Variable Impedance Resonant FCL for Stability Enhancement of Steam-Driven Generators

This paper presents a novel series resonance-based fault current limiter that enhances the transient stability of steam turbine-driven synchronous generators. Unlike conventional series-resonance FCLs with fixed impedance, the proposed design employs duty-cycle modulation enabled by an LQR-based adaptive control strategy to dynamically regulate impedance, thereby enabling adaptability to diverse fault conditions and improving transient stability. Simulation studies show significant improvements in fault current suppression, torque stabilization, rotor speed recovery, active power control, and voltage restoration compared to Bridge-Type fault current limiter (BFCL), Series dynamic braking resistor (SDBR), Parallel resonance fault current limiter (PRFCL), and Series resonance fault current limiter (SRFCL) topologies. A reduced-scale prototype validates fast response, adjustable limitation, and reliable fault ride-Through capability. The key contribution is the integration of dynamic impedance regulation into series resonance-based FCLs, achieving near pre-fault current levels independently of load profile, while offering a compact, cost-effective, and performance-superior solution for modern grids.