Showing papers on "Harmonics published in 2005"
05 Dec 2005
TL;DR: This paper deals with general pure active filters for power conditioning, and specific hybridactive filters for harmonic filtering of three-phase diode rectifiers.
Abstract: Unlike traditional passive harmonic filters, modern active harmonic filters have the following multiple functions: harmonic filtering, damping,isolation and termination, reactive-power control for power factor correction and voltage regulation, load balancing, voltage-flicker reduction, and/or their combinations. Significant cost reductions in both power semiconductor devices and signal processing devices have inspired manufactures to put active filters on the market. This paper deals with general pure active filters for power conditioning, and specific hybrid active filters for harmonic filtering of three-phase diode rectifiers.
954 citations
TL;DR: This study investigated how the classification accuracy of a 4-class BCI system can be improved by incorporating visually evoked harmonic oscillations and revealed that the use of three SSVEP harmonics yielded a significantly higher classification accuracy than was the case for one or two harmonics.
Abstract: Brain-computer interfaces (BCIs) can be realized on the basis of steady-state evoked potentials (SSEPs). These types of brain signals resulting from repetitive stimulation have the same fundamental frequency as the stimulation but also include higher harmonics. This study investigated how the classification accuracy of a 4-class BCI system can be improved by incorporating visually evoked harmonic oscillations. The current study revealed that the use of three SSVEP harmonics yielded a significantly higher classification accuracy than was the case for one or two harmonics. During feedback experiments, the five subjects investigated reached a classification accuracy between 42.5% and 94.4%.
496 citations
TL;DR: Optical-heterodyne-based measurements reveal that the coherent frequency comb structure of the original laser is fully preserved in the high-harmonic generation process and permits the efficient generation of phase-coherent high-order harmonics using only a standard laser oscillator without active amplification of single pulses.
Abstract: We demonstrate the generation of phase-coherent frequency combs in the vacuum utraviolet spectral region. The output from a mode-locked laser is stabilized to a femtosecond enhancement cavity with a gas jet at the intracavity focus. The resulting high-peak power of the intracavity pulse enables efficient high-harmonic generation by utilizing the full repetition rate of the laser. Optical-heterodyne-based measurements reveal that the coherent frequency comb structure of the original laser is fully preserved in the high-harmonic generation process. These results open the door for precision frequency metrology at extreme ultraviolet wavelengths and permit the efficient generation of phase-coherent high-order harmonics using only a standard laser oscillator without active amplification of single pulses.
437 citations
TL;DR: In this paper, a GA optimization technique is applied to determine the switching angles for a cascaded multilevel inverter which eliminates specified higher order harmonics while maintaining the required fundamental voltage.
Abstract: In this letter, a genetic algorithm (GA) optimization technique is applied to determine the switching angles for a cascaded multilevel inverter which eliminates specified higher order harmonics while maintaining the required fundamental voltage. This technique can be applied to multilevel inverters with any number of levels. As an example, in this paper a seven-level inverter is considered, and the optimum switching angles are calculated offline to eliminate the fifth and seventh harmonics. These angles are then used in an experimental setup to validate the results.
399 citations
TL;DR: In this paper, the authors present a Z-source inverter system and control for general-purpose motor drives, which employs a unique LC network in the dc link and a small capacitor on the ac side of the diode front end.
Abstract: This paper presents a Z-source inverter system and control for general-purpose motor drives. The Z-source inverter system employs a unique LC network in the dc link and a small capacitor on the ac side of the diode front end. By controlling the shoot-through duty cycle, the Z-source can produce any desired output ac voltage, even greater than the line voltage. As a result, the new Z-source inverter system provides ride-through capability during voltage sags, reduces line harmonics, improves power factor and reliability, and extends output voltage range. Analysis, simulation, and experimental results will be presented to demonstrate these new features.
390 citations
16 Jun 2005
TL;DR: Simulation and experimental results are used to evaluate the behavior of the synchronization methods under different kind of grid disturbances such as voltage dips, harmonics and notches.
Abstract: Nowadays, it is a general trend to increase the electricity production using distributed power generation systems (DPGS) based on renewable energy resources such as wind, sun or hydrogen. Jf these systems are not properly controlled, their connection to the utility network can generate problems on the grid side. Therefore, considerations about power generation, safe running and grid synchronization must be done before connecting these systems to the utility network. This paper is mainly dealing with the grid synchronization issues of distributed systems. An overview of the synchronization methods as well as their major characteristics is given. New solutions to optimize the synchronization methods when running on distorted grid conditions are discussed. Simulation and experimental results are used to evaluate the behavior of the synchronization methods under different kind of grid disturbances such as voltage dips, harmonics and notches.
