Voltage sag corrector using a variable duty cycle boost converter

• US 9,270,170 B2
• Filed: 04/18/2012
• Issued: 02/23/2016
• Est. Priority Date: 04/18/2011
• Status: Active Grant

• Current Assignee: I-EWM Acquisation, LLC
• Original Assignee: Innovolt Incorporated (EAST Manufacturing Corporation)
• Inventors: Divan, Deepakraj Malhar
• Primary Examiner(s): Berhane, Adolf
• Assistant Examiner(s): DEMISSE, AFEWORK S
• Application Number:
  US13/449,870
• Publication Number:
  US 20120262140A1
• Time in Patent Office: 1,406 Days
• Field of Search: 323/223, 323/282, 323/351, 307/64, 307/65
• US Class Current: 1/1
• CPC Class Codes: H02M 1/0022 the disturbance parameters being input voltage fluctuations
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators

Abstract

A sag corrector apparatus for providing voltages temporarily (ride-through) to a load during momentary electrical disturbances in the power supply line. In one embodiment, the disclosed apparatus compensates for voltage sags by using a variable duty cycle boost converter to boost the sagged line voltage to resemble desired voltage levels during occurrence of voltage sags. The boosted voltage available to a connected load during a sag depends on a sequence of operation of various control pulses. Duty cycle of the boost converter is controlled by changing the width (duration) of the control pulses. To prevent voltage shoot-throughs from over-boosting, an energy clamp circuit is provided to dissipate excess energy. Embodiments of the sag corrector circuit can be additionally integrated with power protection functions.

Claims

1. A system for providing temporary electrical power to a load connected to an input AC line voltage during a voltage sag, comprising:

a selectively variable voltage boost converter including a pulse-width modulated inductance for providing a boosted voltage to the load, the boost converter operative when actuated to provide a boosted voltage as a function of instantaneous value of the input AC line voltage compared to a desired nominal AC line voltage;

a circuit for detecting a voltage sag in the input AC line voltage corresponding to a value in a predetermined range of values in the input AC line voltage less than the nominal voltage for the input AC line voltage and for actuating the boost converter to provide a boosted voltage at a value that increases the voltage provided to the load in response to detecting the voltage sag, for detecting when the voltage sag is over, and for deactuating the boost converter when the voltage sag is over;

a switch for coupling the input AC line voltage to the electrical load during normal operating conditions and for coupling the boosted voltage from the boost converter to the electrical load in response to detection of a voltage sag and actuation of the boost converter; and

a clamping circuit coupled to the boost converter for clamping excess voltage from the inductance in the boost converter when the boost converter is deactuated in response to detection that the voltage sag is over.

2. The system of claim 1, wherein the switch is a first switch, and wherein the boost converter comprises an inductor coupled in series with the first switch to disconnect the input AC line voltage from the load during inductor charging during a boost phase, and further comprising a second switch coupled to provide a path of low resistance to ground to charge the inductor.

3. The system of claim 1, further comprising a component for determining an amount of boost correction for the boost converter based on the difference between a value of the input AC line voltage and the nominal voltage;

and

wherein the boost converter is operative to provide the boosted voltage as a function of said determined difference.

4. The system of claim 1, wherein the voltage sag in the input AC line voltage comprises a plurality of values in the predetermined range of values less than nominal voltage.

5. The system of claim 1, further comprising a programmed microcontroller for controlling the boost converter, detecting the voltage sag and when the voltage sag is over, and for controlling the switch.

6. The system of claim 5, wherein the voltage sag is determined based on a comparison of a set of values of the input AC line voltage to a pre-stored template representing a voltage sag, and

wherein the pre-stored template is stored in the microcontroller.

7. The system of claim 1, wherein the clamping circuit comprises a clamping capacitor, a diode, a semiconductor switch, and a discharge resistance.

8. The system of claim 1, wherein the switch is operative to couple the input AC line voltage to the electrical load during normal conditions on the input AC line voltage;

and

wherein in response to detection of a voltage sag, the switch is operative to disconnect the input AC line voltage from the electrical load during a charging operation of the boost converter.

9. The system of claim 8, wherein the boost converter is actuated subsequent to disconnection of the input AC line voltage from the electrical load after detection of the voltage sag.

10. The system of claim 8, wherein the disconnecting the input AC line voltage, actuating the boost converter, and coupling the boosted voltage to the electrical load during the duration of the voltage sag are repeated at a predetermined frequency during the voltage sag.

11. The system of claim 1, wherein in response to detection of the end of a voltage sag, the switch is operative to disconnect the boost converter from the electrical load to isolate the boost converter from the electrical load, turn off the boost converter subsequent to disconnection of the boost converter from the electrical load, and couple to the boost converter to the clamping circuit to absorb excess voltage from the boost converter upon turn off of the boost converter.

