Voltage sag and over-voltage compensation device with pulse width modulated autotransformer

• US 6,559,562 B1
• Filed: 03/06/2002
• Issued: 05/06/2003
• Est. Priority Date: 12/14/2001
• Status: Expired due to Fees

• Current Assignee: SSI Power, LLC
• Original Assignee: SSI Power, LLC
• Inventors: Rostron, Joseph R.
• Primary Examiner(s): Riley, Shawn
• Application Number:
  US10/091,866
• Time in Patent Office: 426 Days
• Field of Search: 323/255, 323/258, 323/341, 323/343, 323/209, 307/130, 307/129, 307/85, 307/87, 307/125, 327/556, 327/557, 361/91.7
• US Class Current: 307/130
• CPC Class Codes: H02M 5/293 using semiconductor devices only

Abstract

A voltage sag and over-voltage compensation device for an AC electric power distribution system employing cascaded switching devices and a pulse width modulated autotransformer. The autotransformer typically includes lower, center, and upper poles or taps with cascaded switching devices for selectively connecting the voltage source (i.e., a phase of the distribution line) between the lower pole and the center or upper poles. Each stage of the cascaded switching device includes a switching element located within a full-bridge rectifier circuit to allow bi-directional switching through each switching element (i.e., switching through the same switching element during the positive and negative portions of the AC voltage cycle). Each full-bridge rectifier also includes a snubber circuit connected in parallel with a corresponding switching element to absorb the current discharge caused by switching the input power supply to the autotransformer through the corresponding switching device under non-zero current conditions. On the output side, the voltage sag and over-voltage compensation device includes a load capacitor to smooth the voltage-corrected AC power supply toward a sinusoidal power supply at the system frequency, and a notch filter to remove noise created by the switching elements.

Claims

1. A device for selectively receiving electric power from an AC power source oscillating at a system frequency, adjusting the voltage of the power, and delivering a corresponding voltage-corrected AC power supply to a load connected across an upper pole and a neutral pole of the device;

comprising;

an autotransformer having;

a first winding around a flux linking core and connected between the neutral pole and a center pole;

a second winding around the flux linking core and connected between the center pole and the upper pole;

a center-pole switch for selectively connecting the AC power source between the neutral and center poles when the center-pole switch is gated to a closed configuration, and for selectively disconnecting the AC power source from connection between the neutral and center poles when the center-pole switch is gated to an open configuration; and

a control unit for selectively gating the center-pole switch between the open configuration and the closed configuration multiple times per cycle of the system frequency to generate the voltage-corrected AC power supply for delivery to the load.

2. The device of claim 1, wherein the center-pole switch is located within a full-bridge rectifier circuit connected between the AC power source and the center pole.

3. The device of claim 1, further comprising a center-pole snubber connected in parallel with the center-pole switch.

4. The device of claim 1, further comprising:

a center-pole snubber connected in parallel with the center-pole switch; and

the center-pole switch and the center-pole snubber located within a full-bridge rectifier circuit connected between the AC power source and the center pole.

5. The device of claim 1, wherein the center-pole switch comprises a cascade of individual center-pole switching devices connected in series and operated substantially simultaneously.

6. The device of claim 5, wherein each individual center-pole switching device is located within an individual full-bridge rectifier circuit.

7. The device of claim 6, further comprising a plurality of center-pole snubber circuits, each connected in parallel with one of the individual switching devices and located within a corresponding full-bridge rectifier circuit.

8. The device of claim 7, wherein each center-pole snubber circuit comprises a resistor and a capacitor connected in series and a diode connected in parallel with the resistor.

9. The device of claim 1, further comprising a capacitor connected between the neutral and upper poles and configured to smooth the voltage-corrected AC power supply toward a sinusoidal power supply at the system frequency.

10. The device of claim 1, wherein the control unit gates the center-pole switch at a gating frequency, further comprising a notch filter connected between the neutral and upper poles and configured to reduce power disturbances occurring in the voltage-corrected AC power supply within a filter frequency range comprising the gating frequency.

11. The device of claim 10, wherein the notch filter comprises an inductor, a resistor and a capacitor connected in series.

