MMF Components Research Articles

Torque Ripple Reduction in Brushless Wound Rotor Vernier Machine Using Third-Harmonic Multi-Layer Winding

This article aims to realize the brushless operation of a wound rotor vernier machine (WRVM) by a third-harmonic field produced through stator auxiliary winding (X). In the conventional model, a third-harmonic current is generated by connecting a 4-pole armature and 12-pole excitation windings serially with a three-phase diode rectifier to develop a pulsating field in the airgap of a machine. However, in the proposed model, the ABC winding is supplied by a three-phase current source inverter, whereas the auxiliary winding (X) carries no current due to an open circuit. The fundamental MMF component developed in the machine airgap creates a four-pole stator field, while the third-harmonic MMF induces the harmonic current in the specialized rotor harmonic winding. The rotor on the other side contains the harmonic and the field windings connected through a full-bridge rectifier. The electromagnetic interaction of the stator and rotor fields generates torque. Due to the open-circuited winding pattern, the proposed machine results in a low torque ripple. A 2D model is designed using JMAG-Designer, and 2D field element analysis (FEA) is carried out to determine the output torque and machine’s efficiency. A comparative performance analysis of both the conventional and proposed topologies is discussed graphically. The quantitative analysis of the proposed topology shows better performance as compared to the recently developed third-harmonic-based brushless WRVM topology in terms of output torque and torque ripples.

Novel Dual Inverter Sub-Harmonic Synchronous Machines

Sub-harmonic synchronous machines are a relatively new bread of brushless wound field synchronous machines considered alternatives to many electric machines in transportation electrification applications. This paper presents two dual inverter sub-harmonic synchronous machines having unique two-layer and three-layer stator winding topologies. The two inverters provide the stator windings with two sets of balanced three-phase currents. These two and three-layer windings are arranged in such a way that they can generate both fundamental and sub-harmonic magnetomotive force. Furthermore, the fundamental MMF component of this machine is four times the sub-harmonic MMF component used for the brushless operation. In contrast, the sub-harmonic magnetomotive force is used for field excitation, which leads to brushless operation. Two 8-pole, 48-slot, 2-inverter, 2-layer and 3-layer sub-harmonic machines are designed to validate the concept through a 2-D finite element analysis of these new topologies, showing a better overall torque profile and performance as compared with the other sub-harmonic and brushless wound field synchronous machines.

Multilayer Concentrated Windings for Axial Flux PM Machines

Coreless axial flux machines are of interest because of the absence of stator core losses and cogging torque. These machines generally employ concentrated windings. One of the challenges with such a winding is that the torque producing MMF component that corresponds to the fundamental of the magnet excitation is accompanied by substantial asynchronous components. These harmonics cause losses in the rotor core and magnets, which can become significant at high speeds. This paper proposes a new multilayer winding arrangement to eliminate the non-torque producing MMF components. This winding is applied to a 12-coil 16-pole coreless axial flux machine. The efficacy of the winding is established by 3-D finite-element analysis.

Principle of Operation and Performance of a Synchronous Machine Employing a New Harmonic Excitation Scheme

This paper presents a new harmonic current excitation principle for a synchronous machine drive based on control of the spatial third harmonic MMF. Unlike existing harmonic excitation technologies, which utilize the third harmonic components of the rotor magnetic field, this brushless harmonic excitation principle is realized by injecting an ac single-phase current component or dc component into three-phase open stator windings thereby utilizing the resultant third harmonic spatial stator MMF component. This additional component generates either a stationary or time pulsating magnetic field which will induce voltages in a specially designed rotor winding. Through rectification, the induced voltage is used to supply dc current to the rotor excitation winding. To verify the aforementioned principle, theoretical analyses, magnetic field calculations by finite-element analysis and experiments with a 1.0-kW prototype machine have been performed and key influential factors have been investigated. The test results are shown to be consistent with the theoretical analysis, which validates the correctness of the theory.

