Research On Paralleled SiC MOSFETs-based On-board Multiplexing Converter And Its Conducted EMI Characteristics

In the future,electric vehicles will become the mainstream models for global automakers to meet strict fuel consumption and emission regulations.The on-board charger(OBC)can conveniently charge the on-board battery,but it also increases the volume and weight of the on-board converter.Reusing the electric drive system of electric vehicles as OBC is a way to meet the requirements of weight,space and cost.The integration of motor drivers,OBC and high-voltage Boost converters has become a development trend.The use of silicon carbide(SiC)devices in on-board converters can further improve system efficiency and power density.However,the high switching speed and high switching frequency characteristics of SiC devices will significantly increase the electromagnetic interference(EMI)of the system.At the same time,the current capacity of SiC devices is small.For high-power automotive converter applications,multiple devices need to be connected in parallel to increase their current carrying capacity.The parallel current-sharing performance of devices will affect its maximum current-carrying capacity and the long-term operating reliability of the system.Therefore,it is necessary to study the parallel current sharing and system EMI suppression of SiC devices in the application of vehicle multiplex converters,so as to maximize the performance advantages of SiC devices and improve system efficiency and power while meeting the requirements of relevant EMI standards.density.This article first reveals the main reason for the transient current imbalance of the traditional DC capacitor distributed SiC MOSFET parallel scheme,and explains the influence of the power circuit board(PCB)layout on the transient current sharing characteristics.In order to improve the transient current sharing performance,a PCB layout scheme and optimization method are proposed to reduce the coupling effect between SiC parallel bridge arms and reduce the transmission delay difference of the gate drive signal.The double-pulse test verifies the current sharing performance of the optimized SiC parallel unit under normal working and short-circuit fault conditions.Experimental tests show that compared with the traditional SiC parallel unit,the transient current difference of the optimized parallel unit lower arm parallel SiC device is significantly reduced from 10.22% to 2.78%,and the switching loss difference is also reduced to the same degree,and The transient current under shortcircuit fault conditions is also basically the same.The conduction interference characteristics of vehicle-mounted multiplex converter based on SiC MOSFET parallel unit in DC/DC mode and non-isolated OBC mode are analyzed.The switching voltage spectrum distribution characteristics of SiC MOSFET are analyzed and used as the main conduction interference source.The parasitic parameter model of each component of the multiplex converter is established.The parasitic parameter model is introduced into the EMI analysis model of the converter,and the influence of different interference sources and parasitic parameters on the EMI characteristics of the system is analyzed.It reveals the influence of the series resonance between the parasitic inductance of the negative lead of the Boost converter input and the high-frequency transmission line effect of the power inductor on the conduction interference characteristics of the system;theoretically analyzes the effect of improving the high-frequency impedance characteristics of the power inductor and reducing the parasitic inductance of the negative lead of the Boost input to the system Suppression effect of conducted interference.It reveals the influence of the non-isolated OBC mode output shielding inductance on the conduction interference characteristics of the OBC network side,and gives effective measures to reduce the system conduction interference.It provides a theoretical basis for effectively suppressing the conducted interference of the vehicle-mounted multiplex converter.In order to suppress the conduction interference of the vehicle-mounted multiplex converter without affecting the power density of the system as much as possible,an equivalent single-layer winding method applied to power inductors is proposed,which reduces the equivalent parallel capacitance and significantly improves Its high frequency impedance characteristics.A method is proposed to reduce the parasitic inductance of the equivalent negative lead on the battery side by increasing the small package capacitance.The test test shows that: without adding additional EMI suppression measures,only by optimizing the power inductor winding and adding small package capacitors,the conducted interference test results of the vehicle-mounted multiplex converter in the DC/DC mode and the battery side in the OBC mode are suppressed.In order to further suppress the OBC grid-side conducted interference,a grid-side EMI filter is provided and installed in the remaining window space of the power inductor to reduce the impact on the power density of the system.The test test shows that the on-board multiplexing converter meets the B-level standard limit in CISPR 32-2019 in the OBC mode on the grid side.Finally,based on the optimized SiC MOSFET parallel unit and power inductor and filter unit,a high-efficiency and high-power-density vehicle-mounted multiplex converter applied to electric vehicles is realized.The equivalent converter topology is used for small-signal modeling and a closed-loop control system is designed.The electrical parameters of the multiplex converter in different working modes are tested and the system volume,weight and loss distribution are analyzed.Experimental tests show that the system peak efficiency of the multiplex converter in the DC/DC mode(50 k Hz)when the output power is 50 k W is 99.12%,and the system power density is greater than 15 k VA/L when the peak output power is 60 k W;in the OBC mode When the output power is 6.6 k W,the system efficiency is 97.41%,the system power factor is greater than 0.99,the total harmonic distortion rate of the grid-side input current is 2.11%,and the low-frequency current harmonic component meets both EN IEC 61000-3-2:2019 and EN 61000-3-12:2011 corresponding standard limit.