22-04-2014, 11:25 AM
Modeling and fuzzy control of a photovoltaic-assisted watering system
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ABSTRACT
The effective management of water and soil is crucial for countries with main agricultural activities.
Therefore, it is very important to improve practices and irrigation methods to provide suitable and
necessary moisture for proper crop development. In this article, we propose first a study of an irrigation
system suitable for remote sites and using photovoltaic energy as a power source for pumping. After
that, we apply a second fuzzy logic to control the pumping system taking into account the difference
between rainfall soil moisture, temperature, and plant transpiration... We treat the case of vine
plantations located in the region of Mornag, Tunisia.
INTRODUCTION
The consumption of energy is a major global concern;
therefore, it is essential to use renewable energies which
are characterized by their negligible pollution level. The
use of these energies from the single form for remote
sites (small isolated settlements or large agricultural
field), is not supplied by electric power. The use of photo-
voltaic energy for pumping water is an emerging techno-
logy characterized by gradually decreasing cost. Since
the first installations in the late 1970’s, the solar pumping
systems have formed a large part in the implementation
of the projects of solar energy, and they belong to the
most significant applications of photovoltaic systems. This
can be mainly attributed to the fact that it is not
economically feasible to connect such remote sites to the
grid (Moraes-Duzat, 2000).
Solar panel
The operating principle of the photovoltaic cell uses the
properties of solar radiation and semiconductors.
The power supplied by the solar panel can be modified
by the action of temperature and solar irradiations. We
studied the importance of these two parameters on the
control panel located in the Laboratory Research (LACS)
and having the characteristics listed in Table 1.
Figure 1 shows that the power delivered by the panel is
proportional to the irradiations for a constant temperature
T=75°
C. Similarly, the figure (Figure 2) illustrates the
variation I(V) under the effect of temperature for a con-
stant illumination E = 1000 W / m ^ 2.
Pumping system
Photovoltaic pumping is done through an asynchronous
motor that uses either direct or alternate current, leading
to a pump that is made adequate to the needs of drinking
water supply especially in rural or remote sites or for
irrigation as well as watering livestock (Wallace et al.
1998).
Fuzzy logic control
Fuzzy logic (Buhler, 2004; Zadeh, 1996) is a modeling
method that is more effective than most traditional me-
thods, especially for complex systems: systems con-
trolled by human experts, systems with several, inputs /
outputs and non-linear answers systems, where human
observation is the source of input or control rules, sys-
tems where uncertainty persists, especially economics,
natural sciences and humanities (Zimmermann, 1987;
Stopper, 1999; Fustier, 2000; Wang and Tyan, 1994).
The inputs of a fuzzy controller in the system as they
are represented in Figure 9 are: light, temperature, rain-
fall and the added amount of water (irrigation).
The parameters representing the fuzzy controller are
fuzzification using a database of climatic conditions in the
region of Mornag and calculation method that determines
the water requirements of a plant vine throughout the
year, according to the weather conditions (temperature,
rainfall).
Case study: Planting of vines in the region Mornag
The goal of our system is to control the speed and torque
of the motor together and thereafter to ensure good
performance. These pumping systems and solar-electric
driven motors at variable speeds are used more than any
others. In future studies, different methods of command
as the command or fuzzy genetics can be used... For the
good of the systems ordered, it is necessary to determine
the needs of the plant in water, taking into account the
climatic conditions and the nature of this plant (water
needs).
In what follows, we explore the culture of the vine plant-
ings in the region of Mornag to identify these additional
needs in water and model a command to the planting in
this climate (Mornag).
Conclusion
In this paper, we have modeled an irrigation system ope-
rated by solar energy as the only source of energy. This
free and renewable energy is the only available in these
sites.
In the next section, we calculated the water require-
ments of a plant with the formula Riou; we applied this
method on a case study of grape plantation located in
Mornag. We determined from this study, the time of year
where irrigation is necessary to compensate for the lack
of water. We proposed a simple model of an irrigation
system with and without command module. We propose
in future work, control algorithms based on fuzzy logic
and neural network to better optimize the operation of
irrigation system powered hybrid photovoltaic-wind power
taking into account the different climatic parameters
(rainfall, sunshine , humidity, ...) and cultural (nature of
the plant, sun, water requirements ...)