A Three-Phase Grid-Connected PV System Based on SAPF for Power Quality Improvement

TELKOMNIKA, Vol.15, No.3, September 2017, pp. 1003~1011
ISSN: 1693-6930, accredited A by DIKTI, Decree No: 58/DIKTI/Kep/2013
DOI: 10.12928/TELKOMNIKA.v15i3.5439  1003
Received April 30, 2017; Revised August 1, 2017; Accepted August 15, 2017
A Three-Phase Grid-Connected PV System Based on
SAPF for Power Quality Improvement
Rachid Belaidi*
1
, Ali Haddouche
2
, Djamila Ghribi
3
, M.Mghezzi Larafi
4
1,2
Electromechanical Engineering Laboratory, Badji Mokhtar University, BP 12, 23000, Annaba, Algeria
1,3,4
Development Unit of Solar Equipments, UDES, EPST/ CDER, 42415, Tipaza, Algeria
*Corresponding author, e-mail: rachidbelaidi@yahoo.fr
Abstract
This paper proposes a combined system of three-phase four-wire shunt active power filter
(SAPF), and photovoltaic generator (PVG), to solve the power quality problems such as harmonic currents,
poor power factor, and unbalanced load. In addition, the proposed system can inject the issued energy
from the PVG into the utility grid. To increase the efficiency of the PVG and extract the maximum
photovoltaic (PV) power under variable atmospheric conditions, a maximum power point tracking (MPPT)
technique based on perturb and observe (P&O) is implemented in the DC/DC boost converter. The
effectiveness of the proposed PVG-SAPF (PVG and SAPF) based on the use of synchronous reference
frame theory (SRF theory) under unbalanced nonlinear load. The proposed PVG-SAPF is validated
through numerical simulations using Matlab/Simulink software. The simulation results show the
effectiveness of the proposed PVG-SAPF.
Keywords: power quality, shunt active power filter, SRF theory, PV system and MPPT
Copyright © 2017 Universitas Ahmad Dahlan. All rights reserved.
1. Introduction
In the last decades, renewable energy sources have attracted much more attention due
to the advantages such as less environmental impact and offer clean and abundant energy.
Oday solar energy become one of the most famed energy sources. With the growth of
command tools, solar energy is not limited to the generation of active power into the network,
but it also participates in power quality improvement [1-6]. The traditional passive power filters
was a famous solution for harmonics filtering [4, 7, 8]. However, in functional implementation,
they attend many drawbacks such as limited compensation, big size, and resonance with the
network impedances [4, 9].
New active power filters provide high filtering performances with more flexibility and
reduced size. They have many functions such as harmonic mitigation, correction of power factor
and balancing of the load [4, 9].
To take out the maximum power from the PVG, a lot of MPPT algorithms have been
developed in the literature, the most used methods are “perturb and observe” (P&O) [13, 14].
[10-12] and incremental conductance techniques [13, 14].
This paper presents a simulation of a system composed of a three-phase four-wire
SAPF, and PVG to improve the electrical power quality. The PVG-SAPF controller generates
reference currents using SRF theory under unbalanced nonlinear load. the step-up converter is
controlled using a P&O-based MPPT technique.
The remainder of the paper is organized as follows: the next section presents the
modeling of the PV system, its I-V and P-V characteristics, MPPT and (P&O) technique. The
third section presents the design and control of PVG-SAPF, The fourth section displays
simulation results and discussion and the last section of this paper consists of a conclusion.
2. PV System
2.1. PV Model and Characteristics
A PV solar cell is a semiconductor material that converts solar irradiation into electric
energy [15]. Many models of PV cell are presented in the literature, such as a single-diode [10],
and two-diode model [16].

 ISSN: 1693-6930
TELKOMNIKA Vol. 15, No. 3, September 2017 : 1003 – 1011
1004
The model used in this study is the two diodes model, where the shunt and series resistors are
taking into consideration as shown in Figure 1. The model consists of a current source Iph in
parallel with two diodes, a series resistor RS and a parallel resistor RSh.
Table.1 Technical Module Characteristics
Figure 1. PV solar cell Model with two diodes
The following equation gives the exponential equation of the PV cell current and and the
PV cell voltage:
 
sh
sKTn
IRVq
s
KTn
IRVq
sph
R
IRV
eIeIII
ss



)1()1( 2
)(
2
1
)(
1
(1)
Where V and I represent the output voltage and current of the PV cell, Is1 and Is2 are
diodes saturation currents; q is coulomb constant, K is Boltzman’s constant, T is cell
temperature (K); n1 and n2 are P-N junction ideality factor.
In this paper, the used module is CS5P-220M, the technical module characteristics are
given in Table 1. The I-V and P-V PV module characteristics within STC conditions test are
presented in Figure 2.
Figure 2. I–V and P–V PV module characteristics at STC.
Figure 3 shows the I-V and P-V characteristics of a PV module with different irradiations
and at a constant temperature (T=25C°), while Figure 4 shows the P-V and I-V characteristics of
a PV module with different temperature and at a constant irradiations (G=1000 W/m
2
).
As shown in these figures, the PV power increases with the increasing of irradiance.
Thus, the maximum power point (MPP) decreases with the decreases of irradiance. On the
other hand, the PV power decreases with the increasing of temperature. Therefore, the MPP
increases with the decrease of temperature.

