Ferroresonant transformer systems and methods with selectable input and output voltages for use in uninterruptible power supplies
A ferroresonant transformer system has a core, a shunt, first and second input windings, an inverter winding, a tank winding, a resonant capacitor, an output capacitor, and a plurality of switches. The tank winding defines a plurality of switch tap locations and at least two output tap locations. The resonant capacitor is connected across at least a portion of the tank winding. Each switch is operatively connectable between one of the switch tap locations and the resonant capacitor. Each output terminal is operatively connected to one of the at least two output tap locations.
1. A power supply adapted to be connected to a source of utility power and a load, comprising:
a ferroresonant transformer system comprising
a core;
a shunt;
first and second input windings;
an inverter winding;
a tank winding defining a plurality of switch tap locations and at least two output tap locations;
a resonant capacitor connected across at least a portion of the tank winding;
an output capacitor operatively connected to ground;
a plurality of switches, where each switch is operatively connected between one of the switch tap locations and the resonant capacitor; and
a plurality of output terminals, where each output terminal is operatively connected to one of the at least two output tap locations;
a battery system; and
an inverter operatively coupled between the battery system and the inverter winding; whereby
at least one of the first and second input windings is connected to the source of utility power;
at least two output terminals are operatively connected to the load; and
to regulate an output voltage of the ferroresonant transformer system, a selected switch of the plurality of switches is closed while any non-selected switch of the plurality of switches is open such that the output capacitor is operatively connected to a desired switch tap location of the plurality of switch tap locations.
2. A power supply as recited in claim 1 , in which the first and second input windings are connected in series.
3. A power supply as recited in claim 1 , in which the first and second input windings are connected in parallel.
4. A power supply as recited in claim 1 , further comprising a controller for controlling the plurality of switches based on at least one of an output voltage, an output current, and an input voltage.
5. A power supply as recited in claim 1 , further comprising a controller for controlling the plurality of switches based on an output voltage, an output current, and an input voltage.
6. A method of providing power from a source of utility power to a load, comprising the steps of:
providing a ferroresonant transformer comprising
a core;
a shunt;
a first and second input windings;
an inverter winding;
a tank winding defining a plurality of switch tap locations and at least two output tap locations;
operatively connecting a resonant capacitor across at least a portion of the tank winding;
operatively connecting an output capacitor to ground;
operatively connecting each of a plurality of switches between one of the switch tap locations and the resonant capacitor;
operatively connecting each of a plurality of output terminals to one of the at least two output tap locations;
operatively connecting a battery system to an inverter;
operatively connecting the inverter to the inverter winding;
operatively connecting at least one of the first and second input windings to the source of utility power;
operatively connecting at least two output terminals to the load; and
selecting one of the plurality of switches as a selected switch;
controlling the plurality of switches to provide a desired output power signal to the load by closing only the selected switch of the plurality of switches such that the output capacitor is operatively connected to a desired switch tap location of the plurality of switch tap locations.
7. A method as recited in claim 6 , further comprising the step of connecting the first and second input windings in series.
8. A method as recited in claim 6 , further comprising the step of connecting the first and second input windings in parallel.
9. A method as recited in claim 6 , further comprising the step of controlling the plurality of switches based on at least one of an output voltage, an output current, and an input voltage.
10. A method as recited in claim 6 , further comprising the step of controlling the plurality of switches based on an output voltage, an output current, and an input voltage.