Showing papers on "Harmonic published in 1991"

The analysis and compensation of dead-time effects in PWM inverters

Abstract: The quantitative prediction of the dead-time effect in pulse width modulated (PWM) inverters is addressed. Through analysis and simulation it is shown that the effect results in a decrease of the fundamental component and an increase in the low-order harmonics in the output voltage of the inverter. To compensate the effect, two simple methods, which are adequate for sinusoidal PWM and memory-based PWM, respectively, are presented. Experimental results show the validity of the analysis and the usefulness of the compensation methods. >

Analysis of an ac-to-dc Voltage Source Converter Using PWM with Phase

Abstract: This paper presents a comprehensive analysis of a pulse- width modulated (PWM) ac-to-dc voltage source converter under phase and amplitude control. A general mathematical model of the converter, which is discontinuous, time-variant, and nonlinear, is first established. To obtain closed-form solutions, the following three techniques are used: Fourier analysis, transformation of reference frame, and small signal linearization. Three models, namely, a steady-state dc model, a low-frequency small-signal ac model, and a high-frequency model, are consequently developed. Finally, three solution sets, namely, the steady-state solution, various dynamic transfer functions, and the high- frequency harmonic components, are obtained from the three models. The theoretical results are verified experimentally.

Theoretical aspects of intense field harmonic generation

Abstract: The authors present theoretical studies of high-order harmonic generation in a rare-gas medium. The experimental results obtained at Saclay with a 1064 nm Nd-YAG laser in the 1013 W cm-2 intensity range are summarized. The harmonic emission strengths, first decrease rather steeply for the first orders, then form a long plateau up to the 21st harmonic in xenon, or up to the 33rd harmonic in argon, before decreasing again rather abruptly. The theoretical description of these experiments consists first in the calculation of the photoemission spectra emitted by a single atom. The spectra are obtained by numerically integrating a time dependent Schrodinger equation for the laser-excited rare-gas atom. Second, one must account for collective effects in the medium, described by Maxwell's equations. A theoretical framework for describing the generation and propagation of harmonics in strong laser fields is developed. An numerical solution of the propagation equations for the harmonic fields in xenon at 1064 nm provides results which agree well with experimental data.

Hvdc Power Transmission Systems: Technology and System Interactions

Abstract: DC Power Transmission Technology Thyristor Valve Analysis of HVDC Converters Converter and HVDC System Control Converter Faults and Protection Smoothing Reactor and DC Line Reactive Power Control Harmonics and Filters Multiterminal DC Systems Component Models for the Analysis of AC/DC Systems Power Flow Analysis in AC/DC Systems Transient Stability Analysis Dynamic Stability and Power Modulation Harmonic and Torsional Interactions Simulation of HVDC Systems Digital Dynamic Simulation of Converters and DC Systems Appendix Index.

Effects of surface magnetism on optical second harmonic generation

Abstract: We report on the first experiments showing the influence of surface magnetization on optical second harmonic generation in reflection at a Fe(110) surface. The magneto-optical Kerr effect modifies the hyperpolarizability of the surface in the optical field, leading to a dependence of the second harmonic yield on the direction of magnetization relative to the light fields. For the clean surface an effect of 25% was determined, which decays exponentially with surface contamination by the residual gas, thus demonstrating the high surface sensitivity of this technique.

A multiphase harmonic load flow solution technique

Abstract: The operation of nonlinear devices under unbalanced load conditions may cause harmonic problems in power systems. A computer-based multiphase harmonic load flow solution technique for analyzing such problems is described. The harmonic load flows are obtained from iterations between the Norton equivalent circuits of the nonlinear elements and the linear network solutions at harmonic frequencies. Harmonics generated by static VAr compensators with thyristor-controlled reactors under unbalanced load conditions are used to illustrate the method. >

Dynamic state estimation of power system harmonics using Kalman filter methodology

Abstract: A Kalman filter is used to obtain the optimal estimate of the power system harmonic content. The measurements are simulated by adding Gaussian noise to the power system voltage and line flows at different harmonies obtained from a harmonic load flow program (HARMFLO). The effect of load variation over a one day cycle on the power system harmonics and standard are presented. The test results on the IEEE 14 bus system are included. The main difference in this approach from static estimation methods is that this method is dynamic and has the capability of tracking harmonic content versus time. >

