• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.105-105
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• 2012

본 논문에서는 전세계적으로 차세대 에너지절감 반도체로 각광을 받고 있는 GaN 소자의 연구개발 동향에 관하여 발표하고자 한다. GaN 반도체는 와이드 밴드갭(Eg=3.4eV)과 고온 안정성($700^{\circ}C$)등 재료적인 특징으로 인하여 고출력 RF 전력증폭기와 고전력용 전력반도체 응용에 큰 장점을 가진다. 고출력용 GaN RF 전력증폭 소자의 전력밀도는 기존 Si-기반 LDMOS 트랜지스터보다 10배 이상 높아 제품의 소형화와 경량화를 통하여 30% 이상의 전력절감이 가능하며, 레이더, 위성등 송수신 트랜시버 모듈에 GaN 전력증폭기를 이용할 경우 기존 GaAs-기반 전력증폭기에 비하여 높은 전력밀도(>x8)와 높은 효율(>20%)로 인하여 모듈 크기를 50% 이상 줄임과 동시에 경량화를 이룰 수 있어 비행기, 위성등 탑재체의 에너지 절감에 크게 기여할 수 있다. 고전력용 GaN 전력 스위칭 소자는 기존 Si-기반 IGBT에 비하여 스위칭 손실과 온-저항 손실이 낮아 30% 이상의 에너지 절감이 가능하다. 뿐만 아니라, 일본 도요타 자동차사의 보고에 의하면 HEV등 전기자동차의 DC-DC 부스터 컨버터나 DC-AC 인버터에 GaN 전력반도체를 적용할 경우 경량화, 변환효율 향상, 전용 냉각시스템을 제거할 수 있어 연료소모를 10% 이상 줄일 수 있어 연간 400불 이상의 에너지 절감 효과를 가진다. 이러한 에너지절감 효과는 미국, 유럽, 일본등 선진국을 중심으로 차세대 GaN 반도체의 신시장 개척과 선진입을 위한 치열한 경쟁 구도의 구동력이 될 것이며, 본 논문을 통하여 GaN 반도체의 연구개발 방향과 상용화의 중요성을 함께 생각해보고자 한다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.8
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• pp.4723-4728
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• 2014

In this study, a thermoelectric module (TEM) and a diesel engine were modeled using 1-D commercial software AMESim, and the performance of the TEM was evaluated when the engine was operated under the NEDC driving cycle. The goal of TEM modeling was to investigate not only the waste heat recovery (WHR) rate and energy converting efficiency, but also the heat transfer rate by taking the materials characteristics into account. In addition, a diesel oxidation catalyst (DOC) was designed, and it was found that the waste heat recovery with TEM affects the activation of DOC and alters engine exhaust composition. The simulation indicated that the WHR using TEM is beneficial for decreasing the fuel consumption of vehicles, but the reduction in the exhaust temperature affects the activation of DOC, resulting in an approximately 14% increase in CO and HC emissions. Therefore, the effect of waste heat recovery on the automotive emission characteristics must be considered in the development of automotive engine WHR systems.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.4
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• pp.517-522
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• 2019

This paper proposes a new motor parameter estimation method. Because the proposed method is based on difference equations, it does not affect the error in the voltage magnitude so called dead-time effect. Information on the motor constant may be needed to improve the motor control performance. For example, a control technique called DTC (Direct Torque Control) requires a motor constant when calculating the torque and flux magnitude. As another example, in the case of predictive control, information on the motor parameters is required to generate voltage references. Because the constant of the motor fluctuates according to the driving environment, it is essential to estimate the correct motor constant because the control performance is degraded when incorrect motor information is used. In the proposed scheme, the motor constant estimated based on the voltage difference equation is obtained using the RLS (Recursive Least Square) technique. The RLS algorithm is applied to obtain the value through an iterative calculation so that the estimation performance is robust to noise. The simulation results carried out with surface mounted permanent magnet motors confirmed the validity of the proposed method.

