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