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7/22/2019 8407 Slides Topic7-NPC
1/19
1
Topic 7
Multilevel Neutral Point Clamped (NPC) Inverters
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Three-Level NPC Inverter Based MV Drive, Courtesy of ABB (ACS1000)
EE8407
Power Converter Systems
2
Topic 7Multilevel Neutral Point Clamped (NPC) Inverter
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Lecture Topics
Three-level NPC Inverter
Space Vector Modulation
Neutral Point Voltage Control
High-level NPC Inverter
EE8407
7/22/2019 8407 Slides Topic7-NPC
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Inverter Configuration
Clamping diodes: DZ1 and DZ2 (Phase A)
1dC
1S
2S
3S
4S
A
B
CZ
2dC
1D
2D
3D
4D
1ZD
2ZD
E
E
Zi
dV
Ai
OBi
Ci
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Three-Level NPC Inverter
EE8407
4
Switching State
Complementary Switch pairs:
S1and S3; S2and S4;
Device Switching Status(PhaseA)Switching
State
1S 2S 3S 4S
Inverter Terminal
Voltage
ZAV
P On On Off Off E
O Off On On Off 0
N Off Off On On E
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Three-Level NPC Inverter
EE8407
7/22/2019 8407 Slides Topic7-NPC
3/19
5
Gate Signal Arrangements
Inverter phase voltage vAZ has three levels: E, 0 and E
2
ONONONOPOPOPO
0
1gv
2gv
3gv
4gv
AZv
E+
E
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Three-Level NPC Inverter
EE8407
6
Inverter Output Waveforms
2
E+AZ
v
BZv
CZv
ABv
0
0
0
0
t
t
t
t
BZAZAB vvv =
E
E2+
E2
E+
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Three-Level NPC Inverter
EE8407
7/22/2019 8407 Slides Topic7-NPC
4/19
7
Space Vectors
Three-phase voltages
0)()()( =++ tvtvtvCOBOAO
Two-phase voltages
=
)(
)(
)(
3
4sin
3
2sin0sin
3
4cos
3
2cos0cos
3
2
)(
)(
tv
tv
tv
tv
tv
CO
BO
AO
Space vector representation
)()()( tvjtvtV
+=r
(2) (3)
[ ]3/43/20 )()()(32)(
j
CO
j
BO
j
AO etvetvetvtV ++=
r
where xjxe jx sincos +=
(3)
(1)
(2)
(4)
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Space Vector Modulation (SVM)
EE8407
8
Switching state [POO] on-state switches:
Phase A: upper two switches [P]
Phase B: lower two switches [O]
Phase C: lower two switches [O]
dBOdAO VtvVtv
3
1)(,
3
2)( ==
dCO Vtv
3
1)( =and
Substituting (5) to (4) gives a space vector
(5)
(6)0
132 jdeVV =
r
Space Vectors (Example)
from which
Total switching states: 27
Total space vectors: 19
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Space Vector Modulation
EE8407
7/22/2019 8407 Slides Topic7-NPC
5/19
9
Space Vectors Diagram
19 space vectors:
Zero vector: V0Small vectors: V1 V6Medium vectors: V
7 V
12Large vectors: V13 V18
dVV
3
213=r
6/
3
37
jedVV =r
3/
3
214
jedVV =r
0Vr
3Vr
2Vr
4Vr
5Vr
8Vr
6Vr
15Vr
18Vr
12Vr
11Vr
10Vr
9Vr
17Vr
16Vr
3/1 dVV =r
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Space Vector Modulation
EE8407
10
SpaceVector
Switching State Vector ClassificationVector
Magnitude
0Vr
[PPP][OOO] [NNN] Zero Vector (ZV) 0
P-type N-type
PV1
r
[POO]1Vr
NV1
r
[ONN]
PV2
r
[PPO]
2Vr
NV2
r
[OON]
PV3
r
[OPO]
3Vr
NV3
r
[NON]
PV4
r
[OPP]
4Vr
NV4
r
[NOO]
PV5
r
[OOP]
5Vr
NV5
r
[NNO]
PV6
r
[POP]
6Vr
NV6
r
[ONO]
Small Vector (SV)
P-type Small Vector (PSV)
N-type Small Vector (NSV)
dV3
1
Switching States and Space Vectors
Redundancy: Zero vector three switching states
Small vectors two states per vector
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Space Vector Modulation
EE8407
7/22/2019 8407 Slides Topic7-NPC
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Space
VectorSwitching State Vector Classification
Vector
Magnitude
7Vr
[PON]
8Vr
[OPN]
9Vr
[NPO]
10Vr
[NOP]
11Vr
[ONP]
12Vr
[PNO]
Medium Vector (MV) dV
3
3
13Vr
[PNN]
14Vr
[PPN]
15Vr
[NPN]
16Vr
[NPP]
17Vr
[NNP]
18Vr
[PNP]
Large Vector (LV) dV3
2
No redundant switching states for medium or large vectors
Switching States and Space Vectors
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Space Vector Modulation
EE8407
12
Sector Definition
1Vr
13Vr
7Vr
14Vr
0Vr
3Vr
2Vr
4Vr
5Vr
8Vr
6Vr
15Vr
18Vr
12Vr
11V
r
10Vr
9Vr
17Vr
16Vr
refVr
Vref: Reference vector, rotating in space at a certain speedAll other vectors are stationary
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Space Vector Modulation
EE8407
7/22/2019 8407 Slides Topic7-NPC
7/19
13
SVM Principle
For a given length and position in space, Vref can be approximated
by three nearby stationary vectors;
Based on the chosen stationary vectors, switching states are
selected and gate signals are generated;
When Vrefpasses through sectors one by one, different sets of
switches are turned on or off;
When Vrefrotates one revolution in space, the inverter output
voltage varies one cycle over time;
The inverter output frequency corresponds to the rotating speed
of Vref;
The inverter output voltage can be adjusted by the magnitude of Vref.
