Showing papers on "Harmonics published in 2001"

Observation of a Train of Attosecond Pulses from High Harmonic Generation

Abstract: In principle, the temporal beating of superposed high harmonics obtained by focusing a femtosecond laser pulse in a gas jet can produce a train of very short intensity spikes, depending on the relative phases of the harmonics. We present a method to measure such phases through two-photon, two-color photoionization. We found that the harmonics are locked in phase and form a train of 250-attosecond pulses in the time domain. Harmonic generation may be a promising source for attosecond time-resolved measurements.

The Induction Machine Handbook

Abstract: Induction Machines in the Industry. Topology and Operation of Induction Machines Materials and Losses. Windings and their mmfs. No-Load Field Distribution. Equivalent Circuit Parameters. Steady-State Performance Calculations. On-Load Saturation and Frequency Effects on Circuit Parameters. Skewing and Inter-Bar Rotor Currents. Space Harmonics in Airgap Field. Core and Winding Fundamental and Harmonic Losses. Thermal Modeling. Space Phasor Models for Transients and Variable-Speed Operation. Design Specifications. Preoptimization Design Methods and Case Studies. Design Optimization Methods. Design Optimization Case Studies for Constant Frequency Operation. Design Optimization Case Studies for Variable Frequency Variable Speed Operation. Design of Induction Generators. Design of High-Speed Induction Motors Linear Induction Motors. Ultra-High Frequency Effects of Power Electronics Tests on Induction Machines. Induction Motor Monitoring. Single-Phase Induction Motors.

A closed-loop selective harmonic compensation for active filters

Abstract: This paper proposes a control algorithm for parallel active power filters, based on current-controlled pulsewidth-modulated converters, which allows precise compensation of selected harmonic currents produced by distorting loads. The approach is based on the measurement of line currents and performs the compensation of the selected harmonics using closed-loop synchronous frame controllers. Thanks to the closed-loop operation, full compensation of the desired harmonics is achieved even in the presence of a significant delay in the current control. Thanks to the selective approach, active filter interactions with possible dynamic components of the load are minimized. Moreover, the complexity of the synchronous frame controllers is overcome using equivalent stationary frame controllers. Experimental results confirm the theoretical expectations.

Harmonic sources and filtering approaches

Abstract: This article presents 22 configurations of power filters for the harmonic compensation of nonlinear loads. Some of these configurations are novel and result from the newly discovered characteristics of nonlinear loads and circuitry duality, while the others are well known and used in practice. Nonlinear loads can be characterized into two types of harmonic sources: current-source nonlinear loads and voltage-source nonlinear loads. These two types of harmonic sources have completely distinctive and dual properties and characteristics. Based on their properties and characteristics, the current-source nonlinear loads and voltage-source nonlinear loads have their own suitable filter configurations, respectively.

Detection of Rotor Slot and Other Eccentricity-Related Harmonics in a Three-Phase Induction Motor with Different Rotor Cages

Abstract: Detection of rotor slot and other eccentricity related harmonics in the line current of a three phase induction motor is important both from the viewpoint of sensorless speed estimation as well as eccentricity related fault detection. However, it is now clear that not all three phase induction motors are capable of generating such harmonics in the line current. Recent research has shown that the presence of these harmonics is primarily dependent on the number of rotor slots and the number of fundamental pole pairs of the machine. While the number of fundamental pole pairs of a three phase induction motor usually is within one to four (higher pole pairs are generally avoided due to increased magnetizing current), the number of rotor slots can vary widely. The present paper investigates this phenomenon further and obtains a hitherto nebulous theoretical basis for the experimentally verified results. Detailed coupled magnetic circuit simulation results are presented for a four pole, three phase induction motor with 44, 43, and 42 rotor slots under healthy, static, dynamic and mixed eccentricity conditions. The simulation is flexible enough to accommodate other pole numbers also. These simulations are helpful in quantifying the predicted harmonics under different combinations of load, pole pair numbers, rotor slots and eccentricity conditions, thus making the problem easier for drive designers or diagnostic tools' developers. Data from three different induction machines, namely, a 4 pole, 44 bar, 3 hp, a 4 pole, 28 bar, 3 hp and a 2 pole, 39 bar, 100 hp motor have been used to verify the results experimentally. The simulation and the experimental results clearly validate the theoretical findings put forward in this paper.

