Showing papers on "Harmonic published in 1994"

Modeling harmonic generation by a zero-range potential

Abstract: High-order harmonic emission by one electron in a laser field bound to a zero-range potential is extensively discussed. The model yields an expression for the emission rates in the form of a one-dimensional integral that has to be calculated numerically. The solution is based on the quasienergy wave function of the ground state. The approach is very significantly facilitated by suppressing the harmonic components of the wave function at the position of the zero-range potential. This approximation is found to be very accurate except for the third harmonic. In spite of the simplicity of the model, the harmonic spectrum exhibits a very involved structure, occasional harmonics being strongly suppressed, with cusps and spikes for certain evenly spaced intensities. The latter are due to channel closings for the same intensities in above-threshold ionization. The harmonics near and beyond the cutoff of the plateau are amenable to a completely analytical approximation. This approximation shows how the classical model of Krause, Schafer, and Kulander [Phys. Rev. Lett. 68, 3535 (1992)] is embedded in a fully-quantum-mechanical description. Results are also given for the harmonic production rates in an elliptically polarized laser field; they display fair agreement with recent measurements. The model should adequately describe harmonic emission by negative ions with just one bound s state. Moreover, it also gives a fair description of harmonic emission by an atom, particularly if the ground-state energy of the zero-range potential is adjusted not to the binding energy of the atom, but rather to the energy difference between the ground state and the first excited state. The reason why this is appropriate is found in lowest-order perturbation theory, which sheds some light on the physical origin of the plateau.

Fundamental frequency estimation of musical signals using a two‐way mismatch procedure

Abstract: Fundamental frequency (F0) estimation for quasiharmonic signals is an important task in music signal processing. Many previously developed techniques have suffered from unsatisfactory performance due to ambiguous spectra, noise perturbations, wide frequency range, vibrato, and other common artifacts encountered in musical signals. In this paper a new two‐way mismatch (TWM) procedure for estimating F0 is described which may lead to improved results in this area. This computer‐based method uses the quasiharmonic assumption to guide a search for F0 based on the short‐time spectra of an input signal. The estimated F0 is chosen to minimize discrepancies between measured partial frequencies and harmonic frequencies generated by trial values of F0. For each trial F0, mismatches between the harmonics generated and the measured partial frequencies are averaged over a fixed subset of the available partials. A weighting scheme is used to reduce the susceptibility of the procedure to the presence of noise or absence ...

Power system harmonic state estimation

Abstract: A power system state estimation based on (a) multiphase model, (b) voltage and current waveform measurements, (c) synchronized measurements and (d) multifrequency model (i.e. the approach accounts for waveform distortion or harmonics) is formulated. The paper focuses on the following: (a) modeling, (b) implementation, (c) observability and (d) performance. Sensitivity analysis is used to show how transmission line modeling and measurement schemes affect the performance of harmonic state estimation. The overall performance of the system is described in terms of confidence level versus error. These concepts are illustrated with simple systems. The overall harmonic measurement system is scheduled for installation and field evaluation on the NYPA/New York Power Pool transmission system by the end of 1993. >

Power control and delivery in plasma processing equipment

Abstract: The present invention relates to a system and method for control and delivery of radio frequency power in plasma process systems. The present invention monitors the power, voltage, current, phase, impedance, harmonic content and direct current bias of the radio frequency energy being delivered to the plasma chamber. In addition, the plasma mode of operation may be controlled by creating either a capacitively or inductively biased radio frequency source impedance. A radio frequency circulator prevents reflected power from the plasma chamber electrode to damage the power source and it further dissipates the reflected power in a termination resistor. The termination resistor connected to the circulator also effectively terminates harmonic energy caused by the plasma non-linearities. Multiple plasma chamber electrodes and radio frequency power sources may be similarly controlled.

Harmonic and Musical Wavelets

Abstract: The concept of a harmonic wavelet is generalized to describe a family of mixed wavelets with the structure w m, n (x) = {exp (i n 2π x ) – exp (i m 2π x )}/i( n – m ) 2π x . It is shown that this family provides a complete set of orthogonal basis functions for signal analysis. By choosing the (real) numbers m and n (not necessarily integers) appropriately, wavelets whose frequency content ascends according to the musical scale can be generated. These musical wavelets provide greater frequency discrimination than is possible with harmonic wavelets whose frequency interval is always an octave. An example of the wavelet analysis of music illustrates possible applications.

