Server power management with integrated Lithium-Ion Ultracapacitor and bi-directional DC-DC converter for distributed UPS and reactive power mitigation

With the rapid proliferation of cloud computing, the cooling cost of large data centers and the reactive power impact on the grid have become a major concern. This paper presents an improved power architecture for servers with integrated energy storage. Lithium-Ion Ultracapacitors (LIC) are used to provide short-term UPS functionality, while also reducing the reactive power. The control scheme forces the PFC module to operate only in the region of high efficiency and high power factor during dynamic workloads. When the server is operating in idle mode, the PFC module draws only 12% less reactive power compared to having all four CPU cores operating at 100% load, which provides a strong incentive for the proposed scheme. A 200 kHz bi-directional multi-phase dc-dc converter operating in Hysteretic Current Mode Control (HCMC) is demonstrated to interface the 12 V internal bus with the LICs and the server load.