• Journal of Advanced Marine Engineering and Technology
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• v.25 no.4
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• pp.833-845
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• 2001

Quantitative Feedback Theory(QFT) has been used to design a robust power system stabilizer(PSS) to improve transient and dynamic stabilities of a power system. This design technique is basically accomplished in frequency domain. The most important feature of QFT is that it is able to deal with the design problem of complicated uncertain plants. A basic idea in QFT design is the translation of closed-loop frequency-domain specifications into Nichols chart domains specifying the allowable range of the nominal open-loop response and then to design a controller by using the gain-phase loop shaping technique. This paper introduces a new algorithm to compute QFT bounds more efficiently. The propose QFT design method ensures a satisfactory performance of the PSS under a wide range of power system operating conditions.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.51 no.2
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• pp.94-98
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• 2002

QFT(Quantitative Feedback Theory) is a very practical design technique that emphasizes the use of feedback for achieving the desired system performance tolerances in despite of plant uncertainty and disturbance. The gain-phase loop shaping procedure of QFT is employed to design controller, until the bounds at desired frequencies are satisfied. This paper presents a transfer function synthesis using TLS(Total Least Squares) and offers a loop shaping method with the suggested technique. An example illustrates a feasibility of the presented algorithm.

• Transactions of the Korean Society of Automotive Engineers
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• v.21 no.3
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• pp.88-97
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• 2013

This paper presents a robust air-to-fuel ratio (AFR) control algorithm for managing exhaust gas recirculation (EGR) systems. In order to handle production tolerance, deterioration and parameter-varying characteristics of the EGR system, quantitative feedback theory (QFT) is applied for designing the robust AFR control algorithm. A plant model of EGR system is approximated by the first order transfer function plus time-delay (FOPTD) model. EGR valve position and AFR of exhaust gas are used as input/output variables of the plant model. Through engine experiments, parameter uncertainty of the plant model is identified in a fixed engine operating point. Requirement specifications of robust stability and reference tracking performance are defined and these are fulfilled by the following steps: during loop shaping process, a PID controller is designed by using a nominal loop transmission function represented on Nichols chart. Then, the frequency response of closed-loop transfer function is used for designing a prefilter. It is validated that the proposed QFT-based AFR control algorithm successfully satisfy the requirements through experiments of various engine operating points.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.3
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• pp.243-253
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• 2014

This paper deals with the Quantitative Feedback Thoery(QFT) guaranteeing robustness in spite of the plant parametric uncertainty. In the frequency domain, the QFT guarantees the robustness of the design specification on the uncertainty of plant parameters and disturbance. In order to use the QFT, a selected plant is a Quad Rotor Vehicle(QRV) which has excellent maneuverability and possibility of vertical take-off and landing like the helicopter. And attitude control is examined the possibility satisfied the requirement specification under the setting parametric uncertainty of motors driving 4-blades. Additionally, in an attitude control, the pre-filter considering parameter range and operating range of a QRV was used. For these purpose, in this paper, by using QFTCT, that is the QFT Control Toolbox designing the controller in MATLAB by the QFT, each design phases are introduced.

• Journal of the Korean Society of Physical Medicine
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• v.6 no.1
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• pp.9-17
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• 2011

Purpose : The purpose of this study was to compare the effects of performing feedback vs repeative tasks on lower extremity motor function and falls efficacy in chronic hemiplegic patients. Methods : 40 hemiplegic patients took part in this study. The average age of the feedback-task group was 68.45 years and 68.20 in the repeative-task group. All subjects participated in the study for 8 weeks, doing exercises 3 per day per week. All participants were assessed by using the Berg balance scale (BBS), the lower-extremity subscale of the Fugel-Meyer assessment of sensorimotor impairment (FMLE), and the falls efficacy scale (FES). The data were analyzed using a paired t-test. Results : After 8 weeks of exercise training, the results of this study were: the BBS and FMLE of hemiplegic patients showed a feedback-task and repeative-task groups (p<0.05). The FES of hemiplegic patients also showed a significant difference between the quantitative-task and qualitative-task groups (p<0.05). Conclusion : We present findings suggesting that chronic hemiplegic patients could improve their standing balance ability better through a feedback-task exercise program, as opposed to a repeative-task exercise program.

