A Dynamic Voltage Balancing Control Method for Series-Connected SiC MOSFETs in High Voltage Applications

In high voltage applications, multilevel converters and series-connected power devices are two effective ways to improve the voltage blocking capability. When connecting SiC MOSFETs in series, due to its fast switching speed, the dynamic voltage imbalance problem is hard to tackle. Compared with other methods, the capacitive coupling gate drive circuit has a simpler circuit structure and a faster response speed, and is suitable for SiC MOSFETs. However, the driving capability of this approach is directly affected by the DC-bus voltage, and it is difficult to achieve perfect dynamic voltage balancing when the DC-bus voltage changes. In this paper, to handle this problem, an effective dynamic voltage balancing control method based on over-drive characteristic is proposed. When DC-bus voltage changes, dynamic voltage balancing is realized by controlling a variable voltage source, thus adjusting the over-drive depth of high-side device and compensating for the effect of DC-bus voltage variation on the driving capability. Experimental studies are carried out to verify the validity and feasibility of the proposed dynamic voltage balancing control method. In the design range, the dynamic and static voltage between the series-connected SiC MSOFETs are balanced well.