• 한국자동차공학회논문집
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• 제22권1호
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• pp.95-102
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• 2014

This paper presents zero crossing point(ZCP) estimation methods considering discretization error for a high speed brushless DC(BLDC) motor drive. The ZCP is estimated by detecting the change of back-EMF polarity for the BLDC sensorless drive, and the discretization error exist on the estimated ZCP. The discretization error of the ZCP is a cause of the delay of a commutation timing of current and increment of a current ripple factor. Besides a delay of a ZCP estimation brings on the limitation of a speed range for the BLDC sensorless drive. The compensation method based on the error analysis with probability theory for reducing the effects of the discretization error of the ZCP is proposed. Also a ZCP estimation method according to the Back-EMF patterns is proposed to widen the speed range for the BLDC sensorless drive. The proposed methods are verified by the experiment.

• 전기학회논문지
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• 제63권1호
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• pp.35-41
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• 2014

This paper presents a design method of programmable low pass filter(PLPF) which reduce an estimation error of a zero crossing point(ZCP) for a high speed brushless DC(BLDC) motor drive. BLDC motor sensorless drive is possible by estimation of ZCP. The ZCP estimated by detecting a change of back-EMF polarity has the estimation error because noises exist on the measured back-EMF. Therefore a calculated commutation timing using the ZCP is inaccurate. And the inexact commutation timing leads to ripples of 3-phase current and degradation of drive performance. This paper proposes the design method of the PLPF to overcome these problems. First, a speed calculated a inaccurate period of the ZCP is analyzed in the frequency domain. Then, the PLPF that has varying cut-off frequency according to change of the speed is designed on the frequency analysis result. The proposed method is verified by the experiment.

• Journal of Power Electronics
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• 제16권1호
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• pp.1-8
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• 2016

Dead time is typically incorporated in voltage source inverter systems to prevent short circuit cases. However, dead time causes an error between the output voltage and reference voltage. Hence, voltage equation-based algorithms, such as motor parameter estimation and back electromotive force (EMF)-based sensorless algorithms, are prone to estimation errors. Several dead-time compensation methods have been developed to reduce output voltage errors. However, voltage errors are still common in zero current crossing areas, and an effect of the error is much worse in a low speed region. Therefore, employing voltage equation-based algorithms in low speed regions is difficult. This study analyzes the conventional dead-time compensation method and output voltage errors in low speed operation areas. A current shaping method that can reduce output voltage errors is also proposed. Experimental results prove that the proposed method reduces voltage errors and improves the accuracy of the parameter estimation method and the performance of the back EMF-based sensorless algorithm.

• 제어로봇시스템학회논문지
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• 제19권6호
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• pp.508-512
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• 2013

In recent years, sensorless drive schemes have been proposed widely and most of them are based on the ZCP (Zero Crossing Point) detection of the BEMF (Back Electro-Motive Force). These schemes have two main problems. One is that ZCP may not be detected at low speed and thus a forced drive is required. The other problem is that there is $30^{\circ}$ phase difference between ZCP and the motor commutation instant and to ensure proper operation, this gap should be accounted for. To solve these problems a circuit is devised for detecting ZCP of the BEMF difference through the line voltage difference. Experimental results show that the output of this circuit is identical to that of the Hall sensor signal, and velocity control of a BLDC motor is possible without the sensor.

• 대한교통학회지
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• 제24권4호
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• pp.93-101
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• 2006

현재 우리나라에는 철도건널목 인근 신호교차로체 Signal Preemption이 도입되지 인가 열차의 철도건널목 통과 시 철도건널목의 안전이나 인근신호교차로의 운영에 상당한 문제를 야기하고 있다. 철도와 교차하는 신호교차로의 접근로에서는 신호대기로 인한 대기행렬이 철도건널목까지 언제든지 늘어날 수 있고, 이때 열차가 건널목에 접근하게 되면 철도건널목 위에서 대기하고 있던 차량이 열차와 충돌하는 사고가 발생할 수 있다. 그러므로 열차의 철도건널목 도착 전에 철도건널목 위의 대기차량들은 반드시 소거되어야 한다. 또한. 열차의 철도건널목 통과 시에도 철도와 교차되는 접근로의 차단으로 인해 특별한 신호 운명이 필요하다. 따라서 철도건널목과 인근신호교차로의 안전 향상과 합리적인 신호운명을 위해서는 열차 진입 시 교차로 및 철도건널목에 접근하는 교통류를 고려한 Signal Preemption 전략이 구축되어야 한다. 본 연구에서는 Signal Preemption의 효과를 현장조사 및 시뮬레이션을 이용하여 가시적으로 제시하였다. 오전첨두시 교통량과 30대 열차의 철도건널목 도착시간 예측치를 이용하여 시뮬레이션이 실행되었고. Signal Preemption을 적용하였을 경우 차량 당 지체시간은 약 9초가량인 것으로 나타났다. 또한, Signal Preemption의 미적용시 30개 시나리오 모두에서 건널목위의 대기차량과 열차가 충돌하는 것으로 나타난 반면, Signal Preemption 적용 시 모든 시나리오에서 대기차량과 열차의 충돌은 발생하지 않았다.