Class-E, Class-C, and Class-F power amplifiers based upon a finite number of harmonics

Abstract: Class-E operation at UHF and microwave frequencies is achieved by using transmission-line networks to provide the drain harmonic impedances of an ideal class-E power amplifier (PA). This paper develops a technique for analysis of such amplifiers that are based upon a finite number of harmonics. The technique is generally applicable to classes E, C, and F as well as PAs with harmonic reactances not corresponding to those of established classes. The analysis shows that the maximum achievable efficiency depends not upon the class of operation, but upon the number of harmonics employed. For any set of harmonic reactances, the same maximum efficiency can be achieved by proper adjustment of the waveforms and the fundamental-frequency load reactance. The power-output capability depends upon the harmonic reactances and is maximum for class F.

A novel current-tracking method for active filters based on a sinusoidal internal model [for PWM invertors]

Abstract: A new current control method based on the internal model principle in control theory is proposed. It introduces a sinusoidal internal model into the control system. It does not use any coordinate transformations. The method can be used for tracking an arbitrary number of harmonics: a DC component or fundamental frequency component signal. It is applied to a single-phase pulsewidth modulation inverter and active filter. The validity is confirmed by simulation and experimental results.

Micro-damage diagnostics using Nonlinear Elastic Wave Spectroscopy (NEWS)

Abstract: Nonlinear elastic wave spectroscopy (NEWS) represents a class of powerful tools which explore the dynamic nonlinear stress–strain features in the compliant bond system of a micro-inhomogeneous material and link them to micro-scale damage. Hysteresis and nonlinearity in the constitutive relation (at the micro-strain level) result in acoustic and ultrasonic wave distortion, which gives rise to changes in the resonance frequencies as a function of drive amplitude, generation of accompanying harmonics, nonlinear attenuation, and multiplication of waves of different frequencies. The sensitivity of nonlinear methods to the detection of damage features (cracks, flaws, etc.) is far greater than can be obtained with linear acoustical methods (measures of wavespeed and wave dissipation). We illustrate two recently developed NEWS methods, and compare the results for both techniques on roofing tiles used in building construction.

Understanding Power System Hannonics

Abstract: Harmonics – Past to Present Power systems are designed to operate at frequencies of 50 or 60Hz. However, certain types of loads produce currents and voltages with frequencies that are integer multiples of the 50 or 60 Hz fundamental frequency. These higher frequencies are a form of electrical pollution known as power system harmonics. Power system harmonics are not a new phenomenon. Concern over harmonic distortion has ebbed and flowed during the history of electric power systems. Steinmetz published a book in 1916 that devoted considerable attention to the study of harmonics in three-phase power systems. His main concern was third harmonic currents caused by saturated iron in transformers and machines, and he was the first to propose delta connections for blocking third harmonic currents. Later, with the advent of rural electrification and telephone service, power and telephone circuits were often placed on common rights-of-way. Harmonic currents produced by transformer magnetizing currents caused inductive interference with open-wire telephone systems. The interference was so severe at times that voice communication was impossible. This problem was studied and alleviated by filtering and by placing design limits on transformer magnetizing currents. Today, the most common sources of harmonics are power electronic loads such as adjustable-speed drives (ASDs) and switch-mode power supplies. These loads use diodes, silicon-controlled rectifiers (SCRs), power transistors, and other electronic switches to chop waveforms to control power or to convert 50/60Hz AC to DC. In the case of ASDs, the DC is then converted to variable-frequency AC to control motor speed. Example uses of ASDs include chillers and pumps. Due to tremendous advantages in efficiency and controllability, power electronic loads are proliferating and can be found at all power levels – from low voltage appliances to high voltage converters. Hence, power systems harmonics are once again an important problem.

