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Analytical method for the evaluation of electromagnetic vibrations in the seven-phase ac motor

V.M. Tereshkin

Vestnik IGEU, 2019 issue 1, pp. 61—69

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Abstract in English: 

Background. It has been established that with an increase in the number of motor phases, the magnitude of the phase current and the level of vibrations of electromagnetic origin decrease. There are works that provide an analysis of the spectrum of the space-time harmonics of the resulting current of a four-phase winding, as well as five-phase and three-phase windings. However, the problem of studying the effect of time harmonics of phase currents of the symmetric seven-phase winding on the formation of space-time harmonics has not been studied yet. The aim of the work is to identify the unique properties of the seven-phase winding, in which the space-time spectrum of the resulting current contains only the first harmonic.

Materials and method. We used an analytical method for calculating the space-time harmonics of the resulting current of a seven-phase winding for given time phase harmonics. The analytical approach used is original and represents a development of the theory of electric machines. The study assumes that the air gap is uniform. Considering this question with this assumption makes it possible to reveal the main features of the field in the air gap formed by the seven-phase winding as compared with the windings having a different number of phases.

Results. The seven-phase winding of the electric machine is considered, namely, its ability to form a resultant (space-time) sinusoidal current, despite the presence of time harmonics of phase currents. It has been established that the odd time harmonics of the phase currents of the symmetrical seven-phase winding do flow in phases but do not form space-time harmonics of the forward and reverse sequence, which completely excludes one of the factors of vibrations of electromagnetic origin. The phase currents of the seventh time harmonic of the symmetric seven-phase winding do not have a relative time shift, which excludes the very fact that they can flow.

Conclusions. It has been established that there are no higher harmonics in the spectrum of the resulting space-time current of the seven-phase winding that forms the magnetizing force and the flow in the gap. This circumstance may have a favourable effect on the decrease in the level of vibrations of electromagnetic origin. The properties of the seven-phase winding may be of particular interest in the implementation of the electric drive with vector control.

 

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Key words in Russian: 
семифазная обмотка двигателя, результирующий вектор тока, временные гармоники фазных токов, вибрации электромагнитного происхождения
Key words in English: 
seven-phase motor winding, resultant current vector, time harmonics of phase currents, vibration of electromagnetic origin
The DOI index: 
10.17588/2072-2672.2019.1.061-069
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