Showing papers on "Harmonics published in 1997"

Fundamentals of Power Electronics

Abstract: Preface. 1. Introduction. I: Converters in Equilibrium. 2. Principles of Steady State Converter Analysis. 3. Steady-State Equivalent Circuit Modeling, Losses, and Efficiency. 4. Switch Realization. 5. The Discontinuous Conduction Mode. 6. Converter Circuits. II: Converter Dynamics and Control. 7. AC Equivalent Circuit Modeling. 8. Converter Transfer Functions. 9. Controller Design. 10. Input Filter Design. 11. AC and DC Equivalent Circuit Modeling of the Discontinuous Conduction Mode. 12. Current Programmed Control. III: Magnetics. 13. Basic Magnetics Theory. 14. Inductor Design. 15. Transformer Design. IV: Modern Rectifiers and Power System Harmonics. 16. Power and Harmonics in Nonsinusoidal Systems. 17. Line-Commutated Rectifiers. 18. Pulse-Width Modulated Rectifiers. V: Resonant Converters. 19. Resonant Conversion. 20. Soft Switching. Appendices: A. RMS Values of Commonly-Observed Converter Waveforms. B. Simulation of Converters. C. Middlebrook's Extra Element Theorem. D. Magnetics Design Tables. Index.

Quasi-phase-matched third-harmonic generation in a quasi-periodic optical superlattice

Abstract: Quasi-periodic structure can be introduced into nonlinear optical materials such as LiTaO3 crystals. Such structures were used for quasi–phase-matching second-harmonic generation. These materials are now shown to be able to couple second-harmonic generation and sum-frequency generation through quasi–phase-matching. The approach led to a direct third-harmonic generation with high efficiency through a coupled parametric process. The result verifies that high-order harmonics may be generated in a quadric nonlinear medium by a number of quasi–phase-matching processes, and therefore, exhibits a possible important application of quasi-periodic structure materials in nonlinear optics.

Generation of coherent soft x rays at 2.7 nm using high harmonics

Abstract: Ultrafast laser pulses from a Ti:sapphire laser centered at 800nm, with 26fs pulse duration, were used to generate coherent soft-x-ray harmonics, at wavelengths down to 2.7nm (460eV) in He, and 5.2nm (239eV) in Ne. In He, discrete harmonic peaks are observed up to order221, and unresolved harmonic emission is observed up to order297. These wavelengths are well within the {open_quotes}water window{close_quotes} region of x-ray transmission. Our work represents the shortest wavelength coherent light generated to date. The harmonic cutoff from all the noble gases is consistent with analytic theory. {copyright} {ital 1997} {ital The American Physical Society}

Three-phase four-wire shunt active filter control strategies

Abstract: This paper describes a three-phase four-wire shunt active power filter using a conventional three-leg converter, without the need of power supply at DC bus Two approaches have been developed to control the active filter Both control strategies consider harmonics and zero sequence components in the voltage and current simultaneously The first one provides constant power and the second one sinusoidal current to the source, even under unbalanced voltage conditions Simulation results from a complete model of shunt active filter are presented to validate and compare the control strategies

Class-F power amplifiers with maximally flat waveforms

Abstract: Class-F power amplifiers (PA's) employ harmonic-frequency resonators to shape their drain or collector waveforms to improve efficiency. Generally, the output network must present the drain with either an open or short circuit at the harmonic frequencies. At VHF and higher frequencies, the drain capacitance, lead inductance, lead length, and dispersion make implementation of reasonably ideal tuned circuits difficult. However it is possible to control the impedances at a finite number of harmonics. This note first derives the basic relationships among the Fourier coefficients of the waveforms and the performance of the amplifier. Fourier coefficients for maximally flat waveforms are then derived for inclusion of up to the fifth harmonic. Amplifier performance is then tabulated as a function of which harmonics are included in the voltage and current waveforms. Efficiency increases from 50% of class A toward 100% as harmonics are added. Power-output capability increases by up to 27%.

Power system dynamics and stability

Abstract: Power System Components. The Power System in the Steady-State. Electromagnetic Phenomena. Electromechanical Dynamics - Small Disturbances. Electromechanical Dynamics - Large Disturbances. Voltage Stability. Frequency Variations. Stability Enhancement. Advanced Power System Modelling. Power System Model Reduction - Equivalents. Steady-State Stability of Multi-Machine System. Power System Dynamic Simulation. Appendix. References. Index.

