• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제54권9호
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• pp.403-407
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• 2005

Most of the loads in industrial power distribution systems are balanced and connected to three power systems. However, voltage unbalance is generated at the user's 3-phase 4-wire distribution systems with single & three phase. Voltage unbalance is mainly affected by load system rather than power system. Unbalanced voltage will draws a highly unbalanced current and results in the temperature rise and the low output characteristics at the machine. It is necessary to analyse correct voltage unbalance factor for reduction of side effects in the industrial sites. Voltage unbalance is usually defined by the maximum percent deviation of voltages from their average value, by the method of symmetric components or by the expression in a more user-friendly form which requires only the three line voltage readings. If the neutral point is moved by the unbalanced load at the 3-phase 4-wire system. Line and phase voltage unbalance leads to different results due to zero-sequence component. So that it is difficult to analyse voltage unbalance factor by the conventional analytical method, This paper presents a new analytical method for phase and line voltage unbalance factor in 4-wire systems. Two methods indicate exact results.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2018년도 추계학술대회
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• pp.86-88
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• 2018

The three level(3L) neutral point clamped (NPC) voltage source converter (VSC) topology is widely used for grid interface in high power wind energy due to its superior performance as compared to the two level(2L) VS. However, one of the major drawbacks of this topology is the unequal dispersion of loss and therefore the junction temperature among the power devices. The 3L ANPC topology derived from the NPC topology was proposed to resolve this drawback of unequal loss profile of 3L NPC. The 3L ANPC can work under various switching strategies. In this paper a comparative study of the various switching strategies of 3L ANPC using the recently developed 10kV IGCTs which has the capability to raise the current and voltage rating of the wind turbines is carried out. The comparison is performed using ABB make 10kV IGCT 5SHY17L9000 and PLECs simulations.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2005년도 춘계학술대회논문집
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• pp.74-77
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• 2005

Most of the loads in industrial power distribution systems are balanced and connected to three power systems. However, voltage unbalance is generated at the user's 3-phase 4-wire distribution systems with single & three phase. Voltage unbalance is mainly affected by load system rather than power system. Unbalanced voltage will draws a highly unbalanced current and results in the temperature rise and the low output characteristics at the machine. It is necessary to analyse correct voltage unbalance factor for reduction of side effects in the industrial sites. Voltage unbalance is usually defined by the maximum percent deviation of voltages from their average value, by the method of symmetrical components or by the expression in a more user-friendly form which requires only the three line voltage readings. If the neutral point is moved at the 3-phase 4-wire system by the unbalanced load, by the conventional analytical method, line and phase voltage unbalance leads to different results due to zero-sequence component. This paper presents a new analytical method for phase and line voltage unbalance factor in 4-wire systems. Two methods indicate exact results.

• Journal of Power Electronics
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• 제16권5호
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• pp.1773-1780
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• 2016

This paper proposes a wide air-gap control method for the multi-module permanent magnet linear synchronous motor (MM-PMLSM) based on independent vector control. In particular, the MM-PMLSM consists of symmetrical multi-module and multi-phase structures, which are basically three-phase configurations without a neutral point, unlike conventional three-phase machines. In addition, there are no additional magnetic levitation windings to control the normal force of the air-gap between each stator and mover. Hence, in this paper, a dq-axis current control applying a d-q transformation and an independent vector control are proposed for the air-gap control between the two symmetric stators and mover of the MM-PMLSM. The characteristics and control performance of the MM-PMLSM are analyzed under the concept of vector control. As a result, the proposed method is easily implemented without additional windings to control the air-gap and the mover position. The effectiveness of the proposed independent vector control algorithm is verified through experimental results.

