Number Of Harmonic Components Research Articles

Study of spectral structure signal by finite difference method

A method for estimating the spectral parameters of a polyharmonic process by the method of central finite differences of even order is considered for the case when the series of numerical observations is quite large and the number of harmonic components in the process under study is a priori unknown.

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The paper introduces an adaptive algorithm for estimating the frequencies of harmonic components in the signal against the background of additive white noise. This method is iterative, which distinguishes it from the periodogram and parametric spectral estimation methods. The key feature of the algorithm is that it gives a reasonably accurate estimation only for the preset number of harmonic components included in the signal under study. In the original discrete signal, a frequency search was performed at each time sample using the gradient descent method. Frequency estimation is made when the frequency error value tends to a certain value. The search is based on the representation of the value of the current sample of the harmonic signal of a known frequency through the two previous values. Knowing the number of components included in the original signal sequence, it is possible to form the resulting sequence containing only residual noise samples. A mathematical model of the algorithm is given, its work is simulated for different conditions of application, the accuracy of the algorithm, i.e., frequency estimation, and the number of iterations for various signal-to-noise ratios are shown.

Parametric Modeling for Two-Dimensional Harmonic Signals With Missing Harmonics

The problem of parametric modeling for the two-dimensional (2-D) harmonic signals with missing harmonics is addressed. The modeling process consists of two parts. First, we devise the joint spatial-temporal linearly constrained minimum variance beamformer and perform the joint estimation of the spatial and temporal fundamental frequencies for each pitch of the signal based on the maximum harmonic model. Second, we differentiate the competing signal models by the number of harmonic components and derive the maximum $a ~posteriori$ criterion for the 2-D harmonic signals. As a result, the harmonic components of each pitch are detected according to their spectral powers. The simulation and experimental results are provided to show the superiority of the proposed signal modeling methodology over other existing schemes.

Analysis of harmonic resonance mechanism of PV power plant

Great amount of PV inverters connected with the PV power plant causes the power system to become electronically power and affects the operation mode of the traditional power system. High-frequency switching characteristics of PV inverters carry a large number of harmonic components, even lead to the harmonic resonance of a multi-machine parallel system. In the paper, based on physical mechanism of power electronics, a high-order model of harmonic impedance of a typical PV power plant is established, and harmonic resonance mechanism in parallel operation of PV power plant is analyzed, as well as key factors.

Stability Analysis of Digital Microwave Power Amplifiers

This paper presents a stability analysis of microwave power amplifiers (PAs) driven by binary pulse trains, as in the case of class-S PAs. First, using a simplified digital PA test bench in class-D configuration, different qualitative behaviors are obtained when varying the pulsewidth, including subharmonic and incommensurable oscillations. The mechanisms affecting the stability properties are studied with a harmonic balance-based formulation, by means of pole-zero identification and bifurcation detection. A sufficiently high number of harmonic components must be considered, together with the Krylov decomposition for an efficient computation of the inverse of the Jacobian matrix. It is demonstrated that, when varying the pulsewidth, the distinct pairs of complex-conjugate poles may shift to the right-hand side of the complex plane and, therefore, lead to different kinds of unstable behavior. This phenomenon is related to the dependence of the critical poles on the average value of the input signal. Boundaries of the various types of unstable behavior are traced in the plane defined by the pulse repetition rate and pulsewidth, using bifurcation detection techniques. All the predicted phenomena have been confirmed experimentally. In a second step, the algorithms derived from the simple class-D circuit are transferred to study the stability of a more complex tri-band class-S amplifier. It has been analyzed versus the input bitrate, obtaining a fully stable behavior that has been validated experimentally.

Methods of enhancing the estimation efficiency of the number of signal harmonic components by using the surrogate data technology

The problem of enhancing the estimation efficiency of the number of harmonic components of signal based on its observation in the presence of additive white Gaussian noise using the surrogate data technology has been considered. The results of simulation modeling are presented. The application of this technology was shown to be effective at small and large values of the signal-to-noise ratio (SNR), when the frequencies of signal components were a multiple of the observation sampling frequency in the frequency domain.

