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Roum. Sci. Techn.– Électrotechn. et Énerg.
Vol. 64, 4, pp. 371–376, Bucarest, 2019
1Faculty of Technology Sciences, Frères Mentouri-Constantine 1 University, Algeria
2Institute of Electrical Engineering and Computer Science, Silesian University of Technology, Poland
* Correspondent author: rachid.chenni@umc.edu.dz
COMBINED OPERATION OF PHOTOVOLTAIC AND ACTIVE POWER
FILTER SYSTEM CONNECTED TO NONLINEAR LOAD
HASSIBA SERGHINE1, REDA MERAHI1, RACHID CHENNI1*, DAWID BUŁA2
Key words: Photovoltaic system (PV), Active power filter (APF), Grid connected, Instantaneous power theory, Maximum power
point tracking (MMPT).
Currently, photovoltaic inverters are used in electricity production. They must therefore meet the requirements and needs of the
electricity grid. They are not only used to provide active and reactive power, but also contribute to other tasks such as power
quality, frequency and voltage regulation. This paper presents a photovoltaic system connected to the grid via an inverter
combined with a parallel active filter. The model aims to provide active power to the grid as well as reactive power with a higher
power quality. Thus, this model can compensate for harmonics caused by the grid or non-linear loads. The command of this
model requires a robust and reliable control system to perform the three above-mentioned tasks (quality, frequency and voltage
regulation). Consequently, the instantaneous power method was chosen for this model. This system was simulated in the
Matlab/Simulink program to validate its function.
1. INTRODUCTION
In recent years, renewable energy sources (RES) have
required more auxiliary services on the grid such as
conventional power stations. In addition, these renewable
energy sources must provide clean energy to the grid with
minimum total harmonic distortion (THD).
Photovoltaic power plants are currently being developed
in global electricity generation through the development of
solar panels and PV inverters for the main equipment [1].
Unfortunately, photovoltaic systems only operate during the
day and they are switched off during the night. Therefore,
they will not provide continuous active power to the grid
and their availability rate is low compared to the
conventional power plant [2].
Several studies [3–26] have been carried out to improve
the quality of the PV energy system. These studies are
based on the combination of an active filter with
photovoltaic systems to inject active power with low levels
of total harmonic distortion.
The inverter is the key equipment in a photovoltaic
system because it can control and provide several options
such as active and reactive power supply [9]. The PV
system can also contribute to improve power quality,
voltage and frequency regulation [6]. In addition, its main
role is to transform direct current (dc) energy into (ac) to
adapt the PV parameters to the grid [10].
Two types of inverters are commonly used in the PV
system, the voltage source inverter (VSI) and the current
source inverter (CSI). The first converter VSI needs dc link
capacitor to generate a constant dc voltage and requires an
ac filter inductor to generate ac voltage.
In this work, a voltage source inverter (VSI) is used
instead of the current source inverter (CSI) to provide
reactive power supply [7]. To perform the filtration function,
the PV inverter must inject the opposite current to
compensate for the non-linear current [11].This function also
requires a source to supply the voltage source inverter. Two
condensers dc are used in the proposed system [12]. The
filter control must take into account the dc voltage control.
When a photovoltaic system becomes unavailable at
night or during low illumination days, the installation
remains functional and compensates for grid harmonics [2].
This is considered as another advantage of the proposed
model. Several methods have been used to control PV
inverters [13–15]. The majority of these methods can inject
active and reactive power into the grid, with low or high
harmonics.
This paper presents an analysis and a simulation of a grid
connected PV system with an active power filter (APF).
The advantage of this topology is that it operates with one
voltage source inverter to control active and reactive power
and it compensates for harmonics, unlike the conventional
topologies that need two inverters for this function. The
control of the proposed system is based on the
instantaneous power theory applied to this system.
The reminder of the paper is organized as follows:
Section 2 describes the proposed model and the equipment.
Section 3 introduces the controller used in the model. The
results are presented in Section 4, while Section 5 draws
conclusions and presents some future work.