An analytical method for calculating harmonic currents of a three-phase diode-bridge rectifier with DC filter

Abstract: Commonly, three-phase diode bridge rectifiers with an LC filter at the DC side are often used to convert AC input into a DC voltage. It is well known that they generate large amounts of harmonic currents. This paper proposes an analytical method for calculating the harmonic currents for both the continuous and discontinuous current conductions. The equations for the harmonic currents are derived, taking into account the effects of the DC and AC side impedances. All the calculations are conducted only by algebraic calculation with high accuracy. The validity of the proposed method is demonstrated by comparison to the results of time simulation. >

An adaptive high and low impedance fault detection method

Abstract: An integrated high impedance fault (HIF) and low impedance fault (LIF) detection method is proposed in his paper. For a HIF detection, the proposed technique is based on a number of characteristics of the HIF current. These characteristics are: fault current magnitude; magnitude of the 3rd harmonic current; magnitude of the 5th harmonic current; the angle of the third harmonic current; the angle difference between the third harmonics current and the fundamental voltage; and the negative sequence current of HIF. These characteristics are identified by modeling the distribution feeders in EMTP. Apart from these characteristics, the above ambient (average) negative sequence current is also considered. An adjustable block out region around the average load current is provided. The average load current is calculated at every 18000 cycles (5 minutes) interval. This adaptive feature will not only make the proposed scheme more sensitive to low fault current, but it will also prevent the relay from tripping during the normal load current. In this paper, the logic circuit required for implementing the proposed HIF detection method is also included. With minimal modifications, the logic developed for the HIF detection can be applied to low impedance fault detection. A complete logic circuit which detects both the HIF and LIF is proposed. Using this combined logic, the need of installing separate devices for HIF and LIF detection can be eliminated. >

New single-phase active power filter

Abstract: A new algorithm for a single-phase active power filter, based on calculation of the real part of the fundamental load current, is proposed in the paper. The algorithm proposed can maintain the input power factor of the mains close to unity and force the mains current to be a sinewave under distorted or nondistorted mains voltage. A prototype is developed and tested to verify its performance. The experimental results show that the algorithm proposed can compensate for the reactive power and suppress the harmonics of the nonlinear load effectively.

The vibration analysis handbook

Abstract: The physical movement or motion of a rotating machine is normally referred to as vibration. Since the vibration frequency and amplitude cannot be measured by sight or touch, a means must be employed to convert the vibration into a usable product that can be measured and analyzed. Electronics, mechanics, and chemical physics are closely related. Therefore, it would logically follow that the conversion of the mechanical vibration into an electronic signal is the best solution. The means of converting the mechanical vibration into an electronic signal is called a transducer. The transducer output is proportionate to how fast the machine is moving (frequency) and how much the machine is moving (amplitude). The frequency describes what is wrong with the machine and the amplitude describes relative severity of the problem. The motion can be harmonic, periodic, and/or random. All harmonic motion is periodic. However, all periodic motion is not harmonic. Random motion means the machine is moving in an unpredictable manner.

Steady-state oscillation of hysteretic differential model. I: Response analysis

Abstract: This study considers the periodic forced vibration of nonlinear hysteretic system. Multiharmonic steady-state responses of a general hysteretic system adopting the Bouc-Wec differential model, subjected to arbitrary periodic excitation, are analyzed by the Galerkin/Levenberg-Marquardt method. The frequency/time domain alternation and the fast Fourier transformation (FFT) techniques are introduced in this frequency domain solution procedure. The frequency-controlled and amplitude-controlled algorithms are simultaneously formulated to obtain complete, probably multivalued, frequency response curves. This approach gives possible harmonic, superharmonic, and subharmonic responses of the Bouc-Wen hysteretic system. The response characteristics of softening, hardening, and quasilinear hysteretic systems are studied through numerical computations. The proposed procedure is also extended to analyze the periodic vibration of degrading hysteretic system with amplitude-dependent stiffness deterioration. In addition, a verification is given by comparing with the results obtained by a numerical integration procedure.

