A coordinated control strategy for GFL-ES and GFM-ES to enhance PFR performance of interconnected and disconnected power systems

At present, grid-following energy storage (GFL-ES) and grid-forming energy storage (GFM-ES) have been extensively deployed in power systems, both of which exhibit distinct operational characteristics in primary frequency regulation (PFR). However, their independent participation in PFR leads to unsatisfactory PFR performance in interconnected-disconnected power systems. To tackle this challenge, this paper proposes a coordinated control strategy for the collaborative operation of GFL-ES and GFM-ES. First, an extended frequency response model of the multi-area power system integrated with GFL-ES and GFM-ES is established, and the inherent differences in their PFR characteristics are comprehensively analyzed. On this basis, a collaborative control strategy with phased frequency support is proposed for the coordinated operation of the two ESs. In the interconnected phase, the PFR requirements during the frequency drop and frequency recovery periods are fully considered, and the PFR power of GFL-ES and GFM-ES is adaptively adjusted to fully exploit the respective technical advantages of the two ESs. In the disconnected phase, the analytical expressions of key frequency security (FS) indicators are derived to determine the optimal FS trajectory and PFR coefficients of GFM-ES, where the simultaneous optimization of FS and state of charge (SOC) is achieved. Finally, case studies with different scenarios are carried out to verify the effectiveness of the proposed strategy.