Power Quality Improvement using Shunt Active Power Filter:
An Industrial Zone Case Study
FOUAD ZARO
Electrical Engineering Department,
Palestine Polytechnic University,
Hebron City,
PALESTINE
Abstract: - Power quality (PQ) improvement using active power filters (APF) is a topic of growing interest.
APFs are effective in reducing harmonic distortion and improving power factor. They can be used in a variety
of applications to improve the performance and reliability of electrical equipment. To address concerns with PQ
improvement, this study offers an application of shunt APF in an industrial zone smart grid. the non-linear
loads and unpredictable harmonics produced by on-grid PV inverters that represent the architecture of an
industrial smart grid. Utilizing the MATLAB/SIMULINK software suite, a detailed design of the APF and
associated hysteresis current control technique is provided. The findings demonstrate that APF is a useful tool
for reducing total harmonic distortion (THD) and has a quick dynamic reaction to control grid voltage and
power factor.
Key-Words: - Shunt active power filter, Harmonics mitigation, Power factor correction, Distributed generation,
Hysteresis current controller, Power quality improvement
Received: August 25, 2022. Revised: August 21, 2023. Accepted: September 18, 2023. Published: October 26, 2023.
1 Introduction
Power quality (PQ) concerns are brought on by the
integration of utility systems with new renewable
energy sources like solar and wind technology. How
to raise the standard of electrical services is one of
the primary research areas in the field of smart
grids. The main cause of poor PQ issues including
harmonics, poor power factor, sag, and swell
distortions is the continued development of power
electronic devices like nonlinear loads, variable
frequency drives, and soft starters. Therefore, it's
crucial to consider new approaches to raise the
caliber of utility services, [1].
One of the most common power quality
problems is harmonic distortion. Harmonics are
multiples of the fundamental frequency of the power
supply (typically 50 or 60 Hz). They can be caused
by nonlinear loads, such as computers, power
electronics devices, and lighting. Harmonics can
cause a number of problems, including: increased
heating of electrical equipment, reduced efficiency
of electrical equipment, interference with
communication and signaling systems, and
malfunction of electronic equipment, [2], [3].
The two primary methods for reducing PQ
issues are active and passive power filters. Passive
power filters (PPF) have several shortcomings
compared to active power filters (APF), including
the inability to compensate for sub-harmonics,
tuning circuit accuracy, and trouble with their
enormous size, [4].
In addition to reducing harmonics and raising the
power factor to unity, many research subjects in the
field of renewable energy technology center on
providing real power to the loads. Due to their
advantages, such as their quick response to grid
fluctuations, capacity to compensate for random
harmonics and high control accuracy, APFs have
recently emerged as the most efficient method to
eliminate harmonics, inter-harmonics, and sub-
harmonics, [5], [6]. To cancel a wide range of
harmonics that affect the system and raise the grid's
power factor (PF) to unity, APFs inject a current
into the point of common coupling (PCC) that is
equal to but opposite in direction to the grid
harmonics. They also generate and absorb reactive
power into the grid. Furthermore, APFs keep the
grid system balanced and stable with load variations
and grid transients, [7], [8].
There are two types of APF, each one has its
advantages and disadvantages depending on its
effects and capacity: Series active power filter; this
filter, which is used in series with the loads, is
intended to reduce the grid's voltage harmonics by
generating negative voltage harmonics that cancel
the effects of the load's voltage harmonics and
maintain the grid's voltage in a pure sine shape
throughout transient, sag, and swell events. Shunt
active power filter; this filter, which is coupled in
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parallel with nonlinear loads, is used to inject a
negative current harmonic into the grid to lower the
utility's current distortion and raise the grid's power
factor, [9], [10].
Voltage source inverters (VSI) and current
source inverters (CSI) are the two primary types of
inverters. When the grid voltage is distorted, the
output of the shunt APF is also changed to control
the waveform of the grid's voltage and maintain a
clean sine wave. The use of VSI connected in
parallel with the grid depends on network voltage.
CSI was also parallel to the grid but was used to
control how much the current waveform was
distorted. Since the total harmonic distortion (THD)
of the current from industrial areas and renewable
energy sources is substantially higher than the THD
of the grid's voltage, the typical method for
achieving this is VSI with current reference
feedback. Figure 1 shows control strategies of VSI
that are connected to an 11kV 50Hz network.
Fig. 1: Control stages of APF connected to grid, [2].
This study represents design shunt APF to solve
PQ problems of renewable energy sources that
integrate with utility grids to mitigate grid
harmonics and improve the PF of the system. A
phase VSI inverter consists of six IGBTs with anti-
parallel diodes. the output voltage and frequency
obtained from the inverter should be in phase, equal,
and in the opposite direction of the grid’s harmonics
to cancel its effects using phase locked loop control
circuit (PLL), [10].
