Combination current hysteresis and voltage hysteresis control for a power converter

• US 7,417,336 B2
• Filed: 08/31/2004
• Issued: 08/26/2008
• Est. Priority Date: 08/31/2004
• Status: Expired due to Fees

• Current Assignee: Caterpillar Incorporated
• Original Assignee: Caterpillar Incorporated
• Inventors: Johnson, James P.
• Primary Examiner(s): Sherry; Michael J
• Assistant Examiner(s): KAPLAN, HAL IRA
• Application Number:
  US10/929,689
• Publication Number:
  US 20060050458A1
• Time in Patent Office: 1,456 Days
• Field of Search: 307/18, 307/22, 307/29, 307/75, 307/80, 307/82, 361/92, 363/15, 363/95
• US Class Current: 307/22
• CPC Class Codes: H02J 2300/30 The power source being a fuel cell
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02J 3/388 Islanding, i.e. disconnection of local power supply from the network
• CPC Class Codes: H02M 1/007 Plural converter units in cascade push-pull DC/DC converters with pre-regulator H02M3/3374; DC-AC converters following a DC-DC stage including a high frequency transformer H02M7/4807; DC-AC converters following a DC-DC conversion stage generating periodically varying voltages H02M7/4826
• CPC Class Codes: H02M 7/53873 with digital control

Abstract

Consistent with an aspect of the present disclosure, a method is provided for controlling an AC signal, which is supplied to a load and selectively supplied to a utility grid. In response to a fault in the utility grid, the method includes decoupling the AC signal from the utility grid, and determining whether a voltage associated with the AC signal is within a desired band. The method also includes adjusting the voltage associated with the AC signal when the AC signal is outside the desired band, and comparing a magnitude of a current associated with the AC signal with a desired current value to thereby obtain a comparison result. In response to the comparison result, the current associated with the AC signal is adjusted when the voltage associated with the AC signal is within the desired band.

Claims

1. A method of controlling an AC signal, the AC signal being supplied to a load and selectively supplied to a utility grid, in response to a fault in the utility grid, the method comprising:

decoupling the AC signal from the utility grid;

determining whether a voltage associated with the AC signal is within a desired band;

adjusting the voltage associated with the AC signal when the AC signal is outside the desired band;

comparing a magnitude of a current associated with the AC signal with a desired current value to thereby obtain a comparison result; and

adjusting the current associated with the AC signal in response to the comparison result when the voltage associated with the AC signal is within the desired band.

2. A method of controlling an AC signal in accordance with claim 1, wherein the magnitude is an instantaneous magnitude of the current associated with the AC signal, and the desired current value is associated with a predetermined time interval.

3. A method of controlling an AC signal in accordance with claim 2, wherein the desired current value is one of a plurality of desired current values, each of the plurality of desired current values being stored in a memory.

4. A method of controlling an AC signal in accordance with claim 1, wherein the AC signal is a first AC signal and a utility generated AC signal present in the utility grid is a second AC signal, wherein when the utility grid is operational, the method further includes:

supplying the first AC signal to the utility grid; and

synchronizing the first AC signal with the second AC signal.

5. A method of controlling an AC signal in accordance with claim 4, further including:

generating a pulse signal in response to a change in a value of an instantaneous voltage of the second AC signal; and

setting an instantaneous current of the first AC signal to a start current in response to the pulse signal, wherein the first AC signal conforms to a temporal function having a start point, and the start current is associated with the start point.

6. A method of controlling an AC signal in accordance with claim 5, wherein the change in the value is a change from a negative value of the instantaneous voltage of the second AC signal to a positive value of the instantaneous voltage of the second AC signal.

7. A method of controlling an AC signal in accordance with claim 5, wherein the change in the value is a change from a positive value of the instantaneous voltage of the second AC signal to a negative value of the instantaneous voltage of the second AC signal.

8. A method of controlling an AC signal in accordance with claim 1, wherein the AC signal is output from an inverter circuit, and the decoupling of the AC signal from the utility grid includes decoupling the inverter circuit from the utility grid.

