Research on Virtual Synchronous Transient Control Strategy Based on Locking Power Angle at the Instant of Fault

With the increase in the proportion of renewable energy generation, there is a growing demand for grid-forming converters in modern power grids. Grid-forming converters controlled by Virtual Synchronous Generators (VSGs) face transient stability issues similar to those of synchronous generators. However, the active power reference value, frequency, phase, and other factors of VSG are artificially constructed and can be rapidly controlled, providing new approaches to enhance their fault transient synchronization stability. Current improvement strategies are based on the premise of continuous changes in power angle at the instant of fault, but in reality, short circuits can alter the circuit topology, causing phase jumps at the fault point and power angle jumps. These power angle jumps may position the initial working point of the VSG after the fault in an unstable operating region of the power angle curve, leading to instability. To address this issue, this paper proposes two types of instability scenarios based on the magnitude of power angle jumps and introduces a virtual synchronous transient control strategy based on locking power angle at the instant of fault. Considering smooth switching of control strategies after fault clearance, this strategy can stabilize the output active power, frequency, and terminal voltage during faults, effectively addressing both types of instability. Finally, simulation result in Power Factory is given to verify the idea.