Progress In Electromagnetics Research Symposium Proceedings, Moscow, Russia, August 18–21, 2009 1957
Research on Brushless Doubly-fed Machine with a New Wound
Rotor and Its Generating System
Zhongchao Wei, Xuefan Wang, Xia Chen, and Chaohao Kan
Department of Electrical Machines and Drives, Huazhong University of Science and Technology, China
Abstract— The Brushless Doubly-Fed Machine (BDFM) is a new-type of special electrical
device. This kind of machine solve the structural problems of brushless, combining with the
favorable characteristic of the asynchronous motor and synchronous generator.This paper presents
the principle, structure and operation mode of BDFM. Based on the BDFM with the conventional
rotor structure, a novel BDFM with a special rotor structure is proposed according to the tooth
harmonic theory. The design of the rotor coil and the basic theory are discussed in detail.
Furthurmore, aiming to the simulation and practical test research, the prototype is developed
and be tested, which proves its application prospect.
1. INTRODUCTION
The conventional brushless doubly-fed machine employs the special rotor or reluctance motor, in
which the special rotor is the best choice for the large capacity machine. However, the disadvantages
can’t be avoided, such as much harmonic, the low utilization of the conductor [1]. This paper
proposed a new rotor structure, which adopts the wound type instead of the cage type. With a
smaller size and high efficiency, it can reduce the harmonic component considerably. Aimed to the
requirement of the generator for the ship, a prototype of a 50 kW brushless doubly-fed machine
was developed and the principle was discussed combined with the practical application. Due to
reducing the capacity of the frequency converter, the active power and reactive power can be
regulated conveniently without the reactive power compensation device and filter [2]. According
to the design parameters and the test results, it was validated that this type of machine presents
favorable performance.
2. THE PRINCIPLE AND THE MATHEMATICA MODEL
The principle of the brushless doubly-fed machine working in the mode of generation is illustrated
as Fig. 1. The stator has two sets of windings. One is connected with the frequency converter; the
other (the assistant winding) is used as the control winding. Both of the windings are corresponding
to different pole pair number [3]. Whenever the two sets of windings connected at the same time
or respectively, the stator winding will produce two different rotating magnetic filed. It is not
desired that the two rotating magnetic fields interfered each other, so it’s required that the main
control winding will produce the induced potential in the stator winding and no potential difference
between the three output terminals. Moreover, when the control winding is supplied, the additional
current will not arose at the power supply port. Due to the wound rotor, the two sets of windings
can be deemed as the reversal cascade. There is no coupling between the magnetic fields produced
by the two sets of windings. The energy is transferred through the rotor field instead that of the
stator.
p1
Output
power
p2
Frequency
converter
Main winding
side
Prime mover
Assistant winding
side
Figure 1: The operation principle of brushless double-fed machine.
PIERS Proceedings, Moscow, Russia, August 18–21, 2009
1958
The prime mover drives the generator at the speed of nr , and the assistant winding is supplied
by the frequency converter, the frequency of the output voltage is
(p1 + p2 )
nr ± f2
(1)
60
In which, p1 and p2 are the pole pair number of the main winding and assistant winding respectively.
Variable speed constant frequency operation can be realized by changing the output voltage and
frequency of the frequency converter.
On the assumption that the Permeability of iron core is infinite, ignoring the magnetic voltage
drop; regardless of the tooth and slot effects and considering the air gap distributing equally;
the main winding and assistant winding are symmetrical in the space structure, only flowing the
fundamental wave current and the initial phase angle of the current of A phase winding is zero [4].
