Transient stability enhancement control strategy for grid-forming converter and synchronous machine parallel systems considering current limiting

Grid-forming control is currently a research hotspot for renewable energy grid-connected converters due to its inherent capabilities of providing inertia and voltage support, and it can serve as the primary control mode for renewable energy-synchronous machine hybrid transmission systems. During large grid disturbances such as faults, transient instability can readily occur in grid-forming converter-synchronous machine parallel systems. Concurrently, current saturation in the grid-forming converter alters the system's transient instability characteristics, necessitating specific control of the converter to enhance the parallel system's transient stability. To address the aforementioned issues, this paper proposes a transient stability enhancement control strategy based on dynamic current-limiting phase control for parallel systems, activated when the grid-forming converter enters current limiting. By dynamically regulating the current phase angle, the strategy enables active adjustment and dynamic allocation of active and reactive power from the grid-forming converter. This extends the fault critical clearance time of the grid-forming converter-synchronous machine parallel system, thereby enhancing the transient stability. By developing a grid-forming converter-synchronous machine parallel system simulation model on the PSCAD/EMTDC platform and applying a three-phase short-circuit fault to ground, the correctness and effectiveness of the proposed control strategy were validated.