Showing papers on "Harmonics published in 1986"

Experiments on pattern recognition using invariant Fourier-Mellin descriptors.

Abstract: Image descriptors based on the circular-Fourier-radial-Mellin transform are used for position-, rotation-, scale-, and intensity-invariant multiclass pattern recognition. The orders of the radial moments and of the circular harmonics are chosen to obtain an efficient image description. The first-order radial moments of three circular harmonics are sufficient to obtain a satisfactory recognition performance. The influence of additive noise is investigated. Experimental results are shown.

Thresholds for hearing mistuned partials as separate tones in harmonic complexes

Abstract: When a low harmonic in a harmonic complex tone is mistuned from its harmonic value by a sufficient amount it is heard as a separate tone, standing out from the complex as a whole. This experiment estimated the degree of mistuning required for this phenomenon to occur, for complex tones with 10 or 12 equal‐amplitude components (60 dB SPL per component). On each trial the subject was presented with a complex tone which either had all its partials at harmonic frequencies or had one partial mistuned from its harmonic frequency. The subject had to indicate whether he heard a single complex tone with one pitch or a complex tone plus a pure tone which did not ‘‘belong’’ to the complex. An adaptive procedure was used to track the degree of mistuning required to achieve a d’ value of 1. Threshold was determined for each ot the first six harmonics of each complex tone. In one set of conditions stimulus duration was held constant at 410 ms, and the fundamental frequency was either 100, 200, or 400 Hz. For most conditions the thresholds fell between 1% and 3% of the harmonic frequency, depending on the subject. However, thresholds tended to be greater for the first two harmonics of the 100‐Hz fundamental and, for some subjects, thresholds increased for the fifth and sixth harmonics. In a second set of conditions fundamental frequency was held constant at 200 Hz, and the duration was either 50, 110, 410, or 1610 ms. Thresholds increased by a factor of 3–5 as duration was decreased from 1610 ms to 50 ms. The results are discussed in terms of a hypothetical harmonic sieve and mechanisms for the formation of perceptual streams.

Minimization of Torque Ripple in Brushless DC Motor Drives

Abstract: Torque characteristics of brushless dc motors are studied in terms of the EMF and the feed currents for two feeding schemes: two-phase feeding and three-phase feeding. Various techniques for minimizing torque ripple are considered and discussed. For three-phase feeding systems, a selective harmonics elimination technique is studied and its effectiveness is evaluated.

Generalized nonlinear harmonic gyrotron theory

Abstract: The nonlinear efficiency for a gyrotron oscillator operating at harmonics of the cyclotron frequency has been calculated and is presented as a function of generalized parameters for the second through fifth harmonics. The numerical results are valid for a wide range of operating conditions, including voltage, current, beam radius, cavity dimensions, and operating mode. Relatively high efficiencies are found even at high harmonics; the maximum transverse efficiencies for harmonics 2, 3, 4, and 5 are 0.72, 0.57, 0.45, and 0.36, respectively. The calculation of the efficiency in terms of generalized parameters allows the straightforward design and optimization of harmonic gyrotrons. The influence of the axial profile of the rf field in the gyrotron cavity on the efficiency is also investigated. Improved efficiency can be achieved with asymmetric field profiles. The implications of these results for the generation of millimeter and submillimeter wave radiation by harmonic emission are discussed.

New Method for Reducing Harmonics Involved in Input and Output of Rectifier with Interphase Transformer

Abstract: A new effective method for reducing harmonics involved in input ac line currents or output dc voltage of the thyristor rectifier apparatus with an interphase transformer is proposed. This method is based on the sophisticated utilization of several thyristors inserted in parallel between several taps equipped symmetrically for the midpoint of the interphase transformer and the terminal of the dc output circuit. The key point of this method can be understood easily when compared with conventional use of the interphase transformer, where the dc output circuit is taken from the midpoint of the interphase transformer directly. The features of this method are very simple and very economical in circuit construction. Their presentation will take the following form: 1) fundamental theory of the method; 2) analysis of waveforms of input ac line currents under optimum operation; 3) checking the validity of the theory by experiment using the six-phase 12-pulse thyristor polyphase rectifier apparatus; 4) various modifications of this method.

