Skip to Main Content
This paper proposes an autonomous unified var controller to address the system voltage issues and unintentional islanding problems associated with distributed photovoltaic (PV) generation systems. The proposed controller features the integration of both voltage regulation (VR) and islanding detection (ID) functions in a PV inverter based on reactive power control. Compared with the individual VR or ID methods, the function integration exhibits several advantages in high PV penetration applications: 1) fast VR due to the autonomous control; 2) enhanced system reliability because of the capability to distinguish between temporary grid disturbances and islanding events; 3) negligible nondetection zone (NDZ) and no adverse impact on system power quality for ID; and 4) no interferences among multiple PV systems during ID. As the VR and ID functions are integrated in one controller, the controller is designed to fulfill the requirement of VR dynamic performance and ensure small ID NDZ simultaneously. The interaction among multiple PV systems during VR is also considered in the design procedure. Finally, the feasibility of the proposed controller and the controller design method is validated with simulation using a real-time digital simulator and a power hardware-in-the-loop testbed.