2. SYSTEM DESCRIPTION
The system consists of a photovoltaic array, a capacitor,
a boost converter with a maximum power point tracker
(MPPT), an input dc capacitor, a voltage source inverter
(VSI) and an inductive filter (Fig. 1). The global system is
connected to the grid and the nonlinear load. In addition, it
uses an alternative solution with a proportional resonant
controller [8]. With an infinite gain at the resonant
frequency, the proportional resonant (PR) controller can
achieve high performance both in the elimination of steady-
state errors in the stationary frame and in the minimization
of load current distortion.
The simple model of a PV cell includes a dc power
source IL, a bypass diode, a shunt resistance Rsh and a series
resistance Rs (Fig. 2) [10]. Two parameters influence the dc
current, the ambient temperature a
T and the solar
irradiation a
G. The mathematical model of the
372 Combined operation of photovoltaic system with active power filter 2
photovoltaic cell is given by equation (1). Many PV cells
are connected in parallel or in series to produce a
photovoltaic module.
sh
s
as
s
pv R
IRV
TKN
IRVq
III .
1
.
.
exp
0
, (1)
where
pv
I- PV current, 0
I- diode saturation current;
s
N - number of series-connected cells;
k - Boltzmann constant (1.3806503 × 10− 23 J/K);
Ta (Kelvin) - temperature of the p-n junction of the
diode;
q (1.60217646 × 10− 19 C) is the electron charge;
s
Rand sh
Rare the equivalent series and shunt
resistances of the module.
To achieve the desired power, several photovoltaic
modules are connected in series Nss and parallel Npp to form
a PV array (2) and (3).
,
.
..
1
.
..
exp
0
ppsssh
ppsss
as
ppsss
pppppv
NNR
INNRV
TKN
INNRVq
NINII
(2)
cellsss VNNV .., VIPpv . . (3)
3. PROPOSED CONTROLLERS
In this work, two controllers were used to manage the PV
inverter [11]. The first one was the dq current; its role is to
inject only an active and reactive power from the PV array.
The second one was a photovoltaic active power filter that
was used to compensate for harmonics and reactive power
in addition to the first controller [17]. The utility of each
controller was compared in the simulation section.
The PV inverter is a three-phase voltage source inverter
compound type: insulated gate bipolar transistor (IGBT)
semiconductor switch; it has a better efficiency and a fast
dynamic response. The voltage source inverter acts on the
IGBT switches to transit the active and reactive power [26].
In this mode, the active power filter function is integrated
with the voltage source current inverter to provide maximum
power generated by the PV system. It compensates for
harmonics and reactive power [1]. The input variables of the
controller’s active photovoltaic power filter are the active
output power of photovoltaic arrays PV
P, the dc input
voltage Vdc, the main voltages of the grid abcGrid
V, the
output current of the PV inverter abcInv
I and the load
currents abcLoad
I. The p-q theory is used to control the
active and reactive power. Figure 3 shows a simplified
diagram of the controller bloc of this system [21].
In this mode, the control strategy of this system must
have two abilities. The first is the dc voltage regulation to
balance the power between the PV units, grid and the load
[19]. The second one is the ability to produce the reference
current to generate the harmonics and reactive power
compensation.
The instantaneous reactive power theory [20] was used to
generate the reference current [11]. This method is based on
voltage transformation and current variables to the αβ
coordinate based on (4):
c
b
a
c
b
a
i
i
i
i
i
v
v
v
v
v.
2
3
2
3
0
2
1
2
1
1
..
2
3
2
3
0
2
1
2
1
1
(4)
The instantaneous active and reactive power [6] can be
calculated on α β coordinates using (5):
ivivtq
ivivtp . (5)
In terms of instantaneous power [18], the currents value
i and
ican be written as follows:
)(
)(
1
tq
tp
vv
vv
i
i
refInv
refInv , (6)
Fig. 1 – The proposed system model.
Fig. 2 – Equivalent circuit of a PV cell.