2 Problem Formulation
Shunt APF is a three-phase voltage source inverter
that is used to reduce random harmonics and correct
the power factor (PF) by generating a specified
reference current for the IGBT bridge. The three-
phase voltages and currents must be measured to
determine the reference current, which must then be
converted into a two-phase model (direct and
quadrature-dq) using the Clark transformation
method. After analyzing three-phase reference
currents using the inverse Clark transformation, this
two-phase reference current is used to gate the
inverter bridge, [11], [12], [13]. Figure 2 illustrates
the control procedure of reference calculation.
Figure 3 shows the overall transfer matrices.
Fig. 2: control procedure of reference current
calculation, [11].
Fig. 3: Overall transfer matrices of generating
reference currents, [10].
2.1 Two-phase Calculation
The two-phase calculation method is used to convert
three-phase measurements into the two-phase model
(direct and quadrature-dq) using the Clark transform
to simplify the calculations according to equation
(1), [11].
(1)
2.2 Instantaneous Power Calculation
Instantaneous real power (P) and instantaneous
reactive power (Q), both include two components,
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DC components due to the fundamental of the load
current and an AC component corresponding to the
harmonic current of the load. This instant power can
be calculated depending on equation (2).
(2)
Where P = P- + P~ and Q = Q- + Q~
2.3 AC Real Power Calculation
AC real power reference P~ can be extracted from
total power P by a low pass filter to separate the two
components from each other and select the AC
component only. For a given complex power set-
point Sref =Pref +j Qref and an output voltage of
Vo = Vod + j Voq, Thus, the reference current
signals Id-ref and Iq-ref can be calculated
according to equation (3).
(3)
Where Pref and Qref are reference active and
reactive power signals.
2.4 Reference Current Calculation in Two-
Phase Mode
The compensating currents Id-ref and Iq-ref in two-
phase mode can calculated depending on equation
(4).
(4)
2.5 Three-phase Reference Current
Calculation
Compensating current in three-phase mode can be
evaluated depending on two-phase results using
inverse Clark transform according to equation (5).
(5)
To achieve high output current quality, low-pass
filtering of the signal is generated by subtracting the
grid-side current Ig from the reference current Iref as
shown in Figure 4.
Fig. 4: power controller block diagram
2.6 Hysteresis Band Current Controller
It is a controller used to force the compensated
current (If) to follow the calculated reference current
(I-ref). The accuracy of the hysteresis controller
depends on its hysteresis band (HB) to reduce error
value. Figure 5 shows the block diagram of the
hysteresis current controller It is a controller used to
force the compensated current (If) to follow the
calculated reference current (I-ref). The accuracy of
the hysteresis controller depends on its hysteresis
band (HB) to reduce error value. Figure 5 shows the
block diagram of the hysteresis current controller,
[11].
Fig. 5: Block diagram of hysteresis current
controller.
3 Simulation Results and Discussions
To study the performance of the photovoltaic on a
grid system in the presence of local non-linear load
in an industrial zone with the proposed APF
connected in parallel with the network. The overall
simulation time is 100 ms, and shunt APF becomes
in service after the first two cycles (40 ms), the
simulation was done using MATLAB/ SIMULINK
and carried out as follows.
3.1 Overall System Description
Shunt APF is connected to an 11 kV, 50 Hz grid, to
compensate and mitigate the effect of non-linear
load that represents the topology of industrial zone
loads. Figure 6 shows the overall system design
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Fig. 6: Overall system design.
3.2 Non-linear Load
The topology of the industrial zone loads are non-
linear loads that are full of random harmonics
especially the 3rd harmonic, to simulate this
topology, a phase AC-DC converter load with
10MW, 26% THD is chosen. Figure 7 shows the
load current wave shape.
Fig. 7: Selected three-phase AC-DC converter with
its distorted current.
3.3 Two-phase and Instantaneous Power
Calculation
The two-phase calculation is done depending on the
Clark transform, followed by instantaneous real and
reactive power calculation according to equation
(2). Figure 8 and Figure 9 show the block diagram
and curves of instantaneous power respectively.
Fig. 8: Two-phase calculation block diagrams
followed by an instantaneous power
calculation.
Fig. 9: Instantaneous real and reactive power
curves
.
