• 전력전자학회논문지
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• 제12권2호
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• pp.131-138
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• 2007

본 논문은 출력단에 LC필터를 갖는 3상 PWM 인버터의 출력전압을 일정전압/일정주파수로 제어하기 위한 새로운 비선형 제어기법을 제안한다. 출력 LC필터를 포함한 비선형 모델을 궤환선형화(feedback linearization) 이론을 통하여 선형화하고 선형 제어이론에 기초하여 제어기를 설계한다. 이 제어기는 LC 출력필터를 갖는 PWM 인버터를 사용하는 독립형 풍력발전 시스템에 적용된다. 제안한 제어기법은 정상상태와 부하변동의 과도상태에 대한 실험을 통하여 검증된다.

• Geomechanics and Engineering
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• 제17권2호
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• pp.133-143
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• 2019

An optimal hydraulic section is critical for irrigated water conservancy in seasonal frozen ground due to a large proportion of water leakage, as investigated by in-situ surveys. This is highly correlated with the frost heave of underlain soils in cold season. This paper firstly derived a practical model for frost heave of clayey soils, with temperature dependent thermal indexes incorporating phase change effect. A model test carried out on clay was used to verify the rationality of the model. A novel approach for optimizing the cross-section of irrigation canals in cold regions was suggested with live updated geometry characterized by three unique geometric constraints including slope of canal, ratio of practical flow section to the optimal and lining thickness. Allowable frost heave deformation and tensile stress in canal lining are utilized as standard in computation iterating with geometry updating while the construction cost per unit length is regarded as the eventual target in optimization. A typical section along the Jinghui irrigation canal was selected to be optimized with the above requirements satisfied. Results prove that the optimized hydraulic section exhibits smaller frost heave deformation, lower tensile stress and lower construction cost.

• Geomechanics and Engineering
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• 제28권4호
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• pp.359-374
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• 2022

Geology conditions are crucial in decision-making during the planning and design phase of a tunnel project. Estimation of the geology conditions of road tunnels is subject to significant uncertainties. In this work, the effectiveness of a novel regression method in estimating geological or geotechnical parameters of road tunnel projects was explored. This method, called Gaussian process regression (GPR), formulates the learning of the regressor within a Bayesian framework. The GPR model was trained with data of old tunnel projects. To verify its feasibility, the GPR technique was applied to a road tunnel to predict the state of three geological/geomechanical parameters of Rock Mass Rating (RMR), Rock Structure Rating (RSR) and Q-value. Finally, in order to validate the GPR approach, the forecasted results were compared to the field-observed results. From this comparison, it was concluded that, the GPR is presented very good predictions. The R-squared values between the predicted results of the GPR vs. field-observed results for the RMR, RSR and Q-value were obtained equal to 0.8581, 0.8148 and 0.8788, respectively.

• 전자공학회논문지
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• 제50권4호
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• pp.9-16
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• 2013

LTE (long term evolution) 및 LTE-A (LTE-Advanced) 시스템에서는 폐회로 기반의 다중 안테나 기술이 적용되었으며, 최대 비 전송 방식 (maximum ratio transmission, MRT) 보다 성능은 감소되지만, 동 이득 (equal gain) 특성을 유지할 수 있는 동 이득 전송 (equal gain transmission, EGT) 코드북을 채택하고 있다. 본 논문에서는 LTE 및 LTE-A 시스템에서 사용되는 코드북보다 성능을 향상시킬 수 있는 차분 코드북을 제안한다. 특히 동 이득 특성을 그대로 유지하면서 LTE 시스템의 코드북 요구조건을 모두 만족시키는 코드북을 제안한다. 코드북을 구성하는 코드워드들의 인자들 (elements)이 8-PSK(phase-shift keying) 성운 (constellation) 만을 사용하므로, 선부호화 및 복호 시 계산량이 낮아지는 LTE 코드북의 장점을 그대로 유지할 수 있다. 동 이득 성질은 특히 상향 링크에서 첨두 전력 대 평균 전력비 (PAPR)에 상당한 영향을 미치므로 매우 중요하다. 본 논문에서는 각 송신 안테나에 동 이득을 유지하는 성질을 이용한 새로운 차분 코드북을 제안하고, 동작원리를 회전 로크 구조로 설명한다. 컴퓨터 시뮬레이션을 통한 성능 분석에서, 동일한 피드백 비트 수를 갖는 같은 크기의 코드북에서 제안하는 차분 코드북은 기존 LTE 코드북보다 최소 0.9dB 성능 향상을 보인다.

