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Showing papers on "Harmonics published in 1991"


Journal ArticleDOI
TL;DR: A physical mechanism and proposed theory permits a quantitative explanation for the main characteristics of experimentally observed effects of weak magnetic fields with biological systems.
Abstract: A physical mechanism is suggested for a resonant interaction of weak magnetic fields with biological systems. An ion inside a Ca(2+)-binding protein is approximated by a charged oscillator. A shift in the probability of ion transition between different vibrational energy levels occurs when a combination of static and alternating magnetic fields is applied. This in turn affects the interaction of the ion with the surrounding ligands. The effect reaches its maximum when the frequency of the alternating field is equal to the cyclotron frequency of this ion or to some of its harmonics or sub-harmonics. A resonant response of the biosystem to the magnetic field results. The proposed theory permits a quantitative explanation for the main characteristics of experimentally observed effects.

553 citations


Journal ArticleDOI
TL;DR: In this article, an optimal measurement scheme for tracking the harmonics in power system voltage and current waveforms is presented, which is based on Kalman filtering theory for the optimal estimation of the parameters of time-varying harmonics.
Abstract: An optimal measurement scheme for tracking the harmonics in power system voltage and current waveforms is presented. The scheme does not require an integer number of samples in an integer number of cycles. It is not limited to stationary signals, but it can track harmonics with time-varying amplitudes. A review is first presented of the common frequency domain techniques for harmonics measurement. The frequency domain techniques are based on the discrete Fourier transform and the fast Fourier transform. Examples of pitfalls in the common techniques are given. The authors then introduce the concepts of the new scheme. This scheme is based on Kalman filtering theory for the optimal estimation of the parameters of time-varying harmonics. The scheme was tested on simulated and actual recorded data sets. It is concluded that the Kalman filtering algorithm is more accurate than the other techniques. >

373 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present theoretical studies of high-order harmonic generation in a rare-gas medium using a 1064 nm Nd-YAG laser in the 1013 W cm-2 intensity range.
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.

282 citations


Journal ArticleDOI
TL;DR: In this paper, the performance of multiphase machines designed for operation with static power converters is investigated, where the winding distributions are intentionally rectangular to better accommodate the rectangular waveforms of solid-state inverters.
Abstract: The performance of multiphase machines designed for operation with static power converters is investigated. The winding distributions are intentionally rectangular to better accommodate the rectangular waveforms of solid-state inverters. Equations which define the transient as well as steady-state behavior, including the computation of all machine inductances, are derived. In deriving these equations the space harmonics are specifically included. Equations for calculation of terminal voltages and electromagnetic torque are modified to account for nonsinusoidal air-gap-flux distributions. A conventional three-phase induction motor including the effect of space harmonics is simulated. >

265 citations


PatentDOI
TL;DR: In this paper, the pitch estimation method is improved by making the decision dependent on the energy of the current segment relative to energy of recent prior segments; if the relative energy is low, the current segments favors an unvoiced decision; if high, it favors a voiced decision.
Abstract: The pitch estimation method is improved. Sub-integer resolution pitch values are estimated in making the initial pitch estimate; the sub-integer pitch values are preferably estimated by interpolating intermediate variables between integer values. Pitch regions are used to reduce the amount of computation required in making the initial pitch estimate. Pitch-dependent resolution is used in making the initial pitch estimate, with higher resolution being used for smaller values of pitch. The accuracy of the voiced/unvoiced decision is improved by making the decision dependent on the energy of the current segment relative to the energy of recent prior segments; if the relative energy is low, the current segment favors an unvoiced decision; if high, it favors a voiced decision. Voiced harmonics are generated using a hybrid approach; some voiced harmonics are generated in the time domain, whereas the remaining harmonics are generated in the frequency domain; this preserves much of the computational savings of the frequency domain approach, while at the same time improving speech quality. Voiced harmonics generated in the frequency domain are generated with higher frequency accuracy; the harmonics are frequency scaled, transformed into the time domain with a Discrete Fourier Transform, interpolated and then time scaled.

221 citations


Book
01 Aug 1991
TL;DR: DC Power Transmission Technology Thyristor Valve Analysis of HVDC Converters Converter andHVDC 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.
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.

