STATIC TRANSFER SWITCH DEVICE AND METHOD

• US 20050184592A1
• Filed: 11/10/2004
• Published: 08/25/2005
• Est. Priority Date: 02/10/2004
• Status: Active Grant

• Current Assignee: Vertiv Corporation (Vertiv Holdings Co.)
• Original Assignee: Liebert Corporation (Vertiv Holdings Co.)
• Inventors: Marwali, Mohammad N., Bush, Terry D.
• Granted Patent: US 7,459,804 B2
• Time in Patent Office: Days
• US Class Current: 307/52
• CPC Class Codes: H02J 3/007 Arrangements for selectively connecting the load or loads to one or several among a plurality of power lines or power sources for providing uninterruptable power supply H02J9/00
• CPC Class Codes: H02J 9/06 with automatic change-over , e.g. UPS systems
• CPC Class Codes: H02J 9/068 Electronic means for switching from one power supply to another power supply, e.g. to avoid parallel connection

Abstract

Devices and methods for improved voltage source transfer switching. First and second voltage sources (primary and alternate) are connectable to a load via corresponding first and second switches, which may comprise SCRs. A controller operates the switches according to various transfer methods. In some transfer methods, the timing of the switching operation is critical. For example, switching times may be optimized to reduce or prevent transformer saturation due to the dc flux built up during the transfer event. The controller force commutates off the primary source switch by turning on the appropriate alternate source switch for a brief period of time. In this case, the alternate source switches are “pulsed” (rather than being turned on continuously), so that the switches will naturally commutate off at the next current zero cross. Subsequently, the volt-second balancing control logic will permanently turn on these switches at the appropriate time.

Claims

1. A method of controlling switches to switch between first and second voltage sources, comprising:

turning off a first switch associated with the first voltage source;

temporarily pulsing on a second switch associated with the second voltage source; and

turning on the second switch.

2. The method of claim 1, wherein pulsing on the second switch includes pulsing the second switch as many times as is necessary to minimize the output voltage disturbance.

3. The method of claim 1, wherein pulsing on the second switch includes pulsing on the second switch as many times as is necessary to commutate off the first switch.

4. The method of claim 1, wherein the first and second switches include SCRs having gate terminals, wherein pulsing on the second switch includes applying a voltage pulse to the gate terminal of an SCR of the second switch.

5. The method of claim 1, further comprising:

determining a switching time to minimize downstream saturation current; and

turning on the second switch at the determined switching time.

6. The method of claim 5, wherein the second switch is pulsed on prior to the determined switching time.

7. The method of claim 5, wherein determining the second switch includes analyzing waveforms of the first and second voltage sources.

8. The method of claim 7, wherein analyzing the waveforms includes computing the area under the voltage waveforms.

9. The method of claim 8, wherein the switching time is determined in response to the absolute values of the areas under the waveforms of the first and second voltage sources being approximately equal.

10. The method of claim 7, wherein analyzing the waveforms includes computing the time integral of the first and second voltages.

11. The method of claim 10, wherein the switching time is determined in response to the time integrals of the first and second voltages being approximately equal.

12. A transfer switch system, comprising:

a first switch connectable to a first voltage source;

a second switch connectable to a second voltage source; and

a controller connected to the first and second switches to activate and deactivate the first and second switches to selectively connect the first or the second switch to a load via a transformer;

the controller having inputs for receiving signals representing the voltage levels of the first and second voltage sources and the voltage applied to the load, wherein upon a predetermined condition, the controller temporarily pulses on the second switch and thereafter, turns on the second switch.

13. The transfer switch system of claim 12, wherein the first and second switches include SCRs.

14. The transfer switch system of claim 12, wherein the controller pulses on the second switch as many times as is necessary to minimize the output voltage disturbance.

15. The transfer switch system of claim 12, wherein the controller pulses on the second switch as many times as is necessary to commutate off the first switch.

16. The transfer switch system of claim 12, wherein the controller determines a switching time to minimize downstream saturation current and turns on the second switch at the switching time.

17. The transfer switch system of claim 16, wherein the controller temporarily pulses the second switch prior to the switching time.

18. The transfer switch system of claim 16, wherein the controller determines the switching time in response to the signals representing the voltage levels of the first and second voltage sources.

19. An uninterruptible power supply system, comprising:

a first voltage source;

a second voltage source;

a first switch connected to the first voltage source;

a second switch connected to the second voltage source;

a transformer having an input connected to the first and second switches to selectively connect the transformer to the first or second voltage source, the transformer having output terminals connectable to a load; and

a controller connected to the first and second switches to activate and deactivate the first and second switches to selectively connect the first or the second switch to the transformer;

the controller receiving signals representing the voltage levels of the first and second voltage sources and the voltage applied to the transformer input, wherein upon a predetermined condition, the controller temporarily pulses on the second switch and thereafter, turns on the second switch.

20. The transfer switch system of claim 19, wherein the first and second switches include SCRs.

21. The transfer switch system of claim 19, wherein the controller pulses on the second switch as many times as is necessary to minimize the output voltage disturbance.

22. The transfer switch system of claim 19, wherein the controller pulses on the second switch as many times as is necessary to commutate off the first switch.

23. The transfer switch system of claim 19, wherein the controller determines a switching time to minimize downstream saturation current and turns on the second switch at the switching time.

24. The transfer switch system of claim 23, wherein the controller temporarily pulses the second switch prior to the switching time.

25. The transfer switch system of claim 23, wherein the controller determines the switching time in response to the signals representing the voltage levels of the first and second voltage sources.