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Proceedings ArticleDOI

A bi-harmonic five-phase SPM machine with low ripple torque for marine propulsion

01 May 2017-pp 1-7

AbstractThis paper addresses the design of a bi-harmonic five-phase Surface-mounted Permanent Magnet (SPM) machine for marine propulsion. The bi-harmonic characteristic results from the particular 20 slots-8 poles configuration that makes possible high value of third harmonic current injection. Thus the machine performance can be improved in terms of average torque, speed range, losses control and torque quality, this last feature being the scope of the paper. As low ripple torques are wanted at low speed, the magnet layer is defined to reduce the cogging torque and to make third harmonic current injection increasing average torque and reducing pulsating torque in the same time. According to a selection procedure based on the numerical simulations of a high number of machines, it appears that designing the rotor with two identical radially magnetized magnet that cover two-third the pole arc allows to reach this goal. Referring to an equivalent three-phase machine, the torque ripple level of the bi-harmonic five-phase machine is more than three times lower, thus being obtained with a simple control strategy that aims at achieving constant currents in the rotating frames. The time simulations of the drive confirm the significant reduction of the speed oscillation, especially at low speed.

Topics: Torque ripple (74%), Cogging torque (74%), Direct torque control (67%), Torque sensor (67%), Stall torque (67%)

Summary (3 min read)

Introduction

  • Multi-phase motors are widely used in electrical marine propulsion for reasons such as reliability, smooth torque and distribution of power [1].
  • Furthermore, Surface-mounted Permanent Magnet (SPM) rotor facilitates the ripple torque mitigation that is of critical importance at low speed.
  • A machine equipped with this winding can be considered as a bi-harmonic five-phase machine since it inherently offers an electronic pole changing effect [10].
  • This paper focuses on a characteristic not yet described for 20-8-5 SPM machine.
  • The second part addresses the design of the 20-8-5 machine.

A. Multi-machine decomposition of a five-phase machine

  • If the magnetic saturations and the demagnetization issue are not considered, it can be shown that a star-connected five- phase SPM machine behaves as two two-phase virtual machines that are magnetically independent but electrically and mechanically coupled [14].
  • Furthermore, as the rotor saliency can be neglected with SPM machines, the space harmonics are distributed among the two virtual machines: the virtual machine sensitive to the fundamental is called Main Machine (MM) whereas the other sensitive to the third harmonic is called Secondary Machine (SM).
  • MM and SM are also characterized by their cyclic inductances that will be of the same order with a tooth-concentrated winding, thus making easier the current regulation of the two virtual machines in case of PWM controlled voltage inverter.

B. Electromagnetic torque calculation

  • Therefore the five-phase machine electromagnetic torque T is the sum of the torque produced by the Main Machine T1 and the Secondary Machine T3.
  • According to the space harmonic distribution property, the MM pulsating torque t1(γ) results from the interaction of the fundamental of the current with particular back-emf harmonics (1st, 9th, (10k ± 1)th) .
  • The same applies for the SM pulsating torque t1(γ) that results from the interaction of the 3rd harmonic of current with particular back-emf harmonics (3rd, 7th, (10k ± 3)th).

C. Control strategy

  • At low speed, Maximum Torque Per Ampere (MTPA) control is wanted, thus meaning that, for both virtual machines, back-emf and current should be aligned.
  • The trouble is that the average torque enhancement usually comes with more pulsating torque since the SM pulsating torques t3 add up to the MM ones t1.
  • This control strategy is called h1h3-damp: it consists in choosing a particular ratio r that depends of harmonics 7th, 9th, 11th and 13th of the back-emf, that is calculated in order to eliminate the first harmonic of the pulsating torque.
  • Therefore the implementation of the control with simple PI controllers can be used since the necessary bandwidth of the controllers does not relate to the frequency of the torque ripple.

A. Objectives

  • The present section focuses on the 20-8-5 machine design to make the two strategies h1h3-boost and h1h3-damp practically similar.
  • Hence third harmonic current injection will increase the average torque and reduce the pulsating torque in the same time.
  • Due to its particular winding, the 20-8-5 machine should be designed to be supplied with first and third harmonic of current at low speed.
  • As it can be observed in Fig-1 that illustrates the electromagnetic circuit of the machine over one pole pair, the magnet arc length τm has to be chosen as a trade-off between cogging and pulsating torque reduction.
  • The main machine parameters are listed in table I.

