Driving apparatus and method for modular multi-level converter
The present invention relates to a driving method for a modular multi-level converter. The driving method include inputting a current reference value (i* pj2 ) of the upper valve of the modular multi-level converter, measuring a current value (i pj2 ) of the valve, calculating an error value (err pj2 ) between the current reference value and the measured current value of the upper valve, measuring a DC link voltage value (V dc2 ) of the modular multi-level converter, measuring a AC-grid voltage value (E sj ) of the modular multi-level converter, and calculating a voltage reference value (u* pj2 ) using the current reference value (i* pj2 ), the measured current value (i pj2 ), the error value (err pj2 ), the DC link voltage value (V dc2 ), and the AC-grid voltage value (E sj ).
1. A driving method for a modular multi-level converter that converts an alternating current (AC) into a direct current (DC) or converts a DC into an AC using the modular multi-level converter with a plurality of submodules stacked to deliver power in an AC system, the modular multi-level converter comprising a plurality of valves independently driven and an upper valve that is one of valve branches comprising the plurality of valves, the driving method comprising:
inputting a current reference value (i* pj2 ) of the upper valve of the modular multi-level converter;
measuring a current value (i pj2 ) of the upper valve;
calculating an error value (err pj2 ) between the current reference value and the measured current value of the upper valve;
measuring a DC link voltage value (V dc2 ) of the modular multi-level converter;
measuring an AC-grid voltage value (E sj ) of the modular multi-level converter; and
calculating a voltage reference value (u* pj2 ) of the upper valve using the current reference value (i* pj2 ), the measured current value (i pj2 ), the error value (err pj2 ), the DC link voltage value (V dc2 ), and the AC-grid voltage value (E sj ),
wherein the inputting of the current reference value (i* pj2 ) of the upper valve of the modular multi-level converter comprises calculating the current reference value (i* pj2 ) using a following equation:
i
pj
2
*
=
i
dc
2
*
3
+
i
sj
*
2
(
j
=
a
,
b
,
c
)
,
and i* dc2 denotes a DC current reference value flowing in a DC system and i* sj denotes a reference value regarding a phase current.
2. The driving method of claim 1 , further comprising calculating a parameter variation value ({circumflex over (l)} pj2 ) of a circulating current suppression inductor of the modular multi-level converter between the measuring of the AC-grid voltage value (E sj ) of the modular multi-level converter and calculating of the voltage reference value (u* pj2 ) of the upper valve using the current reference value, the measured current value, the error value, the DC link voltage value, and the AC-grid voltage value.
3. The driving method of claim 2 , wherein the calculating of the parameter variation value ({circumflex over (l)} pj2 ) of a circulating current suppression inductor of the modular multi-level converter comprises:
obtaining a differential value of the parameter variation value of the circulating current suppression inductor using a following equation: {circumflex over (l)} pj2 =−m 1 err pj2 ; and
integrating the differential value of the parameter variation value of the circulating current suppression inductor, wherein m 1 is a predetermined tuning constant.
4. The driving method of claim 2 , wherein the calculating of the voltage reference value (u* pj2 ) of the upper valve using the current reference value (i* pj2 ), the measured current value (i pj2 ), the error value (err pj2 ), the DC link voltage value (V dc2 ), the AC-grid voltage value (E sj ), and the parameter variation value ({circumflex over (l)} pj2 ) of the circulating current suppression inductor comprises calculating the voltage reference value (u*.sub.pj2) of the upper valve using a following equation:
u
pj
2
*
=
(
V
dc
2
2
-
E
sj
)
-
{
P
(
err
pj
2
)
+
R
1
(
err
pj
2
)
+
R
2
(
err
pj
2
)
}
+
{
L
s
l
^
pj
2
}
.
