• Journal of Power Electronics
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• v.13 no.5
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• pp.841-853
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• 2013

An application of doubly-fed induction generator (DFIG), which is one of adjustable speed generators, to a gas engine cogeneration system has been investigated. To operate during a blackout as an emergency power supply is one of important roles for the gas engine cogeneration system. However, the DFIG requires initial excitation for startup during a blackout because the DFIG has no excitation source. In this paper, we propose the "blackout start" as a new excitation method to generate a rated voltage at the primary side during a blackout. In addition, a stand-alone operation following a blackout has been investigated by using experimental setup with a real gas engine. Power flows in the generating set with the DFIG at the stand-alone operation have been investigated experimentally. Experimental investigation of the power flow suggests that the generating set with DFIG has optimal speed in minimizing whole system losses.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.3
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• pp.410-425
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• 1997

Buildings are mostly under part load conditions causing an inefficient system operation in terms of energy consumption. It is critical to operate building air-conditioning system with a scientific or optimal manner which minimizes energy consumption and maintains thermal comfort by matching building sensible and latent loads. Little research has been performed in developing general methodologies for the optimal operation of air-conditioning system. Based on this research motivation, system simulation program was developed by adopting various equipment operating strategies which are energy efficient especially for humidity control in summer. A numerical optimization technique was utilized to search optimal solution for multi-independent variables and then linked to the developed system simulation model within a mam program. The main goal of the study is to provide a systematic framework and guideline for the optimal operation of air-conditioning system focusing on air-side. For given cooling loads and ambient outdoor conditions the optimal operating strategies of a commercial building are determined by minimizing a constrained objective function by a nonlinear programming technique. Desired space setpoint conditions were found through evaluating the trade-offs between comfort and system power consumption. The results show that supply airflow rate and compressor fraction play main roles in the optimization process. It was found that variable setpoint optimization technique could produce lower indoor humidity level demanding less power consumption which will be benefits for building applications of humidity problem.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.1002-1007
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• 2009

The research are performed to check the characteristics of the ice slurry transport system for the district cooling. The system are installed at the 1st floored building which is as large as the $1204\;m^2$ ($86\;m{\times}14\;m$). Three kinds of heat exchanger are selected, such as, plate, spiral and shell & tube type, to apply to the ice slurry systems. Experiment was done in the two cases. The first case, circulation water flow fixed at the design conditions for the state to change the flow of the supply of ice slurry. The second case, Ice slurry flow fixed at the design conditions for the state to change the flow of circulation water. Both side of Energy balance was calculated. The performance of plate heat exchanger is higher than others and it's enthalpy effectiveness is higher too.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.2 no.2
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• pp.93-103
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• 1979

As principles of our country's Business Enterprises Account are being developed, Customs of Business Enterprises Account are in the state of change and then Principles of that are in revision. According to systematizing contents of such a principle of Business Enterprises Account, having made an analysis and Investigation from versatile situation, I can deprive of the following conclusions from above facts. 1. The prelude of a general principle involves compulosory character like a forced law rather than a theoretical teaching of original character. 2. Because of making much of supply of account information, To make mistakes, emphasis on function of an information, on the other side, being apt to disregard control function of original account. 3. There is no such a mutual relation as theoretical systematic form among general rule, a profit-and-loss account, balance sheet and drawing principle. These rules which don't form gradual structure are prescribed respectively according to business like necessity. 4. An overall contents of account principle are regarded as principle near financial account rather than the Pivot of administration account. In the future, The whole academic world of account and business practice should become the idealistic account principle with lots of study and effort.

• Health Policy and Management
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• v.24 no.1
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• pp.4-12
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• 2014

Background: The purpose of this study is to investigate current status and investigation of government agencies, communities, corporates, hospitals, non-governmental organization, non-profit organization, and so on which performed Corporate Social Responsibility to global health issues. Methods: This paper focuses on analyzing definition and principle of public-private partnership (PPP), types of PPP, challenge of PPP through delphi survey and interview which need to be discussed by professional groups such as private groups, universities and researches, government decision makers, corporates, and hospitals for successful PPP. Results: Based on this analysis on global health issues of 237 groups, the results were shown that main global health issues of many hospitals were aids of the developing countries (48%). Main program was activities of overseas volunteers (30%) and most 152 groups (42%) supported Asia. Also, this paper gives a definition of PPP that is the growth together in PPPs as a way of fulfilling public tasks in partnership between the state administration and private enterprises to apply both strengths behind transparency, accountability. Conclusion: In conclusion, from the results of analysis, we suggest as prior setting of global issues for both demand and supply side and are served as the effective way by PPP on global health issues. Moreover, this study will be expanded on the sections of findings, multiple researches, discussion, and policy recommendations.

