A Compact Passive-Active Hybrid EMI Filter with Phase Compensation for Power Converters

Passive electromagnetic interference (EMI) filter has been widely used in power converters to suppress conducted EMI. However, due to its limitation on insertion loss, volume and parasitic parameters, it is difficult to meet the electromagnetic compatibility (EMC) standard on the full frequency band from 150kHz to 30MHz. Active EMI filter has a good performance in the low frequency band, but in the frequency band higher than 10MHz, the EMI suppression effect is significantly reduced due to the constant gain-bandwidth product. In this paper, a compact passive-active hybrid filter is proposed to realize the effective full frequency band conducted EMI suppression. Firstly, the hardware structure of the hybrid EMI filter considering the overall insertion loss is analyzed and optimized by adjusting the positions of the active and passive filters. Secondly, based on the analysis of the bandwidth characteristics of active and passive filters, the design flow of hybrid filters is proposed. Then, the modeling method and parameter design of hybrid filters are carried out. Finally, taking a Boost converter as an example, the simulation and experimental platforms are built to verify the effectiveness and advantages of the proposed hybrid EMI filter. The experimental results show that the hybrid EMI filter can achieve 20-30dBμV attenuation in the full frequency band from 150kHz to 30MHz, as well as the volume can be reduced by 75% compared with the pure passive EMI filter.