• Journal of the Korean Society for Precision Engineering
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• v.12 no.6
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• pp.120-127
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• 1995

A nonlinear empirical state-space model of the Artificial Neural Network(ANN) has been developed. The nonlinear model structure incorporates characteristic, so as to enable identification of the transient response, as well as the steady-state response of a dynamic system. A hybrid feedfoward/feedback neural network, namely a Local Time Delayed Recurrent Multi-layer Perception(RMLP), is the model structure developed in this paper. RMLP is used to identify nonlinear dynamic system in an input/output sense. The feedfoward protion of the network architecture provides with the well-known curve fitting factor, while local recurrent and cross-talk connections provides the dynamics of the system. A dynamic learning algorithm is used to train the proposed network in a supervised manner. The derived dynamic learning algorithm exhibit a computationally desirable characteristic; both network sweep involved in the algorithm are performed forward, enhancing its parallel implementation. RMLP state-space and its associate learning algorithm is demonstrated through a simple examples. The simulation results are very encouraging.

• Proceedings of the KIEE Conference
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• 1990.11a
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• pp.303-308
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• 1990

The stand alone induction generator has been excited by capacitor bank or voltage source inverters. The conventional excitation methods offer several restrictions on the operation of the induction generator in various operating conditions. To overcome the restrictions, this paper presents the induction generator system excited by the current controlled inverter which operates on the principle of vector control. The proposed control scheme is based on the rotor flux oriented indirect vector control. The steady state characteristics are investigated to yield control ranges under various operating conditions. Through the simulation, it is confirmed that the system has good dynamic characteristics wi thin the controllable ranges given by the steady state analysis.

• Proceedings of the KIEE Conference
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• 2006.04b
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• pp.229-231
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• 2006

The paper presents a sensorless speed control of interior permanent magnet synchronous motors using an adaptive integral binary observer in view of composition with a main loop regulator and an auxiliary loop regulator. The binary observer has a property of the chattering alleviation in the constant boundary layer; however, the steady state estimation accuracy and robustness are dependent upon with width of the constant boundary. In order to improve the steady state performance of the binary observer, the binary observer is formed by adding extra integral dynamic to the switching hyperplane equation.

• Journal of Power Electronics
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• v.16 no.4
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• pp.1367-1374
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• 2016

This paper presents a discrete-time version of voltage and current limited operation using an enhanced direct torque and flux control method for interior permanent magnet synchronous motor (IPMSM) drives. A command voltage vector for airgap torque and stator flux regulation can be uniquely determined by the finite-settling-step direct torque and flux control (FSS-DTFC) algorithm under physical constraints. The proposed command voltage vector trajectories can be developed to achieve the maximum inverter voltage utilization for the discrete-time current limit (DTCL)-based FSS-DTFC. The algorithm can produce adequate results over a number of the potential secondary upsets found in the steady-state current limit (SSCL)-based DTFC. The fast changes in the torque and stator flux linkage improve the dynamic responses significantly over a wide constant-power operating region. The control strategy was evaluated on a 900W IPMSM in both simulations and experiments.

• The KSFM Journal of Fluid Machinery
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• v.14 no.2
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• pp.29-34
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• 2011

Aerodynamic torque of wind turbine is highly nonlinear due to the nonlinear interactions between wind and blade. The aerodynamic nonlinearity is represented by nonlinear power and torque coefficients which are functions of wind speed, rotational speed of rotor, and pitch angle of blade. It is essential from the viewpoint of understanding and analysis of dynamic characteristics for wind turbine to linearize the aerodynamic torque and define aerodynamic nonlinear parameters as derivatives of aerodynamic torque with respect to the three parameters. In this paper, a linearization method of the aerodynamic torque from power coefficient is presented through differentiating it by the three parameters. And steady-state values of three aerodynamic nonlinear parameters according to wind speed are obtained and their nonlinear characteristics are investigated.

• Phonetics and Speech Sciences
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• v.5 no.4
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• pp.195-200
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• 2013

This study investigates formant transition shapes of Korean front vowels produced by native speakers of Seoul Korean. Sixteen speakers (eight male and eight female speakers) produced [pVt] syllables where the vowels were [i, e, ɛ]. F1, F2, and F3 transition shapes were estimated by presenting formant values at 11 points by dividing the vowel duration into 10 different time intervals. The results indicated that the male and female speakers overall demonstrated similar formant transition shapes and measurement points arriving at the maximum and minimum formant values for the three front vowels. As for the vowels [e] and [ɛ], both male and female speakers showed similar formant values across the 11 measurement points and similar measurement points arriving at the maximum and minimum values, indicating that the two Korean vowels have been merged not only in the steady-state formant values, but also in the dynamic transition shapes.

