This paper aims at the design, control and implementation
of a solar photovoltaic (PV) array fed speed sensorless direct torque control
(DTC) of an induction motor drive (IMD) for water pumping in standalone as well
as battery connected hybrid mode. This stator flux estimated by proposed flux
observer, is used for speed estimation. A DC link current sensor is used to
reconstruct the motor phase currents by modified active voltage vector. One
voltage sensor for DC link voltage sensing and only one current sensor for DC
link current sensing, are used in this system for standalone operation of the
system. All other required quantities are estimated through these two sensed signals.
The IMD is energized by a photovoltaic (PV) array, which is operated at maximum
power point (MPP). A perturb and observe control algorithm with additional flow
rate controller, is proposed for MPP, which tracks MPP throughout the operating
range and provides the facility to control flow rate. The suitability of the
system is judged through simulated results in MATLAB/Simulink as well as test
results obtained on a prototype developed in the laboratory.
KEYWORDS:
1.
PV Array
2.
Single Stage System
3.
Perturb and Observe (P&O) Algorithm
4.
Direct Torque Control (DTC)
5.
Speed Sensorless
6.
Current Reconstruction
7.
Induction Motor
8.
Submersible Water Pump
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
Fig.
1 Scheme of proposed PV-battery system
EXPECTED SIMULATION RESULTS:
Fig.
2 Bode plot showing the frequency response of flux observer with the
conventional
technique
(a) (b)
Fig.
3 Performance indices: (a) PV array during starting to steady-state at
1000W/m2
(b) IMD indices at 1000W/m2
(a)
(b)
(c) (d)
(e)
(f)
Fig.
4 Performance indices during insolation change (a) PV array:1000W/m2-
500W/m2
(b) Induction motor drive:1000W/m2-500W/m2 (c) PV array:
500W/m2-1000W/m2
(d) Induction motor drive: 500W/m2-1000W/m2
(e)
PV array:100W/m2-1000W/m2 (f) Induction motor drive:
100W/m2-1000W/m2
(a) (b)
(c)
(d)
Fig.
5 Simulation results at rated insolation and (a) Rated flow rate (b) 80%
of
rated flow rate (c) 60% of rated flow rate (d) 40% of rated flow rate
Fig.
6 Stator flux trajectory at rated condition of proposed system
(c)
Fig.
7 Performance parameters of hybrid system (a) PV parameters (S, Vdc,
Vpv,
Ipv) (b) Battery indices (Vdc, SOC, Vbat, Ibat)
(c) Motor indices
(a)
(b)
(c)
Fig.
8 Performance parameters during battery charging of hybrid system (a)
PV
parameters (S, Vdc, Vpv, Ipv) (b) Battery indices (Vdc,
SOC, Vbat, Ibat)
(c)
Motor indices
Fig.
9 Starting performance of the drive: (a) 1000W/m2 (b) 500W/m2
CONCLUSION:
The
proposed solar PV array fed water pumping system has been modeled and simulated
in MATLAB/Simulink in standalone and PV array-battery connected modes, and its suitability
is studied experimentally on a prototype in the laboratory. In standalone mode
with PV array feeding water pump, the system comprises of one voltage sensor
and one current sensor, which are sufficient for the proper operation of proposed
system. Moreover, a P&O based MPPT with derating feature technique has been
proposed to regulate the flow rate by controlling the PV array power, thereby
enabling the user to operate the pump for any discharge and flow rate. The
motordrive system performs satisfactorily during starting at various insolations,
steady-state, dynamic conditions represented by changing insolation. The speed
is estimated in stationary flux components by flux observer, which has been
used for DC offset rejection as well as for the satisfactory operation at lower
frequency. The flux and torque, are controlled separately. The direct torque
control (DTC) is achieved with fixed frequency switching technique for reducing
the torque ripple. The line voltages are estimated from this DC link voltage.
Moreover, the reconstruction of three phase stator currents, has been successfully
carried out from DC link current. In addition, a smooth changeover facility
from DTC to scalar control has been provided to ensure the uninterrupted
performance of the system even though the current sensor fails. The switching
signals are generated by space vector modulation technique (SVM) to drive three
phase VSI, which has offered less harmonics distortion (THD) in motor currents
as compared with SPWM technique. Simulation results are well validated by experimental
results. In the second mode, a successful implementation of bidirectional power
flow between PV arraybattery connected systems has been achieved and its
suitability has been checked at various conditions. Owing to the virtues of simple
structure, control, cost-effectiveness, fairly good efficiency and compactness,
it can be inferred that the suitability of the system can be judged by
deploying it in the field.
REFERENCES:
[1] G. M. Masters, Renewable and efficient electric
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[2] R. Foster, M. Ghassemi and M. Cota, Solar
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[3] S. Parvathy and A. Vivek, “A photovoltaic water
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Advancements in Power and Energy (TAP Energy), pp.489-493, 24-26 June 2015.
[4] G. M. Shafiullah, M. T. Amanullah, A. B. M.
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