• The Transactions of the Korean Institute of Power Electronics
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• v.7 no.5
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• pp.427-436
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• 2002

This paper presents an implementation of high-dynamic performance of position sensorless motion control system of Reluctance Synchronous Motor(RSM) drives for an industrial servo system with direct torque control(DTC). The problems of high-dynamic performance and maximum efficiency RSM drives controlled by DTC are saturation of stator linkage flux and nonlinear inductance characteristics with various load currents. The accurate estimation of the stator flux and torque are obtained using stator flux observer of which a saturated inductance $L_d$ and $L_q$ can be compensated by adapting from measurable the modulus of the stator current and rotor position. To obtain fast torque response and maximum torque/current with varying load current, the reference command flux is ensured by imposing $I_{ds} = I_{qs}$. This control strategy is proposed to achieve fast response and optimal efficiency for RSM drive. In order to prove rightness of the suggested control algorithm, the actual experiment carried out at $\pm$20 and $\pm$1500 rpm. The developed digitally high-performance motion control system shown good response characteristic of control results and high performance features using 1.0kW RSM which has 2.57 Ld/Lq salient ratio.

• The Transactions of the Korean Institute of Power Electronics
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• v.5 no.4
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• pp.335-342
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• 2000

A new control method for a single-phase active power filter, based on a load current estimation using a DC capacitor voltage of active power filter without sensing nonlinear load current, is proposed in this paper. Because the method proposed can remove the load current sensor in comparison with a conventional method sensing the load current and DC capacitor voltage together, it can make the active power filter easy installation, low cost, small size with no performance detriment. In addition, sample-hold technique and proportional control method is adopted to control the DC capacitor voltage and as no delay element such as LPF or PI control in the conventional method is used, the transient response is fast and good. Operation of a single-phase active power filter which consist of eight mode is explained according to utility voltage, compensation current and switch state, and compensation characteristics of active power filter using proposed method is verified by experiment.

• The Transactions of the Korean Institute of Power Electronics
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• v.15 no.5
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• pp.361-368
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• 2010

This paper presents high speed position controller using stepping motor. The proposed position controller has close loop and open loop mode. In the high speed region, torque angle which is controlled by PI controller and memory based look-up table, is used to keep the reference position. The memory based look-up table produces a torque angle according to motor speed, and the PI controller can compensate the torque angle error. So, the fast dynamic response can be expected in the same position error. The open loop control mode which is divided by 3-modes control the actual position in the low speed and small position error. Each open loop modes are designed to reduce position error and dynamic brake in the stop command. The proposed position control scheme is verified by the practical stepping motor.

• The Transactions of the Korean Institute of Power Electronics
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• v.14 no.4
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• pp.278-284
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• 2009

This paper presents a firing angle controller of a thyristor converter for DC power supply using PID controller with parallel data loop to improve the dynamic response. The proposed parallel data loop for firing angle controller of 3-phase semi-converter, generates pre-measured firing angle according to reference voltage and load current. With the approximated firing angle according to operating conditions, the output voltage can fast keep the reference value with small voltage error. And the PID controller compensates the output voltage error from the firing angle of parallel data loop. In order to reduce the sudden changing of the data from current ripple, a simple digital low pass filter is used to determine the output data. The proposed control scheme is verified by the experimental test of a practical 50[A] grade thyristor converter system.

• Survey Research
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• v.3 no.2
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• pp.47-76
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• 2002

Starting point bias arises in the iterative bidding framework when the initial bid influences respondent's final bids. The bidding game has become the most commonly used method of asking the valuation question in contingent valuation studies. A bidding game is typically conducted by either personal or telephone interview. Bidding begins with an interviewer positing an initial bid (starting bid) to a respondent. If the respondent is willing to pay the initial bid, the interviewer revises the bid upward until a negative respondent is obtained. A negative response to the initial bid downward until an acceptable amount is found. The final bid is a measure of the respondent's Hicksian compensating or equivalent surplus for the item being valued. This paper explicity tested for starting point bias in bidding games. That is, it was asked whether final bids are influenced by the magnitude of the starting bids in the process of valuating the WTP when to improve the quality of running water in Seoul and its vicinity. The result shows staring point bias exists in the present data and its magnitude is ${\delta}$=-0.265237.

