Low - Voltage ride - through technique for dfig wind turbine system

n (1) and (2), the voltage reference can be derived in a synchronous PI decoupling 
control strategy as 
*
*
i
fdq p p
i
fdq p n
K
V K e
s
K
V K e
s
+
−
 = + 
 = + 
 (3) 
where 
* *
* *
* *
, ,
fq fq
fdq fdq
fd fd
V V
V V
V V
+ −
+ −
+ −
= = 
* *
* *
,
cq cq cq cq
p n
cd cd cd cd
V V V V
e e
V V V V
+ + − −
+ + − −
 − −
= = 
− − 
Low-voltage ride-through technique for DFIG wind turbine system 
25 
SVPWM
θ
dqp
is
if
vc abc
Positive 
sequence 
voltage PI 
controller 
Negative 
sequence 
voltage PI 
controller 
- θ
 θ
dqp
- θ
dqn
+
+
dqs
dqn
abc
dqs
dqs
dqs
dqs
dqs
vg
vg,presag
References of 
compensation voltage
Figure 2. Control block diagram of a series VSC. 
The block diagram of the proposed control scheme is shown in Figure 2, in which the 
components of the positive and negative sequence voltages in the dq-axis are separately 
regulated by using PI controller. Then, the outputs of the voltage controllers ( *
fdqV
+ , *
fdqV
− ) are 
transformed to the voltage references in the abc reference frame ( *
abcfv ), which are employed 
for the space vector pulse-width modulation (SVPWM). 
3.2. Shunt voltage source converter 
C
+
-
Gatings
Cal. of pos. 
& neg. cur. 
components
Cal. of pos. 
& neg. vol. 
components
Lg
SVPWM
Grid
PI
PI
+
-
+
-
PI
PI
+
-
+
-
Negative 
sequence 
current 
controllers
Positive 
sequence 
current 
controllers
Shunt voltage source converter
e e
e
e
dc-link voltage controller
Figure 3. Control block diagram of a shunt VSC. 
Shunt VSC is used to control the DC-link voltage and regulate the PCC voltage or inject 
the reactive current according to the grid code requirement [19]. Figure 3 shows the control 
block diagram of the shunt VSC, in which the components of the positive and negative 
Van Tan Luong, Nguyen Phu Cong 
26 
sequence currents in the dq-axis are regulated, based on the PI controller. The reference of the 
positive sequence current component in q-axis ( *qeI
+ ) achieved from the output of the DC-link 
voltage controller [12], which allows controlling the active power exchange between the shunt 
converter and the electric grid. Meanwhile, the positive-sequence component of the d-axis 
current reference or the grid reactive current ( *deI
+ ) is selected to support the grid voltage 
recovery. The dq-axis current references of negative-sequence components ( *dqI
− ) are set to 
zero to eliminate the unbalanced current components flowing into the grid. Then, the outputs 
of the current controllers are transformed to the three-phase abc reference frame, applied for 
SVPWM. 
4. SIMULATION RESULTS 
PSCAD simulation has been performed out to verify the feasibility of the proposed 
method for a 2 MW-DFIG wind turbine system. For the wind turbine: R = 44 m; ρ = 1.225 kg/m3; 
λopt = 8; and the wind speed is constant at 11 m/s. For the DFIG: the grid voltage is 690 V/60 Hz; 
the rated power is 2 MW; Rs = 0.00488 pu; Rr = 0.00549 pu; Lls = 0.0924 pu; Llr = 0.0995 pu; 
and J = 200 kgm2. The grid voltage is 690 V and 60 Hz. For the two VSCs: the DC-link 
capacitor is 8200 F; the output LC filter of the series VSC is 0.2 mH and 8200 F; the input 
L filter of the shunt VSC is 0.25 mH. 
(a
).
 G
ri
d
 v
o
lt
ag
e 
(p
u
)
(b
).
d
c-
li
n
k
 v
o
lt
ag
e
 (
p
u
)
(f
).
G
e
n
er
at
o
r 
to
rq
u
e 
(p
u
)
(e
).
G
e
n
er
at
o
r 
sp
ee
d
 (
p
u
)
(c
).
 S
ta
to
r 
c
u
rr
e
n
t 
(p
u
)
(d
).
 R
o
to
r 
cu
rr
e
n
t 
(p
u
)
Time (s)
Vgabc
Vdc
iabcs
iabcr
(g
).
