Conducted emi modeling separation and filter analysis for isolated ac dc converters

Abstract

Electro-Magnetic Interference (EMI) emission is always a great newlineconcern for power electronics circuit designers due to fast switching of newlinedevices like Metal Oxide Semiconductor Field Effect Transistor (MOSFET), newlineIntegrated Gate Bipolar Transistor (IGBT) and Gate Turn-Off Thyristor newline(GTO). Fast switching in power converters generate rapid changes in voltages newlineand currents occur with large amount of EMI. Based on frequency, EMI is newlineclassified into Conducted emissions and Radiated emissions. Conducted EMI newlinefrequency in the range of 450 kHz to 30 MHz for Federal Communications newlineCommission (FCC) Class A regulations and 150 kHz to 30 MHz for German newlineVerband Deutscher Elektroniker (VDE) regulations. Radiated EMI is newlinemeasured at higher frequencies beyond 30 MHz upto several GHz. newlineConducted EMI in Switching Power Converter (SPC) consists of newlineDifferential Mode (DM) and Common Mode (CM) noises. These two modes newlineof noises are caused by different noise sources, coupled through different newlinepaths. In SPC, the emission of EMI is unpredictable and filter design is newlinecomplicated. The filter design is based on noise source impedance. This method uses a practical approach for measuring the power converter noise newlinespectrum and uses the data to calculate the maximum value and minimum newlinevalue of the DM and CM noise source impedances. newlineDesigned filter parameters are compared with noise source newlineimpedance. If the comparison result mismatches with the noise source impedance, then the designed filter parameters are altered. Based on the above newlineconcept, filters are designed for CM and DM noises and they attenuate the newlinenoise at entire frequency range. Line Impedance Stabilization Network newline(LISN) is used to measure the Conducted emissions. A simple equivalent circuit modeling approach is proposed to newlinedescribe the EMI coupling mechanism for SPC. Proposed modeling approach newlineconsists of a minimum number of noise sources and essential coupling paths newlinethat allow easy physical interpretations.