How operating in Xtra VFI mode improves UPS energy efficiency

The advent of transformerless technology not only improved double-conversion UPS energy efficiency; it also maintained this high efficiency of UPS over a much wider load range. Nevertheless, if the load drops to about 25% or below, then UPS efficiency levels start to fall away significantly. Xtra VFI is a smart way to minimise the resulting losses and improve uninterruptible power supply efficiency when operating considerably under capacity.

Xtra VFI is based on a concept that has always been inherent in modular UPS topology. Suppose, for example, that a significant number of a data centre’s servers are decommissioned for an extended period, or even permanently. Modular UPS power systems supporting the data centre operations could easily be kept adequately loaded with the remaining servers by switching off or removing UPS modules that have become excess to requirement. The uninterruptible power supply modules can just as easily be restored later, if necessary. Easy adaptation to required load capacity is a natural benefit of modular UPS systems, sometimes referred to as ‘rightsizing’.

Xtra VFI mode is available on KUP’s PowerWAVE 9500 and PowerWAVE 9250 uninterruptible power supplies. This automates the process by detecting the current load level and adjusting the number of active UPS modules accordingly. No operator intervention is required in calculating the efficiency of the UPS systems allowing for optimal results for any desired redundancy levels. UPS redundancy levels for active capacity and highest expected load steps can be user-configured to guarantee the highest power protection level.

Excess modular UPS units are switched to standby but remain ready to start up, become active and share the load again if it increases. If a mains power outage or alarm event occurs, the Xtra VFI mode is deactivated and all UPS modules are switched to ‘active’ status.

The UPS efficiency improvements achieved by this mode of operation are especially significant when the load is less than 25 percent of full UPS system capacity.

A typical UPS installation could comprise a maximum load of 800 kW, with a required electrical redundancy level of N+2. This could be entirely supported by a pair of 500 kW modular UPS frames, each containing five 100 kW modules. If the current load demand drops to 200 kW, the number of active UPS units will be reduced to four to provide 400 kW active capacity. The 200 kW load is being supported with N+2 redundancy, as required. All UPS modules share the load equally, so each is 50% loaded and operating efficiently. The standby UPS capacity becomes 600 kW; some or all of this is available to bring back on-line immediately if the load increases again.

Even in the most carefully managed data centre environments, loads can vary unexpectedly for operational or business reasons. The Xtra VFI mode ensures that uninterruptible power supplies can accommodate these changes without loss of efficiency.

For more information on improving the efficiency of UPS systems with Xtra VFI or any of our uninterruptible power supplies and UPS services, you can get in touch with KUP via our contact page or call us on 0800 731 3269.


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