207 citations


Journal ArticleDOI
TL;DR: It is shown that specific 1-D slices of the fourth-order cumulant of the noisy signal for the direction of arrival (DOA) and retrieval of harmonics in noise (RHN) problems are identical to the autocorrelation of a related noiseless signal, so correlation-based high-resolution methods may be used with fourth- order cumulants as well.
Abstract: A frequently encountered problem in signal processing is that of estimating the frequencies and amplitudes of harmonics observed in additive colored Gaussian noise. In practice, the observed signals are contaminated with spatially and temporally colored noise of unknown power spectral density. A cumulant-based approach to these problems is proposed. The cumulants of complex processes are defined, and it is shown that specific 1-D slices of the fourth-order cumulant of the noisy signal for the direction of arrival (DOA) and retrieval of harmonics in noise (RHN) problems are identical to the autocorrelation of a related noiseless signal. Hence correlation-based high-resolution methods may be used with fourth-order cumulants as well. The effectiveness of the proposed methods is demonstrated through standard simulation examples. >

195 citations


Journal ArticleDOI
TL;DR: In this article, the performance of multiphase induction motors for operation with static power converters is analyzed by means of a digital-computer simulation and it is shown that when operating in conjunction with a converter supply, a specially wound five-phase machine is theoretically capable of a 10% improvement in torque per root-mean-square ampere assuming the same peak air-gap-flux density level in the air gap of the machine as in a conventionally designed induction motor of the same rating.
Abstract: For pt.I. see ibid, vol.6, no.4, p.679-83 (1991). The performance of multiphase machines designed for operation with static power converters is described. The winding distributions are intentionally rectangular to better accommodate the rectangular waveforms of solid-state inverters. Fourier analysis is used for investigation of the effects of different air-gap-field spatial distributions and time harmonics in the supply. The approach to analysis of such machines, derived in Part I, is implemented by means of a digital-computer simulation. Compound results indicate that when operating in conjunction with a converter supply, a specially wound five-phase machine is theoretically capable of a 10% improvement in torque per root-mean-square ampere assuming the same peak air-gap-flux density level in the air gap of the machine as in a conventionally designed induction motor of the same rating. >

179 citations


Journal ArticleDOI
TL;DR: In this paper, a computer-based multiphase harmonic load flow solution technique for analyzing unbalanced load conditions in power systems is described. Butts et al. used static VAr compensators with thyristor-controlled reactors under unbalanced loads to illustrate the method.
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. >

171 citations


Journal ArticleDOI
TL;DR: In this paper, a Kalman filter is used to obtain the optimal estimate of the power system harmonic content and the effect of load variation over a one day cycle on power system harmonics and standard are presented.
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. >

166 citations


Journal ArticleDOI
24 Jun 1991
TL;DR: In this article, 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.
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. >

Patent
16 Dec 1991
TL;DR: In this paper, 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.
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.

Journal ArticleDOI
TL;DR: The weaker variation with pump intensity of the induced dipole in the high-field regime leads to an enormous enhancement in phase matching compared to the perturbative limit and a defocusing of the generated harmonics.
Abstract: We present a completely ab initio calculation of harmonic generation in xenon exposed to a strong laser field. The time-dependent Schrodinger equation for the atomic response and the propagation equation are numerically integrated yielding excellent agreement with experiment. The weaker variation with pump intensity of the induced dipole in the high-field regime leads to an enormous enhancement in phase matching compared to the perturbative limit and a defocusing of the generated harmonics.

Proceedings ArticleDOI
28 Apr 1991
TL;DR: In this paper, the authors introduced some common harmonic analysis techniques and applied them to voltage waveforms recorded on a typical REA transmission and distribution system, and the results showed that the voltage and current waveforms are becoming more distorted and the power quality is deteriorating.
Abstract: With the increase of nonlinear loads on utility distribution systems, the voltage and current waveforms are becoming more distorted and the power quality is deteriorating. Since this is becoming a wide spread problem today, and new, more strict, distortion guidelines are under development, utility engineers are having to deal with analyzing and planning for the control of the distortion. This paper introduces some common harmonic analysis techniques and applies them to voltage waveforms recorded on a typical REA transmission and distribution system. >

