Performance Comparison between Adjustable Field
IPM Motor Based on Permeability Modulation
Technique and Conventional IPM Motor
Kiyohiro Iwama
Graduate School of Integrated Scienceand Technology
Shizuoka University
Hamamatsu, Japan
iwama.kiyohiro.14@shizuoka.ac.jp

Toshihiko Noguchi
Graduate School of Integrated Scienceand Technology
Shizuoka University
Hamamatsu, Japan
noguchi.toshihiko@shizuoka.ac.jp

Abstract—A proposed adjustable field interior permanent
magnet (IPM) motor based on a permeability modulation
technique was discussed in this paper.
The permeability
modulation technique can modulate the permeability of amagnetic material using magnetic saturation with the special
magnetic flux. The proposed IPM motor can control an amountof PM flux which interlinks to the stator windings modulating thepermeability of the leakage magnetic paths. In this paper, it was
confirmed that the proposed IPM motor has superiority of thedriving range, the copper loss when driving at the high-speed,
and torque ripple over the conventional IPM motor through theseveral electromagnetic field analyses.
Keywords—permeability modulation, adjustable field, IPM
motor, magnetic saturation, zero-phase current

I. INTRODUCTION
In recent years, the PM motors have been used widely
because these motors can realize the high output power density
in high efficiency. However, it is very difficult to achieve
compatibility design of low-speed-high-torque and high-speedlow-torque driving with the PM motor because the magnetic
field of the PM is constant. Conventionally, the high-speed
driving range of the PM motor has been enlarged utilizing thenegative d-axis current. However, it is a problem that thecopper loss increases in the high-speed driving range.
For this reason, the many adjustable field PM motors arefocused on [1]-[6]. The adjustable field PM motor which is
proposed in reference [1]-[4] can control the magnetic flux
density of an air gap utilizing the static magnetic field

generated by the field winding. However, the DC/DC
converter to generate the static magnetic field is required inthese motors. Therefore, the switching loss of the DC/DC
converter and the copper loss of the field winding increase. In
addition, these motors cannot output the reluctance torquebecause these motors are the surface PM motor. Therefore, theoutput density of these motors is lower than the IPM motor.
The adjustable field PM motor proposed in the reference [5]can achieve compatibility of the high-speed-low-torque andlow-speed-high-torque driving using the magnetization and thedemagnetization of the PM. However, this motor needs thelarge magnetomotive force (m.m.f.) for the magnetization anddemagnetization. Therefore, this motor must control it using
the large DC/AC inverter.
For the above problem, the authors have proposed the new
adjustable field method based on the permeability modulation
technique[10]. The adjustable field method using magnetic
saturation has been researched in reference [7]. However, thismethod uses the magnetic flux in the dq-reference frame formagnetic saturation of the leakage magnetic paths. In constant,the proposed method uses the independent magnetic flux
penetrating vertically for the dq-reference frame. We also haveproposed a 3-phase 4-wire inverter as the motor drive system of
the proposed IPM motor. The 3-phase 4-wire inverter cancontrol not only the d-axis current id and the q-axis
current iq but also the zero-phase current iz independently. This
motor drive system can adjust the field with only one inverter
utilizing iz as the m.m.f. source for the permeability
modulation.
Leakage PM flux

Magnetic saturation

Magnetic flux for permeability modulation
Permanent magnet magnetic flux

Soft magnetic metal(a) Without magnetic saturation.

(b) In case of magnetic saturation.

Fig. 1. Permeability modulation principle.

978-1-7281-3398-0/19/$31.00 ©2019 Crown(a) Without magnetic saturation.

(b) In case of magnetic saturation.

Fig. 2. Basic principle of proposed adjustable field.

DC

DC

AC

AC
Rotor

DC

AC
DC

AC

DC
StatorDC(a) Method using DC/DC converter.

(b) Method using time and/or space harmonics.

Fig. 3. Motor drive circuits of conventional adjustable field PM motor.

This paper described the detailed performances of the
proposed IPM motor obtained by the electromagnetic field
analysis. Besides, these analysis results of the proposed IPM
motor were compared with the conventional IPM motor.
II. BASIC ADJUSTABLE FIELD PRINCIPLE BASED ON
PERMEABILITY MOSULATION TECHNIQUE
A basic principle of the permeability modulation is shownin Fig. 1. As shown in Fig. 1, the main magnetic flux ishorizontally penetrating the soft magnetic metal, which isadjusted by the different magnetic flux for the permeability
modulation penetrating the soft magnetic metal vertically. By
intensifying the magnetic flux for the permeability modulation,
the soft magnetic metal is saturated magnetically, and its
permeability decreases. As a result, the main magnetic flux
penetrating the soft magnetic metal decreases. Therefore, it ispossible to control the main magnetic flux amount by
modulating the permeability of the soft magnetic metal.

