Common Mode Modeling and Reduction of GaN-based Full Bridge Inverters

Although GaN HEMTs show impressive improvements in characteristics compared with Si MOSFETs, the control circuits suffer from high common-mode (CM) noise caused by the high-speed switching actions. CM transient current will lead to failure of controllers and driver ICs if not adequately reduced. Lots of research have been conducted on the generation and propagation of the CM current, but mainly focus on a single phase-leg. This paper investigates the CM current of a full-bridge inverter. A CM propagation model is proposed, in which both phase-legs and all the signal and power paths are considered. The connection between the control ground and the power ground will lead to inequality of the phase-legs, which is also discussed in this paper. To reduce CM current, CM chokes and power supply with low isolation capacitance are employed. In addition, differential voltage sensing method that has high CM transient immunity is adopted. Experimental results on a 500W full-bridge inverter verify the effectiveness of the proposed analysis and methods.