A new control strategy to improve the performance of a PWM AC to DC converter under unbalanced operating conditions

Abstract: Abnormal harmonics of significant magnitude are generated at the output and input terminals of a PWM (pulse-width-modulated) AC-to-DC power converter under unbalanced operating conditions. A new control strategy is presented to selectively cancel the generated lower-order abnormal harmonics at the output and input terminals and thereby to preserve the high-performance features of a PWM AC-to-DC power converter. The proposed technique essentially involves computing the sequence components of the unbalanced input supply and suitably counter-unbalances the PWM gating signals of the power converter switches to cancel the generated abnormal harmonics. The technique is essentially a feedforward approach and is suitable for higher-power GTO (gate turn-off thyristor) type PWM AC-to-DC power converters. A procedure for implementing this technique in real time is discussed. Selected results are verified experimentally on a prototype PWM AC-to-DC power converter. >

Model for second-harmonic generation in glass optical fibers based on asymmetric photoelectron emission from defect sites.

Abstract: We present a self-consistent calculation of anomalous second-harmonic generation in glass optical fibers. Quantum interference between multiphoton absorption processes leads to asymmetric photoelectric emission from defects, creating a spatially periodic space-charge electric field. The second harmonic is found to grow exponentially along the fiber, then saturate to a maximum value proportional to the square of the fundamental intensity. The predicted conversion efficiency is in reasonable agreement with experiments.

System and method for reducing harmonic currents by current injection

Abstract: A circuit is provided for generating a current that is a harmonic of the frequency of the utility system and which is of a selected amplitude and phase to reduce the total harmonic distortion of a system that converts alternating current to direct current, or vice versa. The DC signal is sampled and by controlling switches, a sinusoidal current at the desired harmonic is generated, and is provided to impedance network that injects this current into the multiphase AC system used by the utility in a very low cost, easily controlled, and highly effective manner. The impedance network comprises a single inductor and capacitance connected in series through each of the phases of the utility, with the current signal having an amplitude that is selected to substantially eliminate harmonics which cause high distortion of the utility signal.

Harmonics from compact fluorescent lamps

Abstract: The measured performance of compact fluorescent lamps (CFLs) and some rectified incandescent lamps, which can cause considerable harmonic distortion of the input power, is discussed. These include both the electronically and magnetically ballasted CFLs with poor power factors and/or high harmonics. Using the model of a building's electrical load, it is shown that there is little cause for concern for power supply quality problems when the CFLs are less than 25% of the building's total load. Several reasonable low-cost passive circuits that can improve the power factor as well as suppress the harmonic distortion are described. The use of active circuits will be more effective but more costly and are best considered for CFLs above 30 W and for special applications where minimum harmonics are required. >

Characteristics of load resonant converters operated in a high power factor mode

Abstract: The performance of the parallel resonant converter and the combination series/parallel resonant converter (LCC converter) when operated above resonance in a high power factor mode are determined and compared for single-phase applications. When the DC voltage applied to the input of these converters is obtained from a single-phase rectifier with a small DC link capacitor, a relatively high power factor inherently results, even with no active control of the input line current. This behaviour is due to the pulsating nature of the DC link and the inherent capability of the converters to boost voltage during the valleys of the input AC wave. With no active control of the input line current, the power factor depends on the ratio of operating frequency to tank resonant frequency. With active control of the input line current, near unity power factor and low input harmonic currents can be obtained. >

A novel control method for forced commutated cycloconverters using instantaneous values of input line-to-line voltages

Abstract: The authors present a novel control method for forced commutated cycloconverters (PWM cycloconverters). Using this control method the sinusoidal input and output current waveforms and the unity input displacement factor can be obtained. Moreover, the compensation of the asymmetrical and/or harmonic contaminated input source voltages is easily realized. This control method allows the input displacement factor not to be controllable, but to be fixed at approximately unity. Since a unity input displacement factor is desirable for motordrive use for the PWM cycloconverters, this constraint is not a new obstacle. Feasibility of the proposed control method is verified by simulations and experiments. >

Effects of nonlinear loads on optimal capacitor placement in radial feeders

Abstract: The nonlinear portion of electrical loads has increased significantly in recent years. Harmonic currents injected by these loads into the distribution system should be considered when solving the capacitor placement problem in order to assure that the optimal solution does not result in excessive harmonic distortion. A voltage-dependent current injection load model is presented to determine voltage waveform characteristics and additional losses at harmonic frequencies. Computer simulations show that the optimal capacitor sizes and locations depend heavily on the load model used at fundamental frequency and on harmonic signals, especially when limits are imposed on voltage waveforms. >

