Showing papers on "Harmonic published in 1990"

A new multilevel PWM method: a theoretical analysis

Abstract: A generalization of the PWM (pulse width modulation) subharmonic method for controlling single-phase or three-phase multilevel voltage source inverters (VSIs) is considered. Three multilevel PWM techniques for VSI inverters are presented. An analytical expression of the spectral components of the output waveforms covering all the operating conditions is derived. The analysis is based on an extension of Bennet's method. The improvements in harmonic spectrum are pointed out, and several examples are presented which prove the validity of the multilevel modulation. Improvements in the harmonic contents were achieved due to the increased number of levels. >

Pitch identification and discrimination for complex tones with many harmonics

Abstract: Four experiments are reported that deal with pitch perception of harmonic complex tones containing up to 11 successive harmonics. In particular, the question is raised whether the pitch percept of the missing fundamental is mediated only by low‐order resolvable harmonics, or whether it can also be conveyed by high‐order harmonics that the cochlea fails to resolve. Melodic interval identification performance was found to remain significantly above chance level even if the range of harmonics extended from the 20th to the 30th. Just‐noticeable differences (jnd) in the pitch of the missing fundamental were found to increase with increasing harmonic order, but to level off when all harmonics are above the 12th. These results are consistent with the notion of the existence of two distinct neural pitch mechanisms in the auditory system, but are, in principle, also compatible with a single central‐spectrum mechanism that uses the interspike interval histograms of auditory‐nerve fibers as inputs.

Active and reactive power control for doubly-fed wound rotor induction generator

Abstract: A power control system for a doubly fed wound rotor induction generator has been developed. This power control system applies a control method using a rotating reference frame fixed on the gap flux of the generator, and can control active and reactive power independently and stably. The characteristics of the control system have been proved by experiment. Harmonic currents fed to the rotor windings are transmitted to the stator winding changing its frequency. The transmitting characteristics of the harmonic currents have been analyzed and verified by experiments. >

Powers in nonsinusoidal situations-a review of definitions and physical meaning

Abstract: The author expands on the physical meaning of the reactive power in nonsinusoidal situations. The sinusoidal waveform case is surveyed, viewing the active current as a component of identical waveform with the voltage. This approach, when extended to nonsinusoidal waveforms, supports Fryze's model for apparent power, S/sup 2/=p/sup 2/+Q/sup 2//sub F/. It is proved that the total reactive power Q/sub F/ is composed from four distinctive types of elementary reactive powers. Each of the basic reactive powers is identified as the amplitude of an oscillation of instantaneous power. The separation of Q/sub F/ in Q/sub 1/, the reactive power at the system frequency, and in Q/sub H/, the reactive power at harmonic frequencies, is recommended as an effective mean for monitoring filter efficacy and power-factor compensation. Two major recommendations are supported by the results of this study: abolish the power model using distortion power, and measure the active power of the system frequency separately from the active power of the harmonics. >

A novel PWM scheme of voltage source inverters based on space vector theory

Abstract: A novel PWM scheme which can considerably reduce harmonic currents is proposed. It is explained analytically that the harmonic currents depend on the amplitude and phase angle of the reference voltage vector, the inverter output voltage vectors used in a switching period, and the sequence of these output voltage vectors. In the novel PWM scheme, the switching sequence is selected so that the harmonic currents are minimum. An experimental system which generates the PWM patterns by software at real time is constructed. Compared with the conventional sinusoidal PWM scheme, it is confirmed that the current ripple is decreased and the spectrum is shifted and dispersed to a higher frequency region.

Realization of a new concept for visible frequency division : phase locking of harmonic and sum frequencies

Abstract: We explore and demonstrate the feasibility of an optical-frequency-to-radio-frequency division method that is based on visible or near-infrared laser oscillators only. Comparing harmonic and sum frequencies, we generate the arithmetic average of two visible frequencies. Cascading n stages provides difference-frequency division by 2(n). For a demonstration we have phase locked the second harmonic and the sum frequency of two independent diode lasers.

