Self-adaptive control for grid-forming converter with smooth transition between microgrid operating modes

This paper proposes a new solution for multiple grid-forming converters to achieve the four main objectives required: (i) accurate output active and reactive power control in grid-connected mode; (ii) seamless transitioning from grid-connected to islanded mode; (iii) autonomous power sharing among dispersed converters; and (iv) smooth reconnection of multiple gridforming converters to the main grid. The first three objectives are guaranteed with the well-known three cascade control loops (power-voltage-current) implemented with saturators at the power controller; besides, this paper contributes with a method to properly design the power-loop controllers and orientations for practical applications. The fourth objective is the reconnection process that uses the triple-loop control and a central controller with a synchrocheck relay at the microgrid point-of-commoncoupling. The synchronization is based on slip frequency that does not require high-speed communication between distributed generators and central controller. Such feature is the main novelty proposed herein, besides of its resilience to grid voltage variation and absence of critical islanding detection. Real-time hardware-in-the-loop results show the feasibility of the proposed self-adaptive grid-forming converter.