Pvg based smart energy modelling for agricultural sector

International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –
6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME
450
PVG BASED SMART ENERGY MODELLING FOR AGRICULTURAL
SECTOR
Ch.Venkateswra rao1
, S.S.Tulasiram2
, B. Brahmaiah3
1
(PHD Scholar JNTUK, Kakinada, AP, India)
2
( Professor in EEE Department, JNTUH, Hydrabad, AP, India)
3
(Principal at PIT, Tirupati, India)
ABSTRACT
In this paper evaluates ways in which they can be made efficient. The role of
efficiency standards in achieving this goal and the appropriateness of existing standards is
evaluated. With the continuous decrease of the cost of solar cells, there is an increasing
interest and needs in photovoltaic (PV) system applications following standard of living
improvements. Water pumping system powered by solar-cell generators are one of the most
important applications. The fluctuation of solar energy on one hand and the necessity to
optimize available solar energy on the other, it is useful to develop new efficient and flexible
modes to control motors that entrain the pump. A vectorial control of an asynchronous motor
fed by a photovoltaic system is proposed. This paper investigates a photovoltaic-electro
mechanic chain, composed of a PV generator, DC-AC converter, a vector controlled
induction motor and centrifugal pump. The PV generator is forced to operate at its maximum
power point by using an appropriate search algorithm integrated in the vector control. The
optimization is realized without need to adding a DC-DC converter to the chain. The motor
supply is also ensured in all isolation conditions. Simulation results show the effectiveness
and feasibility of such an approach. Results are presented based on MATLAB/SIMULINK.
Keywords: Vector Control, Induction Motor, Solar Power, PV system, Water Pumping
System.
INTERNATIONAL JOURNAL OF ELECTRICAL
ENGINEERING & TECHNOLOGY (IJEET)
ISSN 0976 – 6545(Print)
ISSN 0976 – 6553(Online)
Volume 4, Issue 2, March – April (2013), pp. 450-458
© IAEME: www.iaeme.com/ijeet.asp
Journal Impact Factor (2013): 5.5028 (Calculated by GISI)
www.jifactor.com
IJEET
© I A E M E

451
I. INTRODUCTION
In this paper, the authors present an indirect rotor field oriented control of an
induction motor (IM) associated to a water photovoltaic pumping system. The motor is used
to drive a centrifugal water pump. A modeling study was performed for the components of
the proposed photovoltaic pumping system were established and used in the proposed control
scheme. An extensive simulation work was performed to extract the significant results. To
show up the high system performances, presented results are discussed and prove how the
proposed methodology is an efficient water photovoltaic pumping system control procedure.
In the isolated sectors as the islands, the rural zones and the mountains, the use of the
renewable energy such as wind energy [7-10], photovoltaic [11-13] and hybrid system [14-
17] is a better solution to produce the needed electric energy for such applications as the
pumping systems. The photovoltaic PV water pumping systems are usually composed of a
PV generator, power(s) converter(s) and an electric motor which is usually coupled to a
centrifugal pump load. Currently, for the power conditioning, the PV generator is followed
by a DC-DC converter. Many types are used such as boost, buck and boost-buck converters.
Different types of motors are used in the photovoltaic water pumping system. The DC motor
is used in the photovoltaic water pumping system with different coupling mode [15], [17],
[18]. The Permanent Magnet Synchronous Motors (PMSM) is also used with different
control strategies [10], [19]. Some applications of the pumping system call for the
asynchronous motor [15], [16]. Many techniques of control have been applied to induction
motor as direct torque control (DTC) and field oriented control. The concept of field oriented
control (FOC) is firstly developed by Blasche. The FOC is a flux-torque decoupling
technique applied to AC machines. Two approaches are possible: the direct field orientation
(DFO) based on the rotor flux angle given by a flux observer or estimator and the indirect
field orientation (IFO) based on the rotor slip calculation. In this paper an indirect rotor field
oriented control is synthesized for an induction motor (IM) associated to a water photovoltaic
pumping system in order to produce the required load power. A synchronous boost converter
is used in the control scheme to adapt the DC voltage required by the load when the
insulation or the load varies.
The increasing of the world energy demand, due to the modern industrial society and
population growth, is motivating a lot of investments in alternative energy solutions, in order
to improve energy efficiency and power quality issues. The use of photovoltaic energy is
considered to be a primary resource, because there are several countries located in tropical
and temperate regions, where the direct solar density may reach up to 1000 W/m. One of the
most popular applications of the photovoltaic energy utilization is the water pumping system
driven by electrical motors. The two main restrictions for using solar energy are the high
initial installation cost and the very low photovoltaic cell conversion efficiency. The cell
conversion ranges vary from 12% of efficiency up to a maximum of 29% for very expensive
units [7]. In spite of those facts, there has been a trend in price decreasing for modern power
electronics systems and photovoltaic cells, indicating good promises for new installations.
Moreover, the maximum power of a photovoltaic system changes with solar intensity, and
temperature; and dynamic loads influence the performance by changing continuously the
operating point. In order to amortize the initial investments, it is very important to optimize
the photovoltaic water pumping system, by the use of power electronics converters to adapt
dynamically the electrical impedance to the PV generation for different operating conditions
[2, 3]. Various studies have been carried out on optimizing, PV based systems and induction

