• Journal of Electrical Engineering and Technology
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• v.11 no.1
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• pp.65-75
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• 2016

Aiming at analyzing the power flow of the distribution systems with distribution transformer (DT) branches and PV nodes, a hybrid three-phase power flow methodology is presented in this paper. The incidence formulas among node voltages, loop currents and node current injections have been developed based on node-branch incidence matrix of the distribution network. The method can solve the power flow directly and has higher efficiency. Moreover, the paper provides a modified method to model DT branches by considering winding connections, phase shifting and off-nominal tap ratio, and then DT branches could be seen like one transmission line with the proposed power flow method. To deal with the PV nodes, an improved approach to calculate reactive power increment at each PV node was deduced based on the assumption that the positive-sequence voltage magnitude of PV node is fixed at a given value. Then during calculating the power flow at each iteration, it only needs to update current injection at each PV node with the proposed algorithm. The process is very simple and clear. The results of IEEE 4 nodes and the modified IEEE 34 nodes test feeders verified the correctness and efficiency of the proposed hybrid power flow algorithm.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.4
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• pp.59-65
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• 2014

In this paper, in order to improve efficiency performance of power amplifiers, a mode changeable autotransformer is proposed. Efficiency performance at the low-power mode can be improved by adopting the mode changeable autotransformer. A dual-mode autotransfomrer CMOS power amplifier using a standard 0.18-${\mu}m$ CMOS process is designed in this work. Number of turns in a primary winding is re-configurated according to mode change between the high-power mode and the low-power mode. Thus, the efficiency performance of the power amplifier at each mode is optimized. EM and total circuit simulation results verify that low-power mode power added efficiency(PAE) at 24dBm output power is improved from 10.4% to 26.1% using the proposed multi-mode operation.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.11a
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• pp.169-172
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• 2005

A flywheel system is an electromechanical energy storage device that stores energy by rotating a rotor. The rotating part, supported by magnetic bearings, consists of the metallic shaft, composite rims of fiber-reinforced materials, and a hub that connects the rotor to the shaft. The delamination in the fiber wound composite rotor often lowered the performance of the flywheel energy storage system. In this work, an advanced hybrid composite rotor with a split hub was designed to both overcome the delamination problem in composite rim and prevent separation between composite rim and metallic shaft within all range of rotational speed. It was analyzed using a three-dimensional finite clement method. In order to demonstrate the predominant perfom1ance of the hybrid composite rotor with a split hub, a high spin test was performed up to 40,000 rpm. Four radial strains and another four circumferential strains were measured using a wireless telemetry system. These measured strains were in excellent agreement with the FE analysis. Most importantly, the radial strains were reduced using the hybrid composite rotor with a split hub, and all of them were compressive. As a conclusion, a compressive pressure on the inner surface of the proposed flywheel rotor was achieved, and it can lower the radial stresses within the composite rotor, enhancing the performance of the flywheel rotor.

• Journal of KIISE
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• v.43 no.4
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• pp.419-429
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• 2016

Generating a 3D surface model from coronary artery segmentation helps to not only improve the rendering efficiency but also the diagnostic accuracy by providing physiological informations such as fractional flow reserve using computational fluid dynamics (CFD). This paper proposes a method to generate a triangular surface mesh using vessel structure information acquired with coronary artery segmentation. The marching cube algorithm is a typical method for generating a triangular surface mesh from a segmentation result as bit mask. But it is difficult for methods based on marching cube algorithm to express the lumen of thin, small and winding vessels because the algorithm only works in a three-dimensional (3D) discrete space. The proposed method generates a more accurate triangular surface mesh for each singular vessel using vessel centerlines, normal vectors and lumen diameters estimated during the process of coronary artery segmentation as the input. Then, the meshes that are overlapped due to branching are processed by mesh merging and merged into a coronary mesh.

• Korean Journal of Food Science and Technology
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• v.33 no.6
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• pp.808-811
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• 2001

Performance of pilot plant scale extraction and concentration of purple-fleshed sweet potato anthocyanin pigment was tested and the characteristics of pigment extracts and concentrates were investigated. Fifty kilograms of purple-fleshed sweet potato was extracted with 500 L of 1% citric acid in 20% ethanol. As a whole, extraction pattern of the large scale extraction was similar to that of the laboratory scale extraction. The extracted pigment solution was filtered twice with a bag filter and a winding type microfilter and the filtrate was concentrated by a large scale vacuum evaporator at $40^{\circ}C$ and 600 mmHg vac. The mean values of total optical density (TOD) of the extract and the concentrate were 6.53 and 120.45, respectively. Browning index (BI) and Degradation index (DI) of extract were 5.86 and 1.55 and those of concentrate were 5.89 and 1.56, respectively, which indicated that the pigments were not changed or degraded through the extraction and concentration process.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.933-935
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• 2017

