• The Transactions of the Korean Institute of Power Electronics
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• v.26 no.2
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• pp.82-89
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• 2021

This study proposes a DAB two-stage series structure with insulated bidirectional DC-DC converter for two-way power transfer between the renewable energy of high voltages (1 kV and above). The proposed circuit transforms the existing DAB converter into a two-stage series structure to reduce the pressure in the switch. The problem of power imbalance occurring in the design of the DAB converter second-stage series is improved by applying the cell balancing method circuit and the common mode coupled inductor using an external flying capacitor instead of reflecting the existing improvement measures, voltage balance control, and inductor current control. In addition, a no-load supercharging sequence is proposed in high voltages and high-speed switching by using the fixed duty output method. This study presents the analysis results through the structure of the proposed circuit, the principle of improving the power imbalance problem, and simulations. Prototypes were manufactured to meet the specifications of input/output voltage of 1700 V, maximum load of 65 kW, and switching frequency of 51kHz, and the validity of the topology was verified using the experimental results and efficiency data.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.3
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• pp.355-360
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• 2012

It is difficult to converge power flow for the power system planning data. The main cause of power flow diverse is reactive power imbalance. A active power could be adjust by ELD or merit order but a reactive power couldn't dispatch before power flow analysis. The lack of reactive power of power system is cause a inadequate voltage drop This paper suggest new reactive power dispatch algorithm using switched shunt admittance. This algorithm uses reactive power sensitivity called switch shunt jacobian. When proposed algorithm applies to real system data that couldn't be conversed in PSS/E the power flow analysis is converged.

• Journal of Korean Ophthalmic Optics Society
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• v.13 no.1
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• pp.95-99
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• 2008

Purpose: Even refractive error is perfectly corrected by glasses power, the glasses wearer can feel imbalance and uncomfortable by prism effects. The purpose of this study was to investigate subjective imbalance to vertical yoked prism in visually normal subjects. Methods: Visually normal 37 subjects (aged 20 to 31 y) were fully corrected by soft contact lens and worn vertical yoked prism, base up and base down 1, 2, 4, 6, 8 prism diopter(pd) at random order. A rating scale questionnaire was administered to assess quantitatively subjective imbalance to the yoked prism. The near phoria tests were done using Howell-Kim phoria card at 40 cm distance. Results: For the subjective response of imbalance, base up yoked prism was higher than base down yoked prism (t-test: t=4.67, p=0.00) in over 2 prism diopters. The frequency of subjects who feel imbalance by base up vertical yoked prism is higher for near esophoric group than for exophoric group. Conclusions: To reduce subjective imbalance caused by glasses such as dizzy, it needs to make the minimum prism effect, and base down yoked prism is more effective than base up yoked prism in prism effects.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.11
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• pp.1584-1590
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• 2017

This paper presents a implementation method of reliable speed limitation controller considering motor parameter variation in high speed operation. In spinning process of drum washing machine, speed increase has to be limited when unallowable imbalance mass is detected. Otherwise, severe noise and vibration can happen because noise and vibration are proportional to imbalance mass. To detect imbalance mass, d-axis current magnitude is used. However, we have to compensate for back-emf and power supply variation by means of detecting them because d-axis current is affected by both of them. On the other hand, we have to carefully estimate back-emf because back-emf is affected by stator resistance variation and inverter voltage error. Stator resistance variation can happen by manufacturing process for mass production or temperature variation in running. And there are inverter voltage errors between command voltage from micro-computer to inverter and real voltage from inverter to motor because of rising and falling time delay and turn-on resistance of power semiconductor switch. To solve this problem, we propose 2-step align current injection method which is to inject step-wise current right before starting. By this method, we can simply obtain stator resistance by ratio of voltage without inverter voltage error and current, and we can measure inverter voltage error. So we can obtain more exact model current, and then by simple calculation with compensation gain, we can estimate more accurate motor back-emf. We show that this method works well. It is verified through experiments.

• The Transactions of the Korean Institute of Power Electronics
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• v.22 no.1
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• pp.9-17
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• 2017

A parallel control algorithm of thyristor dual-converter power system for the DC power supply of railway is proposed. The circulating current and current imbalance generated during parallel operation can be limited to control the output voltage of each power system by using the proposed parallel control algorithm. The proposed control algorithm can also eliminate output current sensor to achieve the same output response without additional costs. The validity of the proposed algorithm is verified through simulation and experiment.

• Journal of the Korean Society of Clothing and Textiles
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• v.36 no.1
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• pp.56-67
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• 2012

This research investigates the effect of the antecedents (i.e. specific investment, opportunistic behavior, communications, uncertainty, interdependence, power imbalance, shared value, and flexibility) that influence the trust and commitment of domestic apparel manufacturers toward contractors as well as the effect of trust and commitment on firm performance and relationship satisfaction. A total of 128 apparel manufactures participated in this study. Factor analysis, Cronbach's alpha coefficient, and path analysis were conducted for the statistical analysis. Specific investment, communication, shared value, and flexibility had a positive effect on trust; however, opportunistic behavior had a negative effect. Interdependence, shared value, and flexibility had a positive effect on commitment; however, power imbalance and uncertainty had a negative effect. Trust did not exert an effect on commitment in this research; however, trust and commitment had a positive effect on firm performance; in addition, trust and commitment had a positive effect on relationship satisfaction. The findings offer insight on how to better manage apparel manufacturer-contractor relationships to ensure success.

