Ferroresonant transformer for use in uninterruptible power supplies

Abstract

A ferroresonant transformer is adapted to be connected to a primary power source, an inverter system, and a resonant capacitor. The ferroresonant transformer comprises a core, a main shunt arranged to define a primary side and a secondary side of the ferroresonant transformer, first windings arranged on the primary side of the ferroresonant transformer, second windings arranged on the secondary side of the ferroresonant transformer, and third windings arranged on the secondary side of the ferroresonant transformer. The first windings are operatively connected to the primary power source.

Description

TECHNICAL FIELD

The present invention relates the generation of a standby power signal and, more specifically, to uninterruptible power supply systems and methods using ferroresonant transformers.

BACKGROUND

Uninterruptible power supplies (UPS's) have long been used to provide at least temporary auxiliary power to electronic devices. Typically, a UPS is configured to switch between a primary power source and a standby power source as necessary to maintain constant power to a load.

For example, the primary power source may be a utility power supply, and the standby power source may take the form of a battery system. The UPS will normally operate in a line mode in which the utility power signal is passed to the load when the utility power signal is within predefined parameters. In the line mode, the UPS will typically also charge the battery system. When the utility power falls outside of the predefined parameters, the UPS will switch to standby mode in which an AC signal is generated based on the energy stored in the battery system.

A class of UPS's employs a ferroresonant transformer. A ferroresonant transformer is a saturating transformer that employs a tank circuit comprised of a resonant winding and capacitor to produce a nearly constant average output even if the input to the transformer varies. A typical UPS employing a ferroresonant transformer takes advantage of the voltage regulating properties of a ferroresonant transformer in both line and standby modes. In the context of a UPS, a ferroresonant transformer thus provides surge suppression, isolation, short circuit protection, and voltage regulation without the use of active components.

Conventionally, a ferroresonant transformer configured for use in a UPS system includes a core and an inductor arranged relative to the core to define: (a) a primary or input side of the transformer and (b) a secondary or output side of the transformer. A conventional ferroresonant transformer used in a UPS will further comprise input windings and inverter (resonant) windings arranged on the primary or input side and output windings on the secondary or output side.

An object of the present invention is to provide improved ferroresonant transformers for use in UPS systems.

SUMMARY

The present invention may be embodied as a ferroresonant transformer adapted to be connected to a primary power source, an inverter system, and a resonant capacitor. The ferroresonant transformer comprises a core, a main shunt arranged to define a primary side and a secondary side of the ferroresonant transformer, first windings arranged on the primary side of the ferroresonant transformer, second windings arranged on the secondary side of the ferroresonant transformer, and third windings arranged on the secondary side of the ferroresonant transformer. The first windings are operatively connected to the primary power source.

The present invention may also be embodied as an uninterruptible power supply system adapted to be connected to a primary power source, a battery system, and a load. An uninterruptible power supply of the present invention comprises a ferroresonant transformer, an inverter, and a resonant capacitor. The ferroresonant transformer comprises a core, a main shunt, and first, second, and third windings. The main shunt is arranged relative to the core to define a primary side and a secondary side of the ferroresonant transformer. The first windings are arranged on the primary side of the ferroresonant transformer. The second windings are arranged on the secondary side of the ferroresonant transformer. The third windings arranged on the secondary side of the ferroresonant transformer. The inverter is operatively connected to the second windings. The resonant capacitor is operatively connected to the third windings. The first windings are operatively connected to the primary power source. The inverter is operatively connected to the battery system. The resonant capacitor is operatively connected to the load.

