Uniformity of Frequency Support Between Grid-Following and Grid-Forming Converters

Grid-connected renewable energy for frequency support of the grid is conducive to improving the grid frequency security level. Grid-following (GFL) converters and grid-forming (GFM) converters are two important types of equipment to support renewable energy integration into the grid. Both GFM and GFL have a variety of different control strategies when performing frequency support. Clarifying the relationship between different strategies of GFM and GFL when performing frequency support will provide guidance for renewable energy frequency support. This paper investigates the grid frequency regulation characteristics of five common control schemes applied in converters of renewable energy. First, it reveals the uniformity between the damping path and governor path in virtual synchronous generator (VSG)-based GFM control. Then, the necessary conditions for achieving frequency-support uniformity among droop-based GFL control, integrated inertia-based GFL control, droop-based GFM control, and VSG-based GFM control are revealed. Furthermore, the application scenarios and limitations of the established uniformity theory are discussed. Finally, using the doubly-fed induction generator (DFIG) as an example in MATLAB/Simulink and Opal-RT, the proposed theory is comprehensively validated.