AU2017203737B2 - Ferroresonant transformer for use in uninterruptible power supplies - Google Patents

Abstract

A ferroresonant transformer system, which is adapted to be connected to a primary power source, an inverter system, a resonant capacitor, and at least one load, comprises a ferroresonant transformer and a select switch. 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 select switch is arranged to selectively connect or disconnect the third windings from the resonant capacitor.

Description

FERRORESONANT TRANSFORMER FOR USE IN UNINTERRUPTIBLE POWER SUPPLIES

RELATED APPLICATIONS [0001] The present application is a divisional application from Australian Patent Application No. 2015203667, which is a divisional application from Australian Patent Application No. 2011218269, the entire disclosures of which are incorporated herein by reference.

[0002] The present application also claims priority from U.S. Patent Application No. 12/803,787 filed on 7 July 2010, which claims benefit of U.S. Provisional Patent Application No. 61/305,926 filed on 18 February 2010, the contents of both of which are to be taken as incorporated herein by this reference.

TECHNICAL FIELD [0003] 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 [0004] 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.

[0005] 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

-12017203737 02 Jun 2017 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.

[0006] 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.

[0007] 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.

[0008] It would be desirable to provide improved ferroresonant transformers for use in UPS systems.

[0009] The discussion of the background to the invention included herein including reference to documents, acts, materials, devices, articles and the like is included to explain the context of the present invention. This is not to be taken as an admission or a suggestion that any of the material referred to was published, known or part of the common general knowledge in Australia or in any other country as at the priority date of any of the claims.

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SUMMARY [0010] An aspect of the present invention provides a ferroresonant transformer system adapted to be connected to a primary power source, an inverter system, a resonant capacitor, and at least one load, the ferroresonant transformer system comprising a ferroresonant transformer and a select switch. 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, where the first windings are configured to be operatively connected to the primary power source, second windings arranged on the secondary side of the ferroresonant transformer, where the second windings are configured to be operatively connected to the inverter system, and third windings arranged on the secondary side of the ferroresonant transformer. The select switch is arranged to selectively connect or disconnect the third windings from the resonant capacitor.

[0011] Another aspect of the present invention provides an uninterruptible power supply system adapted to be connected to a primary power source, a battery system, and at least one load. The uninterruptible power supply system comprises a ferroresonant transformer, a select switch, an inverter, and a resonant capacitor. The ferroresonant transformer comprises a core, a main shunt, first windings, second windings, and third windings. The main shunt is arranged 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 are arranged on the secondary side of the ferroresonant transformer. The inverter is operatively connected to the second windings. The select switch is arranged to selectively operatively connect the resonant capacitor to or disconnect the resonant capacitor from the third windings. The first windings are operatively connected to the primary power source. The inverter is operatively connected to the battery system. In a line mode, the resonant

-32017203737 02 Jun 2017 capacitor is connected to the third windings and power flows from the primary power source to the at least one load through the ferroresonant transformer. In a standby mode, the resonant capacitor is disconnected from the third windings and power flows from the inverter to the at least one load through the ferroresonant transformer.

[0012] Another aspect of the present invention provides a method of supplying uninterruptible power to at least one load from a primary power source and a battery system. The method comprises the step of providing a ferroresonant transformer. 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 method also comprises the steps of operatively connecting an inverter to the second windings, operatively connecting the first windings to the primary power source, and operatively connecting the inverter to the battery system. The method also comprises in a line mode, operating a select switch to operatively connect a resonant capacitor to the third windings such that power flows from the primary source to the at least one load through the ferroresonant transformer. The method also comprises in a standby mode, operating the select switch to operatively disconnect the resonant capacitor from the third windings such that power flows from the inverter to the at least one load through the ferroresonant transformer.

DESCRIPTION OF THE DRAWINGS [0013] 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;

-42017203737 02 Jun 2017 [0014] FIG. 2 is a somewhat schematic view of a ferroresonant transformer forming a part of the UPS system depicted in FIG. 1;

[0015] FIG. 3 is a perspective view of the ferroresonant transformer depicted in FIG. 2;

[0016] FIG. 4 is a side elevation view of the ferroresonant transformer depicted in FIGS. 2 and 3; and [0017] FIG. 5 is a section view taken along lines 5-5 in FIG. 4.

DETAILED DESCRIPTION [0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

-52017203737 02 Jun 2017 [0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

-62017203737 02 Jun 2017 [0026] 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.

[0027] 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.

[0028] 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.

[0029] 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	3x3 interleaved
stack height	approximately 109.73 MM (4.32)

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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-l compaction to reduce noise
lamination	compact E-l 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-l lamination; grain orientation as shown in FIG. 3
varnish	penetrate at least 80% of the windings and be fully cured

[0030] 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,

-82017203737 02 Jun 2017 while the second load 22b comprises second and third load connectors 154 and 156.

[0031] 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.

[0032] 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.

[0033] Where the terms comprise, comprises, comprised or comprising are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other features, integers, steps or components, or group thereto.

