Modeling and Mitigation of Common-Mode EMI Noise for LLC Resonant DC/DC Converter for Grid-connected Applications

The LLC resonant DC/DC converter is widely used in DC/DC states within grid-connected applications, such as computing applications and battery charging situations. Typically, it is connected in series to AC/DC states, which commonly function as power factor correction (PFC) converter. For these applications, it's required to meet the Electromagnetic interference (EMI) standard. The presence of parasitic capacitors between windings in the transformer leads to issues associated with common-mode (CM) noise. This problem becomes serious when the LLC converter employs a planar transformer. The capacitance values can even extend into the nanoFarad (nF) range. This research introduces a common mode noise model for the LLC converter. It serves to estimate levels of common mode noise and to provide analytical approaches for mitigating its impact. Additionally, simple techniques are implemented to mitigate common mode noise across both low and high frequency ranges. The validity of the proposed model and the effectiveness of these techniques are verified through simulations conducted using LTspice XVII.