A Communication-Less Pre-Synchronization Strategy for Microgrids Based on Temporary Master-Slave Scheme

Pre-synchronization is necessary to reconnect microgrid to utility grid in order to avoid inrush current. The droop control is widely adopted for the operation of microgrid in islanded mode as it ensures power sharing in a decentralized way without critical communication, but during pre-synchronization it needs communication with every inverter to avoid large power sharing error, while in master-slave control scheme only the master inverter needs communication. This paper proposes a new pre-synchronization strategy for three-phase microgrid, in which the microgrid transfers seamlessly from droop control to temporary master-slave scheme after the start of the pre-synchronization, so the need of communication is greatly reduced and the power sharing during the pre-synchronization is ensured. An islanding detection method is incorporated, which facilitates the mode transfers. Besides, simple synchronization criteria are proposed which take into consideration differences of amplitude, phase and frequency without using PLL or arctangent function. Simulation and experimental results are provided to show the effectiveness of the proposed method.