This paper analyzed different faults of three phase full controlled bridge rectifier circuit, gets the quantitative relationship between trigger angle and output excitation voltage, proposes relevant measure, and then simulates the model of excitation power unit by using MATLAB/Simulink platform. The results showed that the proposed method can effectively reduce the adverse effects of the fault on the system and obtain time for switching standby devices when pulses disappear or make for controlling generators existing smoothly to avoid stability problems when thyristors break down.