Paralleling Inverters Study of EAST Vertical Stability Coil Power Supply

Experimental advanced superconducting tokamak vertical stability (VS) coil power supply is a large capacity single phase inverter power supply. To meet the requirement of large current and fast response, multi-inverters in parallel is presented, which based on carrier phase-shifted modulation technology. In parallel inverter system, the disperse circuit parameters and phase-shift carriers between parallel inverter units will cause circulating current, which contains fundamental component and a large number of harmonic components. In this paper, the model of circulating current is analyzed when VS coil power supply is working in voltage given mode, and an instantaneous current sharing control strategy is proposed based on the combination of current sharing inductor and instantaneous circulating current feedback control. Parallel inverter units are connected together through current sharing inductors which can change the impedance characteristic of the circulating impedance and well restrain the high-frequency circulating current. Then, the real part of the circulating impedance will be increased and the ability to restrain the low-frequency circulating current will be advanced by introducing virtual resistance, which is realized in the instantaneous circulating current feedback routine. The designations of the current sharing inductor and the virtual resistance are provided. The results of simulation and experiment verify that this current-sharing strategy is available and efficient.

Improving acoustic vehicle classification by information fusion

We present an information fusion approach for ground vehicle classification based on the emitted acoustic signal. Many acoustic factors can contribute to the classification accuracy of working ground vehicles. Classification relying on a single feature set may lose some useful information if its underlying sound production model is not comprehensive. To improve classification accuracy, we consider an information fusion diagram, in which various aspects of an acoustic signature are taken into account and emphasized separately by two different feature extraction methods. The first set of features aims to represent internal sound production, and a number of harmonic components are extracted to characterize the factors related to the vehicle’s resonance. The second set of features is extracted based on a computationally effective discriminatory analysis, and a group of key frequency components are selected by mutual information, accounting for the sound production from the vehicle’s exterior parts. In correspondence with this structure, we further put forward a modified Bayesian fusion algorithm, which takes advantage of matching each specific feature set with its favored classifier. To assess the proposed approach, experiments are carried out based on a data set containing acoustic signals from different types of vehicles. Results indicate that the fusion approach can effectively increase classification accuracy compared to that achieved using each individual features set alone. The Bayesian-based decision level fusion is found to be improved than a feature level fusion approach.

Numerical studies on time-domain responses of on-off-keyed modulated optical signals through a dense fog.

We present a numerical technique to simulate the propagation characteristics of an on-off-keyed modulated optical signal through fog. The on-off-keyed modulated light (a square wave) is decomposed into a finite number of harmonic components, and a numerical solution for the vector radiative transfer equation is obtained for each harmonic that corresponds to the modulation frequency. With this method we study the distortion and the pulse spread in the received signal due to attenuation and scattering. We investigate the propagation characteristic of the modulated signal with different communication system parameters. This information can be used to study communication channel reliability.

Linear systems analysis approach to inlet–bay systems

Fluctuating water levels in tidal inlet-bay systems are investigated by comparison of bay water levels resulting from a linearization of the combined continuity and integrated equation of motion to bay water levels from a numerical model with the complete non-linear equation terms. In this approach a linearized friction factor is computed using results from the non-linear model. The present paper addresses the possibility of utilizing this alternate approach to assessment of water level elevation changes in the bay for realistic tides consisting of a number of harmonic components.

HOMOCLINIC BIFURCATION OF MULTIHARMONIC PERTURBED SYSTEMS

The dynamics of homoclinic tangencies for a multiharmonic perturbed system (MHPS) is studied. By applying the singularity theory to Melnikov function the normal forms at the homoclinic tangency points are obtained, and then the details of the homoclinic bifurcation are quite clear. An important result is that the behavior of homoclinic bifurcation for MHPS is strongly related to the number of harmonic components.

Influence of Draft Variation on Heave Added-Mass and Hydrodynamic Damping Coefficients of Floating Bodies

A general nonlinear theory for solving the radiation problem for floating or immersed bodies in a periodic heave motion, composed of a number of harmonic components, is applied for calculating the influence of draft variations on the linear hydrodynamic coefficients for heave. It is shown that a calculation method for added-mass and damping coefficients of axisymmetric bodies based on a boundary integral equation method can easily be modified to obtain numerical values of the first and second derivatives with respect to draft of the hydrodynamic coefficients as well. The method is illustrated by experimental and numerical data for a floating cone.

Design principles of vibroacoustic diagnostic equipment

A diagnostic method has been used extensively in recent years, whereby nondefective and defective objects are distinguished according to the spectral composition of the vibroacoustic signal. However, such a method has low accuracy for a definite class of objects (e.g., those containing gear elements), because their vibroacoustic spectra are characterized by a large number of harmonic components and it is difficult to find an informative diagnostic criterion.

A Note on the Reproduction of Pulses

The present note aims to demonstrate the relative significance of rise time and percentage energy content in the reproduction of rectangular pulses. Formulas are derived and their dependence upon various factors discussed. It is also shown that the rise time for periodic rectangular pulses is in general not the same as that for a step signal or a single transient pulse; it depends upon the number of harmonic components, the pulse repetition period, and the pulse duration in a more complicated way.