• The Journal of the Acoustical Society of Korea
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• v.18 no.7
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• pp.112-117
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• 1999

In case of spectral subtraction for noise robust speech recognition system, this method often makes loss of speech signal. In this study, we propose a method that variation and determination of Gaussian function at semi-continuous HMM(Hidden Markov Model) is made on the basis of SNR criteria function, in which SNR means signal to noise ratio between estimation noise and subtracted signal per frame. For proving effectiveness of this method, we show the estimation error to be related with the magnitude of estimated noise through signal waveform. For this reason, Gaussian function is varied and determined by SNR. When we test recognition rate by computer simulation under the noise environment of driving car over the speed of 80㎞/h, the proposed Gaussian decision method by SNR turns out to get more improved recognition rate compared with the frequency subtracted and non-subtracted cases.

• The Transactions of the Korean Institute of Power Electronics
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• v.6 no.6
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• pp.506-513
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• 2001

The torque of an SRM depends on the phase current and derivative of inductance. But an SRM is difficult to control the desired torques because of saturation in magnetic circuit An SRM is controlled by parameters of input voltage, and switch on , off angle The switch on off angles of an SRM regulate the magnitude and shape of current waveform and decide the magnitude and shape of torque This paper proposes an the optimization control scheme by adjusting both the switch on an switch off angle . The switch off angles are decided by reference of efficiency using simulation and experiments. The switch on angles are decided by load torque , And the dwell angles are controlled for torque control and speed control using GA-neural network which is used to simulated the reasonable switching angle.

• Journal of Power Electronics
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• v.14 no.2
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• pp.249-256
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• 2014

A novel topology generation method for the no dead-time three-phase AC/DC converter is proposed in this study. With this method, a series of no dead time topologies are generated and their operation principles are analyzed. The classic three-phase bridge AC/DC converter can realize a bidirectional operation. However, dead-time should be inserted in the driving signals to avoid the shoot-through problem, which would cause additional harmonics. Compared with the bridge topology, the proposed topologies lack the shoot-through problem. Thus, dead time can be avoided. All of the no dead time three-phase AC/DC converters can realize bidirectional operation. The operating principles of the converters are analyzed in detail, and the corresponding control strategies are discussed. Comparisons of waveform distortion and efficiency among the converters are provided. Finally, 9 KW DSP-based principle prototypes are established and tested. Simulation and experimental results verify the theoretical analysis.

• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.1225-1227
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• 1992

This paper presents a study on the variable structure PI(proportional and integrate) control which is insensible to the variation of parameters or external disturbance for driving DC motor. In the presented variable structure PI control (VSPIC), the sliding mode control was used at the below of 4000 rpm and PI control also used at the above of 4000 rpm with no load. In other way, the PI control was used at the below of 4000 rpm and the sliding mode control at the above of 4000 rpm with some loading, and then the output waveform following the variation of load was measured. intel 8031 microcomputer unit and IBM PC was combined to form the full system and the speed control was performed with it. The experimental result of the fast response to speed was more improve than it was open loop state. For load varing, the sliding mode insensible to external disturbance was applied and the improved response was obtained.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.9
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• pp.1597-1604
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• 2016

The speed at which the SRM (Switched Reluctance Motor) makes a transition from chopping control to single pulse operation. (i.e., low speed to high speed operation). It is unsatisfied with performance at all operational regimes. In this paper, the operational performance of SRM can be improved by using current hysteresis control method. This method maintains a generally flat current waveform. At the high speed, the current chopping capability is lost due to the development of the back-EMF. Therefore SRM operates in single pulse mode. By using zero-current switching and zero-voltage switching technique, the stress of power switches can be reduce in chopping mode. When the commutation from one phase winding to another phase winding, the current can be zero as fast as possible in this period because several times negative voltage of DC-source voltage produce in phase winding. This paper is compared to performance based on energy efficient C-dump converter topology and the proposed resonant C-dump converter topology. Simulation and experimental results are presented to verify the effectiveness of the proposed circuit.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.53 no.12
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• pp.718-724
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• 2004

This study investigates the design factors of Interior Permanent Magnet Synchronous Motor(IPMSM) which is applied to Hybrid electric vehicle as a driving power. Recently, there are many studies of IPMSM for application to Hybrid Electric Vehicle, because IPMSM has characteristics of high torque, high power density and high efficiency which come from reluctance torque due to difference of inductance as well as magnet torque. This study analyzes the inductance and design characteristics of IPMSM by using finite element method and focuses on design and analysis of IPMSM which can operates with high efficiency at low speed range. For this embodiment, magnet shape is changed from conventional block type to arc type without any change of outline dimension of motor and this change of magnet shape makes it possible to increase back EMF and sinusoidal waveform. Analysis results are verified by test of improved and embodied motor. As a test result , increased back EMF and sharply decrease of harmonics are secured and through this contribution of reduced fuel consumption of Hybrid electric vehicle is expected.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.594-597
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• 2002

We studied the effect of secondary electron emission from the back plate of AC-PDP, on the ramp waveform driving of the system, using two-dimensional PDP cell discharge simulator. It is found that the secondary electron emission from back plate plays a significant role in getting a stable weak discharge during the ramping up of X-Y electrode voltage. This is because grounded address electrode acts as a cathode during the setup of surface charge, and the secondary electron emission from phosphor in the back plate must be large enough to accumulate surface charges on the dielectric layers without strong plasma discharge. We have concluded that the secondary electron emission coefficient(${\gamma}$) of phosphor, besides MgO, must be known to understand the characteristics of the PDP system. A few suggestions for improvement of the system is also made and tested.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.54 no.11
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• pp.540-546
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• 2005

This paper presents a boost circuit topology driving in high - frequency It solves the problem which arised from hard-switching in high-frequency using a period of resonant circuit and operating under the principle of ZCS turn-on and ZCZVS turn-off commutation schemes. In the existing circuit, it has the high voltage and current stress in free- wheeling diode. But in the proposed circuit, it has voltage and current stress which is lower than voltage and current stress of existing circuit with modifing a location of free-wheeling diode. In this paper, it explained the circuit operation of each mode and the waveform of each mode. Also the experiment results compare the voltage and current stress of free-wheeling diode in the existing circuit with the voltage and current stress of that in the proposed circuit. Moreover, it compares and analyzes the proposed circuit's efficiency with the existing circuit's efficiency according to the change of load current.

• Proceedings of the Korean Vacuum Society Conference
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• 2008.02a
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• pp.203-203
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• 2008

• Proceedings of the KIEE Conference
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• 1998.07e
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• pp.1800-1802
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• 1998

The Pohang Light Source (PLS) is a third generation 2 GeV synchrotron machine. An injection kicker modulator is positioned in the PLS storage ring tunnel. The kicker modulator is driving four kicker magnets simultaneously. The kicker magnets produce magnetic field to deflect the stored beam orbit in the storage ring closer to the injected beam from the PLS beam transfer line. The injected beam then falls into the storage ring beam dynamic aperture. The current kicker modulator was upgraded and installed on August 1995. Since then, the kicker modulator has shown very reliable and stable performance. The kicker modulator specifications are ${\sim}6.0{\mu}s$ full width, ${\sim}24$ kA peak current, and 10 Hz repetition rate. Output current waveform is a half sinusoid. Two thyratron switches(EEV CX-1536AX) are used in the kicker modulator. Total accumulated thyratron heater run hour is about 15,000 hours as of May 1998. Measurement result of spatial magnetic field distribution in the kicker magnet shows good uniformity.