Shunt-Connected Solar Microinverter for Induction Motor Soft-Starting and Active and Reactive Power Compensation

Induction motors (IMs) are being widely used in irrigation systems due to their high reliability and line-connected starting capability without variable speed drives. However, a line-connected IM requires a high starting current, which can cause power grid instability, high demand charge cost, and premature failure of the irrigation system due to high water pressure. This paper proposes a novel shunt-connected solar microinverter and a novel three-port delta-connected relay configuration that can be retrofitted to the existing line-connected IM system and addresses the high starting current issue. The shunt-connected solar microinverter can soft-start the IM with simple and robust V/Hz control method. Once the IM reaches its rated operating condition, the power source is switched to the power grid within one electrical cycle to minimize the transient current while insuring continuous irrigation system operation. The solar microinverter can continuously provide active and reactive power for a year-long energy saving during both on and off-irrigation season. The proposed solar microinverter can be sized as small as 50% of the irrigation system to substantially reduce the peak starting current.