• Journal of Electrical Engineering and Technology
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• v.11 no.3
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• pp.653-661
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• 2016

This paper proposes a capacitance estimation method of the dc-link capacitor for brushless DC motor (BLDCM) drive systems. In order to estimate the dc-link capacitance, the BLDCM is operated in quadrant-II or -IV among four-quadrant operation. Quadrant-II and -IV are called reverse braking and forward braking, respectively. During the braking operation of the BLDCM, the capacitor is charged by the phase current and then the voltage is increased during the braking operation time. The capacitor current and voltage can be obtained by using the phase current sensor of BLDCM and the dc-link voltage sensor. The capacitance and be easily obtained by the voltage equation of the capacitor. The proposed method guarantees the reliable and simple calculation of the dc-link capacitance without additional hardware system except several the sensors already installed for the motor control system. The effectiveness of the proposed method is verified through both the simulation and experimental results.

• Journal of Power Electronics
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• v.12 no.4
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• pp.587-594
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• 2012

When a PWM rectifier has a low DC-link voltage during startup, the output voltage vector cannot be high enough to regulate the input current. This lack of a PWM rectifier output voltage vector can cause an unregulated inrush current when the rectifier operation starts. This paper presents a PWM rectifier start-up current control algorithm for when it starts operation with a lower DC-link voltage than unloaded condition case. To avoid the unregulated inrush current caused by a lack of DC-link voltage, the proposed control scheme regulates the one phase current with one switch chopping and it generates the current command considering the uncontrolled current magnitude information, which is calculated in advance. Simulation and experiment results support the validity of the proposed method.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.36 no.2
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• pp.175-180
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• 2020

The purpose of this study was to clarify precautions during the design and operation phases for energy reduction in a public office building. To check the operation status of the building, we measured the indoor temperature and humidity in the office space of the building installed central heating and cooling systems. And we analyzed these data and annual BEMS data. As a result, we found six problems related to decreasing system efficiency. Based on these, we presented the information to improve the efficiency of the system from the design and operation phase. Also, we present the need for a system to support the decision-making of operational managers in real-time for the energy efficiency of the building.

• Journal of the Korean Institute of Landscape Architecture
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• v.47 no.6
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• pp.24-36
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• 2019

This study shows that the role of residents in landscape management is becoming increasingly important. The purpose of this study is to suggest elements that can continue the operation of landscape agreements and directions for promoting them. Therefore, 1)the operational elements considering the sustainability of the landscape agreements were proposed by way of literature research, expert interviews, and surveys. 2)The sustainable operation of elements of the landscape agreement were applied and best practices were developed through interviews with participants and literature analysis. 3)The final plan operational elements considering the sustainability of the landscape agreements and the directions for implementation were presented. As for the results, it was first presented that the elements of continuous operation of the landscape agreement, consisted of 3 major categories, 10 subcategories, and 25 details. These include resident awareness, practical applicability, effectiveness of administrative means, securing the budget, maintenance, public relations, expert support, dedicated support organization, sustainability of participation, and resident participation and communication methods. It is a detailed list of items that should be considered in the preparation phase, maintenance phase, and conclusion phase. Second, it suggested the direction for the sustainable operation of the landscape agreements be highly backed by the residents, and after reaching consensus on a landscape agreement, it is necessary that the agreement is based on contents that the residents can execute themselves. In addition, it was found that there is a need for a system to prepare the basis for securing the budget for the continuity of work, preparation of the landscape agreements, and consultation and activity costs during the maintenance phase. In addition, continuous exchanges and capacity building among residents have signed landscape agreements, and step-by-step support from experts in accordance with the level of involvement of residents is necessary. Third, even if a landscape agreement is concluded in connection with public projects, it is understood that the residents have the capacity to participate and can continue to support the administration and experts to enable the continued operation of the landscape agreement.

