D5-5

Back E.M.F. Waveform Optimization of Magnetically Modulated Motor
Sawanth Krishna Machavolu*, Toshihiko Noguchi, Masahiro Aoyama (Shizuoka University)
1. INTRODUCTION
This paper focuses on improvement of back electromotive force(e.m.f) of a magnetically modulated motor (MMM).

The structureof the motor is quite different from standard PMSMs because it has
two rotating parts, i.e., an inner PM rotor and an outer modulator.
Computer simulations conducted in the open stator winding circuit
case show that the induced e.m.f. becomes imbalanced at lowerspeeds.

Therefore, this paper discusses the nature of the induced

e.m.f. of the prototype, and improvement of the e.m.f. waveform isachieved by optimizing the modulator shape by introducing air
gaps in the iron bridge parts.

4. CONCLUSION
This paper discussed improvement of the induced e.m.f.
waveform of a magnetically modulated motor by optimizing themodulator shape.

The THDs when the modulator is rotating andwhen it is locked are estimated to be 28 % and 52 % for theprototype, but they can be reduced down to 5.7 % and 6.2 % for theoptimized one, respectively.

REFERENCES[1] Y. Takeuchi, H. Kato, M. Tago, S. Ogasawara, and H. Sakai, “OperatingPrinciple and Control Method of the Magnetic Modulated Motor,” IEEJNational Convention Record, no.5-041, 2013, pp. 73-74.

2. WAVEFORM OF ORIGINAL PROTOTYPE
Fig. 1 shows a cross-section view of the original prototype
MMM.

The prototype MMM has a relationship among the statorpole-pair number Ps, the inner PM rotor pole-pair numbers Ppm, andthe number of the outer modulator iron cores Pmod, which can berepresented by Ps: Ppm: Pmod = n: 2n: 3n (n is a natural number),respectively.

The prototype has been made with n = 4, and thestator has 48 slots with distributed windings.

Fig. 1. Cross section of original prototype MMM.

The electricalfrequency fs for this motor is given by the following equation:f s  Pmod f mod  Ppm f pm ,(1)

where fmod and fpm are the mechanical frequencies of the modulator
and the inner rotor, respectively.

Fig. 2 shows the 2D FEA resultsof the induced e.m.f. waveforms at various speeds and their FFTresults.

Here the stator frequency has been kept at 120Hz.

Thesimulation tests reveal that the induced e.m.f. gets distorted atlower speeds.

Fig. 2. Induced e.m.f. of prototype MMM.

The major harmonic components are the fifth andthe seventh, and are generated due to the magnetic paths in thestator-side iron bridge parts of the modulator.

3. OPTIMIZATION OF MODULATOR
The induced e.m.f. is detrimentally distorted by the harmoniccomponents; hence the modulator shape should be optimallymodified to reduce them.

The modification has been applied tothe stator-side iron bridge parts of the modulator by inserting theair gaps.

(a) Modified modulator. (b) Flux density FFT.
Fig. 3. Modulator with modified iron bridge parts.

Fig. 3(a) shows the magnetic flux density along thestator-side air gap for different inserted air gaps. it is possible toimprove the symmetry of the waveform.

Fig. 4 shows the induced

e.m.f. waveforms and the corresponding FFT results of the
optimally modified modulator configuration.

As can be seen fromthe simulation results, even a small air gap length such as 1 mm isgood enough to reduce the harmonics in the induced e.m.f.
Fig. 4. Induced e.m.f. of optimaized MMM.

平成30年度 電気・電子・情報関係学会東海支部連合大会（2018年9月3日14日 於名城大学）