Optimal Configuration of Grid-Forming Energy Storage Considering PV Transient Voltage Support Capability

To address rapid frequency decline, transient voltage violations, and excessive configuration costs caused by competition between active and reactive power support in weak grids, this paper proposes an optimal configuration method that incorporates the fault-period voltage-support capability of photovoltaic (PV) inverters into the planning of a grid-forming energy storage system (ESS). A coordinated response model for the ESS and PV inverter is developed, in which the PV inverter provides reactive power through Q-V droop control while smoothing its active power output. An optimization model is then formulated to minimize the annualized ESS cost while satisfying constraints on transient frequency security, voltage recovery, islanded operation, and state of charge (SOC). Frequency security indices, including the rate of change in frequency, frequency nadir, and quasi-steady-state frequency deviation, are explicitly linked to the rated power and energy capacity of the ESS. A hierarchical solution framework integrating capacity search, scheduling while connected to the grid, stepwise transient verification, and steady-state assessment under islanded operation is adopted to improve computational efficiency. Case studies on a weak distribution network show that PV transient voltage support reduces the reactive power requirement of the grid-forming ESS and lowers its configuration cost by approximately 5.2%. Meanwhile, all frequency and voltage indices remain within the prescribed security limits. Further multi-scenario evaluations and sensitivity analyses confirm the broader applicability of the proposed method across different operating conditions.