• Journal of Power Electronics
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• v.12 no.2
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• pp.344-356
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• 2012

In recent years, multilevel technology has become an effective and practical solution in the field of moderate and high voltage applications. This paper discusses an APF with a three-level NPC inverter. Obviously, the application of such converter to APFs is hindered by the problem of the voltage unbalance of DC capacitors, which leads to system instability. This paper comprehensively analyzes the theoretical limitations of the neutral-point voltage balancing problem for tracking different harmonic currents utilizing current switching functions from the space vector PWM (SVPWM) point of view. The fluctuation of the neutral point caused by the load currents of certain order harmonic frequency is reported and quantified. Furthermore, this paper presents a close-loop digital control algorithm of the DC voltage for this APF. A PI controller regulates the DC voltage in the outer-loop controller. In the current-loop controller, this paper proposes a simple neutral-point voltage control method. The neutral-point voltage imbalance is restrained by selecting small vectors that will move the neutral-point voltage in the direction opposite the direction of the unbalance. The experiment results illustrate that the performance of the proposed approach is satisfactory.

• Journal of the Korean Society of Safety
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• v.16 no.4
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• pp.200-207
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• 2001

The transmission of harmonic vibratory power form a vibrating rigid body into a supporting plate through passive and active isolators is investigated theoretically and experimentally. The theoretical model allows for the transmission of vertical and horizontal harmonic forces and moments about all three coordinate sun. The experiment is to use vibration actuators attached to the intermediate mass of the two-stage mount to minimize the rotational and translational vibration of the intermediate mass. The performance is done by measuring the vibration at the error sensors due to the primary vibration source and measuring the transfer functions from the control sources to the error sensors. Results show that over a frequence range from 1 to 100Hz, transmission into the supporting plate can be reduced substantially by employing in parallel with existing passive isolators, active isolators adjusted to provide appropriate control force amplitudes.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.2
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• pp.285-291
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• 2009

In this paper, comparative analysis of offset voltage PWM method and $V_{max}-V_{mid}$ PWM method for three-phase matrix converter is addressed by using a simple analytical and graphical method. Offset voltage PWM method calculates PWM patterns in terms of offset voltage and variable slope of carrier, and it simplifies matrix converter modulation algorithm significantly. $V_{max}-V_{mid}$ PWM method generates patterns by using two phases and maintaining a remaining phase to base phase, and it is implemented in the industrial products. The most important performance criterion of modulation method is a magnitude of current ripples and it is analytically modelled. The graphical illustration of theses complex multivariable functions make per-carrier cycle and per fundamental cycle behavior of two PWM methods understood. Two modulation methods are analysed with the analytical formulas and graphics, and the analysis shows offset voltage PWM method is superior to $V_{max}-V_{mid}$ PWM method with respect to input current ripples and output voltage ripples.

• Korean Journal of Optics and Photonics
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• v.4 no.1
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• pp.90-100
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• 1993

A computer routine for personal computer(PC/AT class) is developed to analysize the mode characteristics of silica based optical waveguides whose cross sections are of semi circular and other typical shapes. The basic algorithm used in the routine is to convert the wave equation into a matrix equation by expanding the wave function in terms of simple harmonic functions. The matrix elements are a set of overlap integrals of sinusoidal funtions with appropriate weight given by the distribution of refractive index over the waveguide cross section. The eigenvectors and eigenvalues of the matrix is then computed via diagonalization. We explain some practical problems that arises when implementing the algorithm into the routine. By using this routine we analyze the mode characteristics of silica based optical waveguides of semi circular and some other typical cross sections.

• Journal of IKEEE
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• v.26 no.1
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• pp.95-103
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• 2022

In this paper, the efficiency of a sensorless method with square-wave injection for a low-cost inverter, so called B4 inverter is presented. This inverter comprises only 4 switches to reduce system cost. It is distinguished from the conventional B6 inverter that has 6 of switching elements. The B4 inverter, injected a 1 kHz of harmonic wave, has been modelled using the functions and library in Matlab/Simulink. This paper described each component of sensorless algorithm. Among them, the Notch Filter is used to extract the harmonic component of the phase current and a second-order low-pass filter was used to reduce the ripple of the estimated speed. It is shown through simulation that the rotor angle of a permanent magnet synchronous motor is detected by multiplying the current waveform extracted using the notch filter by the harmonic voltage. The feasibility of the proposed method is shown through Simulink simulation.

