• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.85.4-85
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• 2001

A learning controller is presented for repetitive walking motion of biped robot. The learning control scheme learns the approximate inverse dynamics input of biped walking robot and uses the learned input pattern to generate an input profile of different walking motion from that learnt. In the learning controller, the PID feedback controller takes part in stabilizing the transient response of robot dynamics while the feedforward learning controller plays a role in computing the desired actuator torques for feedforward nonlinear dynamics compensation in steady state. It is shown that all the error signals in the learning control system are bounded and the robot motion trajectory converges to the desired one asymptotically. The proposed learning control scheme is ...

• Journal of the Korean Institute of Telematics and Electronics B
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• v.32B no.7
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• pp.1003-1009
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• 1995

In This Paper, Linearization problem is discussed to reduce distortion of a nonlinear system based on Schetzen's pth-orfer inverse theorem. We propose a nonlinear adaptive prefiltering algorithm which can reduse nonlinear distortion up to pth order by tandemly connecting a pth-order Volterra filter before the nonlinear system under the consideration and by adjusting the filter coefficients adaptively. The feasibility of applying the proposed algorithm to a nonlinear system is conformed via computer simulation by observing significant reduction of total nonlinear distortion for the case of random input and sinusoidal input excitation.

• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.1
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• pp.49-57
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• 2016

A modular multilevel converter is widely adapted for a high-voltage direct current power transmission system. This study proposes a design methodology for a novel digital control that mitigates the negative effects caused by time delay, including communication transport delay for a modular multilevel converter. The modeling and negative effect of time delay are analyzed theoretically in a frequency domain, and its compensation methodology based on an inverse model is described fully with practical considerations. The proposed methodology is verified through several simulation results using a modular 21-level converter system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.9
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• pp.2456-2469
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• 1996

A digital satellite communication channel has a nonlinearity with memory due to saturation characeristis of the high poer amplifier in the satellite and transmitter/receiver linear filter used in the overall system. In this paper, we propose a complex radial basis function network(CRBFN) based adaptive equalizer for compensation of nonlinearities in digital satellite communication channels. The proposed CRBFN untilizes a complex-valued hybrid learning algorithm of k-means clustering and LMS(least mean sequare) algorithm that is an extension of Moody Darken's algorithm for real-valued data. We evaluate performance of CRBFN in terms of symbol error rates and mean squared errors nder various noise conditions for 4-PSK(phase shift keying) digital modulation schemes and compare with those of comples pth order inverse adaptive Volterra filter. The computer simulation results show that the proposed CRBFN ehibits good equalization, low computational complexity and fast learning capabilities.

• Proceedings of the KIEE Conference
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• 2004.05a
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• pp.47-49
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• 2004

In this correspondence, an new approach to design a fuzzy controller for system with uncertain output backlash to have good tracking performance is presented. Without using a compensation mechanism or backlash inverse, the fuzzy control mechanism is designed to implicitly compensate the delay effect arising from an uncertain output backlash and to make the output backlash stable without limit cycles. The proposed method designs a model-based fuzzy controller for a one-input one-output linear plant with output backlash. The effectiveness of the designed fuzzy controller is illustrated by the simulation.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.11
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• pp.76-82
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• 1998

In this study, the Ball screw and Servo motor Mechanism is considered as a High Speed Tool Feed System for the machining of a piston of a reciprocating engine. For the machining of a piston, that shapes oval, high speed servo mechanism is needed as a positioning of a cutting tool, and the stroke of tool is 0.1 mm ~ 1 mm. Ball screw and servo motor Mechanism is available very much because this mechanism is used widely in general machine. This Mechanism has been designed with the use of the decrease in mass and partial wear of the ball screw for high speed positioning of tool. Also the periodic learning control method with the inverse transfer function compensation has been applied to the positioning control for the high accuracy positioning of tool. These applications lead the achievement of the machining of a piston with an accuracy of 5${\mu}{\textrm}{m}$ at 2500 rpm in CNC turning.

• Journal of Power Electronics
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• v.18 no.6
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• pp.1760-1770
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• 2018

This paper presents a control bandwidth extension method for inverters with a low carrier ratio. The bandwidth is extended at the price of decreasing the phase margin. Then the phase margin is compensated by introducing an extra leading angle into an inverse Park transformation. The model of the controller with the proposed method is established. The magnitude and phase characteristics are also analyzed. Then the influence on system stability when the leading angle is introduced is analyzed. The proposed method is applied to design an inverter controller with both a large bandwidth and a desired phase margin, and the experimental results verify that the controller performs well in the steady-state and in terms of transient response.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.6C
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• pp.857-864
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• 2004

Many image compression standards such as JPEG, MPEG or H.263 are based on the discrete cosine transform (DCT) and quantization method. Quantization error. is the major source of image quality degradation. The current dequantization method assumes the uniform distribution of the DCT coefficients. Therefore the dequantization value is the center of each quantization interval. However DCT coefficients are regarded to follow Laplacian probability density function (pdf). The center value of each interval is not optimal in reducing squared error. We use mean of the quantization interval assuming Laplacian pdf, and show the effect of correction on image quality. Also, we compare existing quantization error to corrected quantization error in closed form. The effect of PSNR improvements due to the compensation to the real image is in the range of 0.2 ∼0.4 ㏈. The maximum correction value is 1.66 ㏈.

• Journal of Sensor Science and Technology
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• v.16 no.1
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• pp.44-51
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• 2007

A hybridized simulator for generating blood pressure waveform is proposed to study the remedy and/or evaluation of the conventional sphygmomanometer utilizing the oscillometric method which is widely applied. The blood pressure of a flowing fluid was controlled for the blood vessel's condition caused by a rhythmical and periodical contraction/relaxation because of the special excitatory and conductive system of the heart. In this study, a hybridized controller composed of the PI feedback controller and the feedforward controller. The inverse dynamics function is proposed to operating the control valve while the pressure is applied in an oil pressure tank. The proposed hybrid simulator reproducing the blood pressure waveform in an artificial blood vessel has kept the control performance consistent over all range. Based on these results, the proposed simulators could be applied to the development and compensation of the non invasive sphygmomanometer type as well as to study the characteristics of the blood pressure and blood vessel.

• Journal of Satellite, Information and Communications
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• v.3 no.1
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• pp.15-21
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• 2008

The high peak to average power ratio (PAPR) of OFDM (Orthogonal Frequency Division Multiplexing) system introduces inevitable non-linear distortion in the transmission due to the amplifier non-linear property. This causes both in-band distortion and out of band spectrum re-growth. In this paper we tried to compensate the problem by using polynomial based pre-distortion. Estimation of both the non-linear and inverse non-linear polynomial is achieved using the Least Square Error (LSE) method. Using these parameters closed form pre-distorter can be easily created. We also used the 'partial peak cancellation and clipping' method to remove the high peak present in the non constant amplitude of the OFDM signal responsible to drive the amplifier in near saturation region for better performance of the system