12. The system of claim 11, further comprising a component for imposing a predetermined delay after disconnecting the boost converter before reconnecting the input AC line voltage to the electrical load,

whereby any excess voltage from the boost converter is diverted to the clamping circuit.

13. The system of claim 1, wherein the switch is operative to reconnect the input AC line voltage to the electrical load after excess voltage from the boost converter has been diverted to the clamping circuit in response to the detection of the end of the voltage sag.

14. The system of claim 1, further comprising a sensor for detecting the instantaneous value of the voltage at the clamping circuit;

and further comprising a fourth switch (S4) for discharging the clamping circuit in response to detection that the voltage on the clamping circuit has exceeded a predetermined threshold value.

15. The system of claim 1, further comprising a control circuit operative for receiving signals from a first voltage sensor coupled to input AC line voltage, detecting the occurrence of a voltage sag based on the signal from the first voltage sensor, for actuating the boost converter to provide the boosted voltage, for detecting the end of the voltage sag based on the signal from the first voltage sensor, and for turning off the boost converter in response to detection of the end of the voltage sag.

16. The system of claim 15, further comprising a second voltage sensor coupled to detect the voltage on the clamping circuit, and

wherein the control circuit is operative for discharging the clamping circuit in response to a signal from a second voltage sensor indicating that the voltage on the clamping device has exceeded a predetermined threshold value.

17. The system of claim 1, wherein the clamping circuit comprises a diode with its cathode coupled to the clamping capacitor and a discharge resistor Rc coupled from a terminal of the clamping capacitor through a fourth switch (S4);

and

wherein the clamping capacitor is discharged when the fourth switch is closed.

18. The system of claim 17, wherein boost converter provides boosted voltage to the electrical load independently of discharge of the clamping circuit.

19. The system of claim 1, further comprising a circuit for controlling the boost converter to provide a variable boost as a function of the difference between the input AC line voltage and the nominal AC line voltage.

20. The system of claim 19, wherein the variable boost is provided by varying the duty cycle of the boost converter with pulse width modulation (PWM).

21. The system of claim 1, further comprising:

control circuit;

a first voltage sensor coupled to the control circuit for detecting the input AC line voltage;

a second voltage sensor coupled to the control circuit for detecting the voltage on the clamping circuit;

a first switch (S1, S2) for connecting the input AC line voltage and the boosted voltage from the boost converter to the load;

a third switch (S3) for coupling an inductor in the boost converter to a potential for charging the inductor;

a fourth switch (S4) coupled to the clamping circuit for discharging the clamping circuit; and

wherein the control circuit provides outputs for controlling the first switch (S1, S2) and the third switch (S3) for charging the boost converter and coupling the boosted voltage to the electrical load, and the fourth switch (S4) for discharge of the clamping circuit.

22. The system of claim 21, wherein the control circuit comprises a programmed microcontroller that controls the operation of the first switch (S1, S2) and the third switch (S3) for boosting the voltage independently of control of the fourth switch (S4) for discharge of the clamping circuit.

23. A method for providing temporary electrical power to a load connected to an input AC line voltage during a voltage sag, comprising the steps of:

detecting a voltage sag in the input AC line voltage corresponding to a value in a predetermined range of values in the input AC line voltage less than a nominal voltage for the input AC line voltage;

in response to detecting the voltage sag, actuating a selectively variable voltage boost converter that includes a pulse-width modulated inductance to provide a boosted voltage to the load, the boost converter operative when actuated to provide a boosted voltage as a function of instantaneous value of the input AC line voltage compared to a desired nominal AC line voltage;

detecting the end of the voltage sag; and

in response to detecting that the voltage sag is over, deactuating the boost converter and clamping excess voltage from the inductance in the boost converter to a clamping circuit so as to prevent the excess voltage from being transmitted to the load.

24. The method of claim 23, wherein the boost converter comprises an inductor coupled in series with a first switch to disconnect the input AC line voltage from the load during inductor charging, and a second switch coupled to provide a path of low resistance to ground for charging the inductor.

25. The method of claim 23, further comprising the step of determining an amount of boost correction based on the difference between a value of the input AC line voltage and the nominal voltage;

and

activating the boost converter to provide the boosted voltage as a function of said determined difference.

26. The method of claim 23, wherein the voltage sag in the input AC line voltage comprises a plurality of values in the predetermined range of values less than nominal voltage.

27. The method of claim 23, wherein the voltage sag is determined based on a comparison of a set of values of the input AC line voltage to a pre-stored template representing a voltage sag.