• Journal of Microbiology and Biotechnology
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• v.12 no.1
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• pp.14-17
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• 2002

To increase the efficiency of a two-stage anaerobic wastewater digestion system, various polymers were added to the methanogenic reactor as supports. The addition of polyurethane addition (6%, w/v) to the methanogenic reactor facilitated the organic loading rate (2-day Hydraulic Retention Time), higher than that of the conventional methanogenic reactor (6-day HRT). During the operation of the polyurethane-added reactor, a significant decrease in the organic mass in the effluent (COD 5-6 kg/l) was achieved, compared to that of the conventional reactor (COD 15-20 kg/l). The methane gas production rate also improved about 3-fold in the polyurethane-added reactor. More biomass was found to accumulate in the polyurethane-liquid phase (volatile solid, 26-28kg) than in the free-liquid phase (volatile solid, 5- 7 kg/l) after 90 days of operation. A scaled-up experiment with a polyurethane-added 2.5-1 reactor confirmed the previous results, and no adverse effects such as plugging or channeling due to decreased efficiency was observed even after 4 months of operation.

• Journal of the Korean Society for Railway
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• v.18 no.1
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• pp.25-32
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• 2015

It has been subject to question whether a conventional traffic signal controller can support efficient operation at grade intersections in which vehicles and tram lines cross concurrently. This study proposes a list of functional requirements for a traffic signal controller to support effective operation of trams at such an intersection. The considered details includes the combinations of geometric conditions at which vehicle, bus, and tram lines are aligned, the types of exclusive tram signals, and the combinations of various signal phases, including exclusive tram phases, which are currently undefined in the nation. The results suggest that the controller should be capable of dealing with the NEMA standard overlap relays and a quadruple-ring phase representation scheme.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.10
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• pp.4418-4425
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• 2012

The demand on applying the performance-based logistics (PBL) in the operational phase of the weapon systems development is increasing these days. Therefore, the enhancement of the PBL concept and process needs to be done. This is the objective of the paper. As a method of approach, a modeling method is adopted to cover the whole life cycle of the weapon systems development from the concept development to the operation. The modeling results for the PBL process yield an useful suggestion for improvement. Also, by analyzing the interrelationship model between the PBL process and the integrated logistics support (ILS) procedure, it is possible to take advantage of the PBL concept in the ILS elements development, which is usually carried out from the beginning of the development phase, a lot earlier than the operational phase. Note that the PBL concept has been restrictively applied in only the supply support among many ILS elements up until now. However, the results obtained in the paper can make it also possible to consider the availability, reliability, logistics support, cost and so on from the early phase of the weapon systems development.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.1
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• pp.200-214
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• 1993

This paper presents the results of fluidelastic instability analysis performed for the U-tube bundle of a Westinghouse model 51 steam generator, one of the recirculating types designed at an early stage, in which the principal region of external cross-flow is associated with the U-bend portion of tube. The prerequisites for this analysis are detailed informations of the secondary side flow conditions in the steam generator and the free vibration behaviours of the U-tubes. In this study, the three-dimensional two-phase flow field in the steam generator has been calculated employing the ATHOS3 steam generator two-phase flow code and the ANSYS engineering analysis code has been used to calculate the free vibration responses of specific U tubes under consideration. The assessment of the potential instability for the suspect U-tubes, which is the final analysis process of the present work, has been accomplished by combining the secondary side velocity and density distributions obtained from the ATHOS3 prediction with the relative modal displacement and natural frequency data calculated using the ANSYS code. The damping of tubes in two-phase flow has been deduced from the existing experimental data by taking into account the secondary side void fraction effect. In operation of the steam generator, the tube support conditions at the tube-to-tube support plate intersections due to either tube denting degradation or deposition of tube support plate corrosion products or ingression of dregs. Thus, various hypothetical cases regarding the tube support conditions at the tube-to-tube support plate intersections have been considered to investigate the clamped support effects on the forced vibration response of the tube. Also, the effect of anti-vibration bars support in the curved portion of tube has been examined.

• Bulletin of the Korean Space Science Society
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• 1999.09a
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• pp.75-75
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• 1999

No Abstract, See Full Text

• International journal of advanced smart convergence
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• v.10 no.4
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• pp.45-51
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• 2021

Polar transmitter can support multi-band and multi-mode operation. The efficiency of frequency usage can be increased if polar transmitters can transmit multi-carrier signals. In this paper the configuration of polar transmitters is investigated to generate multi-carrier signals. Spectrum and CCDF Simulation results of two-carrier signals generated by the polar transmitter can be used to design of PM and AM path in a polar transmitter.