Design and precise modeling of a novel Digital Active EMI Filter

Digital Active EMI Filtering (DAEF) technique is a new direction of conductive EMI suppression technologies for switched-mode power converters. However, the conventional DAEF topology only suppresses EMI to ground on the AC (or DC) ports. It doesn't definitely aim to Common Mode (CM) or Differential Mode (DM) EMI. In this paper, a novel DAEF topology is proposed. It can flexibly suppress CM and DM EMI, and also effectively adjust EMI suppression ability as well as prevent interconversion between CM and DM EMI. On the other hand, because of the parasitic parameters of circuit and the time delay of controlling system, the traditional model of DAEF cannot describe the system behavior accurately. This paper proposes a precise model of DAEF system. The model not only considers the passive device parasitic parameters of sense circuit, injection circuit and decoupling circuit, but also considers the time delay of the digital control system. This model can accurately describe filter performance of DAEF. Finally, simulation and experimental results show that the proposed DAEF effectively suppress CM EMI. Moreover, the precise model can predict the system filter performance accurately.