International Journal of Advance Electrical and Electronics Engineering (IJAEEE)
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Suppression of Harmonics and THD in Three Phase Inverter Drive
using Two stage Damping Filter
1
Rajesh B, 2Manjesh
Dept. of Electronic Science Bangalore University, Bangalore, India
2
Email: 1rajesb0201@gmail.com, manjesh1972@gmail.com
Abstract: Total harmonic distortion in power electronic
system deteriorates the performance of the converters and
inverters, many researchers working on power electronic
systems to reduce the fault and THD that causes various
problems in the power electronic system. In this paper a
simulation work has been carried to suppress the
harmonics generated in Three Phase PWM inverter. The
industry needs high quality power electronic converter and
inverter system for their applications, most of the industry
prefers high reliable, long life time inverter drives to work
long period, The inevitable property of a inverter is that it
generates harmonics, and common problems like Common
mode (CM), differential mode (DM) noise, dv/dt, line
current, bearing currents are severe in PWM inverters.
These serious problems can be minimized using two stage
damp filter at the output of the inverter.
Keywords: PWM inverter, Total Harmonic Distortion,
Harmonics, Damp filter,
I. INTRODUCTION
Power electronics has become essential for electrical
conversion. In the present technology static converters
are used in almost every electrical system in different
fields like industry, renewable energy, embedded
system, transport or domestic applications. The increase
of power convertor number is very problematic for
electromagnetic compatibility (EMC). Indeed, each
convertor generates a high frequency harmonics, hence
electrical network becomes more and more
"polluted"[1,2]. The improvements in switching
frequency combined with size reduction of the
components enable to reduce active components, sizes
implying reduction in converter sizes. In Traditional
inverters for three-phase drive applications the
occurrence of common mode voltage is inherent due to
asymmetrical output pulses[3,4]. The high dv/dt and
high switching frequency together with the common
mode voltages generated by PWM inverters have cause
many adverse effects. The major objective of this
research is to investigate and suppression of the
harmonic content produced by PWM inverter in
electrical machine system [5].
The rise of switching frequency combined with microelectronic improvements reduces active components
sizes and so convertors sizes. This rise has also made
EMC problems worse, presently filters have to be more
and more effective on larger frequency range [6,7,8,].
The electromagnetic emissions produced by adjustablespeed AC drive systems will become interesting subject
for researchers and industry. In typical three-phase
power inverter drives, there exists substantial commonmode voltage between the load neutral and earth ground.
Switching frequencies of 1 to 20 kHz and rising time of
0.1μsec.are possible with modern insulated gate bipolar
transistors (IGBTs) rated at 600V or 1,200V [6-8]. This
makes it possible for being widely used in medium
voltage system and a great contribution to improve the
controllability of voltage, current, and torque in the
PWM inverter with motor is used as load. When using a
PWM inverter to drive a motor there are several
problems along with the flexibility. Initially the inverter
is a source of differential mode (DM), DM voltage is the
voltage between two lines and has a rectangle shape at
the output of the inverter. The steeper the slew rate of
inverter output DM voltage and the longer, the motor
leads the higher potential for over voltages at the motor
because of reflections [10]. These over voltages may
destroy the motor insulation and are avoided easily with
a motor line inductor. Common Mode (CM)
disturbances appear because the inverter output voltages
is not equal to zero, so that a CM current is driven over
the parasitic capacitances of the motor and the feed back
through the power supply to the DC link, which is the
reference potential of the CM voltage [11].
II. MODELING
A. Three phase inverter drive:
In this paper a simulation work is carried out for the
three phase inverter drive. The load used in the work is
the exact value of the three phase induction motor used
in the laboratory. The circuit diagram of the three phase
inverter drive with RL load has been shown in Fig.1.
