In order to solve the problem of the constant voltage at the armature terminal of the hybrid excitation synchronous generator under different operating conditions, an excitation control system based on the full-bridge converter topology was designed. The excitation system adopts a double closed-loop control strategy with the armature winding voltage as the outer loop and the stator harmonic excitation winding current as the inner loop. Taking the terminal voltage of the harmonic brushless hybrid excitation synchronous generator as the feedback signal, the generator terminal voltage is kept constant by adjusting the current of the stator harmonic excitation winding. The basic structure and working principle of the hybrid excitation generator with double harmonic windings are expounded, the software and hardware of the excitation control system are designed, and the performance of the excitation control system is tested. The experimental results show that the terminal voltage of the generator can be well adjusted by adjusting the current of the stator harmonic excitation winding, and the output voltage of the generator can be kept constant under different loads through the automatic adjustment function of the excitation control system.