Delay and Decoupling Analysis of a Digital Active EMI Filter Used in Arc Welding Inverter

Arc welding inverter supply with switch and digital control is widely used, due to the advantages of high controllability, small size, and high efficiency. With the constant increasing of switching frequency and decreasing of arc welding machine size, the conducted electromagnetic interference (EMI) becomes serious, especially for common mode (CM)-conducted EMI. Meanwhile, as the development of digital processing technique, digital active EMI filter (DAEF) technology, which uses digital control and embedded mode, has become a hot research topic. However, the conventional DAEF fails to consider time delay effect. Its model cannot accurately describe DAEF filtering behavior. Moreover, decoupling circuit lacks scientific design method. To cope with these, this paper proposes a precise DAEF model which considers both the time delay of digital processing portion and the parasitic parameters of passive components. Moreover, based on impedance matching principle, a detailed and scientific design method of decoupling circuit is put forward. Meanwhile, the arc welding inverter system with embedded DAEF is designed, modeled, and compensated. Finally, experiment results show that the proposed precise model can predict the system filtering performance accurately. And the proposed design method of decoupling circuit is very effective to suppress the CM-conducted EMI. The embedded DAEF can improve system stability and dynamic performance.