International Journal of Advanced Science and Technology
Vol. 29, No. 4s, (2020), pp.1022-1033
LEVEL SHIFT AND PHASE SHIFT MODULATION FOR NINE LEVEL
INVERTERS
R.K.Padmashini,
Assistant professor, AMET University, Dept of EEE
Shweta
Assistant professor, Noida International University, Dept of E&I
Abstract
This paper demonstrated a disparity between two techniques of modulation, both using sine wave as
the reference wave. The FFT study was carried out after the correlation of voltage an current levels
for the two techniques and the THD of the two techniques was addressed with the aid of the
simulation carried out on MATLAB 2015 a Software. For a 9 level cascaded inverter, the two
techniques were discussed. Since IGBT is highly efficient and quickly switched compared to other
semiconductor switching devices. Under carrier based pulse width modulation, although there are
many techniques compared to phase shift modulation method, just level shift modulation (i.e. in phase
disposition (IPD)) was compared. Finally, based on the FFT analysis, the method having less THD
can be used for any kind of speed control of motors.
Index Terms-DC-AC inverter, Sinusoidal pulse width modulation, THD, MATLAB Software R2015a
I. Introduction
The performance of power obtained from power electronics circuits should be a pure sine wave as
technology development is in advance. Because most device inverters are used where power
conversion from DC to AC is expected to be strictly sinusoidal. The conventional power converter
produces a square wave and not a proper sine wave to convert direct current to alternate current .The
number of levels are increased to obtain an exact accurate sine wave. With this need Inverters with a
higher level of conversion play an important role. Multi level Inverter technology is a substitute for
High power and Average level Voltage control, The output waveforms obtained are therefore more or
less closer to the sinusoidal waveforms of higher level.
Fig(1) Classification of conventional inverters
The conventional classification of inverters are described in the fig .(1).Modern inverters are
categorized under multilevel inverter.
High output power from medium voltage source can be attained by multilevel converter .Based on
the number of levels the switches are selected. The advantages of multilevel inverter are
 Lower rating devices produce higher voltage.
 Improved voltage waveform can be gained by increasing the number of levels.
 For PWM Operation Switching frequency can be decreased.
Based on the construction and the types of devices used ,thetaxonomy of multilevel inverters are
depicted in fig(2)
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Vol. 29, No. 4s, (2020), pp.1022-1033
Fig.(2)Taxonomy of multilevel inverter
MULTILEVEL CASCADED H-BRIDGE INVERTER
Rewards
Weaknesses
Applications
Motor Drivers
Output voltages levels =2* the
Separate
Voltage Active Filters
number of sources
source is required
Eco friendly vehicle drives
Manufacturing, Packaging and for each H-Bridge
Direct Current power source
Layout are very simpler
usage
Cost
Effective,since
Used with renewable energy
transformer is used to control
Less Applications.
resources like solar,wind.
Table (1)-Rewards,Weakness,Applications
Since this inverter has motor drive application and also these inverters provide a modular structure
and more reliable ,the THD analysis for 9-level for both modulation technique was carried out on a
cascaded H-Bridge multilevel inverter[1]. Cascaded multi level inverters found wide spread usage in
low and medium level application. The advantage of using multilevel topology is the reduction in
Total Harmonic distortion, lower EMI, reduced dv/dt and optimal size.
The different modulation techniques [9] used for multi-level inverters are considered by taking Sine
wave as reference and triangular wave as carrier, concepts based on reverse harmonic injection, and
also third harmonic signal as carrier.The simulation was carried out on MATLAB R2015a software.
The proposed system uses the carrier based sinusoidal modulation with sine wave as reference and
triangular wave with some variation.
III. Symmetric Cascaded H-Bridge 9 level inverter
The proposed system consists of Symmetric H-Bridge cascaded inverter and the quantity of cells
chosen for the H-bridge cascaded was determined by the formula (2*n+1),where n be the no of cells
in an inverter. So ,for 9 level inverter 4 cells or 4 H-Bridges are required and all the four bridges are
connected in series. Therefore for each leg, two end connection are there .In that one end (i.e) point
Nis connected in series with the other two phases. And the next end (i.e)pointAis connected to the
load similarly all the other two phases also connected to the load.
In the H-Bridge cascaded inverter itself , based on an input voltage chosen,they are classified into two
types.
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Vol. 29, No. 4s, (2020), pp.1022-1033
Fig.(3) Symmetric Cascaded H-Bridge nine level inverter
If input voltagelevels of all cells are E then that type is known as Symmetric Cascaded bridge
inverter.If there is any variation in the input voltage level then that type is known as Asymmetric
Cascaded Bridge inverter.
The no of switches used for nine level inverter are calculated using the formula 6(m-1).So ,for 9
level inverters the no of switches used are 48.For each phase the switches used are 16 so 16*3=48
which is the total no of switches.
The total no of switching states for 9-level inverter are 98 which can be framed as follow
4E
3E
2E
E
0
-E
2E
3E
4E
1
8
16
16
16
16
16
8
1
Table-(2) Total no of Switching states for different levels
IV. PHASE SHIFT AND LEVEL SHIFT MODULATION
There were many topologies for multilevel inverters, one of the topologies for the proposedsystem
was cascaded multilevel inverter.Cascaded multilevel inverter output depends on the devices ' switc
h ON and turn OFF.The modulation technique classification[7 ] is shown in fig(4).LEVEL SHIFTE
D PWM (IPDIn Phase Disposition)(LSPWM) and PHASE SHIFTED PWM(PSPWM) were chosen
for study in the proposed system.
