Grid-forming inverters have gained significant attention for their ability to improve stability in weak and islanded power systems; however, the full extent of their potential benefits for the future bulk power system remains uncertain. One potential benefit is increasing stability margins in regions affected by inverter-driven instabilities, such as series-compensated areas within the ERCOT system. This thesis explores their potential in mitigating Wind Sub-Synchronous Control Oscillations (W-SSCI) in series-compensated systems with Type-3 wind plants when a grid-forming configured battery plant is co-located with the wind plant. A novel frequency-dependent virtual impedance (FDVI) controller is proposed to improve the performance of grid-forming battery energy storage systems (BESS). Comparative analyses of grid-forming and grid-following inverters are performed to evaluate their damping capabilities.

This thesis includes the development and verification of models in EMTDC/PSCAD, incorporates impedance scanning, eigenvalue analysis, and time-domain simulations, with the objective of quantifying the minimum capacity of grid-forming BESS needed to provide stability. The results indicate that grid-forming BESS can provide substantial damping to mitigate W-SSCI, even under severe series compensation scenarios. The FDVI controller further reduces the required BESS capacity by up to 45%, demonstrating improved stability through targeted conductance tuning.

Conversely, grid-following BESS inverters are found to be unsuitable for W-SSCI mitigation because of their low admittance at sub-synchronous frequencies and susceptibility to instability under high gains or large BESS ratings. The findings strongly support the adoption of grid-forming inverters as a cost-effective solution for stability-constrained regions, offering superior damping performance compared to conventional technologies.