Analysis of high-impedance fault generated signals using a Kalman filtering approach

Abstract: High-impedance faults are accompanied by variations in the 60 Hz and harmonic components. An approach that accounts for the time-varying nature of the fundamental and harmonic components is developed. This approach is based on Kalman-filtering theory to obtain the best estimation of the time variations of the fundamental and harmonic components. Four actual recorded data sets for staged arcing fault on different types of soil are investigated by the proposed Kalman-filtering technique. The time variations of fundamental and low-order harmonic components significantly contribute to high-impedance fault detection using the features presented. >

Hearing a mistuned harmonic in an otherwise periodic complex tone

Abstract: The ability of a listener to detect a mistuned harmonic in an otherwise periodic tone is representative of the capacity to segregate auditory entities on the basis of steady‐state signal cues. By use of a task in which listeners matched the pitch of a mistuned harmonic, this ability has been studied, in order to find dependences on mistuned harmonic number, fundamental frequency, signal level, and signal duration. The results considerably augment the data previously obtained from discrimination experiments and from experiments in which listeners counted apparent sources. Although previous work has emphasized the role of spectral resolution in the segregation process, the present work suggests that neural synchrony is an important consideration; our data show that listeners lose the ability to segregate mistuned harmonics at high frequencies where synchronous neural firing vanishes. The functional form of this loss is insensitive to the spacing of the harmonics. The matching experiment also permits the measurement of the pitches of mistuned harmonics. The data exhibit shifts of a form that argues against models of pitch shifts that are based entirely upon partial masking.

Phase‐matched second‐harmonic generation in a polymer waveguide

Abstract: Quasi‐phase‐matched second‐harmonic generation has been observed in a periodically poled nonlinear optical polymer waveguide. Key elements in this demonstration include novel nonlinear optical polymers that can be spin coated, the design and fabrication of periodic electrodes for periodic poling and the optimization of waveguide parameters to obtain single‐mode waveguides with a large overlap between fundamental and harmonic modes. Phase matching of the d33 nonlinear optical coefficient occurs over a distance L=230 μm.

Harmonic source monitoring and identification using neural networks

Abstract: Neural networks are applied to make initial estimates of harmonic sources in a power system with nonlinear loads The initial estimates are then used as pseudomeasurements for harmonic state estimation, which further improves the measurements This approach permits measurement of harmonics with relatively few permanent harmonic measuring instruments Simulation tests show that the trained neural networks are able to produce acceptable estimates for varying harmonic sources and that the state estimator will generally pull these estimates closer to the correct values The process successfully identified and monitored a suspected harmonic source that had not previously been measured >

A novel passive waveshaping method for single-phase diode rectifiers

Abstract: A novel passive waveshaping method for single-phase diode rectifiers is presented. It is shown that application of the proposed method maintains high-input power factor, lowers rectifier current stresses, and lowers the volt-ampere (VA) rating of the associated reactive components as compared to the standard diode rectifier. Relevant input and output current waveforms, component ratings, and power factor values are derived. Different modes of operation are discussed as a means of obtaining high performance. Key predictions, such as input/output waveforms and associated harmonic spectra, have been verified experimentally on a 1 kVA laboratory prototype unit. >

Optical transmitters linearized by means of parametric feedback

Abstract: The invention discloses a general technique of taking advantage of the stability of the modulator transfer characteristic in order to correct for second and third order distortion. These objectives are achieved in a way compatible with the nature of the video distribution frequency formats. The method of this invention for linearizing the amplitude transfer characteristic of integrated optic devices for analog transmission is accomplished by injecting pilot signals, monitoring the harmonic and intermodulation distortion content of the optical output, and feeding back bias signals to parametrically tune the operating points of the integrated optic modulator and of a predistortion network. General principles for realizing suitable parametrically tunable predistortion networks are also presented.

Powers in nonsinusoidal networks: their interpretation, analysis, and measurement

Abstract: A nonlinear or periodically time-variant load sometimes has to be considered not as the receiver, but as the source of energy, at least for some harmonic frequencies. This can be explained in terms of its equivalent circuit, usually composed of passive elements and harmonic sources which make the power phenomena in such a circuit much more complex than in a linear circuit. The necessity of comprehension of these phenomena stems from the fact that they determine the efficiency of the power transmission and the possibility of power factor improvement. They also affect the energy accounts. A method is suggested for the apparent power decomposition into components related to current components of distinctively different physical interpretation. A digital analyzer for measuring these powers is described. >

Frequency analysis of the peripheral pulse wave detected in the finger with a photoplethysmograph

Abstract: A photoelectric plethysmograph that performs a frequency analysis of the peripheral volume pulse wave using a portable computer is described. It was used to determine how the pulse shape varied with age using 54 subjects in three age groups: 10-29, 30-59, and 60-89 years. The youngest group had a larger power in the second harmonic (normalized to the fundamental), with p >

Communications Frequency Analysis of the Peripheral Pulse Wave Detected in the Finger with a Photoplethysmograph

Abstract: A photoelectric plethysmograph is described that per- forms a frequency analysis of the peripheral volume pulse wave using a portable computer. It was used to determine how the pulse shape varied with age using 54 subjects in three age groups, 10-29, 30-59, and 60-89 years. The youngest group had a larger power in the second harmonic, (normalized to the fundamental), with p < 0.05 than the older two groups. The decrease of power in the harmonics of the pe- ripheral pulse wave with age may be a useful noninvasive measure of aging and vascular disease.