• 조명전기설비학회논문지
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• 제15권6호
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• pp.65-72
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• 2001

본 논문에서는 UPS용 인버터의 강인한 디지털제어를 위하여 인버터 출력측 LC필터의 커패시터 전압과 전류의 2중 제어루프로 구성된 새로운 제어기법을 제안한다. 제안된 전압·전류의 2중 제어루프는 전압 제어루프의 커패시터 전압을 전류 제어루프의 커패시터 전류의 위상중심으로 두고, 2중 데드비트 제어를 수행함으로써 커패시터 전류의 위상지연이 보상된 완전한 진상전류 제어가 가능하게 된다. 전류 제어루프는 디지털 제어기의 시간 지연요소를 시스템의 고유한 파라미터로 가정한 2차 데드비트 제어기로 설계하여 디지털 제어기의 고유한 연산 지연시간에 의한 성능저하를 개선한다. 또한, 외란에 의한 데드비트 제어의 영향을 제거하기 위하여 부하전류 예측기법을 전류 제어루프에 부가하여 외란을 피드포워드 보상함으로써 외란에 강인한 전류제어를 수행한다.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2005년도 학술대회 논문집
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• pp.387-390
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• 2005

A This paper presents a novel three-phase current-fed Pulse Width Modulation converter with switched- capacitor type resonant DC link commutation circuit operating PWM pattern strategy under a design consideration of low-pass filter, which can operate on the basis of the principle of zero current soft-switching commutation. In the first place, the steady-state operating principle of this converter with a new resonant DC link snubber circuit is described in connection with the equivalent operation circuit, together with the practical design procedure of the switched-capacitor type resonant DC link circuit is discussed from a theoretical viewpoint on the basis of a design example for high-power applications. The actively delayed time correction method to compensate distorted currents due to a relatively long resonant commutation time is newly implemented in the open loop control scheme so as to acquire the new optimum PWM pattern. Finally, the experiment or set-up in laboratory system or this converter is concretely demonstrated herein to confirm a zero current soft-switching commutation of this converter. The comparative evaluations between current-fed hard switching PWM and soft-switching PWM converters are carried out from a viewpoint of their PWM converter characteristics.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.2
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• pp.15-22
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• 2006

This paper presents a novel signal tracking algorithm for GNSS receivers using a MLE technique. In order to perform a robust signal tracking in severe signal environments, e.g., high dynamics for navigation vehicles or weak signals for indoor positioning, the MLE based signal tracking approach is adopted in the paper. With assuming white Gaussian additive noise, the cost function of MLE is expanded to the cost function of NLSE. Efficient and practical approach for Doppler frequency tracking by the MLE is derived based on the assumption of code-free signals, i.e., the cost function of the MLE for carrier Doppler tracking is used to derive a discriminator function to create error signals from incoming and reference signals. The use of the MLE method for carrier tracking makes it possible to generalize the MLE equation for arbitrary codes and modulation schemes. This is ideally suited for various GNSS signals with same structure of tracking module. This paper proposes two different types of MLE based tracking method, i.e., an iterative batch processing method and a non-iterative feed-forward processing method. The first method is derived without any limitation on time consumption, while the second method is proposed for a time limited case by using a 1st derivative of cost function, which is proportional to error signal from discriminators of conventional tracking methods. The second method can be implemented by a block diagram approach for tracking carrier phase, Doppler frequency and code phase with assuming no correlation of signal parameters. Finally, a state space form of FLL/PLL/DLL is adopted to the designed MLE based tracking algorithm for reducing noise on the estimated signal parameters.

