• Journal of Magnetics
• /
• v.16 no.1
• /
• pp.71-73
• /
• 2011

Hybrid electric vehicles have attracted much attention of late, emphasizing the necessity of developing traction motors with a high input current and a wide speed range. Among such traction motors, various researches have been conducted on interior permanent-magnet synchronous motors (IPMSMs) with high power density and mechanical solidity. Due to the complexity of its parameters, however, with nonlinear motor characteristics and current vector control, it is actually difficult to accurately estimate the base speed within an actual operating speed range or a voltage limit. Moreover, it is impossible to construct an efficiency map as the efficiency differs according to the control mode. In this study, a simulation method for operation performance considering the nonlinearity of IPMSM was proposed. For this, datasets of various nonlinear parameters were made via the finite-element method and interpolation. Maximum torque-per-ampere and flux-weakening control were accurately simulated using the datasets, and an IPMSM efficiency map was accurately constructed based on the simulation. Lastly, the validity of the simulation was verified through tests.

• Korean Journal of Materials Research
• /
• v.29 no.6
• /
• pp.343-348
• /
• 2019

Structural and mechanical effects of the dynamical precipitation in two copper-base alloys have been investigated over a wide range of deformation temperatures. Basing upon the information gained during the experiment, also some general conclusion may be formulated. A one concerns the nature of dynamic precipitation(DP). Under this term it is commonly understood decomposition of a supersaturated solid solution during plastic straining. The process may, however, proceed in two different ways. It may be a homogeneous one from the point of view of distribution and morphological aspect of particles or it may lead to substantial difference in shape, size and particles distribution. The effect is controlled by the mode of deformation. Hence it seems to be reasonable to distinguish DP during homogeneous deformation from that which takes place in heterogeneously deformed alloy. In the first case the process can be analyzed solely in terms of particle-dislocation-particle interrelation. Much more complex problem we are facing in heterogeneously deforming alloy. Deformation bands and specific arrangement of dislocations in form of pile-ups at grain boundaries generate additional driving force and additional nucleation sites for precipitation. Along with heterogeneous precipitation, there is a homogeneous precipitation in areas between bands of coarse slip which also deform but at much smaller rate. This form of decomposition is responsible for a specially high hardening rate during high temperature straining and for thermally stable product of the decomposition of alloy.

• Proceedings of the KIPE Conference
• /
• 2019.07a
• /
• pp.92-94
• /
• 2019

양방향 스위치를 가지는 Bridgeless PFC 컨버터(BBPFC)는 구조상 복잡한 플로팅 게이트 드라이버를 활용함에도 불구하고 좋은 공통모드 잡음 즉, Common-Mode (CM) 노이즈 특성과 간단한 제어 방법으로 인해 많은 브리지리스 PFC 컨버터 중에서도 고전력 응용분야에서 매우 매력적인 토폴로지이다. 이러한 BBPFC는 도통 경로 상에 위치한 정류 다이오드의 역회복 특성의 상대적인 편차를 활용하여 전력 밀도를 감소시키지 않고도 좋은 공통모드 (CM) 노이즈 특성의 확보가 가능하다. 하지만 이러한 장점을 가지는 BBPFC 구조를 고전력 서버용 전원장치분야에서 활용할 경우, 이미 등록된 특허로 인해 매우 높은 개런티를 지불해야 하므로 그 활용이 매우 제한적이다. 따라서, 본 논문에서는 이미 등록된 특허를 회피하고, 동시에 기존 BBPFC 회로가 가지는 단점인 플로팅 게이트 드라이버를 활용하는 단점을 개선하는 새로운 형태의 브리지리스 PFC 컨버터를 제안한다. 제안된 컨버터는 기존 BBPFC가 가지는 장점인 좋은 (CM) 노이즈 특성을 가지며, 동시에 높은 효율을 달성 할 수 있다. 또한 제안된 컨버터의 경우, 복잡한 플로팅 형태의 게이트 드라이버 회로가 아닌 간단한 부트스트랩 회로를 활용하여 회로를 운용할 수 있다. 더불어 제안된 컨버터는 입력의 양과 음의 주기에서 단 하나의 스위치를 사용하여 회로를 구동할 수 있기 때문에 기존회로 대비 적은 손실을 가져 높은 효율의 획득이 가능하다. 본 논문에서는 제안된 구조에 대해 하이라인 $230V_{RMS}$ 입력과 800W / 400V 출력의 조건을 적용하여 제안하는 구조의 효용성을 검증하고자 한다.

• Journal of Drive and Control
• /
• v.16 no.2
• /
• pp.80-90
• /
• 2019

Fuel cell hybrid electric vehicle is an attractive solution to reduce pollutants, such as noise and carbon dioxide emission. This study presents an approach for energy management and control algorithm based on energetic macroscopic representation for a fuel cell hybrid electric vehicle that is powered by proton exchange membrane fuel cell, battery and supercapacitor. First, the detailed model of the fuel cell hybrid electric vehicle, including fuel cell, battery, supercapacitor, DC-DC converters and powertrain system, are built on the energetic macroscopic representation. Next, the power management strategy was applied to manage the energy among the three power sources. Moreover, the control scheme that was based on back-stepping sliding mode control and inversed-model control techniques were deduced. Simulation tests that used a worldwide harmonized light vehicle test procedure standard driving cycle showed the effectiveness of the proposed control method.