Higher-harmonic production in a model atom with short-range potential

Abstract: Production of higher harmonics in a model atom described by a three-dimensional \ensuremath{\delta}-function potential in the presence of a monochromatic linearly polarized field is investigated. The rates for production of the individual harmonics can be expressed as one-dimensional integrals. The only property of the atom that enters the model is its ionization energy. The results are in qualitative agreement with many of the data. In particular, the model exhibits a ``rising plateau.''

Microprocessor based harmonic elimination in chopper type AC voltage regulators

Abstract: A control strategy for firing instances in pulse-width-modulated (PWM) AC voltage regulators is presented. In this type of regulator, output voltage is controlled by varying the on/off time ratios of a series-controlled switch. Using a microprocessor as a controller makes it possible to vary firing instances at will according to a predetermined timing regime. One of these regimes, proposed here, involves adjusting firing instances so that selected dominant lower-order harmonics can be eliminated. This in turn leads to improved system power factor and efficiency. The theoretical principles used in evaluating firing instances are described, and experimental results verifying the analysis are presented. >

Friction and wear in microfabricated harmonic side-drive motors

Abstract: Polysilicon variable-capacitance rotary harmonic side-drive micromotors and results from operational and frictional studies of these motors are described Quantitative studies of wear under electric excitation are also reported Voltages as low as 26 V across 15- mu m gaps are sufficient for operation Frictional force estimates of 015 mu N at the bushings and 004 mu N in the bearings are obtained from measurements of stopping voltages Extended operation of these motors to near 100 million wobble cycles at excitation frequencies of 10000 rpm and 25000 rpm for operational durations of 150 h and 71 h, respectively, are studied The results indicate that bearing wear is significant and results in changes in the gear ratio of the motors by as much as 20% Typical gear ratios are near 90 at the start of motor operation and decrease to about 70 as the bearings wear out >

Propagation effects in high-order harmonic generation in rare gases

Abstract: We study the role of propagation effects in high-order harmonic-generation experiments. The phase-matching integrals are calculated in the weak-field limit by taking into account the dispersion of the rare-gas medium at each harmonic frequency and the absorption of the harmonics. The refractive indices of the rare gases are deduced from a calculation of the dynamic polarizabilities within the framework of many-body perturbation theory and the random phase approximation. We also study the influence of the ionization of the gaseous medium and the presence of free electrons on the harmonic conversion efficiency by numerically integrating the propagation equation. These results are compared with experimental data.

Efficient conversion of picosecond laser pulses into second-harmonic frequency using group-velocity dispersion

Abstract: A computer model has been used to investigate frequency doubling of 1-psec duration high-power pulses in potassium dihydrogen phosphate (KDP) for type-II phase matching. It has been found that group-velocity dispersion can be used to advantage by predelaying the ordinary and extraordinary polarizations appropriately in a thin KDP crystal with its axes aligned at 90\ifmmode^\circ\else\textdegree\fi{} to the main conversion crystal. In that situation power conversion g100% from the fundamental to the second harmonic can be obtained with simultaneous ``compression'' of the output pulse duration by up to a factor of 5.

Inelastic neutron scattering analysis of low-frequency motions in proteins : harmonic and damped harmonic models of bovine pancreatic tryspin inhibitor

Abstract: Inelastic neutron scattering spectra are calculated from harmonic and damped harmonic models of the internal dynamics of a small protein, the bovine pancreatic trypsin inhibitor (BPTI). Numerical Fourier transformation of the intermediate scattering function Fvibinc (q, t) is used to calculate the inelastic scattering. This permits the inclusion of multiphonon scattering and frictional damping effects. Although for a typical experimental configuration, the multiphonon contribution does not significantly alter the form of the scattering at frequencies below about 30 cm−1, it does have a significant effect on the scattering intensity at higher frequencies. Frictional damping is introduced into the harmonic model by assuming that each mode acts as an independent damped Langevin oscillator. With this model and the assumption that the lowest frequency modes are overdamped while the higher frequency modes are underdamped, improved agreement with the experimental BPTI powder results is obtained. The measured sca...