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Space Vector Modulation
EE8407
14
Dwell Time Calculation
4
bT PNNcT
bT
3
PON
PPN
PPO
OON
1
aT
ONN
POO
2
cT
39
13Vr
7Vr
1Vr
14Vr
0Vr
2Vr
refVr
aT
Use volt-second balancing principle
Select three nearest stationary vectors
721 and, VVVrrr
Sector I
=++
=++
scba
srefcba
TTTT
TVTVTVTVrrrr
271
Four Regions
Dwell time is the duty-cycle time
of selected switches during the
sampling period Ts .
(a)
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Space Vector Modulation
EE8407
7/22/2019 8407 Slides Topic7-NPC
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Dwell Time Calculation
=
+=
=
])3
(sin21[
]1)3
(sin2[
]sin21[
asc
asb
asa
mTT
mTT
mTT
Ta , Tb and Tc dwell times for V1 , V7and V2
d
ref
a
V
Vm 3= modulation index
From equation (a)
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Space Vector Modulation
EE8407
16
Switching Sequence (Seven-segment)
General Design Requirements
a) The transition from one switching state to the next involves only
two switches in the same inverter leg, one being turned on and
the other turned off; and
b) The transition for Vrefmoving from one sector (or one region)
to the next requires no or minimum number of switchings.
Note:
The switching sequence design is not unique, but the above
requirements should be satisfied for switching frequency
minimization.
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Space Vector Modulation
EE8407
7/22/2019 8407 Slides Topic7-NPC
9/19
17
Switching Sequence (Seven-segment)
Voltage Vector NV2r
7Vr
14Vr
PV2
r
14Vr
7Vr
NV2
r
Dwell Time4
cT
2
bT
2
aT
2
cT 2
aT
2
bT
4
cT
PhaseA O P P P P P O
PhaseB O O P P P O OSwitching
State
Phase C N N N O N N N
,0]O[,]P[ ==E E=]N[ .
Assuming Vrefis in Region 4 of Sector I,
three vectors are selected: V2 , V7and V14
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Space Vector Modulation
EE8407
18
Switching Sequence (Seven-segment)
2
aT
BZv
AZv
CZv
E+
4
cT
2
bT
sT
ABv
E+
E
E+
2
cT
2
bT
4
cT
NV2r
7Vr
14Vr
PV2
r
14Vr
7Vr
NV2
r
2
aT
Switching sequence requirementa) is satisfied
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Space Vector Modulation
EE8407
7/22/2019 8407 Slides Topic7-NPC
10/19
19
Switching Sequence (Seven-segment)
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Space Vector Modulation
EE8407
20
Switching Sequence (Seven-segment)
14Vr
15Vr
17Vr
18Vr
13Vr
16Vr
refVr
refVr
Switching sequence requirementb) is satisfied
2/2/ 1, fff spdevsw +=
ssp Tf /1=
Device switching frequency:
Sampling frequency:
Fundamental frequency:
1f
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Space Vector Modulation
EE8407
7/22/2019 8407 Slides Topic7-NPC
11/19
21
AZv
ABv
0
1gv
4gv
0
2 3
Simulated Waveforms (Seven-segment)
f1 = 60Hz, Ts = 1/1080 sec,ma = 0.8, fsw = 570Hz
vAB is not half wave symmetrical; andcontains both even- and odd-order harmonics
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Space Vector Modulation
EE8407
22
Simulated Waveforms (Seven-segment)
f1 = 60Hz, Ts = 1/1080 sec,ma = 0.8, fsw = 570Hz
dAZ VV n /
dAB VV n /
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Space Vector Modulation
EE8407
7/22/2019 8407 Slides Topic7-NPC
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dnAB VV /
am
am
dnAB VV /
Harmonic Content (Seven-segment)
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Space Vector Modulation
EE8407
24
Laboratory Prototype at Ryerson
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Space Vector Modulation
EE8407
7/22/2019 8407 Slides Topic7-NPC
13/19
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Measured Waveforms
AZv
ABv
8.0)a( =am 9.0)b( =am
d
n
V
VAB
d
n
V
VAZ
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Space Vector Modulation
EE8407
26
Measured waveforms (with even-order harmonic elimination)