5. The driving method of claim 2 , wherein the calculating of the voltage reference value (u* pj2 ) of the upper valve using the current reference value (i* pj2 ), the measured current value (i pj2 ), the error value (err pj2 ), the DC link voltage value (V dc2 ), the AC-grid voltage value (E sj ), and the parameter variation value ({circumflex over (l)} pj2 ) of the circulating current suppression inductor comprises calculating the voltage reference value (u* pj2 ) of the upper valve using a following equation:
u
pj
2
*
=
(
V
dc
2
2
-
E
sj
)
-
{
P
(
err
pj
2
)
+
R
1
(
err
pj
2
)
+
R
2
(
err
pj
2
)
}
-
{
L
s
i
pj
2
*
-
L
s
l
^
pj
2
}
6. The driving method of claim 1 , wherein the calculating of the voltage reference value (u* pj2 ) of the upper valve using the current reference value (i* pj2 ), the measured current value (i pj2 ), the error value (err pj2 ), the DC link voltage value (V dc2 ), and the AC-grid voltage value (E sj ) comprises calculating the voltage reference value (u* pj2 ) of the upper valve using a following equation:
u
pj
2
*
=
(
V
dc
2
2
-
E
sj
)
-
{
P
(
err
pj
2
)
+
R
1
(
err
pj
2
)
+
R
2
(
err
pj
2
)
}
.
7. The driving method of claim 1 , wherein the calculating of the voltage reference value (u* pj2 ) of the upper valve using the current reference value (i* pj2 ), the measured current value (i pj2 ), the error value (err pj2 ), the DC link voltage value (V dc2 ), and the AC-grid voltage value (E sj ) comprises calculating the voltage reference value (u* pj2 ) of the upper valve using a following equation:
u
pj
2
*
=
(
V
dc
2
2
-
E
sj
)
-
{
P
(
err
pj
2
)
+
R
1
(
err
pj
2
)
+
R
2
(
err
pj
2
)
}
-
{
ρ
pj
2
sgn
(
err
pj
2
)
}
wherein a sign function denotes a function operated by following equations:
sgn(err pj2 )=1(err pj2 >0)
sgn(err pj2 )=0(err pj2 ≦0)
and ρ pj2 denotes a proportional gain.
8. The driving method of claim 1 , wherein the calculating of the voltage reference value (u* pj2 ) using the current reference value (i* pj2 ), the measured current value (i* pj2 ), the error value (err pj2 ), the DC link voltage value (V dc2 ), and the AC grid voltage value (E sj ) comprises calculating the voltage reference value (u* pj2 ) of the upper valve using a following equation:
u
pj
2
*
=
(
V
dc
2
-
E
sj
)
-
{
P
(
err
pj
2
)
+
R
1
(
err
pj
2
)
+
R
2
(
err
pj
2
)
}
-
{
L
s
i
′
*
pj
2
+
ρ
pj
2
sgn
(
err
pj
2
)
}
wherein:
a sign function denotes a function operated by following equations:
sgn(err pj2 )=1(err pj2 >0)
sgn(err pj2 )=0(err pj2 ≦0)
ρ pj2 denotes a proportional gain; and
L s denotes a circulating current suppression inductor of the upper valve.
9. The driving method of claim 4 , wherein P(err pj2 ), R 1 (err pj2 ), and R 2 (err pj2 ) are calculated using a following equations:
P
(
err
pj
2
)
=
(
K
p
)
err
pj
2
R
1
(
err
pj
2
)
=
(
K
i
1
s
s
2
+
(
ω
o
)
2
)
err
pj
2
,
and
R
2
(
err
pj
2
)
=
(
K
i
2
s
s
2
+
(
2
ω
o
)
2
)
err
pj
2
,
wherein K p , K i1 , and K i2 denote predetermined gain values, and ω o denotes a AC-grid frequency.
10. The driving method of claim 1 , wherein the reference value regarding the phase current expressed in a stationary reference frame is calculated using a following equation:
[
i
sa
*
i
sb
*
i
sc
*
]
=
[
1
0
-
1
2
3
2
-
1
2
-
3
2
]
[
i
s
α
*
i
s
β
*
]
,
and i* sα and i* sβ denote the reference value regarding the phase current expressed in a rotating stationary reference frame.
