• Journal of the Korean Institute of Intelligent Systems
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• v.17 no.3
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• pp.374-379
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• 2007

This paper focuses on the improvement of fault detection algorithm in FRTU(feeder remote terminal unit) on the feeder of distribution power system. FRTU is applied to fault detection schemes for phase fault and ground fault. Especially, cold load pickup and inrush restraint functions distinguish the fault current from the normal load current. FRTU shows FI(Fault Indicator) when the fault current is over pickup value or inrush current. STFT(Short Time Fourier Transform) analysis provides the frequency and time Information. FCM(Fuzzy C-Mean clustering) algorithm extracts characteristics of harmonics. The neural network system as a fault detector was trained to distinguish the inruih current from the fault status by a gradient descent method. In this paper, fault detection is improved by using FCM and neural network. The result data were measured in actual 22.9kV distribution power system.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.5
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• pp.145-151
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• 2010

Voltage unbalance is regarded as a power quality problem of significant at the user application. Although the voltages are quite well balanced at the transmission system, the voltage level of utilization can be unbalanced due to the unequal system impedances and the unequal distribution of single phase loads. Capacitor is generally used for power-factor compensation and reducing harmonics of non linear load with reactor. If voltage unbalance exists, current unbalance is generated and it will be reflected in the capacity variance. When the reactor and condenser are used at the same location, generally its trouble rate is high. And it is very important checking out that how the variance of voltage, current and capacity of condenser is proceeded by the voltage unbalance. In this paper, we calculated that voltage, current and capacity of condenser are within the tolerance limit of official regulations in the event of voltage unbalance with/without reactor.

• The Transactions of the Korean Institute of Power Electronics
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• v.15 no.3
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• pp.207-217
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• 2010

Recently, the use of DC power increased due to the increased use of digital load. Power factor of input current decrease and input current harmonics increase, and conversion loss which is occurred in the AC / DC converter is a problem to provide the proper DC voltage to the device equipped with an internal AC / DC converter. Hybrid system supplies the AC power and DC power to AC load (motor load and the transformer load) and DC loads (computers, TV, LED fluorescent light) at the same time it supplies the renewable energy and utility energy taken power from Utility to user for improving the efficiency and renewable energy improvements in ease of use. This paper studies DC characteristics of traditional AC load for Hybrid distributions.

• The Transactions of the Korean Institute of Power Electronics
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• v.15 no.3
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• pp.235-243
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• 2010

This paper describes a design method of LCL filter for grid-connected three-phase PWM inverter. First, by analyzing the ripple component of phase voltages and currents according to the PWM pattern of grid-connected three-phase inverter, the RMS value of the current ripple can be calculated. Then based on the analysis, the current THD in the inverter-side can be defined. After that by analyzing the dependency between the current THD of the system and the current ripple attenuation, the parameter of LCL filter can be designed. Finally, the described LCL filter design method is verified by showing a good agreement between the target current $THD_g$ and the actual one through the simulation and experiment.

• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.1
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• pp.100-108
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• 2014

Low noise amplifier (LNA) is an integral component of RF receiver and frequently required to operate at wide frequency bands for various wireless system applications. For wideband operation, important performance metrics such as voltage gain, return loss, noise figure and linearity have been carefully investigated and characterized for the proposed LNA. An inductive shunt feedback configuration is successfully employed in the input stage of the proposed LNA which incorporates cascaded networks with a peaking inductor in the buffer stage. Design equations for obtaining low and high impedance-matching frequencies are easily derived, leading to a relatively simple method for circuit implementation. Careful theoretical analysis explains that input impedance can be described in the form of second-order frequency response, where poles and zeros are characterized and utilized for realizing the wideband response. Linearity is significantly improved because the inductor located between the gate and the drain decreases the third-order harmonics at the output. Fabricated in $0.18{\mu}m$ CMOS process, the chip area of this wideband LNA is $0.202mm^2$, including pads. Measurement results illustrate that the input return loss shows less than -7 dB, voltage gain greater than 8 dB, and a little high noise figure around 6-8 dB over 1.5 - 13 GHz. In addition, good linearity (IIP3) of 2.5 dBm is achieved at 8 GHz and 14 mA of current is consumed from a 1.8 V supply.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.10
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• pp.56-61
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• 2008

Because the harmonic disturbance characteristic which makes voltage drop and the deterioration of instantaneous power quality in electrical power system overheats the NGR and the customer capacitor and malfunctions the OCGR and AMR, it is necessary for electric power company to take active measures to reduce this disturbance. International Electrotechnical Commission(IEC) 61000-3-2 specifies limits for harmonic current emissions generated by low voltage(LV) electrical equipment whose input current $\leq$ 16(A) per phase. Analysis shows that limits for Class A equipment in IEC are calculated using the reference impedance of LV system and maximum permissible voltage and limits for other Classes are also calculated based on limits for Class A. Therefore we have calculated four(4) internal limits for LV electrical equipment using the korea reference impedance and maximum permissible voltage in this paper.

