• Journal of Power Electronics
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• 제14권1호
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• pp.175-182
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• 2014

Tracking harmonic current quickly and precisely is one of the keys to designing active power filters (APF). In the past, the current state feedback decoupling PI control was an effective means for three-phase systems in the current control of constant voltage constant frequency inverters and high frequency PWM reversible rectifiers. This paper analyzes in detail the limitation of the conventional PI conditioner in the APF application field and presents a novel PI control method. Canceling the delay of one sampling period and the misadjustment for tracking the harmonic current is the key problem of this PI control. In this PI control, the predictive output current value is obtained by a state observer. The delay of one sampling period is remedied in this digital control system by the state observer. The predictive harmonic command current value is obtained by a repetitive predictor synchronously. The repetitive predictor can achieve better predictions of the harmonic current. By this means, the misadjustment of the conventional PI control for tracking the harmonic current is cancelled. The experiment results with a three-level NPC APF indicate that the steady-state accuracy and dynamic response of this method are satisfying when the proposed control scheme is implemented.

• KCI Concrete Journal
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• 제11권3호
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• pp.45-52
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• 1999

A Computer-based iterative method is provided for the calculation of minimum thickness values for one-way slabs to satisfy the maximum permissible limits given in the ACI Building Code. An algorithm includes the effects of cracking and time-dependent effects due to creep and shrinkage. Comparison of the calculated minimum thickness values with the current ACI limits is conducted to investigate limitations of the current tabulated minimum thickness. which are constant to a range of design conditions.

• 전자공학회논문지SC
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• 제41권2호
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• pp.61-68
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• 2004

전기를 이용한 치아의 자극은 치수의 생활력 평가의 한 방법이다. 전기 치수 검사의 기본원리는 치아 내의 치수에 전류 자극을 가하여 유발되는 통증 유무로 치수의 생활력을 평가한다. 그러나 치아의 에나멜질의 임피던스가 크고 개인에 따라 차이가 많기 때문에 치아의 상태에 영향을 받지 않으면서 자극을 제어하기가 불가능하다. 대부분의 치수검사기가 전압 자극 방법을 사용하고 있어 개인에 따라 자극 역치 값이 크게 변화한다 그러므로 치아 에나멜질의 두께 차에 의해 발생하는 영향을 최소화하기 위해 정 전류 치수 검사기가 필요하다. 그리고 치아 임피던스에 관계없이 넓은 전류 범위를 갖는 치수 검사기가 필요하다. 본 연구에서는 전류 안정 회로를 사용하여 최대 150 uA의 전류와 통증을 완화하는 버스트 파형을 발생시킬 수 있는 정 전류원 치수 검사기를 개발하고 그 성능을 확인하였다.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제49권10호
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• pp.559-563
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• 2000

The $(Sr_{1-x}Ca_x)TiO_3(SCT)$ thin films are deposited on Pt-coated(Pt/TiN/$SiO_2$/Si) using RF sputtering method with substitutional contents of Ca. The maximum grain of thin films is obtained by substitution of Ca at 15[mol%]. Also the composition of SCT thin films were closed to stoichiometry(1.081∼1.117 in A/B/ ratio). The dielectric constant was increased with increasing the substitutional contents of Ca, while it was decreased if the substitutional contents of Ca exceeded over 15[mol%]. The dielectric constant changes almost linearly in temperature ranges of -80∼+90[^${\circ}C$]. The temperature properties of the dielectric loss have a stable value within 0.02 independent of the substitutional contents of Ca. All SCT thin films used in this study show the phenomena of dielectric relaxation with the increase of frequency, and the relaxation frequency is observed above 2000[kHz]. The current-voltage characteristics of SCT15 thin films showed the increasing leakage current as the measuring temperature increase.

