lamkaddem2016

Design and Modeling of a Photovoltaic System
Connected to the Electrical Network
Ali LAMKADDEM *
Khalil KASSMI*
Laboratory of Electromagnetic, Signal Processing &
Renewable Energy LESPRE,
Team Electronic Materials & Renewable Energy EMRE
Mohamed First University, Faculty of Science, Department
of Physics, Oujda, Morocco
E- mail: [email protected]
Laboratory of Electromagnetic, Signal Processing &
Renewable Energy LESPRE,
Team Electronic Materials & Renewable Energy EMRE
Mohamed First University, Faculty of Science, Department
of Physics, Oujda, Morocco
E-mail. [email protected]
Abstract— in this paper we propose the structure and the
functioning of a photovoltaic (PV) connected to the electric
distribution and transmission network, equipped with the
malfunction detection blocks. The studies that were carried
focused on the injection of a power of 16 KW, produced by a PV
panel field, on the electrical network of medium voltage (25 KV).
In order to the reliability of the injection system on the network
and minimize power losses, we have inserted the blocks that
control the opening and closing of power switches of the DC / AC
converter that synchronize the phase, amplitude and that the
frequency of the voltage and the current injected on the power
grid. The obtained results show that the designed system detects
the dysfunction of the network side system (voltage dips, phase
load shedding, frequency fluctuation, imbalance three-phase
system), the field side of PV panel (distrust converters ...) and
ensures the injection of electrical energy on the network during
operation of the PV system.
Keywords— Photovoltaic Energy; DC / DC converter; Threephase inverter; PWM control; MPPT control; Injection on the
electrical network; Electrical network disturbances; Detection of
malfunction, Power electronics.
I.
INTRODUCTION
The connection of PV Photovoltaic systems to the
distribution network can have some impact on the power
grids: impacts on the change in power flows, in the voltage
plane, in the protection plan, in the quality of the energy or in
the Network planning [1][2][11].... The characteristics,
operation and disturbances on the distribution networks induce
problems, not yet solved, which influence the functioning of
PV systems [5] [1][7] [8]. This induces is the failure of the
blocks constituting the PV chain [4][14]: PV generator, DC /
DC converter and inverter, control blocks (MPPT ...),
To solve these problems, we propose an optimized PV
system structure, connected to the network through DC / DC
boost converters and a three-phase inverter controlled by an
MLI control. In order to control and synchronize the phase and
the amplitude as well as the frequency of the voltage and
current injected into the electrical network, we use a reliable
MLI control which provides a signal obtained by comparing a
triangular signal with three signals obtained by transforming
Park and PLL[3][6][14].
In this article, we present the first results concerning the
design and simulation of the functioning of the PV system
designed, connected to the distribution and transport network.
II.
STRUCTURE OF THE PV SYSTEM CONNECTED
TO THE NETWORK
The structure of the PV system, connected to the electrical
network, designed during this work is shown in figure1.
The different blocks of this system are:
• PV generator
•
Optimization block of the PV generator which is
formed by a DC / DC converter and an MPPT control,
•
DC / AC (three-phase inverter) converter is controlled
by a MLI control which provides a signal obtained by
the comparison between a triangular signal and three
signals obtained by the Park and PLL transform. The
objective of this control is to control and synchronize
the phase and the amplitude as well as the frequency
of the voltage and the current injected on the electrical
network,
978-1-5090-4947-9/16/$31.00 ©2016 IEEE
A malfunction detector which has the function of
detecting any malfunctions in the chain and ensuring
the production of the electrical energy optimized by
the PV system,
•
Transformer to isolate the photovoltaic system from
the network, as well as the output voltage of the DC /
AC converter to the desired level (depending on the
network)
•
Electricity network (25 KV) to inject the energy
produced by the PV system into the medium voltage
power grid.
DC/DC
converter
DC/AC
converter
Transformer
320V/20KV
Le=800W/m2
MPPT
contrôle
Le=600W/m2
voltage (V)
fig.2 . Electrical quantities P (V) and I (V) of the PV panel fields
as a function of the illumination.
Electricity
network
T=20°C
Power (W)
PV
generator
Le=1000W/m2
Current (A)
•
T=40°C
T=60°C
PWM
contrôle
voltage (V)
Malfunction detector
III.
