Uninterruptible power supply and ferroresonant transformer for use therewith
First Claim
1. An uninterruptable power supply (UPS), comprising:
- a ferroresonant transformer having a first input winding adapted to be coupled to an external primary source of power, a second input winding, and an output winding, said first input winding containing at least two winding taps;
an output tank capacitor coupled across said output winding;
a secondary power source coupled to said second input winding;
at least two tap-switching relays interposed between said at least two winding taps and the external primary source of power, each of said tap-switching relays selectively coupling the external source of power to one of said winding taps; and
a controller in sensory communication with a voltage of the external source of power, said controller selectively commanding said tap-switching relays to open and close based on said sensed voltage.
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Accused Products
Abstract
A line-interactive single conversion uninterruptible power supply (UPS) utilizing a multiple tapped ferroresonant transformer and a square wave PWM inverter is presented. During normal utility line operation, the line voltage is not modified in any way, except for ferroresonant filtering and regulation. Tap control circuitry insures proper tap selection based on the utility input voltage. During tap transitions in utility out of specification operation, a second power source, such as an inverter, is operated to provide output power to the connected loads. The control of the inverter switching angles may be accomplished through a look-up table. This look-up table contains the converter pulse widths for monitored battery voltage. No output voltage feedback is required. Based on the inherent regulation provided by the ferroresonant transformer, the PWM control may be accomplished in course steps.
77 Citations
57 Claims
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1. An uninterruptable power supply (UPS), comprising:
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a ferroresonant transformer having a first input winding adapted to be coupled to an external primary source of power, a second input winding, and an output winding, said first input winding containing at least two winding taps;
an output tank capacitor coupled across said output winding;
a secondary power source coupled to said second input winding;
at least two tap-switching relays interposed between said at least two winding taps and the external primary source of power, each of said tap-switching relays selectively coupling the external source of power to one of said winding taps; and
a controller in sensory communication with a voltage of the external source of power, said controller selectively commanding said tap-switching relays to open and close based on said sensed voltage. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
where;
Vpeak=Peak voltage across winding=Vbattery−
Vdrop;
Vdrop=Voltage drop in the inverter path;
τ
half cycle=½
of an operating line frequency of said ferroresonant transformer; and
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19. The UPS of claim 16, wherein said controller operates open loop with regard to voltage at said ferroresonant transformer output.
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20. The UPS of claim 16, wherein said controller is adapted to control said inverter to alternate between a power pulse and a freewheel mode of operation.
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21. The UPS of claim 16, wherein said inverter comprises four switches configured in an H-bridge configuration.
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22. The UPS of claim 16, wherein said inverter comprises three switches configured in a push-pull configuration.
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23. A power supply, comprising:
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a ferroresonant transformer having an input winding, and an output winding;
a tank capacitor coupled across said output winding;
an inverter having an input coupled to a source of dc power and an output coupled to said input winding, the inverter further having a plurality of controllable switches operable to construct a square wave voltage on said output from said dc power on said input; and
a controller having stored therein a table of pre-calculated inverter switch control signals associated with voltage levels of the source of dc power, said controller monitoring the voltage level of the source of dc power and selecting said inverter switch control signals based thereon. - View Dependent Claims (24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41)
where;
Vpeak=Peak voltage across winding=Vbattery−
Vdrop;
Vdrop=Voltage drop in the inverter path;
τ
half cycle=½
of an operating line frequency of said ferroresonant transformer; and
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27. The power supply of claim 23, wherein said controller operates to control said inverter in open loop with respect to said output winding.
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28. The power supply of claim 23, wherein said controller is adapted to control said inverter to alternate between a power pulse and a freewheel mode of operation.
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29. The power supply of claim 23, wherein said plurality of controllable switches comprises four switches configured in an H-bridge configuration.
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30. The power supply of claim 23, wherein said plurality of controllable switches comprises three switches configured in a push-pull configuration.
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31. The power supply of claim 23, further comprising at least two tap changers, each having an input adapted to be coupled to a source of ac power and an output, and wherein said ferroresonant transformer further comprises a utility input winding having at least two taps associated therewith, and wherein each of said outputs of said at least two tap changers are coupled to one of said at least two taps.
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32. The power supply of claim 31, wherein said controller further controls selection of one of said at least two tap changers based on a monitored voltage of the source of ac power.
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33. The power supply of claim 23, wherein said ferroresonant transformer further comprises a compensation winding coupled in series with said output winding.
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34. The power supply of claim 31, wherein said utility input winding further comprises at least three winding taps, and further comprising at least three tap changers interposed between said at least three winding taps and the source of ac power.
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35. The power supply of claim 34, wherein said controller is adapted to utilize at least three predetermined threshold values to determine a proper configuration of said tap changers.
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36. The power supply of claim 34, wherein said tap changers are solid state switching devices.
