Abstract: According to the brazing techniques of large generators and high power transformers,a high efficiency of induction heating welding power supply is needed.But the traditional induction power systems are working in frequency modulation,which output is associated with frequency and cannot be used in the brazing situation successfully.In this paper,an ultra-audio induction heating welding power supply which based on a novel frequency scout technology is provided.This 20 kHz/30 kW power system always works as ZCS and has good characteristics such as high power factor,high efficiency,low EMI,small size.