• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• 제14권4호
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• pp.65-72
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• 2000

This paper proposes a Push type High Frequency DC-DC Converter using Zero Voltage Switching to reduce turn on and off loss at the switching instants. This paper has a advantage which is able to operating safely in load short, because DC reactor is connected with resonance reactor in order to supply a fixed safely in load short, because DC reactor is connected with resonance reactor in order to supply a fixed current with low ripple from DC power supply. The capacitor $(C_1, C_2)$ connected in switch are a common using as resonance capacitor and ZVS capacitor. The analysis of the proposed high frequency resonance DC-DC converter is generally described by using normallized parameter, and we has evaluated characteristic values which is needed to design a circuit. We conform a rightfulness of theoritical analysis by comparing a theoretical values and experimental values obtained from experiment using MOSFET as switching devices.

• The Transactions of the Korean Institute of Power Electronics
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• 제14권3호
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• pp.220-227
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• 2009

A self oscillation DC/DC converter which has a very desirable characteristics of the high input-output voltage conversion ratio for high voltage DC power supply applications is proposed in this paper. The proposed converter is composed of one power switch, one inductor, several capacitors and diodes. Compared with conventional high-voltage DC/DC converters, it performs the high- voltage power conversion using the inductor instead of the bulky step-up transformer. Therefore, it can reduce the size of magnetic device and save the cost. Moreover, since it needs no control IC by using self oscillation circuit and has lower voltage stress on output diodes, it features a lower cost, simpler structure and more improved performance. Finally, a comparative analysis and experimental results are presented to show the validity of the proposed converter.

• Transactions of the Korean Society of Mechanical Engineers B
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• 제35권11호
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• pp.1163-1168
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• 2011

Compared with the spark-ignition gasoline engine, the compression-ignition diesel engine has reduced fuel consumption due to its higher thermal efficiency. In addition, this reduction in the fuel consumption also leads to a reduction in $CO_2$ emission. Diesel engines do not require spark-ignition systems, which makes them less technically complex. Thus, diesel engines are very suitable target engines for using biofuels with high cetane numbers. In this study, the spray characteristics of biofuels such as vegetable jatropha oil and soybean oil were analyzed and compared with those of diesel oil. The injection pressures and blend ratios of jatropha oil and diesel oil (BD3, BD5, and BD20) were used as the main parameters. The injection pressures were set to 500, 1000, 1500, and 1600 bar. The injection duration was set to $500{\mu}s$. Consequently, it was found that there is no significant difference in the characteristics of the spray behavior (spray angle) in response to changes in the blend ratio of the biodiesel or changes in the injection pressure. However, at higher injection pressures, the spray angle decreased slightly.

• Journal of the Korea Society of Computer and Information
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• 제25권2호
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• pp.189-195
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• 2020

In this study, the inlet duct and guide vane of the gas floating absorption tower were redesigned to improve the desulfurization efficiency so that the exhaust gas can be uniformly introduced into the absorption tower. In order to reduce the sulfur oxide pollutants among the main sources of air pollutants in industrial boilers, the existing equipment is redesigned and solved. For this purpose, change the exhaust gas, the slurry and recycling the adsorbent to improve the removal efficiency of SOx component in the exhaust gas inside the gas floating absorption tower so as to uniformly contact. And the initial design value and CFD value for the pressure loss from the boiler outlet to the gas floating absorption tower outlet are verified. Also, the velocity distribution of the exhaust gas, the concentration distribution of the recycled adsorbent, the liquid slurry behavior, and the pressure loss were compared. The results confirmed that the desulfurization efficiency was improved because the pressure loss from the boiler outlet to the absorption tower outlet was reduced and the deflection of the exhaust gas was minimized.

• Journal of the Korea Institute of Information and Communication Engineering
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• 제13권12호
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• pp.2618-2624
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• 2009

Harmonics (or distortion in wave form) has always existed in electrical power systems. It is harmless as long as its level is not substantial. However, with the recent rapid advancement of power electronics technology, so-called nonlinear loads, such as variable frequency drives for motor power/speed control, are increasingly finding their way to shipboard or offshore applications. In this paper a new approach to direct torque control (DTC) of induction motor drive is presented. In comparison with the conventional DTC methods the inverter switching frequency is constant and is dramatically increased, requiring neither any increase of the sampling frequency, nor any high frequency dither signal. The well-developed space vector modulation technique is applied to inverter control in the proposed DTC-based induction motor drive system, thereby dramatically reducing the current harmonics. As compared to the existing DTC approach with constant inverter switching frequency, the presented new approach does not invoke any concept of deadbeat control, thereby dramatically reducing the computations.