FUNCTIONING AND DISCUSSION
A. PV generator:
In order to produce a photovoltaic power 16 kW, we used a
photovoltaic panel field with a power of 60W. Typical currentvoltage characteristics and power - voltage module array are
shown in Figure 2-a, as a function of the illumination. It
appears that under the standard conditions, illuminance of
1000W/m2 and temperature of 25 ° C, the field of PV panels
delivers a power of 16.78 KW, a current of 76.28A and a
voltage of 220V (Figure 2).
Otherwise, as shown in figure 3, the performance of a PV
generator is strongly influenced by the temperature: an
increase of 10 ° C. induces a degradation of 9%.
Le=1000W/m2
Power (W)
Le=800W/m2
Le=600W/m2
voltage (V)
Current (A)
T=20°C
fig.1 . Block diagram of the PV system designed, connected to the grid.
T=40°C
T=60°C
voltage (V)
fig.3 . Electrical quantities P (V) and I (V) of the PV panel field
as a function of temperature for 1000 W/m2 illumination.
B. DC / DC converter with MPPT
In order to extract at each instant the maximum power
supplied by the field of panels and to transfer it to the load and
therefore to the electrical network, we used as a matching
stage a boost DC / DC converter controlled by a Digital MPPT
command. The role of the MPPT controller is to calculate and
monitor the power, following an algorithm of Figure 4 that
based on the Hill-Climbing technical [16] [17], the principle is
to calculate the derivative of the power and to modify the duty
ratio as a function of several parameters such as the derivation
of the power at the end of the time delay and of the variable
state used, in order to generate an optimal duty cycle which
controls the DC / DC converter.
The typical electrical quantities obtained at the output of
the Boost converter and the MPPT control is shown in figure
6. It appears that the duty cycle of the PWM signal (the order
of 0.44) and the electrical quantities at the output of the
converter = 16 kW, current = 28.40A, voltage = 565V are
consistent with the optimal ones (Figures 2 and 3).
Ce
D
L
Ipv
Is
D
Vpv
Vs
CS
G
Current Is
Rch
S
Vpv
PV
generator
MPPT
Control
Ipv
Power Ps in (KW)
fig.4 . Structure of Boost Converter equipped with digital MPPT control.
Power calculation derived
YES
NO
Dp>0
fig.6 . MPPT control, Electrical quantities of the Boost converter
(voltage, current, power).
NO
NO
YES
NON
YES
Vmax >V >Vmin
Time> Delay
V<Vmin
YES
NO
YES
DV>0
YES
DV<0
NO
V state
TMP
Vstate
YES
A
A+n
1-V state
0
T1
1-Vstate
Vstate=1
C. DC / AC converter (Three-phase inverter)
The switches of the three-phase DC / AC inverter (figure
14) are MOSFET transistors, equipped with freewheeling
diodes, with voltages greater than 600V and current of the
order of 60A.
Va
Vb
Vc
A-n
T4
T2
fig.5 .
T5
Vdc
NO
A
T3
T6
MPPT control algorithm (Hill-Climbing)
MPPT Control
fig.7 .
Circuit de l’onduleur triphasé.
1) System for protection and control of three-phase
inverter switches.
Voltage Vs
The power system uses a closed-loop control to regulate
the power of the three-phase inverter. Power electronics
systems, loads tend to have dynamic properties and power
conditioning, the system equipment possesses dynamic
properties like inductors and capacitors and some controllers
introduce delays. The power converters behave as a nonlinear impedance which contains discontinuous nonlinear
differential equations. These systems are still difficult to
analyze although they have been simplified. For a regular
three-phase voltage, the equation is given by [13]:
=
cos(
)
=
cos
−2
+2
=
(
3
3)
(eq.1)
The equation (eq.1) clearly indicates the three-phase
voltages are out of phase by 120 degrees of delay for each
phase. In order to organize this non-stationary system in a
fixed system, the transformation of the three simple DC
component phase systems is necessary. To achieve this
objective, three phase voltages can be seen as three voltage
vectors that are rotating in three-dimensional space
[13][14][6].