Journal ArticleDOI
TL;DR: In this article, the Fourier series of the optimum APLC injection current waveform was determined using nonlinear optimization theory and applied to a single-phase APLC in a balanced three-phase network.
Abstract: Active power line conditioner (APLC) is a type of active filter that compensates for power system waveform distortion The objective is to develop and illustrate a procedure for calculating the APLC injection current needed to minimize voltage harmonic distortion throughout a power network The procedure is intended for use with APLC frequency domain correction in networks that are experiencing periodic harmonic distortion The injection currents are determined using nonlinear optimization theory The chief contribution lies in developing a simple procedure for finding the Fourier series of the optimum APLC injection current waveform The procedure is intended to apply in any of the following situations: (1) one single-phase APLC in a single-phase network; (2) one single-phase APLC in a three-phase network; or (3) one three-phase APLC in a balanced three-phase network >

Journal ArticleDOI
28 Sep 1991
TL;DR: In this article, 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.
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. >

Proceedings ArticleDOI
10 Mar 1991
TL;DR: In this article, the performance of the parallel resonant converter and the combination series/parallel resonant converters when operated above resonance in a high power factor mode is determined and compared for single-phase applications.
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. >

Proceedings ArticleDOI
28 Sep 1991
TL;DR: In this paper, a new modulation technique for 3 Phi -3 Phi forced commutated cycloconverters (FCCs) is presented, based on the space vector representation of the output voltages and input currents in the complex plane.
Abstract: A new modulation technique for three phase to three phase (3 Phi -3 Phi ) forced commutated cycloconverters (FCCs) is presented. It is based on the space vector representation of the output voltages and input currents in the complex plane. The resultant output line voltages and input phase currents do not contain low frequency harmonics. The input current displacement factor and the converter voltage gain can be freely varied, regardless of the load power factor; the only restriction being the equality of input and output active powers. The modulation technique holds for any input and output frequencies, so that it can be also applied for 3 Phi AC to DC and DC to 3 Phi AC conversion, thus making FCC a universal power conversion module. >

Journal ArticleDOI
TL;DR: In this article, a voltage-dependent current injection load model is presented to determine voltage waveform characteristics and additional losses at harmonic frequencies, and 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.
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. >

Journal ArticleDOI
TL;DR: In this paper, the 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.
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. >

Journal ArticleDOI
TL;DR: In this paper, the authors report seven-day measurements of harmonic current and voltage made at the sending out of five feeders, including one large apartment building, three industrial customers, and two commercial.
Abstract: The authors report seven day measurements of harmonic current and voltage made at the sending out of five feeders. The comprehensive survey monitored voltage and current distortion at eleven locations: five distribution feeders, one large apartment building, three industrial customers, and two commercial. The major goals are to present different ways of recording and displaying harmonics, to explain the results, and to compare them with existing engineering recommendations. >

Journal ArticleDOI
TL;DR: In this paper, a novel method for the detection of high-impedance faults is proposed which uses the incremental variance of a normalized even order ratio measure, based on which three criteria, (even-order power, even-order ratio, and evenorder incremental variance) for fault detection are presented, all of which are based on the changes of normalized evenorder harmonic power in fault currents.
Abstract: A novel method for the detection of high-impedance faults is proposed which uses the incremental variance of a normalized even order ratio measure. Staged fault tests were extensively carried out in Korean electric power systems. From the analysis of the staged fault test data, it was found that there exists an intermittent arcing phenomenon in most high-impedance faults and that the waveforms of this arcing fault current have an asymmetrical shape in each cycle. Based on these facts, three criteria, (even-order power, even-order ratio, and even-order incremental variance) for fault detection are presented, all of which are based on the changes of normalized even-order harmonic power in fault currents. These criteria are compared through the analysis of staged fault data and normal switching event data. It is shown that the even-order incremental variance criterion is superior to the other two criteria and that, with this criterion, high-impedance faults can be distinguished from normal switching events, including special loads such as electric furnaces and subways. Microprocessor-based protective relays, which can detect high-impedance faults by using the proposed methods, have been constructed, installed in Korea Electric Power Corporation substations, and tested during the last two years. Details of these field tests are given. >

