• Proceedings of the KIEE Conference
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• 2006.07d
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• pp.1838-1839
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• 2006

In this paper, a loss-minimization nonlinear torque control for Electrical Vehicle(EV) induction motors is proposed. To improve the efficiency of the induction motors, it is important to find the optimal flux reference that minimize power losses. The proposed optimal flux reference is derived using a power loss function that is constructed with stator resistance losses, rotor resistance losses and core losses. And the time-varying load torque and the rotor resistance variation are considered in the power loss function. An algorithm that identifying the load torque is used. The rotor flux observer is used to obtain an accurate flux value regardless of the rotor resistance variation. Simulation results show a significant reduction in energy losses.

• Wind and Structures
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• v.22 no.1
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• pp.65-87
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• 2016

The wind velocity profile over the height of a structure in high intensity wind (HIW) events, such as downbursts, differs from that associated with atmospheric boundary layer (ABL) winds. Current design codes for lattice transmission structures contain only limited advice on the treatment of HIW effects, and structural design is carried out using wind load profiles and response factors derived for ABL winds. The present study assesses the load-deformation curve (capacity curve) of a transmission tower under modeled downburst wind loading, and compares it with that obtained for an ABL wind loading profile. The analysis considers nonlinear inelastic response under simulated downburst wind fields. The capacity curve is represented using the relationship between the base shear and the maximum tip displacement. The results indicate that the capacity curve remains relatively consistent between different downburst scenarios and an ABL loading profile. The use of the capacity curve avoids the difficulty associated with defining a reference wind speed and corresponding wind profile that are adequate and applicable for downburst and ABL winds, thereby allowing a direct comparison of response under synoptic and downburst events. Uncertainty propagation analysis is carried out to evaluate the tower capacity by considering the uncertainty in material properties and geometric variables. The results indicated the coefficient of variation of the tower capacity is small compared to those associated with extreme wind speeds.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.51 no.2
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• pp.68-76
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• 2002

This paper presents an implementation of high-dynamic performance control system of Reluctance Synchronous Motor (RSM) drives for an industrial servo system with direct torque control (DTC). The problems of DTC for high-dynamic performance and maximum efficiency RSM drives are the nonlinear variable flux and inductance due to a saturated stator linkage flux and nonlinear inductance curve with various load currents. The accurate estimation of the stator flux and torque are obtained using stator flux observer of which a saturated inductance Ld and Lq can be compensated by using the adapted neural network from measuring the modulus and angle of the stator current. To obtain fast torque response and maximum torque/current with varying load current, the reference command flux is ensured by imposing Ids=Iqs. This control strategy is proposed to fast response and optimal efficiency for RSM drive. In order to prove rightness of the suggested control algorithm, we have some actual experimental system using 6000 pulse/rev encoder at ${\pm}10$ and ${\pm}1500rpm$. The developed digitally high-performance control system are shown some good response characteristics of control results and high performance features using 1.0kW RSM of which has 2.57 Ld/Lq salient ratio.

• 한국공간정보시스템학회:학술대회논문집
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• 2004.05a
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• pp.131-138
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• 2004

The cable structure is a kind of ductile structural system using the tension cable and compression column as a main element. From mechanical characteristics of the structural material, it is profitable to be subjected to the axial forces than bending moment or shear forces. And we haweto consider the local buckling when it is subjected to compression forces, but tension member can be used until the failure strength. So we can say that the tension member is the most excellent structural member. Cable dome structures are made up of only the tension cable and compression column considering these mechanical efficiency and a kind of structural system. In this system, the compression members are connected by using tension members, not connected directly each other. Also, this system is lightweight and easy to construct. But, the cable dome structural system has a danger of global buckling as external load increases. That is, as the axisymmetric structure is subjected to the axisymmetric load, the unsymmetric deformation mode is happened at some critical point and the capacity of the structure is rapidly lowered by this reason. This phenomenon Is the bifurcation and we have to reflect this in the design process of the large space structures. In this study, We investigated the nonlinear unstable phenomenon of the Geiger, Zetlin and Flower-type cable dome.

