• Journal of Electrical Engineering and Technology
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• v.11 no.2
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• pp.309-319
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• 2016

This paper presents a new recognition and classification method for power quality (PQ) disturbances on the basis of pattern linguistic values. This method solves the difficulty of recognizing disturbances rapidly and accurately by using fuzzy logic. This method uses classification disturbance patterns to define the linguistic values of fuzzy input variables and used the input variables of corresponding disturbance pattern to set membership functions. This method also sets the fuzzy rules by analyzing the distribution regularities of the input variable values. One characteristic of this method is that the linguistic values of fuzzy input variables and the setting of membership functions are not only related to the input variables but also to the character of classification disturbance and the classification results. Furthermore, the number of fuzzy rules is equal to the number of disturbance patterns. By using this method for disturbance classification, the membership function and design of fuzzy rules are directly related to the objective of classification, thus effectively reducing the complexity of the design process and yielding accurate classification results. The classification results of the simulation and measured data verify the feasibility and effectiveness of this method.

• Progress in Superconductivity
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• v.6 no.1
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• pp.46-51
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• 2004

We fabricated a resistive type superconducting fault current limiter (SFCL) of 3-phase $6.6 kV_{rms}$ / rating, based on YBCO thin films grown on sapphire substrates with a diameter off inch. Each element of the SFCL was designed to have the rated voltage of $600 V_{rms}$ $/35A_{rms}$. The elements produced a single phase with 8${\times}$6 components connected in series and parallel. In addition, a NiCr shunt resistor of 23 $\Omega$ was connected in parallel to each of them for simultaneous quenches between the elements. Prior to investigating the performance of the 3 phase SFCL, we examined the quench characteristics for 8 elements connected in series. For all elements, simultaneous quenches and equal voltage distribution within 10% deviation from the average were obtained. Based on these results, performance of the SFCL for single line-to-ground faults was investigated. The SFCL successfully limited the fault current of $10 kA_{ rms}$ below 816 $A_{peak}$ within 0.12 msec right after the fault occurred. During the quench process, average temperature of all components did not exceed 250 K, and the SFCL was totally safe during the whole operation.

• The Transactions of the Korean Institute of Power Electronics
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• v.9 no.4
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• pp.334-340
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• 2004

In this paper, an efficient switching pattern to equalize the size of transformer is proposed for a multi-level inverter employing cascaded transformers. It is based on the prior selected harmonic elimination PWM(SHEPWM) method. Because the maximum magnetic flux imposed on each transformer becomes exactly equal each to each, all transformers can be designed with the same size regardless of their position. Therefore, identical full-bridge inverter units can be utilized, thus improving modularity and manufacturability. The fundamental idea of the proposed switching pattern is illustrated and then analyzed theoretically. The validity of the proposed switching strategy is verified by experimental results.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.4
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• pp.417-426
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• 2010

This paper describes the 6-way power divider to be used as a feeding structure of the waveguide array antenna generating the plane wave at the near distance. The SMA connector has been connected at the center of the power divider in order to feed the radiating element. The six output ports made of waveguide are positioned on the peripheral of the divider. This paper proposes the method utilizing the inductive post in order to decrease the return loss. The height of the feeding pin, the diameter of the inductive post, and the distance between the feeding pin and inductive post have been investigated, and as a result, the power divider has been optimized. The simulated and measured results show the low return loss of about -40 dB. The calculated and measured transmission coefficients are -7.78 dB and -8.06 dB, respectively. The output power of the six waveguide port show equal-amplitude and equal-phase distribution. Since the power divider proposed in this paper can be expanded to the divider having several output ports, it could be easily applied to the various array antennas.

• Journal of Distribution Science
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• v.9 no.4
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• pp.63-73
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• 2011

The relationship between buyers and sellers is changing into a long-term relationship. A number of distribution channel researchers have determined that the behavior of distribution channel members can be characterized by relational exchanges. The members of relational distribution channels may be perceived as strategic partners; however, even within these arrangements, member asymmetries may exist, which can create unequal distributions of power and dependence. Thus, as all distribution channel members may not be equal in power, it is possible that a less-dependent channel leader may emerge. Therefore, leadership in distribution channels is a very important variable. Distribution channel leadership can be defined as the activities undertaken by the distribution channel leader to influence the marketing programs and strategies of channel members. A distribution channel's performance is influenced by the leadership style of the channel leader. Although research on channel leadership styles can be broadly categorized, many researchers have dealt with analyzing distribution channel leadership by using the power-influence approach, which includes looking at variables, such as power, power base, and influence strategies. Moreover, they have examined the direct relationship between leadership styles and performance. Many distribution channel scholars have attempted to justify the application of leadership styles identified in alternative leadership theories to the inter-organizational context of distribution channels. They have made suggestions regarding how great the usefulness of leadership style as a strategy is to secure the compliance of distribution channel members and have conceptually and empirically linked it to channel-related phenomena, such as manifest conflict, cooperation, channel efficiency, and effectiveness. However, as few empirical studies have examined the antecedents and consequences of leadership styles, research on leadership style can be considered nascent. Thus, it is required to investigate the antecedents and consequences of the leadership style of a distribution channel leader. This study aims to empirically identify whether there are influences of the antecedents of leadership on two different leadership styles, and to reveal whether these leadership styles induce any consequences. The research subjects were 220 franchisees. Research findings are as follows: First, the results show a positive effect of technological capability on transformational relationships. However, it does not have a significant effect on transactional leadership. Second, innovation-oriented organizational culture has negatively influenced both leaderships. However, task-oriented organizational culture positively and significantly influenced both forms of leadership. Third, the ethics of leaders has influenced both leadership styles positively and significantly. Fourth, regarding consequences, transformational leadership strengthens financial performances, whereas it weakens relational citizenship behaviors. However, transactional leadership positively influences relational citizenship behavior whilst negatively affecting financial performance.

