Quasi-regulation and mismatch mitigation technique for switched tank converters

Data center power consumption has been increasing remarkably in the last decades, mainly due to the massive adoption of cloud computing. Due to the vast amount of power consumed, server rack architecture has switched from 12 V to (48 V - 60 V). The commonly used power delivery system employs two stages of DC-DC conversion, cascading an unregulated first-stage converter and a regulated one. The 4-to-1 switched tank converter (STC) is one of the main topologies used as a first stage thanks to its very high efficiency and power density. However, a limitation of the STC is its large inrush current during the startup phase. To avoid this, usually the converter is preceded by a DC-DC converter, a hot-swap controller or an eFuse. Moreover, ensuring the zero current switching condition in both resonant tanks is not straightforward in presence of a mismatch between the resonant frequencies. In this paper, a novel control technique that avoids a large inrush current at startup without the usage of an auxiliary converter and a strategy to minimize the mismatch in the resonant frequencies are proposed for the STC. Experimental results for a 600 W prototype show the validity of these approaches.