• 대한조선학회논문집
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• 제52권3호
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• pp.187-197
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• 2015

This study aims the development of a semi-analytic method for the parametric roll of large containerships advancing in longitudinal waves. A 1.5 Degree-of-Freedom(DOF) model is proposed to account the change of transverse stability induced by wave elevations and vertical motions (heave and pitch). By approximating the nonlinearity of restoring moment at large heel angles, the magnitude of roll amplitude is predicted as well as susceptibility check for parametric roll occurrence. In order to increase the accuracy of the prediction, the relationship between righting arm(GZ) and metacentric height(GM) is examined in the presence of incident waves, and then a new formula is proposed. Based on the linear approximation of the mean and first harmonic component of GM, the equation of parametric roll in irregular wave excitations is introduced, and the computational results of the proposed model are validated by comparing those of weakly nonlinear simulation based on an impulse-response-function method combined with strip theory. The present semi-analytic doesn’ t require heavy computational effort, so that it is very efficient particularly when numerous sea conditions for the analysis of parametric roll should be considered.

• Journal of Power Electronics
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• 제16권6호
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• pp.2099-2108
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• 2016

The cascaded multilevel converter is widely adopted to medium/high voltage and high power electronic applications due to the small harmonic components of the output voltage and the facilitation of modularity. In this paper, the operation principle of a T-type H-bridge topology is investigated in detail, and a carrier phase shifted pulse width modulation (CPS-PWM) based control method is proposed for this topology. Taking a virtual five-level waveform achieved by a unipolar double frequency CPS-PWM as the output object, PWM signals of the T-type H-bridge can be obtained by reverse derivation according to its switching modes. In addition, a control method for the T-type H-bridge based cascaded multilevel converter is introduced. Then a single-phase T-type H-bridge cascaded multilevel static var generator (SVG) prototype is built, and a repetitive controller based compound current control strategy is designed with the DC-link voltage balancing control scheme analyzed. Finally, simulation and experimental results validate the correctness and feasibility of the proposed modulation method and control strategy for T-type H-bridge based cascaded multilevel converters.

• ETRI Journal
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• 제31권6호
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• pp.680-687
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• 2009

This paper reports on an improved piezoelectric microspeaker with a high sound pressure level of 90 dB, a total harmonic distortion of less than 15%, and coherence higher than 0.9. The fabricated Pb(Zr,Ti)$O_3$ (PZT) microspeakers have a thickness of only 1 mm including the speaker frame and an active area of 18 mm${\times}$20 mm. To achieve higher sound pressure and lower distortion, the PZT piezoelectric microspeaker has a well-designed speaker frame and a piezoelectric diaphragm consisting of a tilted PZT membrane and silicone buffer layer. From the simulation and measurement results, we confirmed that the silicon buffer layer can lower the first resonant frequency, which enhances the microspeaker's sound pressure at a low frequency range and can also reduce useless distortion generated by the harmonics. The fabricated PZT piezoelectric microspeakers are implemented on a multichannel speaker array system for personal acoustical space generation. The output sound pressure at a 30 cm distance away from the center of the speaker line array is 15 dB higher than the sound pressure at the neighboring region 30 degrees from the vertical axis.

• 전자공학회논문지T
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• 제35T권3호
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• pp.37-45
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• 1998

본 논문에서는 웨이브렛 변환을 이용하여 EMI(Electromagnetic Interference: 전자파 장해) 신호로부터 각각 다른 주파수 성분과 시간정보를 동시에 추출하고, 시간과 주파수 영역에서 웨이브렛 변환의 수행결과를 해석할 수 있도록 하였다. Daubechies-4 필터 계수를 사용한 다중해상도 해석(multiresolution analysis)을 수행하여 EMI 신호로부터 대상 신호의 주파수 성분이 속하는 주파수 대역을 추출하고, 웨이브렛 변환 결과를 통하여 시간정보를 얻었다. 또한 웨이브렛 변환 결과를 평가하기 위해 상관해석법을 시도하고, 웨이브렛 함수에 따른 변환 결과를 비교함으로써 해석하고자 하는 신호에 가장 적합한 웨이브렛 함수를 선택하여 신호의 파형분석과 고조파 해석을 시뮬레이션으로 검증하였다. 그리고 soft thresholding 기법을 이용하여 EMI 신호에 대한 잡음제거의 효과를 입증하였다.

• 전자공학회논문지 IE
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• 제47권3호
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• pp.47-52
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• 2010

본 논문에서 P-HEMT를 이용한 100 mW급 중전력 주파수체배기를 제안한다. 3차 고조파 성분을 발생 시키는 비선형 장치를 이용하여 2.4GHz의 입력을 3체배 하여 7.2GHz 주파수를 얻도록 설계하였다. 주파수 체배기는 로드풀 모의실험 방식을 이용하여 설게 하였고 기본파와 2차 고조파가 억압된 노치 필터를 사용 하였다. 15dBm 입력에 약21dBm의 출력을 얻도록 하였다 즉 6dB의 변환 이득을 얻었고 기본파에서 20dBc 2차 고조파에서 30dBc의 고조파 억압을 하였다.