Practical approaches for AC system harmonic impedance measurements

Abstract: AC supply system harmonic impedance measurements are discussed. On the basis of a given and known switchable shunt impedance and/or nonlinear load and site measurements, three methods are presented. The first approach assumes a no-load distorted busbar and uses basic circuit theory to calculate the required harmonic impedance. The second method disregards any previous busbar distortion and the harmonic injection but it takes into account any busbar distortion prior to the nonlinear load connection. Using a laboratory model and by comparing harmonic impedance results it is shown that both no-load busbar distortions and the correct measurement of harmonic phase angles may strongly affect the accuracy of calculation. >

Estimating the frequency of a periodic function

Abstract: SUMMARY The problem of estimating the frequency and other parameters of a cyclical oscillation is considered, where the data consists of a periodic function observed subject to stationary additive noise. An estimation procedure is proposed and the asymptotic properties of the estimators established. Tests for unknown frequencies to be harmonics of a fundamental frequency are also developed and their asymptotic properties investigated. The procedures are applied to observations on the variable star S. Carinae.

Impedance-matched, class F high-frequency amplifier

Abstract: An impedance matched class-F high frequency amplifier includes an input matching circuit receiving high frequency signals connected to the gate of the FET. The drain of the FET is connected to an output matching circuit which matches the fundamental frequency and the second harmonic frequency, and the output of the output matching circuit is connected to an even harmonic terminating circuit. The stray reactance componance at the output impedance of the FET is offset by the output matching circuit, and therefore the even harmonics terminating circuit can more accurately terminate the second harmonic frequencies.

A current source PWM inverter with instantaneous current control capability

Abstract: A new approach for the control of a current source pulse width modulated (PWM) inverter is proposed to achieve instantaneous current control capability. The proposed scheme provides instantaneous current response in the AC motor by altering the modulation index of the current source PWM patterns. In order to achieve this task, optimum programmed PWM patterns with selective elimination of lower order harmonics in the motor line currents are used. Output filter capacitors are provided to bypass the current harmonics in the inverter output and allow for the instantaneous changes in the line currents. This method of control provides sinusoidal output voltages and sinusoidal currents in the AC motor. The proposed scheme guarantees fast response characteristics combined with high-performance steady-state behavior. A design procedure for the current source PWM and selection of programmed PWM current patterns for a variable-speed situation is illustrated. Selected results are verified experimentally. >

A new multiharmonic loading method for large-signal microwave and millimeter-wave transistor characterization

Abstract: A multiharmonic loading method for nonlinear microwave and millimeter-wave transistor characterization using six-port techniques is presented. The system allows independent load tuning of an excitation signal and its harmonics. Load-pull measurements on a MESFET which have been performed at the fundamental frequency f/sub 0/ and at the second (2f/sub 0/) and third (3f/sub 0/) harmonics are discussed. The results highlight the importance of such measurement in designing and modeling nonlinear devices and circuits. The experimental results are found to be directly applicable for optimizing efficiency and output power in high-power MESFET amplifiers and MESFET frequency multipliers. >

Control of Sound Radiation with Adaptive Structures

Abstract: Active control of sound radiation from a vibrating simply supported rec tangular plate excited by a steady state harmonic point force disturbance is experimentally studied A variety of test cases were studied for controlling sound radiation due to a distur bance both on and off structural resonance Control structural inputs are achieved by three piezoceramic actuators bonded to the surface of the plate The control approach is based upon a Filtered-X version of the adaptive LMS algorithm Error information for the con troller was taken from two sensor formats, either microphones placed in the acoustic far- field, or polyvmylidene fluoride (PVDF) piezoelectric distributed sensors bonded to the surface of the structure The two narrow strip PVDF sensors were positioned on the plate such that the dominant observed response was due to the odd-odd and to a lesser degree, the odd-even modes (ie, the more efficient acoustic radiators) Results from these experi ments indicate that piezoceramic elements provi

The computation of second-order wave loads

Abstract: The second-order wave loads which act on an offshore structure include mean, difference-frequency, sum-frequency, and second harmonic components. These are of special importance to vessels with low- or high-frequency resonant features outside the spectral range of wave encounter. Special numerical techniques are required to evaluate the second-order loads. The most difficult component, associated with the boundary condition on the free surface, requires the evaluation of slowly-convergent oscillatory integrals over this surface. Numerical methods are described for evaluating the second-order loads, based on extensions of the first-order panel method and applicable to three-dimensional structures of arbitrary geometric form. Illustrative results are presented for the second-harmonic and sum-frequency diffraction loads on the ISSC TLP, in monochromatic and bi-chromatic waves. Emphasis is given to the solution of the second-order free-surface condition, which is the dominant source of sum-frequency vertical loads.

