Co-Optimization of Inertia and Droop Control Coefficient for Grid-Forming Photovoltaic-Storage System Considering Capacity Limits

As the renewable energy's share in the power system continues to increase, the inertia level of the system gradually decreases. The effective approach to tackle frequency stability issues is to configure energy storage to enable photovoltaic (PV) power generation to provide inertia and primary frequency regulation support. Excessively small frequency support parameters cannot fully utilize the frequency regulation capabilities of the photovoltaic-storage system, while excessively large parameters may lead to power limit violations of the energy storage or converter during transient processes, posing a risk of equipment damage. To address this, an optimized configuration method for the inertia and primary frequency regulation parameters of photovoltaic-storage systems, considering capacity constraints, is proposed. Firstly, an analytical relationship between frequency deviation, frequency dead zone, primary frequency regulation coefficient, and converter output is established based on the control equations of the grid-forming photovoltaic-storage system. This relationship allows deriving the feasible boundary of the primary frequency regulation coefficient that ensures the converter and energy storage outputs do not exceed their limits. Secondly, with the constraints of the photovoltaic-storage system's capacity limits and its dynamic equations for participating in transient frequency support, an optimization model for maximizing the frequency nadir of the photovoltaic-storage system is established to determine the optimal virtual inertia coefficient. Finally, simulation analyses verify that the proposed method can fully utilize the transient frequency support capabilities of the photovoltaic-storage system under various scenarios while satisfying capacity constraints.