• The Transactions of the Korean Institute of Power Electronics
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• v.20 no.1
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• pp.19-30
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• 2015

A static synchronous compensator (STATCOM) applied to rapidly changing, highly unbalanced loads such as electric arc furnaces (EAFs), requires both positive-sequence and negative-sequence current control, which indicates fast response characteristics and can be controlled independently. Furthermore, a delta-connected STATCOM with cascaded H-bridge configuration accompanying multiple separate DC-sides, should have high performance zero-sequence current control to suppress a phase-to-phase imbalance in DC-side voltages when compensating for unbalanced load. In this paper, actual EAF data is analyzed to reflect on the design of current controllers and a pioneering zero-sequence current controller with a superb transient performance is devised, which generates an imaginary -axis component from the presumed response of forwarded reference. Via simulation and experiments, the performance of the positive, negative, and zero-sequence current control of a cascaded H-bridge STATCOM for EAF is verified.

• Journal of Power Electronics
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• v.9 no.2
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• pp.215-223
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• 2009

A design methodology for transformers including integrated and center-tapped structures for LLC resonant converters is proposed. In the LLC resonant converter, the resonant inductor in the primary side can be merged in the transformer as a leakage inductance. And, the absence of the secondary filter inductor creates low voltage stress on the secondary rectifiers and is cost-effective. A center-tapped structure of the transformer secondary side is widely used in commercial applications because of its higher efficiency and lower cost than full-bridge structures in the rectifying stages. However, this transformer structure has problems of resonance imbalance and transformer inefficiency caused by leakage inductance imbalance in the secondary side and the position of the air-gap in the transformer, respectively. In this paper, gain curves and soft-switching conditions are derived by first harmonic approximation (FHA) and operating circuit simulation. In addition, the effects of the transformer including integrated and center-tapped structures are analyzed by new FHA models and simulations to obtain an optimal design. Finally, the effects of the air-gap position are analyzed by an electromagnetic field simulator. The proposed analysis and design are verified by experimental results with a 385W LLC resonant converter.

• Korean Journal of Health Education and Promotion
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• v.31 no.1
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• pp.57-70
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• 2014

Objectives: The purpose of this study was to build a conceptual framework of bullying in nursing workplace. Methods: A comprehensive literature review was conducted to identify concepts in relation to bullying in nursing workplace by searching research articles published between 1995 and 2013. In-depth interviews were performed with 14 nurses who experienced bullying at work. The Hybrid Model was applied for concept analysis which led to identify attributes of bullying in nursing workplace. Results: The antecedents of bullying in nursing workplace were offenders, victims, and administrators. They create negative effects on organizational culture and imbalance of power between authority and subordinate workers in the organization. Bullying in nursing workplace that occurred in the forms of inefficient organizational culture, imbalance of power, and the vulnerability of individual or individuals and groups of individuals formed an unstable dynamic. It is expressed as verbal and nonverbal bullying, work-related bullying, and external threats. Consequently, workplace bullying causes physical and psychological withdrawal and increased negative energy in an organization. Conclusions: Workplace bullying consisted of verbal abuse, alienation, unreasonable work processes, restriction on work-related rights, and external threat.

• Korea Journal of Hospital Management
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• v.25 no.3
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• pp.1-13
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• 2020

Purpose: This study was conducted to identify the conceptual definition and attributes of 'Taeoom' (or workplace bullying) inflicted to newly employed nurses in Korea. Method: Walker & Avant(2011)'s eight-stage process was used to perform a conceptual analysis of 'Taeoom'. Literature review of 40 studies published between Jan. 2009 and March 2018 published in Korea was followed by the in-depth interview with nine newly employed hospital nurses and the ex-post review of results by nursing experts. Findings: 'Taeoom' was associated with five attributes: (1) bullying for no reason, (2) peer rejection for no reason, (3) decreased physical function and psychological withdrawal, and (4) verbal abuse, defamation and nagging, (5) impotent feeling due to power imbalance. Four antecedents found in this study include offensive action, distrust, power imbalance, and undue workload exceeding capacity. As consequences of Taeoom, negative physical and psychological symptoms and turnover intention were increased while nursing performance was decreased. Conclusion: This study suggests the need for more qualitative researches with more comprehensive approach on Taeoom and the development of effective program to improve the organizational culture in nursing field. This study is significant in that it provides a qualitative but comparative review on the attributes, antecedents and consequences of Taeoom through literature review accompanied by focus group interview and expert review.