B. Design exploration

  • The best design is found by using a numerical two-dimensionnal field calculation (Finite Elements Analysis FEA software FEMM, [17]).
  • Skewing the rotor or the stator would be necessary to mitigate the cogging torque, thus making the manufacturing more complex.
  • Finally, the investigated 20-8-5 machines with two magnets per pole is compared with an equivalent 12-8-3 one, thus meaning that the equivalent 3- phase machine is also equipped with a rotor made with two identical radially magnetized magnets per pole.
  • One can observe that the peak cogging torque can be minimized by choosing τm equal to 0.33 for the 5-phase machine and by choosing τm equal to 0.36 for the 3-phase one: nevertheless, according to the FEA predictions, the minimum cogging torque for the 5-phase machine is about two times lower than the 3-phase machine one.
  • For 20-8-5 machine, it is worth mentioning that the h1h3-boost control reduces the pulsating torques referring to h1 control if the magnet arc length is between 0.29 and 0.40 the pole pitch, which is quite compliant with the analytical predictions reported in Fig-2.

C. Results

  • The resulting electromagnetic circuit is depicted in Fig.1.
  • For the designed 20-8-5 machine, the average values of the 1-q and 3-q are almost equal, which complies with the back-emf spectrum analysis.
  • For the 5-phase machine, the FEA torque estimations with the three possible control strategies are shown: h1h3-boost, h1 and h3.
  • It is also worth mentioning that, with these two controls (h1 and h3), the resulting ripple torques are almost equal to the one obtained with the best 12- 8-3 machine (whereas h1 and h3 controls are not the proper control for the optimal 20-8-5 machine).

B. Results

  • Fig.-8 shows the resulting torque waveforms for the 12-8-3 and 20-8-5 machines according to the simulation of the drives (in steady state).
  • The torque ripple reduction with the 5-phase machine is about three times which complies with the FEA results given in Fig-4.
  • The significant speed oscillation reduction is then illustrated.
  • In particular, at low speed (250rpm), the difference between the maximum speed and the minimum speed is about 70 times lower with the 20-8-5 machine (against 8 times at 1000rpm).

V. CONCLUSION

  • This paper addresses the design of a bi-harmonic fivephase SPM machine for marine propulsion.
  • As low ripple torques are wanted at low speed, the magnet layer is defined to reduce the cogging torque and to make third harmonic current injection increasing average torque and reducing pulsating torque in the same time.
  • Designing the rotor with two identical radially magnetized magnets that cover two-third the pole arc appears as a possibility to reach this goal.
  • Numerical simulations of the five-phase machine confirm this approach and show a significant torque quality improvement: referring to an equivalent three-phase machine, the torque ripple level is reduced by more than three times.
  • The possibility to eliminate the ripple torques with a simple control that aims at achieving constant currents in the rotating frames is evaluated with a time simulation of the drive.

