Identification of Common Mode Noise Current Path in a SiC Power Module

Common mode current constituents a large part of EMI generated in power converters especially those power modules with a baseplate. It is most useful to be able to illustrate the noise current paths especially the CM current which flows through stray capacitance. This work illustrates a method to work out the critical current paths. FEA software computes the capacitances from the module layout structure. Power device capacitances are also included. Circuit simulation computes currents in various branches and verified by experiment. This work reveals that in addition to the knowledge that the switching node produces significant common mode current, the power rails are also essential coupling paths above the module baseplate. This is because of the linkage to the switching node by high device capacitances.