• The Transactions of the Korean Institute of Power Electronics
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• v.5 no.4
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• pp.386-393
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• 2000

This paper presents an improved ZVS partial series resonant DC/DC converter (PSRC) with low conduction losses, suitable for high power and high frequency applications. The proposed PSRC have advantages of zero-voltage-switching (ZVS) of main switches for entire load ranges low conduction losses of main switches by decreasing current stresses. Also the reduction of the effective duty cycle is not occurred during the resonant period of the main circuit because the auxiliary circuit of the proposed converter is placed out of the main power path. The auxiliary circuit is composed with passive components, which are an inductor, two capacitors, two diodes, and a saturable inductor. An improved ZVS PSRC has so much characteristics with respect to the overall system efficiency and to the reduction of current stresses. The operation principles of the proposed converter are explained in detail and the various simulated and experimental results show the validity of the proposed converter.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.7
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• pp.9-15
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• 2018

The turbochargers, which are used widely in diesel and gasoline engines, are an effective device to reduce fuel consumption and emissions. On the other hand, turbo-lag is one of the main problems of a turbocharger. Bearing friction losses is a major cause of turbo lag and is particularly intense in the lower speed range of the engine. Current turbochargers are mostly equipped with floating bearings: two journal bearings and one thrust bearing. This study focused on the bearing friction at the lower speed range and the experimental equipment was established with a drive-motor, load-cell, magnetic coupling, and oil control system. Finally, the friction losses of turbochargers were measured considering the influence of the rotating speed from 30,000rpm to 90,000rpm, oil temperature from $50^{\circ}C$ to $100^{\circ}C$, and oil supply pressure of 3bar and 4bar. The friction power losses were increased exponentially to 1.6 when the turbocharger speed was increased. Friction torques decreased with increasing oil temperature and increased with increasing oil pressure. Therefore, the oil temperature and pressure must be maintained at appropriate levels.

• Water Engineering Research
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• v.7 no.1
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• pp.1-8
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• 2006

Recently, the population growth and agricultural development are rapidly undergoing in the South-West Texas. The junction of three river basins such as Lavaca river basin, Colorado-Lavaca Coastal basin and Lavaca-Guadalupe Coastal basin, are interesting for non-point and point source pollutant modeling: Especially, the 2 basins are an intensively agricultural region (Colorado-Lavaca Coastal/Lavaca-Guadalupe Coastal basins) and several cities are rapidly extended. In case of the Lavaca river basin, there are many range land. Several habitat types wide-spread over three relatively larger basins and five wastewater discharge regions are located in there. There are different hazardous substances which have been released. Total nutrient loads are composed of land surface load and river load as Non-point source and discharge from wastewater facilities as point source. In 3 basins region, where point and non-point sources of poll Jtion may be a big concern, because increasing fertilizers and pesticides use and population cause. This project objective seeks to how to assess and control the accumulation of non-point and point source and discuss the main impacts of agriculture and environmental concern as non-point source with water quality related to pesticides, fertilizer, and nutrients and as point source with wasterwater discharge from cities. The GIS technique has been developed to aid in the point and non-point source analysis of impacts to natural resource within watershed. This project shows the losses in $kg/km^2/year$ of BOD (Biological Oxygen Demand), TN (Total Nitrogen) and TP (Total Phosphorus) in the runoff from the surface of 3 basins. In the next paper, sediment contamination will show how to evaluate in Estuarine habitats of these downstream.

• Structural Engineering and Mechanics
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• v.70 no.2
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• pp.169-178
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• 2019

The replacement of damaged components is an important task for long-span bridges. Conventional strategy for component replacement is to close the bridge to traffic, so that the influence of the surrounding environment is reduced to a minimum extent. However, complete traffic interruption would bring substantial economic losses and negative social influence nowadays. This paper investigates traffic control technologies without interruption for component replacement of long-span bridges. A numerical procedure of traffic control technologies is proposed incorporating traffic microsimulation and site-specific data, which is then implemented through a case study of cable replacement of a long-span cable-stayed bridge. Results indicate traffic load effects on the bridge are lower than the design values under current low daily traffic volume, and therefore cable replacement could be conducted without traffic control. However, considering a possible medium or high level of daily traffic volume, traffic load effects of girder bending moment and cable force nearest to the replaced cable become larger than the design level. This indicates a potential risk of failure, and traffic control should be implemented. Parametric studies show that speed control does not decrease but increase the load effects, and flow control using lane closure is not effectual. However, weight control and gap control are very effective to mitigate traffic load effects, and it is recommended to employ a weight control with gross vehicle weight no more than 65 t or/and a gap control with minimum vehicle gap no less than 40 m for the cable replacement of the case bridge.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.54 no.2
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• pp.94-100
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• 2005

Korea Electrotechnology Research Institute(KERI) has successfully developed a 100hp-1800rpm-class high temperature superconducting(HTS) motor with high efficiency under partnership with Doosan Heavy Industries & Construction Co. Ltd. This motor has a HTS field winding and an air-cooled stator. The advantages of HTS motor can be represented by a reduction of 50% in both losses and size compared to conventional motors of the same rating. The cooling system is based on the heat transfer mechanism of the thermosyphon by using GM cryocooler as cooling source. The cold head is in contact with the condenser of a Ne-filled thermosyphon. Independently, the rotor assembly was tested at the stationary state and combined with stator. The HTS field winding could be cooled into below 30K. Test of open-circuit characteristics(OCC) and short-circuit characteristics(SCC) and load test with resistive load bank were conducted in generator mode. Also, load tests in motor mode driven by inverter were finished at KERI. Maximum operating current of field winding at 30K was 120A. From OCC and SCC test results synchronous inductance and synchronous reactance were 2.4mH, 0.49pu, respectively. Efficiency of this HTS machine was 93.3% in full load(100hp) test. This paper will present design, construction. and experimental test results of the 100hp HTS machine.

