• Journal of Electrical Engineering and Technology
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• v.10 no.2
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• pp.443-451
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• 2015

The stability of a multi-terminal direct current (MTDC) system is often influenced by its control strategy. To improve the stability of the MTDC system, the control strategy of the MTDC system must be appropriately adopted. This paper deals with estimating stability of a MTDC system based on the line-commutated converter based high voltage direct current (LCC HVDC) system with an inverter with constant extinction angle (CEA) control or a rectifier with constant ignition angle (CIA) control. In order to evaluate effects of two control strategies on stability, a MTDC system is tested on two conditions: initialization and changing DC power transfer. In order to compare the stability effects of the MTDC system according to each control strategy, a mathematical MTDC model is analyzed in frequency domain and time domain. In addition, Bode stability criterion and transient response are carried out to estimate its stability.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.21 no.48
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• pp.263-268
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• 1998

An efficient agricultural marketing system is very important to producers and consumers to keep the reasonable prices. In these days, the main policy for the efficient agricultural marketing system is to enlarge the direct transaction market. But it is not easy to enlarge the direct transaction market in a few years. This paper proposes a new efficient agricultural marketing system that gives a similar effect with the direct market. The proposed system is mainly composed of three associations; producers', consumers' and retailers'association, and the function of the system is devided into material affairs and commercial affairs. The structure of the system also can be simplified as two to three steps. So the system can reduce the cost of logistics and keep the reasonable prices for both producers and consumers.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.653-657
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• 2007

Since the direct normal insolation is a main factor for designing any solar thermal power system, it is necessary to evaluate its characteristics all over the country. We have begun collecting direct normal insolation data since December 1990 at 16 different locations and considerable effort has been made for constructing a standard value from measured data at each station. KIER(Korea Institute of Energy Research's new data will be extensively used by solar thermal concentrating system users or designers as well as by research institutes. From the results, we can conclude that 1) Yearly mean 5.41kWh/$m^2$/day of the direct normal insolation was evaluated for clear day all over 16 areas in Korea. 2) Clear day's direct normal insolation of spring and summer were 5.54kWh/$m^2$/day and 5.86kWh/$m^2$/day, and for fall and winter their values were 5.32kWh/$m^2$/day and 4.92kWh/$m^2$/day respectively. So, spring and summer were higher, and fall and winter were lower than the yearly mean value.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.27 no.10
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• pp.15-20
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• 2013

In this paper, wireless power transfer system using the magnetic resonance was designed and applied to LED lighting for implementation of wireless lighting. This lighting was made by the converted DC driving type and the direct AC driving type. In the former, transferred AC power was rectified into DC and regulated to the specified voltage value, which leads to produce the loss at the rectifying and regulating circuit. In the latter, wireless-transferred AC power was directly applied to LED, which get rid of the loss derived from the additional circuit. For the efficiency-comparison between the former and the latter, the power at each stage was measured when the same optical output radiated from LED lighting part. The result revealed that the direct AC driving type had 18% higher efficiency than the DC driving type and confirmed that LED lighting using magnetic resonance wireless power transfer system can be efficient by direct AC power supply. And the direct AC driving type had the simple circuit structure and the simple LED lighting formation, so this can leads to various application.

• Journal of Mechanical Science and Technology
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• v.15 no.2
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• pp.268-276
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• 2001

In order to improve the efficiency of a direct contact heat exchanger for a solar thermal energy system, the working fluid should be dispersed into small and uniform droplets, and stay within a heat exchanger for a long time. Therefore, installation of meshes in a direct contact heat exchanger is suggested in the present study, and the performance of the direct contact heat exchanger with several layers of meshes is experimentally investigated. Diethyl phthalate is used as the working fluid, and the performance of the heat exchanger is tested for several different operating conditions and compared to that of the heat exchanger without meshes. The results of this investigation show that meshes make droplets uniform and small when the flow rate is low. The relationship between the Peclet number and the Nusselt number becomes linear if it is steady. And, the Nusselt number for the direct contact heat exchanger with meshes becomes greater than that without meshes as the Peclet number increases.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.130.1-130.1
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• 2011

Since the direct normal insolation is a main factor for designing any solar thermal power system, it is necessary to evaluate its characteristics all over the country. We have begun collecting direct normal insolation data since December 1992 at 16 different locations and considerable effort has been made for constructing a standard value from measured data at each station. KIER(Korea Institute of Energy Research)'s new data will be extensively used by solar thermal concentrating system users or designers as well as by research institutes. From the results, we can conclude that 1) Yearly mean $2.67kWh/m^2/day$ of the all day's direct normal insolation was evaluated for all days all over the 16 areas in Korea. 2) All day's direct normal insolation of spring and summer were $2.91kWh/m^2/day$ and $2.23kWh/m^2/day$, and for fall and winter their values were $2.78kWh/m^2/day$ and $2.77kWh/m^2/day$ respectively. So, spring, fall and winter were higher, and summer was lower than the yearly mean value.