• 전기학회논문지
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• 제66권9호
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• pp.1325-1333
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• 2017

The sensorless control of blushless DC motor(BLDCM) is based on the $120^{\circ}$ control in which the back electromotive force(Back EMF) for estimating the position of the rotor can be detected. However, the $120^{\circ}$ control has a disadvantage that the torque constant is small as compared with $180^{\circ}$ control which can not detect the back EMF. The $150^{\circ}$ control which complements these problems makes it possible to detect the back EMF and improve the torque constant by 12.5% compared to the $120^{\circ}$ control. Therefore, this paper compares the output characteristics of BLDCM through finite element method analysis (FEA) by the conventional and proposed control methods of BLDCM for water circulation system and proposes design for downsizing and weight reduction of BLDCM according to secured torque constant. The validity of the proposed control and design proposal is proved through simulation and experimental results by comparing the output characteristics of $120^{\circ}$ control and $150^{\circ}$ control.

• Bulletin of the Korean Chemical Society
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• 제12권4호
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• pp.441-444
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• 1991

The intramolecular proton transfers of 2-hydroxy-4,5-naphthotropone in room temperature solutions are studied using static and time-resolved absorption and emission spectroscopy. Dual normal and tautomer fluorescence is observed in ethanol solution, while only the tautomer fluorescence is observed in cyclohexane solution. The fluorescence lifetimes and quantum yields in ethanol and cyclohexane solutions indicate that in hydrocarbon solvents, rapid intersystem crossing competes with proton transfer in the first excited singlet state. Transient absorption spectra and kinetics indicate that proton transfer also undergoes in the first triplet state with a transfer time of ∼ 3 ns. No transient absorption from the tautomer ground state indicates a rapid back proton transfer in the ground state.

• International Journal of Industrial Entomology and Biomaterials
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• 제20권2호
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• pp.45-59
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• 2010

It is well established fact that under tropical condition, unlike polyvoltines, bivoltines are more vulnerable to various stresses i.e. hot climatic conditions of tropics, poor leaf quality and improper management during summer which are not conducive for bivoltine rearing. Therefore, attempt has been made in this study to develop promising bivoltine breeds tolerant to high temperature and high humidity conditions of the tropics. In the present study, by utilizing temperature tolerant breeds six breeding lines were made and at every generation the 5th instar larvae were exposed to high temperature and high humidity and the survived ones were back crossed with the breeds moderately tolerant to diseases were made to improve the quantitative traits. From F6 generations, alternate rearing in normal temperature and high temperature were conducted. At the end of F12 generation, it was possible to isolate three dumbbell breeds viz., HH8, HH10 and HH12 with improvement in quantitative traits. The methodologies followed for the development are discussed.

• 대한전기학회논문지:시스템및제어부문D
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• 제54권5호
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• pp.338-347
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• 2005

A computer-based low back muscle evaluation system was designed to simultaneously acquire, process, display, quantify, and correlate electromyographic(EMG) activity with muscle force, and range of motion(ROM) in the lumbar muscle of human. This integrated multi-channel system was designed around notebook PC. Each channel consisted of a time and frequency domain block, and T-F(time-frequency) domain block. The captured data in each channel was used to display and Quantify : raw EMG, histogram, zero crossing, turn, RMS(root mean square), variance, mean, power spectrum, median frequency, mean frequency, wavelet transform, Wigner-Ville distribution, Choi-Williams distribution, and Cohen-Posch distribution. To evaluate the performance of the designed system, the static and dynamic contraction experiments from lumbar(waist) level of human were done. The experiment performed in five subjects, and various parameters were tested and compared. This system could equally well be modified to allow acquisition, processing, and analysis of EMG signals in other studies and applications.

• Journal of Power Electronics
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• 제16권6호
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• pp.2129-2138
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• 2016

The full-bridge inverter, widely used for single-phase photovoltaic grid-connected applications, presents a leakage current issue. Therefore, an AC bypass branch is introduced to overcome this challenge. Nevertheless, existing modulation strategies entail drawbacks that should be addressed. One is the zero-crossing distortion (ZCD) of the AC current caused by neglecting the AC filter inductor voltage. Another is that the system cannot deliver reactive power because the AC bypass branch switches at the power frequency. To address these problems, this work proposes an optimized hybrid modulation strategy. To reduce ZCD, the phase angle of the inverter output voltage reference is shifted, thereby compensating for the neglected leading angle. To generate the reactive power, the interval of the negative power output is calculated using the power factor. In addition, the freewheeling switch is kept on when power is flowing into the grid and commutates at a high frequency when power is fed back to the DC side. In this manner, the dead-time insertion in the high-frequency switching area is minimized. Finally, the performances of the proposed modulation strategy and traditional strategies are compared on a universal prototype inverter. Experimental results validate the theoretical analysis.