The values of RL1=RL2=RL3 are same in all the three
branches, with the values R=11.3Ω and L= 45.3mH. The
value of the load has been kept constant though out the
simulation work. PWM signals are generated using
pulse generator block. The IGBT’s are used as switches,
gating signal to each IGBT is provided through a pulse
generator. Each phase is1200 out of phase with each
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ISSN (Print): 2278-8948, Volume-3 Issue-4, 2014
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International Journal of Advance Electrical and Electronics Engineering (IJAEEE)
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other. The IGBT-3 is turned on with a phase delay of
1200 with respect IGBT-1, similarly IGBT-5 is tuned on
with a phase delay of 120° with respect IGBT-3. The
IGBT’s-1,3,5 are the upper switches and IGBT’s-2,4,6
are the lower switches. A dead time is provided between
upper and lower IGBT’s to avoid short circuit, at any
instant of time no two switches in the same leg can be
ON. The switching pattern of the IGBT switches are
obtained, one from the lower group and two from the
upper group or one from the upper group and two from
the lower group are ON. This produces a three phase
output power used to drive the load shown in Fig.3.
Fig 1: Three phase inverter drive with RL Load
B. Three phase inverter drive with two stage damp
filter in common mode:
The filter can be constructed invariably with proper
choice of passive elements, in this filters there is no
proper design. The filters used in this work is a damped
passive filter, the filter has two stages, the first stage is
combination of for 1st leg L1 which is connected in
parallel to R1,L11,C1, for leg 2 L2 which is connected
in parallel to R2,L12,C2 and for leg 3 L3 which is
connected in parallel to R3,L13,C3 all the three
capacitors(C1,C2,C3) are connected in common mode
elimination
method
between
the
input
capacitors(CC1,CC2). The Second stage is combination
of 1st leg L4 which is connected in parallel to
R4,L21,C4, for leg 2 L5 which is connected in parallel
to R5,L22,C5 and for leg 3 L6 which is connected in
parallel to R6,L23,C6 all the three capacitors(C4,C5,C6)
are connected in common mode elimination method to
mid-point of the input capacitors CC1, the
comprehensive construction of inverter with filter has
been shown in Fig 2.
Fig2: Three phase inverter drive with Damp filter
The values of the different elements used are given
Table 1.
Table 1: Inductor, Capacitor and Resistor values.
Inductor
L1=L2=L3=10mH
L4=L5=L6=10mH
L11=L21=90mH
L12=L22=90mH
L13=L23=90mH
Capacitor
C1=C2=C3=47µF
C4=C5=C6=47µF
CC1=CC2=1mF
-
Resistor
R1=R2=1KΩ
R3=R4=1KΩ
R5=R6=1KΩ
R=0.1Ω
-
III. RESULTS
The simulation work has been carried out for Three
Phase Inverter drive without filter and with damping
filter. The Harmonics and THD of Three phase Inverter
drive with and without filters are studied and plotted.
The line to neutral voltage wave form is as shown Fig.3
without filter, various harmonics generated for Three
Phase Inverter are plotted using a bar graph as shown in
Fig4.
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ISSN (Print): 2278-8948, Volume-3 Issue-4, 2014
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International Journal of Advance Electrical and Electronics Engineering (IJAEEE)
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The harmonics plot of line to neutral voltage of three
phase inverter drive with two stage damp filter is as
shown in Fig. 6.
Fig 3: Line to neutral voltage wave form with out filter
Fig.6: Harmonics plot of Line to neutral voltage of three
phase inverter drive with filter.
IV. CONCLUSION
Fig 4: Harmonics plot of Line to neutral voltage of
Three phase inverter drive without filter.
The line to neutral voltage wave form of Three phase
Inverter drive with damping filter is as shown in Fig.5. It
has been observed that the wave shape is more
sinusoidal than waveform obtained with Three phase
Inverter drive without filter.
Table 2: THD in percentage with and without filter
Filter
THD in %
Without filter
31
With Damp filter
The simulation work has been carried out for Three
Phase Inverter drive, the harmonics and total harmonic
distortion has been studied without filter and with
damping common mode filter, the concept of using the
damp common mode filter is used to minimize the THD
at the output of the PWM inverter. The harmonic
content in the output of voltage is drastically suppressed,
the THD is also reduced. This simulation work is
extended to implement in Three Phase PWM motor
drives to study temperature analysis of stator windings
of the Induction motor.
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Fig 5: Plot of Line to neutral voltage Three phase
inverter drive with damp filter.
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ISSN (Print): 2278-8948, Volume-3 Issue-4, 2014
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International Journal of Advance Electrical and Electronics Engineering (IJAEEE)
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