28. The method of claim 27, wherein the pre-stored template is stored in a microcontroller utilized to control the system.

29. The method of claim 23, further comprising the step of charging a capacitor connected across the load that supplies electrical power to the load during a voltage sag.

30. The method of claim 23, wherein the clamping circuit comprises a clamping capacitor, a diode, a semiconductor switch, and a discharge resistance.

31. The method of claim 23, further comprising the steps of:

coupling the input AC line voltage to the electrical load during normal conditions on the input AC line voltage;

in response to detection of a voltage sag, disconnecting the input AC line voltage from the electrical load during a charging operation of the boost converter.

32. The method of claim 31, wherein the step of actuating the boost converter is conducted subsequent to disconnection of the input AC line voltage from the electrical load after detection of the voltage sag.

33. The method of claim 31, wherein the steps of disconnecting the input AC line voltage, actuating the boost converter, and coupling the boosted voltage to the electrical load during the duration of the voltage sag are repeated at a predetermined frequency during the voltage sag.

34. The method of claim 23, wherein the step of turning off the boost converter and clamping excess voltage comprises:

in response to detection of the end of a voltage sag, disconnecting the boost converter from the electrical load to isolate the boost converter from the electrical load;

subsequent to disconnecting the boost converter from the electrical load, turning off the boost converter; and

coupling to the boost converter to the clamping device to absorb excess voltage from the boost converter upon turn off of the boost converter.

35. The system of claim 34, further comprising the step of imposing a predetermined delay after disconnecting the boost converter before reconnecting the input AC line voltage to the electrical load,

whereby any excess voltage from the boost converter is diverted to the clamping circuit.

36. The method of claim 23, further comprising the step of reconnecting the input AC line voltage to the electrical load after excess voltage from the boost converter has been diverted to the clamping device in further response to the detection of the end of the voltage sag.

37. The method of claim 23, further comprising the steps of:

detecting the instantaneous value of the voltage at the clamping circuit; and

in response to detection that the voltage on the clamping circuit has exceeded a predetermined threshold value, discharging the clamping circuit.

38. The method of claim 23, wherein steps of the method are effected by a control circuit operative for receiving signals from a first voltage sensor and a second voltage sensor, detecting the occurrence of a voltage sag based on the signal from the first voltage sensor, for actuating the boost converter to provide the boosted voltage, for detecting the end of the voltage sag based on the signal from the first voltage sensor, and for turning off the boost converter in response to detection of the end of the voltage sag.

39. The method of claim 38, wherein the control circuit is further operative for discharging the clamping circuit in response to a signal from a second voltage sensor indicating that the voltage on the clamping device has exceeded a predetermined threshold value.

40. The method of claim 23, wherein the clamping circuit comprises a diode with its cathode coupled to the clamping capacitor and a discharge resistor Rc coupled from a terminal of the clamping capacitor through a fourth switch (S4);

and

further comprising the step of discharging the clamping capacitor when the fourth switch is closed.

41. The method of claim 40, wherein the steps of providing the boosted voltage to the electrical load via the boost converter and the steps of discharging the clamping circuit are carried out independently.

42. The method of claim 23, further comprising the step of controlling the boost converter to provide a variable boost as a function of the difference between the input AC line voltage and the nominal AC line voltage.

43. The method of claim 42, wherein the variable boost is provided by varying the duty cycle of the boost converter with pulse width modulation (PWM).

44. The method of claim 23, wherein the method is carried out in part with a control circuit that receives inputs from a first voltage sensor and a second voltage sensor, and provides outputs for controlling a first switch (S1, S2) and a third switch (S3) for charging the boost converter and coupling the boosted voltage to the electrical load, and a fourth switch (S4) for controlling discharge of the clamping circuit.

45. The method of claim 44, wherein the control circuit comprises a programmed microcontroller that controls the operation of the first switch (S1, S2) and the third switch (S3) for boosting the voltage independently of control of the fourth switch (S4) for discharge of the clamping circuit.

