Control of voltage compensation to enhance ride - Through of dfig wind turbine during symmetrical and asymmetrical grid faults

and 
series grid-side converter are listed in Table 1, 2 and 3, respectively. 
Control of voltage compensation to enhance ride-through of DFIG wind turbine 
35 
Table 1. Parameters of wind turbine 
Table 2. Parameters of 2 MW- DFIG 
Parameter Value 
Rated power 2 MW 
Grid voltage 690 V 
Stator voltage/frequency 690 V/60 Hz 
Stator resistance 0.00488 pu 
Rotor resistance 0.00549 pu 
Stator leakage inductance 0.0924 pu 
Rotor leakage inductance 0.0995 pu 
Generator inertia 200 kg.m2 
 Table 3. Parameters of SEGSC 
 Parameter Value 
Capacity 0.8 MW 
DC-link capacitor 8200 F 
Inverter output filter L=0.1 mH, C =1000 F 
Switching frequency 2.5 kHz 
Series transformer 0.8 MW, 690 V/ 690 V 
4.1. Symmetrical grid fault 
Figure 4 shows the system performance for balanced grid voltage fault (symmetrical grid 
fault) without using SEGSC system, where the wind speed is assumed to be constant (16.5 m/s) 
for easy investigation. The fault condition is 50% sag in three phases for 0.1 s which is between 
1.4 s and 1.5 s. When there is the grid balanced voltage sag (
gabcV ) as shown in Figure 4(a), 
the negative-sequence component of the grid voltage does not exist. As can be seen from 
Figure 4 (b), the DC-link voltage (
dcV ) of the DFIG converter without using SEGSC reaches 
1.2 pu, which can damage the dc capacitor and the converter switches. Also, the stator and 
Parameter Value 
Rated power 2 MW 
Blade radius 45 m 
Air density 1.225 kg/m3 
Max. power conv. coefficient 0.4 
Cut-in speed 3 m/s 
Cut-out speed 25 m/s 
Rated wind speed 16.5 m/s 
Blade inertia 6.3x106 kg.m2 
Nguyen Thi Thanh Truc, Van Tan Luong, Phan Thi Chieu My 
36 
rotor currents (
abcsi , abcri ), as illustrated in Figure 4(c) to 4(d), respectively, are increased. 
Especially, the rotor currents are twice higher than rated values (1pu). In this case, the 
generator speed (
r ) which are illustrated in Figure 4(e) accelerates to achieve the optimal value 
for tracking the maximum power point. Similarly, the generator torque (
gT ) in Figure 4(f) is also 
decreased under the grid voltage fault. 
(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)Time (s)
Vga
Vdc
Vdc*
Vgb Vgc
ias ibs ics
iar ibr
icr
Figure 4. Performance of DFIG wind turbine system for balanced voltage sag (in pu). 
(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
)
(f
).
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
)
Time (s)
(d
).
In
je
ct
e
d
 q
-a
x
is
v
o
lt
ag
e 
(p
u
)
Time (s)
Pc
Qc
Vcq
*Vcq
(e
).
In
je
ct
e
d
 d
-a
x
is
v
o
lt
ag
e 
(p
u
)
Vcd
*Vcd
Vga Vgb Vgc
Vca Vcb Vcc
Vas Vbs Vcs
Figure 5. Performance of series grid-side converter system for balanced voltage sag (in pu). 
Figure 5 shows the performance of SEGSC system under balanced grid voltage fault. Due 
to balanced voltage sag, as shown in Figure 5(a), the compensation voltages (
cabcV ) in Figure 5(b) 
are injected by the SEGSC system. With the compensation, the stator voltages (
abcsV ) in Figure 
5(c) compensated, are kept at the rated value. The dq-axis voltages (
cdqV ) of the SEGSC are seen 
Control of voltage compensation to enhance ride-through of DFIG wind turbine 
37 
from Figure 5(d) and (e), respectively. Aslo, the active and reactive powers (
cP , cQ ) injected by 
the SEGSC are shown in Figure 5(f). Without SEGSC for voltage compensation, the stator 
and rotor currents, and torque give high ripples, as illustrated in Figure 4(c), 4(d) and 4(f), 
respectively. However, they are kept almost constant with compensation. 