358 citations
TL;DR: In this article, a femtosecond Ti:sapphire laser was used for high-harmonic generation in helium using a two-color laser field that consisted of the fundamental and second harmonic fields of a femto-cond Ti-sappire laser.
Abstract: Highly efficient high-harmonic generation was achieved in helium using a two-color laser field that consisted of the fundamental and the second harmonic fields of a femtosecond Ti:sapphire laser. By applying a high intensity second harmonic, the harmonics generated in the orthogonally polarized two-color field were stronger than those obtained in the fundamental field by more than 2 orders of magnitude, and even stronger than those of the parallel polarization case. A conversion efficiency as high as $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ was obtained for the 38th harmonic at 21.6 nm. The physical origin of this enhancement was deduced by analyzing the electron behavior in the two-color field.
332 citations
01 Jan 2005
TL;DR: In this paper, a multilevel power conversion concept based on the combination of neutralpoint-clamped (NPC) and floating capacitor converters is proposed, where the voltage balancing across the floating capacitors is achieved by using a proper selection of redundant switching states, and the neutral-point voltage is controlled by the classical dc offset injection.
Abstract: This paper proposes a multilevel power conversion concept based on the combination of neutral-point-clamped (NPC) and floating capacitor converters In the proposed scheme, the voltage balancing across the floating capacitors is achieved by using a proper selection of redundant switching states, and the neutral-point voltage is controlled by the classical dc offset injection Experimental results are illustrated in the paper to demonstrate the system operation
308 citations
TL;DR: This paper presents a simple and straightforward approach to develop an indirect field-oriented control (FOC) scheme for a six-phase induction machine with an arbitrary displacement between the two three-phase winding sets, and shows the effectiveness of the proposed indirect FOC scheme.
Abstract: Multiphase (more than three phases) drives possess several advantages over conventional three-phase drives, such as reducing the amplitude and increasing the frequency of torque pulsations, reducing the rotor harmonic currents, reducing the current per phase without increasing the voltage per phase, lowering the dc-link current harmonics, and higher reliability. By increasing the number of phases it is also possible to increase the power /torque per rms ampere for the same volume machine. This paper, therefore, presents a simple and straightforward approach to develop an indirect field-oriented control (FOC) scheme for a six-phase induction machine with an arbitrary displacement between the two three-phase winding sets. The two current-controlled pulsewidth-modulation three-phase voltage-source inverter independently feeds the two sets of three-phase stator windings. The scheme is based on simple two-axis (d-q) model of the six-phase induction machine, and can be easily extended to any number of phases, which are multiples of three. The unbalanced current sharing between the two three-phase stator-winding sets observed in earlier schemes is automatically eliminated, and the practical implementation of the scheme is simple. Necessary experimental and simulation results are presented to show the effectiveness of the proposed indirect FOC scheme. In the study, online analysis has been performed using C/sup ++/, while MATLAB /SIMULINK has been used to perform the offline analysis.
278 citations
TL;DR: The numerical solution of the time-dependent Schrodinger equation for vibrating hydrogen molecules in few-cycle laser pulses shows that high-harmonic generation is sensitive to the laser-induced vibrational motion.
Abstract: The numerical solution of the time-dependent Schrodinger equation for vibrating hydrogen molecules in few-cycle laser pulses shows that high-harmonic generation is sensitive to the laser-induced vibrational motion. More intense harmonics are generated in heavier isotopes, the difference increasing with the harmonic frequency. Analytical theory reveals a dependence of the harmonics on the vibrational autocorrelation function. With the help of a genetic algorithm, the nuclear motion can be reconstructed from the harmonic spectra with sub-fs time resolution.
252 citations
TL;DR: It is shown that the theory of symmetric polynomials can be exploited to reduce the degree of the polynomial equations that must be solved which in turn greatly reduces the computational burden.