3.4 AC Real Power Calculation
Real power (P) out of the previous step consists of
two components, P-ac and P-dc components,
applying LPF can separate the P-ac and P-dc
components from each other. P-ac is also depending
on the voltage level across the capacitor at the input
of the inverter bridge, it is critical to keep the
voltage level stable on a pre-determined value by
applying a PI controller, [14], [15]. Figure 10 shows
the block diagram of evaluating P-ac. Figure 11
shows the P-ac and P-dc curves respectively.
Fig. 10: The block diagram of evaluating P-ac
Fig. 11: AC and DC components of real power
curves.
3.5 Three-phase Reference Current
Calculation
Compensating currents are reference currents of the
inverter's performance to mitigate random
harmonics and increase the grid's PF up to unity.
Generating reference current process depends on
evaluating reference currents in a two-phase model
according to equation (4) followed by inverse clack
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transform to get the references in a three-phase
model. Figure 12 shows a block diagram of the
phase reference current calculation.
Fig. 12: The block diagram of three-phase reference
current calculation.
Note that the summation of references at any
instant of time equals zero to make the system stable
and balanced. Figure 13 shows reference current
curves in the phase and three-phase models
respectively.
Fig. 13: Reference current curves in two phases and
three-phase models respectively.
3.6 Hysteresis Current Controller Design
The compensating current in Figure 13 is an analog
signal and is not able to be used as a firing signal of
the inverter bridge. The hysteresis controller is used
to convert analog signals into digital pulses that are
used to fire IGBT gates. Figure 14 shows the block
diagram of the hysteresis current controller.
Fig. 14: Hysteresis Current Controller block
diagram.
The Hysteresis Controller makes the grid current
follow reference currents with a small hysteresis
band (HB) to minimize the error value and increase
the accuracy of the output current. Figure 15 shows
the input and output signal of the Hysteresis
Controller with HB = 0.02.
Fig. 15: Input and output signal of hysteresis
controller with HB = 0.02.
4 Simulation Results Discussion
APF is connected in parallel to the industrial zone
grid to mitigate a wide range of harmonics and keep
the output voltage and current pure sine wave, low
THD, stable with load variations. Figure 16 shows
the current wave shapes before and after installing
APF.
Fig. 16: Current wave shapes before and after
installing APF. (a) grid current, (b) load current,
(c) filter current.
The SAPF was installed at the point of common
coupling (PCC) between the industry's power supply
and its nonlinear loads. The SAPF was rated at 500
kVA and was designed to compensate for harmonic
currents up to the 50th order. Table 1 shows the
THD of voltage and current and PF measurements
before and after the installation of the SAPF.
The installation of the SAPF resulted in a
significant improvement in the power quality at the
load. The THD of voltage and current was reduced
significantly, and the power factor was improved.
The energy consumption of the industry was also
reduced by 5%.
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Table 1. The power quality measurements before
and after the installation of the SAPF
Parameter
Before
SAPF
After
SAPF
THD of Voltage
5.5 %
1.5 %
THD of
Current
25 %
4 %
Power Factor
0.8
0.96
4 Conclusion
This study used a hysteresis current controller
constructed by the MATLAB/SIMULINK software
to analyze the performance of SAPF in a real
industrial zone with a non-linear load that is full of
harmonics for PQ enhancement. The results of the
proposed SAPF's design using instantaneous
reactive power theory (p-q theory) show that adding
SAPF can significantly enhance the performance of
the smart grid.
SAPFs are a valuable tool for improving power
quality. They are effective in reducing harmonic
distortion and improving power factor. SAPFs can
be used in a variety of applications to improve the
performance and reliability of electrical equipment.
With the suggested method, harmonics in the source
current and load voltage under nonlinear load are
successfully compensated. The outcomes of the
simulation demonstrate that the THD complies with
IEEE standard 519, i. e. that is, less than 5%. The
suggested strategy performs well in the system
under various load variations.
To further enhance power quality and efficiency,
the manufacturing plant may consider implementing
additional technologies such as voltage regulators
and energy management systems. Additionally,
continuous monitoring and periodic maintenance of
the SAPF are crucial for long-term success.
In future work, the author suggests designing and
developing a parallel-serial topology (Unified
Power Quality Conditioner (UPQC)) given the
many benefits they offer, such as voltage and
current harmonics filtering.
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Contribution of Individual Authors to the
Creation of a Scientific Article (Ghostwriting
Policy)
The author contributed to the present research, at all
stages from the formulation of the problem to the
final findings and solution.
Sources of Funding for Research Presented in a
Scientific Article or Scientific Article Itself
No funding was received for conducting this study.
Conflict of Interest
The author has no conflicts of interest to declare.
Creative Commons Attribution License 4.0
(Attribution 4.0 International, CC BY 4.0)
This article is published under the terms of the
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