The present invention may also be embodied as a method of supplying power to a load based on an AC power signal and a DC power signal, the method comprising the following steps. A ferroresonant transformer is formed by arranging a main shunt relative to a core to define a primary side and a secondary side of the ferroresonant transformer, arranging first windings on the primary side of the ferroresonant transformer, arranging second windings on the secondary side of the ferroresonant transformer, and arranging third windings on the secondary side of the ferroresonant transformer. An inverter is operatively connected to the second windings. A resonant capacitor is operatively connected to the third windings. The load is operatively connected to the resonant capacitor. Power is supplied to the load based on the AC power signal in a line mode. The inverter is operated based on the DC power signal to provide power to the load in a standby mode.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of a first embodiment of an uninterruptible power supply system using a ferroresonant transformer system constructed in accordance with, and embodying, the principles of the present invention;

FIG. 2 is a somewhat schematic view of a ferroresonant transformer forming a part of the UPS system depicted in FIG. 1;

FIG. 3 is a perspective view of the ferroresonant transformer depicted in FIG. 2;

FIG. 4 is a side elevation view of the ferroresonant transformer depicted in FIGS. 2 and 3; and

FIG. 5 is a section view taken along lines 5-5 in FIG. 4.

DETAILED DESCRIPTION

Referring initially to FIG. 1 of the drawing, depicted therein is a first example of an uninterruptible power supply (UPS) system 20 constructed in accordance with, and embodying, the principles of the present invention.

The example UPS system 20 supplies power to a load 22 based on a primary power signal present on an AC power line 24 (line mode) or a secondary power signal generated by a battery pack 26 (standby mode). While the example secondary power signal is generated by a battery pack in the example UPS system 20, alternative power sources such as generators, fuel cells, solar cells, and the like may be used as the secondary power source.

The example UPS system 20 comprises an input section 30, an output section 32, an inverter section 34, a cable assembly 36, and a ferroresonant transformer 38.

The example input section 30 comprises a main switch 40 and first and second select switches 42 and 44. The example output section 32 comprises an output or resonant capacitor 50 and, optionally, a select switch 52 and a filter capacitor 54.

When the select switch 52 is closed, the output capacitor 50 forms a resonant or tank circuit with the transformer 38 as will be described in further detail below. When the select switch 52 is open, the output capacitor 50 is removed from the circuit formed by the output section 32 and transformer 38, and the filter capacitor 54 filters the output of this circuit.

The inverter section 34 comprises an inverter circuit 60. The inverter circuit 60 may be an H-bridge circuit or any other circuit capable of producing an appropriate AC power signal based on a DC power signal obtained from the battery pack 26. In particular, the inverter circuit 60 is pulse-width modulated, and the inverter section 34 functions as a switch mode power supply when the UPS system operates in the standby mode. The inverter section 34 and the inverter circuit 60 are or may be conventional and will not be described herein in further detail.

A controller 62 may be optionally included in the inverter section 34. If used, the controller 62 operates the switches 40 and 52 and controls the inverter circuit 60. The controller 62 may further control the charging of the battery pack 26 when the UPS system 20 operates in line mode based on the temperature, voltage, and/or current signals associated with the battery pack 26.

The ferroresonant transformer 38 comprises a core 70, input windings 72, an inductor 74, inverter windings 76, and output windings 78. The core 70 is or may be a conventional laminate structure. As shown in FIG. 2, the inductor 74 defines a primary side 80 and a secondary side 82 of the transformer 38. In the example transformer 38, only the input windings 72 are on the primary side 80 of the transformer 38. The inverter windings 76 and output windings 78 are on the secondary side 82 of the transformer 38. In particular, the output windings 78 are arranged between the inverter windings 76 and the inductor 74, and the inductor 74 is arranged between the output windings 78 and the input windings 72.

As perhaps best shown in FIGS. 3 and 5, the transformer 38 depicted in FIGS. 1 and 2 defines the following arrangement of windings and shunts: the input windings 72, a large (or main) shunt formed by the inductor 74, output windings 78, and inverter windings 76. FIGS. 3 and 5 further illustrate that, in the example transformer 38, a small (or minor) shunt 90 is arranged between the output windings 78 and the inverter windings 76. The small shunt 90 does not significantly affect the electromagnetic properties of the transformer 38 in the context of the overall UPS system 20 but is used in the example transformer 38 to allow the transformer 38 to operate as described herein in the context of the UPS system 20.