• Journal of Power Electronics
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• v.14 no.2
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• pp.271-281
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• 2014

Fluctuating wind conditions necessitate the use of a variable speed wind turbine (VSWT) with a AC/DC/AC converter scheme in order to harvest the maximum power from the wind and to decouple the synchronous generator voltage and frequency from the grid voltage and frequency. In this paper, a combination of a three phase diode bridge rectifier (DBR) and a modified topology of the diode clamped multilevel inverter (DCMLI) has been considered as an AC/DC/AC converter. A control strategy has been proposed for the DCMLI to achieve the objective of grid interface of a wind power system together with local load compensation. A novel fixed frequency current control method is proposed for the DCMLI based on the level shifted multi carrier PWM for achieving the required control objectives with equal and uniform switching frequency operation for better control and thermal management with the modified DCMLI. The condition of the controller gain is derived to ensure the operation of the DCMLI at the fixed frequency of the carrier. The converter current injected into the distribution grid is controlled in accordance with the wind power availability. In addition, load compensation is performed as an added facility in order to free the source currents being fed from the grid of harmonic distortion, unbalance and a low power factor even though the load may be unbalanced, non-linear and of a poor power factor. The results are validated using PSCAD/EMTDC simulation studies.

• Journal of electromagnetic engineering and science
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• v.8 no.2
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• pp.59-63
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• 2008

The adaptive symbol selection scheme(ASSS) is popular in reducing peak to average power ratio(PAPR) for orthogonal frequency division multiplexing(OFDM) signals. The probability density function(pdf) of the samples' amplitudes of the adaptively selected OFDM signal without over-sampling has been considered to be approximately equal to the Rayleigh pdf. In this paper, we derive a more precise pdf which shows the relationship between the probability distribution of the samples' amplitudes and the number of the candidate symbols for ASSS. Using the newly derived pdf in the theoretical analysis, more accurate calculation results can be obtained.

• Proceedings of the KIEE Conference
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• 2000.07a
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• pp.513-515
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• 2000

This paper deals with a method for determining an optimal operation strategy of dispersed generating sources considering thermal merits. The optimal operation of these sources can be determined by the principle of equal incremental fuel cost. This paper presents an optimal operation strategy using the Kuhn-Tucker's optimal conditions and also an priority method to decide the optimal location of those sources in power systems. The validity of the proposed algorithms are demonstrated using a model system.

• Journal of Electrical Engineering and Technology
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• v.11 no.3
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• pp.543-550
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• 2016

The Active Superconducting Current Controller (ASCC) is a new type of Superconducting Fault Current Limiters (SFCL) which can limit the fault current in different modes. It also has the particular abilities of compensating active and reactive powers for electrical networks. In this paper, it is confirmed that the performance of ASCC in different operating modes introduces a limiting impedance in series with the network which can even degrade the transient stability and the operation of the Over-Current Relays (OCR) employed in a power system. In addition, the model of a three-phase ASCC is simulated, and the effect of descriptive modes on the current limiting level is investigated. For the transient stability analysis, a single machine-infinite bus system is tested, and the effect of operation modes is studied based on an equal area criterion obtaining the critical time and the critical angle. Modifying the setting parameters of OCR such as time dial and pick-up current, the protective coordination is also studied in different operating modes.

• Journal of Electrical Engineering and Technology
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• v.7 no.6
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• pp.977-982
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• 2012

In order to find out partial discharge (PD) phenomena in the cable joint due to the poor workmanship during the installation, the relationship between PD inception voltages and joint defects was investigated. For the purpose, in the joint of 22.9kV CNCV cables, electric fields were calculated for various semiconductive layer wrong positioning (WP) defects. And, PDIV were investigated through the experiments and compared with the results of electric field analysis. In all WP defect cases, the PD inception field calculated using measured PDIVs was similarly shown to be the average value of 1.84kV/mm. In addition, the calculated PDIV and the measured PDIV were almost equal, from the PDIV calculation using maximum electric fields and the measured PDIV for the normal case. Throughout this study, it is possible to analyze WP defects due to the poor workmanship and to establish better joint design for the distribution grade extruded cable system.