The filter includes the DC smoothing reactor and the low-harmonic filter circuit. The inductance of the smoothing reactor should be large enough to ensure the stability of the system during low power operation and to limit the rate of current increase in the event of an overcurrent or short circuit fault, thus allowing the electronic protection system to have sufficient time to complete the automatic protection function. At the same time, the air gap of the reactor core should meet the requirements to ensure that the inductance of the reactor will not be significantly decreased during high current operation. The role of the harmonic filter circuit is to minimize the harmonic peak of the AC power grid and harmonic circuit output in order to provide the inverter circuit with smooth voltage, which avoids the high-frequency current to be modulated by low-frequency harmonics in high-frequency solid-state power source, causing the problem of poor quality welding of product.
