Showing papers on "Harmonic 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.

An AC-to-DC Converter with High Quality Input Waveforms

Abstract: An ac-to-dc converter which draws sinusoidal and inphase current waveforms from the ac power source is described. Harmonic and power factor measurements obtained from a field- effect transistor (FET) converter operating at 45 kHz for a single- phase and a three-phase connection are presented. A stability analysis and design methodology are given.

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.

Periodic response of a sliding oscillator system to harmonic excitation

Abstract: SUMMARY This paper deals with the periodic response of an oscillating system which is supported on a frictional interface. The base excitation is assumed harmonic and the frictional force is assumed to be of the Coulomb type. Though each segment of the motion of such a system is described by linear equations, its complete response is highly non-linear and varied. The most fundamental periodic solutions are derived analytically and numerically. The results indicate that such a system has several subharmonic resonant frequencies and that while the friction reduces the peak response of the system when it is excited at its ‘fixed-base’ natural frequency, w,, the sliding can induce considerably higher levels of response, when compared with those of a non-sliding, fixed-base system, for frequencies less than w,. The results obtained herein may find application in the area of vibration isolation.

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.

Forced Nonlinear Oscillations of an Autoparametric System—Part 1: Periodic Responses

Abstract: Forced oscillations of a two degree-of-freedom autoparametric system are studied with moderately high excitations. The approximate results obtained by the method of harmonic balance are found to be satisfactory by comparing with those obtained by numerical integration. In the primary parametric instability zone, separate regions of stable and unstable harmonic solutions are obtained. In the regions of unstable harmonic solutions, depending on the forcing amplitude and frequency, the solutions may be amplitude modulated or completely nonperiodic. In the latter case the numerical integrations do not converge.

Distortion of finite amplitude ultrasound in lossy media

Abstract: A form of Burgers’ equation is used to derive an algorithm for calculating harmonic generation by a continuous plane wave of ultrasound propagating in a nonlinear, lossy, nondispersive medium. The algorithm accounts for attenuation that is not quadratically related to the frequency of the wave. Attenuation strongly affects the rate of harmonic production. The effect of variations of the relationship between attenuation and frequency is shown. Biological tissue is an example of a highly lossy medium where the attenuation does not increase with the square of the frequency. Calculations for several types of tissue and biological fluids are presented that show, for certain conditions, finite amplitude distortion is possible.

Optical Second-Harmonic Generation with Long-Range Surface Plasmons

Abstract: The first observation of enhanced optical second-harmonic generation due to excitation of the long-range surface plasmon is reported. When the fundamental mode of this plasmon is excited on both surfaces of a thin silver film bounded by a nonlinear quartz crystal and an index-matched liquid, the harmonic generation is over 2 orders of magnitude larger than that due to a single-boundary surface plasmon. Nonlinear excitation of the harmonic long-range surface-plasmon mode is also observed.

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.

Theoretical contribution to the design of millimeter-wave TEO's

Abstract: Systematic simulations of GaAs millimeter-wave transferred-electron devices have been performed, using a realistic model taking into account spatial nonuniformity as well as relaxation effects. Operating temperature is also considered. These simulations indicate the possibility of a fundamental accumulation layer transit mode up to 100 GHz, with higher conversion efficiency than that obtained with a harmonic mode. Significant improvement in output power is expected from InP fundamental oscillators in the upper part of the millimeter band.

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.

Field of a finite‐amplitude focusing source

Abstract: An analytical description for the field of a harmonic focusing source is derived. It is valid for spherically concave sources with small aperture angle and high ka, under conditions of quasilinear distortion (strong shocks precluded). The solution furnishes access to the phase and amplitude of second harmonic sound. Underwater experiments conducted with an f/2 lens coupled to a low‐density source array are discussed. The results support the utility and validity of the analytical model for describing the amplitude and phase distribution of the second harmonic along the acoustic axis. It is shown that phase shifting in the focal region differs from that of linear radiations, and that both nonlinear propagation and diffractive effects are important in determining phase properties.

