Lithium UPS systems use lithium battery technology to provide backup power in the event of a mains power supply outage or interruption. A lithium-ion or (Li-ion) battery set is used in place of the standard lead acid battery type and the battery may be internal or supplied in a battery extension cabinet. UPS systems with high density lithium ion batteries are more compact than those with valve regulated lead acid batteries and can support faster and more numerous charge/discharge cycles. Lithium batteries are also more temperature tolerant than lead acid UPS batteries.
Lithium-ion batteries offer several advantages of lead acid batteries and the Valve Regulation Lead Avid (VRLA) batteries typically used within a UPS system. Due to the needs of lithium-ion for a more sophisticated battery management system, these advantages come with a price premium over a like-for-like sized lead acid battery-based UPS.
The lithium-ion batteries for UPS systems should be certified to IEC62133, UL1973 (Sec 5.7 & 5.8) and UN38.3. Aside from the cost of the batteries themselves, the UPS system using a lithium battery set must also have a more sophisticated battery management and charging circuit than the traditional types required for VRLA UPS batteries.
The battery management system must be able to monitor individual lithium-ion battery cells for temperature and voltage (for overtemperature and overvoltage conditions) which could lead to thermal runaway at the individual cell and battery pack level. The battery management system must be able to quickly detect any of these conditions and protect the battery pack and UPS installation with short-circuit protection to shut down the charging circuit.
The use of a higher cyclic battery set such as a lithium-ion one allows a UPS to perform as an energy storage system than a purely standby power backup one. Energy can be stored from off-peak rate electricity services and used to power the load during higher peak-charge periods, allowing the UPS to function as a virtual power plant to the connected loads.
This type of storage function also helps the UPS to assist national grids and demand side response (DSR) programmes. Here the UPS powers the load from its batteries to reduce demand on the grid and earns a fee from the grid operator.
Energy can also be stored from local renewable power plants including hydro, sola PV and wind turbine within the battery set for use by the UPS system to either protect the load or operate as a DSR generating system.
All these functionalities are suited to larger three phase uninterruptible power supplies due to their size (kW/kVA or MW/MVA) and the capital and operational costs involved.
For more information on lithium-ion UPS systems please contact our projects team.