at the same time, before the diode bridge rectifier it uses filter circuit with a simple harmonic suppression which can not fulfil the complete harmonic suppression.
同时在二极管整流桥前用简单滤波电路抑制谐波造成谐波抑制不彻底。
for welding inverter's input circuit is made up by a capacitor as filter after a diode bridge rectifier, it injects harmonics to the power as a voltage source.