Connection of a Passive Filter in Parallel for Harmonic
Compensation in a Grid-connected PV System
Sara Khalil, Naima Oumidou, Mouna Lhayani and Mohamed Cherkaoui
Engineering for Smart and Sustainable Systems Research Center, Mohamadia School of Engineers, Mohammed V
University in Rabat, Morocco
cherkaoui@emi.ac.ma
Keywords: Passive filter, harmonic, distributed energy resources, photovoltaic, power quality.
Abstract: The quality of electrical energy concerns all the actors of the energy field. It represents a subject of great
interest since the electrical disturbances have a high cost for the industrialists because they generate a fall in
the quality of the production, premature ageing of the equipment. In this research work, we are faced with a
significant problem that affects the quality of electric power, namely the harmonic pollution within an electric
network, which is due to the heavy use of power electronic devices. These devices exhibit non-linear
behaviour. At the same time, distributed energy resource systems, can impose some harmonics in the network.
With the presence of harmonic currents, an increasing variety of the maximum winds, so the value of the
effective current and therefore an increase in the rate of harmonic distortion led to the deformation of the
sinusoid of the fundamental. One of the solutions that we can propose to reduce this harmonic pollution is to
mount passive filtering in parallel the systems. This filtering has a low cost and can be efficiently adapted to
a high power electrical network connection. A simulation of a grid-connected PV system under
Matlab/Simulink with and without filtering was realised to analyze the power quality related to the PV system
and show the interest in adding passive parallel filtering. The Simulation results demonstrated the
effectiveness of adding the passive filtering system in parallel to the output of the inverter to attenuate the
harmonics.
1 INTRODUCTION
To satisfy the high energy demand, Distributed
Energy Resources (DER) systems appear as a
favoured means to cope with this situation. Owing to
the insertion of DER, power flows and voltages are
impacted not only by loads but also by sources. So,
the connection of the photovoltaic (PV) system to the
distribution grid can have some effect on the
electrical network; on the one hand, the impact on the
power flow, the voltage plan, the protection plan and
the power quality (G. B. Alers, 2011). On the other
hand, the characteristics, the process and the
disturbances of the distribution network can influence
the operation of a PV system. To avoid the
malfunctioning or even the destruction of the
electrical network components, it is crucial to find out
the origin of the disturbances and look for adequate
solutions. Among the main types of disruptions that
can degrade the quality of electrical energy: voltage
dips and short interruptions, voltage unbalance,
harmonic disturbances and overvoltages (Vanya
Ignatova, 2009).
Several literature studies have presented various
studies concerning the impact of a grid-connected PV
systems on the power quality of a distribution
network. Although the active power generated is
linearly proportional to solar irradiance, it may show
an inverse trend at varying irradiance values. In
addition, the use of a low switching frequency
inverter with a PV system can generate high harmonic
distortion. This can justify that in a connected PV
system, the Total Harmonic Distortion (THD) level
should be monitored throughout the day (ICEEE,
2014). Two solutions to improve power quality are
proposed (Walaa and Walid, 2018). The first one
relies on switching at shallow current flow
conditions. However, the second one is based on
adding filters. Both proposed approaches are
implemented using MATLAB Simulink and
compared in terms of effectiveness and applicability.
Moreover, the results are also demonstrated by
130
Khalil, S., Oumidou, N., Lhayani, M. and Cherkaoui, M.
Connection of a Passive Filter in Parallel for Harmonic Compensation in a Grid-connected PV System.
