• Journal of the Institute of Electronics Engineers of Korea SC
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• v.40 no.3
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• pp.99-108
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• 2003

This paper is concerned with the problem of designing a guaranteed cost state feedback controller for singular systems with time-varying delays. The sufficient condition for the existence of guaranteed cost controller, the controller design method, and the optimization problem to get the upper bound of guaranteed cost function are proposed by LMI(linear matrix inequality), singular value decomposition, Schur complements, and change of variables. Since the obtained sufficient conditions can be changed to LMI form, all solutions including controller gain and the upper bound of guaranteed cost function can be obtained simultaneously. Moreover, the proposed controller design method can be extended to the problem of robust guaranteed cost controller design method for singular systems with parameter uncertainties and time-varying delays. The validity of the proposed design algorithm is investigated through a numerical example.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.11
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• pp.195-205
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• 2013

The analysis of electroencephalographic signal associated with the attention is essential for the understanding of human cognition. In this paper, the characteristic differences between the attention and inattention status in the brain were inspected by nonlinear analysis. The recurrence quantification analysis was applied to the relatively small number of samples of evoked potential having time varying characteristics, where the recurrence plot (RP), the color recurrence plot (CRP), and mean and time-sequential trend parameters were extracted. The dimension and the time delay in phase transformation can be determined by the paired set of extracted parameters. It is observed from RP, CRP, and parameters that the brain dynamics in attention is more complex than that in the inattention, as well as the synchronized brain response is stable in the mean sense but locally time varying. It is feasible that the non-linear analysis method can be useful for the analysis of complex brain dynamics associated during visual attentional task.

• Journal of Communications and Networks
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• v.16 no.3
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• pp.293-300
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• 2014

As energy harvesting communication systems emerge, there is a need for transmission schemes that dynamically adapt to the energy harvesting process. In this paper, after exhibiting a finite-horizon online throughput-maximizing scheduling problem formulation and the structure of its optimal solution within a dynamic programming formulation, a low complexity online scheduling policy is proposed. The policy exploits the existence of thresholds for choosing rate and power levels as a function of stored energy, harvest state and time until the end of the horizon. The policy, which is based on computing an expected threshold, performs close to optimal on a wide range of example energy harvest patterns. Moreover, it achieves higher throughput values for a given delay, than throughput-optimal online policies developed based on infinite-horizon formulations in recent literature. The solution is extended to include ergodic time-varying (fading) channels, and a corresponding low complexity policy is proposed and evaluated for this case as well.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.6 no.3
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• pp.184-189
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• 2006

This paper deals with a fractional model reduction for T-S fuzzy systems with time varying delayed states. A contractive coprime factorization of time delayed T-S fuzzy systems is defined and obtained by solving linear matrix inequalities. Using generalized controllability and observability gramians of the contractive coprime factor, a balanced state space realization of the system is derived. The reduced model will be obtained by truncating states in the balanced realization and an upper bound of model approximation error is also presented. In order to demonstrate efficacy of the suggested method, a numerical example is performed.

• 제어로봇시스템학회:학술대회논문집
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• 1988.10a
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• pp.584-589
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• 1988

Tuning of digital STC parameters for the system with unknown and time varying parameters as well as delays presents many preconditions and difficulties. In order to eliminate these difficulties and to enhance STC control functions, the present study employs the metbod of expert control for STC and to implement it in nod-minimum phase plants. In this paper, implimedtation of the Expert STC for process control, STC. parameters is carried out by tuning systematically and by applying these parameters to non-minimum phase plant. This controller supervises a status of the plant, and robust control function for time delay or change of the plant is demonstrated by computer simulations.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.9
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• pp.2731-2743
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• 1996

When modeling error is large of plant is time-varying, it is hard to obtain good robust performance and robust stability by conventional contorl methods. Here, we need to design a robust controller bearing modeling error. In this paper, based on recently developed Time Delay Control(TDC) and Disturbance Observer the output feedback Robust Disturbance Observer(RDO), which is easily combined with general linear control, is proposed. Proposed RDO is derived from extending the main idea of Disturbance Observer to multi-input multi-output linear system. RDO solves robust stability problem of Disturbance Observer and has the robust performance same as nominal performance. RDO controlled dual stage positioning system shows excellent robust performance.

• Proceedings of the KIEE Conference
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• 2007.10a
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• pp.55-56
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• 2007

In this paper, a delay-dependent stability criterion for time-delayed linear parameter varying (LPV) systems is considered. Stability criterion has been developed on the basis of including x(t-h) and x(t) and introducing free variables to eliminate model dynamics. Since the resultant criterion is formed parameterized linear matrix inequalities (PLMIs), we propose a relaxation technique that allows to find an LMI formulation. Examples demonstrate the efficiency of the criterion over the existing results.

• The Transactions of the Korean Institute of Power Electronics
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• v.1 no.1
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• pp.7-11
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• 1996

From the cost-effective point of view, it is very important to design a current with the highest utilization factor of current capacity of power devices. This can be accomplished by a current controller without overshoot irrespective of the varying bounds of control voltage in PWM converters and the dead time due to the time delay. This paper suggests a novel decoupled controller with Smith-Predictor which has the fast control response without overshoot and steady stats error and also deal with the design method of the controller for PWM converters. The extensive digital simulations done by SIMULINK/MATLAB show that the suggested controller guarantees the full utilization of current capacity of power devices and the decoupled current control behavior.

• Clinical and Experimental Pediatrics
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• v.65 no.1
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• pp.10-20
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• 2022

The prevalence of developmental disabilities is increasing worldwide over time. Developmental issues in infancy or early childhood may cause learning difficulties or behavioral problem in school age, further adversely affecting adolescent quality of life, which finally lead to low socioeconomic status in family, increase in medical expenses, and other relevant issues in various ways. Early childhood has brain plasticity, which means there is a high chance of recovering from developmental issues by early detection and timely intervention. Pediatricians are placed an ideal position to meet with young children till 6 years of age, of which age range is the time applicable to early intervention. Determining child's developmental status can be made by 2 pathways such as developmental surveillance and developmental screening tests. For better results, pediatricians should update their knowledge about developmental issues, risk factors, and screening techniques through varying educational program or other relevant educating materials. This paper will update reports on the prevalence of developmental disabilities and review the recent results of the Korean developmental screening test and discuss relevant issues. Finally, it will be addressed the pediatrician's role in early detecting developmental issues and timely intervention.

• The Journal of the Acoustical Society of Korea
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• v.33 no.1
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• pp.48-53
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• 2014

The underwater acoustic communication (UAC) is characterized by doubly spread channel. It is included in the time-variant doppler shift and delay-time spreads due to multiple paths. To compensate such distorted signals, various techniques including time-reversal processing, spatial diversity, phase estimator, and equalizer are being applied. In this paper, a spatial filter based on the beamforming is proposed as a method to mitigate such inter-symbol interferences that are generated in time-varying multipath channels. The proposed technique realizes coherent communications by steering the direction of the desired signals and improves the performance of UAC by increasing the signal-to-interference plus noise ratio using the array gain.