Study On The Effect Of Parasitic Parameters In SiC Power Module On Switching Loss And Conducted EMI,and Optimization Of Parasitic Parameters

Silicon Carbide(SiC)power devices have higher switching speed and lower switching loss than Silicon(Si)devices,which can improve the efficiency and power density of power electronic converters,but high switching speed can exacerbate the effects of parasitic parameters on switching loss and Electromagnetic Interference(EMI).In this paper,the influence of parasitic parameters on switching loss and conducted EMI is studied by theoretical calculations,simulation analysis,and experimental verification.And the parasitic parameters of SiC half-bridge power modules are optimized by improving the package structure to reduce switching loss and suppress conduction EMI.The main research work of this paper is as follows.To clarify the internal mechanism of the switching process of SiC devices and quantitatively evaluate the switching performance of SiC devices under the influence of parasitic parameters,an improved switching model is proposed.It is found that a new state occurs in the SiC devices switching process.By introducing the new state,the improved model solves the deficiency of the conventional analytical model,which cannot calculate accurate results when SiC devices turn off under low current.And the improved module shows the internal mechanism and the conditions for achieving quasi-zero-loss switching of SiC devices.In addition,the parasitic parameters introduced by the package and the nonlinear parameters of the SiC device are taken into account to ensure calculation accuracy.The double-pulse test results confirm the improved model’s analysis of the switching process of SiC devices and verify the accuracy of calculation results under different switching conditions.The effect of different parasitic inductance on the switching loss and conducted EMI is analyzed,and the parasitic inductance is optimized by the package structure.Based on the improved switching model and the frequency domain analysis method,the effects of parasitic inductance on the switching loss of SiC devices,EMI source,and EMI conduction path are analyzed comprehensively.The results show that the effects of parasitic inductance on switching loss and EMI is the opposite.In general,reducing the common-source inductance to reduce switching loss and reducing the non-common-source inductance to suppress Common Mode(CM)EMI in the oscillation frequency is more beneficial to improving the performance of SiC power modules.A mutual-inductance-canceling structure is proposed,which uses PCB+DBC integrated package to form a multilayer commutation loop,so that it can reduce the commutation loop inductance by mutual-inductance-canceling.A SiC half-bridge module is designed and processed based on this structure,and the commutation loop inductance is reduced to3.8 n H.This module is compared with discrete SiC devices by double-pulse test and conducted EMI test,and show a significant reduction in switching loss and EMI noise at oscillation frequency.Using the same analysis method,the effect of parasitic capacitance of the power module is investigated,and the package structure is optimized.The comprehensive analysis on the switching loss,EMI sources,and EMI conduction path shows that the parasitic capacitance has insignificant effects on the switching loss and significant effects on conducted EMI,so reducing the output-ground capacitance can suppress CM EMI.A partially-shielded package structure is proposed,in which part of the output copper layer is shielded by the DC copper layer by layout optimization,so that the ground capacitance can be reduced.Based on this structure,a SiC half-bridge module is designed and processed,in which the output-ground capacitance is reduced to 6.8 p F.The experimental results show that the partially-shielded structure can suppress CM EMI effectually.To solve the mutual constraints of parasitic inductance and parasitic capacitance in optimization,this paper presents a comprehensive comparison study of various SiC package structures on parasitic inductance,parasitic capacitance and thermal resistance.An improved Multi-DBCs package structure is proposed,in which the Multi-DBCs form a multilayer structure so that the ground capacitance can be reduced by shielding effect,and the commutation loop inductance can be reduced by mutual inductance canceling.Besides,the embedded package of Multi-DBCs+PCB can simplify the processing and improve the integration.The SiC half-bridge module based on this structure has low parasitic inductance(4.5 n H)and ultra-low ground capacitance(<1 p F).The experimental results show that the improved stacked-DBC module has low switching loss and can further suppress CM EMI.