On discussion of mixed mode noise in H-bridge converters

This paper presents the analysis of mixed mode noise in an H-bridge PWM converter. Based on the definition of differential mode (DM) and common mode (CM) noise voltage source and noise current and the time domain voltage and current relationship, noise prediction models are proposed in frequency domain for CM, DM and mixed mode (MM) noise with the consideration of system symmetry regarding the noise propagation path impedance. The model indicates that the mixed mode noise is the cross-coupling between CM/DM noise source and DM/CM noise current due to circuit asymmetry. With the noise source calculated using double Fourier integral transformation method and circuit impedance measured from real circuits or calculated from detailed switching models in frequency domain, the mixed mode noise can be predicted based on the proposed models. This paper also presents the impact of circuit asymmetry on EMI filter performance which indicates that the circuit asymmetry also cause the cross-coupling between CM and DM filters that increase the complexity of EMI filter design. The proposed models and analyzing results are verified through both simulation and experiments on a 1kW H-bridge single-phase PWM converter.