Research On Electromagnetic Interference Of High Power Density Power Converter

High power density converter is a new switching mode power converter which was developed to meet the tendency of miniaturization and lightweight in innovative electronic products. It has the advantage on reducing the power module volume. At present, the academic community still focuses on the characteristics of its dynamic characteristics, temperature characteristics and efficiency.However, the unique EMI characteristics have not been studied sufficiently. As one of the certification standard, EMI has an important impact on the reliability of the converter. Therefore,the study of the EMI characteristics of high power density converters is worthy in both academic and practical.In this paper, EMI model methodology, the effect of planar transformer and multilayer PCB on the EMI characteristics and the near-field coupling interference gate-driver caused by the via coupling were studied. The innovative achievements of this paper include:1. A novel hybrid analytical/numerical (HAN) EMI modelling approach of the LLC resonant power converter is proposed. This model which combines the noise path and the calculation algorithm of EMI receiver can efficiently reduce the model complexity and the calculation resource consumption. By this model, the EMI noise can be predicted during the design stage. The simulation error can be observed below±3dB?V.2. A calculation method of parasitic capacitance for planner transformer winding voltage gradient correction is proposed based on the defects in existing algorithms. A three-capacitor planner transformer is then presented. Also, the mechanism of EMI noise passing through the primary and secondary mutual capacitance is then revealed based on this model3. A novel parallel equipotential planar transformer structure is proposed. The structure can reduce the mutual capacitance between the primary and secondray windings, without reducing the coupling efficiency and density of integration. The results show that the mutual capacitance between the primary and secondray windings can be reduced by more than 90%.4. The characteristics of parasitic parameters of multilayer PCB and its influence on EMI noise path are revealed. Then a new shielding structure of Ground layer is proposed based on the analysis. The simulation results show that this new type of PCB structure reduces the equivalent capacitance between noise source and ground by 56% compared that in the shieldless structure.5. The optimized demo is designed based on the novel structure of planner transformer and PCB. EMI measurements show that, EMI noise is reduced more than 9dB?V. At certain individual frequency, the reduction can be observed up to 32 db?V6. Based on the physical structure of the via hole, the analytical calculation method the parasitic parameters of the vias and the parasitic parameters between vias and PCB are proposed.Then the error of impedance calculation in the P/G layer resonance theory is fixed when the resonant frequency exists. And the near-field coupling interference model between vias in double-layer and multi-layer P/G layer is proposed by using the Z-parameter conversion. The model is used to analyze the relationship between the near-field interference and the parameters of the vias. Experimental results show that the coupling noise spike decreases by more than 30% in the improved PCB.