• Journal of Power Electronics
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• 제19권1호
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• pp.146-157
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• 2019

The inverter is an essential part of permanent magnet synchronous motor (PMSM) drive systems. The performance of an inverter is greatly influenced by its modulation strategy. Using a proper management of modulation strategies can guarantee high performance from a PMSM under various speed conditions. Switching between modulations is a pivotal technique that determines the performance of a PMSM. Most works on hybrid methods focus on two-level induction motors drive systems. In this paper, in order to improve the performance of PMSMs under various speed conditions, a hybrid method of a pulse width modulation (PWM) control scheme based on a neutral-point-clamped (NPC) three level topology was proposed. This hybrid PWM modulation comprised space vector PWM (SVPWM) and selective harmonic elimination PWM (SHEPWM). Under low speed conditions, the SVPWM is employed to cause the PMSM to start smoothly, and to obtain a rapid response from the control system. Under high speed conditions, the SHEPWM is employed to reduce the switching frequency and to eliminate particular current harmonics. Moreover, the harmonic characteristics of different modulations are analyzed to obtain a smooth transition between the SHEPWM and the SVPWM. Experimental and simulation results indicated the effectiveness of the proposed control method.

• 한국철도학회논문집
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• 제19권5호
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• pp.617-628
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• 2016

본 논문은 철도차량의 추진용 유입식 변압기 및 AC/DC 컨버터를 대체하기 위한 지능형 변압기의 구조를 제안한다. 제안된 지능형 변압기는 반도체 스위칭 소자 및 고주파 변압기를 사용한 양방향 전력 변환 컨버터의 형태로써, 기존 변압기에 비해 경량화 되고, 역률 제어 등의 능동적인 제어 성능으로 인해 단상 계통 전원의 효율적인 활용을 가능하게 한다. 제안하는 지능형 변압기는 60Hz 교류 고전압을 직류 고전압으로 변환하기 위한 정류단으로 Neutral point clamped type 의 H-bridge 컨버터를 여러 개 직렬 연결해 구성했다. 직류로 변환된 입력단 전력은 고주파 변압기와 Neutral point clamped type H-bridge 컨버터 2개로 구성된 Dual-Active-Bridge 컨버터를 이용해 출력측에 필요한 저전압을 공급할 수 있도록 했다. 또한, 본 논문에서는 다수의 컨버터 모듈 내부 직류단 전압을 균형제어하며, 단상 교류 전원에서 직류 출력 전원간의 양방향 전력 제어를 가능하게 하는 제어 알고리즘을 제안한다. 제안한 지능형 변압기의 구조 및 제어 시스템은 75kVA 급 3.3kVrms 입력, 750VDC 출력의 지능형 변압기를 설계 및 회로 시뮬레이션 결과를 통해 검증했다.

• 전기전자학회논문지
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• 제26권2호
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• pp.265-270
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• 2022

본 논문에서는 정지 좌표계 dq-축 전류를 기반으로 하는 비대칭 6상 PMSM의 스위치 개방 고장 검출 알고리즘을 제안한다. 본 논문에서의 해당 모터는 2개의 3상 권선이 30°의 전기적 위상차를 갖고 중성점이 분리된 비대칭 구조를 갖는다. 따라서 듀얼 3상 PWM 인버터와 스위치 개방 고장으로 인한 검출기법이 반드시 필요하다. 본 논문에서는 비대칭 6상 PMSM을 구동하기 위해 듀얼 dq축 전류 제어 방식을 사용하며 전역 통과 필터와 저역 통과 필터를 사용해 전류 변동을 감지하여 개방 고장이 발생한 스위치를 검출하는 방식을 제안한다. 제안한 방법의 효과와 유용성은 여러 실험을 통해 검증하였다.