G
e
n
er
at
o
r 
a
ct
iv
e 
p
o
w
er
 (
p
u
) Pgen
(h
).
G
e
n
er
at
o
r 
re
ac
ti
v
e 
p
o
w
er
 (
p
u
)
Time (s)
Qgen
Figure 4. Performance of DFIG wind turbine system for the three-phase voltage interruption (in pu). 
Low-voltage ride-through technique for DFIG wind turbine system 
27 
(a
).
 G
ri
d
 v
o
lt
ag
e 
(p
u
)
(c
).
S
ta
to
r 
v
o
lt
a
g
e 
(p
u
)
(b
).
In
je
ct
e
d
 v
o
lt
ag
e
 (
p
u
)
(d
).
In
je
ct
e
d
 p
o
si
ti
v
e 
v
o
lt
ag
e 
in
 q
-a
x
is
(p
u
)
(f
).
In
je
ct
e
d
 n
eg
at
iv
e 
v
o
lt
ag
e 
in
 q
-a
x
is
(p
u
)
(g
).
In
je
ct
e
d
 n
eg
at
iv
e 
v
o
lt
ag
e 
in
 d
-a
x
is
(p
u
)
(h
).
C
o
m
p
en
sa
te
d
 a
ct
iv
e 
an
d
 r
ea
c
ti
v
e
 p
o
w
e
rs
 (
p
u
)
(e
).
In
je
ct
e
d
 p
o
si
ti
v
e 
v
o
lt
ag
e 
in
 d
-a
x
is
(p
u
)
Time (s)
Time (s)
Pc
Qc
Vgabc
Figure 5. Performance of series VSC for the three-phase voltage interruption (in pu). 
Figure 4 shows the system performance for three-phase voltage interruption without 
compensation, where the wind speed is assumed to be constant (16.5 m/s) for easy 
examination. The fault condition is three-phase voltage interruption for 0.1 s which is between 
1.5 s and 1.6 s. Since the fault type is a balanced one, the negative-sequence component of the 
grid voltage does not exist. Due to the grid fault as shown in Figure 4(a), the DC-link voltage 
(see Figure 4(b)) of the DFIG converter without compensation reaches 2.8 pu, which is high 
enough to damage the dc capacitor and the converter switches. Also, the stator and rotor 
currents, which are shown from Figure 4(c) to 4(d), respectively, are much increased. Even 
the rotor currents in the case of the grid fault increase more than double, compared with the 
rated ones. In this case, the generator speed in Figure 4(e) accelerates to obtain the optimal 
value for the maximum power point tracking. However, due to the three-phase voltage 
interruption of the grid and the current limitation of the converters, the active and reactive 
generator powers are still decreased to zero without compensation are illustrated in Figure 4(g) 
and (h), respectively. Likewise, the generator torque which are illustrated in Figure 4(f), is also 
reduced with high oscillations during the grid voltage fault. 
Figure 5 shows the performance of series VSC for three-phase voltage interruption. When 
the fault occurs as illustrated in Figure 5(a), the compensation voltages in Figure 5(b) are 
injected by the series VSC. With this compensation, the stator voltages in Figure 5(c) are still 
sinusoidal and kept at the rated value. The dq-axis positive sequence voltages of the series 
VSC are clearly seen from Figure 5(d) and (e), respectively. Figure 5(f) and (g) show the 
negative-sequence components of the grid voltage in dq-axis. With compensation, the injected 
active and reactive powers are produced from the series VSC, as illustrated in Figure 5(h). 
Figure 6 shows the performance of shunt VSC for three-phase voltage interruption. 
When there is the fault as shown in Figure 6(a), the DC-voltage is regulated to be constant 
Van Tan Luong, Nguyen Phu Cong 
28 
(see Figure 6(b)). Figure 6(c) shows the postitive current in q-axis. The reactive current is 
controlled to inject for the grid voltage recovery, which is selected, depending on the grid code 
requirement. In this case, the reactive current is selected to be 0.3 pu, as illustrated in Figure 6(d). 
By applying both VSCs (series VSC and shunt VSC), the grid voltage is fully 
compensated for the three-phase interruption condition. 
(a
).
 G
ri
d
 v
o
lt
ag
e 
(p
u
)
(b
).
 d
c-
li
n
k
 v
o
lt
ag
e 
(p
u
)
Vdcv
*
Time (s)
Time (s)
(c
).
