Angit Kumar.G et al. / International Journal of Engineering Science and Technology (IJEST)
Control Strategy of Three Phase Shunt
Active Power
Filter for Power Quality Improvement
Angit Kumar.G1
Ramesh Babu.U2
1
MRITS, Secunderabad, India, gak.mrits@gmail.com
NBKR, VidyaNagar, India, uramesh25@gmail.com 2
ABSTRACT: The increasing use of power electronics-based loads (adjustable speed drives, switch
mode power supplies, etc.) to improve system efficiency and controllability is increasing the concern for
harmonic distortion levels in end use facilities and overall power system. The application of passive tuned filters
creates new system resonances which are dependent on specific system conditions. In addition, passive filters
often need to be significantly over-rated to account for possible harmonic absorption from the power system.
Passive filter ratings must be coordinated with reactive power requirements of the loads. Parallel (or shunt)
active filters have been recognized as a valid solution to current harmonic and reactive power compensation of
non-linear loads. The basic principle of Shunt Active Power filter is that it generates a current equal and
opposite in polarity to the harmonic current drawn by the load and injects it to the point of coupling thereby
forcing the source current to be pure sinusoidal. The control strategy is Synchronous Detection Algorithm. This
technique relies in the fact that the three phase currents are balanced. The average power is calculated and
divided equally between the three phases. The signal is then synchronized relative to the mains voltage for each
phase. Then the desired reference current is evaluated.
1. Introduction: Methods for limitation and elimination of disturbances and harmonic pollution in the power
system have been widely investigated. This problem rapidly intensifies with the increasing amount of electronic
equipment (Computers, radio set, printers, TV sets etc.). This equipment, a nonlinear load, is a source of current
harmonics, which produce increase of reactive power and power losses in transmission lines. The harmonics
also cause electromagnetic interference and, sometimes, dangerous resonances. They have negative influence on
the control and automatic equipment, protection systems, and other electrical loads, resulting in reduced
reliability and availability. Moreover, nonlinear loads and non-sinusoidal currents produce non-sinusoidal
voltage drops across the network impedance’s, so that non-sinusoidal voltages appear at several points of the
mains. It brings out overheating of line, transformers and generators due to the iron losses.
Reduction of harmonic content in line current to a few percent allows avoiding most of the
mentioned problems. Restrictions on current and voltage harmonics maintained in many countries through IEEE
519-1992 in the USA and IEC 61000-3-2/IEC 61000-3-4 in Europe standards, are associated with the popular
idea of clean power.
Many of harmonic reduction method exist. These techniques based on passive components, mixing
single and three-phase diode rectifiers, and power electronics techniques as: multi pulse rectifiers, active filters
and PWM rectifiers are shown in Figure 1. They can be generally divided as:
A) Harmonic reduction of already installed non-linear load.
B) Harmonic reduction through linear power electronics load installation.
2. Active Power Filters:
Parallel (or shunt) active filters have been recognized as a valid solution to current harmonic and reactive power
compensation of nonlinear loads. The principle of operation of active filters is based on the injection of the
current harmonic required by the load. Thus the basic principle of shunt active power filter is that it generates a
current equal and opposite in polarity to the harmonic current drawn by the load and injects it to the point of
coupling thereby forcing the source current to be pure sinusoidal. As a consequence, the characteristic of the
harmonic compensation are strongly dependent on the filtering algorithm employed for the calculation of load
current harmonics.
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Angit Kumar.G et al. / International Journal of Engineering Science and Technology (IJEST)
Harmonic Reduction Technique A B FILTERS MIXING SINGLE & THREE PHASE DIODE RECTIFIERS PWM RECTIFIERS BUCK RECTIFIER PASSIVE FILTER MULTI‐PULSE RECTIFIERS BOOST RECTIFIER HYBRID FILTER ACTIVE PWM FILTER
2‐LEVEL
3‐LEVEL Fig 1. Most popular three-phase harmonic reduction techniques of current
A) Harmonic reduction of already installed non-linear load.
B) Harmonic reduction through linear power electronics load installation.
3. Synchronous Detection Algorithm:
The Synchronous Detection Algorithm relies in the fact that the three phase currents are balanced. The average
power is calculated and divided equally between the three phases. The signal is then synchronized relative to the
mains voltage for each phase. Then the desired reference current is evaluated in this algorithm, the three phase
mains current are assumed to be balanced after compensating. Thus,
Imu = Imv = Imw
(1)
Where Imu, Imv, Imw are the amplitudes of the three phase mains currents after compensating, respectively. The
real power consumed by the load can be represented as,
P=ሾ݁௨
݁௩
݅௅௨
݁௪ ሿ ൥ ݅௅௩ ൩
݅௅௪
(2)
The real power is sent to a low pass filter to obtain its average value Pdc. The real power is then split into the
three phases of the mains supply:
(3)
Pu = (PdcEu)/ Etot
(4)
Pv = (PdcEv)/ Etot
(5)
Pw = (PdcEw)/ Etot
Where Eu, Ev and Ew are the amplitudes of the mains voltages, and Etot is the sum of the Eu, Ev and Ew. The
desired mains currents can be calculated as,
(6)
Imu=2eu Pu /Eu ²
Imv=2ev Pv /Ev²
(7)
(8)
Imw=2ew Pw/Ew²
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The reference compensation currents can be calculated and represented as,
(9)
i*cu = iLu - imu
(10)
i*cv = iLv - imv
(11)
i*cw = iLw - imw
iLu eu 2eu /Eu ² iLu ev iLv 2ev /Ev ² ε LPF iLv Power Distributor
iLw ew iLw 2ew /Ew ² Icw Fig 2. Block diagram for implementing synchronous detection algorithm
Fig 3. SIMULINK BLOCK DIAGRAM OF SYNCHRONOUS DETECTION ALGORITHM
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500
0
-500
0
0.05
0.1
0.15
0.2
0.15
0.2
0.15
0.2
0.15
0.2
(a)
50
0
-50
0
0.05
0.1
(b)
40
20
0
-20
-40
0
0.05
0.1
(c)
100
50
0
-50
-100
0
0.05
0.1
(d)
800
700
600
0
0 05
01
(e)
0 15
02
Fig 4. Simulation results for the ideal mains voltage with diode rectifier load. (a) Three phase mains voltages (b) load current in
u-phase (c) compensating current for the u-phase (d) source current in the u-phase (e) the dc capacitor voltage
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(a)
(b)
Fig.5 spectral analysis of the (a) load current, magnitude Vs frequency in Hz. (b) source current, magnitude Vs frequency in Hz, for the ideal
mains voltage with diode rectifier load
4. Control of the dc capacitor:
The dc capacitor voltage regulation is achieved and the instantaneous active power consumed in the power
converter losses are compensated by an active component drawn from the supply. Thus the dc voltage regulation
of the capacitor is achieved. This is achieved in one cycle of the supply voltage waveform.
Conclusion:
. The performance is evaluated by total harmonic distortion (THD) in the compensated mains current
and detailed discussions are presented here. Under balanced and sinusoidal mains voltage condition, this control
strategy provides good compensation of the harmonics. The compensated mains current spectrum contains only
the fundamental components in this method. In case of unbalanced and sinusoidal mains voltage conditions, the
synchronous detection method provide low value of THD to provide compensation. To study further, the effect
of the mains voltage distortion on the control strategies a system with distorted mains with fifth harmonic is
considered, which feeds a nonlinear load that takes pure sinusoidal load current under this condition. The
simulation results show the control strategy by Synchronous Detection Method is good for supply unbalances.
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