DOI: 10.5220/0010729700003101
In Proceedings of the 2nd International Conference on Big Data, Modelling and Machine Learning (BML 2021), pages 130-134
ISBN: 978-989-758-559-3
Copyright
c
2022 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved
determining the THD as a function of the
Photovoltaic load flow to the connected grid and
applied on a case study tested during the spring and
summer seasons. In (Masoud Farhoodnea & al, 2012
and Pedro González & al, 2011), a study on the
impact of a grid-connected PV system has been
investigated. Simulation results using
Matlab/Simulink software showed that the active
power produced by the PV systems causes an increase
in voltage and a reduction in power factor, which can
then create severe problems for the system
components. Thus, an internal control strategy is
needed in storage devices and the inverter to adjust
the injected power according to the grid’s needs. To
upgrade the stability of the system, limit voltage
instability and improve the reliability of the whole
power system, a Large-Scale photovoltaic (L-S PV)
system is proposed, and simulation results have
shown their performance (Shady S.Refaat & al,
2018). In today's power electronics markets, there is
a wide variety of inverter designs attached to PV
systems to meet the increasing demand for solar
systems in Distributed Generation (DG) using
modern control technologies. As a result, the
harmonics supplied to the electrical grid vary
depending on the type of inverter and the control
strategy used. Utility operators must address and fix
the impact of these components that accompany PV
generation (Tiago E. C. de Oliveira & al, 2018). In
this work, research was carried out on grid-connected
photovoltaic (PV) systems to study the impact of grid
injection. Then a simulation of a grid-connected PV
system was performed in Matlab/Simulink to analyze
power quality related to the system. The use of
passive parallel filtering is proposed to reduce
harmonic pollution due to its advantages in terms of
cost, performance and efficient adaptation to a high
power grid connection. Simulation results have been
performed in Matlab/ Simulink software to show the
interest in adding a passive filter in parallel. The solar
irradiation data are extracted from the Benguerir site
during the year 2017.
The rest of this paper is organized as follows.
Section 2 presents a description and modelling of the
overall system. The simulation results and discussion
are provided in Section 3. Finally, Section 4 ends this
paper with a conclusion and perspectives.
2 SYSTEM DESCRIPTION AND
MODELING
The studied system includes a photovoltaic generator
connected to the common DC bus by a boost chopper,
and connected to the grid via a DC/AC inverter. A
passive filter is installed in the output of the system
with an aim to reducing the harmonic content, as
shown in the figure below.
Figure 1: Synoptic of the studied system
2.1 Photovoltaic System
To understand the electrical behaviour of the
conventional cells, the use of the equivalent electrical
circuit is necessary. The equivalent electric circuit of
the PV cell is depicted by the following.
Figure 2: A PV cell equivalent circuit
The output current can be expressed as follows:
I
I
I
e
1
(1)
The voltage across the load resistor is:
VV
R
I
(2)
By deducing from the previous equation we finally
find the following expression:
I
I
I
e
1 (3)
We were assuming that Rs<<Rsh, our case then
becomes that of the equivalent circuit of an ideal cell
without losses.
Then (1/ Rsh) →0, So the equation (3) becomes:
Connection of a Passive Filter in Parallel for Harmonic Compensation in a Grid-connected PV System
131
I
I
I
e
.
1, Or: V
(4)
Where q is the electron charge. It is equal to
1,602. 10
𝐶 . K is the Boltzmann Constant
1,381.10
𝐽 𝐾
⁄
. n is the Non-ideality factor of the
junction between 1 and 5 in practice, and T is the
effective temperature of the cell in kelvin.
From equations (2) and (4), we can see the influence
of the temperature that varies overtime on the voltage
and current output of photovoltaic cells. For this
purpose, it must be taken into consideration, in
particular the THD%, which can be calculated from
equation (5) as follows (Si-Hun Jo & al, 2013):
THD
∑
THD
∑
N is the maximum number of harmonics from
obtained samples during one period T, and the
subscript k of voltage and current denotes the order of
the harmonic.
2.2 Passive Filter in Parallel
As shown in figure 3, the parallel passive filter
consists of an inductor parallel with a capacitor. It
has a low impedance for all harmonics and a
sufficiently high impedance for the fundamental,
preventing harmonic currents from propagating to the
network. This filter has an inductive behaviour for
frequencies lower than the fundamental frequency
and a capacitive behaviour for frequencies higher
than the fundamental frequency, which is a
significant advantage for controlling the current in the
inductor.