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To cite this version :
Franck SCUILLER, Hussein ZAHR, Eric SEMAIL - A bi-harmonic five-phase SPM machine with
low ripple torque for marine propulsion - In: 2017 IEEE International Electric Machines and Drives
Conference (IEMDC), Etats-Unis, 21-05-20 - A bi-harmonic five-phase SPM machine with low
ripple torque for marine propulsion - 2017
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978-1-5090-4281-4/17/$31.00
c
2017 IEEE.
A bi-harmonic ve-phase SPM machine with low
ripple torque for marine propulsion
Franck Scuiller
1
, Hussein Zahr
2
, Eric Semail
2
1
Ecole Navale; Naval Academy Research Institute, Brest, France, franck.scuiller@ecole-navale.fr
2
Ecole Nationale Sup
´
erieure d’Arts et M
´
etiers; Laboratory of Electrical Engineering and Power Electronics, Lille, France
Abstract—This paper addresses the design of a bi-harmonic
five-phase Surface-mounted Permanent Magnet (SPM) machine
for marine propulsion. The bi-harmonic characteristic results
from the particular 20 slots-8 poles configuration that makes
possible high value of third harmonic current injection. Thus
the machine performance can be improved in terms of average
torque, speed range, losses control and torque quality, this last
feature being the scope of the paper. As low ripple torques are
wanted at low speed, the magnet layer is defined to reduce the
cogging torque and to make third harmonic current injection
increasing average torque and reducing pulsating torque in the
same time. According to a selection procedure based on the
numerical simulations of a high number of machines, it appears
that designing the rotor with two identical radially magnetized
magnet that cover two-third the pole arc allows to reach this
goal. Referring to an equivalent three-phase machine, the torque
ripple level of the bi-harmonic five-phase machine is more than
three times lower, thus being obtained with a simple control
strategy that aims at achieving constant currents in the rotating
frames. The time simulations of the drive confirm the significant
reduction of the speed oscillation, especially at low speed.
I. INTRODUCTION
Multi-phase motors are widely used in electrical marine
propulsion for reasons such as reliability, smooth torque and
distribution of power [1]. For low power propulsion system
(less than 10kW), the power partition constraint results from
the low DC voltage (less than 60V) that supplies the drive.
Hence increasing the phase number enables to limit the rating
of the power electronic components. In addition, compactness
objective can be more easily achieved if the phase number is
considered as a design parameter. For instance, with ve-phase
machine, third harmonic current injection can be performed
to boost the torque [2], [3]. Regarding the rotor, Permanent
Magnet (PM) structure contributes to enhance the power den-
sity [4], [5]. Furthermore, Surface-mounted Permanent Magnet
(SPM) rotor facilitates the ripple torque mitigation that is of
critical importance at low speed. If fractional-slot windings
facilitate the reduction of cogging torque for SPM machine [6],
they also generate magnetomotive force harmonics that could
result in excessive magnet losses. Machine with 0.5 slots per
phase and per pole (s
pp
=0.5) are known to limit this effect
[7]. In addition, the slot filling can also be improved with this
solution [8]. Therefore the machine here considered is a five-
phase machine with 20 slots and 8 poles (20-8-5 configuration)
for a marine propeller.
Three-phase machine with 12 slots (12-8-3 configuration)
could be chosen but this solution does not provide fault
tolerant ability. Furthermore, in [9] where 20-8-5 and 12-8-
3 machines are compared for the same design specifications
(rated torque, power and external diameters are identical) and
the same volume of magnetic materials (magnet, copper and
iron), it is shown that the 5-phase configuration makes possible
a significant reduction of the magnet losses, according to
numerical computations.
20-8-5 configuration is a particular winding distribution in
so far as the third harmonic factor (0.98) is higher than the
fundamental one (0.57). A machine equipped with this wind-
ing can be considered as a bi-harmonic five-phase machine
since it inherently offers an electronic pole changing effect
[10]. With this characteristic, the efficiency of the machine
can be improved for the whole speed range: the possibility
of limiting the magnet losses at high speed is shown in [9],
[10]. The speed range can be enlarged: this is true for SPM
machine [11] but also for Interior PM machine [12].
This paper focuses on a characteristic not yet described
for 20-8-5 SPM machine. In [13], it is shown that, for five-
phase SPM machine, a quite simple third harmonic current
injection can be used to virtually eliminate the pulsating
torque. The trouble is, except in case of particular design,
the smoother torque is obtained for a lower average torque.
The present study shows that, with a proper but quite simple
design of the rotor magnet layer, it is possible to inject third
harmonic to increase the average torque and to reduce the
ripple torque in the same time, which is particularly useful
at low speed. The paper will be divided into three parts.
The first part introduces the multi-machine decomposition for
ve-phase SPM machine in order to determine bi-harmonic
(first and third) current control strategies. The second part
addresses the design of the 20-8-5 machine. A high number of
machines are simulated with Finite-Elements Analysis (FEA)
in order to select the best solution regarding the ripple torque
reduction. To demonstrate the improvement regarding three-
phase machines, 12-8-3 machines are also examined. The last
part focuses on the time simulation of the drive to preliminary
evaluate the possible influence of the current control on the
ripple torque and the rotating speed deviation.
II. M
ULTI-MACHINE DECOMPOSITION OF FIVE-PHASE
SPM MACHINE TO DETERMINE CONTROL STRATEGIES
A. Multi-machine decomposition of a five-phase machine
If the magnetic saturations and the demagnetization issue
are not considered, it can be shown that a star-connected five-

