Partial Soft-switching Operation of Parallel Buck-type Semi-bridge Switching Cells with Coupled Inductors

The paper proposes a novel soft-switching scheme for parallel semi-bridge switching cells formed by power MOSFETs and diodes. In this scheme, differential-mode inductors are established between the midpoints of parallel semi-bridge cells, and then a corresponding control strategy is implemented to manipulate the circulating current. Based on this configuration, the soft-switching operation is achieved in which the leading cell operates under zero-current switching (ZCS) and the lagging one operates under zero-voltage switching (ZVS). The operating principle of the parallel semi-bridges is characterized by two complementary working modes: desynchronized mode with low switching loss in light load condition and synchronized mode with low conduction loss in heavy load condition, respectively. The proposed scheme is featured by high efficiency in a full load range and zero auxiliary devices and its operation is verified by a Buck dc-dc converter. Experimental results demonstrate that the light-load efficiency of the proposed paralleling strategy is improved by up to 1.34% while the heavy-load efficiency remains that of a traditional CCM Buck converter.