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International Journal of Advanced Science and Technology
Vol. 29, No. 4s, (2020), pp.1022-1033
Fig(4)Classification of Modulation Technique
The sine wave consists of amplitude, frequency and phase. Thus, in the case of modulation technique
either one of the parameters can be varied by keeping all the other parameters constant[9].
In the case of phase shift modulation, the reference wave consists of two sinusoidal waveforms with 1
80 degree phase shift of power frequency to which the higher frequency triangular carrier
is compared and the pulses produced. The number of carriers depends on the number of cells. Thus,
for nine level inverter, 4 cells are necessary and therefore 4 carriers are required.
The amplitude
as well as the frequency remains constant and the phase is varied. The phase change is observed to be
45 degrees for four carrier wave[8].
The Level shift modulation can be carried out by comparing a single reference wave with no carrier
s determined by the number of levels[10]. Here, the reference wave is a sinusoidal waveform of hig
her frequency power frequency and carrier wave, and the number of carriers is
determined by the number of levels.Therefore, there are 9 level inverters[3],4 cascaded HBridges and four triangular carrier waves are needed in front of them with a phase shift angle of 45
degree[7]. Here, too, the carrier's amplitude and frequency remains constant for the chosen
carrier for comparison[.The Level shifted modulation uses triangular carrier of level shifted.The no
of carriers chosen for level shifted modulation are 8(ie.m-1) since this is a nine level inverter.The
Eight carriers are compared with a single sinusoidal reference, the pulses are given to the
corresponding switches[14].
V.MATLAB MODEL OF LEVEL SHIFT MODULATION
In level shift modulation[1],the no of carriers are chosen based on the no of levels.Here for the
proposed system 8 carriers are chosen because the inverter is a nine level inverter .
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International Journal of Advanced Science and Technology
Vol. 29, No. 4s, (2020), pp.1022-1033
Fig.(5) MATLAB model for level shift modulation -PWM pulses for of nine level inverter -single
phase
The pulses for the switches are produced by level shifted modulation.As discussed
above , the pulses are produced by comparing the sine wave of power frequency with a triangular
carrier wave of higher frequency nearly 1000 Hz.For the proposed nine level inverter,according to the
formula for ɵcr the phase shift between each carrier is calculated .So ,for nine level inverter 8 carriers
are chosen and each carrier is having a phase shift of 45 degree.In a comparator ,the sinusoidal
waveform of power frequency and phase shifted carrier are compared[12].The original pulses are
given to switches in the upper leg and the the pulses are NOTed and given to the corresponding lower
leg.
Fig.(6)Gate pulses for single phase leg
The pulses are given to the respective switches.The voltage across each cell is produced based on the
switching states.
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Vol. 29, No. 4s, (2020), pp.1022-1033
Fig(7).MATLAB model for LEVEL shift modulation -Phase A
Fig.(8)MATLAB Model for three phase 9-level inverter-using LEVEL shifted PWM
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International Journal of Advanced Science and Technology
Vol. 29, No. 4s, (2020), pp.1022-1033
Fig.(7)Voltage across each cell of one phase leg
Fig(8).Line to Line voltage across the load
Fig(10)Line to Line Voltage -FFT Analysis
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Vol. 29, No. 4s, (2020), pp.1022-1033
Fig(11).Line current
VI.MATLAB Model for PHASESHIFTED modulation
In the phase shift modulation,the pulses are produced by comparing two reference sine wave of 180
degree phase difference with a triangular carrier whose phase difference for each cell can be
calculated from
ɵcr= 360˚
m-1
The pulses are producedand is given to the corresponding switches
Fig(12).MATLAB model for phase shift modulation using two reference and one carrier waveSingle phase leg
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Fig(13).MATLAB model for phase shift modulation using two reference and one carrier wavethree phase 9-level CHB inverter
Fig(14).Line to Line voltage across each phase leg respectively R,Y,B
Fig(15) Line to Line voltage- FFT Analysis
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Vol. 29, No. 4s, (2020), pp.1022-1033
Fig(16) Line current of all the three phases
THD VALUE
CELL NO
R PHASE
Y PHASE
BPHASE
CELL 1
40.10%
40.12%
40.12%
CELL 2
30.29%
30.33%
30.40%
CELL 3
41.30%
40.95%
41.27%
CELL 4
91.27%
91.36%
92.80%
Table(3).THD Analysis of each cell for LEVEL SHIFTED PWM
THD VALUE
CELL NO
R PHASE
Y PHASE
BPHASE
CELL 1
52.71%
52.69%
52.69%
CELL 2
52.74%
52.79%
52.54%
CELL 3
52.51%
52.86%
52.86%
CELL 4
52.74%
52.54%
52.79%
Table(4).THD Analysis Of each cell for PHASE SHIFTED modulation
The above table (3) and (4) shows the THD values for every cell both for level shifted and phase
shifted modulation.while analyzing all the values,for phase shifted modulation the THD Value across
each cell is constant but for Level shifted modulation the values are different across each cell.But the
THD value for level shifted modulation is comparitively less compared with phase shifted modulation
Types
THD Value
Level Shifted
10.62%
Phased shifted
13.73%
Table(5).THD Analysis Of LEVEL SHIFTED AND PHASE SHIFTED modulation
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VII.CONCLUSION
Simulation studies was done on H-bridge Nine level cascaded Inverter ,Total Harmonic distortion of
Level shift and Phase shift techniques was compared .In the comparison,it was found that Level shift
modulation is having lesser THD and it can be used for further application.It was found that due to the
reduced level of THD for level shift modulation,the lower order harmonics are reduced significantly
and by designing an efficient filter it is easy to filter out higher order harmonics.From the result ,it is
concluded that Level shift modulated PWM technique is best suited for open loop speed control of
induction motor .
VIII.References
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