Abstract: A method is presented to compute the switching angles in a multilevel converter so as to produce the required fundamental voltage while at the same time not generate higher order harmonics. Previous work has shown that the transcendental equations characterizing the harmonic content can be converted to polynomial equations which are then solved using the method of resultants from elimination theory. A difficulty with this approach is that when there are several dc sources, the degrees of the polynomials are quite large making the computational burden of their resultant polynomials (as required by elimination theory) quite high. Here, it is shown that the theory of symmetric polynomials can be exploited to reduce the degree of the polynomial equations that must be solved which in turn greatly reduces the computational burden. In contrast to results reported in the literature that use iterative numerical techniques to solve these equations, the approach here produces all possible solutions.
07 Nov 2005
TL;DR: The derived model is valid for both small and large amplitude drive signals, correctly predicts even and odd harmonics through cascaded chains of functional blocks, simulates accurately load-pull behavior away from 50 /spl Omega/, and predicts adjacent channel power ratio and constellation diagrams in remarkably close agreement to the circuit model from which the behavioral model was derived.
Abstract: We present an optimal experiment design methodology and a superior and fully automated model generation procedure for identifying a class of broad-band multiharmonic behavioral models in the frequency domain. The approach reduces the number of nonlinear measurements needed, minimizes the time to generate the data from simulations, reduces the time to extract the model functions from data, and when used for simulation-based models, takes maximum advantage of specialized simulation algorithms. The models have been subject to extensive validation in applications to real microwave integrated circuits. The derived model is valid for both small and large amplitude drive signals, correctly predicts even and odd harmonics through cascaded chains of functional blocks, simulates accurately load-pull behavior away from 50 /spl Omega/, and predicts adjacent channel power ratio and constellation diagrams in remarkably close agreement to the circuit model from which the behavioral model was derived. The model and excitation design templates for generating them from simulations are implemented in Agilent Technologies' Advanced Design System.
13 Jun 2005
TL;DR: In this article, an asymmetric spiral defected ground structure (DGS) was used to suppress the second and third harmonics of the Wilkinson power divider, and the transfer function of the asymmetric DGS showed signal rejection characteristics at two different resonance frequencies.
Abstract: In this paper, we present an effective technique of second and third harmonic suppression for a Wilkinson power divider by using an asymmetric spiral defected ground structure (DGS). With the proposed technique, a single asymmetric DGS provides two different resonance frequencies because of the different sizes of spiral-shaped defects on the ground plane. The transfer function of the asymmetric DGS shows signal rejection characteristics at two different resonance frequencies and the characteristics of asymmetric DGS is modeled by two parallel RLC resonance circuits in cascade. With the insertion of asymmetric spiral DGS into a quarter-wave line of the Wilkinson power divider, the second and third harmonics are suppressed simultaneously. In experimental results, 18-dB suppression for the second harmonic and 15-dB suppression for the third harmonic, respectively, are achieved. Using asymmetric DGS, the size of a quarter-wave line is reduced by 9.1% compared to that of the conventional divider without a DGS.
TL;DR: In this paper, an adaptive hysteresis band current controller is proposed for active power filter to eliminate harmonics and to compensate the reactive power of three-phase rectifier, which is found effective to meet IEEE 519 standard recommendations on harmonics levels.
TL;DR: In this article, a more general formulation is proposed, removing the quarter-wave symmetry constraint for two classes of the m-level, n-harmonic harmonic control problem, and the special cases of two-and three-level harmonic elimination are presented in detail along with representative solutions for each harmonic control problems.
Abstract: Selective harmonic elimination/control has been a widely researched alternative to traditional pulse-width modulation techniques. Previous and current work has made fundamental assumptions that enforce output waveform quarter-wave symmetry, presumably in order to reduce the complexity of the resulting equations. However, the quarter-wave symmetric assumption is not strictly necessary. It restricts the solution space, which can result in sub-optimal solutions with regards to the uncontrolled harmonic distribution. A more general formulation is proposed, removing the quarter-wave symmetry constraint for two classes of the m-level, n-harmonic harmonic control problem. The special cases of two- and three-level harmonic elimination are presented in detail along with representative solutions for each harmonic control problem. New solutions previously unattainable based on quarter-wave symmetric techniques are identified.
TL;DR: It is shown that, by controlling the alignment of molecules, it is possible to influence the high harmonic generation process by observing strong intensity modulation and spectral shaping of high harmonics produced with a rotational wave packet in a low-density gas.