Control Strategy and Site Selection of a Shunt Active Filter for Damping of Harmonic Propagation in Power Distribution Systems

Abstract: This paper deals with a shunt active filter which will be installed by an electric utility, putting much emphasis on the control strategy and the best point of installation of the shunt active filter on a feeder in a power distribution system. The objective of the shunt active filter is to damp harmonic propagation, which results from harmonic resonance between many capacitors for power factor improvement and line inductors in the feeder, rather than to minimize voltage distortion throughout the feeder. Harmonic mitigation is a welcome "by-product" of the shunt active filter, which comes from damping of harmonic propagation. This paper concludes that the shunt active filter based on detection of voltage at the point of installation is superior in stability to others, and that the best site selection is not the beginning terminal but the end terminal of the primary line in the feeder. Computer simulation is performed to verify the validity and effectiveness of the shunt active filter by means of an analog circuit simulator, which is characterized by installing it on a feeder of a radial distribution system in a residential area.

Generalized phase-matching conditions for high harmonics: The role of field-gradient forces

Abstract: We present an approach to describe the phase matching of high harmonics emitted by laser driven atoms in a nonperturbative regime, for which the atomic response displays an intrinsic intensity-dependent phase. We show that the traditional phase-matching conditions involving conservation of wave vectors should be modified by taking into account the gradient of this atomic phase. We investigate various focusing geometries and interpret the numerical results of Sali`eres et al. [Phys. Rev. Lett. 74, 3776 (1995)]. Within the framework of the two-step model, we demonstrate that the gradient of the intensity-dependent phase can be considered as the canonical momentum gained by the electron in the continuum due to acceleration by field-gradient forces, including in particular the ponderomotive force.

Finite amplitude distortion-based inhomogeneous pulse echo ultrasonic imaging

Abstract: Ultrasonic pulse echo imaging in inhomogeneous media suffers from significant lateral and contrast resolution losses due to the defocusing effects of the inhomogeneities. The losses in lateral and contrast resolution are associated with increases in the width of the mainbeam and increases in sidelobe levels, respectively. These two forms of resolution loss represent significant hurdles to improving the clinical utility of biomedical ultrasonic imaging. A number of research efforts are currently under way to investigate the defocusing effects of tissue and to consider corrective measures. All of these efforts assume linear propagation, and base the image-formation process on the reception of the transmitted pulse. A novel pulse echo imaging scheme in which the image is formed using the finite amplitude distortion components of the received pulse is considered here. Alternatively, this could be described as image formation using the nonlinearly-generated higher harmonics. In homogeneous beam propagations, it has been established that the sidelobes of nonlinearly-generated higher harmonics are much lower than their linear counterparts. Computations considered here suggest that this relationship also holds for the case of propagations through abdominal wall and breast wall tissue. These computations also suggest that the lateral resolution limits imposed by abdominal wall and breast wall tissue are slightly smaller for nonlinearly-generated second harmonics than for their linear counterparts. The resulting potential of these higher harmonics to improve image resolution is investigated.

Nonlinear propagation applied to the improvement of resolution in diagnostic medical ultrasound

Abstract: Medical B-mode scanners operating under conditions typically encountered during clinical work produce ultrasonic wave fields that undergo nonlinear distortion. In general, the resulting harmonic beams are narrower and have lower sidelobe levels than the fundamental beam, making them ideal for imaging purposes. This work demonstrates the feasibility of nonlinear harmonic imaging in medical scanners using a simple broadband imaging arrangement in water. The ultrasonic system comprises a 2.25-MHz circular transducer with a diameter of 38 mm, a membrane hydrophone, also with a diameter of 38 mm, and a polymer lens with a focal length of 262 mm. These components are arranged coaxially giving an imaging geometry similar to that used in many commercial B-scanners, but with a receiver bandwidth sufficient to record the first four harmonics. A series of continuous wave and pulse-echo measurements are performed on a wire phantom to give 1-D transverse pressure profiles and 2-D B-mode images, respectively. The refle...

