Showing papers on "Harmonics published in 1983"

Generalized Structure of a Multilevel PWM Inverter

Abstract: A generalized structure of a multilevel voltage source thyristor inverter is proposed. The multilevel concept is used to decrease the harmonic distortion in the output waveform without decreasing the inverter power output. A simple uniform PWM control of the output voltage is seen to be sufficient to practically remove all remaining harmonics. Harmonic analysis of n-step waveform is given, and the experimental results obtained on a three-step inverter are presented.

High Phase Order Induction Motors - Part I-Description and Theoretical Considerations

Abstract: The characteristics of induction motors having more than three phases are presented. The sequence sets of the symmetrical component method are used to determine the inductances with time harmonics in the source waveform such as for inverter sources. The effect of stator coil pitch on these inductances is explained. It is shown that some of these harmonics cannot induce rotor currents in motors having many phases, thereby reducing the torque pulsations and rotor I2R loss below the values for three-phase motors. Other advantages are lower current per phase and the ability of the motor to start and run with one phase open. Six and nine-phase motors are found to be especially attractive.

Wind Energy Conversion Using A Self-Excited Induction Generator

Abstract: A wind energy conversion scheme using an induction machine driven by a variable speed wind turbine is described. Excitation control has been obtained by employing a single value capacitor and thyristor controlled inductor. Wind speed cube law is proposed to be followed in loading the induction machine for maximising energy conversion. Performance characteristics of the generation scheme have been evaluated over a wide speed range. Harmonic analysis of the proposed scheme shows that harmonic currents and their associated power loss is negligible.

High Phase Order Induction Motors - Part II-Experimental Results

Abstract: Experimental tests have been carried out on a small induction motor connected for six phases and for nine phases. These include torque measurements over the entire speed range and load tests with balanced source and with one phase open. Some of the machine impedances, including sequence impedances, were measured and these generally agree with predicted values. The motor was subjected to source voltages having harmonics and the measured currents show good agreement with theoretical values based on the analysis in a companion paper.

Small-Signal Theory of a Large-Orbit Electron-Cyclotron Harmonic Maser,

Abstract: The small‐signal theory of a harmonic gyrotron is presented for the case of axis‐encircling electron orbits. The beam current required for oscillation is found to be highly dependent on the electron energy. Gyrotron cavities operating on this principle at very high harmonic numbers (n≂10) and high frequency in weak magnetic fields are well matched to low‐current, moderate‐energy, rf‐accelerated electron beams (≂50 mA, ≂250 keV), resulting in compact submillimeter wave systems.

A Comparison of PWM Strategies for Inverter-Fed Induction Motors

Abstract: Several sophisticated or "optimum" modulation strategies have been suggested for voltage source pulsewidth modulated (PWM) inverters for ac motor control. These modulation strategies may suppress specific low-order harmonics or minimize total harmonic content and have been successfully implemented in practical drive systems. The effectiveness of these PWM techniques in minimizing harmonic losses and reducing torque pulsations is investigated analytically, and their performance is compared with that of the usual sinusoidal or subharmonic PWM approach. The influence of skin effect on rotor 12R copper loss is taken into consideration, and harmonic core losses are compared. Peak current is also an. important factor in inverter design, and the various modulation strategies are again compared on this basis. Fourier analysis techniques are used in order to allow skin effect phenomena to be taken into consideration, and performance criteria are developed to allow comparisons of waveform quality in respect of harmonic copper and iron losses.

The rotational spectrum of g-modes in the sun

Abstract: Observations and calculations are presented which strongly suggest that the unique sequence of rotation rates due to g-modes is active in the sun. It is found that all angular harmonics from 1 = 2-11 appear to be resolved, while higher harmonics up to at least 1 = 20 also seem to be active. The extreme narrowness of many of the spectral lines indicates that the g-modes are locked in sets of constant 1 by a local mechanism which excites the modes and possibly regulates the long-term precision of their rotation. These sets act as a system of resonant, or nearly resonant, clocks which impose a degree of periodicity upon solar activity and measure the mean solar interior rotation

Brake rotor with vibration harmonic suppression, and method of manufacture

Abstract: A ventilated disc brake rotor in which spacing between and/or radial length of cooling fins are varied around the rotor for frequency and/or amplitude modulated damping of vibration harmonics, and for balancing the rotor.

