A multi-mode active frequency support strategy for a grid-friendly integrated PV-ES system

The integration of photovoltaic (PV) and energy storage (ES) is an effective solution to mitigate PV output fluctuations and enhance solar energy utilization. However, existing PV-ES coordination schemes are often limited by insufficient consideration of source-side support capability, grid-side frequency demands, and source-grid interaction. These systems typically operate in a passive manner, merely complying with grid codes rather than actively supporting the grid, thereby limiting the development of power systems with high penetration of renewable energy. To address these limitations, this paper makes the following contributions. First, theoretical analysis reveals that the dual-stage PV system possesses inherent advantages in active frequency support due to its wide-range power regulation capability, which provides a topological guideline for designing grid-friendly integrated PV-ES systems. Second, the active frequency support performance of the PV-ES system is enhanced by optimizing the reserved capacity of the energy storage system. It is theoretically proved that state-of-charge (SOC) balancing among ES units can maximize the system’s transient frequency support capability. Third, a multi-mode active frequency support strategy that simultaneously considers grid-side and source-side requirements is proposed. It enables a coordinated and flexible interaction between the grid and PV-ES system, achieving a balance between active support and economic operation. Experimental validation confirms that the proposed control strategy is both feasible and effective.