dc-to-ac converters week 10 1. generic five-level inverter 2
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1
DC-to-AC Converters
Week 10
GENERIC FIVE-LEVEL INVERTER
2
vo
V1
C1
C2
C3
C4
V3
Vi4
S4
S5
S3
S2
S1
Vi4
Vi4
V2
V4
V5
Vi4
Vi
HALF-BRIDGE VOLTAGE-SOURCE INVERTER
3
io
V i
i i
vo
THREE-LEVEL NEUTRAL-CLAMPED INVERTER
4
V i
i i
C2
C1
G
D6
D5S1
S2
S3
S4
D1
D2
D3
D4
v
A
AN
iA
B
C
i iB C
v v
N
BN CN
vBN
v vAB BC
vCA
• Synthesis of higher voltage levels using power devices of lower voltage ratings
• Increased number of voltage levels which leads to better voltage waveforms and reduced Total Harmonic Distortion (THD) in voltage
• Reduced switching stresses on the
devices
ADVANTAGES OF MULTILEVEL INVERTERS OVER THE TWO-LEVEL
INVERTERS
CAo
S11
S12
S13
S14
S21
S24
S23
S22
S31
S32
S33
S34
B
C1
C2
Vd
c
+
_
3-ph Ac mains
NEUTRAL CLAMPED INVERTER TOPOLOGY FOR 3-LEVEL INVERSION
• The neutral point fluctuates as the capacitors C1 and C2 carry load currents
• Bulkier capacitors are needed to check the neutral point fluctuation
• PWM strategies aim to balance the neutral point dynamically
VOLTAGE SPACE VECTORS OF A THREE-LEVEL NEUTRAL-CLAMPED
INVERTER
7
d
jq
V6 V15 V24
V12 = V25
V18V=V9 22V8
V7 V21
V2 V20V11
V19
-1 1
__V 32
__V 32
-j
V=V1 14 V = V10 23V5
V16=V3
V=V4 17
STATES, SWITCHING VARIABLES, AND WAVEFORMS OF OUTPUT VOLTAGE IN A THREE-LEVEL
NEUTRAL-CLAMPED INVERTER IN THE SQUARE-WAVE MODE
8
c
b
a
t
t
t
2
t
t
t
t
t
vCN
vBN
vAN
vCA
vBC
Vi
STATE: 18 21 24 15 6 7 8 5 2 11 20 19
t
0
vAB
WAVEFORMS OF OUTPUT VOLTAGE AND CURRENT IN A THREE-LEVEL NEUTRAL-CLAMPED INVERTER IN THE SQUARE-
WAVE MODE
9
3_ Vi 2
3_2 Vi
43t
iA
vAN
-
02
ONE PHASE OF A MULTILEVEL CASCADED H-BRIDGE INVERTER
10
SWITCHED NETWORK FOR ILLUSTRATION OF THE OPERATING
PRINCIPLE OF A RESONANT DC LINK
11
V i
R L
C
i i
vo I oDS
iS
iC
iD
WAVEFORMS OF VOLTAGE AND CURRENT IN THE RESONANT DC LINK
12
t0
I2
t3t2t1
iC
g
iS
0
0
0
0
0
0ii
Io
vo
t
t
t
t
t
Vi
0
t iD
THREE-PHASE RESONANT DC LINK INVERTER WITH AN ACTIVE CLAMP
13
V i
A B C
N
C c l S
L
D
C
WAVEFORMS OF LINE-TO-LINE OUTPUT VOLTAGES IN A RESONANT
DC-LINK INVERTER
14
t
t
t
vBC
vAB
vCA
0
0
0
AUXILIARY RESONANT COMMUTATED POLE INVERTER: (A) ONE PHASE WITH THE AUXILIARY CIRCUIT, (B)
THE ENTIRE INVERTER
15
(a)
A C
A C
A C
L rV i
C i
C i
AC
D1
D2
S1
S2
C r
S
C r
A
L f
A B C
(b)
IDEALIZED LINE-TO-NEUTRAL VOLTAGE AND LINE CURRENT WAVEFORMS IN A VSI IN THE
SQUARE-WAVE MODE
16
a
a
iSA iDA'
iDA iSA'
0
iSA'
iSA
0
vAN
vAN
t0
(a)
t0
(b)
BLOCK DIAGRAM OF A PHOTOVOLTAIC UTILITY INTERFACE
17
D IO D E R E C TIF IE R
T R ANS F O R ME R
INVE R T E R
D C LIN K
F ILTE R
C O NT R O LLE D R E C T IF IE R
GR
ID
P V AR R AY
BLOCK DIAGRAM OF AN ACTIVE POWER FILTER
18
WAVEFORMS OF VOLTAGE AND CURRENT IN AN ACTIVE POWER FILTER
19
UPS SYSTEM
20
LINEFILTER
RECTIFIER DC LINK
GR
ID
LO
AD
LOADFILTER
BATTERY
STATIC SWITCH
INVERTER
BLOCK DIAGRAM OF AN AC DRIVE SYSTEM WITH SCALAR SPEED CONTROL
21
LOAD
SPEEDSENSOR
MOTOR
INVERTERDC LINK
RECTIFIER
AC
LIN
E
VOLTAGE CONTROLLER
SLIP CONTROLLER
*
*
*sl
M
MM*
M
v *
p
*sy n
USE OF THE MODULAR FREQUENCY CHANGER OF FIGURE 2.24 IN AN AC DRIVE:
(A) SYSTEM WITH A BRAKING RESISTOR, (B) SYSTEM WITH A STEP-UP CHOPPER
22
RECTIFIER
INVERTER BRAKINGRESISTOR
AC
LIN
EA
C L
INE
RECTIFIER INVERTER
BOOSTINDUCTOR
(a )
(b )TO MOTOR
TO MOTOR
PWM RECTIFIER-INVERTER CASCADES FOR BIDIRECTIONAL POWER FLOW IN AC MOTOR DRIVES: (A) CURRENT-TYPE RECTIFIER, INDUCTIVE DC LINK, AND
CURRENT-SOURCE INVERTER, (B) VOLTAGE-TYPE-RECTIFIER, CAPACITIVE DC LINK, AND VOLTAGE-SOURCE INVERTER
23
AC
LIN
E
LINEFILTER
DC LINK
AC
LIN
E
LINEFILTER
RECTIFIER DC LINK
(b )
(a)
INV ERTER
INV ERTERRECTIFIER
MOTOR
MOTOR
SWITCHING PATTERN OF THE INVERTER IN EXAMPLE 7.2
24
1
0
1
S TATE : X Y(7)
111
Y X(1) (5)
Z(5) (1)
001 101 101 001
( )s
( )s
( )s
a
b
c
t
t
t
0 32 92 .5 15 7.5 21 8 25 0
1
0
0
PER-UNIT VOLTAGE VECTORS OF THE THREE-LEVEL INVERTER IN
EXAMPLE 7.3
25
V 2 4
V=V 9 2 2
V1 2 = V2 5
jq
d
V2 1
V1 8
v *
V1 5
0 0.5 1
32j
3j 4
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