• Journal of Power Electronics
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• 제15권1호
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• pp.190-201
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• 2015

This paper uses the switching function approach to present a simple state model of the Vienna-type rectifier. The approach introduces the relationship between the DC-link neutral point voltage and the AC side phase currents. A novel direct power control (DPC) strategy, which is based on the sliding mode control (SMC) for Vienna I rectifiers, is developed using the proposed power model in the stationary ${\alpha}-{\beta}$ reference frames. The SMC-based DPC methodology directly regulates instantaneous active and reactive powers without transforming to a synchronous rotating coordinate reference frame or a tracking phase angle of grid voltage. Moreover, the required rectifier control voltages are directly calculated by utilizing the non-linear SMC scheme. Theoretically, active and reactive power flows are controlled without ripple or cross coupling. Furthermore, the fixed-switching frequency is obtained by employing the simplified space vector modulation (SVM). SVM solves the complicated designing problem of the AC harmonic filter. The simplified SVM is based on the simplification of the space vector diagram of a three-level converter into that of a two-level converter. The dwelling time calculation and switching sequence selection are easily implemented like those in the conventional two-level rectifier. Replacing the current control loops with power control loops simplifies the system design and enhances the transient performance. The simulation models in MATLAB/Simulink and the digital signal processor-controlled 1.5 kW Vienna-type rectifier are used to verify the fast responses and robustness of the proposed control scheme.

• 비교문화연구
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• 제29권
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• pp.25-53
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• 2012

The attitude of observer in the painting of history is to exclude a prejudice and a subjective view of an artist and to introduce a photograph, which is a record of objectivity, in the process of painting. Its ultimate intent is to redescribe the fact of an event's image intactly without any prejudice and to represent the event as a proven evidence that it was. The representation of history based on fact had already been conceived in imagination of renowned artists such as Francisco Goya or $Th{\acute{e}}odore$ $G{\acute{e}}ricault$ even before cameras were invented. What they portrayed was their own truth of reality which is gained through their observation, not a history that have corresponded to political ideologies, for all reliance on a limited tool of representation, painting. Furthermore, history was necessary for 19th century impressionism artists to be represented under proven fact in a neutral perspective excluding all subjective prejudice, not based on the representation with imagination. Edouard Manet in particular reconstited an instant moment on the basis of real proof of photograph without personal prejudice or opinion as if today's photojournalism. The catastrophic series by Andy Warhol and the photographic painting by Gerhard Richter show another role of painting in the realm of art, each of them implying information distortion and abuse by current media and intentional deformation toward history as Manet's painting of history. Today, the representation of an historical event that we experience in the era of the Internet and social networks having a great deal of information already came to be the exclusive property of the cutting edge mass media. Nevertheless, the attitude of observer which is realistic and contemplative in the realm of art is the crucial point in terms of artists' act as ever.

• Journal of Power Electronics
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• 제13권6호
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• pp.939-954
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• 2013

The Direct Torque Control (DTC) technique for Permanent Magnet Synchronous Motors (PMSM) is receiving increased attention due to its simplicity and robust dynamic response when compared with other control techniques. The classical switching table based DTC results in large flux and torque ripples in the motors. Several studies have been reported in the literature on classical DTC. However, there are only limited studies that actually discuss or evaluate the classical DTC. This paper proposes, novel switching table / DTC methods for PMSMs to reduce torque ripples. In this paper, two DTC schemes are proposed. The six sector and twelve sector methodology is considered in DTC scheme I and DTC scheme II, respectively. In both DTC schemes a simple modification is made to the classical DTC structure. The two level inverter available in the classical DTC is eliminated by replacing it with a three level Neutral Point Clamped (NPC) inverter. To further improve the performance of the proposed DTC scheme I, the available 27 voltage vectors are allowed to form different groups of voltage vectors such as Large - Zero (LZ), Medium - Zero (MZ) and Small - Zero (SZ), where as in DTC scheme II, all of the voltage vectors are considered to form a switching table. Based on these groups, a novel switching table is proposed. The proposed DTC schemes are comparatively investigated with the classical DTC and existing literatures through theory analysis and computer simulations. The superiority of the proposed DTC method is also confirmed by experimental results. It can be observed that the proposed techniques can significantly reduces the torque ripples and improves the quality of current waveform when compared with traditional and existing methods.