Common mode noise in three-level DC-DC converters

This paper demonstrates how conducted Electromagnetic Interference (EMI) can be easily analysed utilising an inexpensive and user friendly software package called Micro Cap 9 developed by Spectrum Software (R) Other software packages generally used for accurate conducted EMI simulation purposes, such as SABER (R) is inaccessible to the general designer due to cost. The buck converter is shown as an example. Comparison is made between common mode currents in a standard two-level converter and also three-level derivations. Advantages of three-level converters include reduced switch voltage stress, lower distortion reactive power demand and improved dynamic response. The lower dv/dt should lead to lower electromagnetic noise generation. This paper will show that three-level buck DC-DC converters in general generate much lower common mode currents than conventional two-level buck converters. Further, reductions in common mode currents are achieved by using the improved three-level topologies that have been recently proposed.