• Korean Journal of Occupational Health Nursing
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• v.22 no.2
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• pp.83-92
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• 2013

Purpose: This study was to compare job stress and job satisfaction between ward nurses and outpatient nurses, and to identify the correlation between job stress and job satisfaction. Methods: The subjects of this study were 200 ward nurses and 85 outpatient nurses in G and I University Hospital in Incheon. The data were collected in March 2010 and analyzed with t-test and Pearson correlation coefficient. Results: There was no significant difference in overall job stress between two groups, but slightly higher stress level for ward nurses. In sub-area of job stress, 'nursing duty' was primary for both groups. And in 'nursing duty' (t=2.05, p=.041), 'conflict with patients' (t=2.73, p= .007), and 'working environment' (t=3.37, p<.001) ward nurses showed significant higher level of stress than outpatient nurses. For job satisfaction, outpatient nurses showed higher level significantly (t=-2.98, p=.003). And both groups of nurses' job satisfaction was negatively correlated with job stress significantly (r=-.31, p<.001). Conclusion: It will be possible to reduce job stress and promote job satisfaction level for both groups of nurses by adding staffs, and specifically for ward nurses by improving facilities for relax and appropriate supply, and for outpatient nurses by managing interpersonal stress and reducing side tasks.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.10
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• pp.1225-1231
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• 2014

This paper presents the performance characteristic of a Francis hydro turbine with an inline casing. This turbine is designed for city water supply system. Due to large changes in ground elevation with high points and low points, some systems may experience larger-than-normal required pressures in areas with low ground elevations. One way to dissipate these excess pressures is by the use of an inline-turbine instead of an inline-pressure reducing valve. For best applicability and minimal space consumption, the turbine is designed with an inline casing instead of the common spiral casing. As a characteristic of inline casing, the flow accesses to the runner in the radial direction, showing a low efficiency. The installation of vanes improves the internal flow and gives the positive encouragement to the output power. For the power transmission to the outside of the turbine casing from the runner axis, a belt passage is designed in the inline casing, as its influence, the region after the belt passage shows a relatively low output power. The clearance gap in the runner side space is considered, in which a small volume of flow is contracted into the clearance gap, forming the leakage flow. The leakage flow leads to a decrease in the efficiency.

• Proceedings of the KIPE Conference
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• 1998.10a
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• pp.724-729
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• 1998

In general, a single-phase current-fed PWM inverter using IGBTs has some unique advantages for small scale distributed utility-interactive power supply system as compared with voltage-fed PWM inverter. In particular, this is more suitable and acceptable for a non-isolated type utility-interactive power conditioner, which is going to be widely used for residential solar photovoltaic (PV) power generation system in Japan. However, this current-fed PWM inverter has a significant disadvantage. The output current of this inverter includes large harmonic contents when the inductance of smoothing reactor in its DC side is not large enough to eliminate its current ripple components of this inverter. In order to overcome this problem, a new conceptual pulse area modulation scheme for this inverter is introduced in difference with conventional PWM strategy. This paper presents a new effective control implementation of this PV power conditioner which is able to reduce the harmonic component in the output current produced by the single-phase current-fed PWM inverter even when the ripple current in the smoothing DC reactor is relatively large. The operating principle of the proposed control strategy introdued for this inverter system is described, and its simulation results are evaluated and discussed herein.

• Journal of Power Electronics
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• v.16 no.2
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• pp.786-797
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• 2016

This paper describes the design and development of a novel semiconductor-based solid-state switch for damped oscillating voltage test system. The proposed switch is configured as two identical series-connected switch stacks, each of which comprising 10 series-connected IGBT function units. Each unit consists of one IGBT, a gate driver, and an auxiliary voltage sharing circuit. A single switch stack can block 20 kV-rated high voltage, and two stacks in series are proven applicable to 30 kV-rated high voltage. The turn-on speed of the switch is approximately 250 ns. A flyback topology-based power supply system with a front-end power factor correction is built for the drive circuit by loosely inductively coupling each unit with a ferrite core to the primary side of a power generator to obtain the advantages of galvanic isolation and compact size. After the simulation, measurement, and estimation of the parasitic effect on the gate driver, a prototype is assembled and tested under different operating regimes. Experimental results are presented to demonstrate the performance of the developed prototype.

• Journal of Electrical Engineering and Technology
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• v.6 no.3
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• pp.293-301
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• 2011

This paper presents a novel theoretical method based on power analysis to obtain voltage reference values for an inverter-based compensator. This type of compensator, which is installed in parallel with the load, is usually referred to as the active filter. The proposed method is tailored to design the compensator in such a way that it can simultaneously balance the asymmetric load, as well as correct the power factor of the supply side. For clarity, a static compensator is first considered and a recursive algorithm is utilized to calculate the reactance values. The algorithm is then extended to calculate voltage reference values when the compensator is inverter based. It is evident that the compensator would be asymmetric since the load is unbalanced. The salient feature associated with the proposed method is that the circuit representation of system load is not required and that the load is recognized just by its active and reactive consumptions. Hence, the type and connection of load do not matter. The validity and performance of the new approach are analyzed via a numerical example, and the obtained results are thoroughly discussed.