phase SPM machine behaves as two two-phase virtual ma-
chines that are magnetically independent but electrically and
mechanically coupled [14]. Furthermore, as the rotor saliency
can be neglected with SPM machines, the space harmonics
are distributed among the two virtual machines: the virtual
machine sensitive to the fundamental is called Main Machine
(MM) whereas the other sensitive to the third harmonic is
called Secondary Machine (SM). The space harmonics are
distributed according to the following law:
MM is sensitive to 1
st
, 9
th
, (10k ± 1)
th
harmonics
SM is sensitive to 3
rd
, 7
th
, (10k ± 3)
th
harmonics
Actually the virtual machine is a physical reading of the
mathematical subspace built on the linear application that
describes the phase-to-phase magnetic couplings: this two-
dimension subspace is usually represented with αβ-axis circuit
in stationary frame or with dq-axis circuit in rotating frame.
MM and SM are also characterized by their cyclic inductances
that will be of the same order with a tooth-concentrated
winding, thus making easier the current regulation of the two
virtual machines in case of PWM controlled voltage inverter.
B. Electromagnetic torque calculation
Therefore the five-phase machine electromagnetic torque T
is the sum of the torque produced by the Main Machine T
1
and
the Secondary Machine T
3
.Ifγ denotes the electrical angle,
the following expression is obtained:
T (γ)=T
1
(γ)+T
3
(γ) (1)
In case of first and third harmonic current control strategy,
MM and SM torques can be expressed as follows:
T
1
(γ)=
5
2
1
I
1
cos θ
1
+ t
1
(γ) (2)
T
3
(γ)=
5
2
3
I
3
cos θ
3
+ t
3
(γ) (3)
In (2) and (3),
1
and
3
are the first and third harmonics
of the no-load back-emf (at one rad/s speed), I
1
and I
3
are
the first and third harmonics of the current and θ
1
and θ
3
are the current-to-back-emf angles for first and third harmonic
respectively. t
1
and t
3
denote the pulsating torques. According
to the space harmonic distribution property, the MM pulsating
torque t
1
(γ) results from the interaction of the fundamental
of the current with particular back-emf harmonics (1
st
, 9
th
,
(10k ± 1)
th
) . The same applies for the SM pulsating torque
t
1
(γ) that results from the interaction of the 3rd harmonic of
current with particular back-emf harmonics (3
rd
, 7
th
, (10k ±
3)
th
).
C. Control strategy
At low speed, Maximum Torque Per Ampere (MTPA) con-
trol is wanted, thus meaning that, for both virtual machines,
back-emf and current should be aligned. Thus the current-to-
back-emf angles equal zero. Therefore, if r denotes I
3
rms
current to I
1
rms current ratio and I
b
the rated rms current of
the machine (that determines the copper losses), the control
strategy can be summarized as follows:
(I
1
1
)=
I
b
1+r
2
, 0
(I
3
3
)=
rI
b
1+r
2
, 0
(4)
MTPA is obtained if ratio r equals back-emf
3
to back-emf
1
ratio:
r
boost
=
3
1
(5)
With this approach, third harmonic current injection increases
the average torque. This strategy is called h1h3-boost. With
this strategy, the trouble is that the average torque enhancement
usually comes with more pulsating torque since the SM
pulsating torques t
3
add up to the MM ones t
1
.
In [13], a control strategy that aims at using the SM to
compensate the pulsating torque of the MM is introduced. This
control strategy is called h1h3-damp: it consists in choosing a
particular ratio r that depends of harmonics 7th, 9th, 11th and
13th of the back-emf, that is calculated in order to eliminate
the first harmonic of the pulsating torque.
r
damp
=
11
9
13
7
(6)
The limitation of this strategy is that the SM operates as gener-
ator to absorb the pulsating torques of the MM, thus reducing
the average torque and the efficiency. The two introduced
controls (h1h3-boost and h1h3-damp) can be considered as
quite simple control in so far as they aim to regulate constant
currents in the dq-frames. In particular, h1h3-damp control
does not require a time varying d or q current components
to mitigate the ripple torques (as in [15]). Therefore the
implementation of the control with simple PI controllers can
be used since the necessary bandwidth of the controllers does
not relate to the frequency of the torque ripple.
III. M
ACHINE DESIGN
A. Objectives
The present section focuses on the 20-8-5 machine design to
make the two strategies h1h3-boost and h1h3-damp practically
similar. Hence third harmonic current injection will increase
the average torque and reduce the pulsating torque in the
same time. Due to its particular winding, the 20-8-5 machine
should be designed to be supplied with first and third harmonic
of current at low speed. Therefore the base idea consists in
designing the rotor such as third harmonic current injection
results in average torque increase (boost effect, see (5)) and
pulsating torque reduction (damp effect, see (6)) in the same
time. However attention must be drawn to the cogging torque
that can be very large for this kind of machine: magnet
segmentation is a solution to mitigate the cogging torque.
It should be mentioned that a quite simple design is aimed
for: simple magnet shape and no rotor or stator skewing.
Finally, in order to satisfy the pulsating and cogging torque
reduction constraints, solutions where the rotor consists in two