Fig. 4. Motor drive circuit ofproposed adjustable field IPM motor.

III. DRIVE SYSTEMS OF ADJUSTABLE FIELD IPM MOTOR
A. Drive Systems of Conventional Adjustable Field PM Motor
Fig. 3 shows the motor drive system of the conventional
adjustable field IPM motor. The motor drive circuit shown in
Fig. 3(a) is used in [1]-[4]. The switching loss increases in thismotor drive system because this motor drive system uses the
DC/DC converter in addition to the DC/AD inverter. On theother hand, the adjustable field PM motor proposed in [6] uses
the motor drive system shown in Fig. 3(b). This motor drive
system can utilize the time and/or space harmonics byrectifying these harmonics in the rotor. However, the switchingloss increases as with Fig. 3(a) because this motor needs the
AC/DC rectifier in the rotor. Furthermore, this motor drive
system has drawbacks that the magnetic field is incontrollable
because the time and/or space harmonics increase in proportion
to the rotating speed based on Faraday’s law.

B. Drive System of Proposed Adjustable Field IPM Motor
Fig. 2 illustrates an application of the permeability
modulation technique described above, which makes it possible
The proposed motor drive system is depicted in Fig. 4. As
to control the leakage magnetic flux between the PM poles.
shown in Fig. 4, the proposed IPM motor connected to the 3This figure shows a cross-section of the 1/4 model of thephase 4-wire inverter. Therefore, it is possible to control not
proposed IPM motor. The leakage magnetic paths between the
only the three-phase current but also the iz. The iz is utilized as
PMs are modulated by the magnetic flux for the permeability
the permeability modulation m.m.f. source. The voltage
modulation. As already described, the permeability modulation
equation of the proposed motor drive system is as follows:is carried out by using the differently allocated special winding
 v0  ( Ra + 3Rz ) + pL000   i0   0 
in the stator in addition to the standard 3-phase windings.
    
 , (1)−ω Lq  id  +  0 
Ra + pLd
0
Therefore, this special winding is not called the field winding=vd  but the modulation winding. As shown in Fig. 2(a), when the vq  
ω Ld
Ra + pLq   iq  ωΨ f 0  leakage magnetic paths are not magnetically saturated, the shortmagnetic circuits are caused between the PMs. Therefore, thewhere the variables and the parameters are defined as
main magnetic flux of PMs hardly interlinks to the statorv0, vd, and vq: voltages on the 0dq reference frame,
windings. On the other hand, because the permeability
between the PMs decreases due to the magnetic saturation ofi0, id, and iq: currents on the 0dq reference frame,
the leakage magnetic paths, most of the PM flux interlinks to
Ra and Rz: three-phase and zero-phase winding resistance,
the stator windings, which corresponds to the intensified field
control as illustrated in Fig. 2(b). As described above, theL0, Ld, and Lq: winding inductances on the 0dq reference frame,
proposed strategy achieves the adjustable field control utilizing
p: differential operator, andthe permeability variation caused by the magnetic saturation of
the leakage magnetic paths between the PMs. Many of theω: angular speed.
adjustable field approaches give the motor some kinds ofFrom Eq. (1), we can control the iz using a brock diagram
electromagnetic energy in the high-speed driving range asshown
in Fig. 5. The switching loss of this motor drive systempresented [1]-[4] and [6]. However, in the proposed adjustable
is almost the same as the conventional motor drive systemfield method, the m.m.f. for the permeability modulation is
because switching times do not change. Furthermore, thedeceased in high-speed driving range. Therefore, the proposed
potential level at the neutral point does not vary because the iz
adjustable field method is completely different from any otheris used as the DC in this proposed adjustable field method.
approach in the past.

