Comparative Study of Different Five level inverters Using POD Control Strategy

ISSN 2349-7815
International Journal of Recent Research in Electrical and Electronics Engineering (IJRREEE)
Vol. 4, Issue 2, pp: (53-60), Month: April - June 2017, Available at: www.paperpublications.org
Page | 53
Paper Publications
Comparative Study of Different Five level
inverters Using POD Control Strategy
Jisha Gopinath1
, Neena Mani2
, Veena Mathew3
1
PG Scholar, Mar Athanasius College of Engineering, Kothamangalam, Kerala , India
2
Assistant Professor, Mar Athanasius College of Engineering, Kothamangalam, Kerala , India
3
Assistant Professor, Mar Athanasius College of Engineering, Kothamangalam, Kerala , India
Abstract: Multilevel converters are increasingly being considered for high power applications because of their
ability to operate at higher output voltages while producing lower levels of harmonic components in the switched
output voltages. This paper proposed a simulation model of four different typologies of single phase five-level
inverter. The study investigated four topologies of multilevel inverter namely Flying Capacitor Multilevel Inverter
(FCMLI), Diode Clamped Multilevel Inverter (DCMLI), Cascaded H-bridge Multilevel inverter (CHMLI) and
POD inverter. These topologies were compared in terms of Total Harmonic Distortion (THD and the number of
power electronic components being utilized. The simulation result was conducted using MATLAB/SIMULINK.
The findings showed that the POD PWM H-Bridge topology has the lowest total harmonic distortion (THD).
Keywords: Cascade, DCMLI, FCMLI, Multicarrier PWM, Multilevel, multilevel inverter, total harmonic
distortion, stepped wave inverter.
I. INTRODUCTION
Inverters are used to create single or polyphase AC voltages from a DC supply. In the class of polyphase inverters, three-
phase inverters are by far the largest group. A very large number of inverters are used for adjustable speed motor drives.
The typical inverter for this application is a “hard-switched” voltage source inverter producing pulse-width modulated
(PWM) signals with a sinusoidal fundamental [Holtz, 1992]. Recently research has shown detrimental effects on the
windings and the bearings resulting from unfiltered PWM waveforms and recommend the use of filters [Cash and
Habetler, 1998; Von Jouanne et al., 1996]. A very common application for single-phase inverters are so-called
“uninterruptable power supplies” (UPS) for computers and other critical loads. Here, the output waveforms range from
square wave to almost ideal sinusoids.
Now a day’s many industrial applications have begun to require high power. Some appliances in the industries however
require medium or low power for their operation. Using a high power source for all industrial loads may prove beneficial
to some motors requiring high power, while it may damage the other loads. Some medium voltage motor drives and
utility applications require medium voltage. The multilevel inverter has been introduced since 1975 as alternative in high
power and medium voltage situations. The multilevel inverter is like an inverter and it is used for industrial applications
as alternative in high power and medium voltage situations. The need of multilevel converter is to give a high output
power from medium voltage source. Sources like batteries, super capacitors, solar panel are medium voltage sources. The
multilevel inverter consists of several switches. In the multilevel inverter the arrangement switches’ angles are very
important.
Multilevel inverters are three types Diode clamped multilevel inverter, Flying capacitors multilevel inverter and Cascaded
H- bridge multilevel inverter. The main concept of diode clamped multilevel inverter is to use diodes and provides the
multiple voltage levels through the different phases to the capacitor banks which are in series. A diode transfers a limited

