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.
- PV Array
- Single Stage System
- Perturb and Observe (P&O) Algorithm
- Direct Torque Control (DTC)
- Speed Sensorless
- Current Reconstruction
- Induction Motor
- Submersible Water Pump
Fig. 1 Scheme of proposed PV array fed IMD
EXPECTED SIMULATION RESULTS:
Fig. 2 Bode plot showing the frequency response of flux observer with the conventional technique
Fig. 3 Performance indices: (a) PV array during starting to steady-state at
1000W/m2 (b) IMD indices at 1000W/m
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
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 Performance parameters of hybrid system (a) PV parameters (S, Vdc, Vpv, Ipv) (b) Battery indices (Vdc, SOC, Vbat, Ibat) (c) Motor indices
Fig. 7 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
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 motor drive 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 array battery 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.
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