INFORMATION PAPER
International Journal of Recent Trends in Engineering, Vol 1, No. 4, May 2009
Reduction in Total Harmonic Distortion in a NonLinear Load with Harmonic Injection Method
Arindam Dutta1, Tirtharaj Sen2, S. Sengupta2
1
Techno India/Electrical Department, Kolkata, India
Email: arindamdutta190@hotmail.com
2
University of Calcutta /Applied Physics Department, Kolkata, India
Email: {samarsgp, thirtharaj.sen}@rediffmail.com
current. Moreover, these harmonic currents cause
additional harmonic losses in the utility system and may
excite electrical resonance, leading to large over voltages.
Abstract— In this paper a sixth-order harmonic injection
PWM concept at a constant switching frequency is
established, and a sixth-order harmonic injection technique
is developed for the harmonic reduction of a single-switch
three-phase boost rectifier. It has been extended to propose
a circuit topology for a three-phase active filter using
harmonics current injection method. An optimal injection
current is achieved in order to obtain an input current of
sinusoidal waveforms to meet the IEC 1000-3-2 (A) standard
and the output power can be pushed up to 10 kW for the
application with a three phase 110 V, 60 Hz input and a 600
V output. The injection principle is graphically explained in
current waveforms and mathematically proved. Simulation
results have been presented to validate the propositions.
Figure 1. Current and Voltage Waveform in a Practical Bridge Rectifier
Another problem caused by harmonics in the line current
is to overload the circuit wiring. However, the singleswitch three-phase boost rectifier cannot be pushed to
high power levels because its input current harmonics
cannot meet the on-harmonic analysis. It is found that the
current distortions are related to the rectifier voltage gain
M, which is defined as:
Index Terms—Active filter, Band pass filter, Fixed
frequency control, PID controller, PWM rectifier, Total
Harmonic Distortion
I. INTRODUCTION
(1)
Traditionally, three-phase AC-to-DC conversions are
performed by phase-controlled rectifiers or diode
rectifiers. Since the loads of rectifiers draw nonsinusoidal currents or reactive power from the source, the
power quality of the distribution network is greatly
deteriorated, resulting in low efficiency of utilities.
where V0 is rectifier output voltage and Vlp is input lineline peak voltage. The higher the M is, the lower the
harmonics become. A larger M means a high output
voltage, yielding a high voltage stress on the devices.
Harmonic current in a power circuit can cause various
problems, such as line voltage distortion, heating of
power factor correction capacitors and so on. Power
factor correction (PFC) rectifiers, which suppress the
harmonics current, are still a very important technology.
One of the most popular PFC methods for three-phase
input is a full-bridge type pulse width modulation (PWM)
rectifier, which consists of six arms and a boost-up
reactor. The conventional PWM rectifier can obtain a
sinusoidal input current without harmonic distortion.
However, in regard to cost, the conventional PWM
rectifier is not the best solution for the PFC. Rather,
three-phase PFC rectifiers using current injection
methods can be realized at a low cost, because they do
not require many switching devices in comparison with a
conventional PWM rectifier
Figure 2. A single-switch three-phase boost rectifier
A. Implementation of Harmonic Injection Method in this
Simulation and Related Theory
II THEORITICAL BACKGROUND
Typically ac current waveforms in a three phase diode
rectifier are far from sinusoid. The power factor is also
very poor because of the harmonic contents in the line
Figure 3. Single line diagram of active filter
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INFORMATION PAPER
International Journal of Recent Trends in Engineering, Vol 1, No. 4, May 2009
Active filters can prevent harmonic currents from
entering the utility system, if harmonic current produced
nonlinear loads are being supplied by utility. The load
current is sensed and filtered to provide a signal
proportional to the distortion iL. In this paper, the fixed
frequency control has been used to operate a dc to ac
converter delivering the current iL distortion to the utility.
Therefore in ideal case the harmonics in the utility current
are eliminated. On the dc side of the converter only a
capacitor with minimum energy storage is needed,
because the dc voltage across it is maintained by the
switch mode converter and it supplies the utility a small
current i1 to compensate for its own losses.
Figure 5 The bridge rectifier connected to line with nonlinear load
B. Fixed frequency control
Figure 6. Timing diagram of I_La1, I_La2, I_La3
Figure 4 Diagram of fixed frequency control
The fixed frequency control has been shown in figure 4
in which the error between the reference and actual
current is fed through a PI controller which integrates the
error between the feedback and reference current to
generate a variable voltage value; then, this value is fed
into a triangle pulse-width modulator to produce gate
signal. The output Vcontrol of the amplifier is compared
with a fixed frequency (switching frequency fs) triangular
waveform Vtri. A positive error (iA*-iA) and hence a
positive Vcontrol result in a larger inverter output voltage,
thus bringing iA to its reference value. Similar action
takes place in other two phases.
Figure 7. Timing diagram of I_La1 only
III. SIMULATION
In this simulation the prototype is designed with the
following parameters:
Figure 8. Frequency diagram of I_La1 only
1. Input: Three phase 110 V, 60 Hz, Inverter Voltage =
600 V
2. Source impedance R= 0.5 ohm, L= 0.1mH
3 Parameters of Transmission Line are L1= 0.0005H,
L2= 0.002H, R= 0.1Ohm, C = 2uF
4. Parameters of Nonlinear Load are C=440 uF, L=
0.003H, R= 0.5 ohm
Table 1 Typical % harmonics of only Bridge
Typical
Harmonics %
3rd
5th
7th
9th
Ih/I1
7.8%
12%
4.8%
5.06%
%THD= 55% …………….
