Indirect Current Control Algorithm for Utility Interactive Inverters for Seamless Transfer

Distributed generation (DG) systems should goes into intentional islanding operation to back up private emergency loads when the main grid is out of electric power. Conventional utility interactive inverters which are normally operated in current mode must change their operation into voltage mode to ensure stable supply voltage for emergency loads when intentional islanding operation occurs in DG systems. During the transfer between current mode and voltage mode, serious transient problem may occur on the output terminal voltage of the utility interactive inverter. This paper proposes reasonal inverter topology and its control algorithm for seamless transfer during intentional islanding operation in DG systems. Filter design guide line and data for LCL filter that is appropriate for the proposed control algorithm are also presented