11. The driving method of claim 10 , wherein:
an expression of the reference value regarding the phase current at a d-q frame is converted into an expression of the reference value regarding the phase current at the rotating stationary reference frame i* sα and i* sβ using a following equation:
i* sαβ =i sdq 9 *e jωt +i sdq n *e −jωt ;
i sdq p * is an abbreviation of a d-axis and a q-axis (i sq p *, i sd p *) of a positive sequence component current reference value;
i sdq n * is an abbreviation of a d-axis and a q-axis (i sq n *, i sd n *) of a negative sequence component current reference value;
i sd p * denotes the d-axis of the positive sequence component current reference value;
i sq p * denotes the q-axis of the positive sequence component current reference value;
i sd n * denotes the d-axis of the negative sequence component current reference value;
i sq n * denotes the q-axis of the negative sequence component current reference value;
i sq p *, i sd p *, i sq n *, and i sq n * are calculated using a following equations:
i
sq
p
*
=
PI
(
P
s
*
-
P
s
)
,
i
sd
p
*
=
PI
(
Q
s
*
-
Q
s
)
,
i
sq
n
*
=
-
E
sd
n
E
sq
p
i
sd
p
-
E
sq
n
E
sq
p
i
sq
p
,
and
i
sd
n
*
=
E
sq
n
E
sq
p
i
sd
p
-
E
sd
n
E
sq
p
i
sq
p
;
and
P s denotes active power in an AC system, P* s denotes a reference value of active power in the AC system, Q s denotes reactive power in the AC system, Q* s denotes a reference value of reactive power in the AC system, E sd p denotes a d-axis voltage of a positive sequence voltage flowing in the AC system, E sq p denotes a q-axis voltage of a positive sequence voltage flowing in the AC system, E sd n denotes a d-axis voltage of a negative sequence voltage flowing in the AC system, and E sq n denotes a q-axis voltage of a negative sequence voltage flowing in the AC system.
12. The driving method of claim 1 , wherein the reference value (i* dc2 ) of the DC system is calculated using a following equation:
i
dc
2
*
=
3
2
(
E
sq
p
V
dc
2
)
i
sq
p
*
,
and
E sq p denotes a q-axis voltage of a positive sequence component voltage flowing in an AC system and i sq p * denotes a q-axis current of a positive sequence component current reference value flowing in the AC system.
13. The driving method of claim 1 , after the calculating of the voltage reference value u* pj2 using the current reference value (i* pj2 ), the measured current value (i pj2 ), the error value (err pj2 ), the DC link voltage value (V dc2 ), and the AC-grid voltage value (E sj ) comprising:
calculating a number of submodules to be triggered among submodules of the upper valve;
selecting submodules corresponding to the calculated number of submodules; and
applying a pulse width modulation signal to the selected submodules.
14. A driving method for a modular multi-level converter that converts an alternating current (AC) into a direct current (DC) or converts a DC into an AC using the modular multi-level converter with a plurality of submodules stacked to deliver power in an AC system, the modular multi-level converter comprising a plurality of valves independently driven and a lower valve that is one of valve branches comprising the plurality of valves, the driving method comprising:
inputting a current reference value (i* nj2 ) of the lower valve of the modular multi-level converter;
measuring a current value (i nj2 ) of the lower valve;
calculating an error value (err nj2 ) between the current reference value and the measured current value of the lower valve;
measuring a DC link voltage value (V dc2 ) of the modular multi-level converter;
measuring an AC-grid voltage value (E sj ) of the modular multi-level converter; and
calculating a voltage reference value (u* nj2 ) using the current reference value (i* nj2 ), the measured current value (i nj2 ), the error value (err nj2 ), the DC link voltage value (V dc2 ), and the AC-grid voltage value (E sj ),
wherein the inputting of the current reference value (i* nj2 ) of the upper valve of the modular multi-level converter comprises calculating the current reference value (i* nj2 ) using a following equation:
i
nj
2
*
=
i
dc
2
*
3
-
i
sj
*
2
,
and
i* dc2 denotes a DC current reference value flowing in a DC system and i* sj j denotes a reference value regarding a phase current.
15. The driving method of claim 14 , further comprising calculating a parameter variation value ({circumflex over (l)} nj2 ) of a circulating current suppression inductor of the modular multi-level converter between the measuring of the AC-grid voltage value (E sj ) of the modular multi-level converter and calculating of the voltage reference value (u* nj2 ) using the current reference value, the measured current value, the error value, the DC link voltage value, and the system voltage value.
16. The driving method of claim 15 , wherein the calculating of the parameter variation value ({circumflex over (l)} nj2 ) of a circulating current suppression inductor of the modular multi-level converter comprises:
obtaining a differential value of the parameter variation value of the circulating current suppression inductor using a following equation:
{circumflex over (l)} nj2 =−m 2 err nj2 ; and
integrating the differential value of the parameter variation value of the circulating current suppression inductor, wherein m 2 is a predetermined tuning constant.
