Download Multiphase Induction motor

Multiphase Induction motor-a Novel Design
Prof. Dr.Archana S. Nanoty, Principal, Dr. Jivraj Mehta Institute of Technology, Mogar, Anand, Gujarat
Abstract— Variable-speed AC motor drives with more
than three phases (multi-phase drives) have several
advantages when compared to the standard three-phase
realizations [1,2]: the current stress of the semiconductor
devices decreases proportionally with the phase number,
torque ripple is reduced, rotor harmonic currents are
smaller, power per rms ampere ratio is higher for the
same machine volume and harmonic content of the DC
link current for VSI fed drives is reduced. Other
advantages include an improvement in the noise
characteristics [3] and a reduction in the stator copper
loss, leading to improved efficiency [4]. Further
advantages are related to the higher reliability at the
system level, since a multi-phase drive can operate with
an asymmetrical winding structure in the case of loss of
one or more inverter legs/machine phases [5,6]
generate a rotatory field. Consequently, if one phase is
lost the drive continues operating although at different
rating values. Because of this reason, during the last
three decades there is a growing interest to research
several issues related to the use of multi-phase drives as
a potential alternative for the conventional three-phase
systems. This is especially true for dual three phase
induction motor drives and their applications [4]. This
induction machine has two sets of three-phase windings
which are spatially phase shifted by 30 electrical
degrees, as shown in figure 1.
Applications of multi-phase induction motor drives are
mainly related to the high-power/high-current
applications, such as for example in electric ship
propulsion [7,8], in locomotive traction [9,10] and in
electric/hybrid electric vehicles [11].
Keywords— six-phase induction machines, split phase
Winding.
Magnetic circuit, Dual Stator machines
INTRODUCTION:- Conventional 3-phase drives have
been extensively used in industry applications. However,
if one of the phases is lost, the rotatory field also
disappears and the machine stops. The multi-phase
drives offer the improvement of the system reliability,
which is of great interest in specialized applications such
as electric/hybrid vehicles or aerospace applications.
Independently of the number of phases the multi-phase
machine has, it only needs two degrees of freedom to
Figure 1:- Six phase Induction Motor
Split-phase electrical machines consist of two similar
stator windings sharing the same magnetic circuit. Such
a construction made it possible to extend the power
range of solid-state based drives by sharing the total
power between two drives [2,4]. Usually a split-phase
machine is built by splitting the phase belt of a
conventional three-phase machine into two equal parts
with spatial phase separation of 30 electrical degrees. By
using this arrangement, for the same air gap flux, the
inverter dc bus voltage can be reduced by approximately
a half, compared to a three-phase system, since the
number of turns per phase is reduced [4]. Such structure
has a disadvantage of the need for two or more inverters
to drive the machine. Another advantage of using this
kind of winding arrangement is harmonic cancellation.
The sixth harmonic torque pulsation, which is common
in a six-step three-phase drive, can be eliminated by
using split-phase arrangement, [5, 6].
As in split-phase machines, the dual-stator machines
consist basically of two independent stator windings
sharing the same magnetic frame. Differently, a dual
stator machine does not necessarily have similar winding
groups. For example, a 6 different voltage rating or a
different number of phases could be used for each
winding group.
The six-phase machine uses the same magnetic frame
with the baseline machine. We have the 4-pole machine
with 36 stator slots. In order to keep the leakage
distribution balanced, the phases are displaced among
the two stator layers. The six-phases are constructed
such that one three-phase group is displaced from the
other one by 30 electrical degrees. Thus we have an
asymmetrical six phase machine where;
One of the three-phase groups has the same structure of
the baseline machine with
half of the circuits and winding distributed in 3 slots per
pole per phase (qA = 3).
The second group is distributed into 4 slots per pole per
phase (qX = 4) but keeping the same number of
conductors per pole per phase.
The stator size used is the stator used for 7.5 HP motor
as the torque is very high about 40 % more than that of
the original 3 phase 3 HP motor .The details of the stator
dimensions are as follows.
STATOR DIMENSIONS:-
Stator Bore or Inner Diameter
=125 mm
Stator Slots
= 36
ROTOR DIMENSIONS:θm = 2. θe / p
θm = 2 . 30° / 4 = 15° mechanical
(I)
(II)
Slot pitch = 360° / 36 = 10° mechanical (III)
Outer Diameter
=125 mm
Rotor Slots
= 28
Conductor size:- 22 SWG
Conductors per slot = 104
Hence, the 30 electrical degrees displacement
corresponds to 15°/10° = 1.5 slots.
No. of Turns per phase= 312
Insulation:- ClassF
We cannot implement such a configuration and have to
use an approximation. This is how it is done:
Figure 4:- Winding Diagram of ‘Phase C’
Figure 2:- Winding Diagram of ‘Phase A’
Figure 5:- Winding Diagram of ‘Phase X’
Figure 3:- Winding Diagram of ‘Phase B’
Figure 6:- Winding Diagram of ‘Phase Y’
Figure 7:- Winding Diagram of ‘Phase C’
Conclusion:- The motor testing results are as given
below:When terminals ABC are supplied with 3
phase Ac.
Supply
Voltage
Current
Speed
In Amp in
ABC
In RPM
60 V
0.94,0.9,0.9
1475
105 V
1.27,1.27,1.24 1489
152 V
1.82,1.77,1.75 1491
202 V
2.33,2.30,2.37 1492
When terminals XYZ are supplied with 3 phase AC.
Actual Photograph of 6 ph stator at the time of
winding
Actual photograph of the motor with two three phase
sets abc and xyz
Supply
Voltage
Current
Speed
In Amp in
ABC
In RPM
60 V
0.91,0.84,0.84 1467
108 V
1.36,1.34,1.38 1484
154 V
1.8,1.88,1.82
200 V
2.41,2.32,2.38 1492
1486
Now the motor is to be run when both the
three phase sets are supplied simultaneously
i.e. six phase operation. For that we need to
supply the motor through inverter.
The torque obtained very high upto 40 %
more than the three phase motor of same
rating. Motor finds its application in Ship
Propulsion, Air craft, Hybrid electric Vehicle
Etc. where Large torque at lower speed is
required. Also overall efficiency of the motor
increases.
Future Scope:- The motor stability can be
calculated. The same motor may be
controlled using other methods than Vector
control, e.g. DTC or SLMC.
Acknowledgement:- This motor design is carried out
at JSL, Mogar. This has become possible only
because of encouragement of Dr.K.K.Thakkar,
Director,JSL and the staff at JSL Mogar in design
section.
References
[1] Maria Imecs, Andrzej M. Trzynadlowski, Fellow,
IEEE, Ioan I. Incze, and Csaba Szabo “Vector
control schemes for Tandem converter fed induction
motor
drives”
IEEE
transactions
on
power
electronics, vol. 20, no. 2, march 2005.
[2] Bimal Bose, “Modern Power Electronics and AC
Drives”, Prentice Hall
[3] R. H. Nelson and P. C. Krause, “Induction machine
analysis for arbitrary displacement between multiple
windings,” IEEE Transactions on Power Apparatus
and Systems, vol. 93, pp. 841-848, May 1974.
[4] T. A. Lipo, “Flux sensing and control of staticac
drives by use of fluxcoils,” IEEE Transactions on
Magnetics, vol. MAG-13, Sept 1997
[5] O. Ojo and I. E. Davidson, “PWM-VSI inverterassisted stand-alone dual stator winding induction
generator,” IEEE Transactions on Industry
Applications, vol. 36, pp. 1604-1611,Nov 2000.