The transformation function used in this paper is Park
Transformation (equation 2) and their inverses transform
(equation 3), given by:
Va =Vd sin(wt) +Vq cos(wt) +V0
Vb =Vd sin wtVc =Vd sin wt+
2π
3
2π
3
+Vq cos wt-
2π
+Vq cos wt+
3
2π
3
+V0
éq(2)
+V0
Vd =
(
)+
+
+
+
Vq =
(
)+
−
+
−
V0 = (
+
+
éq(3)
Various disturbances can occur on the power grid (voltage
dips, phase jump, harmonic, and imbalance…). The purpose
of the PLL synchronization system is to reconstruct
information on the direct component of the fundamental
voltage and the PV system (Variation Of illumination,
variation of temperature) the synchronization between the
inputs signal and the output signal of the PLL is given in
figure 15.
The characteristic of the voltages (Vdr, Vqr) of the threephase voltages of the network (Vra, Vrb, Vrc) expressed by
the PLL in the Park domain is given in figure 17.
The results of the simulation obtained from our control and
control system show that the system is synchronized for a
short time (in the order of 0.08s), then the PLL block ensures
the synchronization of the control with respect to l The
evolution of electrical network voltages.
Ia Ib Ic
Va Vb v c
)
θ
ABC
DQ
The various simplifications carried out after analysis of the
system enabled us to conclude that the setpoint currents at the
output of the upstream control will be injected at the point of
connection of the PV production. These currents are calculated
by means of the power references and the voltage
measurement at the connection point; these will be calculated
in the Park repository according to Equations (4) and (5) [9]:
=
.
+
.
= (
.
−
. ) éq(5)
PWM
Control
Vdr
DQ-PLL
ω
Iqref
Vdc
+ Vdc_ref
∑
Voltage
Regulator
ABC
DQ
Park
Transformation
Vqr
Idr
Iqr
+ ∑
+ ∑
éq(4)
θ
Current
Regulator
dd
dq
=
( .
.
(
( .
(
.
)
)
)
)
ABC
inverse Park
transformation
fig.8 . Structure of the protection system.
From the latter equation, the following two equations (7)
and (8) are deduced [9]:
=
DQ
a
éq(6)
éq(7)
With:
 P and Q: are the reference powers of photovoltaic
production.
b
 Vd and Vq: are the direct and quadratic components
of the voltage, in the Park repository.
 Id and Iq: are the direct and quadratic components of
the current produced by PV production on the
network.
Figure 16 shows the voltage of the normalized amplitude
network and the variation of the angle q which varies from 0
to 2π. The results obtained show that at the beginning of the
simulation, the signal obtained at the output of the PLL (sinθ,
cosq) is ahead of the signal of the voltage of the electrical
network, after some time the PLL seeks to render the two
Signals in phase.
fig.9 . a- Synchronization at start of simulation.
b- Synchronization after some time of the simulation.
K1
K2
K3
fig.10 . Synchronization between the input signal and the output signal
of the PLL
K4
K5
K6
fig.11 . Characteristics of the voltages (Vdr, Vqr) expressed in the Park
domain.
2) PWM control
The block of the MLI control is done by means of simple
assembly given in figure 12. The principle of this control is to
compare the reference signal obtained by the Park transform
with a signal called carrier signal. This comparison results in
obtaining the control of the power switches in order to obtain a
modulated sinusoidal voltage of amplitude, phase and
frequency compatible with that of the electrical network.
This block is composed of a comparator which compares a
triangular signal with a reference sinusoidal signal, the
reference signals are shifted by 2π / 3, going from one inverter
arm to the other.
This block is composed of a comparator which compares a
triangular signal with a reference sinusoidal signal, the
reference signals are shifted by 2π / 3, going from one inverter
arm to the other.
The mission of the last block (NOT) is to invert the result
of the RELAY to send it to the MOSFET at the bottom of the
arm. figure 12 shows the waveform of the MLI control of the
switches of the MOSFET transistors.
fig.13 . Control MOSFETs
D. Overall operation of the PV system connected to the
grid:
The voltage inverter connected to the electrical network is
specified mainly by voltage and current injected into the
distribution network produced by a PV panel field [10].
