• Journal of Power Electronics
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• v.12 no.6
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• pp.935-946
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• 2012

A new kind of resonant impedance type hybrid active filter (RITHAF) is proposed for dynamic harmonic current suppression and high capacity reactive compensation in medium and high voltage systems. This paper analyzed the different performance of the RITHAF when the active part of the RITHAF is controlled as a current source and as a voltage source, respectively. The harmonic suppression function is defined in this paper. The influences of the changes caused by the grid impedance and the detuning of the passive power filter on the compensating characteristics of the RITHAF are studied by analyzing the suppression function. Simulation and industrial application results show that the RITHAF has excellent performances in harmonic suppression and reactive compensation, which is suitable for medium and high voltage systems.

• Journal of Korea Technology Innovation Society
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• v.8 no.1
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• pp.277-295
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• 2005

The objective of the study is to verify the discriminatory power of valuation indexes in predicting IT small and medium sized manufacturing firms' going concern or firms' failure. The result of the study is expected to be useful in loan evaluation, investment decision, internal management decision making and business improvement. The results of study is as follows. First, we find that at least six valuation index elements are significant ex-ante variable which are discriminating between firms' going concern and firms' failure in IT small and medium sized manufacturing firms in various analysis' results. Second, these index elements are composed of 2 indexes-the ability of technology R&D, the efficient strategy of market penetration and six index elements explain 46% of the total variance. This explainable power of these indexed is similar to that of the existing 16 index elements. Finally, we find that the most important success factor of IT small and medium sized manufacturing firms are the ability of technology R&D and the efficient strategy of market penetration.

• Journal of information and communication convergence engineering
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• v.10 no.2
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• pp.97-102
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• 2012

The differential global positioning system (DGPS) transmits a GPS enhancement signal using a top-loaded monopole antenna in the medium frequency range. The top-loaded antenna in the medium frequency band can attain a radiation efficiency on the order of 10%. The antenna ground plane characteristics affect the antenna radiation efficiency. To improve the radiation efficiency, it is necessary to install the antenna on a ground plane with large enough physical dimensions and good conductivity. The antenna radiation efficiency is a primary factor in determining the DGPS service area. The service area of the DGPS using a medium frequency band is dominantly affected by the antenna radiation efficiency. To determine antenna radiation efficiencies accurately, the antenna radiation efficiencies of DGPS are deduced from the propagation power in this paper. Based on the deduced antenna radiation efficiencies, the service area for the Korean nationwide-DGPS is analyzed and evaluated.

• Journal of Power System Engineering
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• v.3 no.3
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• pp.14-21
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• 1999

The wave nature of heat conduction has been developed in situations involving extreme thermal gradients, very short times, or temperatures near absolute zero. Under the excitation of a periodic surface heating in a finite medium, the hyperbolic and parabolic heat conduction equations and the damped wave equations in heat flux are presented for comparative analysis by using the Green's function with the integral transform technique. The Kummer transformation is also utilized to accelerate the rate of convergence of these solutions. On the other hand, the temperature distributions are obtained through integration of the energy conservation law with respect to time. For hyperbolic heat conduction, the heat flux distribution does not exist throughout all the region in a finite medium within the range of very short times(${\xi}<{\eta}_l$). It is shown that due to the thermal relaxation time, the hyperbolic heat conduction equation has thermal wave characteristics as the damped wave equation has wave nature.

• Journal of Korean Society for Quality Management
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• v.25 no.4
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• pp.154-167
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• 1997

This survey research investigates how the small and medium industries in Pusan area have considered quality management activities in an effort to strengthen their competitive power. It first develops a set of significant questionnaires anddistributes them to a select group of small and medium regional industries. The survey results are analyzed based on both Cronbach's Alpha value and $x^2$ test. This study shows that the awareness level of quality management varies according to the type of industrial field. This study also proposes that a, pp.opriate quality management strategies are necessary for the regional industries in pusan.

