Abstract
This paper explores the use of the recently proposed dual grid-forming control applied to modular multilevel converters and enhanced by embedded energy storage. Dual grid-forming technique enables the converter to form both ac and dc grids by leveraging its internal energy, while the embedded energy storage provides damping to the grid, thereby improving its stability margins. The application of dual grid-forming in a modular multilevel converter is characterized by using its internal power balance as a synchronization mechanism. The addition of controllable and decoupled energy storage provides a new and promising degree of freedom. On this basis, two innovative damping provision methods are proposed and compared with the existing solutions by means of small-signal eigenvalue analysis and time-domain numerical simulations. Results show enhanced system stability margins, with an increased damping ratio of the critical eigenvalue from 10% to 60%, and a lower perturbation of system variables when using the proposed strategies.