SIMULATION OF CASCADED H- BRIDGE MULTILEVEL INVERTER USING PD, POD, APOD TECHNIQUES

Electrical & Computer Engineering: An International Journal (ECIJ) Volume 4, Number 3, September 2015
DOI : 10.14810/ecij.2015.4303 27
SIMULATION OF CASCADED H- BRIDGE
MULTILEVEL INVERTER USING PD, POD, APOD
TECHNIQUES
Sourabh Rathore, Mukesh Kumar Kirar and S. K Bhardwaj
Department of Electrical Engineering, MANIT, Bhopal
ABSTRACT
Multilevel inverter (MLI) can achieve medium voltage high power efficiency inverters in industrial
application. It can generate stepped waveform by reducing harmonic distortion with increase in the
number of voltage level; a full bridge is known as H-bridge inverter because it shows alphabet ‘H’. In this
paper, Multicarrier PWM topologies and there Modulation schemes are discussed. Level Shifted [LS]
Scheme is applied to the Cascade H-bridge multilevel inverter and the complete analysis of THD to 9 levels
is done.
KEYWORDS
Multilevel Inverter, Cascaded H-Bridge, Multicarrier (PWM) topologies.
1. MULTILEVEL INVERTER
The inverter is a power electronic circuit which converts the DC to AC power, used in power
backup at home [1]. Like motor, radio etc. Now days Multilevel Inverters are used in high power
switching application [2-3].Multilevel Inverter consists of several switches, used in industrial
applications, Railway Traction Drives and Electrical Vehicle etc. [4].
Figure 1. Inverter Output Waveform [5]

28
Figure 2. Generalized stepped waveform of multilevel inverters [1]
1.1 Classification of Multilevel Inverter
Figure 3 Shows Inverter is classified into Cascade H-Bridge Multilevel inverter (CHB-MLI),
Flying Capacitor Multilevel inverter (FC-MLI), Diode Clamped inverter (NPC-MLI) [2-3].
Figure 3. Classification of Multilevel Inverter [1-3]

29
1.2 Main Topologies of MLI
• Diode Clamped Inverter
• Flying Capacitor
• Cascaded H-Bridge Inverter
1.2.1 Diode Clamped Multilevel Inverter (DC-MLI)
Figure 4 shows 3 level Diode clamped inverter also known as Neutral Point Clamped Inverter
(NPC).The maximum output voltage is half of the input DC voltage. To remove this problem,
simple control technique is applied i.e. increasing the component like switches and diodes [1-5].
Figure 4 3-level Diode-clamped inverter
Table 1. Switching Pattern of diode-Clamped Multilevel Inverter
Output
Voltage
Vo = Van
Switch states
S1 S2 S1
′
S2
′
Vdc/2 1 1 0 0
0 0 1 1 0
-Vdc/2 0 0 1 1

30
Advantages:
• The Control technique is simple.
• When the number of levels increases the distortion content is reduced.
Disadvantages:
• When the number of level is high more clamping diodes are used.
1.2.2 Flying Capacitor Multilevel Inverter (FC-MLI)
Figure 5 shows the 3 level Flying Capacitor Multilevel, also known as Capacitor Clamped
Inverter. Clamping diodes are replaced by flying capacitors. It can control both active and
reactive power flow [5-12].
Figure 5 3-level flying capacitor inverter
Table 2. Switching Pattern of Flying Capacitor Multilevel Inverter
Output
Voltage
Vo = VAN
Switch states
S1 S2 S1
′
S2
′
Vdc 1 1 0 0
0
1 0 1 0
0 1 0 1
-Vdc 0 0 1 1

31
Advantages:
• Similar to NPC inverter to avoid the needs for filters.
• A Large amount of packing capacity.
Disadvantages:
• Inverter control can be complicated.
• Switching losses are high.
1.2.3 Cascaded H-Bridge Multilevel Inverter (CHB-MLI)
Figure 6 shows the 3 level CHB MLI consist of single H-bridge combine with a series of the
power conversion cell. Cascaded H-Bridge Multilevel Inverter is better than the diode clamped
inverter and flying capacitors inverter, it requires less number of the component in each switching
levels. In Cascade H-Bridge Multilevel Inverter, the grouping of switches and capacitors is called
H-bridge consisting of isolated DC Voltage source [10].
Figure 6 3-level cascaded H-bridge inverter
Table 3. Switching Pattern of Cascade H-Bridge Multilevel Inverter
Output
Voltage
Vo = VAN
Switch states
S1 S2 S3 S4
Vdc 1 0 0 1
0
1 1 0 0
0 0 1 1
-Vdc 0 1 1 0

