• 조명전기설비학회논문지
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• 제14권4호
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• pp.8-15
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• 2000

본 논문에서는 F 컨버터의 능동형 PFC 시스템을 구성하고, 진력 변환시 입력 전류를 전원 전압과 동장연 정현파로 제이하는 동시에 출력 전압에 포함되는 고조파 등의 잡음을 제거하고 직류 출력 전압을 제어하기 위한 PWM-PFM 제어 기법을 제시하였다. 부하단에서 필요한 전압과 높은 전력 효율을 얻기 위하여 인버터 단계애서 전류 성형 제어를 실행한 후, 순방­향(forward) 컨버터에 의해 다시 직류 전압으로 변환시켜 부하단으로 출력한다. 입력 전압이 30[V]이교 승압 (boost) 인덕터가 1.1[mH]일 때 정격 출력은 전압 50[V], 전류1[A], 듀티비 0.5 이상으로 하여 부하 처항에 따른 전압 변화를 PWM-PFM 제어 기법을 이용하며 제어하였고, 전류 성형 기법을 이용하여 0.93획 역률로 고조파를 감쇠 및 개선하였다.

• 조명전기설비학회논문지
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• 제24권5호
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• pp.29-36
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• 2010

본 논문에서는 새로운 변조방식을 사용한 단상 인버터 시스템을 제안한다. 제안한 시스템은 buck-boost 변환기와 인버터로 구성되며 새로운 변조방식인 PWAM(Pulse Width/Amplitude Modulation)방식을 사용하여 제어한다. PWAM방식은 PWM(Pulse Width Modulation)방식과 PAM(Pulse Amplitude Modulation) 방식이 혼합된 새로운 변조방식이며 인버터의 입력단에 위치한 buck-boost 변환기는 일정한 직류전압을 입력으로 받아 가변 직류전압으로 변환한다. 인버터는 buck-boost 변환기에서 출력된 가변 직류전압을 입력으로 하며, PWM 구간에서는 PWM 스위칭을 하고 PAM 구간에서는 인버터가 스위칭을 하지 않음으로써 정현 교류전압으로 변환한다. 제안한 PWAM방식을 사용한 단상 인버터 시스템은 PAM 구간에서 스위칭 동작을 하지 않으므로 기존의 방식에 비해 스위칭 횟수가 감소하여 스위칭 손실을 줄일 수 있다.

• 전력전자학회논문지
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• 제20권6호
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• pp.517-525
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• 2015

A grid connected inverter must be operated as the main electricity source under an isolated condition caused by the grid problem. Conventionally, the dual loop controller is used for the grid inverter, and the controller is used for control under the stand-alone mode. Generally, the PI(Proportional - Integral) controller is highly efficient under a synchronous reference frame, and stable control can be available. However, in this synchronous frame-based control, high-quality DSP is required because many sinusoidal calculations are necessary. When the PI control is conducted under a stationary frame, the controller constructions are made simple so that they work even with a low-price micro controller. However, given the characteristics of the PI controller, it should be designed with the phase of reference voltage considered. Otherwise, the phase delay of the output voltage can occur. Although the current controller also has a higher bandwidth than the voltage controller, distortion of the voltage is difficult to avoid only by the rapid response of the PI controller, as a sudden load change can occur in the nonlinear load. In this study, a new control method that solves the voltage controller bandwidth problem and rapidly copes with it even in the nonlinear load situation is proposed. The validity of the proposed method is proved by simulation and experimental results.

• 전력전자학회논문지
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• 제16권6호
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• pp.594-601
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• 2011

본 논문은 상용의 전원 전압이 불평형 및 왜곡을 갖는 경우, 전원전압 불평형 및 왜곡 보상기능을 갖는 전류제어기를 제안한다. 일반적으로 3상 전원 시스템은 공통 입력 단자 (Point of Common Coupling)에 단상 부하 및 비선형 부하가 3상 부하와 같이 연결될 수 있어, 종종 불평형과 왜곡이 발생한다. 이런 조건하에서 3상 PWM 정류기를 일반적인 전류 제어기로 제어 할 경우, 3상 PWM 정류기 입력 전류가 불평형 및 왜곡을 갖는 문제가 발생한다. 본 논문에서는 간단한 모델 기반 적응 제어 시스템(Model Reference Adaptive System)기법을 이용하여 3상 입력 전압의 불평형 및 왜곡을 관측하고 전향 보상하는 전류 제어기를 제안하며, 모의해석과 실험을 통하여 그 효용성을 입증한다.

