Modified grid-forming converter control for black-start and grid-synchronization applications

Alassi, Abdulrahman and Ahmed, Khaled and Egea-Alvarez, Agusti and Foote, Colin; (2021) Modified grid-forming converter control for black-start and grid-synchronization applications. In: 2021 56th International Universities Power Engineering Conference (UPEC). IEEE, GBR, pp. 1-5. ISBN 9781665443890 (

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The increasing grid integration of converter- based generation and distributed resources is necessitating a review to the classical synchronous generators dominant network models, and to equip converters with the necessary control capabilities such as inertia emulation and black-start to carry on the required ancillary services provision. This paper proposes a modified grid-forming converter control technique based on virtual synchronous machine (VSM). The modified controller uses a ramping voltage reference to achieve soft transformer energization and eliminate high-magnitude inrush current that can traditionally exceed converters rating. Grid-synchronizing functionality is added to the VSM controller to achieve smooth transition from black-start to grid-connected mode while maintaining grid-forming operation. This is achieved by gradually adjusting the power loop reference through a dedicated synchronizing controller, which is disconnected once grid-connection is achieved. A MATLAB/ Simulink case study is presented to illustrate the controller performance with a 40 MVA simulated converter. The results demonstrate successful black-start sequence execution, starting by soft transformer energization, followed by a block load pickup and grid-synchronization. The sequence is achieved with minimal transformer inrush current, and with seamless transition to the grid-connected operating mode.