Small-Signal Stability of PV/BESS Grid-Connected System Considering Dynamic of Boost Converter and Negative Sequence Control

Photovoltaic (PV) systems and battery energy storage systems (BESSs) are increasingly integrated into the power grid, raising significant concerns regarding their small-signal stability. Typically, PV and BESS are connected to the grid through a two-stage converter. Under the assumption that the DC bus capacitor is sufficiently large, the dynamics of the two-stage converter are often considered decoupled, with only the dynamics of the grid-connected converter being analyzed. However, due to the drive for smaller capacitor sizes and reduced costs, this assumption may not hold in practice, potentially leading to inaccuracies in the established models. Furthermore, emerging grid codes require grid-connected converters to remain synchronized under non-ideal grid conditions, which necessitates control of the negative-sequence (NS) components in the system. The coordinate transformations with opposite rotation directions, introduced by positive-sequence (PS) and NS control invalidate the Park’s transformation. To address these issues, a linear time-periodic (LTP) model of the PV/BESS grid-connected system is developed by linearizing around the periodic trajectory, incorporating the boost converter and NS control. Based on Floquet theory, the effect of system parameters on the small-signal stability is thoroughly analyzed, especially for the boost converter, which should not be simply overlooked. Finally, the analysis results are verified by simulation.