32
Advantages:
• Reduced THD.
• As Compare to Diode clamped and Flying capacitor inverter it can required less number
of components in each level.
Disadvantages:
• It needs isolated DC voltage sources.
2. MODULATION TECHNIQUES
Modulation Technique is Low and High switching Frequency fort high switching frequency is
considered above 1 KHz [13].
Figure 7. Classification of Modulation Technique

33
2.1 Multicarrier PWM
Multiple Pulse Width Modulation Technique is used in three level or more than three levels.
These are classified into two types: - Level Shift, Phase Shift.
2.1.1 Level Shifted PWM (LS-PWM)
N-1 carrier signals are used which are vertically shifted to each other. A level-shifted PWM can
be classified in three types [14-16-17-18].
• Phase Disposition (PD-PWM): In Phase Disposition all the carrier signals are in same
phase.
Figure 8 PD-PWM
• Phase Opposition Disposition (POD-PWM): In Phase Opposition Disposition all the
carrier signals above the zero are out of phase with those below the zero by 180º.
Figure 9 POD-PWM
• Alternative Phase opposition Disposition (APOD-PWM): In Alternate Phase
Opposition Disposition all the adjacent carrier signals are out of phase by 180º.

34
Figure 10 APOD-PWM
3. SIMULATION AND RESULTS
Table 4. THD Comparisons of PWM Technique
S.No PWM Technique No of Level THD %
1. Phase Disposition 3 Level 52.06%
2. Phase Opposition Disposition 3 Level 54.17%
3. Alternate Phase opposition Disposition 3 Level 54.17%
8 Phase Opposition Disposition 7 Level 22.48%

35
Showing the Phase Voltage 3 Level CHB MLI
THD Analysis of 3 Levels CHB MLI (a) PD (b) POD (c) APOD
(a)
(b)

36
(c)
(a)

37
(b)
(c)

38
(a)
(b)
(c)

39
(a)
(b)

40
(c)
4. CONCLUSION
In this paper has been Discuss the Cascade H-Bridge Topology using Phase Disposition, Phase
opposition Disposition, and Alternate Phase opposition Disposition are compared. The three
techniques it can conclude that the Phase Disposition Topology is better among the three
topologies. Simulation results show that it can see that when we increase the number harmonics
content will be reduced.
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AUTHOR
Sourabh Rathore was born in Bhopal, India in 19 may 1991.He has received BE
(Electrical) degree From Sagar Institute Research Technology and Science Bhopal in
2012 and pursuing his M.Tech degree in Power System from MANIT Bhopal.
Mukesh Kumar Kirar was born in Narsinghpur India in 06 Feb1983.He received the BE
(Electrical) degree from Government Engg. College, Ujjain India in 2006 and M.Tech
(Power System) in 2008 from MANIT Bhopal and PhD in 2014 from MANIT Bhopal.
He is currently working as an assistant professor In the Department of Electrical
Engineering, MANIT, Bhopal, India. His field of Interests are power system stability and
control, transformer and machines.
S.K.Bharadwaj was born in India He received the BE (Electrical) degree from I.T.B.H.U.
Varanasi India In 1975 and M.Tech (Power System) in 1978 from REC Kurukshetra.and
PhD (Application of self Tuning Strategies to electric Drive) in 2000 from Barkatullah
University. He is currently working as a professor in the Department of Electrical
Engineering, MANIT, and Bhopal, India. He has 9 research papers in National
Conference and 7 research papers in International Conference His field of Interest are
power system and energy conservation.

SIMULATION OF CASCADED H- BRIDGE MULTILEVEL INVERTER USING PD, POD, APOD TECHNIQUES

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SIMULATION OF CASCADED H- BRIDGE MULTILEVEL INVERTER USING PD, POD, APOD TECHNIQUES