This document provides an overview of DC to AC converters known as inverters. It discusses various types of inverters including voltage source inverters and current source inverters. It covers topics such as commutation types, single phase and three phase inverter circuit configurations, quantitative analysis of output voltages, and methods for controlling output voltages. The document also discusses connecting multiple inverters in series to generate higher voltage output waveforms and the use of multi-level inverters to reduce harmonic distortion.

1. Chapter 5 DC to AC Converters
Outline
5.1 Commutation
5.2 Voltage source inverters
5.3 Current source inverters
5.4 Multiple- inverter connections and multi- level
inverters

2. 5.1 Commutation types

Basic operation principle of inverters
uo
Ud
S1 io l oadS3
io
uo S4
t1 t2
S2
A classification of inverters
–Square- wave inverters (are discussed in this chapter)
–PWM inverters ( will be discussed in Chapter 6)
The concept of commutation
t

3. 
4 types of commutation
1)Device commutation:
Fully- controlled devices: GTO, IGBT, MOSFET
2)Line commutation:
Phase- controlled rectifier,Phase- controlled AC controller,
Thyristor cycloconverter
3)Load commutation
4)Forced commutation

4. (1) Load commutation
uo
io
Ld
O
id
VT1
Ed
uo
C
R
io
VT2
VT3
L
uo
VT4
i
io
iVT iVT
1
4
O
i
O
uVT
O
a)
ωt
iVT2 iVT3
ωt
uVT4
ωt
t1
uVT1
ωt
b)

5. (2) Forced commutation (capacitance commutation)
S
VT
S
+
S
C
C
VD VT
+
L
VD VT
a)
Direct- Coupled
+
With Coupling-Inductor
b)
L

6. 
Another classification of commutations
4 types of Commutations
Device commutation
Self-commutation
For fully-controlled
devices
Forced commutation
External
commutation
Line commutation
Load commutation
For thyristors

7. 2 classes of inverters
Voltage Source Inverter
Current Source Inverter
(VSI)
(CSI)
Ld
+
V1
Ud
-
C
V2
V3
VD1
R io L
u o V4
VD2
id
VT1
VD3
Ed
VD4
C
io
VT2
R
VT3
L
uo
VT4

8. 5.2 Voltage source inverter (VSI)

Features
DC side is constant voltage, low impedance (voltage source, or bulk cap)
AC side voltage is square wave or quasi- square wave.
AC side current is determined by the load.
Anti- parallel diodes are necessary to provide energy feedback path.
(freewheeling diodes , feedback diodes)
+
Ud
V1
C
V2
VD 1
R
VD 3
io L
uo
VD2
-
V3
V4
VD 4

9. 
Single-phase half bridge VSI
Ud
2
Ud
Ud
2
V1
L
io R
uo
V2
VD 1
VD2
The current conducting path is determined by the polarity of load voltage and load
current. (This is true for analysis of many power electronics circuits.)
The magnitude of output square- wave voltage is Ud/2.

10. 
Single-phase full bridge VSI
Operation principle
+
Ud
-
V3
V1
C
V2
VD1
R io L
uo
VD2
V4
VD3
VD4

11. Quantitative analysis
Fourier series extension of output voltage
uo =
4U d 
1
1

sin ωt + sin 3ωt + sin 5ωt + 

π 
3
5

（5-1）
Magnitude of output voltage fundamental component
U o1m =
4U d
π
=1.27U d
（5-2）
Effective value of output voltage fundamental component
U o1 =
2 2U d
= 0.9U d
π
（5-3）

12. Output voltage control by phase-shift
u G1
o
+
Ud
-
V3
V1
C
V2
VD1
R io L
uo
VD2
V4
t
o
t
u G2
VD3
u G3
o
VD4
θ
u G4
t
o
uo
io
o
t
io
t1 t2
uo
t3
t

13. 
Inverter with center- tapped transformer—push-pull inverter
io
l oad
uo
+
Ud
V1
V2
VD1
VD 2
-

14. Three-phase VSI
uUN´
+
V1
Ud
2
N´
-
Ud
2
V4
V3
VD1
U
V5
VD3
VD5
N
V
VD4
V6
W
VD6
VD2
V2
180° conduction
Dead time (blanking time) to
avoid “shoot through”
a） o
uVN´
b） o
uWN´
c） o
uUV
Ud
t
2
t
t
Ud
d） o
uNN´
e） o
uUN
f） o
iU
g） o
id
h）
o
t
Ud
6
2Ud
3
Ud
3
t
t
t
t

