Backup power supply control

#This application is a U.S. National Stage Application under 35 U.S.C. §371 from International Application No. PCT/US2012/067017, filed Nov. 29, 2012, which is hereby incorporated by reference in its entirety for all purposes.

#Field of the Invention

#At least one example in accordance with the present invention relates generally to the control of square wave power supplies.

#The accompanying drawings are not intended to be drawn to scale, in the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:

#FIG. 1 is a block diagram of an offline uninterruptible power supply according to one aspect of the present invention; and

#FIG. 2 is a flow chart illustrating a process for controlling an uninterruptible power supply according to one aspect of the present invention.

#Embodiments of the invention are not limited to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. Embodiments of the invention are capable of being practiced or of being carried out in various ways. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having,” “containing”, “involving”, and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.

#As discussed above, the use of power devices, such as uninterruptible power supplies (UPS), to provide uninterrupted power for sensitive and/or critical loads, such as computer systems and other data processing systems, is known. At least some backup power devices use an inverter to provide output AC power derived from DC power from a backup power source such as a battery. Depending on the inverter used, the AC power may be more in the form of a square wave than a sine wave. It is becoming more common for loads powered by a UPS to include active Power Factor Correction (PFC) circuitry. Active PFC loads driven by a square wave voltage may become unstable and/or create oscillations on the input power lines. These oscillations may be detected by a UPS powering the load causing the UPS to be powered down and/or potentially causing damage to the UPS.

#For example, an active PFC load receiving power from a UPS may include a PFC circuit which includes a PFC pre-regulator that is configured to monitor and control the power being provided to the load in an attempt to provide a unity power factor. Typical PFC circuits control power factor based on the input RMS voltage. However, since the PFC circuit is typically designed for sine wave AC power, and the ratio between the peak value, average value and RMS value of a sine wave is constant, at least some PFC circuits use average voltage or peak voltage in place of RMS to control power factor.