• Proceedings of the KIPE Conference
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• 2001.07a
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• pp.151-154
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• 2001

This paper propose a new active common-mode voltage damper circuit that is capable of suppressing a common-mode voltage produced in the PWM VSI. The new active common mode voltage damper is consisted of a half-bridge inverter and a common mode transformer with a blocking capacitor. Principle of the active common mode damper is as follow; by applying the compensation voltage which has the same amplitude and opposite polarity to the PWM inverter system. So, common mode voltage and high frequency leakage current can be reduced. Simulated and experimental results show that common-mode voltage damper makes contributions to reducing a high frequency leakage current and common-mode voltage.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.4
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• pp.871-876
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• 2011

In this paper, a voltage-controlled frequency tunable current-mode integrator and a 3rd-order current-mode Chebyshev filter in 1.8V-$0.18{\mu}m$ CMOS is realized for software radio applications in system-on-chips. This filter is used for reconstruction purposes between a current-steering DAC and a current-mode mixer. Power consumption of the designed filter can be reduced by using a current-mode small size integrator. And also, cutoff frequency of this filter is variable between 1.2MHz and 10.1MHz, the power consumption is 2.85mW. And the voltage bias compensated circuit is used to control the voltage variation.in the designed filter.

• Journal of Electrical Engineering and Technology
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• v.6 no.5
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• pp.647-657
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• 2011

The present paper proposes a sliding mode control with fixed switching frequency for three-phase three-leg voltage source inverter based four-wire shunt active power filter. The aim is to improve phase current waveform, neutral current mitigation, and reactive power compensation in electric power distribution system. The performed sliding mode for active filter current control is formulated using elementary differential geometry. The discrete control vector is deduced from the sliding surface accessibility using the Lyapunov stability. The problem of the switching frequency is addressed by considering hysteresis comparators for the switched signals generation. Through this method, a variable hysteresis band has been established as a function of the sliding mode equivalent control and a predefined switching frequency in order to keep this band constant. The proposed control has been verified with computer simulation which showed satisfactory results.

• The Transactions of the Korean Institute of Power Electronics
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• v.26 no.3
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• pp.176-182
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• 2021

This research proposes a high-frequency circuit that can accurately predict the differential mode noise of single-phase inverters at the circuit design stage. Proposed single-phase inverter high frequency circuit in the work is a form in which harmonic impedance components are added to the basic single-phase inverter circuit configuration. For accurate noise prediction, parasitic components present in each part of the differential noise path were extracted. Impedance was extracted using a network analyzer and Q3D in the measurement range of 150 kHz to 30 MHz. A high-frequency circuit model was completed by applying the measured values. Simulations and experiments were conducted to confirm the validity of the high-frequency circuit. As a result, we were able to predict the resonance point of the differential mode voltage extracted as an experimental value with a high-frequency circuit model within an approximately 10% error. Through this outcome, we could verify that differential mode noise can be accurately predicted using the proposed model of the high-frequency circuit without a separate test bench for noise measurement.

• Journal of KSNVE
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• v.8 no.3
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• pp.494-503
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• 1998

In this paper, in order to analyze dynamic characteristics of an automobile steering system consisting of many components, natural frequencies and transfer functions of each component and the total system are found on a FFT analyzer by experiments. Then, the data are transmitted to a commercial package program, CADA-PC. By analyzing the data, the mode shape of each natural frequency and damping values are obtained. Also, the function of a rubber coupling in column and telescoping effects on system are considered. C.A.E commercial programs are used to compare with the results of experiments. For the finite element modeling, I-DEAS is used. Data processing and post processing are operated on NASTRAN and XL, respectively. The ball-bearing and the linkage of shaft with column are modeled by spring element. Stiffness is modified from the results of experiments. The results of those show close agreement. In the mode shape of total system, wheel mode is dominant at lower frequency, while the column mode is main mode at higher. The role of rubber coupling in vibration isolation is clear on mode shape. Telescoping function makes natural frequency of column changed.