Therefore, the proposed motor drive system hardly exerts anadverse influence on the power supply voltage availability.
For these reasons, the proposed motor drive system has
superiorities about the switching loss and controllability
compared with the conventional motor drive systems.
IV. BASIC CHARACTERISTICS OF PROPOSED IPM MOTOR
A. Magnetic Circuit Dseding of Proposed IPM Motor
The proposed adjustable field IPM motor model analyzed
with JMAG-designer19.0TM and motor specifications areshown in Fig. 6 and TABLE Ⅰ, respectively. Both the stator
and the rotor core of the proposed motor is split into 2 parts,and the modulation winding is inserted between these stator
cores. In addition, the 3-dimensional magnetic circuit isrealized because the motor frame and the rotor shaft are madeof S45C. Moreover, the rotor skew is applied to the proposed
motor to reduce the space harmonics. The rotor skew with askew angle of 3.75 deg makes it possible to reduce the 6th andthe 12th order torque ripple.
Fig. 7 shows the relative permeability distribution provided
by only the modulation flux. The modulation m.m.f. Fm of1200 AT is given to the modulation winding in this analysis.
As can be seen from this figure, it is confirmed that thepermeability of the leakage magnetic path is 30. The initial
relative permeability of the electromagnetic steel sheet which isused as the rotor core is around 5000. From the above
simulation result, it can be seen that the proposed IPM motor
can modulate the permeability of leakage magnetic paths
supplying the Fm.
B. Basic Charateristics of Proposed IPM Motor
in No-Load condition
Fig. 8 shows the no-load electromotive force (e.m.f.)
waveforms and FFT analysis results in the two cases of the Fmof 0 and 1200 AT. The rotating speed is 3000 r/min in thisanalysis. According to Fig. 9, when the Fm is not given to themodulation winding, the fundamental component of the noload e.m.f. is 21.3 V. On the other hand, when the Fm of 1200
AT is given to the modulation winding, the fundamental
component of the no-load e.m.f. is 42.1 V. Therefore, thefundamental component of the no-load e.m.f. is adjustable by
49.4%. Moreover, it is confirmed that the odd-number orderharmonics except for the 3rd order harmonics are almost not
generated. This result is attributed to the rotor skew. From theanalysis results, it is confirmed that the proposed IPM motor
can control approximately half the magnetic field without theharmonics.

PM motor

Vdc
INV

i0*

*
－
d
* ＋－
q

i

i

＋
－

＋

vu* Suv0*
vd* 0dqvv* WP Sv↓* uvw * M
vq
vw S w

PI
PI
PI

＋
－
＋

＋

Lq
Ld

＋
＋

Ψa

1
s

θm

i0
id uvw↓
iq 0dq

ωm

iu
iv
iw

Fig. 5. Brock diagram of current controller.
Modulation winding(Copper)
Stator core
(35JN300)
Rotor shaft(S45C)
Rotor core
(35JN300)

PM(N39UH)

Stator frame(S45C)

Fig. 6. Proposed adjustable field IPM motor model.
TABLE Ⅰ. IPM Motor specifications.
Modulation current
Phase current
Current density
Number of poles
Number of slots
Armature windings
Modulation windings
Stator diameter
Rotor diameter
Stack length

10 Adc50 Arms
20 A/mm2
8 poles
48 slots
6 turns, 0.158 Ω
120 turns, 1.800 Ω
ϕ 148 mm
ϕ 96.6 mm
62 mm

Relative permeability

V. PERFORMANCE COMPARISON BETWEEN CONVENTIONAL
IPM MOTOR AND PROPOSED IPM MOTOR
A. Basic Charactetistics of Conventional IPM Motor
The conventional IPM motor model to compare with theproposed IPM motor and the specifications of these motors areshown in Fig. 9 and TABLE Ⅱ, respectively. The magnetic
circuit design of the rotor geometry of the conventional IPM

Fig. 7. Counter plot of relative permeability with Fm of 1200 AT.

10
0
-10
-20
-30
-40

35
30
25
20
15
10

60

120

180

240

300

360

Electrical angle (deg)(a) Waveforms of no-load e.m.f.

0

45

30

40

20

35

10
0
-10
-20
-30

5
0

40

No-load e.m.f. (V)20

Fm = 0 AT
Fm = 1200 AT

40

No-load e.m.f. (V)No-load e.m.f. (V)45

Fm = 0 AT
Fm = 1200 AT

30

No-load e.m.f. (V)40

0 1 2 3 4 5 6 7 8 9 10 11 12 13

-40

60

20
15
10

120

180

240

300

0

360

Electrical angle (deg)

0 1 2 3 4 5 6 7 8 9 10 11 12 13

Order(a) Waveforms of no-load e.m.f. (b) FFT analysis results of no-load e.m.f.