• Journal of Climate Change Research
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• v.9 no.3
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• pp.253-261
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• 2018

As user-involved energy saving activities have become important in recent years, many forms of energy feedback experiments have been conducted. We conducted a study to determine if energy feedback activities affect energy saving for students living in dormitories at a university in Seoul. In particular, smart plugs were used for efficient research and quantitative performance measurements, and the extent of the impact of competition and rewards on participant energy saving behavior was further analyzed. The main findings of this study are as follows. First, the power usage of groups using smart plugs was lower than that of those without them. Second, energy feedback delivered to smart plug users did not have a significant impact on reduction of electric power consumption. Third, competition and compensation strategies had additional effects in reducing power usage for smart plug users. As a result, methods to deliver energy feedback more effectively as ICT technologies develop and efficient energy activities using IoT technologies can be expected to spread widely in the future.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2000.04a
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• pp.330-336
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• 2000

This paper discusses the potential of system dynamics modelling to support balanced scorecard. The balanced scorecard is a conceptual framework for translating an organisation's strategy into a set of performance indicators. These performance indicators are distributed across the 'classic'model's four perspective: Customers, Internal Business Processes, Financial, and Learning and Growth. This balanced scorecard, whilst having significant strength, suffers from the limitation of all performance indicator systems, namely that the interrelationships between indicators are overlooked and there is no way of taking into account the impact of delayed feedback which flows from introduction of new policy and legislative changes. System Dynamics is a methodology for understanding complex problems where there is dynamic behaviour and where feedback impacts significantly on system outcomes. System dynamics provides a rigorous basis for qualitative testing of the effects of performance indicators in complex environments such as health or social security. This can be supplemented with quantitative system dynamics simulation tools that further test the validity of indicators and the business rules implicit in them. System dynamics modelling has an important role to play in extending feedback cycle in performance measurements to a full systems approach.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.45 no.2
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• pp.273-282
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• 1996

This work is conceded with the estimation of output derivatives and their use for the design of robust controller for linear systems with system uncertainties due to modeling errors and disturbances. It is assumed that a nominal transfer function model and quantitative bounds for system uncertainties and known. The developed control schemes are shown to achieve regulation of the system output and ensures boundedness of the system states without imposing any structural conditions on system uncertainties and disturbances. Output derivative estimation is first conducted through restructuring of the plant in a specific parameterization. They are utilized for constructing robust nonlinear high-gain feedback controller of a SMC(Sliding Mode Control)type. The performances of the developed controller are evaluated and shown to be effective and useful through simulation study.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.47.1-47.1
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• 2019

A gas giant formed in a massive protoplanetary disk via gravitational instability migrates inward due to its gravitational interaction with the disk. Planet migration occurs in various ways depending on the disk structure and internal processes, but previous studies only considered quantitative radiative feedback resulting from mass accretion onto the planet. Allowing for accretion feedback, we perform three-dimensional hydrodynamic simulations with GIZMO to investigate orbital evolution of giant planets in a protoplanetary subject to -cooling. This work shows a planet gains mass due to accretion and gradually opens a gap as it moves inward. The migration in the end halts when the planet clears the gas around its orbit. A more massive planet grows its mass faster and migrates more rapidly, stalling at an orbit farther away from the protostar. Models with a cold disk readily construct a circumplanetary disk and result in high mass growth of the planet. Accretion feedback, in general, reduces the rate of the planet growth and delays migration. We discuss our results with GIZMO in comparison with the previous results with different codes.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.11a
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• pp.181-182
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• 2010