• The Transactions of the Korean Institute of Electrical Engineers A
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• v.48 no.5
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• pp.622-628
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• 1999

This paper presented to design a robust turbo-generator control system using {{{{ { H}_{$\infty$ } }}}} control synthesis for improving small-signal stability. Application study of{{{{ { H}_{$\infty$ } }}}} control synthesis is more appropriate in this system since a turbo-generator system is usually operated under circumstance of unmeasurable modelling uncertainty and external disturbance. The{{{{ { H}_{$\infty$ } }}}} control theory was briefly reviewed for good understanding and the reasonable approach. The design results are simulated for a case study and to check the system performance in comparison with currently operating Lead/Lag filtered PSS performance.

• Journal of international Conference on Electrical Machines and Systems
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• v.1 no.2
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• pp.53-57
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• 2012

The mathematical model of a three-phase voltage source pulse-width modulation (PWM) DC/AC inverter is non-linear, and in view of the traditional linear control strategy it can not meet the requirements of designing a high-performance inverter. What's more, when the loads are not pure resistive loads, the inverter further requires that the controller possess high-performance. This paper proposes a nonlinear control strategy for the inverter called Passivity-based Control. We can alter the inverter model in three-phase abc coordinate to two-phase synchronous rotating dq coordinate for establishing the port-control Hamiltonian (PCH) model for this system. We can control the distribution of energy in the system to achieve the control aim. Simulation results show that the passivity-based control method can make this system possess a level of high-performance that is both robust and dynamic.

• Bulletin of the Korean Mathematical Society
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• v.36 no.1
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• pp.147-159
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• 1999

Tabanov investigated the global symmetric perturbation of the integrable billiard mapping in the ellipse [3]. He showed the nonintegrability of the Birkhoff billiard in the perturbed domain by proving that the principal separatrices splitting angle is not zero.In this paper, using the exact separatrix map of an one-degree-of freedom Hamiltoniam system with time periodic perturbation, we show the existence the stochastic layer including the uniformly hyperbolic invariant set which implies the nonintegrability near the separatrices of a Birkhoff's billiard in the domain bounded by $C^2$ convex simple curve constructed by the generic global perturbation of the ellipse.

• Proceedings of the IEEK Conference
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• 2002.07b
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• pp.1141-1144
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• 2002

The research on computer graphics(CG) has been actively studied and developed. Namely, many surface/solid models have been proposed in the field of computer aided geometric design as well as the one of CG. Since it is difficult to visualize the complex shape exactly, an approximation by generating a set of meshes is usually used. Therefore it is important to guarantee the quality of the approximation in consideration of the computational cost. In this paper, a mesh generation algorithm will be proposed for a surface defined by Lie algebra. The proposed algorithm considers the quality in the meaning of validation of invariants obtained by the mesh, using automatic differentiation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.6
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• pp.634-639
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• 2020

In general, the stability and response characteristics of the system can be improved by changing the pole position because a nonlinear system can be linearized by the product of a 1st and 2nd order system. Therefore, a controller that moves the pole can be designed in various ways. Among the other methods, LQ control ensures the stability of the system. On the other hand, it is difficult to specify the location of the pole arbitrarily because the desired response characteristic is obtained by selecting the weighting matrix by trial and error. This paper evaluated a method of selecting a weighting matrix of LQ control that moves multiple double poles with Jordan blocks to real poles. The relational equation between the double poles and weighting matrices were derived from the characteristic equation of the Hamiltonian system with a diagonal control weighting matrix and a state weighting matrix represented by two variables (ρ_d, ϕ_d). The Moving-Range was obtained under the condition that the state-weighting matrix becomes a positive semi-definite matrix. This paper proposes a method of selecting poles in this range and calculating the weighting matrices by the relational equation. Numerical examples are presented to show the usefulness of the proposed method.

• Journal of Power Electronics
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• v.19 no.6
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• pp.1527-1535
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• 2019

Because of the shortcomings of the PID controllers and traditional drive systems of permanent magnet synchronous motors (PMSMs), a PMSM passivity-based control (PBC) drive system based on a quasi-Z source matrix converter (QZMC) is proposed in this paper. The traditional matrix converter is a buck converter with a maximum voltage transmission ratio of only 0.866, which limits the performance of the driven motor. Therefore, in this paper a quasi-Z source circuit is added to the input side of the two-stage matrix converter (TSMC) and its working principle has also been verified. In addition, the controller of the speed loop and current loop in the conventional vector control of a PMSM is a PID controller. The PID controller has the problem since its parameters are difficult to adjust and its anti-interference capability is limited. As a result, a port controlled dissipative Hamiltonian model (PCHD) of a PMSM is established. Thereafter a passivity-based controller based on the interconnection and damping assignment (IDA) of a QZMC-PMSM is designed, and the stability of the equilibrium point is theoretically verified. Simulation and experimental results show that the designed PBC control system of a PMSM based on a QZMC can make the PMSM run stably at the rated speed. In addition, the system has strong robustness, as well as good dynamic and static performances.

• Journal of Magnetics
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• v.17 no.1
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• pp.13-18
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• 2012

Starting with Kubo's formula and using the projection operator technique introduced by Kawabata, EPR lineprofile function for a $Mn^{2+}$-doped wurtzite structure GaN semiconductor was derived as a function of temperature at a frequency of 9.49 GHz (X-band) in the presence of external electromagnetic field. The line-width is barely affected in the low-temperature region because there is no correlation between the resonance fields and the distribution function. At higher temperature the line-width increases with increasing temperature due to the interaction of electrons with acoustic phonons. Thus, the present technique is considered to be more convenient to explain the resonant system as in the case of other optical transition systems.

• Korean Journal of Optics and Photonics
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• v.14 no.1
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• pp.103-106
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• 2003

The microscopic quantum Langevin equations for two-level atom electric dipole systems are derived. starting from the microscopic interaction Hamiltonian of the systems. By averaging those microscopic equations over a macroscopic region, the macroscopic quantum Langevin equations are derived and the effect of local-field corrections on the two-level systems is investigated.

• Journal of KIISE:Computer Systems and Theory
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• v.35 no.6
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• pp.263-272
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• 2008

We propose and analyze a new interconnection network, called petersen-torus(PT) network based on well-known petersen graph. PT network has a smaller diameter and a smaller network cost than honeycomb torus with same number of nodes. In this paper, we propose optimal routing algorithm and hamiltonian cycle algorithm. We derive diameter, network cost and bisection width.

• Progress in Superconductivity
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• v.8 no.1
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• pp.16-21
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• 2006

In this paper, current status of experimental and theoretical work on quantum bits based on the semiconductor quantum dots in the University of Seoul will be presented. A new proposal utilizing the multi-valley quantum state transitions in a Si quantum dot as a possible candidate for a quantum bit with a long decoherence time will be also given. Qubits are the multi-valley symmetric and anti-symmetric orbitals. Evolution of these orbitals is controlled by an external electric field, which turns on and off the inter-valley interactions. Initialization is achieved by turning on the inter-valley Hamiltonian to let the system settle down to the symmetric orbital state. Estimates of the decoherence time is made for the longitudinal acoustic phonon process.