Hybrid Grid-Following and Grid-Forming Control for Cascaded PVES System in a Decentralized PLL-Less Framework

The application of Grid-Following (GFL) and Grid Forming (GFM) control in cascaded system has been widely discussed. However, both of them still face challenges such as high dependence on centralized communication, instability in weak grid with phase-locked loop (PLL) in GFL control or transient overcurrent risk in GFM control. Therefore, this paper proposes a hybrid GFL and GFM control for cascaded photovoltaic energy storage (PVES) System according to the different features of sources. A PLL-less GFL control is put forward for ES units, providing inertia support and primary frequency regulation by directly controlling system current. Additionally, the GFM control for PV units combines Maximum Power Point Tracking (MPPT) with an improved power factor angle droop control. This hybrid control approach ensures optimal power distribution between ES and PV units, supports frequency variations, and eliminates the need for PLLs, addressing limitations in conventional control methods. Furthermore, stability analysis, classification of ES modes and capacity design, simulation and experimental results are provided to verify the effectiveness of the proposed scheme.