Efficiency enhancement of high power vacuum BWO's using nonuniform slow wave structures

Abstract: The Sinus-6, a high-power relativistic repetitively-pulsed electron beam accelerator, is used to drive various slow wave structures in a BWO configuration in vacuum. Peak output power of about 550 MW at 9.45 GHz was radiated in an 8-ns pulse. We describe experiments which study the relative efficiencies of microwave generation from a two-stage nonuniform amplitude slow wave structure and its variations without an initial stage. Experimental results are compared with 2.5 D particle-in-cell computer simulations. Our results suggest that prebunching the electron beam in the initial section of the nonuniform BWO results in increased microwave generation efficiency, Furthermore, simulations reveal that, in addition to the backward propagating surface harmonic of the TM/sub 01/ mode, backward and forward propagating volume harmonics with phase velocity twice that of the surface harmonic play an important role in high-power microwave generation and radiation. >

Dynamics and efficiency of type III solar radio emission

Abstract: Existing calculations of nonlinear coupling coefficients for fundamental and harmonic emission via three-wave interactions are refined and used to calculate the conversion efficiency of Langmuir energy into electromagnetic waves when the Langmuir waves have the observed bursty form. Resulting field strengths for harmonic emission are found to be consistent with typical International Sun Earth Explorer 3 (ISSE 3) observations at 1 AU. Fundamental emission at 1 AU is found to proceed only when stimulated by the presence of a source of ion sound waves. However, it is argued that electrostatic decay of Langmuir waves can supply the necessary waves provided the driving electron beam is sufficiently fast. Under these conditions, the predicted fundamental field strengths can account for both the highest and typical fields observed; they also dominate the predicted harmonic fields, consistent with observations. This mechanism is also consistent with previous observations that fundamental emission generally occurs early in type III events, when the beam is fastest. For typical parameters it is shown that neither fundamental nor harmonic emission saturates its respective source instability, contrary to previous assumptions. However, saturation cannot be ruled out under particularly favorable conditions.

Harmonic heat flow in isotropic layered systems and its use for thin film thermal conductivity measurements

Abstract: A theoretical model is presented describing harmonic heat flow in a two layer system heated by a modulated Gaussian laser beam Amplitude and phase of the modulated temperature rise in the layers, as well as in the backing substrate and adjacent atmosphere, are calculated by solving the three‐dimensional heat conduction equation with a source term including exponential absorption of the laser light in one or two layers Heat conduction is assumed to be isotropic throughout the system, however, a thermal contact resistance between the two layers can be taken into account Results are presented for single and double layer systems of gold and various dielectric thin film materials on glass substrates Amplitude and phase of the harmonic temperature variation are calculated either as a function of position in the sample system or at the surface as a function of the laser beam modulation frequency It is found that both amplitude and phase of the calculated temperature rise exhibit typical thin film features i

Fault mode single-phase operation of a variable frequency induction motor drive and improvement of pulsating torque characteristics

Abstract: Improved reliability and fault tolerant operation of power converter systems are extremely important for industrial AC drives. The paper considers variable frequency variable voltage operation of a three-phase induction motor in single-phase mode for two common faults of a three-phase inverter, i.e., open base drive and device short-circuit. The motor performance has been extensively analyzed in single-phase mode and remedial strategies have been developed to neutralize large second and other lower order harmonic pulsating torques. In a single-phase open loop volts/Hz control made of a faulty three-phase inverter, it has been demonstrated that odd harmonic voltages at appropriate phase angles can be injected to neutralize the low frequency pulsating torques so as to permit smooth drive operation. It has been shown that the pulsating torque can be further reduced by load dependent flux programming rather than operating with constant rated flux. >

High-order harmonic generation with an annular laser beam.

Abstract: High-order harmonics have been generated by the use of an annular laser beam. The nonlinearity of harmonic production and the shorter wavelengths involved cause the harmonics to emerge strongly peaked on the laser axis. Thus the harmonics emerge from the focus inside the missing portion of the laser beam. This permits the laser to be blocked by an aperture that passes the harmonics.

