An Actively Balanced Distributed Regenerative Snubber with Reduced Part Count in Multi-Level Power Converters

This work presents a distributed regenerative snubber network with reduced part count in multi-level converter designs. The proposed technique utilizes the ordinarily detrimental parasitic commutation loop inductance to harvest $C_{OSS}$ -related energy using a network of high-speed diode-capacitor catching circuits. The proposed approach has several attractive features: First, $V_{DS}$ overshoot is greatly reduced, as with conventional snubber design. Second, the speed of switching transitions may be increased substantially for reduced overlap loss. Third, layout design effort is relaxed, with larger commutation loop geometries expected to improve system performance. Fourth, a soft-charged daisy-chain allows multiple snubbers to sequentially transfer harvested energy to a common collection point with high efficiency. Finally, a single active component is used to resonate recovered energy back into the primary power path resulting in increased converter efficiency. A hardware prototype demonstrates intended operation in a 6-level flying capacitor multilevel (FCML) converter, with measured waveforms illustrating further improvement with modified active balancing control.