• Journal of the Korean Institute of Gas
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• 제17권5호
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• pp.8-14
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• 2013

Hydrogen-natural gas blends(HCNG) engine is optimizing technology of performance and emission characteristics with use of hydrogen's fast flame speed and wide flammability limit. As lean-burn limit is extended, the improvement in thermal efficiency and harmful emissions can be achieved. However, the extension of lean-burn limit under a wide open throttle operation point could be realized with the increase in boosting capacity in a lean-burn engine with turbo-charging system. In the present study, the power output characteristics of HCNG engine with turbo-charger change is assessed and feasibility of the increase in boosting capacity is evaluated. The turbo-charger design with high efficiency at higher flow rate rather than higher boosting pressure makes efficient operation possible at relatively rich mixture condition.

• Journal of Convergence for Information Technology
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• 제11권11호
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• pp.166-171
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• 2021

An active mount is devised in same geometric constraints with a conventional rubber mount. The proposed mount features the piezoelectric actuator which can be used to reduce the vibration at marine vessels or automotive vehicles. As a first step, a passive rubber mount is adopted and its dynamic characteristics are experimentally evaluated. Based on the geometry of the rubber mount, a rubber element for the active mount is manufactured and integrated with two piezostacks in series, in which the piezostack is operated as an inertial type of actuator. A conventional PID controller featured by the simple and easy implementation, is then designed to attenuate the non-resonant high frequency vibration transmitted from the base excitation. Finally, the control performances of a proposed active mount are evaluated in the wide frequency range and compared with those of the conventional rubber mount.

• Journal of Ocean Engineering and Technology
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• 제32권6호
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• pp.419-426
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• 2018

Recently, in an effort to reduce the energy efficiency design index (EEDI), studies on energy saving devices (ESDs) have been conducted. In this study, we designed a post-device suitable for a KRISO container ship (KCS) using computational fluid dynamics (CFD). In order to increase the efficiency of the post-device, a twisted rudder was used, which has a proven performance (showing a 1.34% reduction in DHP compared to the bare hull at 24 knots) in previous research at Pusan National University. In addition, an increase in efficiency was expected by the use of a rudder bulb, including the discontinuous section of the twisted rudder and a divergent propeller cap to prevent the contraction of the wake. The optimization criterion was the case where the delivery power was the least compared with the bare hull. We analyzed the cause of the efficiency increase through an analysis of the self-propulsion factor. The case study for optimization was divided into 4 types (1. clearance of the bulb and cap, 2. shape of the bulb, 3. size of the bulb and cap, and 4. asymmetric bulb). Finally, with a clearance of 50 mm from the ship, a spherical bulb with the cap having an angle of $5^{\circ}$, and an asymmetric rudder bulb with a bulb diameter of 1.2HH/1.4H (horizontal/vertical) showed a 2.05% reduction in DHP compared to the bare hull at 24 knots. We will fabricate a post-device that will be optimized in the future and verify the performance of the post-device through model tests.

• Journal of Advanced Navigation Technology
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• 제22권6호
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• pp.545-550
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• 2018

Ministry of Oceans and Fisheries declared action plan for the electric fishing gear using real name in order to prevent overusing the fishing gear and to reduce discarded fishing gear. It is needed for a technique that can efficiently transmit the information including the type and location of the fishing gear and the user's real name to the fishing boat and the control center using IoT-based communication. The marine tracker buoy system, which is placed on the water for a long time, transmit the position data and the state data of the buoys to the control center in the ground by using NB-IoT channels. In this paper, we propose the algorithm for the low-power operation of the marine tracker buoy system is proposed and test results of current consumption in the marine tracker buoy system with the proposed algorithm is investigated.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• 제22권2호
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• pp.123-128
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• 2022

The torque of the SRM((Switched Reluctance Motor)) is proportional to the inductance slope, so it has a non-linear torque characteristic, and has a disadvantage in that the torque pulsation is large and noise is severe. In particular, the biggest obstacle to the commercialization of SRM is the pulsating torque generated from the rotating shaft, which has various adverse effects not only on the device itself but also on the peripheral devices. Therefore, various methods for reducing the pulsating torque have been published by domestic and foreign researchers, and there is a study result that the hysteresis controller has an advantage in that it can flow a smooth current compared to the chopping control. However, in determining the hysteresis band, if the band is too small, it has a disadvantage in that it may cause a switching loss due to many switching and an unstable initial start when the encoder is used. Therefore, in this paper, a variable hysteresis controller that can reduce torque ripple in a steady state while having a more stable and fast speed response through the change of the hysteresis band according to the speed error.