Industrial rack-mounted uninterruptible power supplies (UPS) or battery backup units (BBU) are used in data centers or telecom central offices to provide backup power for servers and switching equipment in the event of power failure. Historically, these UPS’s have relied on lead-acid as the predominant battery type. Currently, lithium-ion (Li-ion) batteries are gaining market share over the incumbent lead-acid battery technology. To differentiate UPS from BBU power sources, we define a typical UPS as double-conversion with ac-dc-ac power conversion, while BBU is the embedded battery with dc voltage input and output. While the input/output of a UPS is more universal by providing either single-phase 120–240 VAC or three-phase 208–480 VAC, the BBU dc output voltage is typically matched to the equipment it is powering. DC powered equipment is gaining acceptance in multiple industries for the simplicity, and efficiency. More and more installations are relying on BBU’s and dc plants to power their equipment directly. Figure 1 presents a BBU and a dc plant installed in a telecom rack with space for other equipment that needs a backup power source.
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