Based on the electrical machine theory, the main winding adopts the generator rule and the
assistant winding adopts the motor rule. The voltage equation of the brushless doubly-fed machine
in d-q coordinate system is as following [5]:
"
#
"
#"
# "
#"
#
"
#
udq1
R1 0
0
idq1
p1 ωr Γ
ψdq1
ψdq1
udq2 =
0 R2 0
idq2 +
p2 ωr Γ
ψdq2 + p ψdq2
udqr
0
0 Rr
idqr
0
ψdqr
ψdqr
#
#
"
#! "
#"
Ã"
# "
ψdq1
Ldq1
idq1
R1 0
0
p1 ωr Γ
idq2 + p ψdq2
Ldq2
p2 ωr Γ
0 R2 0
+
=
ψdqr
idqr
Ldqr
0
0
0 Rr
f1 =
That is:
udq = Rdq idq + Ldq
In which:
"
Γ=
0 −1 0
1 0 0
0 0 0
#
"
R=
R1 0
0
0 R2 0
0
0 Rr
d
idq
dt
#
"
+
(2)
p1 ωr Γ
p2 ωr Γ
#"
0
Ldq1
Ldq2
Ldqr
#
The torque equation is
Te = itdq1 Hsr1 idqr + itdq2 Hsr2 idqr = itdq M idq
In which:
¤
£
itdq = itdq1 itdq2 itdqr ,


0
0
Hsr1
0
Hsr1  ,
M =  0
t
t
Hsr1 Hsr1
0
"
#
0 −1 0
3
Hsr1 = p1 Lm1 1 0 0
2
0 0 0
"
#
0 1 0
3
Hsr2 = p2 Lm2 1 0 0
2
0 0 0
.
I1 r 1 Xl 1
.
U1
X1
rr
s1
.
Ur 1
s2
X lr I. X r 2 s 1
l2
r
X2
.
Ur2
.
I2
. s
U2 2
s1
Figure 2: The equivalent circuit of the double fed machine.
(3)
Progress In Electromagnetics Research Symposium Proceedings, Moscow, Russia, August 18–21, 2009 1959
Simplified expression:
3
3
Te = p1 Lm1 (iq1 idr − id1 iqr ) + p2 Lm2 (iq2 idr + id2 iqr )
2
2
(4)
According to the expression above, the equivalent circuit of the double fed machine is as follows [6].
In which: rr = k12 Rr , r2 = k 2 R2 , Llr = k12 Llr , Ll2 = k12 Ll2 , Xl1 = ω1 Ll1 , Xl2 = ω1 Ll2 , Xlr =
1 f2
2 f1
ω1 Llr , X1 = 23 ω1 Lm1 = 23 ω1 k1 Lsr1 , X2 = 32 ω1 k 2 Lm2 = 32 ω1 kk1 Lsr2 , s1 = pf21f(p1 −p
, s2 = pf12f(p2 −p
1 +p2 )
1 +p2 )
are the slip ratio of the main winding and assistant winding respectively.
3. THE DESIGN OF THE WINDING
The coupling of the stator fields between different pole pairs number is achieved by the modulating
of rotor [4]. Therefore, the machine with different pole pairs number of stator winding such as
P1 , P2 as much as possible, the design of such machine should strengthen the p1 th, p2 th harmonic
and eliminate other order harmonic [7]. The paper proposed a wound rotor structure based on the
tooth harmonic principle. As for the AC winding, the number of the slot is Z and the pole pair
number of the fundamental wave is p.
All υth harmonic (υ = nZ ±p, n = 1, 2, 3 . . .) in the AC winding with fundamental wave pole pair
number p, whose short distance factor and distribution factor are the same as that of fundamental
wave. Such harmonic is the so-called tooth harmonic. This harmonic is featured as the equal
winding coefficient between the magnetomotive force of the tooth harmonic and fundamental wave
emerging as the pair.
Figure 3: 12 slot/14 pole.
Figure 4: 12 slot/10 pole.
Table 1: The rotor harmonic analysis with the method of tooth harmonic.
