Existing research on stability analysis of the power system mainly considers the main voltage control of the excitation system, and the influence of the auxiliary limiters is usually not taken into account. Field experience shows that the function of the excitation auxiliary control loops has an important influence on the dynamic qualities of generators and stabilities of power grid. Taking EXC9100 excitation regulator as an example, this paper derives the extended Heffron-Phillips models with Under Excitation Limiter (UEL), Voltage Frequency Limiter (VFL) and Over Excitation Limiter (OEL) respectively. And then based on these models, it analyzes the influence of important auxiliary control loops parameters on the additional damping torque provided by Power System Stabilizer (PSS) and their own damping torque by damping torque analysis method. Finally, combined with the actual operating conditions of the generator, a typical example of the simulation system validates the correctness and validity of the conclusions proposed. This work is supported by National Natural Science Foundation of China (No. 51577075).