identical radially magnetized magnets are explored. As it can
be observed in Fig-1 that illustrates the electromagnetic circuit
of the machine over one pole pair, the magnet arc length τ
m
has to be chosen as a trade-off between cogging and pulsating
torque reduction.
τ
m
Fig. 1. Machine electromagnetic circuit (for τ
m
=1/3)
0.29 0.3 0.31 0.32 0.33 0.34 0.35
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Magnet arc τ
m
to pole arc ratio
Δ T
h1h3−boost
/ Δ T
h1
1st harmonic
All harmonics
Fig. 2. Magnet arc τ
m
for which boost control reduces the pulsating torques
(referring to sinus control)
At the pre-design step, the influence of the magnet arc
length on the pulsating torque can be analyzed by using an
analytical two-dimensional field calculation that allows a quite
accurate estimation of the electromagnetic torque [16]. Thus
fig-2 shows the variation of the pulsating torque when using
boost control (denoted ΔT
h1h3boost
, corresponding to (5))
out of the pulsating torque when using sinus control (denoted
ΔT
h1
, obtained by chosing r =0in (4)) according to the mag-
net arc length τ
m
. The dash line reports ΔT
h1h3boost
/ΔT
h1
ratio change when only considering the first pulsating torque
harmonic whereas the solid line corresponds to the ratio
change when accounting the whole pulsating torque harmon-
ics. According to Fig-2, the boost control has damp effect if
the magnet arc length is chosen between 0.29 and 0.34 the
pole arc. The main machine parameters are listed in table I.
TABLE I
P
ARAMETERS FOR THE 5-PHASE MACHINE
Base point 9.5Nm @ 1000rpm
Pole pair number p =4
Slot number per phase per pole s
pp
=0.5
Effective length L
m
=0.050m
Stator Diameter 2R
s
=0.100m
Stator yoke thickness t
ys
=0.010m
Mechanical airgap g =0.001m
Rotor yoke thickness t
yr
=0.010m
Magnet layer thickness h
m
=3g
Remanent flux density B
r
=1.17T
Slot width (τ
s
, tooth pitch) 0.5τ
s
Slot width opening 0.25τ
s
Slot-closing thickness t
sc
=0.002m
Slot depth d
s
=0.0405m
B. Design exploration
In this part, the best design is found by using a numerical
two-dimensionnal field calculation (Finite Elements Analysis
FEA software FEMM, [17]). The advantages of the inves-
tigated 20-8-5 machine has to be discussed with regards to
an equivalent 12-8-3 machine (with the same rotor diameter,
magnet height and air gap).
Usually the rotor of 12-8-3 machine is made with a single
magnet per pole that covers two-third the pole pitch. For the
considered design specifications, according to FEA, such a
machine presents an excessive torque ripple: the peak cogging
torque is about 2.2Nm and the max-to-min full torque with
MTPA sinus control strategy is higher than 4.5Nm (that is
mostly 50% the rated torque). Consequently, skewing the rotor
or the stator would be necessary to mitigate the cogging torque,
thus making the manufacturing more complex. Controlling
the currents to mitigate the cogging torque is possible but
more complex and less robust than simply achieving constant
currents in the dq-frame. Finally, the investigated 20-8-5
machines with two magnets per pole is compared with an
equivalent 12-8-3 one, thus meaning that the equivalent 3-
phase machine is also equipped with a rotor made with two
identical radially magnetized magnets per pole.
Practically, by varying the pole arc to pole pitch ratio τ
m
from 0.25 to 0.49 by 0.01 step, 25 3-phase and 25 5-phase
machines are computed: for each of them, no-load and load
torques (9.5Nm) are calculated and recorded. Whatever the
magnet arc length is, the stator current is modified to make
the machine produce the rated average torque (the impact on
the thermal and inverter designs is not examined since the
goal is finding the less ripple torque solution). For the 3-phase
machine, sinus MTPA current control is supposed whereas, for
the 5-phase one, three current control strategies are computed:
the MTPA h1h3-boost control introduced by eq.(5)
the fundamental sinus current control (h1, all the torque
is produced by the MM, using the 4-pole polarity)