• Journal of Power Electronics
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• 제15권1호
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• pp.190-201
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• 2015

This paper uses the switching function approach to present a simple state model of the Vienna-type rectifier. The approach introduces the relationship between the DC-link neutral point voltage and the AC side phase currents. A novel direct power control (DPC) strategy, which is based on the sliding mode control (SMC) for Vienna I rectifiers, is developed using the proposed power model in the stationary ${\alpha}-{\beta}$ reference frames. The SMC-based DPC methodology directly regulates instantaneous active and reactive powers without transforming to a synchronous rotating coordinate reference frame or a tracking phase angle of grid voltage. Moreover, the required rectifier control voltages are directly calculated by utilizing the non-linear SMC scheme. Theoretically, active and reactive power flows are controlled without ripple or cross coupling. Furthermore, the fixed-switching frequency is obtained by employing the simplified space vector modulation (SVM). SVM solves the complicated designing problem of the AC harmonic filter. The simplified SVM is based on the simplification of the space vector diagram of a three-level converter into that of a two-level converter. The dwelling time calculation and switching sequence selection are easily implemented like those in the conventional two-level rectifier. Replacing the current control loops with power control loops simplifies the system design and enhances the transient performance. The simulation models in MATLAB/Simulink and the digital signal processor-controlled 1.5 kW Vienna-type rectifier are used to verify the fast responses and robustness of the proposed control scheme.

• 한국멀티미디어학회논문지
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• 제25권10호
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• pp.1375-1385
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• 2022

In this paper, we propose a semi-supervised domain adaptation solution to deal with practical face recognition (FR) scenarios where a single face image for each target identity (to be recognized) is only available in the training phase. Main goal of the proposed method is to reduce the discrepancy between the target and the source domain face images, which ultimately improves FR performances. The proposed method is based on the Domain Adatation network (DAN) using an MMD loss function to reduce the discrepancy between domains. In order to train more effectively, we develop a novel loss function learning strategy in which MMD loss and cross-entropy loss functions are adopted by using different weights according to the progress of each epoch during the learning. The proposed weight adoptation focuses on the training of the source domain in the initial learning phase to learn facial feature information such as eyes, nose, and mouth. After the initial learning is completed, the resulting feature information is used to training a deep network using the target domain images. To evaluate the effectiveness of the proposed method, FR performances were evaluated with pretrained model trained only with CASIA-webface (source images) and fine-tuned model trained only with FERET's gallery (target images) under the same FR scenarios. The experimental results showed that the proposed semi-supervised domain adaptation can be improved by 24.78% compared to the pre-trained model and 28.42% compared to the fine-tuned model. In addition, the proposed method outperformed other state-of-the-arts domain adaptation approaches by 9.41%.

• Geomechanics and Engineering
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• 제33권2호
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• pp.175-182
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• 2023

In general, the design of structures and its construction processes are fundamentally dependent on their foundation and supporting ground. Thus, it is imperative to understand the behavior of the soil under certain stress and drainage conditions. As it is well known that certain characteristics and behaviors of soils with fines are highly dependent on water content, it is critical to accurately measure and identify the status of the soils in terms of water contents. Liquid limit is one of the important soil index properties to define such characteristics. However, liquid limit measurement can be affected by the proficiency of the operator. On the other hand, dynamic properties of soils are also necessary in many different applications and current testing methods often require special equipment in the laboratory, which is often expensive and sensitive to test conditions. In order to address these concerns and advance the state of the art, this study explores a novel method to determine the liquid limit of cohesive soil by employing video-based vibration analysis. In this research, the modal characteristics of cohesive soil columns are extracted from videos by utilizing phase-based motion estimation. By utilizing the proposed method that analyzes the optical flow in every pixel of the series of frames that effectively represents the motion of corresponding points of the soil specimen, the vibration characteristics of the entire soil specimen could be assessed in a non-contact and non-destructive manner. The experimental investigation results compared with the liquid limit determined by the standard method verify that the proposed method reliably and straightforwardly identifies the liquid limit of clay. It is envisioned that the proposed approach could be applied to measuring liquid limit of soil in practical field, entertaining its simple implementation that only requires a digital camera or even a smartphone without the need for special equipment that may be subject to the proficiency of the operator.