filter, commonly known as passive filter, is a traditional direct current harmonics compensation device compose of inductance and capacitance Efficient filtering, combined with, effectively suppresses common mode and harmonics The circuit consists of three parts, the first part is a single-stage filter circuit, the second part is a common mode filter, and the third part is a two-stage filter circuit It can filter out single or more harmonics in the power supply and purifying the direct current power supply Common mode filtering can suppress fast transiented group interferences problems with repetition rates of several kilohertz at certain user positions