Journal ArticleDOI
TL;DR: In this paper, the authors describe how data from a typical acquisition system can be processed using the fast Fourier transform and discuss possible errors (e.g., those due to leakage) and how to avoid them using techniques such as skewing correction and windowing.
Abstract: Multichannel data acquisition systems and commercially available digital signal processing software packages make the determination of harmonic power flow possible provided the limitations of the analysis techniques are understood. The authors describe how data from a typical acquisition system can be processed using the fast Fourier transform and discuss possible errors (e.g. those due to leakage) and how to avoid them using techniques such as skewing correction and windowing. Guidelines on the practical application of the transform in analyzing measured data are presented. The analysis method has been used successfully to analyze data obtained at a traction (railway supply) substation which had a sixth-harmonic resonance caused by the interaction of a harmonic filter and the only supply system. >

Journal ArticleDOI
TL;DR: In this paper, 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.
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.

Journal ArticleDOI
TL;DR: In this article, a new approach for the control of a current source pulse width modulated (PWM) inverter is proposed to achieve instantaneous current control capability, which provides instantaneous current response in the AC motor by altering the modulation index of the current source PWM patterns.
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. >

Journal ArticleDOI
TL;DR: In this paper, a multiharmonic loading method for nonlinear microwave and millimeter-wave transistor characterization using six-port techniques is presented, which allows independent load tuning of an excitation signal and its harmonics.
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. >

Proceedings ArticleDOI
03 Jun 1991
TL;DR: In this article, the onset of rotating stall has been delayed in a low speed, single-stage, axial research compressor using active feedback control, which was implemented using a circumferential array of hot wires to sense rotating waves of axial velocity upstream of the compressor.
Abstract: The onset of rotating stall has been delayed in a low speed, single-stage, axial research compressor using active feedback control. Control was implemented using a circumferential array of hot wires to sense rotating waves of axial velocity upstream of the compressor. Circumferentially travelling waves were then generated with appropriate phase and amplitude by “wiggling” inlet guide vanes driven by individual actuators. The control scheme considered the wave pattern in terms of the individual spatial Fourier components. A simple proportional control law was implemented for each harmonic. Control of the first spatial harmonic yielded an 11% decrease in the stalling mass flow, while control of the first and second harmonics together reduced the stalling mass flow by 20%. The control system was also used to measure die sine wave response of the compressor, which behaved as would be expected for a second order system.Copyright © 1991 by ASME

Journal ArticleDOI
TL;DR: In this paper, a new method of efficiency maximization that utilizes sensing of the third-harmonic component of air-gap flux is proposed, which is used to determine the resulting instantaneous position of the fundamental component of the air gap flux and, consequently, the torque and flux-producing components of the stator current.
Abstract: A new method of efficiency maximization that utilizes sensing of the third-harmonic component of air-gap flux is proposed. This signal is used to determine the resulting instantaneous position of the fundamental component of the air gap flux and, consequently, the torque- and flux-producing components of the stator current. In addition, the third harmonic signal is also used to determine the rotor speed. Hence, the output power of the machine can be calculated with only a single sensor wire attached to the neutral point of the machine. The flux-producing component can be readily adjusted to produce the minimum input power for a fixed amount of output power (fixed speed). >

Journal ArticleDOI
TL;DR: In this paper, a practical relay for detecting down-conductor high-impedance ground faults (HIGF) is described, with supporting theory and data from live line tests.
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. >

Journal ArticleDOI
TL;DR: Stimulated backscattered harmonic radiation generated by the interaction of an intense pump-laser field with an electron beam or plasma is analyzed using a fully nonlinear, relativistic, fluid theory valid to all orders in the pump- laser amplitude.
Abstract: Stimulated backscattered harmonic radiation generated by the interaction of an intense pump-laser field with an electron beam or plasma is analyzed using a fully nonlinear, relativistic, fluid theory valid to all orders in the pump-laser amplitude. The backscattered radiation occurs at odd harmonics of the Doppler-shifted incident laser frequency. The growth rates, saturation levels (efficiencies), and thermal limitations are calculated for the backscattered harmonic radiation. This mechanism may provide a practical method for producing coherent radiation in the XUV regime.