17. The driving method of claim 16 , wherein the calculating of the voltage reference value (u* nj2 ) of the lower valve using the current reference value (i* nj2 ), the measured current value (u* nj2 ), the error value (err.sub.nj2), the DC link voltage value (V dc2 ), the AC-grid voltage value (E sj ), and the parameter variation value ({circumflex over (l)} nj2 ) of the inductor comprises calculating the voltage reference value (u* nj2 ) of the lower valve using a following equation:
u
nj
2
*
=
(
V
dc
2
2
+
E
sj
)
-
{
P
(
err
nj
2
)
+
R
1
(
err
nj
2
)
+
R
2
(
err
nj
2
)
}
+
{
L
s
l
^
nj
2
}
.
18. The driving method of claim 16 , wherein the calculating of the voltage reference value (u* nj2 ) of the lower valve using the current reference value (i* nj2 ), the measured current value (i nj2 ), the error value (err nj2 ), the DC link voltage value (V dc2 ), the AC-grid voltage value (E sj ), and the parameter variation value ({circumflex over (l)} nj2 ) of the inductor comprises calculating the voltage reference value (u* nj2 ) of the lower valve using a following equation:
u
nj
2
*
=
(
V
dc
2
2
+
E
sj
)
-
{
P
(
err
nj
2
)
+
R
1
(
err
nj
2
)
+
R
2
(
err
nj
2
)
}
-
{
L
s
i
nj
2
*
-
L
s
l
^
nj
2
}
.
19. The driving method of claim 15 , wherein the calculating of the voltage reference value (u* nj2 ) of the lower valve using the current reference value (i* nj2 ), the measured current value (i nj2 ), the error value (err nj2 ), the DC link voltage value (V dc2 ), and the AC-grid voltage value (E sj ) comprises calculating the voltage reference value (u* nj2 ) of the lower valve using a following equation:
u
nj
2
*
=
(
V
dc
2
2
+
E
sj
)
-
{
P
(
err
nj
2
)
+
R
1
(
err
nj
2
)
+
R
2
(
err
nj
2
)
}
+
{
L
s
i
nj
2
*
-
L
s
l
^
nj
2
}
.
20. The driving method of claim 15 , wherein the calculating of the voltage reference value (u* nj2 ) of the lower valve using the current reference value (i* nj2 ), the measured current value (i nj2 ), the error value (err nj2 ) the DC link voltage value (V dc2 ), the AC-grid voltage value (E sj ), and an sgn function comprises calculating the voltage reference value (u* nj2 ) of the lower valve using a following equation:
u
nj
2
*
=
(
V
dc
2
2
+
E
sj
)
-
{
P
(
err
nj
2
)
+
R
1
(
err
nj
2
)
+
R
2
(
err
nj
2
)
}
-
{
ρ
nj
2
sgn
(
err
nj
2
)
}
,
wherein the sign function denotes a sign function operated by following equations:
sgn(err nj2 )=1(err nj2 >0)
sgn(err nj2 )=0(err nj2 ≦0)
and
ρ nj2 denotes a proportional gain.
21. The driving method of claim 15 , wherein the calculating of the voltage reference value (u* nj2 ) of the lower valve using the current reference value (i* nj2 ), the measured current value (i nj2 ) the error value (err nj2 ) the DC link voltage value (V dc2 ), the AC-grid voltage value (E sj ), and an sgn function comprises calculating the voltage reference value (u* nj2 ) of the lower valve using a following equation:
u
nj
2
*
=
(
V
dc
2
2
+
E
sj
)
-
{
P
(
err
nj
2
)
+
R
1
(
err
nj
2
)
+
R
2
(
err
nj
2
)
}
-
{
L
s
i
nj
2
*
+
ρ
nj
2
sgn
(
err
nj
2
)
}
,
wherein the sign function denotes a sign function operated by following equations:
sgn(err nj2 )=1(err nj2 >0)
sgn(err nj2 )=0(err nj2 ≦0)
ρ nj2 denotes a proportional gain; and L s denotes a circulating current suppression inductor of the upper valve.