Fig. 3 – Control block diagram of the proposed system.
3 Hassiba Serghine et al. 373
where, p and q can be considered as the sum of dc and ac
components using (7) :
qqq
ppp ~
~
, (7)
where
p and p
~ are dc and ac components of
instantaneous active power;
q and q
~are dc and ac components of
instantaneous reactive power.
A grid reference current system must involve p
~, qand
q
~and supply the utility with clean energy without
harmonics and eliminate all harmonics caused by the non-
linear load. In addition, the control system must provide the
grid with the maximum active power produced by the PV
system. The last task has the role of the maximum power
point tracker (MPPT) control.
To perform both functions, the reference currents must
be calculated with the coordinates α and β. Equation (5) can
be rewritten using (8):
refInv
refInv
refInv
refInv
q
p
vv
vv
i
i1
, (8)
where refInv
i and refInv
i are reference currents and
vand
v are the grid voltage of the system at α β.
lossgridloadPV PPPP ref , (9)
gridloadrefInv qqq . (10)
Finally, to control the switches of the voltage source
inverter, the above equations must be transformed into the
abc system that coordinates as follows:
ref
ref
cPVref
bPVref
aPVref
i
i
i
i
i
2
3
2
1
2
3
2
1
01
3
2. (11)
4. RESULTS AND DISCUSSION
The system’s performance was tested by simulating the
dq-current and photovoltaic active power filter (PVAPF)
modes in Matlab/Simulink. The objective was to show the
benefits and advantages of the combined system. A three
phase diode bridge rectifier was implemented as a non-
linear load to generate current harmonics in the system.
Table 1 presents the system parameters used in this study.
The system operated in dq current mode during the first
period (0 to 0.1 µs) and as a photovoltaic active power filter
(PVAPF) function during the last second (0.1 µs to 0.2 µs).
The photovoltaic model used in this work is the First Solar
FS -272.
Figure 4 shows that the PV unit can produce 13 kW
during dq current function, but when the photovoltaic
power filter mode is activated, the active power decrease at
10 kW to supply the power necessary for the APF function.
Therefore, this function cannot be use during the day
because the priority is to inject the active power to ensure
the stability and balance of the grid. The APF function can
only be used according to the request of grid dispatcher or
at night to compensate for harmonics and reactive power.
On the other hand, the photovoltaic substation is still
occupied by the MPPT controller to extract the maximum
power from the PV array, thus, it is not logical to use the
active power for other tasks. In this case, the active power
must be retained to supply only the grid and the load
Table 1
System parameters
PV array
Maximum power output Pmax
Output current rating Ipv
Output voltage ratingVpv
13000 kW
35 A
368 V
Dc/ac voltage
source inverter
Output capacitor Cpv
Dc link capacitor
Dc link voltage
L filter
R filter
78.6 μF
154.69 μF
425 V
5 mH
10 Ω
Non-linear
load
R non-linear
Three-phase bridge rectifier
10 Ω
Grid Voltage rms
Frequency
220 V
50 Hz
00.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
0
2000
4000
6000
8000
10000
12000
14000
Tim e(s )
P(W)
PV Active Power
Fig. 4 – Variation of the PV output power.
00.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
0
50
100
150
200
250
300
350
400
450
500
Tim e(s )
Udc(V)
DC Voltage
Fig. 5 – Input dc voltage of PV inverter.
374 Combined operation of photovoltaic system with active power filter 4
because the price of kW and equipment are expensive.
Therefore the dispatcher’s grid promotes the renewable
energy compared to classical energy. Figure 5 shows the
variation of dc voltage.
00.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
-250
-200
-150
-100
-50
0
50
100
150
200
250
Tim e(s )
U(V)
Grid Voltage
Fig.6. a –Grid supplied voltage waveform.
00.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
-50
-40
-30
-20
-10
0
10
20
30
40
50
Tim e(s )
U(V)
Load Voltage
Fig. 6. b – Load voltage waveform.