• Nuclear Engineering and Technology
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• v.52 no.4
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• pp.734-741
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• 2020

A new air-cooled waste heat removal system with a direct contact heat exchanger was designed for SMRs requiring 200 MW of waste heat removal. Conventional air-cooled systems use fin structure causing high thermal resistance; therefore, a large cooling tower is required. The new design replaces the fin structure with a vertical string type direct contact heat exchanger which has the most effective performance among tested heat exchangers in a previous study. The design results showed that the new system requires a cooling tower 50% smaller than that of the conventional system. However, droplet formation on a falling film along a string caused by Rayleigh-Plateau instability decreases heat removal performance of the new system. Analysis of Rayleigh-Plateau instability considering drag force on the falling film surface was developed. The analysis results showed that the instability can be prevented by providing thick string. The instability is prevented when the string radius exceeds the capillary length of liquid by a factor of 0.257 under stagnant air and 0.260 under 5 m/s air velocity.

• Nuclear Engineering and Technology
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• v.34 no.5
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• pp.421-432
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• 2002

As one of the advanced design features of the APR1400, direct vessel injection (DVI) system is being considered instead of conventional cold leg injection (CLI) system. It is known that the DVI system greatly enhances the reliability of the emergency core cooling (ECC) system. However, there is still a dispute on its performance in terms of water delivery to the reactor core during the reflood phase of a large-break loss-of-coolant accident (LOCA). Thus, experimental validation is under progress. In this paper, test results of direct ECC bypass performed in the steam-water test facility tailed MIDAS (Multi-dimensional Investigation in Downcomer Annulus Simulation) are presented. The test condition is determined, based on the preliminary analysis of TRAC code, by applying the ‘modified linear scaling method’with the l/4.93 length scale . From the tests, ECC direct bypass fraction, steam condensation rate and information on the flow distribution in the upper annulus downcomer region are obtained.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.27 no.9
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• pp.74-82
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• 2013

This paper presents a novel maximum power point tracking for a photovoltaic power (PV) system with a direct control plan. Maximum power point tracking (MPPT) must usually be integrated with photovoltaic (PV) power systems so that the photovoltaic arrays are able to deliver maximum available power. The maximum available power is tracked using specialized algorithms such as Perturb and Observe (P&O) and incremental Conductance (indCond) methods. The proposed method has the direct control of the MPPT algorithm to change the duty cycle of a dc-dc converter. The main difference of the proposed system to existing MPPT systems includes elimination of the proportional-integral control loop and investigation of the effect of simplifying the control circuit. The proposed method thus has not only faster dynamic performance but also high tracking accuracy. Without a conventional controller, this method can control the dc-dc converter. A simulation model and the direct control of MPPT algorithm for the PV power system are developed by Matlab/Simulink, SimPowerSystems and Matlab/Stateflow.

• Archives of Plastic Surgery
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• v.32 no.3
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• pp.293-298
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• 2005

Osseointegrated prosthetic auricular reconstruction can be classified as either direct or indirect. In the $Br{\aa}nemark $ system of direct osseointegration, implants are placed into the mastoid process of the temporal bone. In the Epitec system of indirect osseointegration, implants are inserted into a three-dimensional carrier plate that is fixed to the mastoid by means of screws. We experienced forty-four cases using the indirect system and seventeen cases using the direct system. We compared with two systems by complications, such as skin reaction, implant loosening, implant loss. There were no specific differences in the skin reaction around the implants and abutments in relation to age or system used. The degree of skin reaction was different according to the conditions around the implant: in cases of virgin microtia, a skin flap was used to cover the implant, in contrast to grafted skin coverage for failed autogenous reconstruction. In both systems, the skin reaction was more severe and frequent in skin flap than in grafted skin. Loosening of the implant was more frequent in the direct system; however, accidental detachment of the implant from the abutment was more frequent in the indirect system. To reduce complications of skin reaction in osseointegrated prosthetic auricular reconstruction, it is important for soft tissue around implant to immobilize. Therefore, grafted skin is better than skin flap as soft tissue around implant. And immobilization of soft tissue around implant by wound dressing is major facter.