Analysis of Neutral Point Clamped Dual Active Bridge Converter Over a Wide Output Voltage Range

This paper presents an analysis of different operating modes of a dual active bridge (DAB) composed of a three-level Neutral Point Clamped (NPC) converter at the input stage and a full bridge (FB) at the output stage for forward power flow operation in medium-voltage applications. The NPC converter operates in two- and three-level modes near rated power, enabling the use of existing Zero Voltage Switching (ZVS) strategies reported in the literature. As the power level decreases, a five-level operating mode is introduced to improve efficiency and other performance parameters in the low-power range. The optimization of the transformer turns ratio to minimize switching losses across the output voltage range is also presented. An experimental setup and a PLECS simulation model of a 20 kW, 1500 V DC input system are developed to compare various operating parameters, and the results are discussed. The advantages of five-level operation, particularly in the low modulation index region, are highlighted. The output FB operates at a constant 50% duty cycle throughout the analysis.