• The Journal of the Korea institute of electronic communication sciences
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• v.17 no.3
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• pp.441-448
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• 2022

In the distribution system, there are multiple power protection systems such as circuit breakers at substations, and reclosers, minimum circuit ampacities, fault interrupters on distribution lines. They are widely used to prevent partial outages, cascading power failure or blackout so that other healthy systems could maintain the integrity in case of the instant fault or permanent failure on the power lines. However, when a fault happens, it could cause a major black out due to the lack of the protection cooperation between the protection relay of the circuit breaker at a substation and a protection system on the distribution lines. To achieve the power system integrity better, it is required to develop the circuit breaker which can be operational within 1 cycle(16ms). In this study, the high speed circuit breaker which is filled up with eco-friendly gas is developed. This equipment achieved an excellent test results based on IEC 62271-111 standard. It is respected that this equipment would contribute to prevent the wide area blackout by isolating a fault area quicker and faster.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.4
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• pp.282-287
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• 2016

Recently in order to protect the ocean environment and to reduce energy consumption, shipbuilders have been developing highly economized ships. This research analyzed the possibility of adopting the onshore absorption refrigerator to offshore ships having a cooling system with refrigerant by using the waiste heat of the engine jacket cooling water instead of compression refrigerators. The results showed that R236fa could be a suitable medium for absorbing the heat of the absorber and condenser in an absorption refrigerator. The cooling system using R236fa achieved a high COP of 0.798, which is 15% and 5% higher than an air cooling system with a cooling tower and a water cooling system with a heat exchanger, respectively. The cooling system with R236fa achieved high efficiency with a 25% reduction in flow rate of LiBr solution and only 15.7% flow rate of cooling medium as compared to the water cooling system. The heating of sea water by the engine jacket water flowing out from the generator can prevent the crystallization of LiBr solution due to the low temperature of sea water.

• The Journal of the Convergence on Culture Technology
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• v.6 no.3
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• pp.353-359
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• 2020

In this study, the controller structure and control algorithm of medical robot bed developed for pressure ulcer prevention and healing are described. The existing pressure ulcer prevention mattress is operated manually and the remaining maximum body pressure exceeds the pressure of ulcer generation, so there is always room for pressure ulcers. However, the system developed in this study does not generate the pressure ulcers because the body pressure drops to zero when the keyboard of the bed descends using the active electric driving keyboard. In addition, even if the bed is raised and the pressure above the critical body ulcer pressure is abnormal, the device and the control algorithm are designed so that the lasting time is within the pressure ulcer generation critical time and the pressure ulcer itself is not generated. The bed key board motor is a motor designed with the BLDC servos suitable for medical use and these can communicate each other easily through CAN(Car Area Network). The system is new medical robot bed that is effective in preventing pressure ulcers and will be distributed to many patients suffering from pressure ulcers.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.1
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• pp.28-33
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• 2016

Batteries are used for main power engine in the fields such as mobiles, electric vehicles and unmanned submarines, for starter and lamp driver in general automotive, for emergency electric source in ship. These days, lead-acid and the lithium ion batteries are increasingly used in the fields of the secondary battery, and the lead-acid battery has a low price and safety comparatively, The lithium ion battery has a high energy density, excellent output characteristics and long life, whereas it has the risk of explosion by reacting with moisture in the air. But Recently, due to the development of waterproof, fireproof, dustproof technology, lithium batteries are widely used, particularly, because their usages are getting wider enough to be used as a power source for hybrid ship and electric propulsion ship, it is necessary to manage more strictly. Hybrid ship has power supply units connected to the packets to produce more than 500kWh large power source, and therefore, A number of the communication modules and wires need to implement the wire inspection and monitor system(WIIMS) that allows monitoring server to transmit detecting voltage, current and temperature data, which is required for the management of the batteries. This paper implements a low price type wireless inspection and monitoring system(WILIMS) of the lithium ion battery for hybrid vessels using BLE wireless communication modules and power line modem( PLM), which have the advantages of low price, no electric lines compared to serial communication inspection systems(SCIS). There are state of charge(SOC), state of health(SOH) in inspection parts of batteries, and proposed system will be able to prevent safety accidents because it allows us to predict life time and make a preventive maintenance by checking them at regular intervals.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.6
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• pp.397-402
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• 2016