P
o
si
ti
v
e 
q
-a
x
is
cu
rr
en
t 
(p
u
)
Iqe
Iqe
+*
+
Vdcv
Vgabc
(d
).
In
je
ct
e
d
 d
-a
x
is
cu
rr
en
t 
(p
u
)
Ide
+*
Ide
+
Figure 6. Performance of shunt VSC for the three-phase voltage interruption (in pu). 
(c
).
 S
ta
to
r 
a
ct
iv
e 
p
o
w
er
 (
p
u
)
(b
).
d
c
-l
in
k
 v
o
lt
ag
e
 (
p
u
)
(g
).
G
e
n
er
at
o
r 
sp
ee
d
 (
p
u
)
Time (s)
(d
).
 R
o
to
r 
ac
ti
v
e
 p
o
w
er
 (
p
u
)
Time (s)
(e
).
S
ta
to
r 
c
u
rr
e
n
t 
(p
u
)
(h
).
G
e
n
er
at
o
r 
sp
ee
d
 (
p
u
)
(f
) 
R
o
to
r 
cu
rr
e
n
t 
(p
u
)
(a
).
 G
ri
d
 v
o
lt
ag
e 
(p
u
)
Pr
iabcs
iabcr
Vdc
*
Vgabc
Figure 7. Performance of DFIG wind turbine system for three-phase voltage interruption (in pu). 
Low-voltage ride-through technique for DFIG wind turbine system 
29 
Figure 7 shows the performance of DFIG wind turbine system for the three-phase voltage 
interruption. It is obvious from Figure 7 that due to the coordinated control scheme for both 
VSCs, all quantities of the DFIG at the grid faults can be kept the same as those without grid 
faults since the DFIG operation is not influenced by the grid faults. Therefore, the proposed 
method achieves the good operation for the DFIG wind turbine system under all types of the 
grid faults. 
5. CONCLUSION 
This paper has proposed the LVRT technique for a doubly fed induction generator DFIG-
WT system under grid voltage fault conditions. With the proposed scheme, both shunt and 
series VSCs applied, enable to compensate the grid voltage simultaneously during the grid 
faults. The simulation results for 2 MW-DFIG wind turbine system using the proposed method 
at the grid faults gives as good performance as those without grid faults. 
REFERENCES 
1. Flannery P. S., Venkataramanan G. - A fault tolerant doubly fed induction generator 
wind turbine using a parallel grid side rectifier and series grid side converter, IEEE 
Transactions on Power Electronics 23 (3) (2008) 1126-1135. 
2. Lei Y., Mullane A., Lightbody G., Yacamini R. - Modeling of the wind turbine with 
a doubly fed induction generator for grid integration studies, IEEE Transactions on 
Energy Conversion 21 (1) (2006) 257-264. 
3. Akhmatov V. - Analysis of dynamic behavior of electric power systems with large 
amount of wind power, Ph.D. dissertation, Department of Electrical Power 
Engineering, Technical University of Denmark, Kongens Lyngby, Denmark (2003). 
4. Lima F. K. A., Luna A., Rodriguez P., Watanabe E. H., Blaabjerg F. - Rotor voltage 
dynamics in the doubly fed induction generator during grid faults, IEEE Transactions 
on Power Electronics 25 (1) (2010) 118-130. 
5. Meegahapola L. G., Littler T., Flynn D. - Decoupled-DFIG fault ride-through strategy 
for enhanced stability performance during grid faults, IEEE Transactions Sustainable 
Energy 1 (3) (2010) 2178-2192. 
6. Sava G. N., Costinas S., Golovanov N., Leva S., Quan D. M. - Comparison of active 
crowbar protection schemes for DFIGs wind turbine, Proceedings of the 16th 
International Conference on Harmonics and Quality of Power (2014) 669-673. 
7. Haidar A. M. A., Muttaqi K. M., Hagh M. T. - A coordinated control approach for DC 
link and rotor crowbars to improve fault ride-through of DFIG based wind turbines, 
IEEE Transactions Industry Applications 53 (4) (2017) 4073-4086. 
8. Song Q., Liu W. - Control of a cascade STATCOM with star configuration under 
unbalanced conditions, IEEE Transactions on Power Electronics 24 (1) (2009) 45-58. 
9. Zhang W. H., Lee S.-J., Choi M.-S. - Setting considerations of distance relay for 
transmission line with STATCOM, Journal of Electrical Engineering & Technology 5 
(4) (2010) 522-529. 