Modeling and Analysis of Induction Machines Containing Space Harmonics Part I: Modeling and Transformation

Abstract: The coupled-circuit approach is used to derive a mathematical model of a general m-n winding machine in which all MMF harmonics are taken into account. The model, which is applicable to both squirrel cage and phase- wound rotors, has provision for cage rotors with non-integral number of rotor bars per stator pole-pair. The effects of the transformations from polyphase to a-P-0 and to d-q-0 on the machine equations are analyzed. It is shown that the polyphase to a-P-0 transformation, when applied to the stator and rotor of the m-n winding machine, divides the harmonics into different groups of harmonics with possible interaction, whereupon each group of harmonics can then be represented by an a-P or a zero component circuit. This result shows that the usual assumption of representing the cage rotor by independent harmonics circuits is, in general, not valid. It is also shown that the polyphase to rotating d-q transformation is applicable when only one harmonic from each a-P component is to be considered, otherwise a new problem of separating the harmonic voltages within each a-P component is created.

Application of Power Transistors to Residential and Intermediate Rating Photovoltaic Array Power Conditioners

Abstract: An investigation into power conditioners that interface with photovoltaic arrays and utilities has been recently completed. The ratings for this investigation include residential systems (5-30 kW) that interface with a 240-V single-phase utility connection and intermediate systems (30-200 kW) that interface with a 480-V three- phase utility connection. Both systems mandated that an isolation transformer be provided between the array and the utility interface. A trade-off study was performed for many transistor and thyristor circuits and configurations. The weighting criteria included full- and part-load efficiency, size, weight, reliability, ease of control, injected harmonics, reactive power requirements, and parts cost. As the result of this study, a 10-kW high-frequency PWM transistor inverter feeding a high-frequency isolation transformer with a sinusoidally shaped current wave was selected. The output of the transformer is rectified with a diode bridge rectifier. Four thyristors, used as 60-Hz switches, reverse the polarity of the rectified current on every other half-cycle of the utility voltage. This reversal is accomplished slightly before the natural zero crossing of the voltage, thereby providing commutation for the thyristors. The results in the intermediate rating study targeted on a 100-kW design using power transistors in a full-bridge circuit connected to a 60-Hz three-phase transformer. Three bridge circuits are provided to interface with the polyphase utility. The switching strategy for the power transistors is based on a sine wave shape of current with a controlled deadband.

Numerical Steady-State Analysis of Nonlinear Microwave Circuits with Periodic Excitation

Abstract: A new method for determining the steady-state response of nonlinear microwave circuits with periodic excitation is proposed. The method minimizes time-domain calculations by introducing a criterion for selecting the variables to be considered as unknowns and for solving the resulting nonlinear system by a new and efficient algorithm. It has exhibited the capability for handling a large number of harmonics and nonlinearities. To illustrate the generality and usefulness of the method, a pumped diode and a MESFET frequency doubler are analyzed.

Optimum fourier filtering of cardiac data: a minimum-error method: concise communication.

Abstract: Random fluctuations limit the accuracy of quantities derived from cardiac time-activity curves (TACs). To overcome this problem, TACs are often fitted with a truncated Fourier series giving rise to two sources of error: (a) the truncated series may not adequately describe the TAC shape, causing errors in parameters calculated from the fit: and (b) successive TACs acquired from the same subject under identical circumstances will fluctuate due to limited counts, causing the Fourier fits (and parameters derived from them) to fluctuate. These two errors, respectively, decrease and increase as the number of harmonics increases, suggesting the existence of a minimum in total error. This number of harmonics for minimum error (NHME) was calculated for each of six common parameters used to described LV TACs. The “true” value of each parameter was determined from TACs of very high statistical precision. Poisson noise was added to simulate lower count rates. For low-count TACs, use of either a smaller or a larger number of harmonics resulted in significantly greater error. NHME was found to occur at two harmonics for the systolic parameters studied, regardless of the noise level present in the TAC. For diastolic parameters, however, NHME was a strong function of the noise present in the TAC, varying from three harmonics for noise levels typical of regional TACs, to five or six harmonics for high-count global TACs.

Harmonic generation of radiation in a steep density profile

Abstract: It has been observed experimentally that the CO2‐laser Gemini and Helios systems generate very high harmonics with nearly constant efficiency over several harmonics with a cutoff near the local plasma frequency at the upper density shelf. To understand the experimental results, the strongly nonlinear electron response to a time‐dependent inhomogeneous force is studied. The equation of the electron motion in Lagrangian variables is derived and the conditions on the density scale length and power intensities for wavebreaking are found. By transforming the solution back to Eulerian variables, it is shown that the source of a given high harmonic frequency is localized around the density region where the local plasma wave is at that frequency. Using the numerically obtained nonlinear current density we evaluate the intensity of the radiation coming out of the plasma and verify the nearly constant harmonic production efficiency with a sharp decrease at the local plasma wave frequency at the upper shelf density.