Study of the spatial and temporal coherence of high order harmonics

Abstract: We apply the theory of high-order harmonic generation by low-frequency laser fields in the strong field approximation to the study of the spatial and temporal coherence properties of the harmonics. We discuss the role of dynamically induced phases of the atomic polarization in determining the optimal phase matching conditions and angular distributions of harmonics. We demonstrate that the phase matching and the spatial coherence can be controlled by changing the focusing parameters of the fundamental laser beam. Then we present a detailed study of the temporal and spectral properties of harmonics. We discuss how the focusing conditions influence the individual harmonic spectra and time profiles, and how the intensity dependence of the dynamically induced phase leads to a chirp of the harmonic frequency. This phase modulation can be used to control the temporal and spectral properties of the harmonic radiation. Temporally, the harmonic chirped pulse can be recompressed to very small durations. Spectrally, chirping of the fundamental beam may be employed to compensate for the dynamically induced chirp and to control the individual harmonic spectrum. Finally, we discuss the short pulse effects, in particular nonadiabatic phenomena and the possibility of generating attosecond pulses. Comment: Latex file with 37 pages, 25 postscript figures. to appear in Advances in Atomic, Molecular and Optical Physics

An active power filter and unbalanced current compensator

Abstract: This paper presents the synthesis and performance of a shunt active power filter based on the three-phase pulsewidth modulation (PWM) voltage converter connected to the AC mains. Current harmonics and asymmetries caused by nonlinear loads can be compensated. A decoupled system in Park's variables is achieved and so simple controllers with excellent performance can be used. The controllers are implemented directly in the Park's referential. Expressions for the controller's synthesis are derived. Experimental results from a 2 kVA IGBT prototype showing excellent dynamic and steady-state system's performances are presented. The control circuit is implemented with analog and digital electronic circuits. A considerable amount of electronic circuits are needed. The method presented in this paper can also be implemented with a digital signal processor.

Power differential method for discrimination between fault and magnetizing inrush current in transformers

Abstract: To avoid the needless trip by magnetizing inrush current, the second harmonic component is commonly used for the blocking differential relay in power transformers. However, the second harmonic component in fault current is increased by the introduction of underground 500 kV lines. This paper describes a new method to discriminate internal fault from inrush current by the sum of active power flowing into transformers from each terminal. The average power is almost zero for energizing, but an internal fault consumes large power. To check the performance of this method, actual inrush current and voltage waveforms of a 500/154 kV transformer are accurately measured by digital equipment. The usefulness is confirmed by applying the method to the measured inrush and simulated fault data.

High Harmonic Generation from Ultrafast Pump Lasers

Abstract: Using an ultrafast pump pulse affects the spectral and temporal characteristics of high order harmonics in an unexpected and fortuitous way. Calculations of spectra for rare gases using 10100fs, 800nm pulses show that as the pump pulse length decreases the highest harmonics become correspondingly shorter while their conversion efficiencies increase dramatically. Especially significant is that we find these highest harmonics have phase characteristics that allow for the possibility of compression to subfemtosecond time scales. {copyright} {ital 1997} {ital The American Physical Society}

Multi-mode noise analysis of cantilevers for scanning probe microscopy

Abstract: A multi-mode analysis of micro-cantilever dynamics is presented. We derive the power spectral density of the cantilever displacement due to a thermal noise source and predict the cantilevers’s fundamental resonant frequency and higher harmonics. The first mode in the multi-mode model is equivalent to the traditional single-mode model. Experimental results obtained with a silicon nitride cantilever at 300 K are in excellent qualitative agreement with the multi-mode model. The multi-mode model may be used to obtain accurate values of the cantilever properties such as the elastic modulus,effective mass, thickness and moment of inertia.

New 24-pulse diode rectifier systems for utility interface of high-power AC motor drives

Abstract: This paper proposes two new passive 24-pulse diode rectifier systems for utility interface of pulsewidth modulated (PWM) AC motor drives. The first approach employs an extended delta transformer arrangement, which results in near equal leakage inductance in series with each diode rectifier bridge. This promotes equal current sharing and improved performance. A specially tapped interphase transformer is then introduced with two additional diodes to extend the conventional 12-pulse operation to 24-pulse operation from the input current point of view. The proposed system exhibits clean power characteristics with fifth, seventh, eleventh, thirteenth, seventeenth, and nineteenth harmonics eliminated from the utility line currents. The second scheme is a reduced voltampere approach employing autotransformers to obtain 24-pulse operation. The voltampere rating of the polyphase transformer in the second scheme is 0.23P/sub 0/ (PU). Detailed analysis and simulations verify the proposed concept, and experimental results from a 208-V 10-kVA rectifier system are provided.

