A Novel Open-Loop Method to Synchronize an Islanded System With the Main Grid

This paper presents a novel method for synchronizing an islanded system to the main grid without feedback control. The idea is based on the understanding that the main concern in synchronization is the switching transients. Therefore, we propose to use preinsertion impedance to reduce the transients. In addition, the impedance is selected such that the transients are acceptable as long as both parties operate in pre-established operating conditions. As a result, feedback control to adjust generator voltage and frequency and the associated communication link are avoided. The proposed approach could result in significant cost savings for islanded systems located in remote areas. In addition, the extra effort required for generator adjustments, especially for multiple units, can be eliminated. Technical considerations and design method for the selection of the impedance size are presented. Simulation studies are conducted to evaluate the performance of the method. The results prove that the transients can be effectively reduced and open-loop synchronization is indeed achievable.