Noise-Induced Dynamics in Bistable Systems with Delay

Abstract: Noise-induced dynamics of a prototypical bistable system with delayed feedback is studied theoretically and numerically. For small noise and magnitude of the feedback, the problem is reduced to the analysis of the two-state model with transition rates depending on the earlier state of the system. Analytical solutions for the autocorrelation function and the power spectrum have been found. The power spectrum has a peak at the frequency corresponding to the inverse delay time, whose amplitude has a maximum at a certain noise level, thus demonstrating coherence resonance. The linear response to the external periodic force also has maxima at the frequencies corresponding to the inverse delay time and its harmonics.

Maximum efficiency and output of class-F power amplifiers

Abstract: A class-F power amplifier (PA) improves efficiency and power-output capability (over that of class A) by using selected harmonics to shape its drain-voltage and drain-current waveforms. Typically, one waveform (e.g., voltage) approximates a square wave, while the other (e.g., current) approximates a half sine wave. The output power and efficiency of an ideal class-F PA can be related to the Fourier coefficients of the waveforms, and Fourier coefficients for maximally flat waveforms have been determined. This paper extends that theory by determining the coefficients for the maximum power and efficiency possible in a class-F PA with a given set of controlled harmonics.

Synchronisation methods for grid-connected voltage source converters

Abstract: Four different synchronisation methods for a voltage source converter connected to a three-phase grid are investigated. The methods are adapted for use in a digital controller. The performance of the synchronisation methods is studied by response characteristics of phase-shift steps, frequency steps and low-frequency grid voltage harmonics. The low-pass filtering method can be used only if the frequency of the grid is constant and phase jumps do nor occur. If phase jumps occur, the novel space vector filtering method is recommended. The extended space vector filtering method is adapted to handle frequency variations and is also preferred if fast frequency variations occur. This method even has a higher performance than the extended Kalman filter method, in spite of the large number of calculations that must be performed.

The algorithm of interpolating windowed FFT for harmonic analysis of electric power system

Abstract: The fast Fourier transform (FFT) cannot be directly used in the harmonic analysis of an electric power system because of its higher errors, especially the phase error. This paper discusses the leakage phenomenon of FFT and presents a new amending algorithm, poly-item cosine window interpolation, which is based on the interpolating algorithm proposed by V. Jain and T Grandke. This new algorithm improves the accuracy of the FFT, so it can be applied to the precision analysis for electrical harmonics. The simulation result shows that applying different windows has different effects on the accuracy, and the Blackman-Harris window has the highest accuracy.

Synchronous-frame harmonic control for high-performance AC power supplies

Abstract: In order to achieve the reduction of voltage distortion in AC power supplies (ACPSs), this paper describes an implementation of synchronous-frame control for selected frequencies in the output voltage. The regulation of the fundamental output voltage, as well as that of some low-order harmonics, is achieved using a synchronous-frame controller for each selected frequency in addition to a conventional control. The conventional part conserves good dynamic performance under load changes, while rotating-frame controllers allow a slow, but very precise compensation of the residual errors within the assumption that the harmonics produced by distorting load are slowly varying. Moreover, motivated by a fixed-point implementation, a set of refinements and modifications of the original scheme is proposed, allowing a reduction of signal processing requirements and a new control algorithm structure less sensitive to quantization and rounding errors. This solution is particularly effective for high-power fully digitally controlled ACPSs, where the voltage loop bandwidth is usually not large enough to provide regulation at harmonic frequencies. The proposed control scheme has been implemented using a fixed-point single-chip digital signal processor (ADMC401 by Analog Devices). Experimental results on a 3-kVA three-phase converter prototype show the effectiveness of the proposed approach.

Power Systems Harmonics: Fundamentals, Analysis and Filter Design

Abstract: Contents: Introduction - Fundamentals of Harmonics - Causes of Harmonics in Power Systems - Effects of Harmonic Distortion on Power Systems - Mitigation of Power System Harmonics - Limits of Harmonic Distortion - Modelling of System Components for Harmonic Studies -Transformer Modelling - Modelling of Transmission Lines / Cables - A Simple Approach to Power System Harmonic Studies - Bibliography - Appendix A: A Review of Transformation and Symmetrical Components - Appendix B: Phase and Sequence Admittance Matrices for Three-Phase Transformers - Appendix C: Transmission Matrices for Three-Phase Transformers - Index.