TELKOMNIKA ISSN: 1693-6930 
A Three-Phase Grid-Connected PV System Based on SAPF for Power… (Rachid Belaidi)
1005
Figure 3. I–V and P–V characteristics of a PV module within various irradiations and at a
constant temperature T= 25 C°
Figure 4. I–V and P–V characteristics of a PV module within various temperature and at a
constant irradiation G=1000 W/m
2
2.2. Perturb and Observe (P&Q) MPPT Technique
Among the most used MPPT techniques in the literature is Perturb and Observe (P&O),
because of its low cost, and simplicity [17]. The execution of this algorithm needs current and
voltage sensors to find the output power, and provokes a perturbation on the duty cycle D. Each
sampling period the duty cycle is updated as a power variation function. Figure 5 shows the
flowchart of the P&O algorithm, while Figure 6 shows the Simulink block of P&O algorithm.
2.3. Step-up converter
The step-up converter is applied to connect the load and the PVG for optimum
operation of the system. The step-up converter output voltage (Vout), the PVG voltage (Vin) and
the duty cycle D are gives:
1
1
out
in
V
V D


(2)

 ISSN: 1693-6930
1006
Figure 5. Flowchart of the P&O algorithm
Figure 6. Simulink diagram of P&O algorithm
3. Shunt Active Power Filter Topology
The proposed system (PVG-SAPF) consists of a photovoltaic generator, a step-up
converter connected in parallel with a DC side capacitor, a three-phase four-wire shunt active
power filter based on voltage source inverter, and connected to the network in parallel with three
nonlinear loads.
The effectiveness of the proposed PVG-SAPF counted on the method used for
extracting the reference currents and the switching pulses generation. In this work, SRF theory
[18-20] is used under unbalanced nonlinear load.
3.1. Synchronous Reference Frame (SRF) Theory
Synchronous reference frame theory is used first for three-phase three-wire active
power filter (APF) and gave good results. Then this theory is generalized for three-phase four-
wire APF based on the modification of the cross-vector theory of dqo-axes [21, 22]. The three-
phase instantaneous nonlinear load currents (iLa, iLb and iLc) are modified from the (a-b-c)
coordination into (α-β-0) coordination as follows:








































Lc
Lb
La
i
i
i
i
i
i
.
2
1
2
1
2
1
2
3
2
3
0
2
1
2
1
1
3
2
0

 (3)
In this theory, the PLL (phase locked loop) is used to generate cos (θ) and sin (θ) from
the three-phase source voltage vsa, vsb and vsc. Then the cross-vector theory gives:
















































i
i
i
i
i
i
i
q
q
q
d
0
00)sin(
00)cos(
)sin()cos(0
)cos()sin(0
(4)
The id and iq currents include DC and AC values corresponding to the fundamental and
harmonic currents respectively;














qq
dd
q
d
ii
ii
i
i
~
~
(5)

1007
The DC part of id currents is taken out using a low pass filter. Then the currents in α–β–0
by the following equation:












































q
q
q
d
ref
ref
ref
i
i
i
i
i
i
i
~
00)sin()cos(
00)cos()sin(
)sin()cos(00
_
_
_0
(6)
The estimated current in the coordination a-b-c can be calculated as follows:








































ref
ref
ref
reffc
reffb
reffa
i
i
i
i
i
i
_
_
_0
_
_
_
2
1
2
3
2
1
2
1
2
3
2
1
2
1
01
3
2


(7)
The reference currents are compared with their actual compensating currents in a
hysteresis controller to generate the required switching pulses for the SAPF. Figure 7 shows the
SRF theory Simulink diagram.
Figure 7. SRF Theory under Matlab/Simulink
4. Simulation Results and Discussion
Figure 8 shows the design of the developed PVG-SAPF under Matlab/Simulink software
environment. The characteristics of the proposed system are given in table 2. The PV generator
from CS5P-220M panel model consists of eight PV modules connected in series.
Table 2. PVG-SAPF System Characteristics
parameters Values
Power supply Voltage rms, frequency 220 V, 50 Hz
Line mpedan-ce (Rs, Ls) 0.5 mΩ, 0.19 µH
SAPF Inductance Lf 0.32 mH
DC capacitor Capacitor Cdc 4 mF
DC voltage Vdc 750 V
Unbalanced Nonlinear load
Load1 (Rl, Ll) 6 Ω, 0.012 H
Load2 (R2,L2) 4.5 Ω, 0.09 H
Load3 (R3,L3) 3.6 Ω, 0.01 H

