turbulence model for modeling of subcooled flow boiling heat transfer of CO2 at low temperature” in “Applied Physics A” (SCI).
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Jo Oct 26, 2024
Dye solar cells (DSCs), which are based on photosensitization of dyes adsorbed on wide-bandgap oxide semiconductors such as TiO2, have attracted a great deal of attention on account of their semitransparency, color harmony function and simple fabrication processes.
Transparent glass or polymer films with a conductive oxide layer (TCO electrode), such as FTO/GLASS and ITO/PET(Polyethyleneterephthalate), are often used as the substrates in DSCs because of their good conductivity and outstanding transmittance. However, these TCO electrodes account for a lot in the price of inorganic–organic hybrid solar cells such as dye and perovskite solar cells due to their dependence on exclusive deposition techniques.
Ti metallic substrates, such as Ti wire, Ti mesh, Ti foil and the like, are deemed to be a good choice to replace TCO electrodes. However, the Ti metallic substrates suffer from certain shortages. For example, metal foil has no transmittance, metal mesh owns a small effective area for accepting sunlight and metal wire is hard to support the manufacture of large-scale DSCs. Moreover, the high price of titanium substrates limits its wide application.
Jon Sang Mo, a researcher at the Faculty of Chemical Engineering, has proposed a new method of manufacturing a porous Ti back contact layer by using a facile printing method in normal ambient conditions.
In addition, conjugating the new back contact electrode technology with the traditional monolithic structure using the carbon counter electrode, he fabricated low-cost TCO-free DSCs. These four-layer structured DSCs consist of a dye-adsorbed nanocrystalline TiO2 film on a glass substrate, a porous Ti back contact layer, a ZrO2 spacer layer, and a carbon counter electrode in a layered structure, and the interior of the layers is filled with iodine/triiodide redox electrolyte.
For more information, please refer to his paper “Journal of Saudi Chemical Society” in “TCO-free dye solar cells based on Ti back contact electrode by facile printing method” (SCI).
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