Fig. 8. No-load e.m.f. of proposed adjustable field IPM motor.

PM(N39UH)

25

5
0

Order

(b) FFT analysis results of no-load e.m.f.

30

Fig. 10. No-load e.m.f. of conventional IPM motor.
TABLE Ⅱ. Conventional motor specifications.

Armature winding(Copper)Current density
Number of poles
Number of slots
Armature
windings
Stator diameter
Rotor diameter
Stack length
Air gap length
Magnet shape
Magnet volume

Stator core
(35JN300)
Rotor core
(35JN300)

Proposed IPM motor
20 A/mm2
8 poles
48 slots
6 turns0.158 Ωϕ 148 mm
ϕ 96.6 mm
62 mm
0.7 mm
5.0 mm✕9.5 mm
36480 mm3

Conventional IPM motor
20 A/mm2
8 poles
48 slots
6 turns0.146 Ωϕ 148 mm
ϕ 96.6 mm
48 mm
0.7 mm
5.0 mm✕9.5 mm
36480 mm3

Fig. 9. Conventional IPM motor model.

Fig. 10 shows the no-load e.m.f. waveform and FFT analysis
result of the conventional IPM motor under the same condition
as an analysis shown in Fig. 8. However, the no-load e.m.f. of
the conventional IPM motor includes the large odd-number
order harmonics which are the 5th, the 7th, the 11th, and the13th order harmonics. The 6th and the 12th order torqueripples are generated by these e.m.f. harmonics.
B. Driving Range Comparison
Fig. 11 shows the driving ranges of the conventional IPM
motor and the Proposed IPM motor. The range shown with theblack line of Fig. 11(a) is the driving range of the conventional
IPM motor carried out the id = 0 control. Similarly, the blueline of Fig. 11(a) is the driving range of the conventional IPM
motor carried out the field weakening control, and the red lineof Fig. 11(a) is the driving range of the proposed IPM motor.
According to Fig. 11, the comparison results are shown in
TABLE Ⅲ.

20

Torque (Nm)motor model is made with the reference of the 2nd generation
PRIUS released from Toyota Motor Corporation. As can beseen in Fig. 10 and TABLE Ⅱ, the specifications and materialsof the conventional IPM motor is almost the same as the
proposed IPM motor. However, the stack length of theconventional IPM motor is slightly smaller than the proposed
IPM motor because the modulation winding is inserted in the
proposed IPM motor.

id = 0 control
Field weakening control

15

Magnet andreluctance torque10
50

Proposed IPM motor

Magnettorque05000

Magnettorque
10000

15000

20000

Rotating speed (r/min)(a) Conventional IPM motor.

25000

0

5000

10000

Driving range (p.u.)
Maximal output power
Maximal speed
Maximal torque

1.26
7.66 kW
21500 r/min
13.3 Nm

20000

25000

Fig. 11. Analysis results of driving range.

Firstly, the driving range of the proposed IPM motor iscompared with the conventional IPM motor carried out the id =0 control. These motors do not supply the id, and output the
only magnet torque. Moreover, when the iz of 10 Adc and thephase current of 50 Arms is given to the armature winding, thecurrent norm is 86.8 A in the 0dq-reference frame. Therefore,
these driving ranges shown in Fig. 11 was derived as the
maximal current norm in 86.8 A. As can be seen in TABLE Ⅲ,
it is confirmed that the proposed IPM motor has the superiority
in terms of the driving range, maximal output, and maximal
rotating speed. In particular, the driving range of the proposed
IPM motor is larger than the conventional IPM motor byaround 26 %.

TABLE Ⅲ. Comparison results of driving range.
Proposed IPM motor

15000

Rotating speed (r/min)(b) Proposed IPM motor.

