TRANSFER SWITCH DEVICE AND METHOD

• US 20050184591A1
• 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: Bush, Terry D, Marwali, Mohammad N, Powell, Jeffery, Heber, Brian
• Granted Patent: US 7,352,082 B2
• Time in Patent Office: Days
• US Class Current: 307/52
• 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
• CPC Class Codes: H02M 7/4803 with means for reducing DC component from AC output voltage

Abstract

This disclosure is concerned with devices and methods for voltage source transfer switching that reduces or eliminates transformer saturation due to DC flux built up during a transfer event. First and second voltage sources (primary and alternate) are connectable to a load via corresponding switches. A transformer is connected downstream of the switches. A controller operates the switches according to various transfer methods wherein a switching time is determined to minimize downstream saturation current.

Claims

1. A method of switching between first and second voltage sources, comprising:

disconnecting the first voltage source from a load;

computing volt-second areas under voltage waveforms of the first and second voltage sources in real time;

determining a switching time to minimize downstream saturation current based on the real-time computation of the volt-second areas; and

connecting the second voltage source to the load at the determined switching time.

2. The method of claim 1, wherein the real-time computation of the volt-second areas includes assigning a polarity to each volt-second area based on the polarity of the corresponding voltage.

3. The method of claim 2, wherein connecting the second voltage source to the load at the determined switching time includes connecting the second voltage source to the load in response to the absolute values of the areas under the waveforms of the first and second voltage sources being approximately equal and their polarities being opposite.

4. The method of claim 2, wherein connecting the second voltage source to the load at the determined switching time includes connecting the second voltage source to the load in response to the sum of the absolute values of the areas under the waveforms of the first and second voltage sources being approximately equal to the absolute value of the area under the waveform of a complete half cycle of the second voltage, and their polarities being the same.

5. The method of claim 1, wherein disconnecting the first voltage source from the load includes deactivating a first switch.

6. The method of claim 1, wherein connecting the second voltage source to the load at the predetermined switching time includes activating a second switch.

7. A method of switching between first and second voltage sources, comprising:

disconnecting the first voltage source from a load;

determining fluxes corresponding to the first and second voltages in real time;

determining a switching time to minimize downstream saturation current based on the real-time flux determination.; and

connecting the second voltage source to the load at the determined switching time.

8. The method of claim 7 wherein the real time determination of fluxes includes measuring the fluxes.

9. The method of claim 7 wherein the real-time determination of the fluxes includes computing the time integrals of the voltages.

10. The method of claim 9, wherein connecting the second voltage source to the load at the determined switching time includes connecting the second voltage source to the load in response to the time integrals of the first and second voltages being approximately equal.

11. The method of claim 7, wherein disconnecting the first voltage source from the load includes deactivating a first switch.

12. The method of claim 7, wherein connecting the second voltage source to the load at the predetermined switching time includes activating a second switch.

13. A transfer switch system, comprising:

a first switch connectable to a first voltage source;

a second switch connectable to a second voltage source;

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 transformer, wherein upon a predetermined condition, the controller;

deactivates the first switch to disconnect the first voltage source from the load,

computes volt-second areas under voltage waveforms of the first and second voltage sources in real time;

determines a switching time to minimize downstream saturation current based on the real-time computation of the volt-second areas; and

connects the second voltage source to the load at the determined switching time.

14. The transfer switch system of claim 13, wherein the real-time computation of the volt-second areas includes assigning a polarity to each volt-second area based on the polarity of the corresponding voltage.

15. The transfer switch system of claim 14, wherein the controller activates the second switch in response to the absolute values of the areas under the waveforms of the first and second voltage sources being approximately equal and their polarities being opposite.

16. The transfer switch system of claim 14, wherein the controller activates the second switch in response to the sum of the absolute values of the areas under the waveforms of the first and second voltage sources being approximately equal to the absolute value of the area under the waveform of a complete half cycle of the second voltage, and their polarities being the same.

17. A transfer switch system, comprising:

a first switch connectable to a first voltage source;

a second switch connectable to a second voltage source;

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 transformer, wherein upon a predetermined condition, the controller;

deactivates the first switch to disconnect the first voltage source from the load,

determines fluxes corresponding to the first and second voltages in real time;

determines a switching time to minimize downstream saturation current based on the real-time flux determination.; and

connects the second voltage source to the load at the determined switching time.

18. The transfer switch system of claim 17, wherein the real time determination of fluxes includes measuring the fluxes.

19. The transfer switch system of claim 17, wherein the real time determination of the fluxes includes computing the time integrals of the voltages.

20. The transfer switch system of claim 19, wherein the controller activates the second switch in response to the time integrals of the first and second voltages being approximately equal.

21. 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;

deactivates the first switch to disconnect the first voltage source from the transformer;

computes volt-second areas under voltage waveforms of the first and second voltage sources in real time;

determines a switching time to minimize downstream saturation current based on the real-time computation of the volt-second areas; and

connects the second voltage source to the transformer at the determined switching time.

22. The transfer switch system of claim 21, wherein the real-time computation of the volt-second areas includes assigning a polarity to each volt-second area based on the polarity of the corresponding voltage.

23. The transfer switch system of claim 22, wherein the controller activates the second switch in response to the absolute values of the areas under the waveforms of the first and second voltage sources being approximately equal and their polarities being opposite.

24. The transfer switch system of claim 22, wherein the controller activates the second switch in response to the sum of the absolute values of the areas under the waveforms of the first and second voltage sources being approximately equal to the absolute value of the area under the waveform of a complete half cycle of the second voltage, and their polarities being the same.

25. 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;

deactivates the first switch to disconnect the first voltage source from the transformer;

determines fluxes corresponding to the first and second voltages in real time;

determines a switching time to minimize downstream saturation current based on the real-time flux determination; and

connects the second voltage source to the transformer at the determined switching time.

26. The transfer switch system of claim 25, wherein the real time determination of fluxes includes measuring the fluxes.

27. The transfer switch system of claim 26, wherein the real time determination of the fluxes includes computing the time integrals of the voltages.

28. The transfer switch system of claim 27, wherein the controller activates the second switch in response to the time integrals of the first and second voltages being approximately equal.