SiC MOSFET开通电流尖峰的分析及抑制

Analysis and Suppression of Turn-on Current Spike of SiC MOSFET

在桥式结构的电压源型变换器中,IGBT器件需要反并联二极管以保证续流。而碳化硅(SiC)金属氧化物半导体场效应晶体管(MOSFET)由于具有双向导通的能力,且内部寄生体二极管,所以无需外部增加反并联二极管。但是体二极管的反向恢复问题、导通压降过大问题将降低变换器效率。所以目前很多应用中仍然在SiC MOSFET外部反并联SiC肖特基势垒二极管(SBD)进行续流。虽然SiC SBD无反向恢复电流,但是SBD的结电容会导致较大的主开关管开通电流尖峰。为了得到最优的续流方式,此处分析了SiC SBD续流、SiC MOSFET体二极管续流以及两者并联续流3种模式下开通电流尖峰的组成成分及各成分的产生原因。实验结果表明利用体二极管和SBD并联的方式效果最差。为了研究电流尖峰的变化规律,实验中改变直流侧电压和开关速度等外部条件,观察电流尖峰的变化。实验结果表明开关速度对电流尖峰的影响最大。最终,提出了3种抑制开通电流尖峰的方法。

In a voltage-source bridge converter,an additional diode is needed to be antiparalleled with an IGBT for freewheeling.However,it is not necessary for silicon carbide(SiC) metal oxide semiconductor field effect transistor(MOSFET) because of bi-directional conduction and the body diode.However,the reverse recovery current of the body diode and high voltage drop can cause higher turn-on current spike in the main switch,resulting in lower efficiency.One solution is to add an antiparalled SiC Schottky barrier diode(SBD) for freewheeling.Although the SiC SBD has no reverse recovery current,its junction capacitance will aggravate the current spike.In order to identify the way for freewheeling,various freewheeling methods,including SiC SBD freewheeling,body diode of SiC MOSFET and paralleled of both two,have been analyzed.The turn-on current spike has been separated according to their generation mechanism.The experimental result shows that it is worst to freewheel by paralleling the body diode with the SBD.The DC-link side voltage and switching speeds have been varied to investigate the change of the current spike.The results show that the switching speed has the strongest effect on the current spike.Finally,three methods to suppress the turn-on current spike are presented.