Controller design and implementation of indirect current control based utility-interactive inverter system

The indirect current control algorithm has been proposed for seamless transfer of utility-interactive inverters. The inverter is able to provide critical loads with a stable and seamless voltage during control mode change as well as clearing time. This paper proposes an indirect current controller based on classical control theory so that the controller gains can easily be determined. Also, a PLL technique is proposed to maintain the constant frequency during the unintentional islanding. A passive islanding detection based on current variation which is suitable for the indirect current control is proposed. The proposed control method is validated through simulation and experiment.