22. The driving method of claim 19 , wherein P(err nj2 ), R 1 (err nj2 ), and R 2 (err nj2 ) are calculated using following equations:
P
(
err
nj
2
)
=
(
K
p
)
err
nj
2
,
R
1
(
err
nj
2
)
=
(
K
i
1
s
s
2
+
(
ω
0
)
2
)
err
nj
2
,
and
R
2
(
err
nj
2
)
=
(
K
i
2
s
s
2
+
(
2
ω
0
)
2
)
err
nj
2
,
wherein K p , K i1 , and K i2 denote predetermined gain values, and ω o denotes a AC-grid frequency.
23. The driving method of claim 15 , wherein the reference value regarding the phase current expressed in a stationary reference frame is calculated using a following equation:
[
i
sa
*
i
sb
*
i
sc
*
]
=
[
1
0
-
1
2
3
2
-
1
2
-
3
2
]
[
i
s
α
*
i
s
β
*
]
,
and i* sα and i* sβ denote the reference value regarding the phase current expressed in a rotating stationary reference frame.
24. The driving method of claim 23 , wherein: an expression of the reference value regarding the phase current at a d-q frame is converted into an expression of the reference value regarding the phase current at the rotating stationary reference frame i* sα and i* sβ using a following equation:
i* sαβ =i sdq p *e jωt +i sdq n *e −jωt
i sdq p * is an abbreviation of a d-axis and a q-axis (i sq p *, i sd p *) of a positive sequence component current reference value;
i sdq n * is an abbreviation of a d-axis and a q-axis (i sq n *, i sd n *) of a negative sequence component current reference value;
i sd n * denotes the d-axis of the positive sequence component current reference value;
i sq p * denotes the q-axis of the positive sequence component current reference value;
i sd n * denotes the d-axis of the negative sequence component current reference value;
i sq n * denotes the q-axis of the negative sequence component current reference value;
i sq p *, i sd p *, i sq n *, and i sd n * are calculated using following equations:
i
sq
p
*
=
PI
(
P
s
*
-
P
s
)
,
i
sd
p
*
=
PI
(
Q
s
*
-
Q
s
)
,
i
sq
n
*
=
-
E
sd
n
E
sq
p
i
sd
p
-
E
sq
n
E
sq
p
i
sq
p
,
and
i
sd
n
*
=
E
sq
n
E
sq
p
i
sd
p
-
E
sd
n
E
sq
p
i
sq
p
;
and
P s denotes active power in the AC system, P* s denotes a reference value of active power in the AC system, Q s denotes reactive power in the AC system, Q* s denotes a reference value of reactive power in the AC system, E sd p denotes a d-axis voltage of a positive sequence voltage flowing in the AC system, E sd n a denotes a q-axis voltage of a positive sequence voltage flowing in the AC system, E sq n denotes a d-axis voltage of a negative sequence voltage flowing in the AC system, and E sq n denotes a q-axis voltage of a negative sequence voltage flowing in the AC system.
25. The driving method of claim 24 , wherein the reference value (i* dc2 ) of the DC system is calculated using a following equation:
i
dc
2
*
=
3
2
(
E
sq
p
V
dc
2
)
i
sq
p
*
,
and
E sq p denotes a q-axis voltage of a positive sequence component voltage flowing in the AC system and i sq p * denotes a q-axis current of a positive sequence component current reference value flowing in the AC system.
26. The driving method of claim 15 , after the calculating of the voltage reference value (u* nj2 ) using the current reference value (i* nj2 ), the measured current value (i nj2 ), the error value (err nj2 ), the DC link voltage value (V dc2 ), and the AC-grid voltage value (E sj ), comprising: calculating the number of submodules to be triggered among submodules of the upper valve;
selecting submodules corresponding to the number of submodules; and applying a pulse width modulation signal to the selected submodules.
27. The driving method of claim 20 , wherein the driving method for the modular multi-level converter is driven at a valve unit of the modular multi-level converter.
