• 한국신재생에너지학회:학술대회논문집
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• 2007.11a
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• pp.250-254
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• 2007

As photovoltaic(PV) power generation systems become more common, it will be necessary to investigate islanding detection method for PV systems. Islanding of PV systems can cause a variety of problems and must be prevented. However, if the real and reactive powers of the load and PV system are closely matched, islanding detection by passive methods becomes difficult. Also, most active methods lose effectiveness when there are several PV systems feeding the same island. The active frequency drift positive feedback method(AFDPF) enables islanding detection by forcing the frequency of the voltage in the island to drift up or down. In this paper the research for the minimum value of chopping fraction gain applied digital phase-locked-loop (DPLL) to AFDPF considering output power quality and islanding prevention performance are performed by simulation and experiment according to IEEE Std 929-2000 islanding test.

• Journal of the Korean Institute of Telematics and Electronics
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• v.21 no.6
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• pp.42-50
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• 1984

The method of increasing the bandwidth of distributed amplifier by the feedback loop is presented in this paper. In this method, it is tried to increase the gain of the amplifier in the high frequency range by giving a positive feedback on the device, while giving no influence in the low frequency range. For the simplicity of the amplifier design the transmission line theory of periodical structure with a unilateral divice is used in the design, and the 2-ports cascade network theory developed by K.B. Niclas is used in computer analysis for the purpose of precise results. In this simulation, the bandwidth of the amplifier is increased from 16 [GHz] without feedback loop to about 20 [GHz] with the feedback loop.

• Journal of KSNVE
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• v.4 no.2
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• pp.177-185
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• 1994

In this study, the effect of parameter errors on the closed-loop behavior of flexible structure is analyzed for IMSC(Independent Modal Space Control) with PPF(Positive Position Feedback). If the control force designed on the basis of structure model with the parameter errors is applied to control the actual system, the closed-loop performance of the actural system will be degraded depending on the degree of the errors. An asymptotic stability condition has been derived, using Lyapunov approach, which is independent of the dynamic characteristics of the structure being controlled. The extent of deviation of the closed-loop performance from the designed one is also derived and evaluated using operator techniques. It has been found that the extent of the deviation is proportational to the magnitude of the parameter errors, and that the proportional coefficient depends on the control algorithm.

• International Journal of Control, Automation, and Systems
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• v.3 no.4
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• pp.640-645
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• 2005

Closed-loop model-free optimization of positive feedback time delay controllers for dominant time delay systems is presented. Iterative feedback tuning (IFT) is applied to the tuning of positive feedback time delay controller. Three experiments are carried out to perform the model-free gradient descent optimization. The initial controller parameters and duration in specifying the cost function are suggested. The effects of step size, filter function and time weighting function on the performance of the optimized controlled are given. Simulation and experimental studies are included to demonstrate the effectiveness of the tuning scheme.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.779-782
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• 1996

Repetitive control is a proposed control strategy in view of the internal model principle and achieves a high accuracy asymptotic tracking property by implementing a model that generates the periodic signals of period into the closed-loop system. Since the repetitive control system contains a periodic signal generator with positive feedback loop, which reduces the stability margin, in the overall closed-loop system, the stability of the closed-loop system should be considered as an important problem. In case that a real system has plant uncertainties which are not represented through modeling, the robust stability problem of the repetitive control system has not been considered sufficiently. In this paper, we propose the robust stability condition for the system with modeling uncertainty. The proposed robust stability condition will be obtained using the robust performance condition in the H$_{\infty}$ control. Moreover, by use of the proposed robust stability condition, we propose a procedure that designs a repetitive controller and a feedback controller simultaneously which can stabilize the overall closed-loop system robustly and which can also do the closedloop system without repetitive controller..

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.527-535
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• 2012

This paper reports the active vibration control of plates using positive position feedback controller (PPF). The equations of motion of the plate under force and moment pairs were derived and the equations of PPF controllers were formulated. The effect of the parameters - gain and damping ratio - of the PPF controllers on the open loop transfer function was investigated mainly in terms of the system stability. Increasing the gain of the PPF controller tuned at a mode, the magnitude of the open loop transfer function is increased at all frequencies without changing the phase behavior. The increase of the damping ratio of the PPF controller leads to decrease the magnitude of the open loop transfer function and to modify its phase characteristics to be more stable. Two PPF controllers connected in parallel, Each PPF controller is tuned at the $1^{st}$ and $2^{nd}$ modes, respectively. Their parameters were determined to remain the system to be stable based on the results of the parametric study. A significant reduction in vibration at the 2 modes can be obtained.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.52 no.9
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• pp.520-525
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• 2003

A robust controller for large space structures(LSS) is studied from passivity point of view. While velocity sensors are commonly used for proportional-derivative (PD) control law to stabilize large space structures, if the structure can be controlled without velocity measurements, it is desirable against the failure of velocity sensors and for the cost reduction of the sensing system. In a recent result a dynamic output feedback control law has been provided using only displacement measurements. This paper presents a passivity-based controller design method and provides an alternative stability analysis tool for the previous displacement feedback robust control law. The closed-loop system can be viewed as a feedback interconnection of a passivated large space structure (LSS) and a strictly positive real (SPR) system.

• Journal of Chest Surgery
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• v.52 no.4
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• pp.232-235
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• 2019

A 2.5-kg neonate with coarctation of the aorta and a small left ventricle experienced a severe pulmonary hypertensive crisis. An emergency pulmonary artery-to-systemic artery shunt was placed to break the positive feedback loop caused by pulmonary hypertension and functional mitral stenosis. This shunt provided immediate relief of suprasystemic pulmonary hypertension and the resultant low cardiac output.

• Korean System Dynamics Review
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• v.10 no.1
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• pp.97-107
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• 2009

In this paper, a structural similarity between traditional oriental philosophy and systems thinking is discussed. The polarity of causal relationship and feedback loops can be interpreted in terms of yin and yang of oriental philosophy. A positive feedback loop which is linked to the yang is a force or mechanism that accelerates changes in systems. A negative feedback loop which is linked to the yin can be interpreted as a force oppressing any changes. In this sense, systems thinking can be related to the oriental philosophy. With this linking pin between them, systems thinking can be introduced and educated more friendly in oriental society. Furthermore, systems thinking can get a set of rich insights from the oriental philosophy. This paper suggests a linking leverage between systems thinking and oriental philosophy.

• International Journal of Control, Automation, and Systems
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• v.3 no.2
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• pp.195-201
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• 2005

This paper discusses the problem of positive real control for uncertain 2-D linear discrete time singular Roesser models (2-D SRM) with time-invariant norm-bounded parameter uncertainty. The purpose of this study is to design a state feedback controller such that the resulting closed-loop system is acceptable, jump modes free and stable, and achieves the extended strictly positive realness for all admissible uncertainties. A version of positive real lemma for the 2-D SRM is given in terms of linear matrix inequalities (LMIs). Based on the lemma, a sufficient condition for the solvability of the positive real control problem is derived in terms of bilinear matrix inequalities (BMIs) and an iterative procedure for solving the BMIs is proposed.