Figure 6 shows the performance of DFIG wind turbine system in case of unbalanced 
voltage fault. It is obvious from Figure 6 that all quantities of the DFIG with the proposed 
SEGSC such as DC-link voltage, stator active and reactive powers, stator and rotor currents, 
generator speed and torque at grid faults have the same waveforms as those without grid faults. 
On the other hands, the DFIG still operates normally even though the grid fault occur. Thus, 
the proposed method obtains the good operation for the DFIG wind turbine system during 
symmetrical grid fault. 
(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
)
Vdc
*
*
Pr
Vga Vgb Vgc
iar ibr
icr
ias ibs ics
Figure 6. Performance of DFIG wind turbine system for balanced voltage sag (in pu). 
4.2. Asymmetrical grid fault 
Figure 7 shows the system performance for unbalanced grid voltage fault (asymmetrical 
grid fault) without using SEGSC system. The fault condition is 40% sag in both the grid 
A-phase and C-phase voltages for 0.1 s which is between 1.4 s and 1.5 s. Since the fault type 
is an unbalanced one, the negative-sequence components in dq-axis of the grid voltage appear. 
Due to the grid unbalanced voltage sag (
gabcV ) as illustrated in Figure 7(a), the DC-link voltage 
(
dcV ) (see Figure 7 (b)) of the DFIG converter without compensation reaches 3 pu, which is 
high enough to deteriorate the dc capacitor as well as the switches of the converter. In this 
Nguyen Thi Thanh Truc, Van Tan Luong, Phan Thi Chieu My 
38 
case, the stator and rotor currents (
abcsi , abcri ) which are seen in Figure 7(c) and (d), respectively, 
are much increased. The stator current is higher than the rated value (1 pu) and the rotor current 
reaches 2.6 pu. Also, the generator speed (
r ) in Figure 7(e) is increased and the generator 
torque (
gT ) in Figure 7(f) gives high oscillations. 
(a
).
 G
ri
d
 v
o
lt
ag
e 
(p
u
)
(b
).
d
c
-l
in
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)Time (s)
Vdc
Vdc*
Vga VgbVgc
ias ibs ics
iar ibr icr
Figure 7. Performance of DFIG wind turbine system for unbalanced voltage sag (in pu) 
Figure 8 shows the performance of SEGSC system under unbalanced grid voltage fault. 
When there is an unbalanced voltage sag in Figure 8(a), the SEGSC system injects the 
compensated voltages (
cabcV ) into the grid, as shown in Figure 8(b). Thus, the stator voltages 
(
abcsV ) in Figure 8(c) are kept at the rated value (1pu), as if it is in the normal grid condition. The 
components of the dq-axis voltage (
cdqV ) of the SEGSC system are produced, as shown in Figure 
8(d) and (e). Without compensation, the ripples of the stator and rotor currents (
abcsi , abcri ), and 
generator torque (
gT ), as illustrated from Figure 7(c) to 7(f), respectively are significantly 
increased. However, they are kept almost constant with the compensation scheme based on 
the SEGSC. 
Figure 9 shows the performance of DFIG wind turbine system in case of unbalanced 
voltage fault. With the proposed SEGSC under grid faults, the DC-link voltage, stator active 
and reactive powers, stator and rotor currents, generator speed and torque can be kept the same 
as those in the normal grid condition. This means that the DFIG can work well, as if it does 
without the grid faults. Thus, the proposed method gives the good operation for the DFIG wind 
turbine system during asymmetrical grid fault. 
Control of voltage compensation to enhance ride-through of DFIG wind turbine 
39 
(a
).
 G
ri
d 
vo
lt
ag
e 
(p
u
)
(c
).
S
ta
to
r 
v
ol
ta
ge
 (
pu
)
(b
).
In
je
ct
ed
 v
ol
ta
ge
 (
pu
)
(f
).