The near-surface current velocity determined from image sequences of the sea surface

Abstract: A method to measure the ocean's near-surface current velocity vector based on the analysis of remote sea-surface image sequences was developed. The spatial and temporal records were transformed to the wavenumber-frequency domain, resulting in a three-dimensional (3-D) image power spectrum. In the spectrum, the signal energy of the waves is localized on a shell defined by the dispersion relation of surface waves. The sum of the sensor's velocity and the near-surface current profile deforms the dispersion shell due to the Doppler-frequency shift. An iterative least-squares fitting technique and an error-estimation model was implemented. To improve the method's accuracy, spectral wave energy found in higher harmonics of the dispersion shell and aliasing effects are taken into account. The most important nonlinear mechanism leading to higher harmonics is explained as resulting from wave shadowing due to the low grazing angles typical for ground- or ship-based radars. The improved method is examined analytically and is tested with Monte Carlo simulations. The variation of the shape of the measured or simulated 3-D image spectra, especially the peak wavenumber, the directional spread, and the main travel direction, controls the behavior and accuracy of the technique. A comparison of velocities acquired by nautical radar and independent Doppler log current measurements is presented. The technique's accuracy, its limits, and its adaptability are discussed. Additional improvements are proposed.

A novel control method for input output harmonic elimination of the PWM boost type rectifier under unbalanced operating conditions

Abstract: This paper presents a new control strategy to improve the performance of the PWM boost type rectifier when operating under an unbalanced supply. An analytical solution for harmonic elimination under unbalanced input voltages is obtained resulting in a smooth (constant) power flow from AC to DC side in spite of the unbalanced voltage condition. Based on the analysis of the open loop configuration, a closed loop control solution is proposed. Simulation results show excellent response and stable operation of the new rectifier control algorithm. A laboratory prototype has been designed to verify the discussions and analyses done in this paper. Theoretical and experimental results show excellent agreement. Elimination of the possibility of low order AC and DC side harmonics due to unbalance is expected to materially affect the cost of DC link capacitor and AC side filter. The proposed method is particularly useful in applications where the large second harmonic at the DC link may have a severe impact on system stability of multiply connected converters on a common link.

Current monitoring for detecting inter-turn short circuits in induction motors

Abstract: In this paper the stator winding itself is used as the sensor for the detection of abnormalities in the stator winding. To achieve this task, detailed analysis of the air gap flux distribution and its dependence on the particular machine configuration is carried out. The analysis presented is based on the rotating wave approach which accounts for all the stator and rotor MMF harmonics, stator and rotor slot harmonics and harmonics due to saturation. It is shown that the most reliable indicators of the presence of the fault are the lower sideband of field rotational frequency with respect to the fundamental, together with some of the components that are related to slotting. Some of them increase as functions of the link current, in a range from 0 to over 10% and some components decrease in the range 0-12%.

Caching of intra-layer calculations for rapid rigorous coupled-wave analyses

Abstract: Diffraction from periodic gratings is calculated by caching intermediate rigorous coupled-wave computations. The grating cross-section is divided into layers, and the permittivity, electric fields and magnetic fields are formulated as harmonic expansions along the periodicity directions. Applying Maxwell's equations to intermediate layers provides a set of coupled-wave equations with matrix A. Calculation of the eigenvalues and the eigenvector associated with the matrix A is needed to solve these equations. A is a function of intra-layer parameters and incident-radiation parameters; W is the eigenvector matrix; and Q is a diagonal eigenvalue square-root matrix. Look-up of W and Q (and another matrix related to W and Q), which are precalculated and cached for useful ranges of intra-layer parameters (i.e., permittivity harmonics, periodicity lengths, ridge widths, ridge offsets) and incident-radiation parameters (i.e., wavelengths and angles of incidence), provides a substantial reduction in computation time.