• Journal of Power Electronics
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• v.17 no.4
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• pp.892-904
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• 2017

A design of a Class-E inverter with only one inductor and one capacitor is presented. It is operated at the optimal operation mode for domestic cooker. The design principle is based on the zero-voltage derivative switching (ZVDS) of the Class-E inverter with a parallel load network, which is a parallel resonant equivalent circuit. An induction load characterization is obtained from a large-signal excitation test bench, which is the key to an accurate design of the induction cooker system. Consequently, the proposed scheme provides a more systematic, simple, accurate, and feasible solution than the conventional quasi-resonant inverter analysis based on series load network methodology. The derivative of the switch voltage is zero at the turn-on transition, and its absolute value is relatively small at the turn-off transition. Switching losses and noise are reduced. The parameters of the ZVDS Class-E inverter for the domestic induction cooker must be selected properly, and details of the design of the components of this Class-E inverter need to be addressed. A 1,200 W prototype is designed and evaluated to verify the validation of the proposed topology.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.2
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• pp.215-222
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• 2023

Alternative marine power (AMP) is continuously used in ports and on docks because of regulations on global ship emission reduction. In Korea, the use of AMP is also mandatory under the Special Act on Port Air Quality Improvement, and efforts are under way in connection with various eco-friendly ships, such as electric-propulsion ships. In this study, AC load flow analysis was performed by modeling the situation in which onboard power is supplied through AMP. This analysis made it possible to study the electrical parameters and losses when power was supplied to the ship. In addition, through a transient stability analysis, the high-speed generation transfer limit value for uninterruptible conversion through onboard generators in the event of a system accident was derived. The results obtained when it was applied are presented

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.4
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• pp.179-186
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• 2015

In this study, the actual energy consumption of the secondary side District Heating System (DHS) with different hot water supply temperature control methods is compared. The two methods are Outdoor Temperature Reset Control and Outdoor Temperature Predictive Control. While Outdoor Temperature Reset Control has been widely used for energy savings of the secondary side system, the results show that the Outdoor Temperature Predictive Control method saves more energy. In general, the Outdoor Temperature Predictive Control method lowers the supply temperature of hot water, and it reduces standby losses and increases the overall heat transfer value of heated spaces due to more flow into the space. During actual energy consumption monitoring, the Outdoor Temperature predictive Control method saves about 6.6% of energy when compared to the Outdoor Temperature Reset Control method. Also, it is found that at partial load condition, such as during daytime, the fluctuation of hot water supply temperature with Outdoor Temperature Reset Control is more severe than that with Outdoor Temperature Predictive Control. Thus, it proves that Outdoor Temperature Predictive Control is more stable even at partial load conditions.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.6
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• pp.872-877
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• 2015

The Permanent Magnet (PM) machine used at speed control using field-weakening control method. But the field-weakening current, which reduces the field flux for high speeds, causes significant copper and core losses. Therefore, this paper deals with the PM performance evaluations in a pole changing memory motor (PCMM). The PCMM can change the number of magnetic poles and produce two types of torque. When the motor operates with eight poles, it produces a magnetic torque at low rotational speeds. When the motor changes to four poles, it produces both magnetic torque and reluctance torque at high speeds. The paper explain the principle and basic characteristics of the motor by using a finite element method magnetic-field analysis, which consists of a PM magnetized by a pulse d-axis current of the armature winding. The results of our experiment show that the proposed motor reduces core loss by 10% and 55% under no-load and load conditions, and doubles the speed range of the motor.

• Journal of Power Electronics
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• v.13 no.5
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• pp.829-840
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• 2013

The modified sinusoidal pulse-width modulation (SPWM) is one of the PWM techniques used in three-phase AC-DC buck converters. The modified SPWM works without the current sensor (the converter is current sensorless), improves production of sinusoidal AC current, enables obtainment of near-unity power factor, and controls output voltage through modulation gain (ranging from 0 to 1). The main problem of the modified SPWM is the huge starting current and voltage (during transient) that results from a large step change from the reference voltage. When the load changes, the output voltage significantly drops (through switching losses and non-ideal converter elements). The single-input single-output (SISO) approach with minor-loop voltage feedback controller presented here overcomes this problem. This approach is created on a theoretical linear model and verified by discrete-model simulation on MATLAB/Simulink. The capability and effectiveness of the SISO approach in compensating start-up current/voltage and in achieving zero steady-state error were tested for transient cases with step-changed load and step-changed reference voltage for linear and non-linear loads. Tests were done to analyze the transient performance against various controller gains. An experiment prototype was also developed for verification.