SELECTED TOPICS in POWER SYSTEMS and REMOTE SENSING
A Dual Stator Winding-Mixed Pole Brushless Synchronous Generator
(Design, Performance Analysis & Modeling)
M EL_SHANAWANY, SMR TAHOUN& M EZZAT
Department (Electrical Engineering Department)
University (Menoufya University)
Address (Shebin El_Kom, Egypt)
COUNTRY (EGYPT)
en.ezzat@yahoo.com
Abstract: - It is well known that critical loads are still excited either from conventional synchronous or
induction generators. Conventional synchronous generators suffer from brushes and slip ring existence which
reduce its reliability and increase the need for maintenance that conflict with the nature of these loads. Also,
although induction generator is a brushless generator, it has several problems that still under research. This
paper presents a new generator design suitable for these loads. A 3-phase conventional AC stator is used. Two
rotor types, named salient pole and flux barrier rotors, are designed and used with this stator. The experimental
results with these rotors are taken and compared with the theoretical ones.
Key-Words: - Brushless Synchronous Generator, Dual Stator Winding, Mixed Pole, Modeling
1 Introduction wound with two sets of 3-phase windings. One of
Critical loads need a high reliable generation them is wound with 6-pole and the other one with 2-
system. Conventional synchronous generators have pole (Each winding has 55 conductor/slot). The 6-
brushes and slip rings in its rotor that increase its pole winding (Field winding) is connected as open
need for maintenance and of course reduce its delta with two reversed phases and the 2-pole
reliability. Although the brushless version of winding (Generating winding) is connected as a star.
synchronous generators has no brushes and slip Fig. (1) shows the used stator and winding
rings, it has built in diodes in its rotor circuit and arrangement.
needs main and auxiliary exciters that increase its
cost. Beside the increase in cost, the built in diodes
are exposed to excessive heat so they need better
cooling which adds to the cost. Induction generators
are brushless generators, but they don't have the
advantages of synchronous generators. So that there
is a need for a reliable generator with the advantages
of synchronous generators. The paper presents a
new generator design which has both field and
generation windings are wound in the stator side and Winding arrangement
its rotor has no windings or bars.
2 Machine Construction
Construction of the proposed generator is the same
construction as the brushless doubly fed reluctance
machines (BDFRM) [1-8]. It consists of stator and
rotor. The stator is made from silicon steel
laminations in the same way of induction machine
stator. Dual sets of three-phase windings with
different pole numbers are wound in the slots in the A photo of the experimental stator
same manner as in the self-cascaded induction Fig. (1)
machine [9]. In this paper, a standard stator of a 1hp
3-phase induction motor is used. This stator is
ISSN: 1792-5088 159 ISBN: 978-960-474-233-2
SELECTED TOPICS in POWER SYSTEMS and REMOTE SENSING
Different from the self cascaded induction machine,
the rotor of the proposed generator is one of the
reluctance types. In this paper two rotor types are
used. One of them is a solid salient pole rotor with
pole arc to pole pitch ratio equal to 0.5. The other
rotor is a solid flux barrier rotor with pole arc to
pole pitch ratio equal to 0.63 and each rib width
equal to 1mm. These dimensions are chosen to
achieve the highest possible generated voltage and
both rotors are designed to fit the stator. Fig. (2)
shows the used rotors.
Flux density distribution at ө=0
Fig. (4)
Salient pole rotor
Flux Distribution at ө=60o
Flux barrier rotor Fig. (5)
Fig. (2)
3 Theory of Operation
Theory of operation of conventional synchronous
machine depends on Faraday's law. Also, theory of
operation of the proposed generator depends on the
same law but in our case the field winding is wound
on the stator side. Excitation of field winding results
in stationary magnetic field in space. With rotor
rotation the flux linking generating winding, also in
the stator, varies with time which induces an emf in
it. For more clearance in how the flux varies with Flux density distribution at ө=60o
rotor rotation, a finite element tool is used to show Fig. (6)
the flux variation. Figs.(3 to 6) show the flux
variation for two rotor positions only.
4 Theoretical Analysis
Voltage equations for the proposed generator can be
written as follows:
(1)
(2)
Where:
*iF: is the field winding current (DC current).
*iGABC: is the generating winding current (AC
current).
*rF: is the field winding resistance.
Flux Distribution at ө=0
*rG: is the generating winding resistance per phase.
Fig. (3)
ISSN: 1792-5088 160 ISBN: 978-960-474-233-2
SELECTED TOPICS in POWER SYSTEMS and REMOTE SENSING
*VF: is the applied field voltage (DC voltage).
*VGABC: is the generating winding terminal voltage
(AC voltage).
* : is the flux linking field winding.
* : is the flux linking generating winding phases.
To calculate the flux linkage, machine inductances
must be calculated. The technique adopted here is
the winding function analysis (WFA) technique.
Inductances are calculated using the following
formula that presented in [10].
(3)
Figs. (7&8) show the winding functions for a one
phase of the 6-pole winding and a one phase of the Inverse air gap function for salient pole rotor
2-pole winding respectively. Fig. (9)
Winding function of a 6-pole winding phase
Fig. (7) Inverse air gap function for flux barrier rotor
Fig. (10)
Where:
ad: is the inverse air gap function in the d-axis.
aq: is the inverse air gap function in the q-axis.
Based on equation (3), machine inductances are
calculated using a MATLAB M-FILE and the
following results are obtained.
Winding function of a 2-pole winding phase
Fig. (8)
Where:
q: is the slot per pole per phase divided by two.
zsf: is the number of field conductors per slot.
Zs: is the number of generation conductors per slot.