ISSN 2349-7815
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Paper Publications
amount of voltage, thereby reducing the stress on other electrical devices. The maximum output voltage is half of the
input DC voltage. It is the main drawback of the diode clamped multilevel inverter. This problem can be solved by
increasing the switches, diodes, capacitors. Due to the capacitor balancing issues, these are limited to the three levels. This
type of inverters provides the high efficiency because the fundamental frequency used for all the switching devices and it
is a simple method of the back to back power transfer systems.
In the case of Flying Capacitors Multilevel inverter a series connection of capacitor clamped switching cells are used. The
capacitors transfer the limited amount of voltage to electrical devices. In this inverter switching states are like in the diode
clamped inverter. Clamping diodes are not required in this type of multilevel inverters. The output is half of the input DC
voltage. It is drawback of the flying capacitors multilevel inverter. It also has the switching redundancy within phase to
balance the flaying capacitors. It can control both the active and reactive power flow. But due to the high frequency
switching, switching losses will takes place.
The cascaded H-bride multilevel inverter is to use capacitors and switches and requires less number of components in
each level. This topology consists of series of power conversion cells and power can be easily scaled. The combination of
capacitors and switches pair is called an H-bridge and gives the separate input DC voltage for each H-bridge. It consists of
H-bridge cells and each cell can provide the three different voltages like zero, positive DC and negative DC voltages. One
of the advantages of this type of multilevel inverter is that it needs less number of components compared with diode
clamped and flying capacitor inverters. The price and weight of the inverter are less than those of the two inverters. Soft-
switching is possible by the some of the new switching methods. Multilevel cascade inverters are used to eliminate the
bulky transformer required in case of conventional multiphase inverters, clamping diodes required in case of diode
clamped inverters and flying capacitors required in case of flying capacitor inverters. But these require large number of
isolated voltages to supply the each cell.
II. SINGLE PHASE MULTI LEVEL INVERTER TOPOLOGIES
A. Diode Clamped Multilevel Inverter:
The main concept of this inverter is to use diodes and provides the multiple voltage levels through the different phases to
the capacitor banks which are in series. A diode transfers a limited amount of voltage, thereby reducing the stress on other
electrical devices.. Due to the capacitor balancing issues, these are limited to the three levels. This type of inverters
provides the high efficiency because the fundamental frequency used for all the switching devices and it is a simple
method of the back to back power transfer systems.
In diode clamped inverter, the diode is used as the clamping device to clamp the dc bus voltage so as to achieve steps in
the output voltage. Thus, the main concept of this inverter is to use diodes to limit the power devices voltage stress. The
voltage over each capacitor and each switch is Vdc. An n level inverter needs (n-1) voltage sources, 2(n-1) switching
devices and (n-1) (n-2) diodes. By increasing the number of voltage levels the quality of the output voltage is improved
and the voltage waveform becomes closer to sinusoidal waveform. The maximum output voltage is half of the input DC
voltage. It is the main drawback of the diode clamped multilevel inverter. This problem can be solved by increasing the
switches, diodes, capacitors. Applications of Diode Clamped Multilevel Inverter are Static var compensation, variable
speed motor drives, High voltage system interconnections and High voltage DC and AC transmission lines
Fig.1: Diode clamped multilevel inverter

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B. Flying Capacitor Multilevel Inverter:
To generate m-level staircase output voltage, m-1 capacitors in the dc bus are needed. Each phase-leg has an identical
structure. The size of the voltage increment between two capacitors determines the size of the voltage levels in the output
waveform. The main concept of this inverter is to use capacitors. It is of series connection of capacitor clamped switching
cells. The capacitors transfer the limited amount of voltage to electrical devices. In this inverter switching states are like in
the diode clamped inverter. Clamping diodes are not required in this type of multilevel inverters. The output is half of the
input DC voltage. It is drawback of the flying capacitors multilevel inverter. It also has the switching redundancy within
phase to balance the flaying capacitors. It can control both the active and reactive power flow. But due to the high
frequency switching, switching losses will takes place.
Fig.2: Flying capacitor multilevel inverter
Applications of flying capacitor multilevel inverter are induction motor control using DTC (Direct Torque Control)
circuit, Static var generation, both AC-DC and DC-AC conversion applications, Converters with Harmonic distortion
capability and Sinusoidal current rectifiers.
C. Cascaded multilevel inverter:
The cascaded H-bride multilevel inverter is to use capacitors and switches and requires less number of components in
each level. This topology consists of series of power conversion cells and power can be easily scaled. The combination of
capacitors and switches pair is called an H-bridge and gives the separate input DC voltage for each H-bridge. It consists of
H-bridge cells and each cell can provide the three different voltages like zero, positive DC and negative DC voltages. One
of the advantages of this type of multilevel inverter is that it needs less number of components compared with diode
clamped and flying capacitor inverters. The price and weight of the inverter are less than those of the two inverters. Soft-
switching is possible by the some of the new switching methods. Multilevel cascade inverters are used to eliminate the
bulky transformer required in case of conventional multiphase inverters, clamping diodes required in case of diode
clamped inverters and flying capacitors required in case of flying capacitor inverters. But these require large number of
isolated voltages to supply the each cell.
Fig.3: Cascaded multilevel inverter

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D. Single Phase Five POD Multilevel Inverter:
The proposed technique is based on POD technique. POD stands for phase opposition and disposition technique . The
proposed technique is used for pulse generation in multilevel inverter shown in figure 3 .In figure 4 if sine wave l is
greater than carrier wave, switches Tp+ is on else Tp- is on . If sine wave 2 is greater than carrier wave ,switch Tn+ is on
else switch Tn- is on .If sine wave 1 is positive then switches Ta+, Tb- are on and if sine wave is negative then switches
Ta-,Tb+ is on. Figure 3 illustrates the proposed multi-level inverter which is based on cascaded H bridge multi-level
inverter. In the proposed multi-level inverter two dc link capacitors and and 8 switches are used Input supply to
inverter is and voltage across each capacitor is . The output of the inverter is connected to LC filter in order to
eliminate the harmonics.
Fig.4 Single phase POD multilevel inverter
III. SIMULATION ANALYSIS AND RESULTS
The proposed 5-level inverter is tested to verify the operating principle of the proposed MLI and all conventional MLI.
The LC filter is inserted between the output of the inverter and the load. Electrical specifications of the proposed inverter
are summarized in Table 1.
Table 1.Simulation Parameters
Parameters Values
dc link voltage 100V
output voltage 200V
dc link capacitor 2200µH
Filter inductor 350mH
Filter capacitor 3300 µH
Output frequency 50HZ
A. Simulink Model of Single Phase Five Level POD Inverter:
Simulation of proposed multi-level inverter is carried out in MATLAB/Simulink. Dc supply of 100 volts is given using
batteries and 2 dc link capacitors are used and 8 MOSFET are used as switches and output of multi-level inverter is
connected to L, C filter to eliminate harmonics. The technique used for pulse generation is POD technique .Generally in
order to turn on 8 switches 8 carrier signals are needed but using proposed technique single carrier wave is used to
generate switching pulses to 8 switches. Voltage measurement device is connected across each capacitor to measure the
voltage across the capacitor.