Signal processing for high resolution electronic still camera

Abstract: In an effort to provide exceptionally high resolution playback of video information recorded in the environment of an electronic still camera, the invention calls for: (a) Use of double side band FM recording, which in the prior art would have been productive of playback interference between the side bands of harmonics and the side bands of corresponding fundamentals unless the relative head-to-media speed was high enough to accommodate high carrier frequencies. (b) Bias recording such FM video information, thereby to prevent the inherent production of harmonic information within the media. (c) Up-converting the harmonic-free playback signal, before the harmonic-causing procedure of amplitude-limiting such playback signal, thereby to cause such signal to have a spectrum-wise wide disparity between the modulated fundamental in question and its harmonics, as caused by such amplitude limiting. (d) Removing the generated harmonics (and their side bands) prior to or during demodulation of the modulated fundamental.

Fundamental and Harmonic Operation of Millimeter-Wave Gunn Diodes

Abstract: Pulsed and CW measurements in the range 26-110 GHz were performed on gallium arsenide (GaAs) Gunn diodes having active lengths of 1.8-2.6 µm, bonded into commercially available packages. The diodes were operated in full-height waveguides in the V-(WR-15), E-(WR-12), and W-(WR- 10) bands, using coaxial-bias circuits aud a disc-post resonator to provide the required resonance at their fundamental frequency in the range from about 25-65 GHz. Frequency and power measurements were performed up to 110 GHz on the fundamental, second, and third harmonics. The main emphasis of this experimental investigation has been the study of frequency changes caused by changes made in the various parameters of the disc, post, diode, diode package, and embedding waveguide sections.

A mechanism for plasma waves at the Harmonics of the plasma frequency in the Electron Foreshock Boundary

Abstract: A bump-on-tail unstable reduced velocity distribution, constructed from data obtained at the upstream boundary of the electron foreshock by the GSFC electron spectrometer experiment on the ISEE-1 satellite, is used as the initial plasma state for a numerical integration of the 1D-Vlasov-Maxwell system of equations. The integration is carried through the growth of the instability, beyond its saturation, and well into the stabilized plasma regime. A power spectrum computed for the electric field of the stabilized plasma is dominated by a narrow peak at the Bohm-Gross frequency of the unstable field mode but also contains significant power at the harmonics of the Bohm-Gross frequency. The harmonic power is in sharp peaks which are split into closely spaced doublets. The fundamental peak at the Bohm-Gross frequency is split into a closely spaced triplet. The mechanism for excitation of the second harmonic is shown to be second order wave-wave coupling. Previously announced in STAR as N83-17315

Direct determination of gravitational harmonics from low‐low GRAVSAT data

Abstract: An efficient method is developed to compute gravitational harmonics from low-low satellite-satellite range rate measurements. The satellites are assumed to be in nearly the same low eccentricity orbits. The residual range rate signal is modeled with frequencies derived from linear perturbation theory to an accuracy of about 99%. Significant nonlinear effects involving J2, not currently modeled, require both J2 and J3 to be known in the reference trajectories. Each harmonic (l, m) generates l+ 1 principal frequencies, but they are not unique. Yet it appears possible to design a low-altitude mission which keeps the pair at nearly constant separation and where the frequencies for all terms to (180,180) are separable after only about 4 weeks. A simple demonstration of the method is shown to recover (in two iterations) a complete (4,4) model (less J2 and J3) from 1 day of “perfect” measurements (every 7 min) generated by numerical integration. In this result, the effects of orbit determination are included in a crude way, but no other gravitational effects (of higher degree or from luni-solar attraction) are present. Nevertheless, the method is easily extended to high degree with rapid new techniques (which are described) for calculating the required inclination functions of the orbits.

Determination of Synchronous Machine Electrical Characteristics by Test

Abstract: A method of obtaining synchronous machine d and q axis impedances by test as function of frequency of d, q components is presented. The test involves running the machine at reduced speeds, with a line-to-line short circuit between phases, and temporarily applying excitation to produce line-to-line short circuit current at fundamental frequency corresponding to the particular running speed. Records of line-to-line voltages and short circuit current, along with measurement of rotor angle, are processed to yield d and q components of voltages, currents and flux linkages which turn out to be periodic functions of the fundamental frequency plus harmonics. Straight forward Fourier analysis yields the complex values of operational inductances or impedances L d (j2?), L q (j2?), Z d (j2?) or Z g (j2?) where ?is equal to the speed of the machine at which the tests are conducted.