Advanced pricing in electrical systems. I. Theory

Abstract: This paper sets forth a comprehensive theory for the real-time pricing of electricity that includes selected ancillary services and extends the theory to incorporate constraints on power quality and environment impact that often influence the operation of a power system. This paper is Part I of a two paper set. It sets forth the mathematical development of the extended model for real-time pricing. The formulation is novel in that it combines the dynamic equations for load-frequency control with the static equations of a constrained optimal power flow. Part II derives optimal nodal specific real-time prices for both real and reactive power. The prices derived include additive premia, or opportunity costs, reflecting the effects of voltage regulation, maintenance of generation and transmission reserves, regulation of frequency and tie-line flows, removal and/or control of power harmonics and others.

A statistical method for predicting the net harmonic currents generated by a concentration of electric vehicle battery chargers

Abstract: This paper presents a method for predicting the net harmonic currents produced by a large number of electric vehicle (EV) battery chargers. The problem is stochastically formulated in order to account for randomness in individual charger start-time and battery state-of-charge. The authors introduce a model that allows for partial harmonics cancellation due to diversity in magnitudes and phase angles. A general solution technique is presented along with an example using data from a commercially available EV charger. Their results show that a limiting distribution of 7-10 chargers is adequate for accurately predicting harmonic injection currents using the central limit theorem. They also show that the expected values of net harmonic currents are considerably less than the peak values that would have been realized if the same number of chargers were operated in unison.

High-order harmonic generation in plasmas

Abstract: The phenomenon of harmonic generation by electrons oscillating in high-intensity laser fields is surveyed and assessed as a means of producing short-wavelength radiation. Starting from the seminal early work by Sarachik and Schappert (1970), simple motivatory examples are given of incoherent harmonic generation via nonlinear scattering from single electrons. More recent studies aimed at observing the coherent version of this effect in underdense plasmas are then reviewed and some problems noted in distinguishing these harmonics from those produced via the analogous nonlinear mechanism from bound electrons in rare gases. Finally, the revival of interest in harmonics reflected from overdense plasmas is considered. Short-pulse laser-generated "surface" harmonics appear to offer a very promising, compact, and efficient means of upshifting coherent radiation to sub-10-nm wavelengths.

A method for sensorless on-line vibration monitoring of induction machines

Abstract: This paper proposes a method for sensorless on-line vibration monitoring of induction machines based on the relationship between the current harmonics in the machine and their related vibration harmonics. Initially, the vibration monitoring system records two baseline measurements of current and vibration with the machine operating under normal conditions. The baseline data is then evaluated to determine the critical frequencies to monitor on-line. Once these frequencies are determined, the baseline vibration measurement is simply used to scale the current harmonic signal to an estimated vibration level. Based on theoretical analysis, simulation results, and the experimental results shown here, a linear relationship between the current harmonics and vibration level can be assumed. The results of two experiments on a three-phase 230 V, 10 HP induction motor operating under no load are discussed and show the feasibility of this method for sensorless on-line vibration monitoring.

A unified theory of high-harmonic generation: Application to polarization properties of the harmonics

Abstract: A general framework is given of how to derive expressions for high-harmonic generation in close analogy to the derivation of the Keldysh amplitude for ionization. As in the former, the approximation made consists of neglecting the effect of the binding potential in intermediate states. The approach can be used for arbitrary binding potentials, but is best suited to short-range potentials at high intensities. It is almost exact for a zero-range potential for arbitrary intensity. Various models that have been used before by some of the authors, such as the effective dipole model and the zero-range potential model, emerge as special cases. The relation between the $S$-matrix element for high-harmonic generation and the dipole-moment expectation value is discussed, as well as the relation of both to the dipole-dipole correlation function. An exact functional relationship between high-harmonic generation and the total ionization rate is presented. For the case of an elliptically polarized monochromatic driving field, the polarization properties of the emitted harmonics, viz. their ellipticity and the offset angle of their polarization ellipse, are evaluated for both the zero-range potential model and the effective-dipole model, and compared. The predictions of both models generally agree, there are, however, some qualitative differences for the harmonics around the end of the plateau.

