The transient synchronization stability of grid-forming converters (GFMCs) is significantly challenged under grid voltage sags. Continuous efforts have been devoted to analyzing the GFMC transient stability

with limited attention paid to the impacts of control loop dynamics. However

the complex control dynamics

especially the interactions between the active/reactive power control loops and the current saturation process (CSP)

are crucial for accurately describing the transient behavior and evaluating the stability. Thus

in this study

a new large-signal GFMC model is established

considering the reactive power control (RPC) with different kinds of controllers and the CSP simultaneously. It is revealed that GFMC does not switch to the current-limited mode immediately

and the dynamics of RPC further affect the transient behavior before the current limiting significantly. Hence

the complex control dynamics can alter the mode switching point of current saturation

thereby increasing the risk of loss of synchronization (LOS). Based on the above findings

comprehensive comparisons of typical RPC controllers are presented to facilitate practical engineering applications. A unified stability enhancement method is proposed for solving the problem of LOS. Finally

experiments validate the correctness of the analysis and the effectiveness of the proposed control strategy.