Adjustable Speed Drive and Power Rectifier Harmonics-Their Effect on Power Systems Components

Abstract: The use of the electrochemical rectifiers and the increasing application of ac and dc adjustable speed drives dictates that the effect of harmonic "pollution" on other equipment in the power system be considered An example power system is examined, and the necessary calculations are performed to show the effect harmonics have and investigate the probability of a harmonic resonance situation occurring The tolerances that various power system components have to harmonic currents and voltages are examined These components include transformers, reactors, capacitors, cable, switchgear, relaying, generators, and motors

Harmonics from Transformer Saturation

Abstract: Saturation effects in transformers and shunt reactors can produce harmonics in power systems. Their magnitude can sometimes be found with an electromagnetic transients program, by going from an approximate linear ac steady-state solution directly into a transient simulation in which the nonlinear effects are included. In lightly damped systems, such simulations can take a long time, however, before the distorted steady state is reached. Therefore, another method was developed which uses superposition of steady-state phasor solutions at the fundamental frequency and at the most important harmonic frequencies, with nonlinear inductances represented as harmonic current sources. This method can either be used by itself, or as an improved initialization procedure for electromagnetic transients programs.

An analytical function for absorption correction

Abstract: A new analytical function is proposed for absorption correction. It is expressed by surface harmonics with polar angles that specify the primary and secondary beam directions. This function has an advantage over Fourier expansion because it is rotationally invariant. Two empirical, methods are used to determine the expansion coefficients. One uses the intensity deviations of equivalent reflections, and the other uses the calculated intensities at the stage of structure refinement. The utility of the analytical function is demonstrated with a model and with actual data.

Active filter for reactive power and harmonics compensation

Abstract: This paper describes a three-phase active filter aimed at the compensation of reactive power and current harmonics of a symmetrical load. The filter employs an inductor for energy storage and a two-quadrant PWM bridge converter.

Aging of Electrical Appliances Due to Harnmonics of the Power System's Voltage

Abstract: Average values for the exponents of a weighted harmonic factor are derived for transformers, induction and universal machines as they occur in electrical appliances. The derivation is based on a theoretical loss analysis and on experimentally obtained temperature data [1,2]. The influence of the temperature on the lifetime of the above electromagnetic devices is discussed. An attempt has been made to recommend a limit for the value of the weighted harmonic factor which indirectly limits the sum of the weighted amplitudes of occurring voltage harmonics in a distribution system. Thus a criterion has been devised which judges harmonic voltage spectra based on the temperature increase they produce in an electromagnetic apparatus. As an example, two possible sets of voltage harmonic spectra are discussed that would protect consumers, as well as utility systems, from adverse effects. The work described has been supported by the U.S. Department of Energy.

Pitch detection using the short-term phase spectrum

Abstract: A new frequency domain method for determining the fundamental frequency of speech is presented in this paper. This method uses the information contained in the short-term phase spectral whereas the previous methods were limited to the amplitude spectrum. The short-term spectrum is computed by DFT and it is interpreted as the output of a bank of band-pass overlapping filters. Harmonic components are detected by searching for sets of three contiguous filters having the same instantaneous frequency. The frequency of a detected harmonic is given by the instantaneous frequency itself. A conventional harmonic numbering algorithm is used to convert the set of detected harmonics to a value of the fundamental frequency. Preliminary results show the validity of the method.

Magnetic resonance imaging systems

Abstract: Novel apparatus and methods for magnetic resonance imaging are disclosed which improve imaging speed and resolution as well as increase efficiency, particularly in superconducting systems. In one aspect of the invention, it has been discovered that the eddy currents and harmonics which normally interfere with MRI operations can be suppressed by the construction of an active shield about the gradient-forming components of the system. The active shield, for example, can be implemented by another set of coils, placed between the gradient coils and the cryostat in a superconducting MRI system to zero particular harmonics and prevent eddy currents in the cryostat shells. By employing a set of active secondary coils the problems associated with eddy currents induced by the gradient producing coils are substantially controlled.