the third harmonic current control (h3, all the torque is
produced the SM, using the 3×4-pole polarity).
Fig-3a represents the peak cogging torque change according
to the magnet arc length τ
m
. One can observe that the peak
cogging torque can be minimized by choosing τ
m
equal to
0.33 for the 5-phase machine and by choosing τ
m
equal
to 0.36 for the 3-phase one: nevertheless, according to the
FEA predictions, the minimum cogging torque for the 5-phase
machine is about two times lower than the 3-phase machine
one. This can be explained by lower slot openings for the
5-phase machine.
Fig-3b focuses on the pulsating torque change with magnet
arc length τ
m
for the 12-8-3 and 20-8-5 machines. The
pulsating torque can be reduced up to about 0.6Nm with the 3-
phase machine if the magnet arc length is 0.42 the pole pitch.
It can be observed that the possible pulsating torque reduction
is significantly better with the 5-phase machine: in case of
h1h3-boost control, a magnet arc length equal to 0.32 the
pole pitch corresponds to a pulsating torque of about 0.2Nm
(that is three times lower that the best 12-8-3 solution). For
20-8-5 machine, it is worth mentioning that the h1h3-boost
control reduces the pulsating torques referring to h1 control
if the magnet arc length is between 0.29 and 0.40 the pole
pitch, which is quite compliant with the analytical predictions
reported in Fig-2. Furthermore, with regards to h3 control, the
resulting pulsating torques are always reduced with the h1h3-
boost control if the magnet arc length is higher than 0.3 the
pole pitch. Finally, according to the numerical predictions, the
boost control has a damp effect if the magnet arc length is
between 0.3 and 0.4 the pole pitch.
Fig-3c reports the full ripple torque (cogging and pulsating)
for the 3-phase and 5-phase machines. As in Fig-3b, 5-phase
machine ripple torque is estimated for three current control
strategies: h1h3-boost, h1 and h3. First, one can observe that
the best torque ripple reduction is obtained for the 20-8-5
machine with h1h3-boost control: if the magnet pole arc is
0.33 the pole pitch, the max-to-min ripple torque is about
0.5Nm that is more than four times lower the value obtained
with the best 12-8-3 machine (about 2.2Nm, corresponding to
τ
m
=0.39). In addition, if the analysis is restricted on the 5-
phase machine, Fig-3c clearly shows that such a ripple torque
reduction can not be obtained with h1 or h3 controls. For these
two controls, the best result is obtained for h1 current control
applied to a machine with τ
m
=0.44: the ripple torque is then
about 1Nm, that is two times the best values (τ
m
=0.33 with
h1h3-boost control).
C. Results
The final design is the 20-8-5 machine with magnet length
equals one-third (0.33) the pole arc. The resulting electromag-
netic circuit is depicted in Fig.1. It is worth mentioning that
the final 5-phase machine has the same magnet volume as the
usual 12-8-3 one (with a single magnet per pole covering two-
third the pole pitch), examined at the beginning of subsection
III-B.
0.25 0.3 0.35 0.4 0.45 0.5
0
0.5
1
1.5
2
2.5
3
3.5
4
Magnet Arc Length to Pole Pitch ratio τ
m
Max Cogging Torque (Nm)
12−8−3
20−8−5
(a) Peak cogging torque change with τ
m
0.25 0.3 0.35 0.4 0.45 0.5
0
1
2
3
4
5
6
7
Magnet Arc Length to Pole Pitch ratio τ
m
Max−to−min Em Torque (Nm)
12/8/3
20/8/5 (h1h3−boost)
20/8/5 (h1)
20/8/5 (h3)
(b) Max-to-min eletromagnetic torque change with τ
m
0.25 0.3 0.35 0.4 0.45 0.5
0
1
2
3
4
5
6
7
8
Magnet Arc Length to Pole Pitch ratio τ
m
Max−to−min Em Torque (Nm)
12/8/3
20/8/5 (h1h3−boost)
20/8/5 (h1)
20/8/5 (h3)
(c) Max-to-min full torque change with τ
m
Fig. 3. Magnet pole arc choice with regard to ripple torque

Citations
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Proceedings ArticleDOI
01 Sep 2018
Abstract: The paper addresses the design of a seven-phase Surface-mounted Permanent Magnet (SPM) machine with tooth-concentrated winding. As the fundamental winding factor is lower than the third, the rated control strategy aims at generating a third harmonic current component greater than the fundamental. For this control, the magnet layer is designed with the constraint of maximizing the average torque and minimizing the ripple torques. Solutions where the pole consists of several identical radially-magnetized magnets (regularly space shifted along the pole arc) are explored: designing the rotor with two identical radially magnetized magnets that cover about three-quarters the pole arc appears as the best solution. In addition, fifth harmonic current injection can be performed to slightly enhance the torque without increasing the ripples. 2D FEA confirms these results. Furthermore, according to analytical approach, positive impacts on some parasitic effects (as the radial stress and the magnet losses) are expected.

4 citations


Cites background from "A bi-harmonic five-phase SPM machin..."

  • ...5 slot per phase and per pole is studied in [7] and [8] (with 4 poles): referring to an equivalent 3-phase machine (12 slots and 4 poles), the possible advantages of this bi-harmonic 5-phase machine regarding the ripple torques, the magnet losses limitation and the speed range enlargement for given Volt-Ampere inverter are discussed....