Abstract: We show that, by controlling the alignment of molecules, we can influence the high harmonic generation process. We observed strong intensity modulation and spectral shaping of high harmonics produced with a rotational wave packet in a low-density gas of N2 or O2. In N2, where the highest occupied molecular orbital (HOMO) has sigma(g) symmetry, the maximum signal occurs when the molecules are aligned along the laser polarization while the minimum occurs when it is perpendicular. In O2, where the HOMO has pi(g) symmetry, the harmonics are enhanced when the molecules are aligned around 45 degrees to the laser polarization. The symmetry of the molecular orbital can be read by harmonics. Molecular wave packets offer a means of shaping attosecond pulses.
TL;DR: In this paper, the authors considered the problem of eliminating harmonics in a multilevel converter in which the separate dc sources vary, and they converted the transcendental equations that specify the elimination of the harmonics into an equivalent set of polynomial equations.
Abstract: Eliminating harmonics in a multilevel converter in which the separate dc sources vary is considered. That is, given a desired fundamental output voltage, the problem is to find the switching times (angles) that produce the fundamental while not generating specifically chosen harmonics. Assuming that the separate dc sources can be measured, a procedure is given to find all sets of switching angles for which the fundamental is produced while lower order harmonics are eliminated. This is done by first converting the transcendental equations that specify the elimination of the harmonics into an equivalent set of polynomial equations. Then, using the mathematical theory of resultants, all solutions to this equivalent problem can be found. Experimental results are presented to validate the theory.
TL;DR: In this paper, a nonlinear, adaptive mechanism is proposed for the extraction and measurement of individual harmonics of a signal with time-varying frequency, which offers higher degree of accuracy, structural/performance robustness, and frequency-adaptivity.
Abstract: A novel method of extraction and measurement of individual harmonics of a signal with time-varying frequency is presented. The proposed method is based on a nonlinear, adaptive mechanism. Compared with the well-established techniques such as DFT, the proposed method offers (i) higher degree of accuracy, (ii) structural/performance robustness, and (iii) frequency-adaptivity. The structural simplicity of the algorithm renders it suitable for both software and hardware implementations. The limitation of the proposed method as compared with DFT-based methods is its slower transient response. Based on simulation studies, performance of the method is presented and its accuracy and response time are compared with a DFT-based method.
TL;DR: In this article, a new control design using artificial neural networks is proposed to make the conventional shunt active filter adaptive, which can compensate for harmonic currents, power factor and nonlinear load unbalance.
Abstract: Problems caused by power quality have great adverse economical impact on the utilities and customers. Current harmonics are one of the most common power quality problems and are usually resolved by the use of shunt passive or active filters. In this paper, a new control design using artificial neural networks is proposed to make the conventional shunt active filter adaptive. The proposed adaptive shunt active filter can compensate for harmonic currents, power factor and nonlinear load unbalance. A self-charging technique is also proposed to regulate the dc capacitor voltage at the desired level with the use of a PI controller. The design concept of the adaptive shunt active filter is verified through simulation studies and the results obtained are discussed.
01 Jan 2005
TL;DR: In this article, the authors analyzed different space vector PWM (SVPWM) schemes for a five-phase VSI, which can be used for 5-phase motor drives.
Abstract: Application of power electronics in electric drives enables utilisation of AC machines with a phase number higher than three. Such multiphase motor drives are nowadays considered for various applications. Multiphase drives are invariably supplied from multiphase voltage source inverters (VSIs) and adequate methods for VSI pulse width modulation (PWM) are therefore required. This paper analyses different space vector PWM (SVPWM) schemes for a five-phase VSI, which can be used for five-phase motor drives. A detailed model of a five-phase VSI is presented first in terms of space vectors. Next, the existing technique of utilising only large space vectors is elaborated. It is shown that this SVPWM method leads to generation of high amounts of low-order output voltage harmonics. Finally, a novel SVPWM method is introduced, which enables operation with pure sinusoidal output voltages up to a certain reference voltage value, which is smaller than the maximum achievable with the given DC link voltage. To enable full utilisation of the DC bus voltage, this SVPWM scheme is complemented with another one, which unavoidably does lead to generation of some low order harmonics. These harmonics are however of significantly lower values than when only large vectors are used. A detailed performance evaluation of the existing and newly developed schemes is done and it is presented in terms of quality of the output voltage waveforms. Simulation results are included throughout the paper to illustrate and verify the theoretical considerations
TL;DR: In this article, a technique called Resonance Mode Analysis (RMA) is proposed for power system harmonic analysis, which is based on the singularity of the network admittance matrix.