Downshifted maximum features in stimulated electromagnetic emission spectra

Abstract: New and detailed experimental and theoretical results concerning the prominent downshifted maximum (DM) feature in spectra of stimulated electromagnetic emissions are reported. The experimental results were obtained at the Sura ionospheric modification facility in Russia by transmitting a powerful high-frequency ordinary mode pump wave into the ionospheric F region. We present detailed experimental results of the dependence of the DM on the pump frequency. Different frequency components of the DM have slightly different growth times after pump turn-on and are suppressed in different pump frequency ranges at harmonics of the electron cyclotron frequency. The pump frequency range near the cyclotron harmonics in which the DM does not develop, decreases significantly with increasing harmonic, from several kilohertz at the fourth harmonic to an extremely narrow range of 0.2 kHz or less at the seventh harmonic. We discuss conditions for plasma wave propagation to explain this dependence on the cyclotron harmonics.

Optimal pulsewidth modulation for AC servos and low-cost industrial drives

Abstract: An optimal pulsewidth modulation method is described in which the durations of switching subcycles are considered as optimization variables, a subcycle being the time sequence of three consecutive switching state vectors. Operation at variable subcycle duration entails a prediction of the controlling reference voltage vector. It is a special advantage that the optimization and prediction can be carried out off line. The optimal technique exhibits high dynamic performance. It can be used for synchronized and asynchronous modulation in a wide range of switching frequencies. The optimization reduces the harmonic currents at a given switching frequency. The Fourier spectrum lacks dominant carrier frequencies

A Vector Corrected High Power On-Wafer Measurement System with a Frequency Range for the Higher Harmomcs up to 40 GHz

Abstract: A high power on-wafer measurement system based on the new microwave transition analyzer (MTA) HP 71500A has been developed for the complete characterization of the large signal behavior of transistors. One key feature of the MTA based measurement system is that during power sweeps the harmonic behavior, up to 40 GHz, can be measured. To improve the accuracy of power measurements the vector measurement capability of the MTA is also utilized to allow full vector calibration of the measurement system. In addition, this vector measurement feature allows both the input reflection and the transmission coefficients of a device under test (DUT) to be measured as a function of frequency and input power. The input and output voltage waveforms at the transistor terminals are also calculated from the measurement data. This improved capability is possible since the vector calibrated measurement system allows both the measurement of the fundamental and the higher harmonics with respect to magnitude and phase.

Harmonic resonance at a medium sized industrial plant

Abstract: Harmonic resonance is a concern for industrial plants because approximately 50% of the normal electrical load consists of computer equipment, switch mode power supplies and AC induction motor adjustable speed controllers. Due to the nonlinear characteristics of these loads, significant harmonic voltages and currents are produced on the electrical distribution system. Measurements were made with a harmonic analyzer at several locations in an electrical distribution system to quantify harmonic currents and voltages. The system impedance diagram, prepared from the system one line diagram, was used to model the electrical system and calculate power system natural frequencies. Calculations indicated harmonic resonance occurs near the seventh harmonic frequency depending on configuration of the electrical power system. The plant equivalent circuit was prepared for several harmonic frequencies to show the amplification of currents and voltages due to the effects of harmonic resonance. Calculations to determine network harmonics are presented using a simplified system representation in combination with traditional circuit reduction methods. The results of these calculations are shown to be valid by actual system measurement. >

Harmonic measurements, analysis, and power factor correction in a modern steel manufacturing facility

Abstract: Maximizing electric power transfer directly affects the productivity of an electric arc furnace operation. Arc furnaces and rolling mill loads operate at power factors that result in penalty charges and lower bus voltages. In addition, the nonlinear characteristics of the furnace arcs and rolling mill drives generate significant harmonic currents that flow through the plant and utility power system. These harmonic currents cause system voltage distortion and power loss in the system, and can interact with power factor correction capacitor banks leading to equipment failures. This paper presents the analytical technique used to correct power factor in a modern steel manufacturing facility. The study included field measurements, harmonic analysis, and filter design work to reduce the amount of harmonic distortion in the plant. The modeling of arc furnaces and rolling mills for a harmonic analysis study is also discussed. The solutions recommended in this paper to increase power factor and reduce harmonics can be applied to other steel manufacturing facilities to improve power quality and therefore plant productivity.

