• Journal of Power Electronics
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• v.8 no.4
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• pp.301-308
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• 2008

This paper proposes a method of improving the stability in sensor-less control of permanent magnet synchronous motors. The control method for low-speed region is divided into two: One is a high frequency method, which involves a problem of reverse rotation once misdetection of the permanent magnet polarity should occur, and another one is a current drive method, which has a problem that phase and speed oscillations are caused by quick speed changes. Hence, authors propose adoption of the current drive method for the basic control system with added compensation of stabilization by means of the high frequency method. This combination secures stable control with no risk of reversal and less vibration. In addition, authors have also considered a frequency separation filter of a shorter delay time so that current control performance will not lower even when high frequencies are introduced. This filter has achieved simplified compensation using repetitive characteristic through the utilization of the periodicity of high frequency current. Simulation and experiment have been conducted to verify that the stable performance of this system is improved.

• 제어로봇시스템학회:학술대회논문집
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• 2000.10a
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• pp.360-360
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• 2000

In this paper, a new criterion f9r determining the sampling rate of digital conroller is proposed. This paper will introduce a method fur determining the appropriate sampling rate of digital controller which can be substituted with the given analog controller, using phase margin and gain cross over frequency, not rising time or bandwidth of the closed-loop system. This method also guarantees performance of the system. Without exact modeling functions of the plant, abstracting those functions, this paper can achieve stability and aimed performance of the system, and this paper proved it with proper modeling functions.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.10
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• pp.1982-1988
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• 2009

$TiO_2$ films are fabricated using silk printing method. Heat treatment temperature of films is 600[$^{\circ}C$]. From the analysis of microstructure, grain size of $TiO_2$ films is about $0.2{\sim}0.3[{\mu}m]$. Thickness of films is 30.19[${\mu}m$] and surface uniformity of films is good. From the analysis of crystalline structure, $TiO_2$ films transform anatase phase to rutile phase. Capacitance of films increases according to increase relative humidity and decrease measuring frequency. Hysteresis characteristics of capacitance and impedance are best at 45[%RH] and 75[%RH] respectively. Impedance of films increases according to decrease measuring frequency.

• Journal of the Korea Society of Computer and Information
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• v.7 no.3
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• pp.36-41
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• 2002

This study was carried out develope a ultrasonic transducer displacement generator through 26KHz and 38KHz of the frequency phase modulation on the ultrasonic transducer. This system was producted a power output generation such as 100W, 300W, 400W and 600W. Ultrasonic power output had a change of time. We made use of a Thiram hydration and detected it measurement by the ACAO method. It was to decide the result of ultrasonic power supply for time duration and the result of comparison in the 26KHz & 38KHz by UV/VIS spectrophotometer.

• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.5
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• pp.446-454
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• 2022

This study proposes a carrier-based pulse width modulation (PWM) method for leakage current reduction and neutral point (NP) current control in a three-phase three-level converter, which is a carrier-based PWM version of the previously proposed low-frequency common mode voltage PWM. Three groups of space vectors with the same common mode voltage are used. When the averaged NP current needs to be positive or negative, the specific groups are employed to produce low-frequency common mode voltages. The validity of the proposed PWM method is verified through experiments.

• Journal of the Korean Solar Energy Society
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• v.32 no.6
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• pp.106-112
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• 2012

As a fuel cell converts the chemical energy of the fuel cell into electrical energy by electrochemical reaction, the fuel cell system is uniquely integrated technique including fuel processor, fuel cell stack, power conditioning system. The residential fuel cell-PCS(Power Conditioning System) needs to convert efficiently the DC current produced by the fuel cell into AC current using single-phase DC-AC inverter. A single-phase DC-AC inverter has naturally low frequency ripple which is twice frequency of the output current. This low frequency(120Hz) ripple reduces the efficiency of the fuel cell. This paper presents notch filter with IP voltage controller to reject specific 120Hz current ripple in single-phase inverter. The notch filter is designed that suppress just only specific frequency component and no phase delay. Finally, the proposed notch filter design method has been verified with computer simulation and experimentation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.3A
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• pp.196-204
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• 2002

The Sinusoidal Transform Coding(STC) is a vocoding scheme based on a sinusoidal model of a speech signal. The low bit-rate speech coding based on sinusoidal model is a method that models and synthesizes speech with fundamental frequency and its harmonic elements, spectral envelope and phase in the frequency region. In this paper, we propose the 2.4kbps low-rate speech coding algorithm using the sinusoidal model of a speech signal. In the proposed coder, the pitch frequency is estimated by choosing the frequency that makes least mean squared error between synthetic speech with all spectrum peaks and speech synthesized with chosen frequency and its harmonics. The spectral envelope is estimated using SEEVOC(Spectral Envelope Estimation VOCoder) algorithm and the discrete all-pole model. The phase information is obtained using the time of pitch pulse occurrence, i.e., the onset time, as well as the phase of the vocal tract system. Experimental results show that the synthetic speech preserves both the formant and phase information of the original speech very well. The performance of the coder has been evaluated in terms of the MOS test based on informal listening tests, and it achieved over the MOS score of 3.1.

• The Transactions of the Korean Institute of Power Electronics
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• v.2 no.2
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• pp.41-48
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• 1997

Nowadays, EMI emission characteristics, which causes harmful effect on power distribution system and other equipments, have been studied in field of Power electronics, vigoriously. So, in this paper, the conducted EMI emission is measured and compared for 3-phase diode rectifier and PWM converter according to switching frequency variation and current control method change using LISN(Line Impedance Stabilization Network) and spectrum analyzer.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.43 no.6
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• pp.906-915
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• 1994

Line-Current harmonics resulting from ac to dc power conversion interfere with power system operation and reduce power factor, hence resulting in increasing power source unnecessarily. This study describes a 3 phase phase-controlled converter eliminating low frequency harmonics in the output by inserting notches. Notch points are calculated by Newton-raphson method, The impacts of the choppings on ac and dc sides are analyzed in the steady state. Potential applications of the study are dc motor controls, high power dc power supplies for telecommunications, static var compensators and HVDC.

• Proceedings of the KIEE Conference
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• 1988.07a
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• pp.73-76
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• 1988

In this paper, the governing equation of the three phase linear induction motor is induced by the method that current in the primary winding is assumed as a current sheet. The steady state flux and the flux that is produced by end effect are mathematically analysed by electromagnetic equation. Each thrust of these flux is respectively induced. So in this paper, it is proved that linear motor is highly affected by end effect at high speed and speed-thrust characteristics of three phase linear induction motor are shown by frequency variation in the actual model.