The switching of automatic voltage control system plays an important role in improving the voltage stability of the power system

but changes the dynamic stability of original generator system. On the basis of considering the main control of existing automatic voltage control

the Heffron-Phillips model containing automatic voltage control is adopted to analyze the influence of adding the automatic voltage control on low excitation limit configuration of the generator. The stabilization is judged by the Rolls criteria of the Heffron-Phillips model system of the generator. The automatic voltage control is considered as the limiting condition so to set up single machine infinite model and obtain the low excitation limit stability curve. The method takes into account the influence of various modes of the automatic voltage control system and has good instructions for real production. The applicability of the method is verified throughout calculation example analysis of certain actual generator.