Conventional IPM motor
id = 0 control
Field weakening control
1
1.17
6.20 kW
7.70 kW
10500 r/min
14000 r/min
14.8 Nm
14.8 NmD. Torque Ripple Comparison
The comparison results of the torque ripple factor are shownin Fig. 13. As can be seen in Fig. 13, the torque ripple factor of
the proposed IPM motor is lower than the conventional IPM
motor all over the driving range. This result is caused by thedifference of the odd-number order harmonics of no-load e.m.f.
shown in Fig. 8 and Fig. 10. Fig. 14 shows the torquewaveforms when both the motor output the equivalent averagemagnet torque. Because the odd-number order harmoniccomponents of the no-load e.m.f. of the proposed IPM motor islower than the conventional IPM motor, the 6th and the 12thorder torque of the proposed IPM motor are lower than theconventional IPM motor. Moreover, the torque ripple factor of
the conventional IPM motor increase in high-speed driving
range as illustrated in Fig. 13 (b). Fig. 15 shows the torquewaveforms and FFT analysis results when the id = 0 control andthe field weakening control are applied to the conventional IPM
motor. As indicated in Fig. 15, both the average torque is equal,
and the 12th order torque increases applying the field

C

Torque (Nm)

15

10

5

0

0

5000

10000

15000

20000

25000

Rotating speed (r/min)(a) Proposed adjustable field IPM motor.
20

Copper loss (W)1000

Torque (Nm)

15

800
600

10

400
5

0

200
0
0

5000

10000

15000

20000

25000

Rotating speed (r/nin)(b) Conventional IPM motor.

Fig. 12. Copper loss comparison results.
20

T

15

Torque (Nm)C. Copper Loss Comparison
Fig. 12 shows the copper loss map of the proposed IPM
motor and the conventional IPM motor. The three driving
ranges which are low-speed-high-torque, medium-speed-hightorque, and high-speed-low-torque driving range are consideredin the following. The rotating speed is from 0 r/min to 4000
r/min, and torque is from 10 Nm to 15 Nm in low-speed-hightorque driving range. As can be seen in Fig. 12, the copper lossof the proposed IPM motor is slightly larger than theconventional IPM motor because the modulation current is
supplied to the proposed IPM motor in this driving range.
Moreover, when the rotating speed becomes higher to around5000 r/min, this gap of the copper loss becomes wide. The
field weakening control is applied to the conventional IPM
motor in this driving range. Therefore, the conventional IPM
motor outputs the high reluctance torque because negative id is
supplied. For this reason, the conventional IPM motor outputs
the high torque with less current than the proposed IPM motor.
However, the similar characteristic is expected in the proposed
IPM motor because the proposed IPM motor can also output
the reluctance torque supplying the negative id. Furthermore,
the copper loss of the proposed IPM motor is lower than theconventional IPM motor in the high-speed-low-torque driving
range. The proposed IPM motor does not supply themodulation current. In constant, the conventional IPM motor
supplies the lots of the negative id for the field weakening
control. Hence, the proposed IPM motor can drive with lesscurrent than the proposed IPM motor.

20

10

5

0

0

5000

10000

15000

20000

25000

Rotating speed (r/min)(a) Proposed adjustable field IPM motor.
Torque ripple factor
(%)
40

20

15

Torque (Nm)Secondly, the effects of the field weakening control areconsidered by making a comparison between the black line andthe blue line of Fig. 11. As can be seen from this comparison,
The high-speed driving range is expanded by the field
weakening control. There are two main reasons for this result.
The first reason is the PM flux is weakened by d-axis flux. The
second reason is the conventional IPM motor outputs not only
the magnet torque but also the reluctance torque. In thefollowing examination, the driving range of the proposed IPM
motor is compared with the conventional IPM motor carriedout the field weakening control.

30
10

20

5

0

10
0
0

5000

10000

15000

20000

25000

Rotating speed (r/nin)(b) Conventional IPM motor.

Fig. 13. Torque ripple factor comparison results.

2.0
1.5
1.0

Conventional IPM motor
Proposed adjustable field IPM motor
0

60

120

180

240

300

360

Electrical angle (deg)(a) Waveforms of magnet torque.

2.0
1.5
1.0

2.5
2.0
1.5

id = 0 control
Field weakening control

0.5
0.0

1.0

0 1 2 3 4 5 6 7 8 9 10 11 12

id = 0 control
Field weakening control

2.5

Torque (Nm)Magnet torque (Nm)Magnet torque (Nm)

2.5

2.5

3.0

3.0

Conventional IPM motor
Proposed adjustable field IPM motor

Torque (Nm)

3.0

3.0

0

60

120

180

240

300

Electrical angle (deg)Order(b) FFT result of magnet torque.

(a) Waveforms of torque.

Fig. 14. Analysis results of magnet torque.

2.0
1.5
1.0
0.5

360

0.0

0 1 2 3 4 5 6 7 8 9 10 11 12

Order(b) FFT result of torque.

