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On Discussion of Mixed Mode Noise in H-Bridge Converters

Fig. 1 : Single Phase PFC with H-Bridge Converter
Based on the time domain voltage, current relationship and the definition of DM and CM noise source and noise current, a noise prediction model is proposed in frequency domain with the consideration of system symmetry regarding the noise propagation path impedance. The model indicates that the mixed mode noise is the coupling between the CM/DM noise source and the DM/CM noise current due to circuit asymmetry. With the noise source calculated and circuit impedance measured or modeled in frequency domain, the mixed mode noise can be predicted based on the proposed model.

Fig. 2 : EMI model in frequency domain

Figure 3. (a) EMI noise comparison (predicted: blue; Simulated: red CM noise with symmetric load
Fig. 3. (b) CM noise with asymmetric load

Figure 4. (a) Measured EMI noise with different circuit asymmetry CM noise with asymmetric load

Fig. 4. (b) DM noise with asymmetric load
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