Estimating Effect of System Harmonics on Losses and Temperature Rise of Squirrel-Cage Motors

Abstract: With increasing application of static converter power supplies the magnitude of harmonic voltages to which other motors connected to the power system will be exposed must be considered. The additional losses and heating that will occur in these motors may require derating. A simplified expression defined as the harmonic voltage factor (HVF) for estimating the effect of harmonic voltages on polyphase squirrel-cage motors is developed.

Low‐frequency electromagnetic waves driven by gyrotropic gyrating ion beams

Abstract: The origin of left- and right-hand-polarized low-frequency waves in space plasmas is analyzed. It has been shown that a gyrotropic gyrating ion beam, a ring in velocity space, can excite electromagnetic modes in the plasma near the beam gyrofrequency. It excites left-hand-polarized shear Alfven waves and their harmonics via the coupling of Alfven modes with the beam modes. It can also excite right-hand-polarized fast-mode magnetosonic waves and their harmonics as well. The excitation is possible for beam ions heavier than the plasma ions. The growth rate varies as one-third power of the beam density and decreases with the angle of wave propagation with respect to the ambient magnetic field. The nonlocality has a stabilizing effect on the instability. The predicted values of the wave frequencies compare reasonably well with those observed in satellite data.

Iterative technique for the synthesis of optical-correlation filters

Abstract: Optical-correlation filters that are translationally and rotationally invariant are made target specific by incorporating all the angular harmonics of the target image. An iterative design method similar to the technique of convex projections allows the image angular harmonics to be rephased so that the filter exhibits a constant-amplitude rotational response. Rotating this filter in the Fourier plane forms the Fourier summation of all angular harmonics of the input image. Ari image to be detected must have angular-harmonic terms that have an amplitude and a phase that are keyed exactly to the target image. This lock-and-tumbler filter exhibits excellent discrimination capability while preserving rotational invariance.

Song harmonic content as a parameter determining acoustic orientation behaviour in the cricket Teleogryllus oceanicus (Le Guillou)

Abstract: Analyses of natural songs from the cricketTeleogryllus oceanicus confirm (after Hutchings and Lewis 1984) that the songs are rich in harmonics which extend up to around 55 kHz. A series of synthetic song models with a varying harmonic content were used to determine the relevance of these harmonics to the orientation behaviour of the insects. In two-choice experiments in which song models were presented simultaneously, crickets showed a clear discrimination between a song with harmonics and a song without. Female insects orientated preferentially to a song with harmonics. Interestingly, males preferred a song model without harmonics in the two-choice situation. Two experimental regimes were used to test orientation accuracy, a forced-choice (Y maze) phonotactic experiment and a study of free phonotaxis in the behavioural arena. The results of both experimental approaches confirm that crickets orientate more accurately to a song with harmonics and can discriminate smaller angles to sound sources ahead and lateral to the insect. Presentations of song models in which the fundamental (5 kHz) was attenuated relative to the 2nd harmonic have given results that imply a process of neural integration (two-tone or side band suppression) of the fundamental and the high-frequency harmonics.

High gain and high extraction efficiency from a free electron laser amplifier operating in the millimeter wave regime

Abstract: Experiments at the Electron Laser Facility have generated peak microwave power of 180 MW at 35 GHz. The facility is operated as a single pass amplifier. Gain in excess of 30 dB/m has been observed up to saturation of the amplifier. For the 3.6 MeV, 850 A electron beam, the radiation corresponds to 6% energy extraction from the electron beam. Beyond saturation, the electron beam output power exhibits oscillations corresponding to the synchrotron motion of the trapped electrons in the ponderomotive well. In addition, the TE 21 and TM 21 modes have been studied and have power levels comparable to the fundamental. Third harmonic (105 GHz) radiation has been measured at power levels on the order of a few percent of the peak fundamental power.

Effective potentials: A new approach and new results for one-dimensional systems with competing length scales.