• Journal of IKEEE
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• v.28 no.1
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• pp.72-77
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• 2024

In this paper, a triple-mode frequency-tunable filter is proposed to meet the recent demands of various frequency bands of mobile communication services. This filter has a tunable structure that can adjust the resonance frequency using a variable capacitor. To improve the quality factor, a SIW(Substrate Integrated Waveguide) structure was introduced and a structure that induces three resonance modes was implemented through a circular hole located in the center. The change in electric field distribution and resonance frequency by the variable capacitor was simulated using HFSS, and the change in electric field distribution and resonance frequency of Triple Mode mode was confirmed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.8
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• pp.702-710
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• 2007

Direct numerical simulation (DNS) is performed to investigate suppressed wake transition and occurrence of lock-on in the wake of a circular cylinder disturbed by sinusoidal perturbation at the Reynolds number of 220 (A-mode instability regime). The sinusoidal perturbation, of which the frequency is near twice the natural shedding frequency, is superimposed on the free stream velocity. It is shown that the wake transition behind the circular cylinder can be suppressed due to the perturbation of the free stream velocity. This change causes a jump in the Strouhal number from the value corresponding to A-mode instability regime to the value corresponding to retarded wake transition regime (extrapolated from laminar shedding regime) in the Strouhal-Reynolds number relationship. As a result, vortex shedding frequency is locked on the perturbation frequency depending not on the natural shedding frequency but on the modified shedding frequency.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.12 no.5
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• pp.94-100
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• 2003

One of unique characteristics of guided waves is a dispersive behavior that guided wave velocity changes with an excitation frequency and mode. In practical applications of guided wave techniques, it is very important to identify propagating modes in a time-domain waveform for determination of detect location and size. Mode identification can be done by measurement of group velocity in a time-domain waveform. Thus, it is preferred to generate a single or less dispersive mode But, in many cases, it is difficult to distinguish a mode clearly in a time-domain waveform because of superposition of multi modes and mode conversion phenomena. Time-frequency analysis is used as efficient methods to identify modes by presenting wave energy distribution in a time-frequency. In this study, experimental guided wave mode identification is carried out in a steel plate using time-frequency analysis methods such as wavelet transform. The results are compared with theoretically calculated group velocity dispersion own. The results are in good agreement with analytical predictions and show the effectiveness of using the wavelet transform method to identify and measure the amplitudes of individual guided wave modes.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.55 no.7
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• pp.265-272
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• 2006

This paper describes a method of parameter estimation of time series data using discrete Fourier transform(DFT). DFT have been mainly used to precisely and rapidly obtain the frequency of a signal. In a dynamic system, a real part of a mode used to learn damping characteristics is a more important factor than the frequency of the mode. The parameter estimation method of this paper can directly estimate modes and parameters, indicating the characteristics of a dynamic system, on the basis of the Fourier transform of the time series data. Real part of a mode estimates by subtracting a frequency of the Fourier spectrum corresponding to 0.707 of a magnitude of the peak spectrum from a peak frequency, or subtracting a frequency of the power spectrum corresponding to 0.5 of the peak power spectrum from a peak frequency, or comparing the Fourier(power) spectrum ratio. Also, the residue and phase of time signal calculate by simple equation with the real part of the mode and the power spectrum that have been calculated. Accordingly, the proposed algorithm is advantageous in that it can estimate parameters of the system through a single DFT without repeatedly calculating a DFT, thus shortening the time required to estimate the parameters.

• International Journal of Precision Engineering and Manufacturing
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• v.2 no.4
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• pp.81-88
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• 2001

We present a new digital phase measuring method for heterodyne optical interferometry, which providers high measuring speed up to 6 m/s with a fine displacement resolution of 0.1 nanometer. The key idea is combining two distinctive digital phase measuring techniques with mutually complementary characteristics to earth other one is counting the Doppler shift frequency counting with 20 MHz beat frequency for high-velocity measurement and the other is the synchronous phase demodulation with 2.0 kHz beat frequency for extremely fine displacement resolution. The two techniques are operated in switching mode in accordance wish the object speed in a synchronized way. Experimental results prove that the proposed dual mode phase measuring scheme is realized with a set of relatively simple electronic circuits of beat frequency shifting, heterodyne phase detection. and low-pass filtering.