• 한국통신학회논문지
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• 제12권5호
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• pp.478-491
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• 1987

본 논문에서는 정현파 입력 신호의 위상을 PGZC(Positive Going Zero Crossing)에 대해 주기당 한번씩 추적하는 디지털 위상동기회로(DPLL)의 성능 개선을 위해 반주기마다 표본화를 행함으로써 위상오차를 감소시킬 수 있는 DPLL을 제시하였다. 제안된 DPLL은 두개의 샘플러에 의해 정현파 입력 신호의 위상을 PGZG에 대해 주기당 2회씩 추적함으로써 기존의 DPLL보다 동기대역의 손실없이 정상상태 위상오차 변동의 범위를 전체적으로 1/2 정도 감소시킬 수 있었다. 또한, 연속 표본간의 오차간격과 양자화 레벨이 동일할 경우에 있어서 반주기 표본화를 이용하는 DPLL이 기존의 DPLL보다 빠른 동기를 이루게 됨을 알 수 있었다. 이 제시된 루우프에 대한 해석 결과를 실제적으로 요구되는 조건들에 대하여 컴퓨터 시뮬레이션 행함으로써 검증하였다.

• Advances in aircraft and spacecraft science
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• 제3권2호
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• pp.113-148
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• 2016

In a whole variety of higher order plate theories existing in the literature no consideration is given to the transverse normal strain / deformation effects on flexural response when these higher order theories are applied to shear flexible composite plates in view of minimizing the number of unknown variables. The objective of this study is to carry out cylindrical bending of simply supported laminated composite and sandwich plates using sinusoidal shear and normal deformation plate theory. The most important feature of the present theory is that it includes the effects of transverse normal strain/deformation. The displacement field of the presented theory is built upon classical plate theory and uses sine and cosine functions in terms of thickness coordinate to include the effects of shear deformation and transverse normal strain. The theory accounts for realistic variation of the transverse shear stress through the thickness and satisfies the shear stress free conditions at the top and bottom surfaces of the plate without using the problem dependent shear correction factor. Governing equations and boundary conditions of the theory are obtained using the principle of minimum potential energy. The accuracy of the proposed theory is examined for several configurations of laminates under various static loadings. Some problems are presented for the first time in this paper which can become the base for future research. For the comparison purpose, the numerical results are also generated by using higher order shear deformation theory of Reddy, first-order shear deformation plate theory of Mindlin and classical plate theory. The numerical results show that the present theory provides displacements and stresses very accurately as compared to those obtained by using other theories.

• Steel and Composite Structures
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• 제17권6호
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• pp.891-906
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• 2014

This study aims to present a three dimensional finite element model to investigate the wave propagation in a concrete filled steel tubular column (CFSC) due to transient impact load. Both the concrete and steel are regarded as linear elastic material. The impact load is simulated by a semi sinusoidal impulse. Besides the CFSC models, a concrete column (CC) model is established for comparing under the same loading condition. The propagation characteristics of the transient waves in CFSC are analyzed in detail. The results show that at the intial stage of the wave propagation, the velocity waves in CFSC are almost the same as those in CC before they arrive at the steel tube. When the waves reach the column side, the velocity responses of CFSC are different from those of CC and the difference is more and more obvious as the waves travel down along the column shaft. The travel distance of the wave front in CFSC is farther than that in CC at the same time. For different wave speeds in steel and concrete material, the wave front in CFSC presents an arch shape, the apex of which locates at the center of the column. Differently, the wave front in CC presents a plane surface. Three dimensional effects on top of CFSC are obvious, therefore, the peak value and arrival time of incident wave crests have great difference at different locations in the radial direction. High-frequency waves on the waveforms are observed. The time difference between incident and reflected wave peaks decreases significantly with r/R when r/R < 0.6, however, it almost keeps constant when $r/R{\geq}0.6$. The time duration between incident and reflected waves calculated by 3D FEM is approximately equal to that calculated by 1D wave theory when r/R is about 2/3.

