Switched-mode Control of Battery Backup Unit in Data Center for Online Impedance Detection

This paper presents an evaluation of switched-mode control for battery backup unit (BBU) in data center to realize Busbar voltage regulation and battery impedance detection. There are two control modes in the presented BBU control system. In control mode I, the Busbar voltage is regulated at the desired reference value by regulating the duty cycle of DC-DC power converter. In the control mode II, the BBU is bypassed from Busbar and connected to a test load. During mode II, both the DC impedance or AC impedance of BBU can be measured online. The DC impedance can be measured through changing the load current with adding a pulse signal to the duty cycle of the power converter. While the AC impedance can be measured by adding a perturbation signal at a given frequency to the duty cycle of power converter to perturb voltage and current of li-ion battery in BBU. The DC impedance or AC impedance can be further utilized to evaluate the BBU State-of-Health (SOH). With the presented switched-mode control, only one DC-DC power converter is required to realize Busbar voltage regulation and impedance detection, which reduces the volume, cost and size of BBU. Proof of concept results are provided in the paper to evaluate the performance of the presented switched-mode control in BBU.