Method and device for continuous adjustment and regulation of transformer turns ratio, and transformer provided with such device

• US 5,969,511 A
• Filed: 01/30/1998
• Issued: 10/19/1999
• Est. Priority Date: 08/01/1995
• Status: Expired due to Fees

• Current Assignee: Rendel BV
• Original Assignee: N.V. Eneco
• Inventors: Paap, Gerardus Chr., van de Water, Cornelis J., de Haan, Sjoerd W. H., Bauer, Pavol, Griffioen, Jan Hendrik, Asselman, Paulus G. J. M.
• Primary Examiner(s): BERHANE, ADOLF D
• Application Number:
  US09/016,243
• Time in Patent Office: 627 Days
• Field of Search: 323/209, 323/255, 323/257, 323/258, 323/340, 323/343
• US Class Current: 323/258
• CPC Class Codes: G05F 1/20 semiconductor devices only
• CPC Class Codes: H02P 13/06 by tap-changing; by rearranging interconnections of windings

Abstract

In a method and a device for continuously adjusting, within a certain adjustment range, the turns ratio between the primary winding and the secondary winding of a power transformer provided with at least one regulating winding, a first tap is switched on during a portion of a cycle of the alternating voltage of the transformer and a second tap is switched on during another portion of the cycle of the alternating voltage. For this purpose, the device comprises electronic switches in the form of thyristors or transistors.

Claims

1. A method for adjusting, within a predetermined adjustment range, the turns ratio between a primary and a secondary winding of an AC power transformer comprising the steps of:

providing at least a portion of said primary winding with a plurality of taps;

switching AC voltage to a first one of said taps during a first time period of a cycle of the alternating voltage; and

alternately switching AC voltage to a second one of said taps during a second time period of a cycle of the alternating voltage applied to the transformer to enable a transformer turns ratio that is essentially continuously adjustable within said preset adjustment range.

2. The method of claim 1 further comprising the step of using pulse-width modulation controlled switches to alternately switch said AC voltage between said first and second ones of said taps.

3. The method of claim 2 further comprising the step of switching said pulse-width modulation controlled switches at a frequency which is at least an order of magnitude higher than the frequency of the AC voltage.

4. The method of claim 1 wherein the step of switching said AC voltage between said first one of said taps and said second one of said taps is accomplished with the use of phase control.

5. The method of claim 1 further comprising the step of switching said AC voltage between said first one of said taps and said second one of said taps only when the transformer is essentially in its steady-state operating condition.

6. A switching device for adjusting, within a predetermined adjustment range, the turns ratio between a primary and a secondary winding of an AC power transformer having at least first and second taps on at least a portion of the primary winding of said transformer, the switching device comprising:

at least first and second electronic switches that can be made to conduct unidirectionally or bidirectionally;

a first terminal on each of said switches adapted to be coupled to one of said first and second taps;

a second terminal on each of said switches adapted to be connected to one of the first and second terminals of at least one other of said electronic switches;

a control device coupled to said at least first and second electronic switches for supplying control signals to said switches to obtain a transformer turns ratio that is essentially continuously adjustable within said predetermined adjustment range;

a reference signal coupled to said control device;

a first control signal generated by said control device for causing said first electronic switch to couple an AC voltage to said first tap during a first time period of a cycle of the AC voltage;

a second control signal generated by said control device for causing said second electronic switch to couple said AC voltage to said second tap during another time period of the cycle of the AC voltage; and

the ratio of the time periods in which the first and second taps are switched being dependent upon said reference signal coupled to said control device.

7. The switching device of claim 6 wherein said control device generates pulse-width modulation signals to cause said electronic switches to switch said AC voltage from said first tap to said second tap.

8. The switching device of claim 6 wherein each of said first and second electronic switches comprises:

two transistors connected to each other at a first point in series opposition;

two diodes connected to each other at a second point in series opposition with an opposite polarity with respect to, and in parallel with, said two series connected transistors; and

said first point and said second point being conductively coupled.

9. The switching device of claim 8 wherein said transistors are of the IGBT type.

10. The switching device of claim 6 wherein said control device generates phase control signals to cause said electronic switches to switch said AC voltage from said first tap to said second tap.

11. The switching device of claim 10 wherein said first and second electronic switches comprise thyristors coupled in anti-parallel relationship.

12. The switching device of claim 6 further comprising:

at least one element for limiting the voltage across, and the current through, the electronic switches such that a predetermined voltage or current value, respectively, is not exceeded;

a first terminal on said at least one element being adapted to be connected to one of said taps on said transformer; and

a second terminal on said at least one element being adapted to be connected to one of the first and second terminals of at least one of said electronic switches.

13. The switching device of claim 12 wherein said at least one element is formed by any one of the group comprising an impedance, a thyristor, a voltage-dependent resistor, and a surge voltage protector.

14. The switching device of claim 6 further comprising:

at least one element for limiting the voltage across, and the current through, the electronic switches such that a predetermined voltage or current value, respectively, is not exceeded;

a first terminal on said at least one element being connected to said first terminal of at least one of said electronic switches; and

a second terminal on said at least one element being connected to at least one of said first and second terminals of at least one of said electronic switches.

15. The switching device of claim 14 wherein said at least one element is formed by any one of the group comprising an impedance, a thyristor, a voltage-dependent resistor, and a surge voltage protector.

16. The switching device of claim 6 wherein said switching device receives power from said AC power transformer.

17. An AC power transformer comprising:

at least one regulating winding having a plurality of taps thereon;

a primary and a secondary winding;

a switching device for adjusting, within a predetermined adjustment range, the turns ratio of the primary and secondary windings of the power transformer;

said switching device comprising a plurality of electronic switches, each having the capability of conducting unidirectionally or bidirectionally;

a first and a second terminal on each of said electronic switches;

said first terminal of each of said electronic switches being connected to a corresponding one of said plurality of taps on said regulating winding;

said second terminal of each of said electronic switches being connected to one of said first and second terminals of at least one other of said electronic switches;

a control device for supplying control signals to said electronic switches so as to obtain a transformer turns ratio that is essentially continuously adjustable within said adjustment range;

a reference signal coupled to said control device;

a first control signal generated by said control device for coupling an AC voltage to one of said taps during a first time period of a cycle of the AC voltage; and

a second control signal generated by said control device for coupling said AC voltage to a different tap during a second time period of said cycle of the AC voltage;

the ratio of said first and second time periods being dependent upon said reference signal fed to said control device.