Adaptive Grid-Following/Grid-Forming Fusion Control of a PV-BESS Grid-Connected System Based on Online SCR Identification

The grid integration of photovoltaic battery storage systems under weak-grid conditions exhibits reduced stability, and abrupt switching between grid-following and grid-forming control causes modulation discontinuities. This paper investigates an adaptive grid-following/grid-forming fusion control method for a 500 kVA photovoltaic battery storage case. A bounded piecewise-linear map schedules a grid-forming weight reference from a short-circuit ratio input, and a first-order low-pass filter limits the weight change rate. An online SCR identification framework is formulated for grid strength scheduling. In the reported reduced-order study, the controller behavior is validated using prescribed SCR trajectories, while the identification procedure is discussed as an implementable scheduling mechanism. A low-order phase margin model selects boundaries of short-circuit ratio low = 1.5, short-circuit ratio high = 7, and Tα = 0.5 s. Four event response cases—a short-circuit ratio step, identification noise, voltage sag, and photovoltaic fluctuation—compare adaptive fusion control with pure grid-following, pure grid-forming, and fixed-threshold switching. A check evaluates scheduled-weight sensitivity to the short-circuit ratio input error. In the weak-grid case, adaptive fusion control reduces point-of-common-coupling voltage oscillation by about 70% relative to pure grid-following and reduces the peak current impulse versus fixed-threshold switching. Under a ±10% short-circuit ratio error, the scheduled weight changes by at most 0.055.