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37. The power supply of claim 34, wherein said tap changers are electromechanical devices, the power supply further comprising a static switch interposed between said tap changers and the source of ac power.
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38. The power supply of claim 34, wherein each of said winding taps is positioned approximately 15% from an adjacent winding tap.
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39. The power supply of claim 34, wherein said transformer comprises a first, a second, and a third winding tap, and wherein said first winding tap is positioned on said utility input winding to provide a first turns ratio, wherein said second winding tap is positioned on said utility input winding to provide a second turns ratio, and wherein said third winding tap is positioned on said utility input winding to provide a third turns ratio, said first turns ratio being approximately 15% less than said second turns ratio and said third turns ratio being approximately 15% greater than said second turns ratio.
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40. The power supply of claim 39, wherein said first turns ratio is approximately 88% of said second turns ratio and said third turns ratio is approximately 115% of said second turns ratio.
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41. The power supply of claim 31, wherein said controller is adapted to control said tap-changers to maintain a maximum voltage swing across said first input winding to approximately +/−
- 10%.
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42. A ferroresonant transformer for use in a power supply that supplies electric power to output connected loads from a utility ac input, the utility ac input having a regulated voltage range bound by an upper and a lower voltage value, the ferroresonant transformer comprising:
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a ferromagnetic core;
a first primary winding wound on said core, said first primary winding having a first and a second tap coupled thereto;
an output winding wound on said core and separated from said primary winding by a first magnetic shunt; and
wherein said core contains an amount of ferromagnetic material insufficient to prevent saturation of said primary winding at the upper voltage value of the utility voltage range when the upper voltage value of the utility voltage range is coupled to said second tap. - View Dependent Claims (43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57)
a compensation winding wound on said core and separated from said output winding by a second magnetic shunt, said compensation winding coupled to said output winding; - and
an output tank capacitor coupled to said output winding and said compensation winding, said output tank capacitor having a VA rating; and
wherein said VA rating of said tank capacitor is insufficient to regulate an output of the transformer over the utility voltage range without selectively switching the utility ac input between said first and said second taps.
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45. The transformer of claim 42, further comprising a third tap coupled to said first primary winding, and wherein said core contains an amount of ferromagnetic material insufficient to prevent saturation of said primary winding at the upper voltage value of the utility voltage range when the upper voltage value of the utility voltage range is coupled to one of said second and said third taps.
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46. The transformer of claim 42, further comprising a third tap coupled to said first primary winding, and wherein said primary winding comprises a wire of a size insufficient to prevent overheating of said primary winding at the lower voltage value of the utility voltage range when the lower voltage value of the utility voltage range is coupled to one of said first and said second taps at rated load.
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47. The transformer of claim 42, further comprising:
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a third tap coupled to said first primary winding;
a compensation winding wound on said core and separated from said output winding by a second magnetic shunt, said compensation winding coupled to said output winding; and
an output tank capacitor coupled to said output winding and said compensation winding, said output tank capacitor having a VA rating; and
wherein said VA rating of said tank capacitor is insufficient to regulate an output of the transformer over the utility voltage range without selectively switching the utility ac input between said first, said second, and said third taps.
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48. The transformer of claim 45, wherein said first tap is positioned approximately 15% from said second tap, and said second tap is positioned approximately 15% from said third tap.
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49. The transformer of claim 45, wherein said first tap is positioned on said first primary winding to provide a first turns ratio, wherein said second tap is positioned on said first primary winding to provide a second turns ratio, and wherein said third tap is positioned on said utility input winding to provide a third turns ratio, said first turns ratio being approximately 15% less than said second turns ratio and said third turns ratio being approximately 15% greater than said second turns ratio.
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50. The transformer of claim 49, wherein said first turns ratio is approximately 88% of said second turns ratio and said third turns ratio is approximately 115% of said second turns ratio.
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51. The transformer of claim 45, wherein said taps are positioned on said first input winding to maintain a maximum voltage swing across said first input winding to approximately +/−
- 10% over the regulated voltage range.
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52. The transformer of claim 45, further comprising a second input winding wound on said core.
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53. The transformer of claim 45, further comprising a compensation winding wound on said core and separated from said output winding by a magnetic shunt.
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54. The transformer of claim 53, wherein said compensation winding is coupled in series with said output winding.
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55. The transformer of claim 45, wherein said ferromagnetic core comprises a first number of steel laminations, and wherein said first number is substantially less than a second number of steel laminations required to prevent saturation of said primary winding over the regulated voltage range of the utility ac input without said taps.
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56. The transformer of claim 55, wherein said first number of steel laminations is approximately 20% less than said second number of steel laminations.
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57. The transformer of claim 56, wherein said first number of steel laminations is approximately 30% less than said second number of steel laminations.
Specification