Modeling conducted EMI noise generation and propagation in boost converters

Models to predict generation and propagation mechanisms of conducted EMI noise in switch mode converters comprising of a diode-bridge rectifier input stage, and a 250 kHz boost converter stage are presented. It is demonstrated that a converter employing ZVT PWM generates lower levels of both conducted and radiated EMI emissions compared with hard-switched PWM operation. It is also shown that the effect of active input current wave shaping is to slightly reduce common-mode conducted emissions but increase differential-mode conducted emissions. Additionally, it is shown that the presence of the boost inductor leads to quasi common-mode conduction and that the parasitic capacitance between main switching device's heat sink and ground plane primarily determines common-mode conducted emissions. Mathematical equations to predict both differential- and common-mode conducted emissions are derived. Experimental results and important operational waveforms obtained using a 750 W unit are presented and compared with analytical and simulated results.