• Journal of Power Electronics
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• v.12 no.1
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• pp.104-112
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• 2012

In this paper a new method for the design of a simple PI controller is presented and it has been applied in the control of a Boost based PFC rectifier. The Strength Pareto evolutionary algorithm, which is based on the Pareto Optimality concept, used in Game theory literature is implemented as a multi-objective optimization approach to gain a good transient response and a high quality input current. In the proposed method, the input current harmonics and the dynamic response have been assumed as objective functions, while the PI controller's gains of the PFC rectifier (Kpi, Tpi) are design variables. The proposed algorithm generates a set of optimal gains called a Pareto Set corresponding to a Pareto Front, which is a set of optimal results for the objective functions. All of the Pareto Front points are optimum, but according to the design priority objective function, each one can be selected. Simulation and experimental results are presented to prove the superiority of the proposed design methodology over other methods.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.55.4-56
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• 2015

The Hilbert-Huang Transform (HHT) is composed of the Empirical Mode Decomposition (EMD) and the Hilbert Spectral Analysis (HSA). The EMD decomposes any time series data into a small number of components called the Intrinsic Mode Functions (IMFs), compared to the Discrete Fourier Transform which decomposes a data into a large number of harmonic functions. Each IMF has varying amplitude and frequency with respect to time, which can be obtained by HSA. The time resolution of the modes in HHT is the same as that of the given time series, while in the Wavelet Transform, Constant Q Transform and Short-Time Fourier Transform, there is a tradeoff between the resolutions in frequency and time. Based on the time-dependent amplitudes of IMFs, we develop an Event Trigger Generator and demonstrate its efficiency by applying it to gravitational-wave data.

• Structural Engineering and Mechanics
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• v.32 no.4
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• pp.517-529
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• 2009

A passive vibration mitigation architecture is proposed to damp transverse vibrations of guyed masts. The scheme is based on a number of pendula attached to the mast and tuned to the vibration modes to be controlled. This scheme differs from the well-known autoparametric pendulum absorber system. The equations of motion of the guyed mast with an arbitrary number of pendula are obtained. The leading bending behaviour of a typical truss mast is described by an equivalent beam model whereas the guys are conveniently modeled as equivalent transverse springs whose stiffness comprises the elastic and geometric stiffness. By assuming a mast with an inertially and elastically isotropic cross-section, a planar model of the guyed mast is investigated. The linearization of the equations of motion of the mast subject to a harmonic distributed force leads to the transfer functions of the structure without the dampers and with the dampers. The transfer functions allow to investigate the mitigation effects of the pendula. By employing one pendulum only, tuned to the frequency of the lowest mode, the effectiveness of the passive vibration potential in reducing the motion and acceleration of the top section of the mast is demonstrated.

• Structural Engineering and Mechanics
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• v.67 no.6
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• pp.659-669
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• 2018

The Dynamic equations in the polar coordinates are drawn out using the MLPG method for the non-symmetric FG cylindrical shell. To simulate the mechanical properties of FGM, the nonlinear volume fractions for radial direction are used. The shape function applied in this paper is a form of the radial basis functions, by using this function all the requirements for an effective and suitable shape function are established. Hence in this study, the multiquadrics (MQ) radial basis functions are exploited as the shape function governing the problem. The MLPG method is combined with the the Newmark time approximation scheme to solve dynamic equations in the time domain. The obtained results by the MLPG method to be verified are compared with the analytical solution and the FEM. The obtained results through the MLPG method show a good agreement in comparison to other results and the MLPG method has high accuracy for dynamic analysis of the non-symmetric FG cylindrical shell. To demonstrate the capability of the present method to dynamic analysis of the non-symmetric FG cylindrical shell, it is analyzed dynamically with different volume fraction exponents under harmonic and rectangular shock loading. The present method shows high accuracy, efficiency and capability to dynamic analysis of the non-symmetric FG cylindrical shell with nonlinear grading patterns.

• Journal of the Korean Mathematical Society
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• v.57 no.3
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• pp.721-745
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• 2020

In this paper we study fractional Sobolev spaces characterized by a norm based on eigenfunction expansions. The goal of this paper is twofold. The first one is to define fractional Sobolev spaces of order -1 ≤ s ≤ 2 equipped with a norm defined in terms of Neumann eigenfunction expansions. Due to the zero Neumann trace of Neumann eigenfunctions on a boundary, fractional Sobolev spaces of order 3/2 ≤ s ≤ 2 characterized by the norm are the spaces of functions with zero Neumann trace on a boundary. The spaces equipped with the norm are useful for studying cross-sectional traces of solutions to the Helmholtz equation in waveguides with a homogeneous Neumann boundary condition. The second one is to define fractional Sobolev spaces of order -1 ≤ s ≤ 1 for vector-valued functions in a simply-connected, bounded and smooth domain in ℝ². These spaces are defined by a norm based on series expansions in terms of eigenfunctions of the vector Laplacian with boundary conditions of zero tangential component or zero normal component. The spaces defined by the norm are important for analyzing cross-sectional traces of time-harmonic electromagnetic fields in perfectly conducting waveguides.