In the line mode, the AC power line 24 forms a primary power source that causes a primary signal to be present on the input windings 72. The input windings 72 are electromagnetically coupled to the output windings 78 such that a first output signal is supplied to one or both of the loads 22a and 22b when the UPS system 20 operates in the line mode.

In the standby mode, the battery pack 26 and inverter section 34 form a secondary power source that causes a secondary signal to be present on the inverter windings 76. The inverter windings 76 are electromagnetically coupled to the output windings 78 such that a second output signal is supplied to one or both of the loads 22a and 22b when the UPS system 20 operates in the standby mode.

The construction details of the transformer 38 are not critical to the general principles of the present invention and will depend upon a particular implementation of the UPS system 20 in which the transformer 38 is designed to operate. The example transformer 38 has the following characteristics:

stacking     3 × 3 interleaved
stack height approximately 109.73 MM (4.32″)
shunts       positioned in cores such that there is equal
             overhang on both sides
keeper       cut from E lamination at both ends of stack;
             tape tightly across keeper after E-I
             compaction to reduce noise
lamination   compact E-I lamination together without air
             gap
sleevings    nylon sleevings used with bolts
shims        use wood shims to fill in gaps between
             windings and core
small shunt  approximately 2.00 mm (0.075″) thick (4
             pcs grade H50 or 3 pcs M54 shunt
             lamination); polyester tape
large shunt  approximately 16 mm (0.625″) thick (stack
             height adjusted to meet short circuit current
             requirement); polyester tape
core         E-I lamination; grain orientation as shown
             in FIG. 3
varnish      penetrate at least 80% of the windings and
             be fully cured

The example cable assembly 36 connects the output section 32 to one of first and second example loads 22a or 22b. In particular, the cable assembly 36 comprises first and second winding connectors 120 and 122 operatively connected to a first end 124 of the output windings 78. A second end 126 of the output windings 78 is connected to the output capacitor 50. The cable assembly 36 further comprises first and second tap connectors 130 and 132 operatively connected to first and second intermediate points 134 and 136, respectively, of the output windings 78. The example cable assembly 36 additionally comprises a selection cable 140 comprising a selection connector 142 and first and second output connectors 144 and 146. The first load 22a comprises first and second load connectors 150 and 152, while the second load 22b comprises second and third load connectors 154 and 156.

Using the example cable assembly 36, the selection connector 142 is connected to either the first tap connector 130 or the second tap connector 132 depending upon the voltage requirements of the loads 22a and 22b. The first and third load connectors 150 and 154 are connected to the first and second winding connectors 120 and 122, and the second and fourth winding connectors 152 and 156 are connected to the first and second output connectors 144 and 146, respectively. The cable assembly 36 thus allows one or both of the loads 22a and 22b to be connected to the output section 32 and the output windings 78 and, more specifically, to an appropriate portion of the output windings 78 as determined by the first and second tap connectors 130 and 132. The selection of the appropriate tap connector 130 or 132 is based on the voltage requirements of the loads 22a and 22b.

Given the foregoing, it should be apparent that the principles of the present invention may be embodied in forms other than those described above. The scope of the present invention should thus be determined the claims to be appended hereto and not the foregoing detailed description of the invention.

Claims

1. A ferroresonant transformer adapted to be connected to a primary power source, an inverter system, and a resonant capacitor, the ferroresonant transformer comprising: a core;a main shunt arranged to define a primary side and a secondary side of the ferroresonant transformer;first windings arranged on the primary side of the ferroresonant transformer;second windings arranged on the secondary side of the ferroresonant transformer; andthird windings arranged on the secondary side of the ferroresonant transformer; whereinthe first windings are configured to be operatively connected to the primary power source;the second windings are configured to be operatively connected to the inverter system; andthe third windings are configured to be directly connected to the resonant capacitor.

2. A ferroresonant transformer as recited in claim 1, in which the main shunt is formed by an inductor.

3. A ferroresonant transformer as recited in claim 1, further comprising a minor shunt arranged between the second windings and the third windings.

