• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 B
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• pp.1035-1037
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• 2001

This paper presents an improved hys- teresis current control method for three-phase PWM power inverters using 3-level comparator. Hysteresis current controller using 3-level comparator has an advantage of constant switching frequency compared with conventional hysteresis current controller. However, this method has disadvantage that the longer sampling period, the larger current error because the switching is performed without considering current error magnitude of each phase. The proposed method improves the control performance by selecting the optimum switching pattern in which the magnitudes of current errors are considered introducing space vector concept. Simulation results using Matlab/Simulink show that the proposed control method reduces current error keeping the merit of previous hysteresis current control method.

• 대한전기학회논문지
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• 제43권2호
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• pp.259-267
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• 1994

This paper describes a current control of a single-phase PWM inverter. The proposed PWM inverter utilizes the instantaneous control method which is based on the real-time digital feedback control and the microprocessor-based deadbeat control. The deadbeat current controller is proposed to control the output current regardless of load component variations by the same method as voltage control. That is, in current control, with a very short sampling time and the successive feedback of the output current, the load current is mainly effected by the magnitude of load impedance rather than load component, the load current is mainly effected by the magnitude of load impedance rather than load component. Therefore, by treating the load as an impedance, the system's order is reduced and the instantaneous current control using the proposed deadeat controller is simplified.

• 전자공학회논문지SC
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• 제44권6호
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• pp.57-65
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• 2007

본 논문에서는 DSP(TMS320F2812)를 사용하여 단상 역률개선을 디지털로 설계하였다. 이러한 승압형 역률개선 컨버터를 디지털로 구현하기 위하여 DSP는 컨버터의 입력전압과 인덕터전류, 컨버터의 출력전압이 필요하며 이를 DSP 내부에 있는 12비트 A/D변환기로 구현하였다. 승압을 위한 스위칭소자인 FET가 ON/OFF 될 때 심한 고주파 노이즈와 스위칭 리플이 발생한다. DSP에 의해 구현시 어느 시점에서 A/D 변환을 시작할지 결정하는 것은 대단히 중요하며 스위칭 노이즈가 발생하지 않는 곳에서 A/D 변환을 할 필요가 있다. PWM의 시비율(duty ratio)은 약 5 %에서 95 %까지 가변적이기 때문에 A/D 변환의 고정된 시작점을 찾을 수는 없다. 따라서 본 논문에서는 25 us 마다 PWM의 ON/OFF 폭을 미리 예측한 후 타이머를 이용하여 A/D 변환을 하도록 하였다. 실험 결과들로부터 광범위한 입력전압에 대하여 약 0.99의 역률과 80 Vdc 출력 전압에 대한 리플이 약 5 Vpp임을 확인하였다. 또한 윈도우즈 Xp 환경 하에서 수행되는 응용프로그램을 작성하여 원격에서 단상 PFC 컨버터의 각종 파라미터들과 전압 및 전류 제어기의 이득들을 모니터링하며 원격제어가 가능함을 보여 상용화의 가능성과 유용성을 제시하였다.

• 전기전자학회논문지
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• 제24권4호
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• pp.1058-1063
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• 2020

본 논문은 생체 신호 및 센서 신호 처리를 위하여 저전력으로 동작하는 12비트 SAR A/D 변환기를 제안한다. 기존의 SAR A/D 변환기의 전력소모를 줄이고자, 동적 전류를 감소시켜 전체 전력 소모를 감소시켰다. 동적 전류를 감소시키기 위해서 C-DAC 비트 스위치를 동작시키는 샘플링 시간을 클럭 생성기의 샘플링 시간과 다르게 인가하였다. 추가적으로 SAR A/D 변환기의 전체 전력소모 중 70%를 차지하는 디지털 블록의 공급전압을 0.6V로 낮춰 설계하였다. 제안하는 SAR A/D 변환기는 CMOS 65nm 공정 1-poly 6-metal을 사용하여 설계하였으며, 1.2V의 공급전압으로 동작하며, ENOB는 10.1 비트, INL/DNL은 ±0.5LSB/±1.2LSB이며, 전체 전력소모는 31.2uW이고 FoM은 2.8fJ/step 이다.

• Journal of Power Electronics
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• 제12권6호
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• pp.895-903
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• 2012

This paper presents a fast switching direct torque control (FS-DTC) using only a single DC-link current sensor. In FS-DTC, six new active voltage complex space vectors (CSVs) are synthesized by the conventional active voltage space vectors (SVs). The corresponding sectors are rotated in the anticlockwise direction by 30 degrees. A selection table is defined to select the CSVs. Based on the "Different Phase Mode", the output sequence of the selected CSV is optimized. Accordingly, a reconstruction method is proposed to acquire the phase currents. The core of the FS-DTC is that all of the three phase currents can be reliably reconstructed during every two sampling periods, which is the result of the fast switching between different phases. The errors between the reconstructed and actual currents are strictly limited in one sampling period. The FS-DTC has the advantages of the standard DTC scheme such as simple structure, quick torque response and robustness. As can be seen in the analysis, the FS-DTC can be thought of as an equivalent standard DTC scheme with 86.6% of the maximum speed, 173.2% of the torque ripple, and 115% of the response time of the torque. Based on a dSPACE DS1103 controller, the FS-DTC is implemented in an induction machine drive system. The results verify the effectiveness of the FS-DTC.