This paper deals with the influence of fungi for the thermal protective cork-based exterior insulator which protect a missile system from aerodynamic loads and heating during flight of missile. We consider the adhesion of cork-based composite on the composite motor case which fabricated by filament winding process. We also consider the importance of the requirement analysis for effective, successful system development under given system conditions. In order to develop the basic requirement analysis for the thermal protective cork-based exterior insulator, an experimental requirement analysis was accomplished, and some experimental comparing results, the study for preventing fungi are presented.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.4
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• pp.9-15
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• 2012

In this paper, the bearing strengths and fracture behaviors of the pin-jointed carbon fiber/epoxy composites were investigated through pin loading test with acoustic emission technique. The composites were fabricated by a filament winding process, and three types of laminated patterns were considered. Type 1 was fabricated with stitch, Type 2 was fabricated without stitich and Type 3 was fabricated with prepregs. According to the results, bearing strength of Type 1 was 3.3% lower than that of Type 2 and that of Type 3 was highest. Type 1 and Type 2 revealed a net-tension failure mode, respectively, whereas Type 3 pattern exhibited a bearing failure mode. Also, acoustic emission energy of the Type 3 was higher than that of the Type 1 and Type 2. Therefore, the Type 3 was found to be structurally safer than the Type 1 and Type 2.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.11 no.6
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• pp.732-741
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• 2018

In order to maximize the usable capacity of a BMS (battery management system) that uses several battery cells connected in series, a cell balancing technique that equips each cell with the same voltage is needed. In the active cell balancing circuit using a multi-winding transformer, a balancing circuit that transfers energy directly to the cell (cell-to-cell) is composed of a PMOS switch and a gate driving chip for driving the NMOS switch. The TLP2748 photocoupler and the TLP2745 photocoupler are required, resulting in increased cost and reduced integration. In this paper, instead of driving PMOS and NMOS switching devices by using photocoupler, we proposed 70V BCD process based PMOS gate driving circuit, NMOS gate driving circuit, PMOS gate driving circuit and NMOS gate driving circuit with improved switching time. ${\Delta}t$ of the PMOS gate drive switch with improved switching time was 8.9 ns and ${\Delta}t$ of the NMOS gate drive switch was 9.9 ns.

• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.6
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• pp.1195-1204
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• 2021

In this paper, we present an optimal design method for wave power generators using the response surface analysis. Especially, in our method, we reduce the mechanical loss by selecting the linear generator whose linear movement can be converted to the electrical energy directly with the vertical movement of waves. Therefore, we calculate the exciting force acting on the drive device in a slow-wave condition and determine the winding process with a ratio of the slots and poles for the improvement of energy conversion efficiency. In addition, we employ the regression analysis for deriving the shape factors of the stator and the translator, which have a significant effect on the performance of a generator. We choose the best design variables through the response surface analysis, and then we study the optimization method for designing the efficient experiment using the analysis results. Finally, we show the validity of the proposed method through the simulation results.

• Journal of the Korean Society of Safety
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• v.38 no.1
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• pp.25-33
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• 2023

In this study, we determined the failure rate and fire status of electric motors widely used in domestic and industrial devices and analyzed the associated fire risks by identifying the electrical and temperature characteristics of electric motors under the normal and restrained operation modes in industrial sites and laboratories. A 2.2kW motor used for driving a conveyor during the vulcanization process in a rubber product manufacturing plant was employed as the study object and was exposed to a high- temperature environment as this motor is widely used in industrial sites. The current amplitude was 4.45-4.50 A during normal operation and 38.2-41.5 A during restrained operation due to the pinching of products and semi-finished products (i.e., 8.5 times higher than that during normal operation). The leakage current amplitude was 0.33 mA during both operation modes. The temperature of the workplace in summer was 42.38℃, indicating a poor environment for the installed motor. In the laboratory, the current and temperature of the coil inside a 3.7kW motor were measured under the restrained operation mode as performing measurements of the coil inside the motor in industrial sites is challenging. The current amplitude during normal operation was 3.5 A, whereas that during restrained operation for 30 s was 51.7-58.6 A, which is 14.8-16.7 times higher than that of normal operation. Moreover, the temperature of the motor coil increased from 22.9℃ to 101℃. Based on the experimental data, we derived the temperature increase formula according to the restrained operation time by performing a regression analysis and verified the time at which the temperature exceeded the stipulated limit for the insulation grade. The findings presented in this paper can be utilized to establish fire-prevention measures and perform safety management of motors of the same type or with a similar capacity.