• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.1
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• pp.34-40
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• 2004

The PLDRO(Phase-Locked Dielectric Resonator Oscillator) with low phase noise is designed for X-band. The phase of VCDRO(Voltage Controlled Dielectric Resonator Oscillator) is locked to that of a high stable reference oscillator by using a SPD(Sampling Phase Detector) to improve phase noise performance in the loop bandwidth. And, the VCDRO is implemented using a high impedance inverter coupled with dielectric resonator to improve the phase noise performance out of the loop bandwidth. This PLDRO exhibits the harmonic rejection characteristics of 51.67㏈c and requires below 1.95W. The phase noise characteristics are performed as -107.17㏈c/Hz at 10KHz offset frequency and -113.0㏈c/Hz at 100KHz offset frequency, respectively, at ambient. And the output power of 13.0㏈m${\pm}$0.33㏈ is measured over the temperature range of $-20 ∼ +70^{\circ}C$ .

• Journal of the Korean Society for Nondestructive Testing
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• v.37 no.1
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• pp.7-12
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• 2017

A nonlinear ultrasonic parameter is defined by the ratio of displacement amplitude of the fundamental frequency component to that of the second-order harmonic frequency component. In this study, the ultrasonic displacement amplitude of an SUS316 specimen was measured via a piezo-electric-based method to identify the validity of piezo-electric detection method. For comparison, the ultrasonic displacement was also determined via a laser-based Fabry-Pérot interferometer. The experimental results for both measurements were in good agreement. Additionally, the stability of the repeated test results from the piezo-electric method exceeded that of the laser-interferometric method. This result indicated that the piezo-electric detection method can be utilized to measure a nonlinear ultrasonic parameter due to its excellent stability although it involves a complicated process.

• Journal of Sensor Science and Technology
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• v.11 no.3
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• pp.132-137
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• 2002

The single crystal of $LiTaO_3$ ($x-112^{\circ}$ y) has very stable thermal characteristics in a piezoelectric transformer. In this paper, a piezoelectric transformer made of the crystal is newly designed and its operating characteristics are analyzed. The length of the transformer is determined as twice as its width for Lame'-mode because the single crystal of $LiTaO_3$ has low electro-acoustic efficiency. The electric and vibrational characteristics of the transformer is simulated by the PSpice program, and its results are compared to experimental ones. As the results, the ratio of output voltage to input shows large than 10 at 290.83[kHz], which is the frequency coupled the 2nd harmonic for length and the fundamental for width of the Lame'-mode transformer.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.8
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• pp.54-61
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• 1999

This paper proposes a new optic link structure applicable to broad-band wireless access microcellularsystem servicing in the millimeter wave frequency band. The proposed structure utilizes photonic mixing by exploiting the nonlinear property of EOMs, which leads to the frequency up-conversion at the CS and thus, electrical mixing at a BS is not required. Moreover, via transmitting an additional optical millimeter wave carrier into the Bs, the dispenses with an active optic source, which miniaturizes the BS. We analyze CNR, IM3/C in the downlink and SFDR in the uplink. Through simulation using the typical parameter values we also show the feasibility of the proposed system based on the requirements in the current microcellular system.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.3
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• pp.401-408
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• 2001

This paper shows the design, fabrication and performance analysis of VCO which plays a major role in 5.8 GHz RF module for ITS. The design specifications of the VCO are determined on the basis of 5.8 GHz RF modul performance requirements. The design parameters are optimized through ADS simulation tool. The operating characteristic and performance analysis of the implemented VCO based on the design parameters are accomplished. The frequency variations according to the voltage change(0 ~5 V) of varactor diode are from 5.42 GHz to 5.518 GHz and the power level is 6.5 dBm. The second harmonic suppression are -21.5 dBc at 5.51 GHz and the phase noise characteristics are -83.81 dBc at 10 kHz offset frequency. The implemented VCO is available to not only DSRC and also, 5.8 GHz other systems.

• 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.22 no.1
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• pp.132-140
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• 2008

Power system of Jeju is interconnected to the mainland using HVDC and that is also interconnected two wind farms. Control of Jeju power system will be difficult if HVDC is disconnected or HVDC is overhauled under large scale wind farms interconnected. We measured and analysed the power quality of two substation and two wind farms to assess that wind farms and HVDC overhaul have an effect on Jeju system or not during the HVDC overhaul. We found that the frequency of Jeju system is very unstable and the voltage distortion excess the limitation. Harmonic currents of wind farms flew into Jeju system in proportion to the power of wind turbine. And the voltage of nearby distribution line was distorted by power of wind turbine when the amount is more that 3,000[kW].

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.13 no.1
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• pp.46-52
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• 1999

A new current controlled PWM t'||'&'||'pound;rlmique with NPC(Neutral Point Qarll)ed) structure is IrOIX>Sed in this paper. A current controlled PWM technique with neutral-JXlint-cIamped pulse-width modulation inverter composed of main switching devices which operates as switch for PWM and auxiliary switching devices to clamp the output terminal potential to the neutral point potential is described. The proposed current controller has a first and second current band The switching pattern will be made by the first current band. According to the second current band, the output state of the switching pattern is changed into positivee and negative state. This inverter output contains less hanronic content and lower switching frequency than that of conventional current controlled PWM technique at the same current limit. Thbe induction machine drive with proposed technique is investigated by commputer simulation.

• The Transactions of the Korean Institute of Power Electronics
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• v.8 no.6
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• pp.469-477
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• 2003

This paper proposes a Carrier-Rotation (CR) PWM technique that is a new solution for the voltage unbalancing problem of flying capacitors in the Flying Capacitor Multi-level Inverter (FCMI). The proposed technique equalizes the utilization of phase leg voltage redundancies corresponding to the charging and the discharging state of individual flying capacitors during each switching period of all the switches. Therefore, the charging and the discharging quantity of flying capacitors are equal, which makes the average variation of flying capacitor voltages become zero and keeps their voltage stable during minimum specified period. It also has the reduced harmonic contents of output voltage and the same switch utilization since all the carrier signals are in phase and the switching frequency of each switch is identical. The proposed technique is analyzed precisely in flying capacitor 3-level inverter and then it has expanded to the FCMI (N-level, N>3). Experimental results on the laboratory prototype flying capacitor 3-level inverter confirm the validity of the proposed technique.

• The Transactions of the Korean Institute of Power Electronics
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• v.4 no.6
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• pp.539-546
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• 1999

A new integrated single-stage zero current switched(ZCS) quasi resonant convertedQRC) for the IX)wer f factor correction(PFCl converter is introduced in this paper. The power factor correction can be achieved by t the discontinuous conduction mod$\varepsilon$(DCM) operation of an input current. The proposed converter has the c characteristics of the good IX)wer factor, 10씨 line current harmonics, and tight output regulation. Furthern10re, t the ringing effect due to the output capacitance of the main switch can be eliminated by use of‘ active clamp c circuit. Therefore, the proIX)sed converter is expecttc'(] to be suitable for a compact power converter with a t tightly regulated output voltage requiring a switching frequency of more than several hundrtc'(]s kHz.