• 대한전자공학회논문지
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• 제26권2호
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• pp.112-117
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• 1989

본 논문은 패턴의 모양에 따라서 패턴 데이타 포멥변환시 분할되는 각종 矩形패턴을 크기에 구애됨이 없이 전자선 직접묘사 시간이 일정한 矩形단위로 전자선 직접묘사하는 방법을 제안하였다. 본 실험에서는 SEM을 사용하였으며 矩形의 크기에 따라 일정시간에 요구되는 전자선 전류를 변화시키기 위하여 집속렌즈의 공급전류를 BITMAP-IV CAD 시스템으로 제어하였다. 본방법에서는 패턴 데이타 포맵변환시 밀집된 패턴에 대한 resizing과정이 불필요하며 묘사시간에 근거한 through-put은 unit scan방식에 비하여 172배가 향상되었다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1991년도 추계학술대회 논문집 학회본부
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• pp.171-174
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• 1991

Among the various PWM methods, the hysteresis-band current control PWM method is popularly used because of its simplicity of implementation, fast response characteristics and inherent peak current limiting capability. However, the current control PWM method with a fixed hysteresis-band has the disadvantage that switching frequency decreases and current ripple is high as the increasing of back-EMF. As a result, load current contains excess harmonics. This paper describes a adaptive hysteresis-bandwidth control algorithm so as to maintain the average switching frequency constant and decrease the current ripple where the hysteresis bandwidth is derived as a relation with the switching frequency. This control algorithm is applied to the surface-type brushless DC motor with separated winding and using the computer simulation, the validity of its algorithm is proved.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2015년도 제46회 하계학술대회
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• pp.934-935
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• 2015

This paper presents the sensorless control method that employs the adaptive back-EMF(Electromotive Force) and current model observer of interior permanent magnet synchronous motor(IPMSM). The estimated back EMF considering a saliency is obtained by using the adaptive control method. The estimated EMF is inputted to the current model observer which is connected in series with adaptive back EMF estimator and is used to estimate the position and speed of the rotor. In order to improve the shortcomings of conventional method using the current error components multiplied in the compensation constant, the modified instantaneous reactive power compensator is applied. The validity of the control system presented is verified by the simulation.

• 전기의세계
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• 제30권8호
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• pp.501-508
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• 1981

A novel and simple method of designing the current feedback loop for the velocity controller of an armature controlled dc servo motor is presented. Instead of constructing the usual tight current feedback loop, a loose current feedback loop is suggested in this paper. More specifically, the armature current is not limited to a fixed constant value, but instead the upper bound value is allowed to be variable along with the present motor speed. The control system designed in this manner shows that the motor under control is robust to a wide range of loading conditions and yields a more rapid transient characteristics which is verified experimentally by applying the method in the design of the controller for an Industrial robot.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1994년도 하계학술대회 논문집 A
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• pp.298-302
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• 1994

Brushless DC motors have a trapezoidal back EMF wave form and are fed with rectangular stator currents. Under these conditions, the torque produced is theoretcally constant. However, in practice, torque ripple may exist, one major cause of which conies from phase current commutation. In this paper we propose an improved method of reducing the torque ripple due to phase current commutation of indirectly restricting the uncommutated current through control of the other phase currents. Simulation results are present.

• JSTS:Journal of Semiconductor Technology and Science
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• 제4권4호
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• pp.269-274
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• 2004

Current delivery system, in which the analog current produced by a unique DAC circuit is stored into a current-memory circuit and delivered in a time-divided sequence, shows variation of output current as low as 4% in a current source data-driver IC for AM-OLED driven by a current-programmed method without any fuse repairing after fabrication. This driver IC has 54 outputs and can sink constant current as low as 3 ${\mu}A$ with 6-bit analog levels. Such a low current level without variation can hardly be obtained by an ordinary MOS transistor because the current level is in the sub-threshold region and changes exponentially with threshold voltage variation. Thus we adopted a current mirror circuit composed of bipolar transistors to supply well-controlled current within a nano-ampere range.