• 한국태양에너지학회 논문집
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• 제29권5호
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• pp.65-72
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• 2009

The new method is proposed to improve high speed detection of grid voltage phase and magnitude during a voltage dip due to a grid faults. Usually, A LPF(Low Pass Filter) is used in the feedback loop of PLL (Phase Locked Loop) system because the measured grid voltage contains harmonic distortions and sensor noises. so, a new design method of the loop gain of the PI -type controller in the PLL system is proposed with the consideration of the dynamics of the LPF. As a result, a better transient response can be obtained with the proposed design method. The LPF frequency and PI controller gain are designed in coordination according to the steady state and dynamic performance requirement. This paper shows the feasibility and the usefulness of the proposed methods through the computer simulation and the lab-scale experiments.

• Journal of Power Electronics
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• 제16권2호
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• pp.572-583
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• 2016

In view of the speed control characteristics of induction traction motors and the problems of direct torque control (DTC) algorithms in current applications, this paper presents a DTC algorithm characterized by a symmetrical polygon flux control and a closed loop power control in the constant-torque base speed region and constant-power field-weakening region of induction traction motors. This algorithm only needs to add a stator flux control algorithm to the traditional DTC structures. This has the benefit of simplicity, while maintaining the features of traditional algorithms such as a rapid dynamic response, uncomplicated control circuit, reduced dependence on motor parameters, etc. In addition, it obtains a smoother flux trajectory that is conducive to improvement of the harmonic elimination capability, the switching frequency utilization as well as the torque and power performance in the field-weakening region. The effectiveness and feasibility of this DTC algorithm are demonstrated by both theoretical analysis and experimental results.

• Journal of Power Electronics
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• 제17권5호
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• pp.1363-1371
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• 2017

In this paper, an improved Direct Power Control (DPC) algorithm is presented for grid connected three phase PWM rectifiers. The new DPC approach is based on two main tasks. First the optimization of the look-up table, which is well-known in conventional DPC, is outlined for selecting the optimum converter output voltage vectors. Secondly a very simple and effective method is used to directly calculate their duty cycles from the power errors. Therefore, the measured active and reactive powers are made to track their references using hysteresis controllers. Then two vectors are selected and applied during one control cycle to minimize both the active and reactive power ripples. The main advantages of this method are that there is no need of linear current controllers, coordinates transformations or modulators. In addition, the control strategy is able to operate at constant switching frequencies to ease the design of the power converter and the AC harmonic filter. The control exhibits a good steady state performance and improves the dynamic response without any overshoot in the line current. Theoretical principles of the proposed method are discussed. Both simulation and experimental results are presented to verify the performance and effectiveness of this control scheme.

• Structural Engineering and Mechanics
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• 제39권4호
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• pp.465-498
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• 2011

Concrete structures are generally cracked in flexural tension at working loads. Concrete beams with asymmetric section details and crack patterns exhibit different flexural rigidity depending upon the sense of the applied flexural moment. In this paper, three different models, having the same natural period, of such SDOF bilinear dynamical systems have been proposed. The Model-I and Model-II have constant damping coefficient, but the latter is characterized by two stiffness coefficients depending upon the sense of vibration amplitude. The Model-III, additionally, has two damping coefficients as well. In this paper, the dynamical response of Model-III to sinusoidal loading has been investigated and compared with that of Model-II studied earlier. It has been found that Model-III exhibits regular and irregular sub-harmonics, jump phenomena and strong sensitivity to initial conditions, forcing frequency, system period as well as the sense of peak sinusoidal force. The constant sustained load has been found to affect the natural period of the dynamical system. The predictions of Model-I have been compared with those of the approximate linear model adopted in present practice. The behaviour exhibited by different models of the SDOF cracked elastic concrete structures under working loads and the theoretical and practical implications of the approach followed have been critically evaluated.

• Composites Research
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• 제12권2호
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• pp.26-35
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• 1999

모달변형에너지법과 조화진동해석법을 이용하여 겹침이음부와 부분층댐버를 갖는 보에 대해 유한요소모델을 설정하고 진동감쇠특성을 연구하였다. 모달변형에너지법과 조화진동해석법으로 구한 계의 공진주파수와 손실계수는 거의 같은 값ㅇ르 보였으며, 형상의 변화에 따른 손실계수 변동경향은 이론해석에 의한 결과와 유사하였다. 부분층댐퍼의 위치, 점탄성층과 보강탄성층의 두께 및 탄성계수의 변화가 계의 손실계수에 미치는 영향을 파악하였으며, 점탄성층의 손실계수변화에 따른 영향도 검토하였다. 이들 결과로부터 계의 감쇠효과를 극대화하기 위한 구조물의 형상 및 물성조건을 제시하였다.

