• Proceedings of the KIPE Conference
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• 2005.07a
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• pp.286-288
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• 2005

Conventional phase shift full bridge (PSFB) converter has serious voltage oscillation problem across the secondary rectifier diodes, which would require the dissipate snubber circuit, thus degrades the overall efficiency. To overcome this problem, a new voltage oscillation reduction technique (VORT) which effectively reduce the voltage oscillation of the secondary rectifier diodes for phase shift 1011 bridge converter is proposed. Therefore, no dissipate snubber for rectifier diodes is needed. In addition, since it has wide zero voltage switching (ZVS) range, high efficiency can be achieved. Operational principle, analysis of voltage oscillation, and design consideration are presented compare with that of the conventional PSFB converter. To confirm the validity of the proposed VORT, experimental results from a 420W, 385Vdc/210Vdc prototype are presented.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.06a
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• pp.55-58
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• 1998

Recently, neural networks with self-adaptability like human brain have attracted much attention. It is desirable for the neuron-function to be implemented by exclusive hardware system on account of huge quantity in calculation. We have proposed a novel neuro-device composed of a MFSFET(ferroelectric gate FET) and oscillation circuit with CUJT(complimentary unijuction transistor) and PUT(programmable unijuction transistor). However, it is difficult to preserve ferroelectricity on Si due to existence of interfacial traps and/or interdiffusion of the constitutent elements, although there are a few reports on good MFS devices. In this paper, we have simulated CUJT and PUT devices instead of fabricating them and composed oscillation circuit. Finally, we have resented, as an approach to the MFSFET neuron circuit, adaptive learning function and characterized the elementary operation properties of the pulse oscillation circuit.

• Electrical & Electronic Materials
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• v.9 no.10
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• pp.1019-1026
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• 1996

In this study, we may be presented the carrier oscillation properties for the low-voltage varistor fabricated by a new method of three composition seed grain, in order to analyze the behavior of carriers at the its equivalent circuit model. The oscillation phenomena of carriers appeared from current-voltage characteristics under knee voltage is shown by the transient flow of nontrapped carriers group in the trap level of intergranular layer, surface state and/or depletion layer. In particularly, current oscillation phenomena is hardly shown in the high electric field. It is that the injected carriers from both electrodes are directly from the conduction band of forward biased ZnO grain through the intergranular layer into the reverse biased ZnO grain, because the trap level in the electric field above the knee voltage is mostly filled.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1534-1539
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• 2004

The objective of this study is to simulate the etching characteristics with oscillation angle for the optimization of etching system. The etching characteristics were analyzed under different etching conditions. The spray characteristics were measured by Phase Doppler Anemometer (PDA). The correlation between the spray characteristics and the etching characteristics was investigated and used for fundamental data to simulate the etching characteristics with oscillation angle. The smaller coefficient of variation, the more uniform etching characteristic distribution became. It was found that numerical predictions of etching factor generally agreed well with the measured results with distance from nozzle tip. Oscillation leads to decrease of etching factor and increase of uniformity.

• Journal of the Korean Institute of Telematics and Electronics C
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• v.35C no.3
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• pp.90-96
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• 1998

The self-excited oscillation is the phenomenon which can be observed in the systems composed of nonlinear elements. The phenomenon is of fundamental importance in nonlinear systems and, as far as the design of a nonlinear system is concerned, it should be considered along with the stability analysis. In this paper, the oscillation of a system controlled by a static nonlinear fuzzy controller is theoretically addressed. First, the describing functionof a static fuzzy controller is derived and then, based on the derived describing function, self-excited oscillation of the system controlled by a static fuzzy controller is predicted. To obtain the describing function of the static fuzzy controller, a simple struture is assumed for the fuzzy controller. Finally, computer simulation is included to show an example where the describing function given in the paper is used to predict the self-excited oscillation of a fuzzy-control system.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.282-286
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• 2004

Discharge current oscillation in a 20KHz range is a serious problem for Hall thruster performance, In our previous work, a possibility of controlling the oscillation amplitude by increasing the speed of neutral particles incoming to the ionization zone was predicted in our previous work. In this paper, the effects of diameter of anode orifice on the oscillation phenomena and the thrust performance were evaluated experimentally. The experimental results show that the measured amplitude of oscillation becomes smaller as the diameter of anode orifice. However, the larger orifice makes thrust performance lower. The results of numerical analysis of neutral particles show that these tendencies have much to do with neutral properties.

• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.4
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• pp.339-347
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• 2022

This study proposes the mitigation method for overcurrent and oscillation motor current in an active short-circuit operation. This operation is attracting attention as the safe state of electric vehicle traction inverters. However, the active short-circuit operation generates oscillation and overcurrent of motor currents during a transient state. The proposed method uses two different safe states in PMSM, such as active short circuit and freewheeling. The active short circuit is used for safe state in a steady state. To reduce the overshoot and oscillation, a freewheeling state is injected between active short-circuit operation by comparing the motor phase current with an analytically calculated steady-state motor current. Freewheeling state is only used in a transient state. The performance is demonstrated through simulations and experimental results. The peak current of the motor was reduced from 52 A to 40 A, and oscillation time was reduced.

• Analytical Science and Technology
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• v.6 no.4
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• pp.369-374
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• 1993

Plasma oscillation has been observed during the development of the glow discharge as detector for gas chromatography. The variation of oscillation frequency shows the better stability and detection limits than the changes in the dischange curent. To investigate the range of useful operating conditions and to gain insight into the mechanism, the effect of experimental parameters on plasma oscillation have been studied. This study includes the variation of discharge current, pressure and discharge gap. Frequency ranges of 10KHz to 10MHz have been observed with the various shapes of oscillation. Two kinds of mode for oscillation are observed with the variation of electrode gap at low pressure and low voltage.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.1
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• pp.18-28
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• 1998

A laboratory experiment was made of a control of temperature oscillation in Czochralski convection. Numerical computation was also made to delineate the control of temperature oscillation. The suppression of temperature oscillation was achieved by varying the rotation rate of crystal rod ($\Omega=\Omega_0(1+A sin 2{\pi}ft/t_p)$), where A denotes the amplitude of rotation rate and f the frequency factor. Based on the inherent dimesionless time period of temperature oscillation ($t_p$), the suppression rate of temperature oscillation was characterized by the mixed convection parameter ($0.217{\leq}Ra/PrRe^2{\leq}1.658$). The optimal values of A and f were also scrutinized. To understand the suppression mechanism of temperature oscillation, the controls of isotherm($\theta$) and equi-vorticity($\omega$) were investigated.

• International Journal of Precision Engineering and Manufacturing
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• v.4 no.5
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• pp.15-21
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• 2003

In order to improve the quality of a spindle unit it is important to increase its rotational accuracy. The rotational accuracy of a spindle unit can be defined as the stability or immobility of its spindle axis while rotating. Spindle rotation in the rolling bearings causes the disturbing influence, which leads to the oscillation of a rotation axis. The purpose of this study is to investigate the oscillation sources and find a way to decrease the runout without additional expenses. The main source of oscillation is the interaction between rolling bodies and ring races. The first oscillation source was the out-of-shape imperfection of inner bearing ring. The mutual compensation of oscillation by proper rings orientation was proposed, which sometimes allow to decrease the radial runout of spindle rotation axis by approximate 40％ down. Also the outer ring harmonics were explored as the second oscillation source. The analysis shows the dependency between the number of rolling bodies and the outer ring race harmonics. The conclusion on the orientation of bearing cages and the bearing rings was made, which makes possible to obtain the optimal variant of their mounting in the spindle unit when the rotational accuracy of the spindle is maximal, and the spindle runout considerably less.