Abstract
The utilization of novel cascode GaN devices can significantly increase the power density and the efficiency of convertors. However, owing to high switching speed (high dv/dt or di/dt) and inevitable parasitic inductance in device packages and external circuits, cascode GaN devices are more prone to oscillate, resulting in voltage overshoot, electromagnetic interference (EMI), and even device breakdown, which reduces the reliability of the drive system. Therefore, effective suppression of the switching oscillation becomes highly critical. This paper presents an integrated modelling and a parameter design method for cascode GaN-based bridge convertors. Firstly, a high-frequency equivalent circuit model is derived for the switching oscillation of cascode GaN-based bridge convertors. Secondly, a quantitative RC snubber parameter design method is established based on root locus analysis, which makes up for defects of the previous trial-and-error empirical method. Then impacts of the RC snubber on power loss and EMI are also studied, with the optimal snubber resistance and capacitance obtained by minimizing power loss. Finally, the effect of oscillation suppression is verified by simulation and experiment, and results show good agreement with the theoretical analysis.
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