9. A method of controlling an AC signal in accordance with claim 1, wherein the AC signal is output from an inverter circuit, the inverter circuit including first and second transistors, the first transistor being coupled to a first conductor, the first conductor being at a first potential, and the second transistor being coupled to a second conductor, the second conductor being at a second potential less than the first potential, the AC signal being output on a line coupled to the first and second transistors, the step of adjusting the voltage including:

when the voltage associated with the AC signal is less than the desired band, turning on the first transistor and turning off the second transistor to increase the voltage associated with the AC signal to be within the desired band; and

when the voltage associated with the AC signal is greater than the desired band, turning off the first transistor and turning on the second transistor to decrease the voltage associated with the AC signal to be within the desired band.

10. A method of controlling an AC signal in accordance with claim 1, wherein an inverter circuit includes first and second transistors, the first transistor being coupled to a first conductor, the first conductor being at a first potential, and the second transistor being coupled to a second conductor, the second conductor being at a second potential less than the first potential, the AC signal being output on a line coupled to both the first and second transistors, the step of adjusting the current including:

turning on the first transistor and turning off the second transistor when the comparison result indicates that the magnitude of the current associated with the AC signal is less than the desired band; and

turning off the first transistor and turning on the second transistor when the comparison result indicates that the magnitude of the current associated with the AC signal is greater than the desired band.

15. A power control system in accordance with claim 4, further including:

a pulse generating circuit configured to output a pulse signal to the control circuit in response to a change in a value of an instantaneous voltage associated with the second AC signal, wherein the control circuit is configured to set an instantaneous current of the first AC signal to a start current in response to the pulse signal, the first AC signal conforming to a temporal function having a start point, and the start current being associated with the start point.

16. A power control system in accordance with claim 15, wherein the change in the value is a change from a negative value of the instantaneous voltage of the second AC signal to a positive value of the instantaneous voltage of the second AC signal.

17. A power control system in accordance with claim 15, wherein the change in the value is a change from a positive value of the instantaneous voltage of the second AC signal to a negative value of the instantaneous voltage of the second AC signal.

11. A power control system comprising:

an AC signal source, the AC signal source being coupled to a load, and generating an AC signal;

a switch circuit configured to selectively couple the AC signal source to a utility grid;

a control circuit configured to compare a magnitude of the current associated with the AC signal with a desired current value to obtain a comparison result; and

the control circuit coupled to the AC signal source, wherein when a voltage associated with the AC signal is outside a desired band, the control circuit is configured to control the switch circuit to decouple the AC signal source from the utility grid, and to adjust the voltage associated with the AC signal when the AC signal is outside the desired band and to adjust the current associated with the AC signal in response to the comparison result when the voltage associated with the AC signal is within the desired band.

12. A power control system in accordance with claim 11, wherein the magnitude of the current associated with the AC signal is an instantaneous magnitude of the current associated with the AC signal, and the desired current value is associated with a predetermined time interval.

13. A power control system in accordance with claim 11, wherein the control circuit includes a memory, and the desired current value is one of a plurality of desired current values, each of the plurality of desired current values being stored in the memory.

14. A power control system in accordance with claim 11, wherein the AC signal is a first AC signal and a utility generated AC signal present in the utility grid is a second AC signal, and

when the utility grid is operational, the control circuit further controls the switch circuit to couple the first AC signal to the utility grid, and synchronize the first AC signal with the second AC signal.

18. A power control system in accordance with claim 11, wherein the AC signal source includes:

first and second conductors at first and second potentials, respectively, the second potential being less than the first potential; and

an inverter circuit having first and second transistors, the first transistor being coupled to the first conductor, and the second transistor being coupled to the second conductor, a phase of the AC signal being output on a line coupled to both the first and second transistors.

19. A power control system in accordance with claim 18, wherein, when the voltage associated with the AC signal is less than the desired band, the control circuit is configured to supply first control signals to turn on the first and transistor and turn off the second transistor to increase the voltage associated with the AC signal to be within the desired band;

and

when the voltage associated with the AC signal is greater than the desired band, the control circuit is configured to supply second control signals to turn off the first transistor and turn on the second transistor to decrease the voltage associated with the AC signal to be within the desired band.