An experimental study of the effects of harmonic loading on microwave MESFET oscillators and amplifiers

Abstract: This paper reports an extensive experimental investigation of the effects of second harmonic loading on the performance of microwave GaAs MESFET oscillators and strongly driven amplifiers. The measurement system used is an active load system based on six-port techniques. Harmonic load pull measurements were obtained for the NE72084 MESFET; the measurements show how the second harmonic load can influence the power gain and the power added efficiency in strongly driven amplifiers. The device line characterization technique was combined with the harmonic load pull technique; the measurement results illustrate how the output power and the DC to RF conversion efficiency of an oscillator depend on the choice of the second harmonic load. Amplifier and oscillator circuits have been designed using these measurements; the circuits have been constructed and measured. The results validate the experimental approach used and clearly illustrate the importance of properly selecting the second harmonic load in amplifier and oscillator circuits. Significant improvements in gain, output power and efficiency have been achieved by properly selecting the second harmonic load.

An active filter for unbalanced three-phase system using synchronous detection method

Abstract: This paper presents an active filter using the synchronous detection method. The equal current synchronous detection method is applied to calculate the reactive and harmonic current compensation components for triggering an active power filter in an unbalanced three-phase power system. The simulation and experimental results show that active filter operation using the synchronous detection method is effective to eliminate line current harmonics and compensate the reactive current component. The merits of the proposed method are its capability to operate under an unbalanced three-phase system by perphase calculation, to avoid conversion error by force waveform calculation, to balance the unbalanced load and to accomplish good performance by very simple implementation. >

Series connected voltage-source converter modules for force-commutated SVC and DC-transmission

Abstract: In force-commutated SVC and DC transmission stations, series-connected, multi-converter modules are necessary to build up the DC link voltage rating. Based on digital simulations of 8 modules, it is shown that the total harmonic distortion (THD) of 5% can be achieved from harmonic cancellations by using phase shifting of the triangular carriers in the sinusoidal pulse width modulation technique. The requirement of the DC link capacitor size to ensure ripple-free DC voltage is studied. The 8-module case-study points to the ability to achieve 1% THD for higher voltage rating by increasing the number of modules connected in series. >

Summation of harmonic currents produced by AC/DC static power converters with randomly fluctuating loads

Abstract: A method for analyzing the asymptotic behavior of the sum of randomly varying harmonic currents produced by static power converters is described. It has been shown by virtue of the central limit theorem that as the number of harmonic sources is large enough, the vectorial sum of random harmonic vectors approaches a bivariate normal distribution. However, methods of determining its parameters for realistic harmonic-generating loads need to be developed. This paper deals with the case of AC/DC static power converters. With the operating condition of each converter being known, the parameters of the bivariate normal distribution can be effectively determined. Monte-Carlo simulation is performed to justify the proposed method. >

Modulator with harmonic mixers

Abstract: An improved modulator circuit for mixing a modulation signal with a carrier signal includes first and second harmonic mixers which are operative to produce modulated output signals at an output frequency corresponding to both the sum and the difference of the modulation signal frequency and the even harmonic frequencies of the carrier signal frequency. In one configuration employing a 90° hybrid, the output signals of the harmonic mixers are combined to produce a single sideband modulated output signal. A novel harmonic mixer circuit is also provided along with demodulator circuits and methods of modulating and demodulating modulation signals.

Harmonic analysis of industrial power systems

Abstract: When large harmonic producing loads are added to an industrial plant power system it is good engineering practice to analyze their impact on the power system by performing harmonic modeling analysis of the system at the design stage. Such a study can identify any potentially harmful resonances or other harmonic levels that are predicted to be in excess of IEEE 519 recommended limits and suggest corrective measures (if necessary). This paper discusses the impact of the harmonic limits of IEEE Standard 519-1992 on the industrial power consumer and addresses the differences between the 1992 and 1981 versions of the Standard. Harmonics produced by variable frequency drives are discussed. The data required to conduct a harmonic study, the types of analyses that can be performed, and some of the mitigating measures that can be taken to alleviate a potential harmonic problem are detailed. A case study is presented based on a typical paper mill where a large variable frequency drive was added to the power system.

Cross current control for parallel operating three phase inverter

Abstract: A synthesis method of the cross current control system for parallel operating three phase PWM inverters is proposed. The mathematical descriptions of the steady state, transient response and higher harmonic components of cross current are derived to obtain a guide of design. Simulations are provided to confirm such a theory. >