• Journal of the Korean Society for Precision Engineering
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• v.18 no.5
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• pp.50-56
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• 2001

Fabrication methods are shown to produce slender and cylindrical tungsten shafts by electrochemical etching. The shape of microshatf formed by electrochemical etching is determined by the combination of two conflicting factors, i.e., initial shape and diffusion layer. We can obtain a desirable shaft profile by adjusting the thickness gradient of diffusion layer. The diameter of microshaft is controlled by mathematical model based on relation between process parameters and diameter.

• Proceedings of the KIEE Conference
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• 2001.07e
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• pp.53-57
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• 2001

In the industrial motor drive system which is composed of a motor and load connected with a flexible shaft, a torsional vibration is often generated because of the elastic elements in torque transmission. To solve this problem, the two degrees of freedom $H_{\infty}$ controller was designed. But it is difficult to realize that controller. In this paper, $H_{\infty}$ control of 2-mass system using partial state feedback and resonance ratio control is proposed. Proposed controller has simple structure but satisfies the attenuation of disturbances and vibrations.

• Proceedings of the KIEE Conference
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• 2001.07e
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• pp.90-94
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• 2001

The aim of this paper is twofold: The one is to design BLDC motors for an electric bicycle and the other is to develop a controller of the BLDC motors. A new BLDC Motor has a permanent magnet rotor in which the magnetic arrangement is radial to the shaft and integral to the rotor laminations instead of mounted on the perimeter of the rotor. This technique concentrates flux, giving a higher flux density than a surface-mounted PM motor and has the increase of reluctance torque. The stator of BLDC motor has parallel winding instead of interconnected wye-connection winding, allowing multi-phase separate independent controllability. It gets much more high power than wye-connection at same low voltage. The proposed controller has a technique of exited with modulation(EWM) and one H-bridge and two photo sensors per phase. Experimental results show the performance of the proposed BLDC motors for an electric bicycle.

• Journal of KSNVE
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• v.5 no.2
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• pp.183-195
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• 1995

The mathematical model of the gear reductioner which consists which consists of the geared rotor-bearing system containing case is developed, assuming as the lumped parameter system. Constraints for vibration suppresion as well as strength of gear teeth, and shaft and kinematic conditions in gear pairs are considered. To find the design parameters satisfing the proposed constraints, a direct search method modified by the technique of Taguchi's experimental scheduling is used. One and two stepped gear reductioners are designed so that the criticl speeds due to the gear transmission error are moved out of the operating speed range.

• International Journal of Fluid Machinery and Systems
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• v.4 no.1
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• pp.140-149
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• 2011

For a certain operating point of a horizontal shaft bulb turbine (i.e. volume flow, net head, blade angle, guide vane angle) the efficiency for different pressure levels (i.e. different Thoma-coefficient ${\sigma}$) is calculated using a commercial Computational Fluid Dynamics (CFD-)-code including two-phase flow and a cavitation model. The results are compared with experimental results achieved at a closed loop test rig for model turbines. The comparison of the experimentally and numerically obtained efficiency and the visual impression of the cavitation show a good agreement. Especially the drop in efficiency is calculated with satisfying accuracy. This drop in efficiency in combination with the visual impression is of high practical importance since it contributes to determine the admissible cavitation in a bulb-turbine. It is seen that the incipient cavitation in Kaplan type turbines has no major importance in determing this admissible amount of cavitation.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.50 no.3
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• pp.117-124
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• 2001

The aim of this paper is to develop a controller of multi-phase bipolar brushless DC (MPB BLDC) motors for an electric bicycle. A MPB BLDC motor has a Permanent magnet rotor in which the magnetic arrangement is radial to the shaft and integral to the rotor laminations. This technique concentrates flux, giving a higher flux density than a surface-mounted PM motor and increases reluctance torque. The stator of MPB BLBC motor has parallel winding, allowing multi-phase separate independent controllability. It gets much more high power than wye-connection at same low voltage. The conventional techniques of exited with modulation(EWM), bidirection control, and partial square wale control are Proposed with one H-bridge and two photo sensors per phase. The Proposed controller is satisfied for the limited speed control and designed for system stability Experimental results show the performance of the proposed controller of MPB BLDC motors for an electric bicycle.

• Proceedings of the KIEE Conference
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• 1998.07a
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• pp.200-204
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• 1998

In this paper, a mathematical model of Brushless DC machine fed by pwm inverter is developed. Dynamic and steady state characteristics of Brushless DC motor is simulated and analyzed: electromagnetic torque, speed, phase voltage, and current. In mathematical modeling, the shaft transformation referencing rotor frame from to "a,b,c" three phase frame to "d,g" two phase frame is described.

• Smart Structures and Systems
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• v.9 no.4
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• pp.303-311
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• 2012

The possibility of suppressing critical speeds by using electromagnetic actuators (EMAs) is assessed experimentally in this paper. The system studied is composed of a horizontal flexible shaft supported by two ball bearings at one end and one roller bearing that is located in a squirrel cage at the other end. Four identical EMAs supplied with constant current are utilized. The EMAs associated to the squirrel cage constitutes the hybrid bearing. Results obtained, show that the constant current, when applied to the EMAs, produces a shift of the first critical speed toward lower values. Moreover, the application of constant current for a speed interval around the critical speed enables a smooth run-up or run-down without crossing any resonance.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1999.05a
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• pp.229-234
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• 1999

This thesis presents the design method using CAE(Computer Aided Engineering) with the consideration of reliability for optimal gear driving system. The validity and feasibility of the proposed method are verified by the application to transmission of machine tool. The reliability and life analysis is based on the two-parameter Weibull distribution lives of the gears and bearings. Ninety-percent of reliability life is the life of the component or system in million output rotations or hours at which ninety percent of identical components or system would survive under the given loading conditions.

• KIEE International Transactions on Power Engineering
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• v.4A no.4
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• pp.178-191
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• 2004

This paper presents a new approach to HVDC system control for damping subsynchronous oscillation (SSO) involving HVDC converters and turbine generator shaft systems. This requires a novel eigenvalue analysis (NEA) program, derivation of HVDC system modeling considering steady-state conditions and dynamic conditions in the combined AC/DC system, and an appropriate control scheme. The method suggested makes possible the design of a subsynchronous oscillation damping controller (SODC) to provide positive damping torque for the range of torsional modes in combined AC/DC systems. There are three steps involved in the design of a SODC； first the worst torsional mode is determined using the NEA program, next the SODC parameters are designed for the range of that torsional mode, and then finally an off-line simultaneous time domain program such as PSCAD/EMTDC is used to verify the parameters of the SODC. The suggested SODC design method is applied to two AC/DC systems, and its practicality is verified using the PSCAD/EMTDC simulation program.