Abstract: Harmonic resonance often manifests as high harmonic voltages in a power system. It was found that such resonance phenomenon is associated with the singularity of the network admittance matrix. The singularity, in turn, is due to the fact that one of the eigenvalues of the matrix approaches zero. By analyzing the characteristics of the eigenvalue, one can find useful information on the nature and extent of the resonance. The objective of this paper is to present our findings on this interesting subject. Based on the results, a technique called resonance mode analysis is proposed. Analytical and case study results have confirmed that the proposed method is a valuable tool for power system harmonic analysis.
TL;DR: It is demonstrated analytically and numerically that focusing of high harmonics produced by the reflection of a few-femtosecond laser pulse from a concave plasma surface opens a new way to unprecedentally high intensities.
Abstract: We demonstrate analytically and numerically that focusing of high harmonics produced by the reflection of a few-femtosecond laser pulse from a concave plasma surface opens a new way to unprecedentally high intensities. The key features allowing the boosting of the focal intensity are the harmonics coherency and the small exponent of the power-law decay of the harmonics spectrum. Using similarity theory and direct particle-in-cell simulations, we find that the intensity at the focus scales as ${I}_{\mathrm{C}\mathrm{H}\mathrm{F}}\ensuremath{\propto}{a}_{0}^{3}{I}_{0}$, where ${a}_{0}$ and ${I}_{0}\ensuremath{\propto}{a}_{0}^{2}$ are the dimensionless relativistic amplitude and the intensity of the incident laser pulse. The scaling suggests that due to the coherent harmonic focusing (CHF), the Schwinger intensity limit can be reached using lasers with ${I}_{0}\ensuremath{\approx}{10}^{22}\text{ }\text{ }\mathrm{W}/{\mathrm{c}\mathrm{m}}^{2}$. The pulse duration at the focus scales as ${\ensuremath{\tau}}_{\mathrm{C}\mathrm{H}\mathrm{F}}\ensuremath{\propto}1/{a}_{0}^{2}$ and reaches the subattosecond range.
TL;DR: A system comparison is developed between thyristor and chopper-rectifiers in terms of quality of control, harmonics, power factor, losses, and efficiency, and the most important requirements and specifications to be considered in the applications of these high-power units.
Abstract: This paper presents the different technologies used in the generation of large controlled currents, in the kiloamperes range. After a brief review of processes requiring large currents, the paper discusses the working principles of thyristor phase-controlled rectifiers commonly used in these applications. Chopper-rectifiers using high-current insulated gate bipolar transistors are introduced as an alternative being considered in recent projects. The pulsewidth-modulated current-source rectifier, currently used in medium-voltage motor drives, is also analyzed as a future alternative for rectification in industrial processes. In addition, this paper presents the most important requirements and specifications to be considered in the applications of these high-power units. A system comparison is developed between thyristor and chopper-rectifiers in terms of quality of control, harmonics, power factor, losses, and efficiency.
TL;DR: In this article, the authors used the Prolate Spheroidal coordinate system (PSCG) and expanded the time-dependent wave function in a complex basis of Laguerre polynomials and Legendre functions.
Abstract: We describe a numerical method used previously [Phys. Rev. A 70, 011404(R) (2004)] for solving the three-dimensional time-dependent Schr\"odinger equation for ${\mathrm{H}}_{2}^{+}$ (with fixed nuclei) in interaction with an intense, arbitrary oriented laser pulse. In this approach, we use the prolate spheroidal coordinate system, and expand the time-dependent wave function in a complex basis of Laguerre polynomials and Legendre functions. Our results indicate that ionization, excitation, and harmonic generation are strongly influenced by the orientation of the molecular axis with respect to the laser polarization axis. We evaluate the contribution of each nucleus to harmonic generation, as this permits a quantitative and nonambiguous assessment of interference effects as a function of molecular orientation. A time-profile analysis, using a Gabor transform of the harmonic spectrum around certain harmonics, shows that every half-cycle high-order harmonics are emitted by each nucleus when the electron wave packet returns for a recollision with the molecular core, thus confirming the strong field recollision model in molecules. In general, each nucleus emits both odd and even harmonics, but even harmonics are destroyed by interferences between contributions of each nucleus. These interferences are shown to be maximum at certain harmonic orders as a function of molecular orientation. A comparison of acceleration and dipole formulations of the harmonic emission process is made in order to assess the use of high-order harmonic generation for electron wave-function imaging.