Figure 3: Diagram of a parallel passive filter
It is necessary to adopt a design and specific values
for the inductance L and the capacitor C (in (F)), the
value of L (in (H)) being chosen so that the ripple
content is 10% of the nominal current. The chosen
capacitor depends on the reactive power it provides at
50 Hz. Therefore, for our application, we will work
with a reactive power equal to 10% of the nominal
power, and expressed as follows (NEKKAR Djamel,
2014):
C
10%P
32πfV
I
V
16 ∆I
f
Where f is grid frequency, P
is rated active
power, f
is switching frequency and V
is DC bus
voltage.
3 SIMULATION RESULTS AND
DISCUSSION
Based on the above-proposed grid-connected PV
system model, the implementation and simulation
were realized. The proposed system consists of a
GPV connected to a boost chopper which controlled
by the Maximum Power Point Tracking (MPPT)
control of the "Conductance Increment" type. This
type has the advantage of tracking the maximum
power during the rapid change of illumination. The
energy produced by the PV array is 100 KW, and all
the parameters of the PV panel are shown in Table 1.
Then, the connection of these is made by a DC bus
with the inverter, which is controled by a regulation
system to inject a balanced and sinusoidal current
with the minimum of harmonic distortions and the
minimum of power losses and finally connected to the
electrical network. The global horizontal irradiation
(GHI) and average ambient temperature (T amb)
during 2017 are illustrated in Figure 4.
Figure 4: Global solar radiation in (KWh /m^2), at 31°
angle and ambient temperature
(5)
And
(6)
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132
Table 1: PV panel parameters
Paramete
r
Value
Short circuit current (A) 5.96
O
p
en circuit volta
g
e
(
V
)
64.2
Numbe
r
of cells
p
e
r
module 96
Number of series- connected
modules
p
e
r
strin
g
5
Numbe
r
of
p
arallel strin
g
s 66
Maximu
m
current
(
A
)
5.58
Maximu
m
voltage (V) 54.7
Maximu
m
p
owe
r
(W) 306
Parallel resistance (Ω)
993.51
Serie resistance(Ω)
0.037998
Diode saturation current (A)
1.1753𝑒
Light- generated
p
hotocurrent
(
A
)
5.9602
The connection of inverters to the electrical grid leads
to fluctuations, harmonic distortion and power factor
abasement. For this reason, our objective in this study
is to supply an analysis of a grid-connected PV
system with a focus on total harmonic distortion
(THD). The study will suggest a solution to overcome
the high THD during the operation of the solar
system.
(a) (
b
)
Figure 5: The spectral distribution of the network voltage
and current. (without filter)
(a) (
b
)
Figure 6: The spectral distribution of the network voltage
and current. (with filter)
3.1 Interpretation of Simulation
Results
The shapes of the network voltage and current are
shown in Figures 5 and 6 without and with filter,
respectively. Thus, they offer the spectral distribution
of the network voltage and current.
From the figure (5b), we observe the distorted
shape of the current injected into the network, which
shows that these currents are rich in harmonics with
a THD equal to 639.97% and the same for the voltage
45.60%.
We observe from the figure (6b) the improvement
of the shape of the current injected into the network.
Moreover, we can see from figures (6) the influence
of the filter on improving the voltage and the current
injected into the network. The THD is well improved
for the voltage of 45.57% and the current 18.77%.
A grid-connected PV system was simulated under
different solar irradiations using Matlab/Simulink
software. The simulation results proved that the
connecting a PV system to the grid could cause power
quality problems namely harmonics. Thereby, the
efficiency of coupling the passive filter in parallel to
the output of the inverter showed to improve the
quality of the voltage and current injected into the
grid.
4 CONCLUSIONS
This work presents a photovoltaic generation system
connected to the electrical grid. Our objective is to
study the impact of the injection into the grid. This
system injects energy as active power through a
DC/DC converter (Boost) controlled by a
Conductance Increment MPPT algorithm, and an
inverter. The effect of the harmonic problem on the
quality of the power supplied by the GPV was
introduced. Simulation results under SIMULINK
illustrated the effectiveness of adding a passive filter
in parallel to the output of the inverter to enhance the
quality of the current and voltage injected into the
grid. Our future work will be directed around the
development of a control strategy for the inverter to
reduce harmonics and ensure the stability of the
system.
Connection of a Passive Filter in Parallel for Harmonic Compensation in a Grid-connected PV System
133
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