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Fig.5 Simulink model of POD PWM Inverter
B. Simulink Model for switch pulse generation:
For the simulation of five-level inverter, single carrier wave and two sine waves are generated. Reference voltage for first
sine wave is set as l.7 volts and reference voltage for second sine wave is set as 0.8 volts. Both sine waves are operating at
frequency50 Hz. Time period for one carrier wave is set as 800 ms. DC supply of 100 volts is provided as input. Voltage
is divided equally across two capacitors. Voltage across each capacitor is 50 volts. Voltage across each capacitor is
measured using voltage measurement device .The output of Multilevel Inverter is connected to LC filter in order to
eliminate harmonics and pure sine wave is obtained .Load Voltage are measured using voltage measurement device and
Load current is measured using current measurement device. This type of MLI is mainly used for grid connected
applications.
Fig.6 Simulink diagram for pulse generation

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C. Switching Pulses:
Fig.7 Switching pulses
D. Output Voltage and Output Current of Five Level POD Inverter:
Fig.8 Five Level Output Voltage
The above figure shows the five level output voltage of the proposed inverter without using filter circuit. An input voltage
of 200V dc given and a maximum voltage of 200V dc is obtained by proper switching. The circuit are tested using R load.
So the current are in phase with the voltage.

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E. Comparison of different five level Inverters:
Table 2.1 Comparative Study of different five level inverters
F. THD analysis of different five level inverter:
Table 2.2 Comparative Study of different five level inverters
IV. CONCLUSION
In this paper, a new schemes adopting the phase opposition disposition variable switching frequency single carrier pulse
width modulation concepts are considered. Single phase Five level high frequency multi-level inverter employing
different multi carrier single reference modulation schemes has been investigated and their FFT analysis has been
performed. Multilevel inverter with individual dc sources has been proposed for use in large electric drives. Simulation
and experimental results have shown that with a control strategy operates the switches at the fundamental frequency; these
converters have high output voltage, less THD and high efficiency. In the proposed method semiconductor devices are
reduced. The proposed method will reduce the cost, and also used only 8 switches, harmonic reduction and the heat losses
.It is concluded that PODPWM technique provides output with relatively low harmonic distortion.
REFERENCES
[1] O. Lopez, “Multilevel transformer less topologies for single-phase grid-connected converters ", IEEE. IECON 2006,
pp. 5191-5196,2006.
[2] D.A. B. Zambra ,"Comparison of Neutral Point Clamped, Symmetrical, and Hybrid Asymmetrical Multilevel
Inverters" ", IEEE Transactions on power electronics, Vol. 57, no. 7, pp2297-2306, July 2010.
[3] M. Calais, “Analysis of multicarrier PWM methods for a single-phase five level inverter ", PESC. 2001 IEEE, Vol.
3, pp. 1351- 1356, 2001.
[4] J.Fen, “A novel three phase five level inverter", IEEE eighth international power electronics and motion control
conference, vol. 63, no. 12, 2016.
SL.NO Inverter Type %THD
1 Diode Clamped 30.5
2 Flying Capacitor 34.6
3 Cascaded H Bridge 31.3
4 POD Inverter 26.08

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[5] Pankaj H Zope, Pravin G.Bhangale, Prashant Sonare ,S. R.Suralkar “Design and implementation of carrier based
Sinusoidal PWM Inverter”, International Journal of Advanced Research in Electrical, Electronics and
Instrumentation Engineering, Vol. 1,Issue 4, October 2012 ISSN: 2278 – 8875.
[6] Anand. D & Jeevananthan .S "Modeling and Analysis of Conducted EMI Emissions of a Single-Phase PWM
Inverters" Asian Power Electronics Journal, Vol. 4, No.3 December 2010.
[7] B.Geetalaxmi and P.Dananjayan, “ A Multipulse –Multilevel Inverter Suitable for High Power Application”,
International Journal of Computer and Electrical Engineering,Vol.2 , pp-257-261, April 2012.

Comparative Study of Different Five level inverters Using POD Control Strategy

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