Modeling and control of sigma converter for 48V voltage regulator application

For the new-generation of server voltage regulators modules (VRMs), companies are employing the use of 48V bus to improve system efficiency and to reduce the cost of datacenters. For 48V to 1V VRM, a quasi-parallel topology, the sigma converter, is shown to have 93.4% maximum efficiency and 420W/in3 power-density. In order to design the sigma converter to meet the VRM requirements, the large-signal performance as well as the small-signal behavior of the converter must be studied. In this paper, the small-signal model is examined, a voltage-mode control design is provided, and hardware measurements are presented.