• Asia pacific journal of information systems
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• v.5 no.1
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• pp.186-218
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• 1995

The necessity of installing well adaptable Information Systems are required day by day in all the fields of business management. This paper provides an Information System development for enhancing competitive power of the small and medium-sized firms in Korea. Recent growing Information Technology leads to constructing invisibly some new adaptable Information Systems in accordance with the business size, level, capacity and requirements. Even though some advanced companies and big enterprises are already operating their own appropriate Information Systems so as to get their remarkable productivity at a moment. The rest of those small firms are still trying to find out some proper systems fitting their own business in very poor situations. The basic requirements of the points of views by mail questionaired and interviewed from 1292 small and medium-sized manufacturing firms reflected on this Information System development. As a result, the study introduces some economically efficient, convinient, flexible and useful applied Information Systems with simple methods.

• Journal of Power Electronics
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• v.19 no.3
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• pp.714-726
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• 2019

This paper proposes a hybrid-boost Modular Multilevel Converter (MMC) for the Medium-Voltage (MV) Variable Speed Drives (VSDs) employed in subsea applications, such as oil and gas recovery. In the presented architecture, a hybrid-boost MMC with a reduced number of semiconductor devices driving a multiphase Induction Machine (IM) is investigated. The stepped output voltage generated by the MMC reduces or eliminates the filtering requirements. Moreover, the boosting capability of the proposed architecture eliminates the need for bulky low-frequency transformers at the converter output terminals. A detailed illustration of the hybrid-boost MMC operation, the expected limitations/constraints, and the voltage balancing technique are presented. A simulation model of the proposed MV hybrid-boost MMC-based five-phase IM drive has been built to investigate the system performance. Finally, a downscaled prototype has been constructed for experimental verification.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.8
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• pp.1004-1010
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• 2019

In the EH-WSN (Energy harvesting wireless sensor network), a MAC (medium access control) protocol is required to select a relay node considering the power status of a node. Existing EH-WSN studies emphasize the power aspect, so it does not consider the QoS like the urgency of the sensed data. The required power and transmission delay must be changed according to the urgency so that the medium access control according to the data QoS can be performed. In case of relay node, relaying data without consideration of data urgency and node power may cause delay due to power shortage in case of urgent data. In this paper, we designed a MAC protocol that minimizes the power shortage that can occur during emergency data generation. For this, relay node requirements are set differently according to the urgency of data. The performance was analyzed through simulation. Simulation results show the reduced latency and improved reliability of urgent data transmission.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.776-781
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• 2001

To enhance thermal efficiency of thermal facility through recovery of low and medium temperature waste heat, 1MW organic Rankine cycle system was designed and developed. The exhaust gases of $175^{\circ}C$ at two 100MW power plants in pohang steel works were selected as the representative of low and medium temperature waste heat in industrial process for the heat source of the organic Rankine cycle system. HCFC-123, a kind of harmless refrigerant, was chosen as the working fluid for Rankine cycle. The organic Rankine cycle system with selected exhaust gases and working fluid was designed and constructed. From the operation, it was confirmed that the organic Rankine cycle system is available for low and medium temperature waste heat recovery in industrial process. The optimum operating manuals, such as heat-up of hot water, turbine start-up, and the process of electric power generation, were derived. However, electric power generated was not 1MW as designed but only 670kW. It is due to deficiency of pump capacity for supply of HCFC-123. So it is necessary to increase the pump capacity or to decrease the pressure loss in pipe for more improved HCFC-123 supply.

• Journal of Power System Engineering
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• v.16 no.4
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• pp.17-23
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• 2012

In this study, the numerical simulation and basin model test have been performed to evaluate sea worthiness and resistance performance for a small pre-planning three type of leisure boats which are U, V, Y shapes of hull forms. As a well known commercial CFD code, Maxsurf, was applied for modeling hull forms used as the solver of motion analysis. Also the model resistance test was carried out to estimate the effective power of boat in the basin tank. Numerical simulation and model test results show that Y-shaped hull is better than the other types in terms of heave and pitch motion, having a key effect on a boat sea worthiness. But V-type hull is more efficiency than others cases in resistance performance.