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Journal ArticleDOI
TL;DR: This article investigates maximum possible torque improvement in a two-pole surface permanent magnet synchronous machine with a reduced magnet span, which causes production of highly nonsinusoidal back electromotive force (EMF).
Abstract: This article investigates maximum possible torque improvement in a two-pole surface permanent magnet synchronous machine with a reduced magnet span, which causes production of highly nonsinusoidal back electromotive force (EMF). It contains a high third and a fifth harmonics, which can be used for the torque enhancement, using stator current harmonic injection. Optimal magnet span is studied first, and it is shown that with such a value, the machine would be able to develop an insignificantly lower maximum torque than with the full magnet span. Next, field-oriented control algorithm, which considers all nonfundamental EMF components lower than the machine phase number, is devised. Using maximum torque per ampere principles, optimal ratios between fundamental and all other injected components are calculated and then used in the drive control. The output torque can be in this way increased up to 45% with respect to the one obtainable with fundamental current only. Alternatively, for the same load torque, stator current rms value can be reduced by 45%. Last but not least, a method for position sensor fault mitigation is introduced. It is based on the alternative use of a back-EMF harmonic for rotor position estimation, instead of the torque enhancement. Experimental verification is provided throughout for all the relevant aspects.

2 citations


Cites background from "A bi-harmonic five-phase SPM machin..."

  • ...Five-phase machines have been studied the most [3]–[16]....

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  • ...3007053 [2], marine [3], and aerospace [4] industries....

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  • ...In contrast to, say, [3], where a fractional slot PMSM was considered, the machine is with an integer slot number per phase per pole....

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  • ...A 5-phase 20-slot 8-pole dual-harmonic machine with surface magnets was developed in [3] in order to reduce torque ripple....

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Journal ArticleDOI
Abstract: If multi-phase machines equipped with tooth-concentrated winding with half a slot per pole and per phase offer interesting characteristics (simplified manufacturing, no space subharmonic, fault-tolerant ability), their low fundamental winding factors make their designs and controls challenging. The paper addresses the case of a seven-phase Surface-mounted Permanent Magnet (SPM) machine which has a fundamental winding factor lower than the third. This so-called bi-harmonic specificity is considered in order to achieve good torque quality (average value and ripples). Regarding the design, the magnet layer is segmented into two identical radially magnetized tiles that cover about three-quarters the pole arc. Regarding the control, the rated Maximum Torque Per Ampere (MTPA) supply strategy (h1h3 control) aims at generating a third harmonic current component greater than the fundamental. A prototype has been manufactured: the ability of the machine to provide smooth torque is experimentally confirmed through the implementation of a simple MTPA control which copes with high distortion in no-load voltage.

2 citations


Journal ArticleDOI
Abstract: Model-based sensorless field-oriented control (FOC) suffers from overparameterization and can be laborious to use for a five-phase permanent magnet synchronous motor On the other hand, insulated gate bipolar transistor (IGBT) frequently fails in an electric drive Under IGBT failure, a freewheeling current is observed, and, above all, it carries the failed phase back electromotive force information Based on this observation, this article presents the design of a brand new sensorless FOC by exploiting the freewheeling current to accommodate both IGBT and position sensor failures, which is expected to further enhance the drive's fault-tolerant capability The mathematical model of this current is first established to provide a theoretical basis and a comprehensive understanding of the presented sensorless FOC By virtue of this model, a second-order generalized integrator with a frequency-locked loop can be used as a simple and elegant way to extract position/speed estimates Experimental results are provided to validate the proposed sensorless FOC philosophy

References
More filters

Journal ArticleDOI
TL;DR: An attempt is made to provide a brief review of the current state of the art in the area of variable-speed drives, addressing the reasons for potential use of multiphase rather than three-phase drives and the available approaches to multiphases machine designs.
Abstract: Although the concept of variable-speed drives, based on utilization of multiphase machines, dates back to the late 1960s, it was not until the mid- to late 1990s that multiphase drives became serious contenders for various applications. These include electric ship propulsion, locomotive traction, electric and hybrid electric vehicles, ldquomore-electricrdquo aircraft, and high-power industrial applications. As a consequence, there has been a substantial increase in the interest for such drive systems worldwide, resulting in a huge volume of work published during the last ten years. An attempt is made in this paper to provide a brief review of the current state of the art in the area. After addressing the reasons for potential use of multiphase rather than three-phase drives and the available approaches to multiphase machine designs, various control schemes are surveyed. This is followed by a discussion of the multiphase voltage source inverter control. Various possibilities for the use of additional degrees of freedom that exist in multiphase machines are further elaborated. Finally, multiphase machine applications in electric energy generation are addressed.

1,559 citations


"A bi-harmonic five-phase SPM machin..." refers background in this paper

  • ...Multi-phase motors are widely used in electrical marine propulsion for reasons such as reliability, smooth torque and distribution of power [1]....