28. A driving apparatus for a modular multi-level converter, comprising:
an input unit receiving a current reference value of an upper valve of one valve branch of the modular multi-level converter;
a current measuring unit for measuring a current value of the upper valve of one valve branch of the modular multi-level converter;
a direct current (DC) link voltage measuring unit for measuring a voltage value of a DC link of the modular multi-level converter;
a system voltage measuring unit for measuring a system voltage value of the modular multi-level converter;
an error calculating unit for calculating an error value between the current reference value received by the input unit and the current value measured by the current measuring unit;
a proportional controller proportionally amplifying the error value calculated by the error calculating unit with a predetermined gain value;
a first resonant-type current controller receiving the error value calculated by the error calculating unit to converge an error current equal to an AC-grid frequency to zero;
a second resonant-type current controller receiving the error value calculated by the error calculating unit to converge a harmonic error current about two times larger than the AC-grid frequency to zero; and
a voltage reference value calculating unit for calculating a voltage reference value of the upper valve of the one valve branch of the modular multi-level converter using values calculated by the DC link voltage measuring unit, the system voltage measuring unit, the proportional controller, the first resonant-type current controller, and the second resonant-type current controller.
29. The driving apparatus of claim 28 , further comprising: a submodule selecting unit for selecting submodules to be triggered corresponding to a calculated number of submodules to be triggered using the voltage reference value calculated by the voltage reference value calculating unit; and a pulse width modulation signal generating unit applying a pulse width modulation signal to the submodules selected by the submodule selecting unit.
30. The driving apparatus of claim 28 , wherein the proportional controller amplifies the error value calculated by the error calculating unit to a gain value.
31. The driving apparatus of claim 28 , wherein the first resonant-type current controller multiplies the error value calculated by the error calculating unit and the following equation:
K
i
1
s
s
2
+
(
ω
o
)
2
to converge the error current to zero, and K i1 denotes a predetermined gain value of the first resonant-type current controller and ω o denotes the AC-grid frequency.
32. The driving apparatus of claim 28 , wherein the second resonant-type current controller multiplies the error value calculated by the error calculating unit and the following equation:
K
i
2
s
s
2
+
(
2
ω
o
)
2
to converge the harmonic error current about two times larger than the AC-grid frequency to zero, and K i1 denotes a predetermined gain value of the second resonant-type current controller and .omega . . . sub.o denotes the AC-grid frequency.
33. The driving apparatus of claim 28 , wherein the voltage reference value calculating unit obtains a voltage difference by subtracting the system voltage value measured by the system voltage measuring unit from a half of the voltage value measured by the DC link voltage measuring unit, and calculates the voltage reference value by subtracting a sum of calculated values outputted by the proportional controller, the first resonant-type current controller, and the second resonant-type current controller from the voltage difference.
34. The driving apparatus of claim 28 , further comprising a compensator reducing an error generated from the modular multi-level converter, wherein the compensator obtains an sgn output value by inputting the error value of the error calculating unit into an sgn function and then calculates a compensation value by multiplying the sgn output value and a proportional gain of the sgn function.
35. The driving apparatus of claim 34 , wherein the voltage reference value calculating unit further receives an output value of the compensator to obtain a voltage difference by subtracting the system voltage value measured by the system voltage measuring unit from a half of the voltage value measured by the DC link voltage measuring unit, and calculates the voltage reference value by subtracting a sum of calculated values outputted by the proportional controller, the first resonant-type current controller, the second resonant-type current controller, and the compensator from the voltage difference.
36. The driving apparatus of claim 28 , further comprising an estimator that obtains a variation estimation value by multiplying and integrating the error value calculated by the error calculating unit and a predetermined tuning constant.
37. The driving apparatus of claim 36 , wherein the voltage reference value calculating unit further receives an estimation value of the estimator to obtain a voltage difference by subtracting the system voltage value measured by the system voltage measuring unit from a half of the voltage value measured by the DC link voltage measuring unit, and calculates the voltage reference value by subtracting a sum of calculated values outputted by the proportional controller, the first resonant-type current controller, the second resonant-type current controller, the compensator, and the estimator from the voltage difference.