20. A power control system in accordance with claim 11, wherein the AC signal source includes:

first and second conductors at first and second potentials, respectively, the second potential being less than the first potential; and

an inverter circuit having first and second transistors, the first transistor being coupled to the first conductor, and the second transistor being coupled to the second conductor, a phase of the AC signal being output on a line coupled to both the first and second transistors,

when the comparison result indicates that the magnitude of the current is less than the desired value, the control circuit supplies first control signals to turn on the first transistor and turn off the second transistor to increase the current to be substantially equal to the desired value, and

when the comparison result indicates that the magnitude of the current is greater than the desired value, the control circuit supplies second control signals to turn off the first transistor and turn on the second transistor to decrease the current to be substantially equal to the desired value.

21. A power control system, comprising:

an inverter circuit configured to receive a DC signal and supply an AC signal to a load;

a current transducer circuit configured to receive the AC signal and output a current sense signal in response to a current associated with the AC signal;

a voltage transducer circuit configured to receive the AC signal and output a voltage sense signal in response to a voltage associated with the AC signal;

a switch circuit configured to selectively supply the AC signal to a utility grid;

a pulse generating circuit configured to output a pulse signal in response to a utility AC signal present in the utility grid;

a control circuit configured to receive the current sense signal, the voltage sense signal and the pulse signal, and output control signals to the inverter circuit in response thereto; and

when the switch circuit decouples the AC signal from the utility grid, the control circuit is configured to control the voltage associated with the AC signal when the AC signal is outside a desired band and to control the current associated with the AC signal when the voltage associated with the AC signal is within the desired band.

22. A power control system in accordance with claim 21, wherein when the switch circuit supplies the AC signal to the utility grid, the control circuit is configured to control the current associated with the AC signal.

23. A power control system in accordance with claim 21, wherein the voltage transducer circuit is a first voltage transducer circuit and the voltage sense signal is a first voltage sense signal, the power control system further including a second voltage transducer circuit, the second voltage transducer circuit being configured to supply a second voltage sense signal to the pulse generating circuit, the second voltage sense signal being indicative of the voltage associated with the AC signal.

24. A power control system in accordance with claim 21, wherein the control circuit is configured to synchronize the AC signal with the utility AC signal in response to the pulse signal.

25. A power control system in accordance with claim 21, wherein the pulse generating circuit outputs the pulse signal in response to a change in a value of an instantaneous voltage associated with the utility AC signal, and the control circuit is configured to set an instantaneous current of the AC signal to a start current in response to the pulse signal, the AC signal conforming to a temporal function having a start point, and the start current being associated with the start point.

26. A power control system in accordance with claim 25, wherein the change in value is a change from a negative value of the instantaneous voltage of the utility AC signal to a positive value of the instantaneous voltage of the utility AC signal.

27. A power control system in accordance with claim 25, wherein the change in value is a change from a positive value of the instantaneous voltage of the utility AC signal to a negative value of the instantaneous voltage of the utility AC signal.

28. A power control system in accordance with claim 21, further including:

first and second conductors at first and second potentials, respectively, the second potential being less than the first potential,

wherein the inverter circuit includes first and second transistors, the first transistor being coupled to the first conductor, and the second transistor being coupled to the second conductor, the AC signal being output on a line coupled to both the first and second transistors.

29. A power control system in accordance with claim 28, wherein when the voltage associated with the AC signal is greater than a desired band, the control circuit is configured to adjust the voltage associated with the AC signal to be within the desired band by supplying first control signals to turn off the first and transistor and turn on the second transistor, and

when the voltage associated with the AC signal is less than the desired band, the control circuit is configured to adjust the voltage associated with the AC signal to be within the desired band by supplying second control signals to turn on the first transistor and turn off the second transistor.

30. A power control system in accordance with claim 28, wherein when the voltage associated with the AC signal is within a desired band and the current associated with the AC signal is below a desired current value, the control circuit is configured to adjust the current associated with the AC signal to be substantially equal to the desired current by supplying first control signals to turn on the first transistor and turn off the second transistor, and

when the voltage associated with the AC signal is within the desired band and the current associated with the AC signal is above the desired current value, the control circuit is configured to adjust the current associated with the AC signal to be substantially equal to the desired current by supplying second control signals to turn off the first transistor and turn on the second transistor.