Polarization of high-order harmonics

Abstract: We report measurements and calculations of the polarization state of high-order harmonics generated by a 790-nm Ti:sapphire laser. The problem of completely characterizing the polarization state of a partially polarized radiation in the XUV range is discussed in detail. The comparison between several gases, xenon, argon and neon, and different orders, from the 17th to the 33rd, shows that the rotation angle and ellipticity strongly depends on the position of the harmonic in the spectrum, and in particular, whether it is in the cutoff or in the plateau. In the plateau, the rotation angle is quite large, and the ellipticity follows that of the fundamental, remaining, however, smaller. The radiation is only partially polarized. In contrast, in the cutoff, both rotation angle and ellipticity remain small, independently of the laser ellipticity. Our experimental results compare well with theoretical predictions including the single-atom response and propagation effects.

Minimising rotor losses in high-speed high-power permanent magnet synchronous generators with rectifier load

Abstract: In an early stage of the design of a high-speed 1400 kW synchronous generator with permanent magnet excitation and loaded by a rectifier, it became apparent that rotor losses are a major problem. The stator currents cause asynchronous components in the air-gap field. Analysis shows that a modified polyphase system reduces the number of these components. An approximate solution for the rotor losses caused by the asynchronous field components has been derived. The formulae show the effects of machine dimensions and harmonics and the effect of a conducting shield in the rotor. The main purpose of the study is to have a tool for making an early choice among several stator winding configurations. A modified nine-phase system, combined with a shield around the permanent magnet rotor, is a prospective option.

A new frequency domain arc furnace model for iterative harmonic analysis

Abstract: This paper presents a new frequency domain arc furnace model for iterative harmonic analysis by means of a Newton method. Powerful analytical expressions for harmonic currents and their derivatives are obtained under balanced conditions of the power system. The model offers a three-phase configuration where there is no path for homopolar currents. Moreover, it contemplates continuous and discontinuous evolution of the arc current. The solution obtained is validated by means of time domain simulations. Finally, the model was integrated in a harmonic power flow where studies have been performed in a network with more than 700 busbars and 7 actual arc furnace loads.

Arc fault detection apparatus and circuit breaker incorporating same

Abstract: Arcing-faults in an electric power distribution system are detected by a circuit which includes a band-pass filter generating a low frequency bandwidth limited arcing current signal having a bandwidth above the measurable harmonics of the ac current but below the frequency band of power line communications systems, about 3 KHz to 20 KHz and preferably about 6 KHz to 12 KHz. For each cycle of the ac current that this low frequency bandwidth limited arcing current exceeds a threshold, preferably related to the amplitude of the ac current, for a selected duration of the cycle, a fixed pulse is generated. If a time attenuated accumulation of these fixed pulses reaches a selected level representative of a number of closely spaced cycles in which the arcing current has been detected for the selected duration, an arc indicative signal is output. Preferably, the value of the time attenuated accumulation of pulses at which the arc indicative signal is generated is variable so that fewer pulses are needed to generate the output as the amplitude of the ac current increases.

Designing harmonic filters for adjustable speed drives to comply with IEEE-519 harmonic limits

Abstract: This paper discusses the application of the revised IEEE-519 Harmonics standards to typical industrial facilities employing adjustable speed drives (ASDs). The harmonic generation characteristics of ASDs are described, Requirements for control of the harmonic currents are developed as a function of the ASD characteristics, overall plant loading level, power system characteristics, and power factor correction requirements. Filter design procedures are presented for controlling the harmonic currents injected onto the power system.

Circuit, audio system and method for processing signals, and a harmonics generator

Abstract: A circuit, audio system and method are presented for processing an audio signal, in which a frequency band is selected, harmonics are generated from the selected signal by a harmonics generator, wherein the harmonics are scaled by a level detected in at least a part of the spectrum of the audio signal related to the selected frequency band. Furthermore, a harmonic generator is presented for generating arbitrary harmonics of an input signal.