• Proceedings of the Korea Contents Association Conference
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• 2012.05a
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• pp.345-346
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• 2012

본 연구는 치과진료실의 실내 공기질에 영향을 미치는 요인과 종사자의 실내자각증상과 관련성을 조사하여 치과위생사 개인의 발전과 건강 증진에 필요한 기초자료를 마련하고자 본 연구를 시행하였다. 전국(서울, 경기, 대구, 포항)의 종합병원, 치과병원, 치과의원의 치과위생사 210명을 대상으로 2011년 10월 1일부터 20일까지 자기기입식 설문지 조사를 시행한 후 회수하여 응답이 불분명한 5명을 제외한 205명에 대해서 분석 하였다. 수집된 자료는 SPSS WIN 15.0 프로그램을 이용하여 분석하였다. 그 결과 근무 중 휴식시간 유무별로는 근무 중 휴식시간이 없는 치과위생사가 67.3%로 높은 분포를 보였고, 건물 밖 외출 여부별로는 때때로가 54.6%로 절반 이상을 차지하였으며, 건물 밖 외출횟수별로는 1회 86.1%로 대부분을 차지하였으며, 근무기관의 계절별 자연환기 정도별로는 봄, 여름, 가을, 겨울 모두 1일 2회 이내가 절반 이상을 차지하였으며, 다음으로 1일 4회 이내 19.0%, 기타 9.8%, 1일 10회 이내와 하루 종일 2.4% 순이었다. 실내자각증상 호소율에 대해 살펴본 결과는 4점 만점 중 전체 평균이 2.45로 나타났다. 먼저 영역별로는 평균이 '목증상'과 '눈증상'이 각각 2.54로 가장 높았으며, 문항 중에는 평균이 '눈이 잘 피로해진다'가 3.00으로 가장 높게 나타났다. 근무환경 특성에 따른 실내자각증상은 야간진료 여부별로는 야간진료를 하는 치과위생사가 그렇지 않은 치과위생사보다 실내자각증상이 낮았으며, 야간진료 여부에 따라 유의한 차이를 보였다(t=2.07, p<.05). 실내자각증상과 직무스트레스의 관계는 물리환경(r=.259, p<.001)과 직무요구(r=.311, p<.001), 관계갈등(r=.172, p<.05), 조직체계(r=.158, p<.05), 보상 부적절(r=.197, p<.01), 그리고 직무스트레스(r=.275, p<.001)와 통계적으로 유의한 상관관계를 보였다.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.44 no.4 s.316
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• pp.21-26
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• 2007

Output voltage waves of a DC/AC inverter system are likely to be distorted if variable loads e.g. motors or rectifiers exist in the output terminal. This paper designs a disturbance observer-based PI-controller for a single-phase inverter system that is robust against load changes. In this Paper, we regard the output voltage changes due to various loads as disturbances of the control system. Then we design a disturbance observer for estimation of the disturbances caused by the load current and any other error sources (such as parameter uncertainties and model mismatches etc.). In order to test the performance of the proposed control law, simulation studies are carried out for a single-phase inverter system using SimPowerSystem of Matlab Simuink. Compared to a simple PI-control, the disturbance observer-based controller shows enhanced performance in transient responses for step load changes.

• Journal of IKEEE
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• v.5 no.1 s.8
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• pp.16-23
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• 2001

Passive noise reduction is a classical approach to attenuate industrial noise, and an active noise cancellation has several advantages over the passive noise cancellation. The active noise reduction system offers a better low frequency performance with a smaller and lighter system. This paper presents a simple active closed loop control system which consists of an controller for inverting and compensating the phase delay, a microphone for picking up the external noise, and a loudspeaker for radiating the acoustic out of phase signal to reduce the external noise, and external noise can be reduced after compensating the phase difference to be $180^{\circ}$ in the frequency of maximum value in the amplitude response. The noise of the phase delay covered from $50^{\circ}\;to\;310^{\circ}$ tends to be reduced in the active noise control system and it is possible to obtain a noise cancelling of up to approximately 20[dB] at the ears in the enclosurer.

• Journal of IKEEE
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• v.24 no.1
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• pp.154-160
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• 2020

This paper presents a grid current control algorithm for a grid connected inverter (GCI) system in a stationary reference frame. When a Proportional Integral (PI) controller at a stationary reference frame is used in a GCI system, steady state error and phase lags are presented because AC signals are controlled at a stationary reference frame. In this paper, a feedforward controller is applied to the PI controller to compensate the steady state error and phase lags by improving command tracking performance. In addition, disturbance rejection control is applied to the PI controller to protect the GCI system by eliminating disturbance, grid voltage in a GCI system, when a grid fault such as line-to-line fault, happens. The proposed GCI current control algorithm is analyzed in a frequency domain and a simulation model of the proposed GCI current control system is developed for verification of the performance.

• Korean Journal of Optics and Photonics
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• v.19 no.3
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• pp.161-168
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• 2008

We propose a novel bistable nematic liquid crystal cell, which has a dual-frequency liquid crystal material and pixel-isolating polymer wall formed by an anisotropic phase separation of a mixture of liquid crystals and UV-curable pre-polymers. The proposed cell has two stable states of left- and right-handed ${\pi}$-twist. The switching between the two states is achieved by using a sequential waveform of low and high frequencies. A transmissive bistable liquid crystal display is designed, which achieves high contrast ratio by using the proposed cell and optical films.