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.6
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• pp.760-769
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• 2006

This paper proposes an autopilot system using a fuzzy PID controller to satisfy performances required for the automatic navigation of ships under various marine circumstances. The existing autopilot system using a PD type controller has difficulties in eliminating a steady-state error and compensating nonlinear characteristics of ships. The autopilot system using the proposed fuzzy PID controller has a self-tuning ability, an ability to compensate nonlinear characteristics, and an ability to turn at constant angular velocity. Therefore. it can naturally make a steady-state error zero, compensate nonlinear dynamic effect of ships, have an adaptability to parameter variation owing to shallow water effect, and have an ability to turn ship's course rapidly without overshoot through procedures of acceleration, constant, and deceleration of angular velocity for large course-changing.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.1
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• pp.71-76
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• 2008

Nonlinear dynamic system under random excitation was analyzed by using stochastic method. A linearization method was used in order to linearize non-linear structural characteristics but the parametric excitation was used as it was given. An equivalent energy method which equalizes the expectation value of energy of the original nonlinear system and that of quasi-linearized system was proposed. Ito's differential rule was applied to obtain steady state moments. Quasi-linearization coefficients can be obtained the iterative calculation of linearization scheme and steady state moments. Monte Carlo simulation was used to verify the results of the proposed method. Nonlinear vibration of a slender beam was analyzed in this research. The analysis results were compared with Monte Carlo simulation result and showed good agreement. As the spectral density of the given excitation increased, the analysis results showed the better agreement with Monte Carlo simulation.

• Journal of Korean Society of Transportation
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• v.12 no.4
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• pp.89-97
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• 1994

신호화된 교차로의 운영비율을 측정하기 위해 현재 세계적으로 광범위하게 이용되 는 척도는 교차로 통과차량의 평균지체시간이다. 그간 교차로 분석을 위해 많은 대기행렬 모형이 발표되어 왔고 또 그중 일부가 현재 사용 중에 있는데 이들은 모두 steady-state를 가정한 해법이다. 그러나 steady-state 모형은 시간에 따른 대기행렬 길이의 변화를 고려하 지 못하므로 현실적인 분석에 한계가 있는 방법론이다. 그러므로 정당한 교차로 시간산출을 위해서는 time-dependent한 분석형의 개발이 요구된다. 본 연구에서는 discrete Markov chain을 이용하여 단순히 단위시간 동안의 도착율과 출발율로써 transition probabilities를 계산하는 새로운 대기행렬 모형을 개발하였다. 개발된 불연속 대기행렬 모형을 이용하여 교 차로 분석을 할 경우 기존의 교차로 지체모형과 비교하여 기대되는 개선효과는 다음과 같 다. 변화를 고려한 dynamic한 분석으로 현실적이고 정당한 예측을 할 수 있다. 신호자동에 의한 영향을 분석할 수 있다. 그리고 독립적교차로 뿐만 아니라 간선도로, 나아가서 network 분석을 할 수 있으며, 동시에 주어지 교통여건에 대해 신호자동화를 위한 최적값을 산출해 낸다.

• Nuclear Engineering and Technology
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• v.49 no.8
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• pp.1696-1710
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• 2017

An improved Reactor Regulating System (RRS) logic architecture, which is combined with genetic algorithm (GA), is implemented in this work. It is devised to provide an optimal solution to the current RRS. The current system works desirably and has contributed to safe and stable nuclear power plant operation. However, during the ascent and descent section of the reactor power, the RRS output reveals a relatively high steady-state error, and the output also carries a considerable level of overshoot. In an attempt to consolidate conservatism and minimize the error, this work proposes to apply GA to RRS and suggests reconfiguring the system. Prior to the use of GA, reverse engineering is implemented to build a Simulink-based RRS model. Reengineering is followed to produce a newly configured RRS to generate an output that has a reduced steady-state error and diminished overshoot level. A full-scope APR1400 simulator is used to examine the dynamic behaviors of RRS and to build the RRS Simulink model.