An isolated quasi-resonant multilevel dc-dc converter Multi-Phase Single-Stage Topology for 380 V VRM application

The power supply evolution for data centers and networking applications demands a continuous improvement in the efficiency at system and converter levels. Higher voltage distribution system and less conversion steps are necessary to increase the efficiency of the overall distribution system. To implement more efficient power conversion systems 48 V dc at rack level recently has been adopted ensuring higher overall efficiency, isolation design and phase shedding in light load; but rack-level dc distribution can be performed at a higher level of dc voltage such as 380 V dc. An advantage over 48 V dc distribution is that a more efficient ac/dc converter may beused, resulting in higher overall efficiency. For higher voltage dc distribution system a voltage regulator modules (VRM) is currently realized using a two-stage approach, with an intermediate 12 V dc bus. The challenge is to operate at high-efficiency with a single stage conversion directly from 380 V dc bus operating as high-voltage point-of-load (HV POL) converter, including a multi-phase approach and phase-shedding capabilities, maintaining high power density and dynamic performance comparable with 48 V VRM single-stage. This dissertation presents an innovative single-stage approach for the 380 V VRM based on a quasi-resonant multilevel topology constant on-time(COT) operation. The proposed topology inherently integrates the multiphase approach, providing fast phase shedding and flat high efficiency curves even at light load conditions. This is a unique advantage, which is not possible to establish in the two stage approach, which is very important in server architectures, and where high efficiency is required even at light load conditions. This dissertation analyses different high step down topologies including the aforementioned multilevel one, comprising a control architecture for fast transient response, the current sharing capabilities, and a solution for implementing the integrated magnetics. Experimental results show an efficiency of 93% for a 120 A, 380 V-1.8 V VRM power supply.