• Journal of ILASS-Korea
• /
• v.24 no.2
• /
• pp.51-57
• /
• 2019

In this study, the spray atomization characteristics of urea injector used in SCR system for construction machinery was analyzed, and the uniformity index at the front of mixer and NOx conversion efficiency were evaluated through numerical analysis. Spray visualization and droplet size/velocity measurement were performed and the measured results were used to verify the spray analysis model to calculate the uniformity index in the exhaust gas after-treatment system. For the flow analysis, STAR-CCM, a three-dimensional CFD, was used and the uniformity index of the SCR system at the front of the mixer was calculated using the droplet dissociation model and the wall collision model. Finally, the DeNOx performance for the average condition of the NRTC driving mode was calculated to understand the NOx conversion efficiency reflecting the exhaust gas temperature. The simulation results show that the uniformity index at the front of mixer was calculated as 0.862 and DeNOx efficiency was 75.9%.

• Journal of Multimedia Information System
• /
• v.8 no.2
• /
• pp.121-130
• /
• 2021

Foot bionic robot could be supported and towed through a series of discrete footholds and be adapted to rugged terrain through attitude adjustment. The vibration isolation of the robot could decouple the fuselage from foot-end trajectories, thus, the robot walked smoothly even if in a significant terrain. The gait programming and foot end trajectory algorithm were simulated. The quadruped robot of parallel five linkages with eight degrees of freedom were tested. The kinematics model of the robot was established by setting the corresponding coordinate system. The forward and inverse kinematics of both supporting and swinging legs were analyzed, and the angle function of single leg driving joint was obtained. The trajectory planning of both supporting and swinging phases was carried out, based on the control strategy of compound cycloid foot-end trajectory planning algorithm with zero impact. The single leg was simulated in Matlab with the established kinematic model. Finally, the walking mode of the robot was studied according to bionics principles. The diagonal gait was simulated and verified through the foot-end trajectory and the kinematics.

• Design & Manufacturing
• /
• v.16 no.3
• /
• pp.39-43
• /
• 2022

In this study, we designed an vibration cutting tool that can achieve improvements such as low cutting force, interrupted chip evacuation and better surface quality of cutting performance to obtain high-quality surface roughness and improvement of tool wear, which is an issue in the machining of high-hardness mold steel. Among the resonance frequency modes of the vibration cutting tool, the bending mode was used to maximize the driving amplitude of the vibration tool tip, and the resonance frequency was confirmed through the finite element method. After measuring the actual resonant frequency of the designed tool using an optical fiber sensor, the cutting force and machining surface of vibration cutting and conventional cutting were compared and analyzed in the turning process of high hardness mold steel (STAVAX). As a result of the experiment, the cutting force was reduced by about 20 % compared to the conventional cutting process, and the surface roughness was also improved by about 60 %. This study suggested that the tool wear and surface quality of high-hardness steel can be improved through the vibration cutting method in the machining of high hardness mold steel.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.17 no.4
• /
• pp.1162-1181
• /
• 2023

Tourism flow is not only the manifestation of tourists' special displacement change, but also an important driving mode of regional connection. It has been considered as one of significantly topics in many applications. The existing research on tourism flow prediction based on tourist number or statistical model is not in-depth enough or ignores the nonlinearity and complexity of tourism flow. In this paper, taking Nanjing as an example, we propose a prediction method of urban tourism flow based on deep learning methods using travel diaries of domestic tourists. Our proposed method can extract the spatio-temporal dependence relationship of tourism flow and further forecast the tourism flow to attractions for every day of the year or for every time period of the day. Experimental results show that our proposed method is slightly better than other benchmark models in terms of prediction accuracy, especially in predicting seasonal trends. The proposed method has practical significance in preventing tourists unnecessary crowding and saving a lot of queuing time.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2022.05a
• /
• pp.85-85
• /
• 2022

The world's most extensive and active deltas, Louisiana's wetlands, are deteriorating rapidly due to multiple stressors such as the discharge of the Mississippi River, sea-level rise, and coastal retreat, the substantial but spatially and temporally variable impacts. However, the ecological and anthropogenic histories, the mode of environmental changes on a multi-millennial timescale have not been thoroughly documented. This study, a palynology-based multiproxy analysis, investigates hydrological, geological, geochemical, and anthropogenic impacts on southern Louisiana wetlands and a variety of external forcing agents influencing ecological succession. Sediment cores extracted from a small pond on a mangrove-dominate island near Port Fourchon, Louisiana, USA yielded a 4,000-year record. The site has been transformed from freshwater to saline water environments, to a mangrove dominant island over the late Holocene. The multivariate principal component analysis identified the relative strength of external drivers responsible for each ecological shift. The Mississippi River delta cycle (lobe switching) was the dominant driver of ecosystem changes during the late Holocene, while relative sea-level rise, tropical cyclones, climate, and anthropogenic effects have been the main drivers late in the site's history.

• Journal of ILASS-Korea
• /
• v.28 no.4
• /
• pp.191-197
• /
• 2023

LPG direct injection (LPDi) technology is a method of improving the weaknesses of existing LPG vehicles by directly injection into the combustion chamber. This study was conducted on the comparison of emissions and fuel efficiency performance of the engine and vehicle by applying LPDi technology. The LPDi hybrid engine's maximum output and maximum torque were measured at an equivalent level of less than 1% compared to conventional gasoline fuel. The fuel amount was corrected using the LCU controller, and the THC, CO, and NOx emissions were reduced to 90% in the operating range of the three-way catalyst through air-fuel ratio control. The analysis of THC+NOx and CO emissions in FTP-75 (CVS-75) driving mode satisfied the US LEV III SULEV30 regulation.