IT IS ALL ABOUT METHODS OF HARMONIC REDUCTION IN INVERTER OUTPUT VOLTAGE

1. A
PRESENTATION
ON
Harmonic reduction in inverter output voltage
By
RAJ KUMAR TIWARI
M.E

2. What are Harmonics?
Definition:
Harmonics are integral multiples of some fundamental
frequency that, when added together, result in a
distorted waveform.

3. What are Harmonics?
f(x) = sin(x) f(x) =
sin(5x)
5
+
The resulting wave shows a strong departure from the smooth
waves comprising it:
f(x) = sin(x) + sin(5x)
5=

4. What are Harmonics?
In fact, any function may be constructed from a
sine wave and some number of its harmonics:

5. Where do they come from?
The power company typically supplies a reasonably
smooth sinusoidal waveform:

6. Harmonic Distortion
• DC Drives, UPSs, DC power supplies
(computers, duplicators, fax’s) will cause
current (and voltage) harmonics
• Single phase – 3rd
, 6th
, etc (triplens) can
cause transformer neutral conductor
overheating
• Three phase – 5th
, 7th
, 11th
, 13th
, etc can
cause equipment malfunctions
• Big questions – “How much?” and “How
much is too much?”

7. Common sources of Harmonics
Lighting ballasts
UPS systems
M
AC and DC drives

8. AC drives and Harmonics
Converter
DC bus
&
smoothing
Inverter
Determine the line-side
harmonics
Determines load-side
harmonics

9. AC drives and Harmonics
Inverter
Determines load-side
harmonics
EFFECTS OF LOAD-SIDE
HARMONICS:
Have implications for the motor
insulation and windings.
Essentially have zero effect on
other equipment on the power
system.

10. AC drives and Harmonics
Converter
DC bus
&
smoothing
Determine the line-side
harmonics
LINE-SIDE HARMONICS CAN HAVE
FAR-REACHING EFFECTS ON THE
POWER SYSTEM:
Distribution transformers
Standby generators
Communications equipment
Switchgear and relays
Computers, computer systems
Diagnostic equipment

11. AC drives and Harmonics
Typical 6-step converter waveform:
Harmonic Content
I5 = 22.5%
I7 = 9.38%
I11 = 6.10%
I13 = 4.06%
I17 = 2.26%
I19 = 1.77%
I23 = 1.12%
I25 = 0.86%

12. Recommended limits - IEEE 519
The Institute of Electrical and Electronics Engineers (IEEE)
has set recommended limits on both current and voltage
distortion in IEEE 519-1992.
Voltage distortion limits (@ low-voltage bus):
Application class THD (voltage)
Special system 3 %
General system 5 %
Dedicated system 10 %

13. Recommended limits - IEEE 519
MAXIMUM HARMONIC CURRENT DISTORTION
in percent of IL
Individual harmonic number (odd harmonics)
Isc/IL <11 11<h<17 17<h<23 23<h<35 TDD
<20 4.0 2.0 1.5 0.6 5.0
20-50 7.0 3.5 2.5 1.0 8.0
50-100 10.0 4.5 4.0 1.5 12.0
100-1000 12.0 5.5 5.0 2.0 15.0
>1000 15.0 7.0 6.0 2.5 20.0
Isc: Maximum short-circuit current at the Point of Common
Coupling (PCC).
IL: Maximum demand load current (fundamental) at
the PCC.

14. Attenuation of Harmonics
Inductive Reactance
Method: Add a line reactor or isolation transformer
to attenuate harmonics.
Benefits: Low cost.
Technically simple.
Concerns: Tends to offer reductions in only higher
order harmonics. Has little effect on the 5th
and 7th
harmonics.
Because of the associated voltage drop,
there are limits to the amount of reactance
that may be added.

15. Attenuation of Harmonics
Passive Filters
Method: Provide a low-impedance path to ground
for the harmonic frequencies.
Benefits: May be tuned to a
frequency between two prevalent harmonics
so as to help attenuate both.
Concerns: Tuning the filters may be a labor-intensive
process.
Filters are difficult to size, because they offer
a path for harmonics from any source.
Quite sensitive to any future system changes.

16. Attenuation of Harmonics
Active Filters
Method: Inject equal and opposite harmonics onto the
power system to cancel those generated by
other equipment.
Benefits: Have proven very effective in reducing
harmonics well below required levels.
Concerns: The high performance inverter required for the
harmonic injection is costly.
Power transistors are exposed to conditions
of the line, so reliability may be a problem.