(2)
In the figure 5 the PSIM analysis diagram is shown
and respective timing and frequency diagrams are shown
in figures 6, 7 and 8. As shown in Table 1 and (2),
%THD comes to 55%. So main aim in this simulation is
to reduce the % THD. Simulation of various types of
controllers with various types of filters is done here to get
better performance. A comparative study of various
simulation results is given in Table 2.
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International Journal of Recent Trends in Engineering, Vol 1, No. 4, May 2009
Table 2. Comparative study of % Typical Harmonics
Simulation Type
Only Bridge
PI Controller with no filter
PI Controller with Low Pass filter
PI Controller with High Pass filter
PI Controller with Band Pass filter
PD Controller with Band Pass filter
PID Controller with Band Pass filter
%
T.H.D
A. Simulation Parameters
55
24
22
25
20
23
12.25
1. Input: Three phase 110 V, 60 Hz, Inverter Voltage =
600 V
2. Source impedance R= 0.5 ohm, L= 0.1mH
3 Parameters of Transmission Line are L1= 0.0005H,
L2= 0.002H, R= 0.1ohm, C=2uF
4. Parameters of Nonlinear Load are C=440 uF,
L=0.003H, R= 0.5 ohm
5. Triangular frequency: 10020Hz, Vpeak-to-peak =20v
6. 2nd order band pass filter: Center frequency=60Hz,
Passing Band=20, Gain=1
From Table-2 it is seen that use of PID controller with
Band Pass Filter gives minimum %THD (12.25%) as
compared to only bridge (55%). So we go for the detailed
simulation of three Phase Active Filter with PID
controller and Band Pass Filter.
B. Total Circuit Analysis
In this paper we propose the design of a 3 phase Active
Filter with PID Controller. Here the 3 phase supply
(110V, 60 Hz) is applied to a 3 phase rectifier unit.
Figure 9. Simulation diagram of three phase active filter of three phase active filter with PID controller
controller, which compares the actual value of harmonics
with the desired value and produces a control signal
which will reduces the deviation to zero or to a small
value. The output of simulated waveform of PID
controller is shown by simulated diagram of voltmeter
V2.After this signal is taken to voltage limiter circuit and
the output of voltage limiter is shown by the simulated
waveform of voltmeter V3.The output of voltage limiter
circuit is taken to the input terminal of a comparator and
another high frequency triangular signal is taken to
another input of the comparator. The output of
comparator circuit (which is shown by the simulated
The output of rectifier unit is nonlinear load, and for
the nonlinear load harmonics are generated at the line
currents (figure 9).These harmonics are compensated by
another harmonics which are generated by inverter just
exact replica of previous harmonics and fed in anti phase
to the previous harmonics. A sample of signal which
consists of fundamental and harmonics is taken through
two second order band pass filters connected in cascade.
Then the output of filter (A voltmeter V5 is connected at
the output of filters to see the simulated output of filter) is
fed to a subtractor circuit. The output of subtractor is
harmonics (shown by the simulated waveform of
voltmeter V1). The output of subtractor is taken to a PID
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International Journal of Recent Trends in Engineering, Vol 1, No. 4, May 2009
waveforms of voltmeters Vr, Vy and Vb) is the desired
switching signal for the inverter.
The control signal operates the inverter i.e. turns on or
off the IGBTs to get the desired harmonics which will
lower switching loss and smaller snubber circuit
compensated the harmonics generated by the nonlinear
load. IGBTs are used here for their less size, lower
switching loss and smaller snubber circuit requirements
C. Simulation Results
Figure 14 Simulation results of inverter current in time domain for
3phase active filter
Figure 10 Timing diagram of I_La1 only for 3phase active Filter
Figure 15 Simulation results of i_La1 and V1in time domain for 3phase
active filter
Figure 11 Timing diagram of i_La1, i_La2, i_La3 for 3phase active
Filter
CONCLUSION
In this paper three phase Active Filter using various
controllers and filters have been studied. The required
simulation is done by PSIM simulation package.
From the results of various simulations and after the
comparative study of %THD Table2 we come to the
conclusion that the three phase Active Filter with PID
Controller and Band Pass filter is the best. PD control
improves transient state response and PI control reduces
the steady state response or offset. PID control has both
the feature of PD and PI. It also reduces Filter noise and
Bandwidth. It also increases the rise time. So PID is the
best controller here which can compare the actual value
of harmonics with the desired value and produces a
control signal so that it will reduce the deviation to zero
or to a small value.
Band Pass Filter works to screen out that are too low
or to high, giving easy passage only to frequency of
certain range. Here we take the band pass filters whose
center frequency 60 Hz and passing band 20 Hz. That
means it allows to pass mainly fundamental frequency
and harmonics are eliminated. As the bandwidth is
greater than 1/10th of fundamental frequency it is called
Wide Band Pass Filter. Here two Band Pass filters are
connected in cascade to make 4th order Band Pass filter.
If the order filter is increased, then the actual stop band
characteristics approaches to ideal stop band
Figure 12 Simulation results of Vr in time domain for 3phase active
filter
Figure 13 Simulation results of Vr, Vy, and Vb in time domain for
3phase active filter
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International Journal of Recent Trends in Engineering, Vol 1, No. 4, May 2009
characteristics. So we use 4th order band pass filter to
eliminate the harmonics.
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