Effect of Number of Layers on Performance of Fractional-Slot Concentrated-Windings Interior Permanent Magnet Machines

Interior PM machines equipped with fractional-slot concentrated-windings are good candidates for high-speed traction applications. This is mainly due to the higher power density and efficiency that can be achieved. The main challenge with this type of machines is the high rotor losses at high speeds/frequencies. This paper will thoroughly investigate the effect of number of winding layers on the performance of this type of machines. It will be shown that by going to higher number of layers, there can be significant improvement in efficiency especially at high speeds mainly due to the reduction of the winding factor/magnitude of the most dominant stator mmf subharmonic component. It will also be shown that there is significant improvement in torque density. Even though there is reduction in the winding factor of the stator synchronous torque-producing mmf component, this is more than offset by increase in machine saliency and reluctance torque. The paper will provide general guidelines regarding the optimum slot/pole/phase combinations based on torque density and efficiency. Sample designs of various slot/pole combinations are used to quantify the benefit of going to higher number of layers in terms of torque density, efficiency, and torque ripple.

Dynamic eccentricity in squirrel cage induction motors – Simulation and analytical study of its spectral signatures on stator currents

Most of faults in three-phase induction motors have relationship with airgap eccentricity. There are two forms of airgap eccentricity: static (SE) and dynamic (DE). According to the literatures, the well known signatures of dynamic eccentricity, on the stator current spectra, are sidebands around the principal slot harmonics (PSH). However, many other researches have shown that DE induces also spectral components around the fundamental, but few are reported on the sources and the causes of these components. In this direction and since it is difficult to study experimentally the DE separately from the SE; the present paper attempts to explain, analytically and by simulation, the generation process of all frequency components that are a function of only DE. For that reason, a detailed analytical study for three-phase induction motors working under DE is performed. This study is based on rotating field approach. A general theoretical analysis of the interaction between all harmonics of the eccentric airgap permeance and the stator and rotor MMF components is put forward. The simulation results, obtained from an accurate model, confirm the existence of specific frequency components around the fundamental, caused by the dynamic airgap eccentricity. The interactions between the DE and the inherent SE are also illustrated using this mathematical model.

Analysis of Synchronous Reactances as a Function of Airgap MMF

Saturation modeling in synchronous machines normally involves assumptions in order to formulate proper mathematical models. A problem exists in the characterization of saturated synchronous reactances when they are represented as a function of total airgap ampere-turns. This paper presents a finite element numerical analysis of this saturation representation, and it is shown that it does not hold in all operating conditions. A steady-state model to predict field-current and load angle is presented. It is based on the use of d-q mmf components. Two large turbo-generators of 13.8 kV, 150 MVA and 22 kV, 588 MVA are studied.

Hemispheric lateralization of the processing of consonant-vowel syllables (formant transitions): effects of stimulus characteristics and attentional demands on evoked magnetic fields

It is still unsettled in how far temporal resolution of dynamic acoustic events (formant transitions) or phonetic/linguistic processes contribute to predominant left-hemisphere encoding of consonant-vowel syllables. To further elucidate the underlying mechanisms, evoked magnetic fields in response to consonant-vowel events (synthetic versus spoken) were recorded (oddball design: standards=binaural/ba/, deviants=dichotic/ba/-/da/; 20 right-handed subjects) under different attentional conditions (visual distraction versus stimulus identification). Spoken events yielded a left-lateralized peak phase of the mismatch field (MMF; 150–200 ms post-stimulus onset) in response to right-ear deviants during distraction. By contrast, pre-attentive processing of synthetic items gave rise to a left-enhanced MMF onset (100 ms), but failed to elicit later lateralization effects. In case of directed attention, synthetic deviants elicited a left-pronounced MMF peak resembling the pre-attentive response to natural syllables. These interactions of MMF asymmetry with signal structure and attentional load indicate two distinct successive left-lateralization effects: signal-related operations and representation of ‘phonetic traces’. Furthermore, a right-lateralized early MMF component (100 ms) emerged in response to natural syllables during pre-attentive processing and to synthetic stimuli in case of directed attention. Conceivably, these effects indicate right hemisphere operations prior to phonetic evaluation such as periodicity representation. Two distinct time windows showed correlations between dichotic listening performance and ear effects on magnetic responses reflecting early gain factors (ca. 75 ms post-stimulus onset) and binaural fusion strategies (ca. 200 ms), respectively. Finally, gender interacted with MMF lateralization, indicating different processing strategies in case of artificial speech signals.