A Research On Suppressing Common-Mode Current In Switch Mode Power By Using Electromagnetic Losses

Recently, with development of power electronics technology, miniaturization and digitization of equipment has become the mainstream of development of technology. Switching-mode power supply(SMPS) has been widely used due to its smaller size, higher power factor and other advantages, but the electromagnetic interference(EMI) problem becomes more and more serious.Therefore, the electromagnetic compatibility(EMC) in SMPS is drawing more attention.Firstly, definition of EMC and research status of EMI in SMPS are introduced, the causes of EMI of SMPS are deeply analyzed, and the usual methods which are used to restrain EMI are expressed. Secondly, the transmission line theory and transfer matrix method are introduced, and the experimental method of measuring common mode current with high frequency current probe and digital oscilloscope is introduced. Thirdly, based on the flyback SMPS, the conduction characteristics of the common mode current are analyzed, subsequently, a method to suppress the common mode interference is put forward, which is based on the combination of electromagnetic lossy materials and circuit. The results of numerical simulation prove the reliability of this method,meanwhile, the common mode interference among SMPS and other appliances can be isolated.Finally, experimental sample for suppressing common mode current by using electromagnetic losses is designed and prepared, applying high frequency current probe, common mode current both with and without suppression are measured, which demonstrate the validity of the method.Comparing with traditional suppression methods, our method can effectively inhibit a wide range frequency of common mode current,and can be preparated and applied conveniently.