• Ocean Systems Engineering
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• 제9권2호
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• pp.111-133
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• 2019

Flow through a scaled horizontal axis marine current turbine was numerically simulated after validation and the turbine design was optimized. The computational fluid dynamics (CFD) code Ansys-CFX 16.1 for numerical modeling, an in-house blade element momentum (BEM) code for analytical modeling and an in-house surrogate-based optimization (SBO) code were used to find an optimal turbine design. The blade-pitch angle (${\theta}$) and the number of rotor blades (NR) were taken as design variables. A single objective optimization approach was utilized in the present work. The defined objective function was the turbine's power coefficient ($C_P$). A $3{\times}3$ full-factorial sampling technique was used to define the sample space. This sampling technique gave different turbine designs, which were further evaluated for the objective function by solving the Reynolds-Averaged Navier-Stokes equations (RANS). Finally, the SBO technique with search algorithm produced an optimal design. It is found that the optimal design has improved the objective function by 26.5%. This article presents the solution approach, analysis of the turbine flow field and the predictability of various surrogate based techniques.

• 한국임상수의학회지
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• 제29권1호
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• pp.58-62
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• 2012

To protect aquatic animal health of importing countries from the potential risks associated with exotic diseases introduced through international trade of live aquatic animals, inspection of designated commodities at ports of entry is a critical component of the safeguarding system. The only way to be 100% confident that no fishes in a shipment are infected with a specific agent is to test every fish in the commodity imported with a perfect diagnostic test. For the majority of cases, this is unrealistic since the group of interest may very large particularly for aquatic animals, or imperfect tests are often available. It is, therefore, more common to test a fixed proportion of a group by preplanned sampling schemes. However, decision making based on results of testing the sample can provide quite a chance that infected groups may be misclassified as uninfected, depending on sampling strategy employed. The objective of this study was to determine the possibility that one or more fishes in the group imported being infected but tests negative after inspecting samples. This question is critical to government authorities to examine whether sampling plan is sufficient to achieve the purpose intended for. At fixed population size, the maximum number of infected fishes when all tests negative was decreased as the sampling fraction increased. The probability of including at least one undetected but infected fish in a group for negative tests increased with the number of fish tested or true prevalence. The risk was much lesser where high sensitivity test was assumed; when increasing test sensitivity from 0.9 to 0.99, this risk was dramatically reduced to about a tenth or a fourth for prevalence ranges from 2 to 10%, given sample size ranges from 10 to 200. Based on the preliminary analysis, the author concluded that current sampling plan testing 4-8% of the import proposal for human consumption still can yield high false negative results. Therefore, from the quarantine inspection point of view, an enforced commodity-specific sampling design that accounts for the cost of testing with an imperfect test at the specified design prevalence is urgent.

• 대한전기학회논문지:시스템및제어부문D
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• 제51권12호
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• pp.549-555
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• 2002

While the z-transform method is a basic mathematical tool to relate the imput/output signals only at the sampling instants in analyzing and designing sampled-data control systems, the modified z-transform which is a variation of the z-transform is widely used to represent the details of continuous signals between the sampling instants. To relate the modified z-transform to the corresponding regular z-transform, some properties were established regarding the modified z-transform method. This paper will show that these properties, in their current forms, cause come analytic problems, when they are applied to the signals with discontinuities at the sampling instants, which accordingly limit their applications significantly. In this paper, those analytic problems will be investigated, and the theorems of the modified z-transform will be revised by adopting new notations on the z-transform so that those can be correctly interpreted and used without any analytic problems. Also some additional useful schemes of applying the modified z-transform will be developed.

• Structural Engineering and Mechanics
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• 제32권1호
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• pp.37-53
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• 2009

In this paper the problem of calculating the probability that the responses of a wind-excited structure exceed specified thresholds within a given time interval is considered. The failure domain of the problem can be expressed as a union of elementary failure domains whose boundaries are of quadratic form. The Domain Decomposition Method (DDM) is employed, after being appropriately extended, to solve this problem. The probability estimate of the overall failure domain is given by the sum of the probabilities of the elementary failure domains multiplied by a reduction factor accounting for the overlapping degree of the different elementary failure domains. The DDM is extended with the help of Line Sampling (LS), from its original presentation where the boundary of the elementary failure domains are of linear form, to the current case involving quadratic elementary failure domains. An example involving an along-wind excited steel building shows the accuracy and efficiency of the proposed methodology as compared with that obtained using standard Monte Carlo simulations (MCS).

• 한국멀티미디어학회:학술대회논문집
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• 한국멀티미디어학회 2003년도 추계학술발표대회(하)
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• pp.1006-1009
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• 2003

In a motion estimation method for use in encoding a moving picture, a full-pixel motion vector is estimated by stochastically sampling a pixel to be processed in a predetermined-sized block of a previous frame or a next frame as a reference frame for each of a plurality of equal-sized blocks in a current frame. Then, a half-pixel motion vector is estimated based on the full-pixel motion vector. Accordingly, both the calculation amount and the calculation time required for the motion estimation are effectively reduced. Further, it can be prevented that the hardware becomes complicated. .