Figs. (9&10) show the inverse air gap function (g-1)
adopted for salient pole and flux barrier rotors Mutual inductance with salient pole rotor
respectively. One can see that effect of slotting is Fig. (11)
taken into account for both air gap models.
ISSN: 1792-5088 161 ISBN: 978-960-474-233-2
SELECTED TOPICS in POWER SYSTEMS and REMOTE SENSING
Mutual inductance with flux barrier rotor Self inductance of a 2-pole phase with the salient
Fig. (12) pole rotor
Fig. (15)
From the above figures, it can be seen that mutual
inductance obtained with the flux barrier rotor is
higher than the obtained value with the salient pole
one. So that it is expected that more voltage will be
generated with the flux barrier rotor than the salient
pole one.
Self inductance of a 2-pole phase with the flux
barrier rotor
Fig. (16)
One can see that self inductances either of 6-pole or
2-pole windings are not purely constant but they
Self inductance of a 6-pole phase with the salient have AC components.
pole rotor From equations (1&2) and the calculated
Fig. (13) inductances a MATLAB SIMULINK model is built
to compare the obtained results with the
experimental ones (This will be done in the next
section). Fig. (17) shows the SIMULINK model
used.
Field Currents
3-phase no -load Voltages
In 1 Out1 In1 Out1
Out1 In 1Out2 In2 Out2
Field Voltage In 2
Out3 In3 Out3
Field Circuit Mutual between Generation and Field Generating Winding
Phases Current
Self inductance of a 6-pole phase with the flux
barrier rotor
Fig. (14) In1
Out1In2
In3
mutual between
field and generating windings
SIMULINK model
Fig. (17)
ISSN: 1792-5088 162 ISBN: 978-960-474-233-2
SELECTED TOPICS in POWER SYSTEMS and REMOTE SENSING
5 Results
Figs. (18&19) show the experimental and the
simulated terminal voltage per phase for two phases
at field current (IF) of 2A and at 1500 r.p.m.
Simulated terminal voltage for phases a&b
Experimental terminal voltage for phases a&b (1500r.p.m, IF =2A,IL=0.78A, Flux barrier rotor)
(1500r.p.m,IF=2A,IL=0.5A, Salient pole rotor) Voltage scale=10:1
Voltage scale=10:1 Fig. (19b)
Fig. (18a)
From the above figures, one can see that the
generated phase voltages are displaced by
approximately 120o and its frequency is 100 Hz
(Double the frequency obtained from the
conventional synchronous generator at the same
speed).
Figs. (20&21) show the experimental and the
simulated no load voltage per phase.
Simulated terminal voltage for phases a&b
(1500r.p.m, IF =2A,IL=0.5A, Salient pole rotor)
Voltage scale=10:1
Fig. (18b) Experimental no load per phase voltage
(1500r.p.m,IF=2A,IL=0A, Salient pole rotor)
Voltage scale=10:1
Fig. (20a)
Experimental terminal voltage for phases a&b Simulated no load per phase voltage
(1500r.p.m, IF =2A,IL=0.78A, Flux barrier rotor) (1500r.p.m,IF=2A,IL=0A, Salient pole rotor)
Voltage scale=10:1 Voltage scale=10:1
Fig. (19a) Fig. (20b)
ISSN: 1792-5088 163 ISBN: 978-960-474-233-2
SELECTED TOPICS in POWER SYSTEMS and REMOTE SENSING
Simulated terminal voltage and phase current
(1500r.p.m,IF=2A,IL=0.5A, Salient pole rotor)
Experimental no load per phase voltage Voltage scale=10:1
(1500r.p.m,IF=2A,IL=0A, Flux barrier rotor) Fig. (22b)
Voltage scale=10:1
Fig. (21a)
100
50
V o lta g e in V o lts
0
-50
-100 Experimental terminal voltage and phase current
0.135 0.14 0.145 0.15
Time in seconds
(1500r.p.m,IF=2A,IL=0.78A, Flux barrier rotor)
Simulated no load per phase voltage Voltage scale=10:1
(1500r.p.m,IF=2A,IL=0A, Flux barrier rotor) Fig. (23a)
Voltage scale=10:1
Fig. (21b)
Figs. (22&23) show the experimental and the
simulated terminal voltage per phase and phase
current at 2A and at 1500 r.p.m with resistive load.
Simulated terminal voltage and phase current
(1500r.p.m,IF=2A,IL=0.78A, Flux barrier rotor)
Voltage scale=10:1
Fig. (23b)
Experimental terminal voltage and phase current From figures 20 to 23, one can find that the voltage
(1500r.p.m,IF=2A,IL=0.5A, Salient pole rotor) waveforms approach the sinusoidal waveform with
Voltage scale=10:1 loading or it can be said that ripple voltages appear
Fig. (22a) in no load is reduced with loading.
ISSN: 1792-5088 164 ISBN: 978-960-474-233-2
SELECTED TOPICS in POWER SYSTEMS and REMOTE SENSING
Figs. (24&25) show the steady state characteristics References:
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Fig. (25)
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Introduction to the Space Vector Modeling
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shown that the flux barrier rotor gives a higher
Machine, Electric Power Components and
power than the salient pole type rotor. The low
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values of terminal voltages are due to the use of a
755.
standard stator. In conventional synchronous
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generator the field is wound in the rotor. If the field
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6 Conclusion [10]Tang, Yifan, High Performance
A new brushless generator type suitable for critical Variable Speed Drive System and
loads has been presented. Experimental results on Generating System with Doubly Fed
two rotor designs have been performed and the Machines, PHD Thesis, The Ohio State
obtained results have been compared to the University, 1994.
theoretical results and a good agreement has been
achieved. The obtained performance gives a promise
for a well design. This can be done in a next paper.
ISSN: 1792-5088 165 ISBN: 978-960-474-233-2