• 조명전기설비학회논문지
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• 제12권2호
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• pp.21-28
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• 1998

본 연구는 산업계에서 많이 사용되고 잇는 3상 브리지 다이오드 정류기에서 입력측에 발생하는 고조파 문제를 개선하고자 한다. 다이오드 방식은 제어기가 필요치 않기 때문에 간단하고 높은 신뢰성을 갖지만 입력단 전류의 불연속성으로 인하여 전류파형의 왜곡이 생긴다. 본 연구에서는 기존의 3상 브리지 다이오드 정류기에 부가적으로 부착 가능한 3개의 스위치를 제안하여 매순간 3상의 전류 중에서 다이오드 정류기로 흐르지 못한 한 상의 전류를 제안한 스위치를 통하여 흐르게 하여 전류가 연속적으로 흐르게 하였다. 연속적인 전류의 흐름은 고조파 성분을 감소시키며 역률 또한 개선시키는 것을 모의 실험과 실험을 통하여 입증하였다.

• 조명전기설비학회논문지
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• 제28권11호
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• pp.68-76
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• 2014

This paper presents an offset error compensation algorithm for the accurate phase angle of the grid voltage in single-phase grid-connected inverters. The offset error generated from the grid voltage measurement process cause the fundamental harmonic component with grid frequency in the synchronous reference frame phase lock loop (PLL). As a result, the grid angle is distorted and the power quality in power systems is degraded. In addition, the dq-axis currents in the synchronous reference frame and phase current have the dc component, first and second order ripples compared with the grid frequency under the distorted grid angle. In this paper, the effects of the offset and scaling errors are analyzed based on the synchronous reference frame PLL. Particularly, the offset error can be estimated from the integrator output of the synchronous reference frame PLL and compensated by using proportional-integral controller. Moreover, the RMS (Root Mean Square) function is proposed to detect the offset error component. The effectiveness of the proposed algorithm is verified through simulation and experiment results.

• 조명전기설비학회논문지
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• 제29권12호
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• pp.83-87
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• 2015

This paper presents a simple notch filter, which is so suitable for three-phase unbalanced and distorted power line. In the d-q synchronous transformation, three-phase unbalanced and distorted voltages generate lots of ripple voltages on d-q axes. The ripples make disturbances on controllers such as PLL of phase tracking. Unbalanced state makes ripple of double the frequency of power line. Odd harmonics 5th and 7th on the line make even 4th and 6th ripples on d-q axes due to the rotating reference frame, respectively. Cascaded two comb filters, delay lines 1/4T and 1/8T, are adopted for the ripple rejection. The filter rejects harmonics 2nd, 4th, 6th, 10th and so on. They are very effective to remove the ripples of both unbalance and distortion. The filter, implemented by two FIFOs on an experimental system, is adopted on a PLL controller of power line phase tracking. Through the simulation and experimental results, performance of the proposed comb filter has been validated.

• 전기학회논문지
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• 제65권12호
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• pp.2225-2231
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• 2016

In order to overcome the problem of fossil fuel energy, electric vehicle (EV) has been used in recent years. The important issues of EV are driving distance and lifetime related to EV efficiency. A voltage source converter is one of the main components of EV which can be operated with various pulse width modulation (PWM) schemes such as continuous PWM schemes and discontinuous PWM schemes. These PWM schemes will cause the effects on the efficiency of converter system and the lifetime of EV. Therefore, this paper proposes an analysis of the PWM schemes for the power converter on the EV. The objective is to find out a best solution for the EV by comparing the total harmonic distortion (THD) and transient response between the various PWM schemes. The operation of traction motor on the EV with the PWM schemes will be verified by using Psim simulation program.

• 전기학회논문지
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• 제65권12호
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• pp.1992-1999
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• 2016

The plasma process is applied to various industrial fields such as high-tech IT industry, textiles and medical. Therefore, there is increasing interest in the plasma power supply, and demand for power devices of high efficiency and high power density is increased. Plasma power supply for process must solve the arc problem, when the plasma is unstable. The output capacitor is closely related to the arc problem. If the output capacitor is smaller, the damage from the arc problem is reduced. However, the small value of the output capacitor affects the operating characteristics of the power supply. In this paper, a LLC resonant converter is adopted, because it can achieve high efficiency and power density in the plasma DC power supply. However, due to the small value of the output capacitor, the converter is operated as a LLCC resonant converter. Therefore, a gain characteristic of LLCC resonant converter is analyzed by using the FHA (First Harmonic Approximation) in plasma power supply. Simulation and experimental results are presented to verify the characteristic analysis of LLCC Resonant Converter.