Pole
number
Short
distance
coefficient
Winding
coefficient
2
10
14
22
26
34
38
46
50
0.2588
0.9659
0.9659
0.2588
−0.2588
−0.9659
−0.9659
−0.2588
−0.2588
0.0670
0.9330
0.9330
0.0670
0.0670
0.9330
0.9330
0.0670
0.0670
Natural
rotating
Magnetic
potential of the
(%)
50.2577
0
100.0
0
3.8660
0
36.8421
0
2.0103
Reverse
rotating
Magnetic
potential
(%)
0
140.0
0
4.5689
0
41.1765
0
2.1851
0
1960
PIERS Proceedings, Moscow, Russia, August 18–21, 2009
The operation principle of the brushless double-fed machine requires the rotor winding to produce rotating magnetomotive force of the pole pair number P1 and P2 . The rotating direction of
the two kinds of magnetomotive force is just opposite. So the first task is to determine the required
pole pair number P1 of the main winding and P2 of the assistant winding. Choose the slot number
Z2 as the relationship Z2 = p1 + p2 on the Premise of symmetrical rotor winding.
The slot number phase maps are given in the case of the rotor 12 slot/14 pole and 12 slot/10
pole in Fig. 3 and Fig. 4, and Table 1 shows the corresponding harmonic analysis.
Aiming to the generation requirement for the use of the ship, the design of the new type brushless
double-fed machine with wound rotor is completed. The rated speed of the machine is nr = 600rmp,
the output power 60 kW, the output phase voltage 220 V/50 Hz, the power factor of the inductive
load 0.8. Table 2 has listed the design parameters.
4. THE ANALYSIS OF THE TEST AND RESULT
The prototype shown as Fig. 5 was tested and the principle diagram of the test is shown as Fig. 6.
The three-phase asynchronous motor was employed as the prime mover. The prototype was
connected with the grid and the assistant winding is connected to the output terminal of the threephase frequency converter. The DC bus of the frequency converter is connected with the active
energy feedback device. The results in the case of the no-load and load can be seen from Fig. 7
and Fig. 8.
It can be observed from the test curves that the new type brushless double-fed machine with
wound rotor can achieve the constant frequency generation as the speed of the prime mover changing. The output voltage keep stable, the regulating range of the speed wide, which validate the
correctness of the theory analysis and has the prospect of the practical application.
Table 2: The design parameter of the prototype.
Output power of the main winding(kW)
Output power of assistant winding(kW)
Rated output voltage/frequency V/Hz
Rated rotating speed rpm
Slot number
Rotor number
Pole number of main winding
Pole number of assistant winding
50
10
380/50
600
72
54
8
4
BDFM
ব乥఼
ॳࡼᴎ
Ⳉ⌕⬉⑤
䗚ব఼
Figure 5: The prototype of brushless double-fed machine with wound rotor.
Figure 6: The test principle of the machine.
Progress In Electromagnetics Research Symposium Proceedings, Moscow, Russia, August 18–21, 2009 1961
Figure 7: No load test curves of brushless doubly-fed generator.
Figure 8: Load test curves of brushless doubly-fed generator.
REFERENCES
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2. Boger, M., A. K. Wallace, and R. Spee, “Investigation of appropriate pole number combinations
for brushless doubly fed machines as applied to pump drives,” IEEE Trans. Ind. Appl., Vol. 31,
No. 5, 1022–1028, 1996.
3. Brune, C. S., R. Spee, and A. K. Wallace, “Experimental evaluation of a variable-speed,
doubly-fed wind-power generation system,” IEEE Trans. Ind. Appl., Vol. 30, No. 2, 648–655,
1994.
4. Williamson, S., A. C. Ferreira, and A. K. Wallace, “Generalized theory of the brushless doublyfed machine. Part I: Analysis,” IEE Proc., Electra. Power Appl., Vol. 144, 111–122, 1997.
5. Roberts, P. C. and R. A. McMahon, “Performance of BDFM as generator and motor,” IEE
Proc., Electra. Power Appl., Vol. 153, No. 2, 289–299, 2006.
6. Williamson, S., A. C. Ferreira, and A. K. Wallace, “Generalized theory of the brushless doublyfed machine. Part 2: Model verification and performance,” IEE Proc., Electra. Power Appl.,
Vol. 144, No. 2, 123–129, 1997.
7. Wallace, A. K., P. Rochelle, and R. Sp!ee, “Rotor modeling and development for brushless
doubly-fed machines,” Conf. Record of the Int. Conf. on Electrical Machines, Vol. 1, Cambridge, 1990.