Operation of a millimeter-wave harmonic gyrotron

Abstract: The operation of a millimeter-wave harmonic gyrotron is described in which the interaction is between large-orbit axis-encircling electrons and cylindrical cavity TEnll modes. Efficiencies up to 15% have been measured for moderate harmonic interactions and multi-kW power levels have been attained at the tenth harmonic of the cyclotron frequency. The concept allows the magnetic field of the gyrotron to be reduced by an order of magnitude, thereby making a submillimeter-wave gyrotron feasible.

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.

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%)

Method and apparatus for selective cancellation of subsynchronous resonance

Abstract: Apparatus and process for the selective cancellation of harmonic frequencies of current produced in a multiphase dynamic stabilizer. A plurality of multiphase dynamic stabilizers providing electrical stabilization are interconnected to a multiphase AC electrical network via a coupling transformer. The leakage reactances and turns ratios of the windings of the transformer are such that the phases of selected harmonic frequencies of current produced in each of the stabilizer means are rotated with respect to those of the other stabilizer means with the selected harmonic frequencies being substantially cancelled in each of the stabilizer means. The harmonics are not the cause of subsynchronous resonance. The cancelled harmonic frequencies are dependent upon the number of dynamic stabilizers used. Where a dual stabilizer system is utilized, the coupling transformer is forked wye transformer having the primary windings connected in delta with the principal secondary windings connected in wye and each principal secondary winding having two auxiliary secondary windings connected thereto. By forming the auxiliary secondary windings such that the ratio of the number of turns therein with respect to the principal secondary winding is about the ##EQU1## and the leakage reactance of the principal secondary winding being equal to about twice the common leakage reactance of the auxiliary secondary windings, the phases of the harmonic currents produced in each stabilizer rotates by approximately 30 electrical degrees with respect to one another leading to the substantial cancellation of harmonic currents of each stabilizer characterized by the series 5, 7, 17, 19 . . . n, p where n=5+z; p=7+z; and z=multiples of 12. Addition of shunt capacitors across each of the primary windings creates a static VAR generator having the same harmonic current cancellation attribute.

Fiber optic rotation sensor with extended dynamic range

Abstract: A fiber optic rotation sensor, employing the Sagnac effect comprising all fiber optic components positioned along a continuous, uninterrupted strand of fiber optic material. The rotation sensor includes a detection system utilizing a modulator or modulators for phase modulating at first and second harmonic frequencies light waves which counter-propagate through a loop formed in the fiber optic strand. Each modulator is operated at a specific frequency to eliminate amplitude modulation in the detected optical output signal. A phase sensitive detector generates a feedback error signal proportional to the magnitude of the first harmonic in the output optical signal. The feedback error signal controls a modulator which controls the amplitude of the second harmonic driving signal for the second harmonic phase modulator such that the first harmonic component in the output signal from the rotation sensor is cancelled or held within a small range of amplitudes.

Three-dimensional theory of waveguide-plasma coupling

Abstract: A general, linear theory of coupling electromagnetic fields from free-space waveguide arrays to an inhomogeneous plasma in a magnetic field is presented. In contrast to previous analyses, which assumed parallel-plate waveguides, waveguides having closed cross-sections of arbitrary shape are considered; full account is taken of all the waveguide modes. Far away from the coupling region, the plasma is assumed to be absorptive and the waveguides to propagate only their dominant modes. The formulation is geared to obtain the reflection coefficients in the waveguides and the excitation of waves in the plasma. The results are applicable to RF heating of plasmas whose size is large compared to the waveguide array, as would be the case in a fusion reactor, and valid for the frequency regimes of either ion-cyclotron (harmonic), or lower-hybrid, or electron-cyclotron (harmonic) heating.

Response Of Fiber Gyros To Signals Introduced At The Second Harmonic Of The Bias Modulation Frequency

Abstract: A technique that can be used for the closed-loop operation of dynamically biased optical fiber gyroscopes is discussed. The source wavelength dependence of the scale factor is considerably suppressed and the dynamic range of this system is limited only by that of the phase modulator used. Preliminary experimental results using an all-fiber gyroscope are compared with theoretical predictions.

Statistical performance of the circular harmonic filter for rotation-invariant pattern recognition.

Abstract: Circular harmonic filters of different orders are compared using a criterion of separability between the target and object output probability densities. A holographic computer-generated circular harmonic filter was used to recognize aircraft from an air photograph.