  One critical value microgrids bring to power systems is resilience, the
capability of being able to island from the main grid under certain conditions
and connect back when necessary. Once islanded, a microgrid must be
synchronized to the main grid before reconnection to prevent severe
consequences. In general, synchronization of a single machine with the grid can
be easily achieved using a synchronizer. The problem becomes more challenging
when it comes to a multi-bus microgrid with multiple distributed generators
(DGs) and dispersed loads. All distributed generators need to be properly
controlled in a coordinated way to achieve synchronization. This paper presents
a novel bi-level distributed cooperative control framework for a multi-bus
microgrid. In this framework, DGs work collaboratively in a distributed manner
using the minimum and sparse communication. The topology of the communication
network can be flexible which supports the plug-and-play feature of microgrids.
Fast and deterministic synchronization can be achieved with tolerance to
communication latency. Experimental results obtained from Hardware-in-the-Loop
(HIL) simulation demonstrate the effectiveness of the proposed approach.