• Advances in aircraft and spacecraft science
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• 제3권2호
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• pp.197-209
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• 2016

The Spacecraft (S/C) numerical sine test-predictions are usually performed through Finite Element Method (FEM) Frequency Response Analysis (FRA), that is the hypothesis of steady-state responses to harmonic excitation to the S/C base is made. In the test practice, the responses are transient and may be significantly different from those predicted through FRA. One of the most significant causes of discrepancy between prediction and test consists in the beating phenomena. After a brief overview of the topic, the typical causes of beating are described in the first part of the paper. Subsequently, focus is made on the sine sweep rate effect, which often leads to have beatings after the resonance of weakly damped modes. In this work, the approach illustrated in the literature for calculating the sine sweep rate effect in the case of Single-Degree-Of-Freedom (SDOF) oscillators is extended to Multi-Degrees-Of-Freedom (MDOF) systems, with the aim of increasing the accuracy of the numerical sine test-predictions. Assumptions and limitations of the proposed methodology are detailed along the paper. Several assessments with test results are discussed and commented.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제48권12호
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• pp.691-700
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• 1999

This paper proposes a novel switching strategy of 1Mvar STATCON using cascade multilevel H-bridge inverter(HBI) for FACTS application. To control the reactive power instantaneously, the d-q dynamic system model is described and analyzed. A single pulse pattern based on the SHEM(Selective Harmonic Elimination Method) technique is determined from the look-up table to reduce the line current harmonics and a rotating fundamental frequency switching scheme is presented to adjust the DC voltage of each inverter capacitor at the same value. So the voltage unbalance problem between separately DC bus voltage is improved by using the proposed switching scheme. As a result, the presented inverter configuration not only reduces the system complexity by eliminating the isolation at the AC input side transformer but also improves the dynamic response to the step change of reactive power.

• 한국산학기술학회논문지
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• 제12권11호
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• pp.5306-5313
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• 2011

기존 동조질량감쇠기의 최적설계변수에 관한 연구는 풍하중과 같은 조화하중을 받는 구조물을 대상으로 연구가 수행되었다. 본 연구에서는 수치해석을 통하여 지진하중이 작용하는 건축물에 설치되는 동조질량감쇠기의 최적 감쇠비와 동조진동수비를 구하였다. 지반특성을 단단한 지반, 연약지반, 단층 근처 지반으로 분류하고, 이들 지반특성을 고려한 수치해석을 통해 구한 동조질량감쇠기의 설계변수를 기존 연구 결과와 비교하였다. 수치해석결과 본 연구로부터 구해진 동조질량감쇠기의 설계변수값을 적용한 경우 지진하중에 의한 응답제어에 기존 연구를 통해 얻어진 변수값을 적용한 경우에 비해 더 나은 제어효과를 얻을 수 있음을 알 수 있었다.

• Coupled systems mechanics
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• 제8권3호
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• pp.199-218
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• 2019

This paper studies the forced vibration of the hydro-elastic system consisting of the anisotropic (orthotropic) plate, compressible viscous fluid and rigid wall within the scope of the exact equations and relations of elastodynamics for anisotropic bodies for describing of the plate motion, and with utilizing the linearized exact Navier-Stokes equations for describing of the fluid flow. For solution of the corresponding boundary value problem it is employed time-harmonic presentation of the sought values with respect to time and the Fourier transform with respect to the space coordinate on the coordinate axis directed along the plate length. Numerical results on the pressure acting on the interface plane between the plate and fluid are presented and discussed. The main aim in this discussion is focused on the study of the influence of the plate material anisotropy on the frequency response of the mentioned pressure. In particular, it is established that under fixed values of the shear modulus of the plate material a decrease in the values of the modulus of elasticity of the plate material in the direction of plate length causes to increase of the absolute values of the interface pressure. The numerical results are presented not only for the viscous fluid case but also for the inviscid fluid case.

• 조명전기설비학회논문지
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• 제23권8호
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• pp.33-40
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• 2009

본 논문에서는 HAI(Hybrid Artificial Intelligent) 제어기반의 SV PWM 방식을 이용한 IPMSM의 고성능 제어를 제시한다. HAI 제어기는 적응 퍼지제어 및 신경회로망의 장점을 혼합 적용한다. SV PWM 방식은 지금까지 산업용 전동기 제어분야에 적용되고 있고 출력전류의 고조파 비율, 스위칭 주파수 및 응답특성을 향상시키는 수 있는 기법이다. HAI 제어기는 지령전압을 계산할 때 발생되는 문제점을 해결하기 위하여 종래의 PI 제어기를 대체하여 사용한다. HAI 제어기는 지령모델 기반의 적응제어, 퍼지제어 및 신경회로망으로 구성되어 속도 성능을 개선한다. 본 논문에서는 제시한 HAI 제어기를 적용하여 파라미터 변동, 정상상태 및 과도상태 등의 응답특성을 분석하고 종래의 FNN 제어기 및 PI 제어기의 응답특성과 비교한다. 따라서 본 논문에서는 HAI 제어기의 타당성을 입증한다.