AZv
ABv
8.0)a( =am 9.0)b( =am
d
n
V
VAB
d
n
V
VAZ
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Space Vector Modulation
EE8407
7/22/2019 8407 Slides Topic7-NPC
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Neutral Point Voltage Deviation
The neutral point voltage vz can be controlled byP- and N-types of small vectors
ZdV dV
dV dV
++
+ +
1dC
2dC
1dC
2dC
1dC
2dC
1dC
2dC
Zv
+
Zv
+
Zv+
Zv+
Zi
Zi
Z
ZZ
A
B
C
A
B
C
A
B
C
A
B
C
Zv]POO[affectednot]PPP[ Zv
Zv]ONN[ definednot]PON[ Zv
dV
+
Zv
+
1dC
2dC
Z
A
B
C
affectednot]PNN[ Zv
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Neutral Point Voltage Control
EE8407
28
Neutral Point Voltage Control
aNaPa TTT +=
( )
( )
=
+=
tT
T
tT
T
aaN
aaP
12
12 11 T
Neutral Point Deviation
Level
Motoring Mode0>di
Regenerating Mode0 )( 21 0>t 0
)( 12 0t
ddd Vvv dV ).
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Neutral Point Voltage Control
EE8407
7/22/2019 8407 Slides Topic7-NPC
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Neutral Point Voltage Control
R is used on purpose to make the dc voltage unbalance.
1dv
(sec)t
)(V
21, dd vv
2dZ vv =
A
Z
2dv
Zi
dV
1dv
R
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Neutral Point Voltage Control
EE8407
30
Inverter Topologies
1S
2S
3S
1S
A
1D
22 D
2D
E
E
dV E
E
E
dV
E
E
A
2S
3S
21D
1S
2S
3S
4S
1S
2S
3S
4S
1D
X
22 D
33 D
31D
22 D
3D
X
Y
Y
Z
dC
dC
P
N
ANv ANv
N
P
Ai Ai
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
High Power NPC Inverters
EE8407
7/22/2019 8407 Slides Topic7-NPC
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Switching State
Switch Status
Four-level Inverter
1S 2S 3S 1S 2S 3S
ANv
1 1 1 0 0 0 3E
0 1 1 1 0 0 2E
0 0 1 1 1 0 E
0 0 0 1 1 1 0
Five-level Inverter
1S 2S 3S 4S 1S 2S 3S 4S ANv
1 1 1 1 0 0 0 0 4E
0 1 1 1 1 0 0 0 3E
0 0 1 1 1 1 0 0 2E0 0 0 1 1 1 1 0 E
0 0 0 0 1 1 1 1 0
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
High Power NPC Inverters
EE8407
32
Component Count
Voltage
LevelSwitches
Clamping
Diodes*
dc
capacitors
m 6(m-1) 3(m-1)(m-2) (m-1)
3 12 6 2
4 18 18 3
5 24 36 4
6 30 60 5
* The clamping diodes have the same voltage rating as
other switches.
Note:
The number of clamping diodes increases substantially
with the voltage level.
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
High Power NPC Inverters
EE8407
7/22/2019 8407 Slides Topic7-NPC
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IPD Modulation (four-level)
3gv
2gv
1gv
ANv
ABv
1crv
2crv
3crv
dAB VV n /
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
High Power NPC Inverters
EE8407
34
Harmonic Content (four-level, IPD Modulation)
am
dAB VV n /
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
High Power NPC Inverters
EE8407
7/22/2019 8407 Slides Topic7-NPC
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APOD Modulation (four-level)
1crv
2crv
3crv
ABv
Ai
2 3
dn VVAB /
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
High Power NPC Inverters
EE8407
36
Harmonic Content (four-level, APOD Modulation)
0.2 0.4 0.6aM
0.1
0.2
0.3
00
x
y 612.0=
x
y
n=1
n=13,17
n=11
n=19
0.8
d
n
V
VAB
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
High Power NPC Inverters
EE8407
7/22/2019 8407 Slides Topic7-NPC
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The 3-level NPC inverter widely used in MV drives
Main features
- Low device count
- Good harmonic profile
- Suitable for medium voltage operation
The practical use of 4- or 5-level NPC inverters not reported
Main reasons
- Difficulties in dc capacitor voltage control
- Large number of clamping diodes
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7 Multilevel NPC Inverters
Summary
EE8407
38
Textbook: Bin Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, 2006
Topic 7
Multilevel Neutral Point Clamped Inverters
EE8407