Grid-Connected PV Inverter for Driving Induction Machines With Synchronous Scalar Control

Abstract

Induction machines (IMs) are used extensively in irrigation systems due to their high reliability and line-starting capability directly from the power grid without requiring variable speed drives (VFDs). Nonetheless, line-connected IMs draw a substantial starting current from the grid, leading to grid instability, heightened demand charges, and premature failures in irrigation systems due to excessive water pressure. Although VFDs can effectively alleviate the starting current, their associated costs for equipment, installation, and maintenance are higher than line-connected IMs. Consequently, this results in limited adoption in the market. This paper proposes a shunt-connected photovoltaic (PV) inverter with a newly devised synchronous scalar control technique to tackle this issue. This system can be retrofitted into existing line-connected IM setups to reduce the excessive initial current effectively. Once the IM attains its rated operating state, the power source is seamlessly switched from the PV inverter to the power grid within two electrical cycles. This minimizes transient currents while ensuring uninterrupted operation of the irrigation system. The PV inverter can supply continuous active and reactive power, resulting in energy savings throughout the year during irrigation and off-irrigation seasons. Moreover, the proposed PV inverter can be dimensioned as small as 50% of the irrigation system, significantly reducing the peak starting current. Simulation and experimental results closely align, demonstrating the favorable soft-starting performance of the inverter.

Keywords

• Induction machine
• irrigation
• PV inverter
• scalar control
• soft-starting
• starting current