Xtra VFI Feature

When an uninterruptible power supply (UPS) is operating at significantly under capacity, its energy efficiency can be negatively impacted. With the advanced Xtra VFI mode from KOHLER Uninterruptible Power, this problem is solved. Xtra VFI mode is a smart way to minimize losses and improve efficiency when running in double conversion mode. Available on the KOHLER PW 9250 DPA, 9500 DPA and MF Series.

How does it work?

With Xtra VFI mode enabled, the KOHLER modular UPS automatically adjusts the number of active modules according to the load requirements. Modules that are not needed are switched to standby but remain in state of readiness, primed to kick in and transfer to active mode if the load increases. The efficiency improvements achieved by this mode of operation are especially significant when the load is less than 25 percent of full UPS system capacity. In addition, Xtra VFI has the added benefit of rotating modules between active and standby, therefore extending the service life of the UPS.

Xtra VFI Mode

The figure below shows how the Xtra VFI operating mode can enhance efficiency when running at a low load level for a KOHLER PW 9500DPA modular UPS system, with 10 UPS modules (100 kW) and total available capacity of 1 MW.

VFI image


  • Maximum load = 800 kW
  • Redundancy = N+2
  • 2 x 500 kW frames (10 x 100 kW)
  • Load power = 200 kW
  • No. of active modules = 4
  • UPS active capacity = 400 kW
  • UPS standby capacity = 600 kW


The UPS module is operating at double conversion mode and supplying the load with the other active modules. Each module equally shares the load


    The UPS module is on standby, with the inverter switched off, ready to transfer to active double conversion operation when the load increases

    Key features

    • Xtra VFI scales the UPS module active capacity according to the load to maximise efficiency
    • The system calculates the optimal % value for maximum efficiency, taking into account desired redundancy
    • The redundancy level for active capacity and the highest expected load step can be configured by the user to guarantee highest protection level
    • In case of mains failure or alarm, Xtra VFI gets deactivated automatically. In this situation all modules switch to ‘Active’ status
    • Module rotation between active and standby extends the service life and stabilises aging

    For more information on KOHLER Modular UPS and the Xtra VFI Feature, Contact us on 0800 731 3269, email us at [email protected].

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