In order to study the transient synchronous stability of the new energy delivery system via VSC-HVDC controlled by virtual synchronous generator

a system dynamic model with current restricted is established firstly. It is found that the system switches between voltage control mode and current restricted control mode at a specific angle difference

so that the switching condition described by current algebraic variables is transformed into the switching condition described by the state variables of the angle difference. Secondly

the transient synchronous stability mechanism of the system is explained by the relationship between the transmitted power and the angle difference of the converters. The critical clearing angle and critical clearing time are determined based on the segmental equal area criteria. Finally

the current restricted control parameter optimization method is proposed to improve the transient synchronous stability of the system based on the analytical relationship between the system stability boundary and the controller parameters and the system operating state. The control mode switching phenomenon and synchronous stability of the simulation model under different fault clearing time prove the accuracy of the transient synchronous stability criterion and the influence factor of the transient stability.