• The Journal of the Acoustical Society of Korea
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• 제24권2E호
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• pp.61-66
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• 2005

Experimental work in underwater acoustic communications using passive phase conjugation has shown that the demodulation error depends on the relative drift rate between the source and receiver [Rouseff et al., IEEE J. Oceanic Eng. 26, 821-831 (2001)]. The observed effect involves the mismatch between the initial impulse response and the subsequent response after the source or receiver has changed locations. In the present work, the effect of drifting source is analyzed by numerical simulations and compared to the experimental results. The communications bit error rate is qualified as a function of drift rate, drifting direction, and source-receiver range.

• Journal of Power Electronics
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• 제16권3호
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• pp.915-924
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• 2016

A digital self-sustained phase shift modulation (DSSPSM) strategy that allows for good soft switching and dynamic response performance in the presence of step variations is presented in this paper. The working principle, soft switching characteristics, and voltage gain formulae of a LLC converter with DSSPSM have been provided separately. Furthermore, the method for realizing DSSPSM is proposed. Specifically, some key components of the proposed DSSPSM are carefully investigated, including a parameter variation analysis, the start-up process, and the zero-crossing capture of the resonant current. The simulation and experiment results verify the feasibility of the proposed control method. It is observed that the zero voltage switching of the switches and the zero current switching of the rectifier diodes can be easily realized in presence of step load variations.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1999년도 추계학술대회 논문집
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• pp.303-306
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• 1999

In this study, the piezoelectric ceramics PZT powder was synthesized by Wet-Dry combination method. The flexible 1-3-0 type composites were fabricated with piezoceramic PZT and Eccogel polymer matrix embedded 3rd phase. This paper represents the acoustic properties with various 3rd phase wt.%. The acoustic impedance of 1-3-0 type composites was lower than that of single phase PZT ceramics. The pulse-echo response of transducer fabricated with 1-3-0 type composites was better than solid PZT transducer.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 B
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• pp.681-683
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• 2003

The response surface method (RSM) became a popular meta modeling technique, but it always contains the approximation error. Instead of the conventional RSM, the moving least squares method (MLSM) was used to get more accurate models. The characteristics of a single-phase induction motor for the reciprocal compressor are analyzed by using the lumped method Program (LMP). The proposed method is applied to a single-phase induction motor for increasing the efficiency.

• 전력전자학회논문지
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• 제22권3호
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• pp.231-239
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• 2017

A novel current control technique with fast response and application in an unbalanced system is proposed in this paper. Contrary to the conventional PI and dead-beat current control techniques, the proposed method is adopted to the valley current mode control (VCMC) and average current mode control (ACMC) methods to overcome the phase delay caused by conventional methods. The advantages of the proposed system are simplicity of structure and ease of implementation. The VCMC and ACMC methods are established and applied to the buck converter, boost converter, three-phase PWM converter, and three-phase inverter. The control performances of the proposed systems are shown by computer simulations and verified by experimental results.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 ITC-CSCC -1
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• pp.686-689
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• 2002

This paper proposes a weighted least-squares(WLS) method for designing variable one-dimensional (1-D) FIR digital filters with simultaneously variable magnitude and variable non-integer phase-delay responses. First, the coefficients of a variable FIR filter are represented as the two-dimensional (2-D) polynomials of a pair of spectral parameters: one is for tuning the magnitude response, and the other is for varying its non-integer phase-delay response. Then the optimal coefficients of the 2-D polynomials are found by minimizing the total weighted squared error of the variable frequency response. Finally, we show that the resulting variable FIR filter can be implemented in a parallel form, which is suitable for high-speed signal processing.

• Journal of Power Electronics
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• 제15권6호
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• pp.1577-1583
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• 2015

In this research, a combined adaptive-robust current controller is developed for non-minimum-phase DC-DC converters in a wide range of operations. In the proposed nonlinear controller, load resistance, input voltage and zero interval of the inductor current are estimated using developed adaptation rules and knowing the operating mode of the converter for the closed-loop control is not required; hence, a single controller can be employed for a wide load and line changes in discontinuous and continuous conduction operations. Using the TMS320F2810 digital signal processor, the experimental response of the proposed controller is presented in different operating points of the buck/boost converter. During transition between different modes of the converter, the developed controller has a better dynamic response compared with previously reported adaptive nonlinear approach. Moreover, output voltage steady-state error is zero in different conditions.

• 대한전기학회논문지:전력기술부문A
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• 제48권6호
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• pp.719-727
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• 1999

A robust position control method of the BLDC motor using a new sliding mode control strategy is presented. The main property of variable structure system(VSS) is that the system response is robust and insensitive to parameter variations and external disturbances in the sliding mode. When using the conventional VSS, generally the reaching phase problem occurs, which cause the system response to be sensitive to parameter variations and external disturbances. Furthermore, the speed of response is relatively slow because the swithching surface is a linear function. In order to overcome these problems, VSS with nonlinear sliding surface eliminating reaching phase is proposed. The validity of the proposed scheme is shown by results of simulations of simulations and experiments for the BLDC motor with variable load.

• The Journal of the Acoustical Society of Korea
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• 제15권1E호
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• pp.45-58
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• 1996

This paper addresses the problem of identifying the class of all stable system transfer functions that interpolate the given partial impulse response sequence. In this context, classical Pade approximations that are also stable, are shown to be a special case of this general formulation. The theory developed in this connection is utilized to obtain a new criterion for determining the model order and system parameters for rational systems, and, further, to generate nonminimum phase optimal stable rational approximatinos of nonrational systems from its impulse response sequence.

• Transactions on Control, Automation and Systems Engineering
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• 제2권4호
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• pp.262-267
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• 2000

In this paper, the magnitude of undershoot and overshoot in a prototype second order system with one positive real zero is computed by the analytic methods. Also, it will be shown that the peak times of the undershoot and overshoot can be calculated using the impulse and step response of the second order system. Three different cases are investigated: underdamped(p<ζ<1), critically damped(ζ=1) and overdamped(ζ>1) cases. We deal with the undamped(ζ=0) case as a special case of the underdamped. And a compensation method is proposed to reduce undershoots of the nonmininmun phase system using feedforward compensator.