To produce adequate electricity in nuclear and thermal power plants, an optimal amount of steam should be supplied to a generator connected to high- and low-pressure steam turbines. A turbine output control device, which is a special steam valve employed to supply or interrupt the steam to the turbine, is operated using a hydraulic servo actuator. In power plants, the performance of servo actuators is degraded by the air generated from the hydraulic system, or causes frequent failures owing to an increase in the wear of the seal. This is due to the seal being burnt as generated heat using the produced compressed air. Some power plants have exhausted air using a fixed orifice, and thus they encounter power loss due to mass flow exhaust. Failures are generated in hydraulic pumps, electric motors, and valves, which are frequently operated. In this study, we perform modeling and analysis of the load-sensing air-exhaust valves, which can be passed through very fine flow under normal use conditions, and exhaust mass flow air at the beginning stage as with existing fixed orifices. Then, we propose a method to prevent failures due to the compressed air, and to ensure the control accuracy of hydraulic servo actuators.

• Applied Chemistry for Engineering
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• v.31 no.3
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• pp.291-298
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• 2020

ZITO/Ag/ZITO multilayer transparent electrodes at room temperature on glass substrates were prepared using RF/DC magnetron sputtering. Transparent conductive films with a sheet resistance of 9.4 Ω/㎡ and a transmittance of 83.2% at 550 nm were obtained for the multilayer structure comprising ZITO/Ag/ZITO (100/8/42 nm). The sheet resistance and transmittance of ZITO/Ag/ZITO multilayer films meant that they would be highly applicable for use in polymer-dispersed liquid crystal (PDLC)-based smart windows due to the ability to effectively block infrared rays (heat rays) and thereby act as an energy-saving smart glass. Effects of the thickness of the PDLC layer and the intensity of ultraviolet light (UV) on electro-optical properties, photopolymerization kinetics, and morphologies of difunctional urethane acrylate-based PDLC systems were investigated using new transparent conducting electrodes. A PDLC cell photo-cured using UV at an intensity of 2.0 mW/c㎡ with a 15 ㎛-thick PDLC layer showed outstanding off-state opacity, good on-state transmittance, and favorable driving voltage. Also, the PDLC-based smart window optimized in this study formed liquid crystal droplets with a favorable microstructure, having an average size range of 2~5 ㎛ for scattering light efficiently, which could contribute to its superior final performance.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.11
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• pp.119-125
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• 1990

This paper describes fiber optic voltage sensor using EOM-BSO (Electro-Optic Modulator-Bismuth Silicon Oxcide). Transceiver has an electical/optical converter and an optical/electrical converter which consist of light emitting diode, PIN-PD, and electronic circuits. Multimode fiber cable of $100/140{\mu}m$ core/clad diameter is used for connecting the transceiver to fiber cable and fiber optic voltage sensor. Before our experiments, by applying the Maxwell equations and wave equations, We derive matrix equation on wave propagation in the BSO single crystal. And also we derive optimal equation on intensity modulation arising through an analyzer. According to experi-mental results, fiber optic voltage sensor has maximum $2.5{\%}$ error within the applied AC voltage of 800V. As the applied voltage increases, saturation values of voltage sensor also increase. This phenomenon is caused by optical rotatory power of BSO single crystal. And temperature dependence of sensitivity for fiber optical rotatory power of BSO single crystal. And temperature dependence of sensitivity for fiber optic voltage sensor in the temperature range from$-20^{\circ}C\to\60^{\circ}C$ are measured within ${\pm}0.6{\%}$. And frequency characteristics of the voltage sensor has good frequency characteristics from DC to 100kHz.