C
o
m
p
en
sa
te
d
 a
ct
iv
e 
an
d 
re
ac
ti
ve
 p
ow
er
s 
(p
u
)
(e
).
In
je
ct
ed
 d
-a
x
is
vo
lt
ag
e 
(p
u
)
Time (s)Time (s)
(d
).
In
je
ct
ed
 q
-a
x
is
vo
lt
ag
e 
(p
u
)
Vcq
*Vcq
Vcd
*Vcd
Pc
Qc
Vga VgbVgc
Vca Vcb
Vcc
Vas Vbs Vcs
Figure 8. Performance of series grid-side converter system for unbalanced voltage sag (in pu) 
(c
).
 S
ta
to
r 
ac
ti
v
e 
p
ow
er
 (
pu
)
(b
).
D
c-
li
n
k 
vo
lt
ag
e 
(p
u
)
(g
).
G
en
er
at
or
 s
pe
ed
 (
pu
)
Time (s)(
d
).
 R
o
to
r 
ac
ti
ve
 p
ow
er
 (
pu
)
Time (s)
(e
).
S
ta
to
r 
cu
rr
en
t 
(p
u
)
(h
).
G
en
er
at
or
 s
pe
ed
 (
pu
)
(f
) 
R
o
to
r 
cu
rr
en
t 
(p
u
)
(a
).
 G
ri
d 
vo
lt
ag
e 
(p
u
)
Pr
Vdc
*
*
iar ibr
icr
ias ibs ics
Vga Vgb Vgc
Figure 9. Performance of DFIG wind turbine system for unbalanced voltage sag (in pu). 
Nguyen Thi Thanh Truc, Van Tan Luong, Phan Thi Chieu My 
40 
5. CONCLUSION 
The application of a SEGSC connected to a wind-turbine-driven DFIG to allow 
uninterruptible fault ride through of grid voltage faults is introduced. The SEGSC can 
compensate the faulty line voltage, while the DFIG wind turbine can continue its nominal 
operation. Simulation results for a 2 MW wind turbine under asymmetrical two-phase grid 
fault and symmetrical three-phase fault show the effectiveness of the proposed technique. 
REFERENCES 
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of doubly fed induction generator (DFIG) during network faults, Wind Engineering 
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TÓM TẮT 
ĐIỀU KHIỂN BỒI HOÀN ĐIỆN ÁP ĐỂ CẢI THIỆN KHẢ NĂNG 
LƯỚT QUA ĐIỆN ÁP THẤP CỦA TUA-BIN GIÓ DÙNG MÁY PHÁT DFIG 
TRONG TRƯỜNG HỢP SỰ CỐ LƯỚI ĐỐI XỨNG VÀ BẤT ĐỐI XỨNG 
Nguyễn Thị Thanh Trúc1, Văn Tấn Lượng1,*, Phan Thị Chiêu Mỹ2 
1Trường Đại học Công nghiệp Thực phẩm TP.HCM 
2Trường Đại học Văn Hiến 
*Email: luongvt@hufi.edu.vn 
Bài báo giới thiệu việc áp dụng bộ biến đổi nối tiếp phía lưới (SEGSC) được kết nối với 
tua-bin gió dùng máy phát không đồng bộ nguồn kép (DFIG). Việc thiết lập mô hình này cho 
phép hệ thống tua-bin gió lướt qua sự cố lưới khi có sụt áp sâu. SEGSC có thể bồi hoàn điện 
áp của đường dây sự cố, trong khi tua-bin gió dùng máy phát DFIG có thể tiếp tục hoạt động 
bình thường theo quy luật làm việc của lưới thực tế. Các kết quả mô phỏng đối với hệ thống 
tua-bin gió 2 MW-DFIG có sử dụng bộ bù SEGSC cho kết quả vận hành tốt như trường hợp 
không có sự cố, đặc biệt đối với sự cố lưới không đối xứng. 
Từ khóa: Máy phát không đồng bộ nguồn kép, lướt qua điện áp thấp, bồi hoàn nối tiếp, độ 
võng điện áp lưới, tua-bin gió.