Design and Development of a Solar PV Inverter for Water Pumping Applications
Abstract Proper management of irrigation is one of the major challenges faced by the agriculture sector in India. In a country where agriculture is practiced mostly in the interior parts, the availability of grid is very much irregular thus restricting mechanization and adoption of new technologies in this sector. Power generation from conventional resources cause pollution and their exhaustion is bound to occur very soon. In this context, utilization of the naturally available solar power for operating irrigation pumps could be a plausible solution to the farmers in the rural areas. This paper describes the design and development of a solar photovoltaic (PV) inverter which is used to drive a water pump for irrigation purposes. The inverter output is fed to a three phase ac induction motor which drives the pump. The inverter can be operated in two modes the former, using MPPT (Maximum power Point Tracking) technique, wherein the dc-dc converter is controlled in such a way that the solar PV panel is always operated at the maximum power point and the latter wherein the flow rate of the pump is controlled by varying the speed of the motor by means of an inverter. Design aspects of the inverter and the control strategy involved are also presented in this paper.
Agriculture provides employment opportunities to nearly two-thirds of the Indian population and contributes significantly to the national income. India ranks second worldwide in farm output and earns foreign exchange. Even though agriculture plays a significant role in the Indias socio- economic development its contribution to the GDP is drooping  . Slow agricultural growth is a thought of concern because most of our population is dependent on rural employment for a living. The agricultural practices that are currently followed are neither economically nor environmentally sustainable and hence the yields of many agricultural commodities produced in India are low. Poorly maintained irrigation systems and lack of good infrastructure for implementing modern technologies in farming are some of the important factors responsible for this scenario.
Irrigation in India can be broadly classified into two types- surface irrigation and ground irrigation. In case of surface irrigation, there is no effective management for the volume of water stored, the volume used for irrigation or on what volume can be added to this water. Therefore the farm output and hence the economy relies solely on the Monsoon season. Ground water extraction involves utilization of underground water which causes environmental problems when the user
consumes water disproportionately. This creates problems for the other users and affects the water table as well.
Improving the irrigation systems that are currently prevalent can improve the production and bring about a significant growth in our economy. Water pumps used for irrigation need either electricity or diesel. The non- availability of electricity and the cost of fossil fuels make the farmers reluctant in implementing proper irrigation techniques. Utilization of solar energy to run water pumps could be a blessing in disguise to the rural population who are engaged in agriculture.
Solar water pumps are driven by either dc motors or ac motors. The dc voltage generated by the solar PV arrays are inverted, filtered and fed to an induction motor  . The block diagram of a solar water pump is as shown below.
Fig 1. Block Diagram of a 3 phase Solar Water Pump
For dc motors the dc voltage from the solar panels are used to control the motors which in turn adjusts the flow rate of the pump[3,4] . In case of ac motors, the dc voltage is converted into ac voltage by means of an inverter and then the filtered output is used to run a single phase or a three phase motor.ad then varying the amplitude and frequency of the voltage supplied to the motor with their ratio being a constant results in constant flux and hence constant torque as long as the current remains unchanged. So the motor is capable of providing continuous adjustments of speed and torque to a mechanical load. By keeping the slip constant at any speed for a given load, the losses can be minimized for various load conditions. Flow-restricting valves or moveable air vanes are frequently used to control flow rate for the applications where flow requirements vary. But this may cause frequent maintenance issues for the mechanical equipment involved. Variable-frequency drives enable pumps to operate under fluctuating demand and consuming less energy at the same time meeting the pumping needs.