• Geomechanics and Engineering
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• v.20 no.5
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• pp.433-445
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• 2020

A new code, called PRaFULL (Piled Raft Foundation Under Lateral Load), was developed for the analysis of laterally loaded Combined Pile Raft Foundation (CPRF). The proposed code considers the contribution offered by the raft-soil contact and the interactions between all the CPRF system components. The nonlinear behaviour of the reinforced concrete pile and the soil are accounted. As shallower soil layers are of great relevance in the lateral response of a pile foundation, PRaFULL includes the possibility to consider layered soil profiles with appropriate properties. The shadowing effect on the ultimate soil pressure is accounted, when dealing with pile groups, as proposed by the Strain Wedge Model. PRaFULL BEM code obviously requires less computational resources compared to FEM (Finite Element Method) or FDM (Finite Difference Method) codes. The proposed code was validated in the linear elastic range by comparisons with the code APRAF (Analysis of Piled Raft Foundations). The reliability of the procedure to predict piled raft performance was then verified in nonlinear range by comparisons with both centrifuge tests and computer code PRAB.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.5
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• pp.850-856
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• 2001

Even though the hydraulic servo system has been widely used in industrial and military equipments since it has a lot of advantages, it is not easy to design controller due to the high nonlinearities and the parametric uncertainties. The dynamic behavior of the real process in the hydraulic servo system differs from that described by its model because the model is linearized. Another reason of the difference is caused by the variety of parameters, since the system parameters of the dynamic equation are affected by the operating conditions such as temperature and pressure. In this study, the designing process of the MRNC with a PID compensator is introduced and applied to the load sensing hydraulic servo system. The results show that the designed controller guarantees the robust control performance despite of both the nonlinearities and the parametric uncertainties.

• Journal of the Korean Institute of Intelligent Systems
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• v.10 no.4
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• pp.357-367
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• 2000

A new robust load-frequency control methodology is proposed for nonlinear power systems with valve position limits of the governor in the presence of parametric uncertaines. The TSK fuzzy model is adopted and formulated for fuzzy modeling of the nonlinear power system. A sufficient condition of the robust stabilitry is presented in the sense of lyapunov for the TSK model with parametric uncertainties. The intekkigent digital redesign technique for the uncertain power systems is also studied. The effectiveness of the robust digital fuzzy controller disign mothod is demonstrated through a numerical simulation.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.2
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• pp.201-210
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• 2011

This paper presents a nonlinear finite element analysis procedure for the seismic performance assessment of deep beam-and-interior column joints. A computer program, named RCAHEST(Reinforced Concrete Analysis in Higher Evaluation System Technology), for the analysis of reinforced concrete structures was used. Horizontal cyclic load tests were conducted to estimate the strength, ductility, and behavioral characteristics of deep beam-and-interior column joints. Experimental parameters are axial forces and amount of transverse reinforcement. The proposed numerical method for the seismic performance assessment of deep beam-and-interior column joints is verified by comparison of its results with reliable experimental results.

• Computational Structural Engineering
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• v.11 no.1
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• pp.179-190
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• 1998

A geometrically nonlinear finite element formulation of spatial cable networks is presented using two cable elements. Firstly, derivation procedures of tangent stiffness and mass matrices for the space truss element and the elastic catenary cable element are summarized. The load incremental method based on Newton-Raphson iteration method and the dynamic relaxation method are presented in order to determine the initial static state of cable nets subjected to self-weights and support motions. Furthermore, static non-linear analysis of cable structures under additional live loads are performed based on the initial configuration. Challenging example problems are presented and discussed in order to demonstrate the feasibility of the present finite element method and investigate static nonlinear behaviors of cable nets.

• 전자공학회논문지 IE
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• v.47 no.3
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• pp.47-52
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• 2010

In this paper, a frequency tripler has been designed with 100mW medium-power using P-HEMT. It is designed to obtain 7.2GHz frequency at the output that is an integer multiple of 2.4GHz input frequency by using nonlinear device that produces 3rd harmonic. The frequency tripler is designed by using load-pull simulation. To suppress the 2nd and fundamental, notch filter is used for the frequency tripler. The tripler is designed to obtain about 21dBm output power with 15dBm input, i.e., 6dB conversion gain and the suppression of 20dBc at fundamental, and 30dBc at the second harmonics.