Digital Control of Multiphase Series Capacitor Buck Converter Prototype for the Powering of HL-LHC Inner Triplet Magnets

A major upgrade will be conducted in the Large Hardon Collider (LHC) at CERN. This high-luminosity (HL) version of the LHC will increase the nominal luminosity by a factor of five. One of the key technologies of the HL-LHC is the new superconducting inner triplet (IT) magnets, responsible of producing high magnetic fields to focus particle beams. To power the IT magnets from the grid, a multistage power supply with an intermediate 24-V battery pack is being considered. In such topology, a low-voltage high-current dc/dc converter operating with a very high step-down ratio is required for the final conversion stage. In this work, an interleaved multiphase series capacitor buck converter is proposed to feed the IT magnets from the battery pack. A novel voltage regulation approach that ensures the current balance between the paralleled series capacitor cells is also proposed, where one cell is responsible for the output voltage regulation, while the remaining cells are current-regulated. A balanced current sharing between the series capacitor cells is achieved, when the current-controlled cells are referenced by the actual current of the first one. The proposal is theoretically analyzed and experimentally validated in a six-cell 1000-A prototype unit.