Abstract: Renewable energy sources like wind and photovoltaic power, which utilize power electronic converters as grid-connection interfaces, exhibit fundamentally different characteristics from synchronous generators. The high penetration of these renewable sources significantly alters power system transient stability characteristics and introduces new challenges for stability control. This paper proposes a method to enhance power system transient stability limits by leveraging the virtual synchronous grid-forming capabilities and flexible switching control of power electronic converters. First, we establish a transient stability analysis model for parallel converter-synchronous generator systems based on typical virtual synchronous grid-forming control structures and strategies. The analysis examines how the active power output ratio of virtual synchronous grid-forming converters affects transient stability and demonstrates the fundamental principle of improving system stability limits through flexible converter power control. Building on this foundation, we develop an adaptive active power control method that uses voltage dip depth as a switching criterion to dynamically adjust virtual synchronous grid-forming feedback modes, thereby enhancing transient stability limits. Simulation studies of power electronic converter grid-connected systems ultimately validate the effectiveness of the proposed stability enhancement approach.