452
motor controls [1-20]. DC motors were initially used since they offered easy implementation
with cheap power conversion. A number of existing operational pumping systems have
shown that these schemes suffer from maintenance problems. To overcome this drawback,
brushless permanent magnet motors have been proposed [18]. However, this solution is
limited only for Low power PV systems. The induction motor based PV pumping system
offers an Alternative for a more reliable and maintenance free system [19]. The motor
characteristics are severely affected by the PVG which was considered as a current generator
with dependent voltage source. For such applications, where the PV water pumping system is
driven by an AC motor (PMSM or IM), a chopper and/or an inverter should be included in
order to perform the DC-AC conversion stage. For PV water pumping systems, two types of
pumps are widely used, the volumetric pump and the centrifugal pump. It is found that the
PVG energy utilized by the centrifugal pump is much higher than by the volumetric pump. In
fact, in the case of the centrifugal pumps, the operation takes place for longer periods even
for low insulation levels, and the load characteristic is in closer proximity to the PVG
maximum power locus. In PV water pumping systems, the maximum power point tracking
(MPPT) is usually used as online control strategy to track the maximum output power
operating point of the PVG for different operating conditions of insulation and temperature of
the PVG. Different optimization strategies have been proposed to improve the overall system
efficiency .In this paper a vectoriel control method has been proposed to ensure the
optimization of the whole system showed in Fig. 1. Allowing the improvement of the
efficiency maximization.
Fig. 1. The proposed IM photovoltaic pumping system configuration
II. PV SYSTEM
The PV system considered in this paper contains single PV array as shown in Fig.
2(a).In this paper a PV model is considered from [1-20]. The modeling is attempted by (1),
where, IPV, VPV are the PV array current and voltage respectively. Rsh and Rs are the intrinsic
shunt and series resistances of the array, Isc is being the short circuit current of the array, G is
the solar irradiance (W/m2
), 1910602.1 −×=q C being the electron charge, Boltzman’s constant
23103806.1)( −×=K J/K, p-n junction’s ideality factor 2)( =A , T is array temperature (in 0
K), I0 is

453
diode reverse saturation current, Tr is cell reference temperature and Irr is reverse saturation
current at Tr. For the above PV model, the power-voltage characteristic of the model for
different irradiances is shown in Fig. 2(b).
( )
sh
sPVPVPVsPV
phPV
R
RIV
AKT
VRIq
III
×+
−








−




 +×
−= 1exp0 (1)where [ ]
1000
)(
G
TTkII rscph −+= and














−





=
TTAK
qV
T
T
II
r
oc
r
rr
11
exp
3
0
Fig. 2(a): PV system
Power(kW)
Fig. 2(b): MPPT curves for different irradiances.
Maximum power point tracker (MPPT)
For best utilization, the PV cells must be operated at their maximum power point. To
achieve this, according to the perturb and observe (P&O) algorithm [7-8], MPPT adjusts the
terminal voltage of PV panels to mppV whose value at an instant k, say, is related to the
previous instant by