10. Pirouzy H. M., Bina M. T. - Modular multilevel converter based STATCOM topology 
suitable for medium-voltage unbalanced systems, Journal of Power Electronics 10 (5) 
(2010) 572-578. 
11. Molinas M., Suul J., Undeland T. - Low voltage ride through of wind farms with cage 
generators: Statcom versus svc, IEEE Transaction on Power Electronics 23 (3) (2008) 
1104-1117. 
Van Tan Luong, Nguyen Phu Cong 
30 
12. Zou Y., Elbuluk M., Sozer Y. - Simulation comparisons and implementation of 
induction generator wind power systems, IEEE Transactions Industry Application 49 
(3) (2013) 1119-1128. 
13. Leon A., Farias M., Battaiotto P., Solsona J., Valla M. - Control strategy of a DVR to 
improve stability in wind farms using squirrel-cage induction generators, IEEE 
Transactions on Power System 26 (3) (2011) 1609-1617. 
14. Ramirez D., Martinez S., Platero C., Blazquez F., de Castro R. - Low-voltage ride-
through capability for wind generators based on dynamic voltage restorers, IEEE 
Transactions on Energy Conversion 26 (1) (2011) 195-203. 
15. El Moursi M., Goweily K., Kirtley J., and Abdel-Rahman M. - Application of series 
voltage boosting schemes for enhanced fault ride-through performance of fixed speed 
wind turbines, IEEE Transactions Power Delivery 29 (1) (2014) 61-71. 
16. Wessels C., Gebhardt F., and Fuchs F. - Fault ride-through of a DFIG wind turbine 
using a dynamic voltage restorer during symmetrical and asymmetrical grid faults, 
IEEE Transactions on Power Electronics 26 (3) (2011) 807-815. 
17. Ibrahim A. O., Nguyen T. H., Lee D.-C., Kim S.-C. - A fault ridethrough technique of 
DFIG wind turbine systems using dynamic voltage restorers, IEEE Transactions on 
Energy Conversion 26 (3) (2011) 871-882. 
18. Van T. L., Nguyen N. M. D., Toi L. T., Trang T. T. - Advanced control strategy of 
dynamic voltage restorers for distribution system using sliding mode control input-ouput 
feedback linearization, Lecture Notes in Electrical Engineering 465 (2017) 521-531. 
19. Van T. L. and Ho V. C. - Enhanced fault ride-through capability of DFIG wind turbine 
systems considering grid-side converter as STATCOM, Lecture Notes in Electrical 
Engineering 371 (2015) 185-196. 
TÓM TẮT 
KỸ THUẬT LƯỚT QUA ĐIỆN ÁP THẤP CHO HỆ THỐNG TUA-BIN GIÓ 
DÙNG MÁY PHÁT DFIG 
Văn Tấn Lượng*, Nguyễn Phú Công 
Trường Đại học Công nghiệp Thực phẩm TP.HCM 
*Email: luongvt@hufi.edu.vn 
Bài báo này đề xuất một kỹ thuật lướt qua điện áp thấp (LVRT) cho một hệ thống tua-
bin gió dùng máy phát không đồng bộ nguồn kép (DFIG). Với phương pháp đề xuất, cả bộ 
chuyển đổi nguồn điện áp mắc nối tiếp và mắc song song được sử dụng, cho phép bù đồng 
thời đáp ứng điện áp của hệ thống trong trường hợp sự cố lưới điện. Đối với bộ chuyển đổi 
nguồn điện áp mắc nối tiếp (VSC), thuật toán điều khiển bao gồm bộ điều khiển điện áp kép 
được thực hiện cho hai thành phần thứ tự thuận và nghịch trong hệ tọa độ quay dq. Đối với bộ 
VSC mắc song song, thuật toán điều khiển bao gồm vòng lặp điều khiển dòng điện bên trong 
và vòng lặp điều khiển điện áp DC-link bên ngoài, trong đó vòng lặp điều khiển dòng điện 
được thực hiện trong hệ tọa độ quay dq. Kết quả mô phỏng đối với hệ thống tua-bin gió dùng 
máy phát DFIG công suất 2 MW đã chứng tỏ rằng phương pháp đề xuất cho kết quả vận hành 
tốt như trong trường hợp không có sự cố điện áp lưới. 
Từ khóa: Máy phát không đồng bộ nguồn kép, sự cố lưới, lướt qua điện áp thấp, thành phần 
thứ tự thuận và nghịch, tua-bin gió.