Under significant disturbance

the phase-locked loop of new energy may be unable to track the grid voltage

and transient synchronous instability may occur. The existing transient synchronous stability analysis of new energy is usually based on the assumption of constant output current

ignoring the influence of current change during the low voltage crossing (LVRT) process during the fault

and the transient stability evaluation results have great errors. Therefore

this paper establishes a PLL model that considers the change of new energy output current during LVRT

and compares it to an equivalent rotor. The output current change under LVRT control can be understood as adjusting the equivalent prime mover power. Lyapunov method is used to reveal the mechanism of new energy transient synchronous stability

and the influence of different parameters such as low penetration coefficient

grid side impedance and grid side voltage drop degree on the transient stability is studied. An optimal control strategy during low voltage crossing is proposed

which improves the transient stability of new energy in weak current network by reducing the equivalent prime mover power. Finally

the electromagnetic transient simulation based on Matlab/Simulink verifies the analysis results and the effectiveness of the proposed control.