CMOS OTA-C high-frequency sinusoidal oscillators

Abstract: Several topology families are given to implement practical CMOS sinusoidal oscillators by using operational transconductance amplifier-capacitor (OTA-C) techniques. Design techniques are proposed taking into account the CMOS OTA's dominant nonidealities. Building blocks are presented for amplitude control, both by automatic gain control (AGC) schemes and by limitation schemes. Experimental results from 3- and 2- mu m CMOS (MOSIS) prototypes that exhibit oscillation frequencies of up to 69 MHz are obtained. The amplitudes can be adjusted between 1 V peak to peak and 100 mV peak to peak. Total harmonic distortions from 2.8% down to 0.2% have been measured experimentally. >

A practical protective relay for down-conductor faults

Abstract: A practical relay for detecting down-conductor high-impedance ground faults (HIGF) is described, with supporting theory and data from live line tests. The use of the third-harmonic current magnitude and the phase relation to the system voltage is shown to provide useful information for detecting this type of fault. By suppressing ambient harmonics and utilizing only the change in the harmonics, a fault current sensitivity of 1% of the feeder rating is shown to be feasible. Fault detection concepts include harmonic phase sequence components in the three-phase unit. Relays for both single-phase laterals and three-phase circuits are described. Redundant measurement techniques in both versions are shown to enhance the reliability of the system and to contribute to the feasibility of the noted sensitivity. >

Minimizing the current harmonics RMS value of three-phase PWM converter systems by optimal and suboptimal transition between continuous and discontinuous modulation

Abstract: A given converter voltage space vector can be realized by a three-phase PWM converter system by switching only two bridge legs. There, the third phase is clamped to the positive or negative DC link voltage. This method is called discontinuous modulation, due to the discontinuous shape of the generating phase modulation functions. As a closer analysis shows, the discontinuous method allows an increase in the effective system pulse frequency, dependent on the phase angle between converter output voltage and output current. The basis for a comparison with the continuous method is chosen as equal average switching losses of any converter bridge leg. For harmonic-optimal operation one must change between continuous and discontinuous modulation (or between various variants of the discontinuous modulation), depending on the load status. The harmonic losses of the control methods are calculated directly in the time domain. For this purpose, the space vector calculus is applied and approximations are used which are sufficiently exact for PWM converter systems with high pulse frequency. >

Parametric loudspeaker—characteristics of acoustic field and suitable modulation of carrier ultrasound

Abstract: Due to the inherent nonlinearity of the medium, finite amplitude ultrasound interacts with itself and generates some secondary waves in the sound beam. The parametric loudspeaker, making use of this phenomenon, has a sharp directivity and might be applied to a speech transmission system under the limited environment. In this paper, a numerical analysis method available for high sound pressure levels, where the nonlinear interactions of ultrasound become greatly active, can be used successfully to theoretically design the parametric loudspeaker. It is reported that the numerical computations agree well with the experiments by a circular aperture projector of radius 21 cm and carrier frequency 27 kHz. To develop the parametric loudspeaker for practical uses, the problems on harmonic distortions and the physiological effect on human being must be solved. Based on the theoretical prediction, the reasonable solutions for such problems are considered in accordance with appropriate primary wave modulations.

In search of a linear electrooptic amplitude modulator

Abstract: An electrooptic modulator which offers high linearity and low intermodulation distortion (IMD) is proposed. The modulation characteristics, harmonic and intermodulation distortions, are calculated. In the two-tone test with an optical modulation depth of 16% for each channel, the third-order IMD is expected to be as low as -95 dB. Such a linearized electrooptic modulator used in conjunction with diode-pumped solid-state lasers can be expected to outperform directly modulated injection lasers for CATV transmission systems. >