Nonlinear adaptive torque-ripple cancellation for step motors

Abstract: The modeling of torque-ripple in hybrid step motors and its cancellation using adaptive linearization control are discussed. Although the nonlinear adaptive control of this problem can fit into a general framework, a representation of the torque-ripple which reduces the number of adapted parameters per torque-ripple harmonic by half is used. By doing so, it is possible to prove conditions on exogenous signals to guarantee the persistency of excitation of the regressor, and hence the exponential stability of the unperturbed system. It is shown that the adaptive system is robust to a class of state- and parameter-dependent modeling errors and disturbances even when the adaptation gain and convergence rate of the unperturbed system become small. The adapted parameter errors are proved to converge to a neighborhood of zero whose radius can be made small by slow adaptation. The proposed control scheme is verified in an experiment in which a 32-dB reduction in torque-ripple component at the rotor pole frequency is observed. >

Phase and group velocity matching for second harmonic generation of femtosecond pulses.

Abstract: We theoretically analyze a method for matching group velocities of fundamental and second harmonic femtosecond pulses during phase matched frequncy doubling by predispersing the fundamental pulse with a prism. The method permits improved conversion efficiency by allowing crystal lengths of several millimeters without sacrificing second harmonic pulse duration. Second harmonic pulse energy and duration are analyzed for beta-BaB(2)O(4), and limiting experimental factors are discussed. The results show that the method is most advantageous for incident pulses between 0.1- and 1.0-ps duration and microjoule and higher energies and that second harmonic pulse duration and conversion efficiency are not highly sensitive to optical misalignments of the order of 1 degrees .

Reduced harmonics PWM controlled line-side converter for electric drives

Abstract: A reduced-harmonics pulse-width modulator and its application to the control of a three-level line-side power converter for a speed-variable AC drive are described. The pulse-width modulation scheme for the voltage source inverter determines each individual switching instant on the basis of a continuously updated volt-second balance between the reference vector and the actual switching state vector. The generated pulse sequence is shown to be asynchronous. The Fourier spectra are characterized by the absence of high-amplitude discrete carrier components. The emission of acoustic noise radiated from magnetic components is reduced. Experimental results have been obtained from a transistor converter operated from the 660 V industrial power supply. The DC-link voltage is 1200 V. With appropriate simplifications, the method is suitable for the control of two-level inverters as well. >

Compensating for dead time degradation of PWM inverter waveforms

Abstract: The output voltage waveforms of a bridge inverter using some form of modulation strategy, such as pulse width modulation (PWM), are not the same as the ideal modulated waveforms because of the effect of ‘dead time’. This is the short period of time that is allowed to elapse for safety reasons between switching one device in an inverter leg off and the other device on. It has been found that the dead time causes a reduction in the fundamental component of the output voltage and introduces low order harmonics which are not intrinsically present in the ideal modulated waveforms.In variable speed drive systems the reduction in fundamental voltage causes a reduction in the torque. Furthermore, with synchronous modulation strategies there is a step change in torque when a ‘gear change’ takes place. In uninterruptible power supply (UPS) systems the low order harmonics are difficult to remove, with the result that the fundamental output voltage is contaminated.Methods of compensating for dead time are proposed and investigated and it is shown that its effects can be substantially eliminated. Tests with a compensated variable speed drive, using an inverter fed induction motor, demonstrate that the torque perturbations at a gear change are now negligible. Similarly, in a UPS application the low order harmonics are found to be removed from the filtered output voltage when dead time compensation is introduced.

Method and apparatus for tracing conductors using an alternating signal having two components related in frequency and phase

Abstract: A system for tracing routes of conductors is disclosed. An alternating signal is applied to the object to be traced (12), and the field produced by this signal is detected remotely from the object. In order to distinguish between signals produced by the object being traced and those produced by nearby conductors (14) due to capacitive coupling, the alternating signal has first and second components, related in frequency and phase, and the field is detected at a plurality of positions. The phase relationship of the detected signals is investigated to determine unambiguously the position of the object concerned. In one embodiment, the second frequency component is a harmonic of the other. In another embodiment the frequency of the second component is the frequency of the first, plus or minus a sub-harmonic of the first.