SWITCHING MODE PHOTOVOLTAIC PUMPING SYSTEM

Photovoltaic (PV) pumping systems are widely used due to their simplicity, high reliability and low cost. A directly coupled PV pumping system is the most reliable and least cost PV system. However, the d.c. motor-pump group is not working at its optimum operating point. A battery buffered PV pumping system introduces a battery between the PV array and the d.c. motor-pump group to ensure that the motor pump-group is operating at its optimum point. The size of the battery storage depends on the system economics as discussed hereafter. If the battery is fully charged while solar radiation is available, the battery will discharge through the load while the PV array is disconnected. Hence, a power loss takes place. To overcome the above mentioned difficulty, switched mode PV pumping is proposed in this work. When solar radiation is available and the battery is fully charged, the battery is disconnected and the d.c. motor-pump group is directly coupled to the PV array. To avoid excessive operating voltage for the motor, a part of the PV array is switched off to reduce the voltage. As a result, the energy loss is significantly eliminated. Detailed analysis of the proposed system showed that the discharged water increases by about 10%, compared with the conventional battery buffered system. The system transient performance, just after the switching moment. showed that the system returns to steady state in a short period and the system parameters variation lie within 1% of the rated values.