4. An uninterruptible power supply system adapted to be connected to a primary power source, a battery system, and a load, the uninterruptible power supply comprising: a ferroresonant transformer comprising a core;a main shunt arranged relative to the core to define a primary side and a secondary side of the ferroresonant transformer;first windings arranged on the primary side of the ferroresonant transformer;second windings arranged on the secondary side of the ferroresonant transformer; andthird windings arranged on the secondary side of the ferroresonant transformer; andan inverter, where the inverter is operatively connected to the second windings;a resonant capacitor, where the resonant capacitor is operatively connected to the third windings; anda select switch:whereinthe first windings are operatively connected to the primary power source;the inverter is operatively connected to the battery system;the resonant capacitor is operatively connected to the load;in a line mode, power flows from the primary source to the load through the ferroresonant transformer; andin a standby mode, power flows from the inverter to the load through the ferroresonant transformer, where the select switch is configured to disconnect the reasonant capacitor from the third windings when the uninterruptible power supply is in the standby mode.

5. An uninterruptible power supply as recited in claim 4, in which the main shunt is formed by an inductor.

6. An uninterruptible power supply as recited in claim 4, in which the ferroresonant transformer further comprises a minor shunt arranged between the second windings and the third windings.

7. An uninterruptible power supply as recited in claim 4, in which the inverter is pulse-width modulated.

8. An uninterruptible power supply as recited in claim 4, in which the inverter is a switch mode power supply.

9. An uninterruptible power supply as recited in claim 4, in which the primary power source is a utility power supply.

10. An uninterruptible power supply as recited in claim 4, further comprising a filter capacitor operatively connected across at least a portion of the third windings.

11. A method of supplying power to a load based on an AC power signal and a DC power signal, the method comprising the steps of: forming a ferroresonant transformer by arranging a main shunt relative to a core to define a primary side and a secondary side of the ferroresonant transformer;arranging first windings on the primary side of the ferroresonant transformer;arranging second windings on the secondary side of the ferroresonant transformer;arranging third windings on the secondary side of the ferroresonant transformer;operatively connecting the inverter to the second windings; andoperatively connecting a resonant capacitor to the third windings;operatively connecting the load to the resonant capacitor;supplying power to the load through the ferroresonant transformer based on the AC power signal in a line mode;operating the inverter based on the DC power signal to provide power to the load through the ferroresonant transformer in a standby mode; anddisconncecting the reasonant capacitor from the third windings when the uninterruptible power supply is in the standby mode.

12. A method as recited in claim 11, further comprising the step of operating the inverter to generate a battery charge signal in the line mode.

13. A method as recited in claim 11, in which the step of arranging a main shunt relative to a core comprises the step of providing an inductor.

14. A method as recited in claim 11, in which the step of forming the ferroresonant transformer further comprises the step of arranging a minor shunt between the second windings and the third windings.

15. A method as recited in claim 11, in which the step of operating the inverter in standby mode further comprises the step of pulse-width modulating the DC power signal.

16. A method as recited in claim 11, in which the step of operating the inverter in standby mode further comprises the step of operating the inverter as a switch mode power supply.

17. A method as recited in claim 11, further comprising the step of operatively connecting a filter capacitor across at least a portion of the third windings.

18. A method of supplying power to a load based on an AC power signal and a DC power signal, the method comprising the steps of: forming a ferroresonant transformer by arranging a main shunt relative to a core to define a primary side and a secondary side of the ferroresonant transformer;arranging first windings on the primary side of the ferroresonant transformer;arranging second windings on the secondary side of the ferroresonant transformer;arranging third windings on the secondary side of the ferroresonant transformer;operatively connecting the inverter to the second windings;operatively connecting a filter capacitor across at least a portion of the third windings;operatively connecting a resonant capacitor to the third windings;operatively connecting the load to the resonant capacitor;supplying power to the load based on the AC power signal in a line mode;operating the inverter based on the DC power signal to provide power to the load in a standby mode; anddisconnecting the reasonant capacitor from the third windings when the uninterruptible power supply is in the standby mode.