Development of grid-interactive inverter utilising induction motor driven photovoltaic water pumping system

Abstract

The stand-alone solar photovoltaic water pumping system (SPVWPS) remains idle for a significant period of time, when irrigation is not required and when sun is not available. Due to this large idle period, the effective utilisation of SPVWPS assets, i.e. solar photovoltaic array, power electronics converter, and motor, is poor. This study presents an approach to increase the effective utilisation of SPVWPS under the aforementioned idle period. It is proposed to interface the grid with SPVWPS without adding extra power electronic interface. An innovative integrated photovoltaic inverter is constructed using existing SPVWPS components. The inverter enables the transfer of active power and exchange of reactive power with the grid during an idle period of SPVWPS. The three legs of the voltage source inverter (VSI) are interleaved with motor windings. The VSI switches are controlled with synchronous pulse width modulation to force a cophasal current in the motor windings. This accompanies a net motor torque to zero under grid-interactive operation. Hence, the three-phase VSI operates as a single-phase grid synchronise converter, and the motor windings are used as filter inductance. The control system is presented to establish grid-interactive functionality. A prototype is developed to verify system performance. The control system is implemented using the ARM Cortex-M4 microcontroller.