A Multi-level Multi-phase Single-Stage Switch-Capacitor-Buck DC transformer for Data Center

Switch-capacitor (SC)-based DC transformer is a tendency for voltage regulation in data center, due to bridgeless topology, high voltage gain, and module structure. To achieve high power delivery, SC modules are in multilevel and cascaded with multiphase DC converter. However, the previous high-power SC-based DC transformer is multi-stage, multi-level, and multi-phase structure with massive switches and passive components, causing large volume and neglecting characteristics of SC topology. Thus, a multi-level multi-phase single-stage switched-capacitor-buck (M2SSCB) DC transformer and its corresponding graph theory-based topology simplification method are proposed in this paper. Firstly, the topology evolution based on the graph theory-based topology simplification method is proposed for cascaded switched-capacitor buck DC transformer, to achieve the simplified M2SSCB DC transformer with fewer electrolytic capacitors and switches as a single-stage converter. Moreover, the proposed M2SSCB DC transformer retains the various switching frequency characteristics in traditional cascaded switched-capacitor buck DC transformer, and further proposes dual frequency operation modes as integer multiple dual frequency mode and non-integer multiple dual frequency mode to achieve a wide voltage range. Furthermore, the key parameters design guideline is proposed, and the voltage gain, ZVS, and voltage and current stress of proposed M2SSCB DC transformer are discussed and presented fewer switches in a single-stage structure and various switching frequency operation modes for a wide voltage range, ZVS of switches, high voltage gain, and low volume. Finally, an experimental platform is established to verify the correctness and feasibility of proposed M2SSCB DC transformer. The M2SSCB DC transformer delivers a rated power of 120 W with 48V to 3.3V. Besides, it achieves a peak efficiency of 93% and a power density of 93.5 W/in³. Thus, the proposed M2SSCB DC transformer and its topology simplification method are in line with the development trend of topology single stage.