• Proceedings of the KIEE Conference
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• 1999.11a
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• pp.56-60
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• 1999

This paper presents the high performance real time control system of PWM inverter for uninterruptible power supply(UPS). This system is based on a digital control scheme which calculates the pulse widths of the inverter switches for the next sampling time in digital signal processor(DSP). A PI compensator is used to eliminate the voltage error caused by the difference between the actual values of LC filter and those designed. Double regulation loops which are the inner current loop and the outer voltage loop are used to make the transient response time reduce in load disturbance and nonlinear load. This method makes it possible to obtain better response in comparison to conventional digital control system. The proposed scheme provides good performance such as stable operation, low THD of the output voltage, and good dynamic response for load variations and nonlinear load.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.990-994
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• 2004

This paper presents a method to predict the transient characteristic of the air lubricated slider head in a hard disk drive by using optimization technique. The time dependent modified Reynolds equation based on the molecular slip flow approximation equations was used to describe the fluid flow within the air bearing and the implicit finite difference scheme is applied to calculate the pressure distribution under the slider head. The exhaustive search combined with the Broyden-Fletcher-Goldfarb-Shanno method were employed to obtain optimum design variables which are taper angle, rail width and taper length in order to keep the forces and moments acting on the slider head in dynamic equilibrium. The results show that the optimal head slider of the magnetic head has good stability characteristic that can reach the steady state within 0.5 microsecond.

• 한국전산유체공학회:학술대회논문집
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• 2000.10a
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• pp.15-24
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• 2000

The transient response of an airfoil to a rapidly deploying spoiler is numerically investigated using the turbulent compressible Navier-Stokes equations in two dimensions. Algebraic Baldwin-Lomax model, Wilcox $\kappa-\omega$ model, and SST $\kappa-\omega$ turbulence model are used to calculate the unsteady separated flow due to the rapid spoiler deployment. The spoiler motion relative to a stationary airfoil is treated by an overset grid hounded by a Dynamic Domain-Dividing Line which has been devised by the authors. The adverse effects of the spoiler influenced by the spoiler location and the hinge gap are expounded. The numerical results are in reasonably good agreement with the existing experimental data.

• Journal of KSNVE
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• v.10 no.6
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• pp.977-984
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• 2000

Vibration of disk drive spindle is one of the major limiting factors in achieving higher track densities in hard disk drives. Vibration of a BLDC motor is a coupled phenomenon between mechanical characteristics and magnetic origins through the motor air-gap. In this paper, radial magnetic forces for symmetric and asymmetric BLDC motor are calculated with respect to the various rotor eccentricity using analytic method. Based on the results of the radial magnetic forces, transient whirl responses of the spindle motor are analyzed using finite element and transfer matrices. Results show that an asymmetric motor has a worse effects on unbalanced magnetic forces and vibration when mechanical and magnetic coupling exists.

• Proceedings of the KIEE Conference
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• 2006.07b
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• pp.763-764
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• 2006

In this paper, optimized model was designed for the starting characteristic of the Single-Phase Line-Start Permanent Magnet Synchronous Motor by using the Design of Experiment. A field pole angle, thickness and distance from center axis of permanent magnet were selected as design factor. We executed the transient state characteristic analysis of 8 test models. The transient state characteristic analysis was executed by using the 2 dimensional Finite Element Method and the Time Difference Method. We checked the fact that the selected design factor affected starting characteristic of the Line-Start Permanent Magnet Synchronous Motor. Depend on this result we found the optimized design point by using the response optimization.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.48 no.11
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• pp.604-610
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• 1999

Vibration of a rotor-bearing system driven by an electric motor is a coupled phenomenon between mechanical characteristics and magnetic origins through the air-gap. With the advent of new high-energy magnets together with high precision motor applications, magnetic sources of vibration are becoming more serious. This paper investigates the transient whirl responses of a rotor system with purely mechanical origins and compares it with that of magnetically coupled origins. A perturbation method is applied to model the magnetic field associated with rotor eccentricity. Electromagnetic forces are obtained by the Maxwell stress method, which utilizes the analytical expression of radial flux density distribution. The FEM was applied to a rotor-motor system to illustrate magnetically coupled effects in rotor dynamics. Results show that magnetically coupled sources significantly affect the vibration of the rotor-motor system.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.2087-2092
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• 2005

Using disturbance observer (DOB) is effective in enhancing the performance of dynamic system in the presence of disturbances. Recently the definition of disturbance has been expanded to modeling uncertainty including parameter variation, internal disturbance. Various structures of DOB have been proposed to improve sensitivity of system for better disturbance rejection performance. However in the case of improvement of sensitivity function, it tends to bring poor transient response due to cross-coupling and phase lag. Furthermore it could be very sensitive to measurement noise due to increased peak of complementary sensitivity function. In this paper, a dual disturbance observer (Dual-DOB) is proposed to reduce the effect of such cross-coupling. It is possible for us to improve the sensitivity function with additional external DOB with hardly affecting complementary sensitivity function. Thus it is able to have robustness against measurement noise. Since we are able to design DOBs of internal and external loop independently, we could prevent transient response quality from degrading while improving the sensitivity function. The proposed Dual-DOB is applied to a commercial optical disk drive tracking servo system. The experimental result shows that the Dual-DOB is an effective method in rejecting the disturbance as well as improving the tracking performance.

• The Journal of Engineering Research
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• v.7 no.1
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• pp.5-16
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• 2005

We implemented DPGC(Double-Pass Gain-Clamped) L-band EDFA for highly efficient amplification. A lasing signal generated within the linear cavity, can minimize the fluctuation of surviving channels when several WDM(Wavelength Division Multiplexing) channels are added or dropped. The new method describing the characteristics of transient response of surviving channels quantitatively is suggested. It is to measure the ratio of lasing output before add or drop to that after add or drop. We investigated dynamic characteristics by using this method according to lasing wavelengths and propagation directions within the cavity. The experimental measurements show that the short lasing wavelength and backward propagation direction is the best condition for small fluctuation of surviving channels.

• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.3
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• pp.20-28
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• 2015

Performance parameters of solid rocket motor with multi axis pintle nozzles were analyzed theoretically and modeled. For figuring out the governed variable of dynamic characteristics of system, dynamic analysis was done by using established model. To present characteristics of this system, the model should include not only internal ballistics of propulsion unit but also actuating system to move pintle. For solid rocket motor with multi axis pintle nozzles, not only performance of steady state but also dynamic characteristic of transient state is important design parameter to precise thrust control. Therefore, response time of open-loop system was analyzed by using established model and requirement about response time was satisfied by controlling pressure.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.6
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• pp.4115-4120
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• 2015

To ensure the transient stability of power system connected to a wind farm, wind power plant must be able to supply reactive power at the point of the common coupling(PCC). The reactive power capability of each individual wind turbine may not sufficient to maintain stability. Also, there are large reactive power losses in connection cables between wind farm and PCC. The static synchronous compensator(STATCOM) is considered for transient stability enhancement, because it provides many advantages such as the fast response time and superior reactive power support capability. In this paper, the effectiveness of a STATCOM in enhancing transient stability of power system connected to a wind farm is presented. The results of dynamic simulations show that STATCOM installed at the PCC can enhance transient stability.