38. A driving apparatus for a modular multi-level converter, comprising:
an input unit receiving a current reference value of a lower valve of one valve branch of the modular multi-level converter;
a current measuring unit for measuring a current value of the lower valve of one valve branch of the modular multi-level converter;
a direct current (DC) link voltage measuring unit for measuring a voltage value of a DC link of the modular multi-level converter;
a system voltage measuring unit for measuring a system voltage value of the modular multi-level converter;
an error calculating unit for calculating an error value between the current reference value received by the input unit and the current value measured by the current measuring unit;
a proportional controller proportionally amplifying the error value calculated by the error calculating unit with a predetermined gain value;
a first resonant-type current controller receiving the error value calculated by the error calculating unit to converge an error current equal to a AC-grid frequency to zero;
a second resonant-type current controller receiving the error value calculated by the error calculating unit to converge a harmonic error current about two times larger than the AC-grid frequency to zero; and
a voltage reference value calculating unit for calculating a voltage reference value of the lower valve of the one valve branch of the modular multi-level converter using values calculated by the DC link voltage measuring unit, the system voltage measuring unit, the proportional controller, the first resonant-type current controller, and the second resonant-type current controller.
39. The driving apparatus of claim 38 , further comprising: a submodule selecting unit for selecting submodules to be triggered corresponding to a calculated number of submodules to be triggered using the voltage reference value calculated by the voltage reference value calculating unit; and a pulse width modulation signal generating unit applying a pulse width modulation signal to the submodules selected by the submodule selecting unit.
40. The driving apparatus of claim 38 , wherein the proportional controller amplifies the error value calculated by the error calculating unit to a gain value.
41. The driving apparatus of claim 38 , wherein the first resonant-type current controller multiplies the error value calculated by the error calculating unit and a following equation:
K
i
1
s
s
2
+
(
ω
o
)
2
to converge the error current to zero, and K i1 denotes a predetermined gain value of the first resonant-type current controller and ω o denotes the AC-grid frequency.
42. The driving apparatus of claim 38 , wherein the second resonant-type current controller multiplies the error value calculated by the error calculating unit and a following equation:
K
i
2
s
s
2
+
(
2
ω
o
)
2
to converge the harmonic error current about two times larger than the AC-grid frequency to zero, and K i2 denotes a predetermined gain value of the second resonant-type current controller and ω o denotes the AC-grid frequency.
43. The driving apparatus of claim 38 , wherein the voltage reference value calculating unit obtains a voltage sum by adding the system voltage value measured by the system voltage measuring unit to a half of the voltage value measured by the DC link voltage measuring unit, and calculates the voltage reference value by subtracting a sum of calculated values outputted by the proportional controller, the first resonant-type current controller, and the second resonant-type current controller from the voltage sum.
44. The driving apparatus of claim 38 , further comprising a compensator reducing an error generated from the modular multi-level converter, wherein the compensator obtains an sgn output value by inputting the error value of the error calculating unit into an sgn function and then calculates a compensation value by multiplying the sgn output value and a proportional gain of the sgn function.
45. The driving apparatus of claim 44 , wherein the voltage reference value calculating unit further receives an output value of the compensator to obtain a voltage sum by adding the system voltage value measured by the system voltage measuring unit to a half of the voltage value measured by the DC link voltage measuring unit, and calculates the voltage reference value by subtracting a sum of calculated values outputted by the proportional controller, the first resonant-type current controller, the second resonant-type current controller, and the compensator from the voltage sum.
46. The driving apparatus of claim 38 , further comprising an estimator that obtains a variation estimation value by multiplying and integrating the error value calculated by the error calculating unit and a predetermined constant.
47. The driving apparatus of claim 38 , wherein the voltage reference value calculating unit further receives an estimation value of the estimator to obtain a voltage sum by adding the system voltage value measured by the system voltage measuring unit to a half of the voltage value measured by the DC link voltage measuring unit, and calculates the voltage reference value by subtracting a sum of calculated values outputted by the proportional controller, the first resonant-type current controller, the second resonant-type current controller, the compensator, and the estimator from the voltage sum.
48. The driving apparatus of claim 38 , wherein the driving apparatus for the modular multi-level converter is driven at a valve unit of the modular multi-level converter.
49. The driving method of claim 5 , wherein P(err pj2 ), R 1 (err pj2 ), and R 2 (err pj2 ) are calculated using following equations:
P
(
err
pj
2
)
=
(
K
p
)
err
pj
2
R
1
(
err
pj
2
)
=
(
K
i
1
s
s
2
+
(
ω
o
)
2
)
err
pj
2
,
and
R
2
(
err
pj
2
)
=
(
K
i
2
s
s
2
+
(
2
ω
o
)
2
)
err
pj
2
,
wherein K p , K i1 , and K i2 denote predetermined gain values, and ω o denotes a AC-grid frequency.