12. The device of claim 1, further comprising an upper-pole switch for selectively connecting the AC power source between the neutral and upper poles when the upper-pole switch is gated to a closed configuration, and for selectively disconnecting the AC power source from connection between the neutral and upper poles when the upper-pole switch is gated to an open configuration.

13. The device of claim 12, further comprising an upper-pole snubber connected in parallel with the upper-pole switch.

14. The device of claim 12, wherein the upper-pole switch comprises a cascade of individual upper-pole switching devices connected in series and operated substantially simultaneously.

15. The device of claim 14, wherein each individual upper-pole switching device is located within an individual full-bridge rectifier circuit.

16. The device of claim 15, further comprising a plurality of upper-pole snubber circuits, each connected in parallel with one of the individual switching devices and located within a corresponding full-bridge rectifier circuit.

17. The device of claim 16, wherein each upper-pole snubber circuit comprises a resistor and a capacitor connected in series and a diode connected in parallel with the resistor.

18. The device of claim 12, wherein the control unit is configured for gating the upper-pole and center-pole switching devices in substantial unison to maintain said switches in opposing configurations.

19. The device of claim 12, wherein the control unit is configured for:

detecting a voltage sag or over-voltage condition in the AC power source;

in response to detecting the voltage sag or over-voltage condition, continually gating the upper-pole and center-pole switching devices in substantial unison to maintain said switches in opposing configurations to create a desired voltage-corrected AC power supply;

detecting a cessation of the voltage sag or over-voltage condition in the AC power source;

in response to detecting the cessation of the voltage sag or over-voltage condition, gating the center-pole switching device to an open configuration, gating the upper-pole switching device to a closed configuration, and discontinuing further gating of switching devices.

20. The device of claim 12, wherein the control unit is configured for:

detecting a voltage sag or over-voltage condition in the AC power source;

in response to detecting the voltage sag or over-voltage- condition, gating the upper-pole switching device to an open configuration;

while the upper-pole switching device is in the open configuration, continually gating the center-pole switching device between the open and closed configurations to create a desired voltage-corrected AC power supply;

detecting a cessation of the voltage sag or over-voltage condition in the AC power source; and

in response to detecting the cessation of the voltage sag or over-voltage condition, gating the center-pole switching device to an open configuration, gating the upper-pole switching device to a closed configuration, and discontinuing further gating of switching devices.

21. A device for selectively receiving electric power from an AC power source oscillating at a system frequency, adjusting the voltage of the power, and delivering a corresponding voltage-corrected AC power supply to a load connected across an upper pole and a neutral pole of the device;

comprising;

an autotransformer having;

a first winding around a flux linking core and connected between the neutral pole and a center pole;

a second winding around the flux linking core and connected between the center pole and the upper pole;

a cascade of series connected full-bridge rectifier circuits connected between the AC power source and the center pole;

a plurality of center-pole switching devices, each located within a corresponding full-bridge rectifier circuit, for selectively connecting the AC power source between the neutral and center poles when the center-pole switching devices are gated to a closed configuration, and for selectively disconnecting the AC power source from connection between the neutral and center poles when the center-pole switching devices are gated to an open configuration; and

a control unit for selectively gating the center-pole switching devices a between the open configuration and the closed configuration multiple times per cycle of the system frequency to generate the voltage-corrected AC power supply for delivery to the load.

22. The device of claim 21, further comprising:

a plurality of center-pole snubber circuits, each connected in parallel with a corresponding center-pole switching device; and

each center-pole switching device and each corresponding center-pole snubber circuit located within a corresponding full-bridge rectifier circuit connected between the AC power source and the center pole.

23. The device of claim 22, wherein each snubber circuit comprises a resistor and a capacitor connected in series and a diode connected in parallel with the resistor.

24. The device of claim 23, further comprising a capacitor connected between the neutral and upper poles and configured to smooth the voltage-corrected AC power supply toward a sinusoidal power supply at the system frequency.

25. The device of claim 24, wherein the control unit gates the center-pole switching device at a gating frequency, further comprising a notch filter connected between the neutral and upper poles and configured to reduce power disturbances occurring in the voltage-corrected AC power supply in a filter frequency range comprising the gating frequency.

26. The device of claim 25, wherein the notch filter comprises an inductor, a resistor and a capacitor connected in series.