454
PVPVPVmpp
PV
PV
mppmpp
IVPMV
dV
dP
MkVkV
×===
×+−=
,01.0,0)0(with
)(sign)1()(
(2)
As shown in Fig. 1, since PV panels are directly connected to the dc bus, the dc-link
voltage ( dcV ) equals to the output voltage of PV (VPV). Therefore, the voltage signal, mppV ,
generated by P&O algorithm is, hence forth, treated as the reference dc-link voltage ( *
dcV ).
The direct conversion of the solar energy into electrical power is obtained by solar
cells. A PV generation system is composed by many strings of solar cells in series, connected
in parallel, in order to provide the desired values of output voltage.
III. PROPOSED WORK
The IM Photovoltaic pumping system model
The proposed IM photovoltaic pumping system considered in this work is shown in
Fig. 1.typical model of proposed system is shown in Fig. 3(a). Photovoltaic based water
pumping system is one of the most common applications of distributed energy generation
system. The three-phase inverter generates a variable frequency output waveform to drive the
IM and the motor drives a centrifugal pump that delivers the water output.
In general IM drive can be based on v/f control, indirect field oriented control (IFOC)
and slip control. The IFOC and the slip control ensure the decoupling between the flux
control and the torque control. Those control methods are necessary in order to ensure the
consumption of energy by the machine acting on the electromagnetic torque, Te. Several
types of pumps and motors are available on the PV pumping market. The most commonly
employed pump type is the Centrifugal pump. Single-stage centrifugal pumps are frequently
used in PV shallow water pumping for low head applications. For PV subterranean water
pumping and surface water pumping with higher heads, multistage centrifugal pumps are
more suitable. Other pump types such as progressive cavity pumps and piston pumps have
also been utilized. The centrifugal pump is characterized by its head-flow rate performance
curve at the nominal speed. The flow rate is directly proportional to the impeller speed, the
head is proportional to the square of the speed and the hydraulic power is proportional to the
cube of the speed. The performance curves of the pump with good accuracy at high speeds
but they are not very accurate at low speeds and/or with constant head applications. For very
low speeds, the pressure produced by the pump is less than the static pressure and the rotation
just circulates the water within the pump. When the speed reaches a threshold or base value
(ωt) , the pump starts delivering water and the rate of flow of water (Q, liter/min) varies
linearly with the speed (ω), as expressed in (1) obtained by curve fitting.
Q = aω-b, ω ≥ ωt and Q = 0, ω < ωt Where, a and b are the constants.
The control of induction motor is shown in Fig. 3(b).

455
Fig. 3(a): Typical model of proposed system
Fig. 3(b): overall proposed system
IV. RESULTS
Results are presented based on individual performances of system components and
those are:
Fig. 4 shows the response of dc-link voltage which is equals to the photovoltaic voltage
and from Fig. 4, it is clear that stable dc link voltage is achieved by proposed controller.
The replies in depicted dc voltage are mainly due to rapidly change in temperature and
solar irradiance. The dc voltage of PV system is almost stable at t=0.6sec. initially (at t=0)
it is starting from open circuit voltage because of MPPT algorithm and boost converter.

456
The corresponding output of boost converter is presented in Fig. 5. From Fig. 5, due to
boost controller, it mitigates the ripples in input voltage, i.e., solar panel voltage.
From Figures 4 and 5, it proves that system is working in maximum power point level
with constant voltage algorithm.
Corresponding electromagnetic torque generated by motor and speed of induction motor
are shown in Fig. 6 and Fig. 7 respectively.
The motor speed and torques are reached their reference value, after settling dc-link
voltage. And from Fig. 6 and 7, clearly observed that speed and torques are gradually
increasing because of proper control algorithm implemented in proposed system. And
also, noted that due to good and dynamical enhance of proposed system, almost ripples in
both speed and torque are zero.
Fig. 4: Solar panel voltage
Fig. 5: boost converter output voltage
Fig. 6: electromagnetic torque of induction motor

457
V. CONCLUSIONS
Control strategies to regulate the flow of water supply of a PV based water pumping
system through induction motor is presented in this paper. Hence, proposed system provides cost
effective solution for PV based water pumping system for Agricultural sector. Moreover, for best
utilization of PV, MPPT is incorporated to system. The power balance between PV generation
and load is achieved by maintaining dc link voltage at its reference value (Vmpp) and controlling
the speed of induction motor within permissible limits based on vector control. The proposed
integrated controller requires only measurements of dc link voltage and load current and no need
to measure the power. Through the simulation results it is concluded that performance of the
controllers is satisfactory under steady state as well as dynamic conditions.
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AUTHORS’ DETAIL
Ch. Venkateswara Rao receieved his M.Tech degree from JNTUK, kakinada
and U.G from IE (India, Kolkata) in the year 1993. A life member in
ISTE.&IAENG. This Author won first prize in Energy conservations Award for
the year 2009. He is currently working as a professor in the department of EEE,
Gandhi Institute of Engineering and Technology, Gunupur, Odisha. He guided
many UG & PG Projects. He is having overall Industrial & Teaching experience of
18 years. His major Research interests are energy conservations and Smart Grids.
S S Tulsiram working as a Professor in the Department of EEE in JNTUH,
Hyd. He has 30 years of Teaching experience. He is former Head of the
department of EEE, JNTUCE, Kakinada. The Author has Published many papers
in International & National Journals/ Conferences. His research interests are Power
Systems, High Voltage Engineering & smart grid technology.
B Brahmaiah working as a principal in Priyadharsini institute of techonology,
Tirupati. He has 30 years of Teaching experience .He worked as Head of the
department, EEE & Dean (R&D) in reputed Engineering colleges. Author has
Published many papers in International & National Journals/ Conferences. His
research areas are Electrical machines, Power Electronics &Electric Drives.

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