Abstract: A new method, involving the solution of a nonlinear eigenvalue equation, is proposed for finding the ground-state configurations and energies of the Frenkel-Kontorova and similar onedimensional models which can show complicated transitions between commensurate and incommensurate phases. It is used to show that a distinctive phase diagram can arise if a cosine potential is perturbed by the addition of suitable harmonics.

Dual-inductor buck switching converter

Abstract: A DC-to-DC power converter is constructed by coupling two parallel-connected inductors in series with a DC input power source. A communication switch is connected in series of each of the inductors. One terminal of each of these switches is connected to one terminal of the input power supply, and the other terminal of both of the switches is connected to the common side of the power supply. The commutation switches are controlled so that they have a switching duty cycle that is greater than 50%. Thus, whenever one of the switches turns off or on, the other switch will remain engaged during this switching time. As a result of this construction, the sum of the currents that flow through the inductors provides an output current to the load which has a greatly reduced ripple and a more constant output current. Also, harmonics of lesser amplitude and higher frequency content are drawn from lines, reducing the size of filter components required to reduce these input-current harmonics.

Harmonic structure of compressional Pc5 pulsations at synchronous orbit

Abstract: A harmonic structure of compressional Pc5 oscillations during geomagnetically disturbed conditions is found in magnetic field data from the geostationary satellites, GOES 2 and 3. Compressional Pc5 pulsations sometimes show an interesting property that the compressional component oscillates with a frequency twice as high as that of the transverse component. In addition to these second harmonic events, waves with a transitional character between normal Pc5 waves and second harmonic events are also observed. In the normal Pc5 waves, the compressional component changes out of phase with the radial component in the northern equatorial region. In a transitional event, a small hump appears at the maximum phase of the radial component. These Pc5 oscillations with second harmonics dominant in the compressional component were observed mainly at GOES 3 and rarely at GOES 2 in the winter season. This occurrence pattern suggests that compressional Pc5 with harmonic structure is spatially confined to the equatorial region. It is also suggested that the particular modulation dominant in the compressional component reflects a finite amplitude effect in the inhomogeneity of the hot ring current plasma near the magnetic equator.

The Active Minimization of Harmonic Enclosed Sound Fields

Abstract: The total time averaged acoustic potential energy in a steady harmonic sound field can be expressed as a positive definite quadratic function of the complex strengths of a number of “secondary sources” of sound introduced into the enclosure. For a given number and location of secondary sources, there is a unique set of complex source strengths which minimises this potential energy. This analysis is applied to the case of a lightly damped enclosure excited by a point primary source at a frequency well above the Schroeder large room frequency. It is demonstrated that in this case, the maximum reduction that can be achieved in the potential energy of the sound field is critically dependent on the relative locations of primary and secondary sources.

Vertical dynamic forces from footsteps

Abstract: Vertical dynamic forces from walking and running were measured by load cells placed between temporary supports and the centre of a 17-m-long floor strip. The measurements showed that the dynamic forces are composed of wave trains of harmonics of the walking or running rate. The significant low frequency contributions are generally contained within the first three to four harmonics

A unified treatment of Wigner D functions, spin‐weighted spherical harmonics, and monopole harmonics

Abstract: A unified, self‐contained treatment of Wigner D functions, spin‐weighted spherical harmonics, and monopole harmonics is given, both in coordinate‐free language and for a particular choice of coordinates.

Contribution to the Theory of Stochastically Periodic Harmonics in Power Systems

Abstract: A basic approach for quantitative evaluation of "Stochastically Periodic" harmonics effects on electrical equipment is presented. The main contribution of this paper is in defining and explaining a mathematical method which enables the estimation of the additional losses and the loss of life caused by stochastically periodic current/voltage harmonics. A practical case of N identical converters, randomly operated, is analyzed. The suggested method is applied to determine admissible levels of randomly periodic voltage harmonics for power capacitors.