00.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
-400
-300
-200
-100
0
100
200
300
400
Tim e(s )
U(V)
PV Voltage
Fig. 6.c – PV voltage waveform.
Fig. 7. a – Load current waveform with fast Fourier transform (FFT)
analysis tool.
Fig. 7. b – Grid current waveform with FFT analysis tool.
Fig. 7. c – PV supplied current waveform with FFT analysis tool.
Figures 6 and 7 show the load, utility, PV voltage and
current waveform. It can be observed that the PV inverter
injects the compensating current into the grid system; this
current overlaps the load current to improve the grid
current.
In addition, Fig. 6 shows that the grid current waveforms
are in bad shape due to the nature of the load that generates
harmonics in the grid. From t = 0.1 µs, the photovoltaic
active power filter controller is activated and it begins to
5 Hassiba Serghine et al. 375
reduce the harmonics.
Figure 7 also indicates the fast Fourier transform (FFT)
analysis tool for each current. The total harmonic distortion
(THD) of the load current is 34.08 % and it is higher than
the utility. PV is equal to 26.25 % and 22.66 %,
respectively.
00.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
-20
-15
-10
-5
0
5
10
15
20
25
Tim e(s )
Power(W)
Ac tive power from P V S ys tem
Fig. 8. a – Active power from PV unit.
00.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
-20
-15
-10
-5
0
5
10
15
20
25
Tim e(s )
Power(var)
Reactive power from P V S ys tem
Fig. 8. b – Reactive power from PV unit.
00.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
0
5
10
15
20
25
30
Tim e(s )
Power(W)
Ac tive power from Grid Sy stem
Fig. 9. a – Active power from utility.
00.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
-10
-5
0
5
10
15
Tim e(s )
P ow er(v ar)
Reactive power from G rid System
Fig. 9. b – Reactive power from utility.
00.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
0
5
10
15
Tim e(s )
P ow er(W )
Active power from Load
Fig. 10. a – Active power from load.
00.02 0.04 0.06 0. 08 0.1 0.12 0.14 0.16 0.18 0.2
-6
-4
-2
0
2
4
6
Tim e(s )
P ow er(v ar)
Reactive power from Load
Fig. 10. b – Reactive power from load.
The reactive power from the PV inverter is required to
compensate the reactive power from the grid, as shown in
Fig. 8. From 0.1 µs, the PV system provides the active and
reactive power. In this case, a part of the power is
consumed by the dc capacitor for the APF function. Figure
9 shows that the reactive power is fully compensated by the
APF controller PV.
376 Combined operation of photovoltaic system with active power filter 6
5. CONCLUSION
This paper presented the combination of a grid-connected
PV system connected with a parallel active filter. The
proposed system aimed to provide more options for a
photovoltaic inverter.
In recent years, the photovoltaic inverter has undergone a
major evolution and has become more attractive in the
energy system. Therefore, the combined system can provide
active and reactive power and at the same time it
compensates for harmonics and reactive power generated
by the nonlinear load.
Based on the simulations, it can be noted that the
photovoltaic active power filter (PVAPF) controller is able
to compensate for harmonics and reactive power compared
to the dq-current controller, which can only inject active
and reactive power into the grid.
The control strategy based on the instantaneous p-q
power theory was used in this system to control the voltage
source inverter. The results of the Matlab simulation
demonstrated that the proposed control is more feasible and
effective.
Consequently, other tasks for the PV inverter, such as
voltage and frequency regulation, can be introduced in
future work.
NOMENCLATURE
RnE : renewable energy,
THD : total harmonic distortion,
dc : direct current,
CSI : current source inverter,
VSI : voltage source inverter,
IGBT : insulated gate bipolar transistor,
PVAPF : photovoltaic active power filter,
FFT : fast Fourier transform.
ACKNOWLEDGMENT
The authors would like to thank Mister Nguyen Duc
Tuyen, researcher at Tokyo University of Science, Japan, for
his support in developing the Matlab simulation program.
Received on October 10, 2017
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