Uninterruptible power system

  • US 5,602,462 A
  • Filed: 02/21/1995
  • Issued: 02/11/1997
  • Est. Priority Date: 02/21/1995
  • Status: Expired due to Term
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First Claim
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1. An uninterruptible power system of the type having AC input terminals which may be connected to an AC power system, AC output terminals to which a load may be connected, a transformer with a primary connected to receive AC input power provided to the AC input terminals, a secondary connected to the output terminals, and an auxiliary primary, an inverter connected to the auxiliary primary, a battery supplying DC power to the inverter, the inverter adapted to switch to provide alternating polarity of the battery voltage across the auxiliary primary to provide AC output power at the secondary and at the output terminals to supply the load when power from the AC power system is not available, the improvement comprising:

  • (a) a plurality of primary tap switches connected between the input terminals and the primary and placed at different effective voltage levels along the primary;

    (b) tap closing means for closing a selected one of the plurality of primary tap switches in response to a primary tap control signal;

    (c) a buck-boost winding on the transformer;

    (d) buck-boost winding switching means connected to the primary and the buck-boost winding for selectively responding to a buck-boost control signal to connect the buck-boost winding to act as a boost to effectively increase the secondary to primary turns ratio by passing an opposing current through the buck-boost winding so as to create a flux in the transformer in opposition to a flux in the primary, to act as a buck to effectively reduce the secondary to primary turns ratio by passing an aiding current running in a direction through the buck-boost winding so as to create a flux in the transformer aiding the flux in the primary, or to be bypassed altogether such that there is no current in the buck-boost winding to provide a normal turns ratio between the secondary and primary; and

    (e) control means for providing the primary tap control signal to close a selected one of the primary tap switches and for providing the buck-boost winding control signal to connect the buck-boost winding so that the voltage level at the output terminals is maintained within a selected range of a preferred output voltage level despite changes in the voltage level at the input terminals.

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