46. A system for providing temporary electrical power to an electrical load connected to an input AC line voltage during a voltage sag, comprising:

a selectively variable voltage boost converter including a pulse-width modulated inductor for providing a boosted voltage to the electrical load in response to actuation the boost converter operative when actuated to provide a boosted voltage as a function of instantaneous value of the input AC line voltage compared to a desired nominal AC line voltage;

a clamping device coupled to the boost converter for absorbing excess voltage from the inductance in the boost converter upon turn off of the boost converter;

a first voltage sensor for detecting the instantaneous value of the input AC line voltage;

a second voltage sensor for detecting the instantaneous value of the voltage at the clamping device;

a first switch (S1, S2) for coupling the input AC line voltage to the electrical load during normal conditions on the input AC line voltage, for disconnecting the input AC line voltage during charging of the boost converter, and for coupling the boost converter to the electrical load after charging;

a third switch (S3) operative in alternation with the first switch for coupling the boost converter inductor through a low resistance to ground to charge the inductor;

a fourth switch (S4) for coupling the clamping device through a discharge resistor (Rc) in response to detection that the voltage on the clamping device has exceeded a predetermined threshold value; and

a control circuit for receiving signals from the first voltage sensor and the second voltage sensor, for detecting the occurrence of a voltage sag based on the signal from the first voltage sensor, for actuating the boost converter to provide the boosted voltage, for activating the first switch to couple the input AC line voltage to the electrical load during normal conditions on the input AC line voltage, for activating the third switch for charging the inductor in the boost converter, for detecting the end of the voltage sag based on the signal from the first voltage sensor, for deactuating the boost converter in response to detection of the end of the voltage sag, and for activating the fourth switch to discharge the clamping device in response to the signal from the second voltage sensor indicating that the voltage on the clamping device has exceeded the predetermined threshold value.

47. The system of claim 46, wherein the clamping device comprises a clamping capacitor coupled to receive and absorb excess voltage from the boost converter.

48. The system of claim 47, wherein the clamping device further includes a diode with its cathode coupled to the clamping capacitor, and a discharge resistor Rc coupled from a terminal of the clamping capacitor through the fourth switch (S4) to ground for discharging the clamping capacitor when the fourth switch is closed.

49. The system of claim 46, further comprising a diode bridge for rectifying the output voltage from the boost converter that is coupled in parallel with the third switch, so as to charge the clamping device to the nominal voltage level during normal operations.

50. The system of claim 46, wherein the control circuit operates the fourth switch (S4) independently of the first switch (S1, S2) and the third switch (S3) to discharge the clamping device when the voltage across the clamping device exceeds a predetermined maximum value.

51. The system of claim 46, further comprising a front end protection circuit for the apparatus.

52. The system of claim 51, wherein the front end protection circuit comprises a first MOV and a parallel second MOV coupled to the input AC line voltage, and a relay coupled between the first MOV and the second MOV, and

wherein the control circuit is operative to open the relay to protect the system in response to detection of an overvoltage.

53. The system of claim 52, wherein the overvoltage is detected by the first voltage sensor.

54. The system of claim 46, wherein the control circuit is operative to control the boost converter to provide a variable boost as a function of the difference between the input AC line voltage and the nominal AC line voltage.

55. The system of claim 54, wherein the variable boost is provided by varying the duty cycle of actuation of the first switch (S1, S2) and the third switch (S3).

56. The system of claim 46, wherein the control circuit comprises a microcontroller including inputs for the first voltage sensor and the second voltage sensor, and provides outputs for controlling first switch (S1, S2), the third switch (S3), and the fourth switch (S4).

57. The system of claim 56, wherein the microcontroller controls the operation of the first switch (S1, S2) and the third switch (S3) for boosting the voltage independently of control of the fourth switch (S4) for discharge of the clamping device.

58. The system of claim 46, wherein the control circuit is further operative for disconnecting the boost converter via the first switch (S1, S2) prior to reconnecting the input AC line voltage to the electrical load, and for imposing a predetermined delay after disconnecting the boost converter from the electrical load before reconnecting the input AC line voltage to the electrical load,

whereby any excess voltage from turning off the boost converter is diverted to the clamping device.

59. A method for providing temporary electrical power to an electrical load connected to an input AC line voltage during a voltage sag, comprising:

coupling the input AC line voltage to the electrical load during normal conditions on the input AC line voltage;

detecting the instantaneous value of the input AC line voltage;

in response to detection of a voltage sag, disconnecting the input AC line voltage from the electrical load;

subsequent to disconnection of the input AC line voltage from the electrical load after detection of the voltage sag, turning on a selectively variable voltage boost converter including a pulse-width modulated inductor to provide a boosted voltage to the electrical load, the boost converter operative when actuated to provide a boosted voltage as a function of instantaneous value of the input AC line voltage compared to a desired nominal AC line voltage;

coupling a boosted voltage from the boost converter to the electrical load after charging of the boost converter;

repeating the steps of disconnecting the input AC line voltage, turning on the boost converter, and coupling the boosted voltage to the electrical load during the duration of the voltage sag;

in response to detection of the end of the voltage sag, disconnecting the boost converter from the electrical load to isolate the boost converter from the electrical load;

subsequent to disconnecting the boost converter from the electrical load, turning off the boost converter;

coupling a clamping device to the boost converter to absorb excess voltage from the inductor in the boost converter upon turn off of the boost converter;

in further response to the detection of the end of the voltage sag, reconnecting the input AC line voltage to the electrical load after excess voltage from the boost converter has been diverted to the clamping device;

detecting the instantaneous value of the voltage at the clamping device; and

in response to detection that the voltage on the clamping device has exceeded a predetermined threshold value, discharging the clamping device through a discharge resistor (Rc).