Comprehensive calculation of convertor harmonics with system impedances and control representation

Abstract: The paper describes a computational method for finding the harmonics in large convertor systems, with particular reference to the interdependent effects of convertors, transformers, AC and DC system representation and convertor controls. This work is of particular concern as the number of HVDC schemes and large drive systems increases within AC power systems. The method described is comprehensive in that it can model, for example, unbalanced AC system voltages and impedances; any type of convertor transformer arrangement; virtually any pulse number; harmonic filters, a non-infinite AC system representation; it does not assume a smooth DC side current and can include the effect of system resonances in both the AC and DC system. Within the bridge convertors, such features as firing unbalance, convertor transformer saturation, unequal commutation overlaps and the effect of the two principal control methods are all easily modelled. If a comprehensive method is not used, the results of an harmonic study could give unrealistic results. This is shown by example.

Propagation and Elimination of Torque Ripple in a Wind Energy Conversion System

Abstract: The 2P and 4P harmonics of the torque supplied by a two blade vertical axis wind turbine (WT) propagates in the drive train of the wind turbine and deteriorates the quality of the electric power transmitted to the network. This paper shows how the torque ripple propagates and how it can be eliminated by electrical instead of mechanical means. This elimination is obtained by using a converter-fed synchronous generator and by adopting suitable control strategies.

Generalization of conditions for 100% efficiency and nonzero output power in power amplifiers and frequency multipliers

Abstract: In a previous paper, basic limitations on the switch current and voltage waveforms in single-ended switching-mode tuned power amplifiers have been discussed for perfect filtering of harmonics at the output. This paper expands on the previous idea by providing more general conditions for both nonzero output power and 100-percent efficiency at any number of harmonics in the output power. The load network and load are assumed to be passive and linear. It is shown that it is not possible to achieve both nonzero output power and 100-percent efficiency. In switching-mode circuits, it is not possible to eliminate both the transistor turnon switching loss and the transistor turnoff switching loss while obtaining nonzero output power; at least one of the switching losses must be nonzero at nonzero output power. The results presented here are useful in synthesis and analysis of high-efficiency power amplifiers and frequency multipliers.

An analysis of nonlinear resonance in contoured‐quartz crystal resonators

Abstract: Electroelastic equations containing terms up to cubic in the small mechanical displacement field, but no higher than linear in the electric variables, are applied in the analysis of nonlinear resonance in doubly rotated contoured‐quartz resonators and all terms present in the general anisotropic case are included. Since the modes of motion in contoured‐quartz resonators are essentially thickness modes varying slowly along the plate, only the thickness dependence of the elastic nonlinearities are retained in the equations, as in earlier work. The linear portions of the equations are the same as those that have recently been derived and employed in the analysis of doubly rotated contoured‐quartz resonators. The steady‐state solutions are obtained by means of an asymptotic iterative procedure and an expansion in the linear eigensolutions while retaining the nonlinear correction to the eigensolution that has a resonant frequency in the vicinity of the driving frequency. The slow variations in the mode along the plate are included in the nonlinear correction by averaging over the plate. Lumped parameter representations of the solutions, which are valid in the vicinity of a resonance and relate the amplitude of the mode nonlinearly to the voltage across the electrodes, are obtained. In each instance the expression for the current through the crystal is determined, the external circuitry is incorporated in the description and an equation relating the mode amplitude nonlinearly to the driving voltage and other circuit parameters is obtained. The analysis holds for the fundamental and odd harmonic overtones. Nonlinear resonance curves are calculated for AT‐cut quartz using the known nonlinear coefficients. In particular, it is shown that the order of the harmonic has a more significant influence on the shift in resonant frequency from the linear value than the current through the crystal. An equation relating the change in resonant frequency resulting from the nonlinearity to the current through the crystal, independent of the external circuitry, is derived. This latter equation is employed in the evaluation of the coefficient of nonlinear resonance for SC‐cut quartz from measurements of the shift in resonant frequency with current level in contoured resonators.

Nonlinear surface waves on cubic materials

Abstract: The effect of nonlinearity on the propagation of surface Rayleigh waves on an elastic medium of cubic symmetry is examined by applying the results of an earlier analysis for general anisotropic materials. Explicit calculations are given of the parameters relating to the generation of higher harmonics in an initially sinusoidal wave for a series of thirty-five materials for which experimental measurements of the third-order moduli are available.