• Coupled systems mechanics
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• 제9권3호
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• pp.237-264
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• 2020

This article investigates the static behaviour of functionally graded (FG) plates sometimes declared as advanced composite plates by using a simple and accurate quasi-3D and 2D hyperbolic higher-order shear deformation theories. The properties of functionally graded materials (FGMs) are assumed to vary continuously through the thickness direction according to exponential law distribution (E-FGM). The kinematics of the present theories is modeled with an undetermined integral component and satisfies the free transverse shear stress conditions on the top and bottom surfaces of the plate; therefore, it does not require the shear correction factor. The fundamental governing differential equations and boundary conditions of exponentially graded plates are derived by employing the static version of principle of virtual work. Analytical solutions for bending of EG plates subjected to sinusoidal distributed load are obtained for simply supported boundary conditions using Navier'is solution procedure developed in the double Fourier trigonometric series. The results for the displacements and stresses of geometrically different EG plates are presented and compared with 3D exact solution and with other quasi-3D and 2D higher-order shear deformation theories to verify the accuracy of the present theory.

• 설비공학논문집
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• 제23권10호
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• pp.670-677
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• 2011

Direct numerical simulation are performed in order to investigate the effect of the circular cylinder shape on the forced convection around a circular cylinder at the Reynolds number of 300 and Prandtl number of 0.71. Three-dimensional characteristics of fluid flow and heat transfer around the smooth, wavy and torsional cylinders are investigated. A wavy cylinder has the sinusoidal variation in the cross sectional area along the spanwise direction with the wave length of ${\pi}/3$ and wavy amplitude of 0.1. A torsional cylinder has the twisted elliptic cross section with a torsional period of ${\pi}/2$ and an axis ratio of 1.35 corresponding to the major axis of 1.15 and the minor axis of 0.85. The value of time-and surface-averaged drag coefficient for the smooth cylinder is similar to that for the wavy cylinder, but larger than that for the torsional cylinder. The time and surface-averaged lift coefficient for the smooth cylinder is larger than that for the wavy and torsional cylinders. The time-averaged local heat transfer rate for the wavy and torsional cylinders shows different distribution along the circumferential direction, compared to that for the smooth cylinder because of the shape change in the spanwise direction for the cases of the wavy and torsional cylinders.

• 대한조선학회논문집
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• 제29권3호
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• pp.53-58
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• 1992

파랑중(波浪中)에서 조종운동(操縱運動)을 하는 선박(船舶)에 있어, 실용적으로 선형(線形) 계산(計算)의 경우 파랑력(波浪力)을 단순한 정상(定常) 변동(變動) 외력(外力)으로 취급하는 수가 많다. 본 논문은 이와같은 경우에 있어서 파랑력에 의한 조종(操縱) 운동(運動)에 있어서의 Memory Effect를 조사하여, 이러한 실용 계산법(計算法)의 타당성(妥當性)을 논하였다. 그 결과를 요약하면 (1) $\omega_e$의 주파수(周波數)로 선체에 작용하는 정상(定常) 파랑력에 의한 Memory Effect도 거의 무시(無視)할 수 있다. (2) 따라서, 파랑중(波浪中)에서 조종 운동을 취급하는 경우, 간이 계산법으로서, 정수(靜水)중에서의 조타(操舵) 응답과 규칙파(規則波)중에서의 선체응답(船體應答)을 계산하여 이 둘을 합(合)하여도 무방하다. 그러나, 이상의 결론(結論)은 선형 운동에 국한(局限)된 것으로서, 실제의 조종 운동은 비선형성(非線形性)이 중요시(重要視)되므로 정상(定常) 파랑(波浪) 외력(外力)에 의한 Memory Effect를 좀더 엄밀(嚴密)하게 고찰(考察)하기 위해서는 비선형(非線形) Impulse Response Function을 구(求)하고 이를 이용하여 파랑력(波浪力)에 의한 Memory Effect를 평가(評價)하여야 할 것이다.