Triple Active Bridge Series Resonant Converter for three-Phase Unfolding Based Isolated Converters

Abstract

In this paper, the authors propose a new triple active bridge topology as an isolated DC/DC stage for three-phase rectifiers that are based on an unfolding rectification approach. The three-phase unfolding rectification approach has the potential to improve power density and efficiency for isolated rectifier applications. The DC/DC stage used in this approach is generally implemented by two separate converters for processing different time-varying power from each of the two intermediate soft DC links. Each of these converters must process a peak power equal to the full rated output power and work with an extremely wide voltage gain range. This paper presents an improvement using a single three-port resonant converter with three-active bridges that simultaneously process power from both of the soft-DC links. The converter achieves higher efficiency since it processes a constant power that equals the rated load power with a much narrower voltage gain range. This results in further reduction in size for converters used in unfolding based rectification. A new modulation strategy is proposed for this topology such that all the devices soft switch and the converter has the ability to draw different average currents from each of the two DC links, as required for power factor correction (PFC) action on the grid side. Simulation results are provided to explain the ideal waveforms of the topology, and hardware results are presented for a 2 kW, 600 V output DC/DC hardware prototype at three input voltage conditions that are encountered over the line cycle when applied to a 480 V three-phase unfolding rectifier. The results validate the converter ability to modulate the input currents required for PFC action and also achieve zero voltage switching across the entire AC line cycle.