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Journal ArticleDOI
TL;DR: This paper will cover the theory and design of FSCW synchronous PM machines, achieving high-power density, flux-weakening capability, comparison of single- versus double-layer windings, fault-tolerance rotor losses, parasitic effects, compared of interior versus surface PM machine, and various types of machines.
Abstract: Fractional-slot concentrated-winding (FSCW) synchronous permanent magnet (PM) machines have been gaining interest over the last few years. This is mainly due to the several advantages that this type of windings provides. These include high-power density, high efficiency, short end turns, high slot fill factor particularly when coupled with segmented stator structures, low cogging torque, flux-weakening capability, and fault tolerance. This paper is going to provide a thorough analysis of FSCW synchronous PM machines in terms of opportunities and challenges. This paper will cover the theory and design of FSCW synchronous PM machines, achieving high-power density, flux-weakening capability, comparison of single- versus double-layer windings, fault-tolerance rotor losses, parasitic effects, comparison of interior versus surface PM machines, and various types of machines. This paper will also provide a summary of the commercial applications that involve FSCW synchronous PM machines.

1,065 citations


"A bi-harmonic five-phase SPM machin..." refers background in this paper

  • ...In addition, the slot filling can also be improved with this solution [8]....

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Journal ArticleDOI
18 May 1997
Abstract: The influence of various design parameters on the cogging torque developed by permanent magnet machines is investigated. It is shown that the slot and pole number combination has a significant effect on the cogging torque, and influences the optimal value of both skew angle and magnet arc, as well as determining the optimal number of auxiliary teeth/slots. A simple factor, which is proportional to the slot number and the pole number and inversely proportional to their smallest common multiple, has been introduced to indicate the "goodness"/spl beta/ of the slot and pole number combination. In general, the higher the "goodness" factor the larger the cogging torque.

822 citations


Book
01 Jan 2002
Abstract: Part I: PWM Converters: Topologies and Control 1 Power Electronic Converters 2 Resonant dc Link Converters 3 Fundamentals of the Matrix Converter Technology 4 Pulse Width Modulation Techniques for Three-Phase Voltage Source Converters Part II: Motor Control 5 Control of PWM Inverter-Fed Induction Motors 6 Energy Optimal Control of Induction Motor Drives 7 Comparison of Torque Control Strategies Based on the Constant Power Loss Control System for PMSM 8 Modeling and Control of Synchronous Reluctance Machines 9 Direct Torque and Flux Control (DTFC) of ac Drives 10 Neural Networks and Fuzzy Logic Control in Power Electronics Part III: Utilities Interface and Wind Turbine Systems 11 Control of Three-Phase PWM Rectifiers 12 Power Quality and Adjustable Speed Drives 13 Wind Turbine Systems Index

712 citations


"A bi-harmonic five-phase SPM machin..." refers background in this paper

  • ...The following hypotheses are taken: • the inverter is made with perfect switches and the DC bus voltage continuously equals 60V • an intersective modulation based on a carrier signal at 10kHz is considered • dq-axis currents (classical dq-axis currents for the 3-phase machine and d1q1-axis (MM) and d3q3-axis (SM) for the 5-phase machine) are regulated with PI controllers tuned according to [18] with back-emf compensation • the mechanical load increases with the square of the rotating speed (such as, at full speed, the load torque is the rated machine torque) • the rotating speed is not regulated....

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Journal ArticleDOI
A.B. Proca, Ali Keyhani1, A. El-Antably, Wenzhe Lu1, Min Dai1 
Abstract: This paper presents an analytical method of modeling permanent magnet (PM) motors. The model is dependent only on geometrical and materials data which makes it suitable for insertion into design programs, avoiding long finite element analysis (FEA) calculations. The modeling procedure is based on the calculation of the air gap field density waveform at every time instant. The waveform is the solution of the Laplacian/quasi-Poissonian field equations in polar coordinates in the air gap and takes into account slotting. The model allows the rated performance calculation but also such effects as cogging torque, ripple torque, back-EMF form prediction, some of which are neglected in commonly used analytical models.

171 citations


Frequently Asked Questions (2)
Q1. What are the contributions mentioned in the paper "A bi-harmonic five-phase spm machine with low ripple torque for marine propulsion" ?

This paper addresses the design of a bi-harmonic five-phase Surface-mounted Permanent Magnet ( SPM ) machine for marine propulsion. Thus the machine performance can be improved in terms of average torque, speed range, losses control and torque quality, this last feature being the scope of the paper. Referring to an equivalent three-phase machine, the torque ripple level of the bi-harmonic five-phase machine is more than three times lower, thus being obtained with a simple control strategy that aims at achieving constant currents in the rotating frames. 

Designing the rotor with two identical radially magnetized magnets that cover two-third the pole arc appears as a possibility to reach this goal. The possibility to eliminate the ripple torques with a simple control that aims at achieving constant currents in the rotating frames is evaluated with a time simulation of the drive.