Active noise control for periodic disturbances

Abstract: Proposes an active noise control algorithm for periodic disturbances of unknown frequency. The algorithm is appropriate for the feedback case in which a single error microphone is used. A previously proposed algorithm for the rejection of sinusoidal noise sources is extended for the cancellation of multiple harmonics. Unlike many other approaches, the estimates of the frequencies of the separate harmonics are tied together within the algorithm to account for the integer multiplicative relations between them. The dynamic behavior of the closed-loop system is analyzed using an approximation that is shown, in simulations, to provide an accurate representation of the system's behavior. Experimental results on an active noise control testbed demonstrate the success of the method in a practical environment.

A Precise Calculation of Power System Frequency

Abstract: A precise digital algorithm based on discrete Fourier transforms (DFT) to estimate the frequency of a sinusoid with harmonics in real-time is proposed. This algorithm, that the authors call smart discrete Fourier transforms (SDFT), smartly avoids the errors that arise when frequency deviates from the nominal frequency, and keeps all the advantages of the DFT e.g., immunity to harmonics and the recursive computing can be used in SDFT. These make the SDFT more accurate than conventional DFT based techniques. In addition, this method is recursive and very easy to implement, so it is very suitable for use in real-time. The authors provide the simulation results compared with a conventional DFT method and second-order Prony method to validate the claimed benefits of SDFT.

Tissue harmonic imaging techniques: physical principles and clinical applications.

Abstract: Tissue harmonic imaging (THI) is a new gray-scale sonographic technique that improves image clarity. Harmonics form within the insonated tissue as a consequence of nonlinear sound propagation. Imaging with endogenously formed harmonics means that the distorting layer of the body wall is traversed only once by the harmonic beam--during echo reception. Both image contrast and lateral resolution are improved in harmonic mode compared with conventional (fundamental mode) sonography. This article summarizes the physics and various implementations of harmonic imaging mode, and reviews the clinical applications that have emerged to date.

Power Systems Harmonics : Computer Modelling and Analysis

Abstract: Deregulation has presented the electricity industry with many new challenges in power system planning and operation. Power engineers must understand the negative effect of harmonics on an electrical power network resulting from the extensive use of power electronics-based equipment. Serving as a complete reference to harmonics modelling, simulation and analysis, this book lays the foundations for optimising quality of power supply in the planning, design and operation phases. Features include: MATLAB function codes to aid the development of harmonic software and provide a hands-on approach to the theory presented; Insight into the use of alternative, increased efficiency, harmonic domain techniques; Examination of the harmonic modelling and analysis of FACTS, along with conventional and custom power plant equipment; Clear presentation of the basic analytical approaches to harmonic theory and techniques for the resolution of harmonic distortion. Advanced undergraduate and postgraduate students in electrical engineering will benefit from the unique combination of practical examples and theoretical grounding. Practising power engineers, managers and consultants will appreciate the detailed coverage of engineering practice and power networks world-wide.

Analysis and prediction of inverter switching frequency in direct torque control of induction machine based on hysteresis bands and machine parameters

Abstract: In this paper, the influences of the hysteresis bands on the direct torque control (DTC) of an induction motor are analytically investigated, and the switching frequency of the inverter is predicted based on the analysis. The flux and torque hysteresis bands are the only gains to be adjusted in DTC, and the inverter switching frequency and the current waveform are greatly influenced by them. Therefore, the magnitude of the hysteresis band should be determined based on reasonable guidelines which can avoid excessive inverter switching frequency and current harmonics in the whole operating region. This paper predicts the inverter switching frequency according to torque and flux hysteresis bands based on induction machine parameters and control sampling period, and investigates the effect of hysteresis bands to line current harmonics. The simulated and experimental results prove the usefulness and feasibility of the proposed method.