TL;DR: In this article, a new control algorithm for an active power filter (APF) to compensate harmonic and reactive power of a 3-phase thyristor bridge rectifier under non-ideal mains voltage scenarios is presented.
TL;DR: In this paper, the authors present the results of an experimental study of the detection of mechanical faults in an induction motor by means of analysis of combinations of permeance and magneto-motive force (MMF) harmonics.
Abstract: This paper presents the results of an experimental study of the detection of mechanical faults in an induction motor. As is reasonably well known, by means of analysis of combinations of permeance and magneto-motive force (MMF) harmonics, it is possible to predict the frequency of air gap flux density harmonics which occur as a result of certain irregularities in an induction motor. In turn, analysis of flux density harmonics allows the prediction of induced voltages and currents in the stator windings. Reviewing this theory, equations which may aid in the identification of mechanical faults are presented. These equations include both those which indicate eccentric conditions and those which have been suggested to help identify bearing faults. The development of test facility to create eccentricity faults and bearing fault conditions is described. This test facility allows rapid access to the motor bearings, allowing an investigation into the ability to detect faulted bearing conditions using stator current monitoring. Experimental test results are presented, indicating that it may be possible to detect bearing degradation using relatively simple and inexpensive equipment.
TL;DR: In this article, a VSD power estimation method based on observed correlations between fundamental and higher harmonic spectral content in current was proposed, which can be generalized to any load with signature correlations in harmonic content.
Abstract: Nonintrusive load monitoring can be used to identify the operating schedule of individual loads strictly from measurements of an aggregate power signal. Unfortunately, certain classes of loads present a continuously varying power demand. The power demand of these loads can be difficult to separate from an aggregate measurement. Variable-speed drives (VSDs) are industrially important variable-demand loads that are difficult to track non-intrusively. This paper proposes a VSD power estimation method based on observed correlations between fundamental and higher harmonic spectral content in current. The technique can be generalized to any load with signature correlations in harmonic content, including many power electronic and electromechanical loads. The approach presented here expands the applicability and field reliability of nonintrusive load monitoring.
TL;DR: In this paper, the authors studied the generation of up to the 57th harmonic (λ = 13.96 nm) of a Ti:sapphire laser radiation from the prepulse produced silver plasma.
TL;DR: In this article, the nonlinear aeroelastic response of a two-dimensional airfoil, including a control surface with freeplay placed in an incompressible flow, is studied.
Abstract: The nonlinear aeroelastic response of a two-dimensional airfoil, including a control surface with freeplay placed in an incompressible flow, is studied. The model equations are formulated as a set of first-order ordinary differential equations. First, the dynamic response is investigated by a time integration method, and the time integration results are used for the verification of the harmonic balance results. The interesting hysteresis phenomenon and the effect of initial conditions of the subcritical bifurcation are presented. A higher-order harmonic balance method is then derived to investigate the high harmonics of the airfoil motions. The harmonic balance prediction is verified by comparison to the results from a numerical time marching integration and also by comparison to results from a previous experiment. Nomenclature a = nondimensional distance of the elastic axis from the midchord, with respect to the semichord B = damping submatrix b = semichord Ch = stiffness (per unit span) of wing in deflection C(k) = generalized Theodorsen function Cα, Cβ = torsional stiffness (per unit span) of wing around a and of aileron around c c = nondimensional distance of the control surface (aileron) hinge line from the midchord, with respect to the semichord
15 May 2005
TL;DR: In this paper, the authors present some design considerations of fault-tolerant synchronous motors, characterized by a fractional number of slots per pole per phase, including double-layer and single-layer winding.
Abstract: This paper presents some design considerations of fault-tolerant synchronous motors, characterized by a fractional number of slots per pole per phase. The first advantage of this configuration is a smooth torque, because of the elimination of the periodicity between slots and poles. The second one is a higher fault-tolerant capability making the machine able to work even in faulty conditions. However, the fractional-slot configuration presents a high contents of M.M.F. harmonics that may cause an unbalanced saturation and thus an unbearable torque ripple. A method to design fractional-slot motors is illustrated in the paper, including double-layer and single-layer winding. The analytical computation is extended to determine the harmonics of M.M.F. distribution. Their effect is highlighted in isotropic as well as anisotropic motors. Finally some considerations are reported to avoid unsuitable configurations