50. The driving method of claim 6 , wherein P(err pj2 ), R 1 (err pj2 ), and R 2 (err pj2 ) are calculated using following equations:
P
(
err
pj
2
)
=
(
K
p
)
err
pj
2
R
1
(
err
pj
2
)
=
(
K
i
1
s
s
2
+
(
ω
o
)
2
)
err
pj
2
,
and
R
2
(
err
pj
2
)
=
(
K
i
2
s
s
2
+
(
2
ω
o
)
2
)
err
pj
2
,
wherein K p , K i1 , and K i2 denote predetermined gain values, and ω o denotes a AC-grid frequency.
51. The driving method of claim 7 , wherein P(err pj2 ), R 1 (err pj2 ), and R 2 (err pj2 ) are calculated using following equations:
P
(
err
pj
2
)
=
(
K
p
)
err
pj
2
R
1
(
err
pj
2
)
=
(
K
i
1
s
s
2
+
(
ω
o
)
2
)
err
pj
2
,
and
R
2
(
err
pj
2
)
=
(
K
i
2
s
s
2
+
(
2
ω
o
)
2
)
err
pj
2
,
wherein K p , K i1 , and K i2 denote predetermined gain values, and ω o denotes a AC-grid frequency.
52. The driving method claim 8 , wherein P(err pj2 ), R 1 (err pj2 ), and R 2 (err pj2 ) are calculated using the following equations:
P
(
err
nj
2
)
=
(
K
p
)
err
nj
2
,
R
1
(
err
nj
2
)
=
(
K
i
1
s
s
2
+
(
ω
o
)
2
)
err
nj
2
,
and
R
2
(
err
nj
2
)
=
(
K
i
2
s
s
2
+
(
2
ω
o
)
2
)
err
nj
2
,
wherein K p , K i1 , and K i2 denote predetermined gain values, and ω o denotes a AC-grid frequency.
53. The driving method of claim 4 , wherein P(err nj2 ), R 1 (err nj2 ), and R 2 (err nj2 ) are calculated using following equations:
P
(
err
nj
2
)
=
(
K
p
)
err
nj
2
,
R
1
(
err
nj
2
)
=
(
K
i
1
s
s
2
+
(
ω
o
)
2
)
err
nj
2
,
and
R
2
(
err
nj
2
)
=
(
K
i
2
s
s
2
+
(
2
ω
o
)
2
)
err
nj
2
,
wherein K p , K i1 , and K i2 denote predetermined gain values, and ω o denotes a AC-grid frequency.
54. The driving method claim 5 , wherein P(err nj2 ), R 1 (err nj2 ), and R 2 (err nj2 ) are calculated using following equations:
P
(
err
nj
2
)
=
(
K
p
)
err
nj
2
,
R
1
(
err
nj
2
)
=
(
K
i
1
s
s
2
+
(
ω
o
)
2
)
err
nj
2
,
and
R
2
(
err
nj
2
)
=
(
K
i
2
s
s
2
+
(
2
ω
o
)
2
)
err
nj
2
,
wherein K p , K i1 , and K i2 denote predetermined gain values, and ω o denotes a AC-grid frequency.
55. The driving method claim 6 , wherein P(err nj2 ), R 1 (err nj2 ), and R 2 (err nj2 ) are calculated using following equations:
P
(
err
pj
2
)
=
(
K
p
)
err
pj
2
,
R
1
(
err
pj
2
)
=
(
K
i
1
s
s
2
+
(
ω
o
)
2
)
err
pj
2
,
and
R
2
(
err
pj
2
)
=
(
K
i
2
s
s
2
+
(
2
ω
o
)
2
)
err
pj
2
,
wherein K p , K i1 , and K i2 denote predetermined gain values, and ω o denotes a AC-grid frequency.
56. The driving method of claim 15 , wherein the driving method for the modular multi-level converter is driven at a valve unit of the modular multi-level converter.
57. The driving apparatus of claim 38 , wherein the driving apparatus for the modular multi-level converter is driven at a valve unit of the modular multi-level converter.