• Journal of the Korean Society for Railway
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• v.18 no.6
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• pp.533-542
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• 2015

This paper suggest away to maintain constant power through trolley wire by transferring increased line voltage to the AC main line while changing the mode from Converter(Forward) to Inverter(Reverse) when the line voltage is increased due to regenerative power when the train stops, This paper suggests a Double Converter DC substation that can create regenerative power when the train stops reusable. We also proposed using a simulation tool, the optimal Thyrister firing angle that can minimize the undershoot and overshoot that occurs when transferring the mode from Converter to Inverter for quality improvement of DC voltage in the Double Converter in the DC substation from the Busan Urban Subway.

• Journal of Biosystems Engineering
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• v.33 no.2
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• pp.115-123
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• 2008

This study was conducted to develop an automatic soil water content control system for greenhouse, which consisted of drip irrigation nozzles, soil water content sensors, an on/off valve, a servo-motor assembly and a control program. The control logic adopted in the system was Ziegler-Nichols algorithm and rising time, time constant and over/undershoot ratio as control variables in the system was selected and determined by various control experiments to maintain small delay time and low overshoot. Based on the experimental results, it was concluded that the control system developed in the study could replace the unreliable conventional greenhouse soil water management.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1757-1760
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• 2005

This paper is concerned with spring back after sheet forming of bulk amorphous alloys in the super cooled liquid state. The temperature-dependence and strain-rate dependence of Newtonian/non-Newtonian viscosities as well as the stress overshoot/undershoot behavior of amorphous alloys are reflected in the thermo-mechanical Finite Element simulations. Hemispherical deep drawing operations are simulated for various forming conditions such as punch velocity, die corner radius, friction, blank holder force, clearance and initial forming temperature. Here, spring back by an instantaneous elastic unloading was followed by thermal deformation during cooling and two modes of spring backs are examined in detail. It could be concluded that the superior sheet formability of an amorphous alloy can be obtained by taking the proper forming conditions for loading/unloading.

• Proceedings of the KIEE Conference
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• 2003.11b
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• pp.127-130
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• 2003

In this paper, a hypothesis in order that the impulse response of a stable linear system does not change sign is suggested. For fixed zeros of the systems, the problem of synthesizing such a system is reduced to the problem of finding a proper denominator polynomial so that the step response of the overall system will not overshoot. The hypothesis is associated with the generalized time constant by Kim[5]. Under the hypothesis, we propose several methods that allow to compose a continuous time LTI systems achieving non-negative impulse response.

• Journal of Mechanical Science and Technology
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• v.14 no.6
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• pp.645-654
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• 2000

In this paper, low level control algorithms of a metal belt CVT are suggested. A feedforward PID control algorithm is adopted for line pressure based on a steady state relationship between the input duty and the line pressure. Experimental results show that feedforward PID control of the line pressure guarantees a fast response while reducing the pressure undershoot which may result in belt slip. For ratio control, a fuzzy logic is suggested by considering the CVT shift dynamics and on-off characteristics of the ratio control valve. It is found from experimental results that a desired speed ratio can be achieved at steady state in spite of the fluctuating primary pressure. It is expected that the low level control algorithms for the line pressure and speed ratio suggested in this study can be implemented in a prototype CVT.

• Transactions of Materials Processing
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• v.14 no.9 s.81
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• pp.751-755
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• 2005

This paper is concerned with spring back after sheet forming of bulk amorphous alloys in the super cooled liquid state. The temperature-dependence and strain-rate dependence of Newtonian/non-Newtonian viscosities as well as the stress overshoot/undershoot behavior of amorphous alloys are reflected in the thermo-mechanical Finite Element simulations. Hemispherical deep drawing operations are simulated for various forming conditions such as punch velocity, die comer radius, friction, blank holder force, clearance and initial funning temperature. Here, spring back by an instantaneous elastic unloading was followed by thermal deformation during cooling, and two modes of spring back are examined in detail. It could be concluded that the superior sheet formability of an amorphous alloy can be obtained by taking the proper forming conditions for loading/unloading.

• 제어로봇시스템학회:학술대회논문집
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• 1994.10a
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• pp.449-454
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• 1994

This paper describes new PID control methods based on the fuzzy logic. PID gains are retuned after evaluating control performances of transient responses in terms of performance features. The retuning procedure is based on fuzzy rules and reasoning accumulated from the knowledge of experts on PID gain scheduling. For the case that the retuned PID gains result in worse CLDR (characteristics of load disturbance rejection) than the initial gains, an on-line tuning scheme of the set-point weighting parameter is, proposed. This is based on the fact that the set-point weighting method efficiently reduce either overshoot or undershoot without any degradation of CLDR. The set-point weighting parameter is adjusted at each sampling instant by the fuzzy rules and reasoning. As a result, better control performances were achived in comparison with die controllers tuned by the Z-N (Ziegler-Nichols) parameter tuning formula or by the fixed set-point weighting parameter.

• Proceedings of the KIEE Conference
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• 1993.11a
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• pp.23-25
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• 1993

This paper presents a design technique of self-organizing fuzzy controller using a learning method of fuzzy inference rule by a gradient method for load frequency control of power system. The membership functions in antecedent part and in consequent part of fuzzy inference rules are tuned by the gradient method. The related simulation results show that the proposed fuzzy controller are more powerful than the conventional ones for reduction of undershoot and deviation of load frequency in steady-state, and for minimization of settling time.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.96.1-96
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• 2001

This paper is shown that the impulse and unit step response of second-order system can be computed by the analytic methods using Laplace transform. Also, the transient response specifications are explicitly formulated by the peak undershoot and maximum overshoot of the step response. Three different second-order systems are investigated: prototype system, system with LHP(left half plane) real zero, and system with RHP(right half plane) real zero. Based on these analytic results, this paper presents the sufficient and necessary conditions for the second-order linear SISO(single-input/single-output) stable system to have the nonovershooting or monotone nondecreasing step response.

• 제어로봇시스템학회:학술대회논문집
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• 1999.10a
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• pp.79-82
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• 1999

The right half plane (RHP) zeros may cause severe problems, such as undershoots, oscillations and time delay in the transient response of the systems. In this paper, we formulate a linear quadratic type problem to deal with the effects of the RHP zeros in the nonminimum phase systems. Based on the LQ formulation, this paper shows the trade-off relation between undershoot and rising time performances in nonminimum phase systems by using a new performance index which consists of new state and tracking error. And performances of the proposed method are shown via computer simulations.