• Proceedings of the KIEE Conference
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• 1998.11a
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• pp.201-203
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• 1998

This paper presents the framework for analysis of small-signal stabili1ty. In this framework the equilibrium points of system DAE model are traced using continuation method and instability points are determined on the solution path. Especially Implicit shift QR-modified ARnoldi method is utilized to calculated the rightmost eigenvalues. ISPS measure is utilized to determine critical parameters.

• The Journal of the Korea institute of electronic communication sciences
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• v.9 no.8
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• pp.853-859
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• 2014

This study presents a technique for extracting all the extrinsic parameters of HEMTs by minimizing the residual errors between a pinch-off cold-FET's gate and drain pad de-embedded Z-parameters and its modeled Z-parameters calculated by the cold-FET's remaining parameters. The presented technique allows us to successfully extract the remaining extrinsic parameter values as well as the gate and drain pad capacitance value without the additional fabrications of the gate and drain dummy pad.

• Journal of Korean Association for Spatial Structures
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• v.20 no.1
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• pp.95-102
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• 2020

The structural design of arch roofs or bridges requires the analysis of their unstable behaviors depending on certain parameters defined in the arch shape. Their maintenance should estimate the parameters from observed data. However, since the critical parameters exist in the equilibrium paths of the arch, and a small change in such the parameters causes a significant change in their behaviors. Thus, estimation to find the critical ones should be carried out using a global search algorithm. In this paper we study the parameter estimation for a shallow arch by a quantum-inspired evolution algorithm. A cost functional to estimate the system parameters included in the arch consists of the difference between the observed signal and the estimated signal of the arch system. The design variables are shape, external load and damping constant in the arch system. We provide theoretical and numerical examples for estimation of the parameters from both contaminated data and pure data.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.4
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• pp.743-749
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• 2003

By biasing the gate of cold-HEMT with a voltage slightly lower than the pinch-off point, a new small-signal modeling method that is free from gate degradation problem and requires no additional DC measurement is proposed in this paper. The method has shown excellent agreement between modeled and measured S-parameters up to 62 GHz at 49 different normal operating bias points.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.52 no.9
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• pp.487-492
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• 2003

This paper analyzes an eigenvalue distribution and enhancement of the small signal stabiligy when an Unified Power Flow Controller (UPFC) modeling is connected into the multi-machine power system. Recently a lot of attention has been paid to the subject of dynamic stability. It deals with analysis of eigenvalue sensitivities with respect to parameters of UPFC Controller and damping of interarea and local electromechanical oscillation modes using UPFC Controller. It provides an insight and understanding in the basic characteristics of damping effects of UPFC Controller and shows a very stable frequency response via UPFC in test model. The series branch of the UPFC is designed to damp the power oscillation during transients, while the shunt branch aims at maintaining the bus voltage and angle. Comprehensive time-domain simulation studies using PSS/E show that the proposed robost UPFC controller can enhance the small signal stability efficiently in spite of the variations of power system operating conditions.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.12
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• pp.21-26
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• 2004

In this paper, a direct method is developed to extact RF equivalent circuit of a packaged BJT without optimization. First, parasitic components of plastic package are removed from measured S-parameters using open and short package patterns. Using package do-embedded S-parameters, a direct and simple method is proposed to extract bonding wire inductance and chip pad capacitance between package lead and chip pad. The small-signal model parameters of internal BJT are next determined by Z and Y-parameter formula derived from RF equivalent circuit. The modeled S-parameters of packaged BJT agree well with measured ones, verifying the accuracy of this new extraction method.

• Journal of Power Electronics
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• v.9 no.5
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• pp.757-771
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• 2009

This paper proposes a systematic approach to the modeling of the small-signal characteristics of three-phase bridge boost rectifiers under non-sinusoidal conditions. The main obstacle to the conventional synchronous d-q frame modeling approach is that it is unable to identify a steady-state under non-sinusoidal conditions. However, for most applications under non-sinusoidal conditions, the current loops of boost rectifiers are designed to have a bandwidth that is much higher than typical harmonics frequencies in order to achieve good current control for these harmonic components. Therefore a quasi-static method is applied to the proposed modeling approach. The converter small-signal characteristics developed from conventional synchronous frame modeling under different operating points are investigated and a worst case point is then located for the current loop design. Both qualitative and quantitative analyses are presented. It is observed that operating points influence the converter low frequency characteristics but hardly affect the dominant poles. The relationship between power stage parameters, system poles and zeroes is also presented which offers good support for the system design. Both the simulation and experimental results verified the analysis and proposed modeling approach. Finally, the practical case of a parallel active power filter is studied to present the modeling approach and the resultant regulator design procedure. The system performance further verifies the whole analysis.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.3
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• pp.127-137
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• 2003

Contingency analysis is one of the most important tasks encountered by planning and operation of lafe scale power systems. This paper describes a new contingency analysis methods for small signal security assessment based on the eigen-sensitivity/perturbation of the electromechanical oscillation modes. The eigen-sensitivity/perturbation with respect to line suceptances and controller parameters can he used to find possible sources of the system instability, and to select contingency for small signal stability. Also, the contingency selection to identify critical generators for MW changes can be obtained by computing the relative movement of the system oscillation modes. The proposed algorithm has been successfully tested on the KEPCO systems which is comprised of 791-bus, 1575-branch and program PSS/E

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.550-553
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• 2001

In this study, unity current gain frequency f$\_$T/ of GaAs MESFET is predicted with different temperatures up to 400 $^{\circ}C$. Temperature dependence parameters of the device including intrinsic carrier concentration n$\_$i/ effective mass, depletion width are considered to be temperature dependent. Small signal parameters such as gate-source, gate dran capacitances C$\_$gs/ C$\_$gd/ are correlated with transconductance g$\_$m/ to predict the unity current gain frequency. The extrinsic capacitance which plays an important roles in high frequency region has been taken into consideration in evaluating total capacitance by using elliptic integral through the substrate. From the results, f$\_$T/ decreases as the temperature increases due to the increase of small signal capacitances and the mobility degradation. Finally the extrinsic elements of capacitances have been proved to be critical in deciding f$\_$T/ which are originated from the design rule of the device.

• JSTS:Journal of Semiconductor Technology and Science
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• v.9 no.3
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• pp.125-135
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• 2009

An analytical 2-dimensional model to explain the small signal and noise properties of an AlGaN/GaN modulation doped field effect transistor has been developed. The model is based on the solution of two-dimensional Poisson's equation. The developed model explains the influence of Noise in ohmic region (Johnson noise or Thermal noise) as well as in saturated region (spontaneous generation of dipole layers in the saturated region). Small signal parameters are obtained and are used to calculate the different noise parameters. All the results have been compared with the experimental data and show an excellent agreement and the validity of our model.