27. The device of claim 25, further comprising a plurality of upper-pole switching devices, each located within a corresponding full-bridge rectifier circuit, for selectively connecting the AC power source between the neutral and upper poles when the upper-pole switching devices are gated to a closed configuration, and for selectively disconnecting the AC power source from connection between the neutral and upper poles when the upper-pole switching devices are gated to an open configuration.

28. The device of claim 27, further comprising:

a plurality of upper-pole snubber circuits, each connected in parallel with a corresponding upper-pole switching device; and

each upper-pole switching device and each corresponding upper-pole snubber circuit located within a corresponding full-bridge rectifier circuit connected between the AC power source and the upper pole.

29. The device of claim 28, wherein the control unit is configured for gating the upper-pole and center-pole switching devices in substantial unison to maintain said switches in opposing configurations.

30. The device of claim 28, wherein the control unit is configured for:

detecting a voltage sag or over-voltage condition in the AC power source;

in response to detecting the voltage sag or over-voltage condition, continually gating the upper-pole and center-pole switching devices in substantial unison to maintain said switches in opposing configurations to create a desired voltage-corrected AC power supply;

detecting a cessation of the voltage sag or over-voltage condition in the AC power source;

in response to detecting the cessation of the voltage sag or over-voltage condition, gating the center-pole switching device to an open configuration, gating the upper-pole switching device to a closed configuration, and discontinuing further gating of switching devices.

31. The device of claim 28, wherein the control unit is configured for:

detecting a voltage sag or over-voltage condition in the AC power source;

in response to detecting the voltage sag or over-voltage condition, gating the upper-pole switching device to an open configuration;

while the upper-pole- switching device is in the open configuration, continually gating the center-pole switching device between the open and closed configurations to create a desired voltage-corrected AC power supply;

detecting a cessation of the voltage sag or over-voltage condition in the AC power source; and

in response to detecting the cessation of the voltage sag or over-voltage condition, gating the center-pole switching device to an open configuration, gating the upper-pole switching device to a closed configuration, and discontinuing further gating of switching devices.

32. A device for selectively receiving electric power from an AC power source oscillating at a system frequency, adjusting the voltage of the power, and delivering a corresponding voltage-corrected AC power supply to a load connected across an upper pole and a neutral pole of the device;

comprising;

an autotransformer having;

a first winding around a flux linking core and connected between the neutral pole and a center pole;

a second winding around the flux linking core and connected between the center pole and the upper pole;

a cascade of series connected full-bridge rectifier circuits connected between the AC power source and the center pole;

a plurality of center-pole switching devices, each located within a corresponding full-bridge rectifier circuit, for selectively connecting the AC power source between the neutral and center poles when the center-pole switching devices are gated to a closed configuration, and for selectively disconnecting the AC power source from connection between the neutral and center poles when the center-pole switching devices are gated to an open configuration;

a plurality of center-pole snubber circuits, each connected in parallel with a corresponding center-pole switching device, and each center-pole switching device and each corresponding center-pole snubber circuit located within a corresponding full-bridge rectifier circuit connected between the AC power source and the center pole;

a plurality of upper-pole switching devices, each located within a corresponding full-bridge rectifier circuit, for selectively connecting the AC power source between the neutral and upper poles when the upper-pole switching devices are gated to a closed configuration, and for selectively disconnecting the AC power source from connection between the neutral and upper poles when the upper-pole switching devices are gated to an open configuration;

a plurality of upper-pole snubber circuits, each connected in parallel with a corresponding upper-pole switching device, and each upper-pole switching device and each corresponding upper-pole snubber circuit located within a corresponding full-bridge rectifier circuit connected between the AC power source and the upper pole;

a capacitor connected between the neutral and upper poles and configured to smooth the voltage-corrected AC power supply toward a sinusoidal power supply at the system frequency;

a control unit for selectively gating the center-pole switching devices a between the open configuration and the closed configuration at a gating frequency that is substantially higher than the system frequency to generate the voltage-corrected AC power supply for delivery to the load; and

a notch filter connected between the neutral and upper poles and configured to reduce power disturbances occurring in the voltage-corrected AC power supply in a filter frequency range comprising the gating frequency.