This document describes a three level neutral point clamped (NPC) inverter. It includes: 1. A diagram of the 3-level NPC inverter circuit and descriptions of the switching states. 2. Calculations of the switching vectors for each switching state by analyzing equivalent circuits. 3. Tables listing the 27 possible switching states and their corresponding switching vectors.

1. 1
HYBRID POWER SYSTEM
THREE LEVEL NEUTRAL POINT CLAMPED
INVERTER
COMSATS INSTITUTE OF INFORMATION & TECHNOLOGY,
ABBOTABAD
SUBMITTED TO:
DR. LIAQ KHAN
SUBMITTED BY:
MUQADSA IFTIKHAR FA13-R09-005
ZUNAIB ALI FA13-R09-013
MADIHA NAEEM FA13-R09-024
SEMESTER: 2ND
DEPTT: ELECTRICAL ENGINEERING (POWER)

2. 2
THREE LEVEL NEUTRAL POINT CLAMPED INVERTER
Fig. 1: 3-Level Neutral Point Clamped Inverter
P: Denotes that the upper two switches of any leg is turned ON and the corresponding leg is
connected to i.e. is equal to .
N: Denotes that the lower two switches of any leg is turned ON and the corresponding leg is
connected to i.e. is equal to .
O: Denotes that the inner two switches of any leg is turned ON and the corresponding leg
voltage with respect to neutral point is clamped to zero through clamping diode i.e.
is equal to zero .

3. 3
The number of possible switching states for three level neutral point clamped (NPC) inverter.
S.No Switching State S.No Switching State
0 PPP 14 PNO
1 NNN 15 POO
2 OOO 16 ONN
3 PNN 17 PPO
4 PPN 18 OON
5 NPN 19 OPO
6 NPP 20 NON
7 NNP 21 OPP
8 PNP 22 NOO
9 PON 23 OOP
10 OPN 24 NNO
11 NPO 25 POP
12 NOP 26 ONO
13 ONP

4. 4
CALCULATION OF SWITCHING VECTORS - OUTER HEXAGON
For each switching state there is a corresponding switching vector, to calculate the vector we
need to take advantage of the .
1. PNN
The circuit diagram for this state is given by
R
R R
Z
Vdc
3
2
Vdc
3
1
Vdc
3
1
Vdc
a
cb
The switching vector can be written in terms of .
From the figure:
Substituting in we get:

5. 5
2. PPN
The circuit diagram for this state is given by
R R
Z
Vdc
3
1
Vdc
3
1
+
Vdc
-
R Vdc
3
2
c
a b
The switching vector can be written in terms of .
From the figure:
Substituting in we get:

6. 6
3. NPN
The circuit diagram for this state is given by
R
R R
Z
Vdc
3
2
Vdc
3
1
Vdc
3
1
Vdc
b
ca
The switching vector can be written in terms of .
From the figure:
Substituting in we get:

7. 7
4. NPP
The circuit diagram for this state is given by
R R
Z
Vdc
3
1
Vdc
3
1
+
Vdc
-
R Vdc
3
2
b c
a
The switching vector can be written in terms of .
From the figure:
Substituting in we get:

8. 8
5. NNP
The circuit diagram for this state is given by
R
R R
Z
Vdc
3
2
Vdc
3
1
Vdc
3
1
Vdc
c
ba
The switching vector can be written in terms of .
From the figure:
Substituting in we get:

9. 9
6. PNP
The circuit diagram for this state is given by
R R
Z
Vdc
3
1
Vdc
3
1
+
Vdc
-
R Vdc
3
2
b c
a
The switching vector can be written in terms of .
From the figure:
Substituting in we get:

10. 10
7. PON
The circuit diagram for this state is given by
E=+Vdc/2
E=-Vdc/2
R
R
R
Z
Vdc
2
1
Vdc
2
1
a
b
c
The switching vector can be written in terms of .
From the figure:
Substituting in we get:

11. 11
8. OPN
The circuit diagram for this state is given by
E=+Vdc/2
E=-Vdc/2
R
R
R
Z
Vdc
2
1
Vdc
2
1
a
b
c
The switching vector can be written in terms of .
From the figure:
Substituting in we get:

12. 12
9. NPO
The circuit diagram for this state is given by
E=+Vdc/2
E=-Vdc/2 R
R
RZ
Vdc
2
1
Vdc
2
1
a
b
c
The switching vector can be written in terms of .
From the figure:
Substituting in we get:

13. 13
10. NOP
The circuit diagram for this state is given by
E=+Vdc/2
E=-Vdc/2 R
R
R
Z
Vdc
2
1
Vdc
2
1
a
b
c
The switching vector can be written in terms of .
From the figure:
Substituting in we get:
11. ONP

14. 14
The circuit diagram for this state is given by
E=+Vdc/2
E=-Vdc/2
R
R
R
Z
Vdc
2
1
Vdc
2
1
a
b
c
The switching vector can be written in terms of .
From the figure:
Substituting in we get:
12. PNO
The circuit diagram for this state is given by

15. 15
E=+Vdc/2
E=-Vdc/2
R
R
RZ
Vdc
2
1
Vdc
2
1
a
b
c
The switching vector can be written in terms of .
From the figure:
Substituting in we get:
CALCULATION OF SWITCHING VECTORS - INNER HEXAGON
13. POO

16. 16
The circuit diagram for this state is given by
E=+Vdc/2 R
R
RZ
Vdc
2
1
a
b
c
The switching vector can be written in terms of .
From the figure:
Substituting in we get:
14. ONN
The circuit diagram for this state is given by

17. 17
E=-Vdc/2
R
R
R
Z
a
b
c
The switching vector can be written in terms of .
From the figure:
Substituting in we get:
15. PPO
The circuit diagram for this state is given by

18. 18
E=+Vdc/2 R
R
RZ
a
b
c
The switching vector can be written in terms of .
From the figure:
Substituting in we get:
16. OON
The circuit diagram for this state is given by

19. 19
E=-Vdc/2
R
R
R
Z
a
b
c
The switching vector can be written in terms of .
From the figure:
Substituting in we get:
17. OPO
The circuit diagram for this state is given by

20. 20
E=+Vdc/2
R
R
R
Z
a
b
c
Z
The switching vector can be written in terms of .
From the figure:
Substituting in we get:
18. NON

21. 21
The circuit diagram for this state is given by
E=-Vdc/2 R
R
R
Z
a
b
c
E=-Vdc/2
The switching vector can be written in terms of .
From the figure:
Substituting in we get:
19. OPP

22. 22
The circuit diagram for this state is given by
R
R
R
Z
a
b
c
E=+Vdc/2
The switching vector can be written in terms of .
From the figure:
Substituting in we get:
20. NOO

23. 23
The circuit diagram for this state is given by
R
R
RZ
a
b
c
E=-Vdc/2
The switching vector can be written in terms of .
From the figure:
Substituting in we get:

24. 24
21. OOP
The circuit diagram for this state is given by
R
R
R
Z
a
b
c
E=+Vdc/2
The switching vector can be written in terms of .
From the figure:
Substituting in we get:

25. 25
22. NNO
The circuit diagram for this state is given by
R
R
RZ
a
b
c
E=-Vdc/2
The switching vector can be written in terms of .
From the figure:
Substituting in we get:

26. 26
23. POP
The circuit diagram for this state is given by
R
R
R
Z
a
b
c
E=+Vdc/2
E=+Vdc/2
The switching vector can be written in terms of .
From the figure:
Substituting in we get:

27. 27
24. ONO
The circuit diagram for this state is given by
R
R
R
Z
a
b
c
E=-Vdc/2
Z
The switching vector can be written in terms of .
From the figure:
Substituting in we get:

28. 28
25. PPP
The circuit diagram for this state is given by
R
R
R
a
b
c
E=+Vdc/2
E=+Vdc/2
E=+Vdc/2
The switching vector can be written in terms of .
From the figure:
Substituting in we get:

29. 29
26. NNN
The circuit diagram for this state is given by
R
R
R
a
b
c
E=-Vdc/2
E=-Vdc/2
E=-Vdc/2
The switching vector can be written in terms of .
From the figure:
Substituting in we get:

30. 30
27. OOO
The circuit diagram for this state is given by
R
R
R
a
b
c
Z
Z
Z
The switching vector can be written in terms of .
From the figure:
Substituting in we get:

31. 31
Switching State Switching Vector Vector Definition
PPP
NNN
OOO
POO
ONN
PPO
OON
OPO
NON
OPP
NOO
OOP
NNO

32. 32
POP
ONO
PON
OPN
NPO
NOP
ONP
PNO
PNN
PPN
NPN
NPP
NNP
PNP

33. 33
SPACE VECTOR DIAGRAM