15. Basic equations to obtain voltage
For line voltage
For phase voltage of the load
u UN = u UN' − u NN' 

u VN = u VN' − u NN' 
u WN = u WN' − u NN ' 

uUV = uUN' − uVN' 

uVW = uVN' − uWN' 
uWU = uWN' − uUN' 

u NN'
1
1
= (u UN' + uVN' + u WN' ) − (u UN + uVN + u WN )
3
3
uUN + uVN + uWN =0
u NN'
1
= (u UN' + u VN' + u WN' )
3

16. Quantitative analysis
Fourier series extension of output line- to- line voltage
uUV =
=
2 3U d 
1
1
1
1

 sin ω t − sin 5ω t − sin 7ω t + sin 11ω t + sin 13ω t − 
π 
5
7
11
13

2 3U d
π


1
sin ω t + ∑ (− 1) k sin nω t 

n n


n = 6k ± 1
（5-8）
Magnitude of output voltage (line- to- line) fundamental component
2 3U d
U UV1m =
= .1U d
1
π
（5-10）
Effective value of output voltage (line- to- line) fundamental component
U UV1 =
U UV1m
2
=
6
U d = 0.78U d
π
（5-11）

17. 5.3 Current source inverter (CSI)
Features
DC side is constant current , high
impedance (current source, or
large inductor)
AC side current is quasis-quare
wave. AC side voltage is
determined by the load.
No anti-parallel diodes are needed.
sometimes series diodes are
needed to block reverse voltage
for other power semiconductor
devices.
Ld
i d VT1
Ed
VT2
VT3
C
io
L
R
uo
VT4

18. 
Single-phase bridge CSI
Parallel Resonant Inverter
Ld
uG 1 , 4
I d VT1
LT1
LT2
VT2
VT 3
C
io
R uo
L
LT3
LT4
VT4
uG 2O3
,
O
iT
io
than the resonant frequency so that the
load becomes capacitive and load
current is leading voltage to realize
load commutation.
uo
O
iVT2, 3
Id
O
O
Switching frequency is a little higher
iVT1 , 4
t
t
t1
I d t2
t3
tγ
t
t6
t4
tφ t5
t7
t
tδ
tβ
t
uVT2, 3
O
t
uVT , 4
1
O
t
uAB
O
t

19. 
Three- phase self-commutated CSI
id
VT1 VT3 VT5
Ud
U
iU
o
t
iV
V
W
VT4 VT6 VT2
o
t
iW
o
uUV
o
t
t

20. 
Three- phase force- commutated CSI
+
L
Id VT1
VD1
VT3
C1
C5
VD3
Ud
VD4
VD6
C4
VT1
C13
+ VD1
U V
VT5
C3
VD5
VD2
C6
U
V
W
M
3
-
VT6
VD3
W
C2
VT4
VT3
VD2
VT2
Id
VT2

21. 
Three- phase load-commutated CSI
uU
u
uW
uV
Pulse Distributor
VT1
VT3
Ud
UdM
VT4
O
VT5
VT6
U
V
W
VT2
MS
3~
BQ
ωt
iU
O
iV
O
iW
VT4
VT6
O
uVT1
O
u dM
O
ωt
VT1 VT3
VT2
VT5
ωt
ωt
ωt
ωt

22. 5.4 Multiple- inverter connections and multi-level inverters

Series connection of 2 single- phase VSIs
3rd Harmonics
u1
Ud
·
T1
·u
1
O
u2
·
t
180°
60°
3rd Harmonics
O
T2
·u
2
t
uo
120°
O
t

23. 
Series connection of 2 3- phase VSIs
I
U
V
U U1
(U A1)
O
W
T1
A1
uU1
Ud
uUN
T2
C22 C
21
II
N
O
2 U
3 d
U U2
A22
B21
t
-U B22
C1
B22
t
1
Ud
3
U A21
O
B1
A 21
Ud
uU2
O
U UN
1 U
3 d
t
t
(1+ 1 U d )
3
O
(1+ 2 U d )
3
1 U t
3 d
图5- 24

24. 
Multi-level Inverters 3- level inverter
+
+
VD 11
VD 1
V 11
VD12
U
O'
Ud
+
VD4
Rs
V
VD41
VD42
-
iU
V12
V41
V42
W
Ls