• Journal of Power Electronics
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• 제18권5호
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• pp.1501-1512
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• 2018

This paper proposes a three-phase three-switch buck-type converter as the MSC of a wind turbine system. Owing to a novel switching modulation scheme that can eliminate the unwanted diode rectifier mode switching state, the proposed system exhibits a satisfying ac voltage and current waveform quality and torque ripple up to the level of a typical current source rectifier even under a wide power factor operating range. The proposed system has been verified through simulations and HILS tests on a PMSG wind turbine model of 5MW/4160V. The proposed converter has been shown to provide a stator current THD of 3.9% and a torque ripple of 1% under the rated power condition. In addition to the inherent advantage of the reduced switch count of three-phase three-switch buck-type converters, the proposed switching modulation technique can make this converter a viable solution for the MSC placed inside of a nacelle, which is under severe volume, weight and mechanical vibration design limits.

• Journal of Power Electronics
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• 제14권3호
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• pp.531-540
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• 2014

A novel carrier-based PWM (CBPWM) strategy of a three-level NPC converter is proposed in this paper. The novel strategy can eliminate the low-frequency neutral point (NP) voltage oscillation under the entire modulation index and full power factor. The basic principle of the novel strategy is introduced. The internal modulation wave relationship between the novel CBPWM strategy and traditional SPWM strategy is also studied. All 64 modulation wave solutions of the CBPWM strategy are derived. Furthermore, the proposed CBPWM strategy is compared with traditional SPWM strategy regarding the output phase voltage THD characteristics, DC voltage utilization ratio, and device switching losses. Comparison results show that the proposed strategy does not cause NP voltage oscillation. As a result, no low-frequency harmonics occur on output line-to-line voltage and phase current. The novel strategy also has higher DC voltage utilization ratio (15.47% higher than that of SPWM strategy), whereas it causes larger device switching losses (4/3 times of SPWM strategy). The effectiveness of the proposed modulation strategy is verified by simulation and experiment results.

• Journal of Power Electronics
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• 제14권3호
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• pp.519-530
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• 2014

A novel simplified pulse width modulation(PWM) strategy for neutral point clamped (NPC) three-level converter is proposed in this paper.The direct output voltage modulation is applied to reduce the calculation time. Based on this strategy, several optimized control methods are proposed. The neutral point potential balancing algorithm is discussed and a fine neutral point potential balancing scheme is introduced. Moreover, the minimum pulse width compensation and switching losses reduction can be easily achieved using this modulation strategy. This strategy also gains good results even with the unequal DC link capacitor. The modulation principle is studied in detail and the validity of this simplified PWM strategy is experimentally verified in this paper. The experiment results indicated that the proposed PWM strategy has excellent performance, and the neutral point potential can be balanced well with unequal DC link captaincies.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1999년도 전력전자학술대회 논문집
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• pp.97-100
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• 1999

AC to DC single phase PWM converter for traction application requires rated high power and voltage. Therefor, series or parallel operation converters are necessary with considering the limitation of the power device specification. This paper compares the characteristic between two parallel operation of conventional PWM converter and Single phase three level converter about comparison of power circuit, cooling system control method and harmonic current by computer simulation.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 전력전자학술대회 논문집
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• pp.689-693
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• 2001

The conventional three-level high frequency phase-shifted dc/dc converter has a disadvantage that a circulating current flows through transformer and switching devices during the freewheeling interval. Due to this circulating current and RMS current stress, conduction losses of transformer and switching devices increases. To alleviate these problems, we propose an improved three-level Zero Voltage and Zero Current Switching (ZVZCS) dc/dc converter using a tapped inductor, a snubber capacitor and two snubber diodes attached at the secondary side of transformer. The proposed ZVZCS converter is verified on a 10 kW, 30kHz experimental prototype.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2016년도 추계학술대회 논문집
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• pp.155-156
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• 2016

• 전기전자학회논문지
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• 제22권4호
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• pp.1006-1011
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• 2018