Claims (21)

1. The claims defining the invention are as follows:

   1. A ferroresonant transformer system adapted to be connected to a primary power source, an inverter system, a resonant capacitor, and at least one load, the ferroresonant transformer system comprising:

   a 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, where the first windings are configured to be operatively connected to the primary power source;

   second windings arranged on the secondary side of the ferroresonant transformer, where the second windings are configured to be operatively connected to the inverter system; and third windings arranged on the secondary side of the ferroresonant transformer; and a select switch arranged to selectively connect or disconnect the third windings from the resonant capacitor.
2. 2. A ferroresonant transformer system as recited in claim 1, further comprising:

   a first tap connector operatively connected to a first intermediate point of the third windings;

   a second tap connector operatively connected to a second intermediate point of the third windings; and a cable assembly operatively connected between a selected tap connector selected from the first and second tap connectors and at least one of a plurality of loads.
3. 3. A ferroresonant transformer system as recited in claim 2, in which the cable assembly is operatively connected between the selected tap

   2017203737 02 Jun 2017 connector and a plurality of loads.
4. 4. A ferroresonant transformer system as recited in any one of claims 1 to 3, in which the main shunt is formed by an inductor.
5. 5. A ferroresonant transformer system as recited in any one of claims 1 to 4, further comprising a minor shunt arranged between the second windings and the third windings.
6. 6. An uninterruptible power supply system adapted to be connected to a primary power source, a battery system, and at least one load, the uninterruptible power supply system comprising:

   a 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; and third windings arranged on the secondary side of the ferroresonant transformer;

   a select switch;

   an inverter, where the inverter is operatively connected to the second windings; and a resonant capacitor; wherein the select switch is arranged to selectively operatively connect the resonant capacitor to or disconnect the resonant capacitor from the third windings;

   the first windings are operatively connected to the primary power source;

   the inverter is operatively connected to the battery system;

   in a line mode, the resonant capacitor is connected to the third

   -112017203737 02 Jun 2017 windings and power flows from the primary power source to the at least one load through the ferroresonant transformer; and in a standby mode, the resonant capacitor is disconnected from the third windings and power flows from the inverter to the at least one load through the ferroresonant transformer.
7. 7. An uninterruptible power supply system as recited in claim 6, further comprising a controller configured to operate the select switch to:

   connect the resonant capacitor to the third windings when the uninterruptible power supply is in the line mode; and disconnect the resonant capacitor from the third windings when the uninterruptible power supply is in the standby mode.
8. 8. An uninterruptible power supply system as recited in claims 6 or 7, in which the main shunt is formed by an inductor.
9. 9. An uninterruptible power supply system as recited in any one of claims 6 to 8, in which the ferroresonant transformer further comprises a minor shunt arranged between the second windings and the third windings.
10. 10. An uninterruptible power supply system as recited in any one of claims 6 to 9, in which the inverter is pulse-width modulated.
11. 11. An uninterruptible power supply system as recited in any one of claims 6 to 10, in which the inverter is a switch mode power supply.
12. 12. An uninterruptible power supply system as recited in any one of claims 6 to 11, in which the primary power source is a utility power supply.
13. 13. An uninterruptible power supply system as recited in any one of claims 6 to 12, further comprising a filter capacitor operatively connected across at least a portion of the third windings.

    2017203737 02 Jun 2017
14. 14. A method of supplying uninterruptible power to at least one load from a primary power source and a battery system, the method comprising the steps of:

    providing a 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; and third windings arranged on the secondary side of the ferroresonant transformer, operatively connecting an inverter to the second windings;

    operatively connecting the first windings to the primary power source; operatively connecting the inverter to the battery system;

    in a line mode, operating a select switch to operatively connect a resonant capacitor to the third windings such that power flows from the primary source to the at least one load through the ferroresonant transformer; and in a standby mode, operating the select switch to operatively disconnect the resonant capacitor from the third windings such that power flows from the inverter to the at least one load through the ferroresonant transformer.
15. 15. A method as recited in claim 14, further comprising the steps of: operatively connecting a controller to the select switch;

    operating the controller to cause the select switch to connect the resonant capacitor to the third windings when the uninterruptible power supply is in the line mode; and operating the controller to cause the select switch to disconnect the resonant capacitor from the third windings when the uninterruptible power supply is in the standby mode.

    -132017203737 02 Jun 2017
16. 16. A method as recited in claims 14 or 15, in which the step of providing the ferroresonant transformer comprises the step of arranging an inductor to form the main shunt.
17. 17. A method as recited in any one of claims 14 to 16, in which the step of providing the ferroresonant transformer comprises the step of arranging a minor shunt between the second windings and the third windings.
18. 18. A method as recited in any one of claims 14 to 17, in which the step of providing the inverter comprises the step of providing a pulse-width modulated inverter.
19. 19. A method as recited in any one of claims 14 to 18, in which the step of providing the inverter comprises the step of providing a switch mode power supply.
20. 20. A method as recited in any one of claims 14 to 19, in which the step of operatively connecting the first windings to the primary power source comprises the step of operatively connecting the first windings to a utility power supply.
21. 21. A method as recited in any one of claims 14 to 20, further comprising the step of operatively connecting a filter capacitor across at least a portion of the third windings.