The voltage-source doubly-fed induction generator (DFIG), controlled by the typical grid-forming control method of a virtual synchronous generator (VSG), can provide damping and inertia to the power grid. However, during voltage dip faults, they may encounter similar power angle stability issues to those experienced by synchronous machines. First, the impact of grid-side converter power and variable power reference on transient power angle stability using the equal-area criterion when the grid voltage experiences a three-phase symmetrical voltage dip are analyzed. To adapt the variable power reference control strategy to the dynamic changes of the grid-side converter during the transient period, a stability optimization method for a VSG-controlled DFIG (VSG-DFIG) based on transient power angle feedforward is proposed. The method compensates for the imbalance torque of the VSG by feeding forward the power angle deviation, thus accelerating the deceleration process after the power angle passes the equilibrium point during the transient period. The selection range of the feedforward coefficient is determined by the acceleration and deceleration areas of the transient power angle curve, ensuring that the power angle converges while maintaining the fault ride-through capability of the voltage-source control. Finally, the correctness of the theoretical analysis and the effectiveness of the optimization method are verified through simulation and a hardware-in-the-loop experimental platform.