Synchronization of bus voltages is an essential step before connecting AC microgrids to utility grid, which requires communication among numerous grid-forming converters and thus has become a bottleneck in enabling autonomous operation of microgrids. The Flexible Transfer Converter (FTC) is a viable solution to free microgrids from dependence on communication links, however its potentials have not yet been fully exploited due to the employed conventional linear controllers. Therefore, an optimal control for the FTC to achieve fast and smooth microgrid auto-synchronization is developed in this article. With the derived model-based optimal control trajectories and real-time corrections, global optimization can be obtained in a simple but effective manner. It addresses deficiencies of linear control and model predictive control in handling microgrids with certain inertia. Finally, simulations and experiments of a grid-connected microgrid with FTC are provided to demonstrate its effectiveness.