17. Attenuation of Harmonics
12-pulse Rectifiers
Method: Two separate rectifier bridges supply a single
DC bus. The two bridges are fed from phase-
shifted supplies.
Benefits: Very effective in the elimination of 5th
and 7th
harmonics.
Stops harmonics at the source.
Insensitive to future system changes.
Concerns: May not meet the IEEE standards in every
case.
Does little to attenuate the 11th
and 13th
harmonics.

18. Attenuation of Harmonics
18-pulse Rectifier
Method: An integral phase-shift transformer and rectifier
Input which draws an almost purely sinusoidal
waveform from the source.
Benefits: Meets the IEEE standards in every case!
Attenuates all harmonics up to the 35th.
Stops harmonics at the source.
Insensitive to future system changes.
Concerns: Can be expensive at smaller HP’s

19. Comparison of waveforms
6-pulse converter
12-pulse converter
18-pulse converter
note the level of distortion
and steep current rise.
the waveform appears more
sinusoidal, but still not very
smooth.
virtually indistinguishable
from the source current
waveform.

20. HARMONIC REDUCTION BY PWM
(pulse width modulation)

22. • Amplitude of fundamental component for values of α1 and α2
b1= 4Vs/π{ 1-2cos 23.62+ 2cos 33.304}
=1.0684 Vs
• Amplitude of the fundamental component of unmodulated output
voltage is:
b1=4Vs/ π=1.27324 Vs
• Un modulated voltage wave ,the amplitude of the 7th
,9th
,11th
harmonics are 24.78%,40.86%,30.39 %
• 3rd
and 5th
harmonics are been eliminated
• Amp of fundamental output voltage =83.91%
i.e. .8391 amp of fundamental unmodulated voltage wave.
Harmonics reduction =16.09%

23. Harmonics reduction by Transformer
connections
• Two or more inverters can be combined by means
of transformers to get a net output voltage with
reduced harmonic content .
• Output voltage waveforms from the inverters
must be similar but phase-shifted from each other.

24. By stepped wave inverters
• Pulses of different widths and heights are
superimposed to produce a resultant stepped
wave with reduced harmonic content .
• two transformers are used have different turn ratio
from primary to secondary .
• Turns ratio from primary to secondary is assumed
3 for transformer 1and 1 for transformer 2.
• Inverter 1 is gated that its output voltage is vo1
• During first half cycle output voltage woud be
zero or negative.

25. • This output voltage waveform is named as TWO –LEVEL
MODULATION .
• When inverter2 is triggered output voltage is v02
• level of this voltage is positive, negative or zero for first half cycle.
• For this the inverter has THREE LEVEL MODULATION
• By superimposing both the waveforms the output voltage is 4Vs
and wave for four steps.
• 3rd
,5th
,and 7th
harmonics are eliminated .

26. • A Novel Approach of Harmonic Reduction with
TransformerConnected 3-Phase Multilevel
Inverter
• By:Vipul Rastogi,Sudhanshu Tripathi (Iss.7| July.
2014 )
• This paper proposes a multilevel inverter arrangement
employing a series connectedtransformer to suppress
5th,7th,11th &13th order harmonics.
• eliminates the need of output filter

28. Harmonics reduction in three phase multilevel
inverters using space vector modulation
Published in: 19-20 March 2015
• Harmonic reduction in three
phase multilevel inverter is
an imperative factor to
obtain the quality of output
voltage and current.
• This paper proposes the
switching strategy of space
vector pulse width
modulation uniquely to
minimize THD.
Publisher:IEEE
INSPEC Accession Number:15380959
• To reduce the total
harmonic distortion and
study the harmonic analysis
of five-level inverter in
diode clamped inverter,
flying capacitor inverter and
cascaded H-bridge
multilevel inverters are
simulated in MATLAB

29. International Journal of Engineering Technology, Management and
Applied Sciences www.ijetmas.com June 2015,
Volume 3, Issue 6, ISSN 2349-4476
• New Approach for Harmonics
Reduction in Inverters

30. • This paper primarily compares and analyzes the two DC-
AC power conversion approaches. These two approaches
are
• 1. Cascaded H Bridge inverter
• 2. Multilevel scheme with H-Bridge and level modules.
• The primary advantage of cascaded topology is that it uses
multi-level DC voltage to accurately synthesize an
expected AC voltage .The level of output voltage shape
can be calculated by using appropriate level module.
MATLAB Simulink is used to design the above mentioned
two approaches. Comparatively, the THD produced in the
second approach is more efficient and productive than the
first approach.

33. Multilevel approach

35. THANK YOU