Fig. 15. Torque waveforms and FFT analysis results of
conventional IPM motor.
Magnet flux density(T)(a) 11-th order harmonics.

(b) 13-th order harmonics.

Fig. 16. Contour plots of flux density with id = 0control.

(a) 11-th order harmonics.

(b) 13-th order harmonics.

Fig. 17. Counter plots of flux density with field weakening control.

weakening control. The contour plots of the 11th and the 13thorder harmonic armature flux when the 2 controls applied tothe conventional IPM motor are shown in Fig. 16 and Fig. 17,
respectively. As can be seen from these figures, the 11th andthe 13th order harmonic flux increase supplying the negative id
to the motor. From the above analysis results, the proposedadjustable field method can realize the torque ripple reduction
in comparison with the conventional IPM motor.
VI. CONCLUSION
The adjustable field IPM motor based on the permeability
modulation technique was proposed in this paper. From theanalysis results, it was confirmed that the proposed IPM motor
can adjust the magnetic field of 49.4 %. Moreover, theproposed IPM motor was compared with the conventional IPM
motor in terms of the driving range, the copper loss, and thetorque ripple.
Firstly, according to the driving range
comparison results, it was thought that the proposed IPM motor
has superiority in terms of the driving range and maximal
rotating speed.
Secondly, judging by the copper loss
comparison results, we could see that the copper loss of the
proposed IPM motor tends to decrease in high-speed driving
range as compared with the conventional IPM motor. Finally,
from the torque ripple comparison results, it was confirmed thatthe proposed IPM motor can reduce the torque ripple comparedwith the conventional IPM motor.
The future work is confirming the validity of theelectromagnetic field analysis results through several
experimental verifications.

REFERENCES[1]

T. Mizuno, K. Nagayama, T. Ashikaga, and T. Kobayashi: “Bashic
Principles and Characteristics of Hybrid Excitation Type Synchronous
Machine,” IEEJ Trans. on IA., Vol. 115, No. 11, pp. 1402-1411 (1995)[2] M. Namba, K. Hiramoto, and H. Nakai: “Novel Variable-Field Motorwith a Three-Dimentional Magnetic circuit,” IEEJ Trans. on IA., Vol.
135, No. 11, pp. 1085-1090 (2015)[3] T. Ogawa, T. Takahashi, M. Takemoto, H. Arita, A. Daikoku, and S.
Ogasawara: “The Consequent-Pole Type Ferrite Magnet Axial Gap
Motor with Field Winding for Traction Motor Used in EV,” SAEJ Proc.
EVteC & APE Japan 2016, No.20169094(2016)[4] J.A. Tapia, F. Leonardi, and T.A. Lipo: “Consequent-pole PermanentMagnet Machine with Extended Field-Weakening Capability,” IEEE
Trans. on IA., Vol. 39, No. 39, pp. 1704-1709 (2003)[5] R. Tsunata, M. Takemoto, and S. Ogata: “Investigation of a Variable
Flux Memory Motor Using Delta-type PM Arrangement and Extended
Flux Barrier for Traction Applications, Ver.1,” IEEJ IA Society
Conference, 3-71, pp.III-408–412 (2019)[6] M. Aoyama, K. Nakajima, T. Noguchi: “Proposal and Preliminary
Experimental Verification of Electrically Reversal Magnetic Pole Type
Variable Magnetic Flux PM Motor,” IEEJ Journal of IA., Vol. 7, No. 3,
pp. 270-281 (2018)[7] T. Kato, H. Hijikata, M. Minowa, Kan. Akatsu, and Robert. D. Lorentz,“Design Methodology for Variable Leakage Flux IPM for Automobile
Traction Drives ,” IEEE Trans. on IA., Vol 51, No. 5, pp. 3811-3821(2015)[8] T.C. Julio: “3D cross coupling effect for flux control in magnetic circuitwith Permanent Magnet,” International Symposium on PowerElectronics, Electrical Drives, Automation and Motion, pp. 742-745(2014)[9] Q. Ronghai, M. Aydin, and T.A. Lipo: “Performance comparison of dual
-rotor radial flux and axial-flux permanent-magnet BLDC machines,”
IEMDC’03. IEEE International, Vol. 3, pp. 1948-1954 (2003)[10] T. Noguchi, K. Iwama, and M. Aoyama: “Adjustable Field PM Motor
Based on Permeability Modulation Technique Using Zero-Phase
Current,” ICEMS2019 (2019)