• The Journal of Information Technology
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• v.7 no.1
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• pp.155-161
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• 2004

During normal machine operation, partial discharge(PD) measurements were performed with turbine generator analyzer(TGA) in imitation stator winding of high voltage motors. The motor was energized to 4.47kV, 6.67, respectively. Applied voltage to Imitation winding was used two voltage level, 4.47[kV] and 6.67[kV]. Motors having imitation stator winding were installed with 80pF capacitive couplers at the terminal box. Case of PD Pattern regarding applied voltage phase angel, the PD patterns were displayed two dimensional and three dimensional. TGA summarizes each plot with two quantities such as the normalized quantity number(NQN) and the peak PD magnitude(Qm). As the result, we could discrimidate using TGA the difference of internal and surface discharge for imitation stator winding. We have used the other technique, in order to feature extraction of faulty signals on stator winding, Daubechies Discrete wavelet transform and Harmonics analysis(FFT) about faulty signals.

• The Journal of Korean Institute of Information Technology
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• v.16 no.11
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• pp.97-103
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• 2018

In this paper, the estimation method for the power signal harmonics is proposed by using the time-varying optimal finite impulse response (FIR) filter. To estimate the magnitude and phase-angle of the harmonic components, the time-varying optimal FIR filter is designed for the state space representation of the noisy power signal which the magnitude and phase is considered as a stochastic process. Since the time-varying optimal FIR filter used in the proposed method does not use any priori information of the initial condition and has FIR structure, the proposed method could overcome the demerits of Kalman filter based method such as poor estimation and divergence problem. Due to the FIR structure, the proposed method is more robust against to the model uncertainty than the Kalman filter. Moreover, the proposed method gives more general solution than the time-invariant optimal FIR filter based harmonic estimation method. To verify the performance and robustness of the proposed method, the proposed method is compared with time-varying Kalman filter based method through simulation.

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.4
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• pp.498-503
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• 2019

Electric propulsion ships are gaining widespread interest in the marine industry owing to extreme air pollution concerns. Consequently, several studies are actively being conducted for improving the power quality. Various methods have been developed that incorporate passive filters, notch filters, and active filters for reducing the harmonic content in the input current of a conventional diode front end rectifier. Among such filters, the active front end (AFE) rectifier is considered as an excellent technology. In this paper, current control for an AFE rectifier employing space vector PWM (Pulse Width Modulation) is proposed. Conventional current control methods for the AFE rectifier, hysteresis, SPWM (Sinusoidal Pulse Width Modulation), and SVPWM (Space Vector Pulse Width Modulation) were simulated by employing the PSIM software tool for analysis and comparisons. The results corroborate that SVPWM has the simplest structure and provides the best performance.

• Journal of Korea Entertainment Industry Association
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• v.13 no.7
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• pp.219-227
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• 2019

In this paper, we proactively looked at the structure and characteristics of each instrument in order to compare and analyze the sound colors of the western violin, chinese erhu and korean haegeum, which are representative bow string instruments. Also, many performers have simply been unable to fully explain how the violin is rich in pitch and the haegeum has a unique tone. Also, many performers thinks that violin sounds rich just because it has many overtones and have been unable to fully explain how haegeum makes unique tone. While previous research data show that most instruments are studied and published by analyzing their own frequencies or related cases of acoustic studies, this study provides a visual look how the harmonics composition, which determines musical instruments' timbres, consists of and suggests data specifically by analyzing each sound pressure of integer multiple overtones so that the structure of instruments' unique timbre can be understood. Based on this, we hope that it will be of considerable help to the development of virtual musical instruments of korean traditional instruments, which are relatively small compared to western virtual instruments, by reproducing instrument sounds through the synthesizers in the future.