A three-dimensional multifrequency large signal model for helix traveling wave tubes

Abstract: A three-dimensional (3D) multifrequency large signal model of the beam wave interaction in a helix TWT is described The beam is divided into a set of discrete rays, or "beamlets", instead of the disks or rings used in one-dimensional (1-D) or two-dimensional (2-D) models The RF fields supported by the helix are represented by a tape helix model that uses a modal expansion including the full (Bessel function) radial dependence of the fields; both forward and backward synchronous space harmonics are included in the model RF space charge fields are obtained from solutions of the Helmholtz equations for the RF electric and RF magnetic fields, using the beam current and charge densities as sources The dc space charge electric field is similarly obtained from a solution of Poisson's equation This model has been implemented in a code called CHRISTINE 3D, a generalization of the one dimensional CHRISTINE code The full three dimensional treatment permits the accurate computation of large signal gain and efficiency, taking into account the self-consistent variation of beam radius along the interaction space The code also computes helix interception current and transverse beam distributions at the entrance to the collector-important design data that are unavailable from a 1D model Results from the CHRISTINE 3D code are shown to compare very favorably with measurements of output power, efficiency, and interception current vs drive power Its predictions for spent beam distributions also compare very well with measurements Run times for the code are problem dependent, but for a single case of interest are typically 1 to 5 min on a 450 MHz PC, orders of magnitude shorter than that required for a comparable 3D particle-in-cell simulation

Evaluation of frequency tracking methods

Abstract: This paper presents an analysis of proposed methods for tracking the fundamental power frequency to see if they have the performance necessary to cope with the requirements of future protection and control equipment and are robust enough to cope with the more demanding nature of modern power system conditions. The analysis shows that the linear estimation of phases, decomposition of single phase into orthogonal components and discrete Fourier transform perform extremely well but they all suffer from a periodic error in the estimated frequency if it departs from the assumed frequency. This can be cancelled using a low pass filter although it would introduce delays and obscure any real oscillations in the fundamental frequency. Alternatively, averaging over three phases could be used but higher harmonics in the oscillation of the estimation would be present.

General expressions for IM/DD dispersive analog optical links with external modulation or optical up-conversion in a Mach-Zehnder electrooptical modulator

Abstract: A general derivation of the optical modulation process in a dual-drive Mach-Zehnder modulator (DD-MZM) is introduced. The expressions include all harmonics and are entirely general in terms of bias point. Chromatic dispersion is also included allowing the prediction of a number of important phenomena in photonic signal transmission. Examples of special cases of these general equations are then presented. Similar expressions are introduced for harmonic optical up-conversion through a photonic mixer based on a DD-MZM covering any bias point or phase shift between DD-MZM drives.

Removal of decaying DC in current and voltage signals using a modified Fourier filter algorithm

Abstract: Protecting transmission lines frequently involves applying distance relays. Protective relays must filter their inputs to reject unwanted quantities and retain signal quantities of relevant interest. Accuracy and convergent speed of filter algorithm are essential for protective relays. A widely applied filter algorithm, the discrete Fourier transform (DFT) can easily remove integer harmonics using simple calculation. However, the voltage and current signals contain serious harmonics and decaying DC during the fault interval. In addition, the decaying DC and higher order harmonics seriously decrease the precision and convergence speed of fundamental frequency signal from DFT. In this investigation, the authors derive a novel algorithm which combines the appropriate analog low pass filter and modified full cycle DFT (FCDFT) or half cycle DFT (HCDFT) algorithm to remove the decaying dc in a voltage or current signal. Using the Electromagnetic Transients Program (EMTP) simulates the transient responses of transmission lines during the fault period. Applying the proposed algorithm in distance relays effectively suppresses the decaying DC and quickly decomposes the accurate fundamental frequency components.

Selective harmonic elimination and current/voltage control in current/voltage-source topologies: a unified approach

Abstract: This paper presents a unified approach for generating pulsewidth-modulated patterns for three-phase current-source rectifiers and inverters (CSR/Is) that provides unconstrained selective harmonic elimination and fundamental current control. The approach uses the chopping angles or gating patterns developed for voltage-source rectifiers and inverters in combination with a logic circuit to generate the gating patterns for CSR/Is. The circuit also includes naturally and symmetrically distributed shorting pulses. Thus, the approach avoids the hassle of positioning the shorting pulses and defining and solving a set of nonlinear equations dedicated to CSR/Is. Moreover, the approach can eliminate an even or odd arbitrary number of harmonics (e.g., fundamental current control and elimination of the 5th, 7th, and 11th harmonics). This is an improvement over existing techniques and a new approach to pattern generation. Simulated and experimental results for both static and dynamic operating conditions are presented in order to validate the effectiveness of the approach.