Variable Structure Control of the Active and Reactive Powers for a DFIG in Wind Turbines

Chwa, Dongkyoung,Lee, Kyo-Beum IEEE 2010 IEEE transactions on industry applications Vol.46 No.6

<P>The original direct power control (DPC) is known to give a fast response under transient conditions. However, active power, reactive power, and current pulsations occur in steady-state operation. The variable structure control (VSC) method for a doubly-fed-induction-generator-based wind turbine system is presented, using the principles of an active and reactive power controller known as modified DPC and where VSC and space-vector modulation are combined to ensure high-performance operation. The VSC scheme is designed following the modified DPC philosophy, which provides robust and fast power controls without frame transformation and the current controller that is used in the conventional field-oriented control drive. Simulation and experimental results demonstrate that the proposed methods preserve the effectiveness and robustness during variations of active and reactive power, rotor speed, and converter dc-link voltage.</P>

Global EDF Schedulability Analysis for Parallel Tasks on Multi-Core Platforms

Chwa, Hoon Sung,Lee, Jinkyu,Lee, Jiyeon,Phan, Kiew-My,Easwaran, Arvind,Shin, Insik IEEE 2017 IEEE transactions on parallel and distributed syst Vol.28 No.5

<P>With the widespread adoption of multi-core architectures, it is becoming more important to develop software in ways that takes advantage of such parallel architectures. This particularly entails a shift in programming paradigms towards fine-grained, thread-parallel computing. Many parallel programming models have been introduced for targeting such intra-task thread-level parallelism. However, most successful results on traditional multi-core real-time scheduling are focused on sequential programming models. For example, thread-level parallelism is not properly captured into the concept of interference, which is key to many schedulability analysis techniques. Thereby, most interference-based analysis techniques are not directly applicable to parallel programming models. Motivated by this, we extend the notion of interference to capture thread-level parallelism more accurately. We then leverage the proposed notion of parallelism-aware interference to derive efficient EDF schedulability tests that are directly applicable to parallel task models, including DAG models, on multi-core platforms, without knowing an optimal schedule. Our evaluation results indicate that the proposed analysis significantly advances the state-of-the-art in global EDF schedulability analysis for parallel tasks. In particular, we identify that our proposed schedulability tests are adaptive to different degrees of thread-level parallelism and scalable to the number of processors, resulting in substantial improvement of schedulability for parallel tasks on multi-core platforms.</P>

Range and Motion Estimation of a Monocular Camera Using Static and Moving Objects

Chwa, Dongkyoung,Dani, Ashwin P.,Dixon, Warren E. Institute of Electrical and Electronics Engineers 2016 IEEE transactions on control systems technology Vol. No.

<P>We propose a method of estimating the motion of a monocular camera looking at moving objects and their range. Unlike the previous studies where the camera and object motion should be constrained in estimating structure and motion (SaM) of moving objects, the proposed method do not require those constraints even though only a monocular camera is used. By first arranging the SaM dynamics in terms of the measurable states, we design robust nonlinear observers in a sequential way for both static (stationary) and dynamic (moving) objects. Through the combination of these estimates obtained by nonlinear observers, the reconstruction of the 3-D structure of the dynamic objects can be achieved using just 2-D images of a monocular camera. Simulations are performed in the case of changing camera and object velocities, such that the advantages of the proposed method can be clearly demonstrated.</P>

Synthesis and Properties of CuNx Thin Film for Cu/Ceramics Bonding

Chwa, Sang-Ok,Kim, Keun-Soo,Kim, Kwang-Ho The Korean Ceramic Society 1998 The Korean journal of ceramics Vol.4 No.3

$Cu_3N$ film deposited on silicon oxide substrate by r.f. reactive sputtering technique. Synthesis and properties of copper nitride film were investigated for its possible application to Cu metallization as adhesive interlayer between copper and $SiO_2. Cu_3N$ film was synthesized at the substrate temperature ranging from $100^{\circ}C$ to $200^{\circ}C$ and at nitrogen gas ratio above $X_{N2}=0.4. Cu_3N, CuN_x$, and FGM-structured $Cu/CuN_x$ films prepared in this work passed Scotch-tape test and showed improved adhesion property to silicon oxide substrate compared with Cu film. Electrical resistivity of copper nitride film had a dependency on its lattice constant and was ranged from 10-7 to 10-1 $\Omega$cm. Copper nitride film was, however, unstable when it was annealed at the temperature above $400^{\circ}C$.