본 논문은 멀티비트 플라잉 커패시터의 전압제어를 이용한 3-레벨 벅 변환기를 제안한다. 기존의 3-레벨 벅 변환기는 플라잉 커패시터 전압을 제어하지 못하여 동작이 불안정하거나 플라잉 커패시터 전압을 제어하는 회로가 PWM방식에 적용되지 못하는 문제가 있었다. 또한 부하전류에 증가할 때 인덕터 전압에 오차가 발생하였다. 본 논문에서 제안하는 구조는 입력이 4개인 차동증폭기와 공통모드 피드백 회로를 이용하여 PWM모드에서 플라잉 커패시터 전압을 제어할 수 있다. 또한 3비트 플라잉 커패시터 전압 제어회로를 제안하여 부하전류에 따른 3-레벨 벅 변환기의 동작을 최적화할 수 있으며 슈미트 트리거 회로를 이용한 삼각파 생성 회로를 제안하였다. 제안하는 3-레벨 벅 변환기는 $0.18{\mu}m$ CMOS 공정으로 설계되었으며 2.7~3.6V의 공급 전압 범위와 0.7V~2.4V의 출력 전압 범위를 갖는다. 동작 주파수는 2MHz, 부하전류 범위는 30mA~500mA이며 출력 전압 리플은 최대 32.5mV로 측정되었다. 측정 결과 130mA의 부하전류에서 약 85%의 최대 전력변환 효율을 보인다.

• 전력전자학회논문지
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• 제15권6호
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• pp.451-459
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• 2010

본 논문은 대규모 풍력단지를 교류 전력망에 연계하기 위한 3-레벨 PWM 컨버터와 3-레벨 24-펄스 컨버터로 구성된 하이브리드 Back-to-Back 컨버터의 성능을 비교한 결과에 대해 기술하고 있다. 또한 3-레벨 24-펄스 컨버터를 점호각만 제어하는 경우와 영 전압제어를 같이 수행하는 경우 각각이 제어와 고조파레벨에 미치는 영향을 비교 분석하였다. 구체적인 성능비교를 위해 먼저 PSCAD/EMTDC 소프트웨어를 사용하여 시뮬레이션을 실시하고 이를 바탕으로 2 kVA 용량의 하드웨어 축소모형을 제작하고 실험을 실시하였다. 시뮬레이션과 실험을 통해 영전압과 점호각을 동시에 조절하는 방식과 점호각만 제어하는 방식의 성능비교분석을 하였다.

• Journal of Power Electronics
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• 제14권6호
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• pp.1119-1129
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• 2014

This study proposes a novel five-level three-phase hybrid-clamped converter composed of only six switches and one flying capacitor (FC) per phase. The capacitor-voltage-drift phenomenon of the converter under the classical sinusoidal pulse width modulation (SPWM) strategy is comprehensively analyzed. The average current, which flows into the FC, is a function of power factor and modulation index and does not remain at zero. Thus, a specific modulation strategy based on space vector modulation (SVM) is developed to balance the voltage of DC-link and FCs by injecting a common-mode voltage. This strategy applies the five-segment method to synthesize the voltage vector, such that switching losses are reduced while optional vector sequences are increased. The best vector sequence is then selected on the basis of the minimized cost function to suppress the divergence of the capacitor voltage. This study further proposes a startup method that charges the DC-link and FCs without any additional circuits. Simulation and experimental results verify the validity of the proposed converter, modulation strategy, and precharge method.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2006년도 전력전자학술대회 논문집
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• pp.128-130
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• 2006

We introduce 2[MVA] 3300[V] 7-level voltage source inverter system developed by POSCON and describe the main characteristics of inverter system i.e. PWM converter, H-bridge power module, phase shifted carrier PWM The PWM converter is a three-phase boost converter, which operates in a 4-quadrant and in a nearly unit displacement power factor. Experimental waveforms are also presented to verify the proposed method and performance of the developed system.