The results of simulation of the injection of all the active
power to the power grid as well as the reactive energy which is
practically nil are shown in figure 14. While the power
injected is characterized by a power factor equal to 1 (figure
15).
The typical results of the electrical quantities obtained at
the output of the inverter such as the voltages of the three arms
of the inverter are purely sinusoidal, with an effective
amplitude of 220 V shifted by 2π and a frequency of 60 Hz
(figure 16-b) , While the shape of the voltage obtained after
the transformer is shown in figure 16-a.
It can be concluded from figure. 14 that the reactive power
is zero and the active power reaches a maximum value, which
explains the single injection of the active power on the
electrical network. Moreover, it is seen that the signals are
sinusoidal at the Output of the inverter.
1
1
va-ref
Add
S1
Relay
NOT
Logical
Operator1
2
vb-ref
Add1
NOT
Logical
Operator3
4
V-porteuse
3
4
S4
5
vc-ref
Add2
Active power
S3
Relay1
3
2
S2
S5
Relay2
NOT
Logical
Operator4
fig.12 . PWM control block in MATLAB / Simulink
Reactive power
6
S6
fig.14 . Characteristic of active and reactive power injected into the grid
with that of reference and eliminates the disturbed signal
amplitude (figure. 18).
We also simulated the case of unbalance of frequency on
the signals of the electrical network and we noticed that the
phase locked loop regulated the unbalanced frequency (figure
18). Also, in the case of presence of phase shift in the
electrical network signals (Figure 19), the PLL system has to
control and regulate the phase angle and jumps inflicted with a
very short time.
fig.15 . Power factor
a
b
When triggering the PV Panel field, or one of the converter
power switches, the shape of the voltage and current signals
supplied to the user are not influenced by the presence of the
transformer.
According to the results obtained after the creation of the
disturbances on the electrical network, we find that the
synchronization system aims to reconstruct the information on
the direct component of the fundamental voltage after the
comparison of the currents and the disturbed voltages with its
references. Our control system makes the system stable in a
very short time.
a
c
b
fig.16 . Form of the electrical quantities obtained at the output of the
inverter as well as the voltage of the electrical network in
medium voltage.Tension du réseau électrique
a- The voltage at the inverter output
b- The current injected into the power grid
E. Detection of malfunction
Electrical disturbances affect one of the following
parameters: frequency; The amplitude of the three voltages;
The waveform which should be as close as possible to a
sinusoid; An unbalance of the three-phase voltage system; The
presence of harmonics and / or inter-harmonics.
The influence of the various perturbations mentioned
above on the system realized, such as amplitude variation,
frequency and phase, figures. 17, 18, 19, show that the
protection and control system (Park Transform And PLL)
made it possible to regulate and manage the various
parameters all while keeping their values that is to say,
manages to synchronize the shape of the three-phase voltages
and currents of the system and eliminate the disturbances in a
very low time of order of 2 ms.
Moreover, we observed that when the amplitude of the
disturbances is important, the system compares this amplitude
fig.17 . the shape of the electrical quantities obtained at the output of the
inverter when disrupts the amplitude of the voltage of the
electrical network.
a- The voltage at the inverter output
b- The current injected into the power grid
a
b
[3]
[4]
[5]
fig.18 . The form of the electrical quantities obtained at the output of the
inverter after the change in the frequency of the electrical
network.
a- The voltage at the inverter output
b- The current injected into the power grid
a
[6]
[7]
[8]
[9]
[10]
b
[11]
[12]
fig.19 . The form of the electrical quantities obtained at the output of the
inverter after the phase jump on the electrical network.
a- The voltage at the inverter output
b- The current injected into the power grid
IV.
CONCLUSION
In this paper we have presented the results of the
simulation of the PV system connected to the network,
equipped with malfunction detection blocks. This system,
designed during this work, has the particularity of
synchronizing the waveform, the voltage and the current of the
disturbances (amplitude, frequency, phase, etc.). The results
obtained show, on the one hand, the speed and the precision of
the proposed method and, on the other hand, the good
functioning of the photovoltaic system designed which gives
the network a function independent of the disturbances (purely
sinusoidal, effective 220V and Frequency 60 Hz).
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