Online trajectory planning of robot arms for interception of fast maneuvering object under torque and velocity constraints

Chwa, Dongkyoung,Kang, Junho,Choi, Jin Young IEEE 2005 IEEE TRANSACTIONS ON SYSTEMS MAN AND CYBERNETICS P Vol.35 No.6

This paper presents a novel approach to an online trajectory planning of robot arms for the interception of a fast-maneuvering object under torque and velocity constraints. A body axis is newly introduced as a trajectory-planning coordinate in order to meet the position and the velocity matching conditions for a smooth grasp of the fast-maneuvering object. Using the position of the object and the end-effector in the inertia axis, the acceleration commands are generated in the X-, Y-, and Z-directions of the body axis and the acceleration commands are modified considering the torque and the velocity constraints. The trajectory planning in the X-direction becomes the speed planning to achieve the maximum speed, whereas the trajectory planning in the Y- and Z-directions becomes the direction planning where a missile-guidance algorithm is employed to intercept the maneuvering object. Finally, the acceleration commands in the body axis are transformed into the angle commands of the end-effector in the joint axis, which is used as the actual trajectory commands in robot arms.

On the Euclidean Center Problem

Chwa, Kyung-Yong 한국경영과학회 1982 韓國經營科學會誌 Vol.7 No.2

This paper presents an efficient algorithm for finding a new facility(center) in the Euclidean plane in accordance with minimax criterion: that is, the facility is located to minimize the maximum weighted Euclidean distance. The method given in this paper involves computational geometry. Some possible extensions of this problem are also discussed.

Gas Sensitization of Tin Oxide Film by Resistance

Chwa, Sang-Ok,Park, Hee-Chan,Kim, Kwang-Ho The Korean Ceramic Society 1998 The Korean journal of ceramics Vol.4 No.3

Gas sensitizations of tin oxide film were investigated by measuring the change of film resistance in various gas atmospheres such as $N_2,\; O_2,\; H_2O$. The main test sample, polycrystalline $SnO_2$ film containing small Sb as a dopant was prepared by a sputtering technique and showed a long term stability in base resistance and thus, in gas sensitivity. The adsorption of oxygen on the film surface as a type of $(O_{ads})$ at the temperature of around $300^{\circ}C$ played important roles in sensor operating mechanism. The roles were ⅰ) the increase of base resistance in ambient air, which consequently lead to high sensitivity and ⅱ) the promotion of fast recovery. The reaction of hydrogen gas with the already adsorbed $(O_{ads})$ ions was considered as a decisive sensitization mechanism of tin oxide film. However, the dissociation of hydrogen molecules on film surface, by direct donation of electron to film also took a major part in the sensitization. The effect of humidity on gas sensitization was found to be negligible at the sensor operating temperature of around $300^{\circ}C$.

Fabrication and Characteristics of High-performance Doped-$SnO_2$ Thin Films for Explosive Gas Sensor

Chwa, Sang-Ok,Park, Hee-Chan,Kim, Kwang-Ho The Korean Ceramic Society 1996 The Korean journal of ceramics Vol.2 No.2

Long term stability, sensitization in air, and gas sensing behaviors of tin oxide films were investigated with doping of antimony and palladium. The tin oxide films were prepared on a Corning glass by reactive rf sputtering method and tested for detection of hydrogen gas. Sb-doping improved a long-term stability in the base resistance of $SnO_2$ film sensor. A small amount of Pd doping caused the optimum sensor operating temperature to reduce and also enhanced the gas sensitivity, compared with the undoped $SnO_2$ film. Gas sensitivity depended largely on the film thickness. The important sensitization reactions for sensor operating were $(O_{2ads})+e^-\;{\rightarrow}\;2(O_{ads})^-$ on the surface of $SnO_2$ film at elevated temperature in air and a followed reaction of hydrogen atoms with $(O_{ads})^-$ ions.

여대남반고 (麗代南班考)

조좌호(Chwa Ho Cho) 동국대학교 동국역사문화연구소 1957 동국사학 Vol.5 No.-

N/A

Reliability-Based Topology Optimization with Uncertainties

Kim Chwa-Il,Wang Se-Myung,Bae Kyoung-Ryun,Moon Hee-Gon,Choi Kyung-K. The Korean Society of Mechanical Engineers 2006 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.20 No.4

This research proposes a reliability-based topology optimization (RBTO) using the finite element method. RBTO is a topology optimization based on probabilistic (or reliability) constraints. Young's modulus, thickness, and loading are considered as the uncertain variables and RBTO is applied to static and eigenvalue problems. The RBTO problems are formulated and a sensitivity analysis is performed. In order to compute probability constraints, two methods-RIA and PMA-are used. Several examples show the effectiveness of the proposed method by comparing the classical safety factor method.