Laboratory EXAFS spectrometer with a bent crystal, a solid‐state detector, and a fast detection system

Abstract: A laboratory x‐ray absorption spectrometer is described which consists of a Johansson‐cut bent crystal, a rotating anode x‐ray generator, and a fast SSD (solid‐state detector). Because the SSD can completely discriminate the undesired reflections, contamination of the harmonics is avoided while maintaining a high‐source voltage necessary for strong x‐ray flux. Fast electronics equipment is employed to keep up with high‐x‐ray intensity. It is also possible to utilize higher‐order reflections for high resolving power. The data of quality comparable to those obtained at synchrotron radiation facilities can be obtained in a comparable period of time. In addition, the determination of the absolute absorbance as defined is possible, which makes the problem of the background subtraction in EXAFS analysis easy.

Sources of shape variation in lunar impact craters: Fourier shape analysis

Abstract: R-mode factor analysis of Fourier harmonics that describe the shape-in-plan-view of 716 large (diameter > 15 km) nearside lunar craters shows that two factors explain 84.3% of shape variance observed in the sample. Factor I accounts for 68.2% of the sample variance and describes moderate-scale roughness defined by harmonics 7 through 10. Shape variation described by these harmonics is related to surficial lunar processes of degradation that modify crater shape-in-plan. Dominant among these processes are ejecta scour from large impact events and ongoing aging. Factor II accounts for 16.1% of the observed shape variance and describes polygonal shape elements related to harmonics 2, 3, 4, and 6. Variation in these harmonics is tied to variables that distort the spherical symmetry of crater-forming processes. The dominant contributor among these variables is the nature of geologic structural patterns in impacted material. Unlike transient features described by factor I, polygonal shape elements described by factor II do not change appreciably with time. The permanence of these features and their relation to lunar geologic structure suggest that the shape of old craters carries the imprint of geologic structural relationships present in early lunar crust.

Line Harmonics of Converters with DC-Motor Loads

Abstract: The line current and voltage harmonics generated by thyristor dc-motor drives, in particular with 3-phase 6-pulse dc converters, are analyzed. As industry continues to raise the power level of the converters, it is becoming more and more important to find techniques for calculating the current and voltage harmonics that avoid making the often unrealistic assumptions of the procedures used in the past. Yet these techniques must maintain, in as simple a form as possible, all the necessary curves and expressions for predicting them under the required conditions. A more accurate model of the line- current waveform is analyzed allowing for both the overlap angle and dc-current ripple, and the results are presented as a convenient set of graphs and also as a set of mathematical expressions for use on a programmable calculator. The calculated current harmonics are then used to derive the corresponding voltage harmonics toegther with their phase relationship. These voltage harmonics are then reconstructed into the relevant voltage waveform on a plotter.

An Exact Input Current Analysis of Ideal Static PWM Inverters

Abstract: The precise knowledge of current harmonics generated at the input of static pulsewidth modulated (PWM) inverters is essential in designing the input filter and in determining the interaction between the inverter and supply voltage bus. Despite its importance, however, this topic has been given mostly qualitative treatment. A novel harmonic analysis approach is employed with ideal static voltage source inverters to specify the harmonic spectra of their respective input currents. This information is subsequently used to compute the harmonic distortion of the input current and the ripple current for the input filter capacitor.

Microwave generation from rotating electron beams in magnetron‐type waveguides

Abstract: The production of high power microwave radiation at high harmonics of the electron cyclotron frequency by the interaction of a rotating electron beam with a magnetron‐type conducting boundary has been studied theoretically and experimentally using a 2‐MeV, 1–2‐kA, 10‐ns electron beam pulse. Approximately 10% of the electron beam power has been converted to microwave radiation at the 12th harmonic, and about 2% at the 20th harmonic. Radiation characteristics are in good agreement with a theoretical analysis of the resonant interaction of a beam mode with the modes of the conducting boundary system. Radiation from rotating beams in ‘‘glide‐symmetric’’ boundary systems is also reported.

Theory of quasioptical gyrotrons and gyroklystrons operating at higher harmonics of the cyclotron frequency

Abstract: A multimode, non-linear, time-dependent formulation of the theory of quasioptical electron cyclotron masers operating at high gyrofrequency harmonics is presented Linear calculations of the starting current and numerical analyses of the efficiency of the devices are performed It is shown that with suitable contouring of the DC magnetic field, a stable single mode operation at the second harmonic is possible To improve the efficiency, an alternative configuration, the quasioptical gyroklystron, is also analysed using single mode and multimode dynamics simulations The gyroklystron operating at the second harmonic is shown to lead to a significant increase in efficiency (approximately 30%)