60. The method of claim 59, wherein the step of detecting the instantaneous value of the input AC line voltage is effected with a first voltage sensor.

61. The method of claim 59, wherein the step of detecting the instantaneous value of the voltage at the clamping device is effected with a second voltage sensor.

62. The method of claim 59, wherein the step of coupling the input AC line voltage to the electrical load during normal conditions on the input AC line voltage is effected with a first switch (S1, S2).

63. The method of claim 62, wherein the step of turning on a selectively actuatable boost converter comprises turning on a third switch (S3) to provide a path of low resistance to ground for an inductor in the boost converter while the first switch is turned off.

64. The method of claim 62, wherein the first switch (S1, S2) is operative for coupling the input AC line voltage to the electrical load during normal conditions on the input AC line voltage, for disconnecting the input AC line voltage during charging of the boost converter, and for coupling the boost converter to the electrical load after charging.

65. The method of claim 62, wherein the first switch (S1, S2) and the third switch (S3) operate in alternation to charge an inductor in the boost converter and to couple the boosted voltage from the inductor to the electrical load after charging.

66. The method of claim 65, wherein the frequency of operation of the first switch (S1, S2) and the third switch (S3) for boosting is in the range of about 16 kHz to about 25 kHz.

67. The method of claim 59, wherein steps of the method are effected by a control circuit operative for receiving signals from a first voltage sensor and a second voltage sensor, detecting the occurrence of a voltage sag based on the signal from the first voltage sensor, for activating the boost converter to provide the boosted voltage, for detecting the end of the voltage sag based on the signal from the first voltage sensor, for turning off the boost converter in response to detection of the end of the voltage sag, and for discharging the clamping device in response to the signal from the second voltage sensor indicating that the voltage on the clamping device has exceeded the predetermined threshold value.

68. The method of claim 59, wherein the clamping device comprises a clamping capacitor coupled to receive and absorb excess voltage from the boost converter.

69. The method of claim 68, wherein the clamping device further includes a diode with its cathode coupled to the clamping capacitor, and a discharge resistor Rc coupled from a terminal of the clamping capacitor through a fourth switch (S4) to ground for discharging the clamping capacitor when the fourth switch is closed.

70. The method of claim 59, further comprising the step of rectifying the output voltage from the boost converter so as to charge the clamping device to the nominal AC input voltage level during normal operations.

71. The method of claim 59, wherein steps of providing the boosted voltage to the electrical load via the boost converter and the steps of discharging the clamping device are carried out independently.

72. The method of claim 59, further comprising the step of protecting a system practicing the method from overvoltages occurring on the input AC line voltage.

73. The method of claim 72, wherein the step of overvoltage protection comprises:

providing a first MOV and a parallel second MOV coupled to the input AC line voltage, and a relay coupled between the first MOV and the second MOV, and

opening the relay to protect the system in response to detection of an overvoltage.

74. The method of claim 59, further comprising the step of controlling the boost converter to provide a variable boost as a function of the difference between the input AC line voltage and the nominal AC line voltage.

75. The method of claim 74, wherein the variable boost is provided by varying the duty cycle of the boost converter with pulse width modulation (PWM).

76. The method of claim 59, wherein the method is carried out in part with a control circuit that receives inputs from a first voltage sensor and a second voltage sensor, and provides outputs for controlling a first switch (S1, S2) and a third switch (S3) for charging the boost converter and coupling the boosted voltage to the electrical load, and a fourth switch (S4) for controlling discharge of the clamping device.

77. The method of claim 76, wherein the control circuit comprises a programmed microcontroller that controls the operation of the first switch (S1, S2) and the third switch (S3) for boosting the voltage independently of control of the fourth switch (S4) for discharge of the clamping device.

78. The method of claim 59, wherein the step of disconnecting the boost converter from the electrical load and turning off the boost converter is effected prior to the step of reconnecting the input AC line voltage to the electrical load, and

further comprising the step of imposing a predetermined delay after disconnecting the boost converter from the electrical load before reconnecting the input AC line voltage to the electrical load,

whereby any excess voltage from turning off the boost converter is diverted to the clamping device.