 ISSN: 1693-6930
1008
Figure 8. Matlab/Simulink based simulation of the designed PVG-SAPF
Figure 9(a) shows the different variations of irradiance, the MPPT based on P&O
method follows quickly the prospective maximum power point in a brief time, and it works to
regulate the duty cycle rapidly as presented in Figure 9(b). The P&O MPPT algorithm is robust
against fast variation in atmospheric conditions, with few oscillations around MPP, and with high
efficiency (up to 92%). The output voltage of the PVG is shown in Figure 10(a), while the dc-bus
voltage (Vdc) and its reference voltage (Vdc_ref) are shown in Figure 10.b shows. The results
prove that the system works well because the dc-bus voltage follows the reference voltage
signal under variable irradiance.
The simulation results for the PVG-SAPF performing the current compensation and
considering the three loads presented in Table 2 are illustrated in Figures 11-16. Without PVG-
SAPF, the three nonlinear loads absorb non-sinusoidal currents, the source currents are
deformed, unbalanced, and they are not in phase with their voltages as shown in Figure 11(a).
With PVG-SAPF, which can supply the solar energy from the PV generator into the network, it
injects at the point of common coupling (PCC) a current that is similar to the reference current
(ifabc _ref, Figure 12(a)), but with a phase shift of 180° as shown in Figure 11(b). The
observation of the PVG-SAPF tracking of injected currents ifabc and reference currents iref_abc
is made with nearly zero error for the SRF theory as shown in Figure 12.b. The PVG-SAPF has
enforced waveform sinusoidal source currents as displayed in Figure 11(c); in addition, the
source currents are balanced.
Moreover, the obtained current and the source voltage are in phase as illustrated in
Figure 12(c). Without PVG-SAPF, the form of the neutral current has a maximum value 55 A as
shown in Figure 13(a). With PVG-SAPF, the source neutral current is approximately equal to
zero as shown in Figure 13(b). Figure 14-16 show the FFT analysis of three-phase source
currents (isa, isb, isc) without PVG-SAPF and with PVG-SAPF. The THD’s are given in Table 3.
It can be observed that these THD’s values without PVG-SAPF are very high and unacceptable.
The THD’s are reduced with PVG-SAPF and SRF theory gives very good results under
unbalanced nonlinear loads. The different results affirm the high quality of harmonic mitigation
after using the proposed PVG-SAPF, a flawless compensation of reactive power and the
reduction of the neutral current magnitude are observed.

1009
Figure 9. (a) Variation of Irradiance Ir (W/m2) and (b) duty cycle (D)
Table 3. THD (%) values after and before filtering
Phases THD% before filtering THD after filtering
Phase a 21.11% 2.98%.
Phase b 24.46% 2.67%
Phase c 29.97% 2.50%
Figure 10. (a) PVG voltage V (V),(b) dc-bus voltage ( Vdc( V)) and voltage reference (Vdc_ref
(V)) under varying irradiance
Figure 11. (a) Source currents without PVG-
SAPF, (b) PVG-SAPF injected currents and
(c) source currents with PVG-SAPF
Figure 12. (a) Reference currents, (b) referen-
ce and injected currents and (c) power factor
correction with PVG-SAPF (phase-a)
(b)
(c)
(a)(a)
(b)
(c)
(a)
(b)
(b)(a)

 ISSN: 1693-6930
1010
Figure 12. Neutral source current (a) without PVG-SAPF and (b) with PVG-SAPF
Figure 13. FFT analysis of source current (isa (A)): (a) without PVG-SAPF, (b) with PVG-SAPF
Figure 14. FFT analysis of source current (isb (A)): (a) without PVG-SAPF, (b) with PVG-SAPF
Figure 15. FFT analysis of source current (isc (A)): (a) without PVG-SAPF, (b) with PVG-SAPF
5. Conclusion
In this work, an association of GPV and a three-phase four-wire SAPF and PVG is
proposed. The PVG-SAPF allows harmonics filtering, reactive power compensation for power
factor correction, and load balancing, as well as injecting the issued energy from the PVG into
the network. The SRF theory is used under unbalanced nonlinear loads. A PVG-SAPF
consisting of voltage source inverter is employed. In order to increase the efficiency of
maximum power point tracking, an MPPT control based on P&O is implemented in DC/DC
converter. The simulation of the proposed system has been carried out using Matlab/Simulink
software. The results demonstrate that the source currents have sinusoidal waveforms with very
low THDs after using the proposed PVG-SAPF. In addition, the source voltage and their
corresponding currents are in phase and well balanced, which performs the enhancement of the
electrical power quality.
(a) (b)
(a)
(a)
(a)
(b)
(b)
(b)

1011
The obtained results confirm the high mitigation of harmonic currents, the flawless
compensation of reactive power and the neutral current magnitude reduction for load balancing.
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