Control of a Brushless DoublyFed Induction Machine
The University
Of Chile
Presented by:
Roberto Cárdenas
University of Chile
Doubly-Fed Induction Generators
• This machine is widely used in variable speed
wind energy applications. Currently this
topology occupies close to 50% of the wind
energy market.
Some commercial DFIGs
in the 1MW to 3MW
power range
Typical topology for a DFIG
*
*
Power converters are usually designed for a nominal power
of 30% of that of the doubly-fed machine.
Problems related to the use of Brushes
slip rings
• In most of the applications where robustness
is required, the use of brushes has to be
avoided.
• For instance in remote areas, where regular
maintenance is difficult to achieve.
Proposed Brushless Topology
• This is just a representation.
• Two DFIGs in the same shaft (“cascaded” implementation).
The signals induced in the rotor of the first machine are
used to excite the power machine.
Proposed Brushless Topology
• The Brushless DFIG (BDFIG)
could be also implemented
using two (3 each one) stator
windings.
• Mathematically the BDFIG
implemented
using
two
cascaded machines is similar.
Stator 1
Rotors
Stator 2
3x3
MC
r
r*
Encoder
board
Variac
3
grid
Current
Tranducers
Isolation
Encoder
Cage
Machine
Excitation
DFIM
Power
DFIM
Voltage
Tranducers
Proposed Brushless Topology
r
sc
sg
DFIG
DFIG
r
feg
fsl
fec
To Matrix
Converter
To
Grid
Power Converter used in this
applications
Grid input
Input Filter
Bidirectional
Switch

A

B
s11
s22
s21

s12
s13
s23
C
s31
a
s32
s33
b
c
To the stator of
the excitation machine
Power Converter used in this applications
MC
input
Input
Capacitor
Gate Circuits
for the
Bidirectional
switches
Current
Transducer
Designed in the
University of
Nottingham
MC
output
Clamp
Voltage
Transducers
Vector Control System
e
sg
d
isdg
q
e
isg
e
e
sg
isg
DFIG
DFIG
isqg
q
Control system
Power machine
currents
r
r
DFIG
feg
Power machine
currents
Excitation machine
currents
DFIG
fsl
Excitation machine
currents
fec
Relationship between the currents in the
excitation and power machines
Gd()
Relationship between the currents in the
excitation and power machines
Gq()
Control Loops
Nested control loops. The outer loop is regulating the currents of the power machine.
The inner control loop is regulating the currents of the excitation machine.
Experimental
System
3x3
MC
r
r*
Encoder
board
Variac
3
grid
Current
Tranducers
Isolation
Encoder
Cage
Machine
Excitation
DFIM
Power
DFIM
Voltage
Tranducers
Experimental
System
Encoder
r
r
Excitation Machine
DFIG
Current
Regulation
D/A
A/D
isc
SVM
Algorithm
FPGA Based
Switching
A/D conversion
DSP+FPGA
ir
isg
vs
DFIG
Power Machine
Matrix
Converter
Input
Filter



Grid
Wind speed (ms-1)
Experimental Results
10
8
6
isgq
d-q Currents (A)
10
5
isgd
0
5
iscd
0
-5
iscq
-10
0
5
10
15
20
25
Time (s)
30
35
40
Power (W)
Experimental Results
3000
P
2000
Speed (rpm)
1000
800
750
r
700
650
0
5
10
15
20
25
Time (s)
30
35
40
Experimental Results
10
a)
iasc
b)
iar
c)
iasg
0
Currents (A)
-10
20
0
-20
10
0
-10
0
0.1
0.2
0.3
0.4
0.5
Time (s)
0.6
0.7
0.8
0.9
Conclusions
• The BDFIG is an alternative to the conventional
Doubly-Fed Generator in remote sites where
maintenance is not simple to achieve.
• The simplified model proposed here can be used
to design the control system. The simplifications
arise from the fact that wind energy systems have
slow dynamic due to the relatively large blade
inertia.
• Experimental results have been obtained which
confirm the performance of the proposed
methodology.
Any question?