• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.2410-2413
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• 2005

Finite element method (FEM) has been widely used as a useful numerical method that can analyze complex engineering problems in electro-magnetics, mechanics, and others. CEMTool, which is similar to MATLAB, is a command style design and analyzing package for scientific and technological algorithm and a matrix based computation language. In this paper, we present new 3D FEM package in CEMTool environment. In contrast to the existing CEMTool 2D FEM package and MATLAB PDE (Partial Differential Equation) Toolbox, our proposed 3D FEM package can deal with complex 3D models, not a cross-section of 3D models. In the pre-processor of 3D FEM package, a new 3D mesh generating algorithm can make information on 3D Delaunay tetrahedral mesh elements for analyses of 3D FEM problems. The solver of the 3D FEM package offers three methods for solving the linear algebraic matrix equation, i.e., Gauss-Jordan elimination solver, Band solver, and Skyline solver. The post-processor visualizes the results for 3D FEM problems such as the deformed position and the stress. Consequently, with our new 3D FEM toolbox, we can analyze more diverse engineering problems which the existing CEMTool 2D FEM package or MATLAB PDE Toolbox can not solve.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.10
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• pp.124-129
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• 1990

This paper describes a new method to eliminate some selected harmonics (5,7,11) in PWM waveforms using Walsh and related orthogonal functions. Previous analyses of PWM waveforms are based on the nonlinear equations requiring iterative solution methods which are not practical in real-time systems. In addition, synthesis of low harmonics waveform at high power system is not easy to implement with power electronic hardware. The goal of this paper is to achieve the harmonics elimination in a PWM waveform by replacing the nonlinear equations in Fourier analysis with linear algebraic equations resulting from the use of orthogonal Walsh equation. This paper also describes how to synthesize low ordered harmonic waveforms with practical power electronic hardware. Walsh and Radmacher functions are easily manipulated by Harmuth's array generator, and those algorithms are accurate, computationally efficient and faster than algorithm based on Fourier analysis. In addition, this method is simulated to synthesize periodic PWM waveforms. From the experi-mental results, it is shown that single-phase PWM waveform are identified with the proposed method. And these methods are also extended to three-phase PWM waveforms in this paper.

• The Transactions of the Korean Institute of Power Electronics
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• v.3 no.4
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• pp.365-374
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• 1998

The SHE(Selected Harmonic Elimination) PWM scheme which eliminates specific lower order harmonics can generate h high quality output waveforms in 3-level PWM inverters. However. its application has limited since SHE switching a angles cannot be calculated on-line by a microprocessor-implemented control system. Based on off-line optimization. in which multiple SHE solutions were found and analysed for 2 to 5 switching angles per quarter in the 3-level SHE PWM pattern. this paper presents an algebraic algorithm for an ordinary microprocessor to calculate approximate SHE S switching angles on-line with such high resolution that it makes no practical difference between the accurate and the a approximate SHE switching angles. By employing the variable of the dc-link voltage Vdc' the proposed SHE PWM p pattern can ideally compensate the dc input fluctuation together with selected harmonics eliminated.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.7
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• pp.667-678
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• 2002

In this paper, a new radiating structure with a multi-layered two-dimensional metallic disk array was proposed for shaping the flat-topped element pattern. It is an infinite periodic planar array structure with metallic disks finitely stacked above the radiating circular waveguide apertures. The theoretical analysis was in detail performed using rigid full-wave analysis, and was based on modal representations for the fields in the partial regions of the array structure and for the currents on the metallic disks. The final system of linear algebraic equations was derived using the orthogonal property of vector wave functions, mode-matching method, boundary conditions and Galerkin's method, and also their unknown modal coefficients needed for calculation of the array characteristics were determined by Gauss elimination method. The application of the algorithm was demonstrated in an array design for shaping the flat-topped element patterns of $\pm$20$^{\circ}$ beam width in Ka-band. The optimal design parameters normalized by a wavelength for general applications are presented, which are obtained through optimization process on the basis of simulation and design experience. A Ka-band experimental breadboard with symmetric nineteen elements was fabricated to compare simulation results with experimental results. The metallic disks array structure stacked above the radiating circular waveguide apertures was realized using ion-beam deposition method on thin polymer films. It was shown that the calculated and measured element patterns of the breadboard were in very close agreement within the beam scanning range. The result analysis for side lobe and grating lobe was done, and also a blindness phenomenon was discussed, which may cause by multi-layered metallic disk structure at the broadside. Input VSWR of the breadboard was less than 1.14, and its gains measured at 29.0 GHz. 29.5 GHz and 30 GHz were 10.2 dB, 10.0 dB and 10.7 dB, respectively. The experimental and simulation results showed that the proposed multi-layered metallic disk array structure could shape the efficient flat-topped element pattern.