DSOGI-PLL-Based Coordinated Fault Ride-Through Control Strategy for Direct-Drive PMSG Wind Turbines in Low Frequency Transmission Systems

Low frequency transmission systems (LFTS) can increase the transmission distance and capacity of submarine cables for offshore wind farms by reducing capacitive current, but they also weaken transient stability and fault ride-through (FRT) in permanent-magnet synchronous generator (PMSG) systems. During a voltage sag, the grid-side converter loses most of its active-power transfer capability, while the machine-side converter still keeps nearly constant mechanical power input, which causes DC-bus overvoltage. To address this problem, this paper proposes a coordinated control strategy based on a dual second-order generalized integrator phase-locked loop (DSOGI-PLL) for directdrive PMSG turbines under LFTS without extra hardware. The DSOGI-PLL improves phase tracking and harmonic suppression, while the proposed control shifts DC-bus voltage regulation to the machine-side converter and makes the grid-side converter prioritize reactive current support. Simulation results show that the strategy can suppress DC-bus overvoltage and maintain stable operation under asymmetrical faults and harmonic interference.