Method and apparatus for producing power for an induction heating system

• US 20020036200A1
• Filed: 10/19/2001
• Published: 03/28/2002
• Est. Priority Date: 07/16/1997
• Status: Active Grant

• Current Assignee: Illinois Tool Works Inc.
• Original Assignee: Illinois Tool Works Inc.
• Inventors: Ulrich, Mark
• Granted Patent: US 6,683,286 B2
• Time in Patent Office: Days
• US Class Current: 219/665
• CPC Class Codes: H05B 6/06 Control, e.g. of temperature, of power
• CPC Class Codes: H05B 6/08 using compensating or balancing arrangements

Abstract

An induction heating power supply is disclosed. It includes a power circuit having at least one switch and a power output. The output circuit includes an induction head. The output circuit is coupled to the power output. A controller has at least one feedback input connected to the output circuit, and has a control output connected to the. switch. The controller predicts the switch zero crossing and preferably soft switches the switch. Current feedback is obtained from a-coil placed between the bus bars. Each bus bar is comprised of multiple plates to increase current capacity.

Claims

1. An induction heating power supply comprising:

a power circuit having at least one switch and a power output, wherein the power across the switch crosses zero;

an output circuit including an induction head, wherein the output circuit is coupled to the power output; and

a controller, having at least one feedback input connected to the output circuit, and having a control output connected to the switch, wherein the controller begins to cause the switch to be switched prior to the switch zero crossing.

2. The apparatus of claim 1, wherein the power circuit is a resonant power supply and the output circuit includes a resonant tank.

3. The apparatus of claim 1 wherein the controller includes a zero crossing detector coupled to the output circuit, and a frequency detector coupled to the zero crossing detector.

4. The apparatus of claim 3 wherein the frequency detector includes a ramp and a reset coupled to a zero crossing detector.

5. The apparatus of claim 4 wherein the controller includes an output voltage detector coupled to the output circuit.

6. The apparatus of claim 5 wherein the controller includes a peak voltage detector coupled to the output circuit.

7. The apparatus of claim 6 wherein the controller includes a comparator receiving as input the output of the peak voltage detector, the frequency detector and the output voltage detector.

8. The apparatus of claim 1 wherein the controller includes a peak voltage detector coupled to the output circuit.

9. The apparatus of claim 8 wherein the controller includes a current feedback signal input coupled to the output circuit that provides a current feedback signal, and wherein the controller further includes an error circuit that receives the current feedback signal and produces an error output in response thereto, wherein the error output is provided as an input to the comparator, and wherein the controller causes the switch to be soft switched.

32. The apparatus of claim 1 wherein the output circuit includes a plurality of capacitors connected to the first input, and each of the plurality of plates of the first bus bar is connected to one of the capacitors.

10. An induction heating power supply comprising:

a power circuit means for providing power, including a plurality of switches and a power output, wherein the power across each switch crosses zero;

an output means for providing output power, circuit including an induction head, wherein the output means is coupled to the power output; and

a controller means for switching the plurality of switches, wherein the switching process begins before the switch zero crossing, and having at least one feedback input connected to the output means.

11. The apparatus of claim 10, wherein the power circuit means is a resonant power supply and the output means includes a resonant tank.

12. The apparatus of claim 10 wherein the controller means includes a zero crossing detector means for detecting zero crossing, coupled to the output circuit, and a frequency detector means for providing a signal indicative of frequency, coupled to the zero crossing detector.

13. The apparatus of claim 12 wherein the frequency detector means includes a ramp and a reset for resetting the ramp, coupled to a zero crossing detector.

14. The apparatus of claim 13 wherein the controller means includes an output voltage detector for detecting peak voltage, coupled to the output means.

15. The apparatus of claim 14 wherein the controller means includes a peak voltage detector means for detecting output voltage, coupled to the output circuit means.

16. The apparatus of claim 15 wherein the controller means includes a comparator means for predicting the zero crossing and receiving as inputs the output of the peak voltage detector, the frequency detector means, and the output voltage detector means.

17. The apparatus of claim 10 wherein the controller means includes a peak tank voltage detector for detector peak tank voltage, coupled to the output means.

18. The apparatus of claim 17 wherein the controller means includes a soft switching means for soft switching the switches and a current feedback signal means, coupled to the output means, for providing a current feedback signal, and wherein the controller means further includes an error means for receiving a current feedback signal and producing an error output in response thereto, and for providing the error output as an input to the comparator means.

20. The method of claim 19, wherein the step of providing power includes the step of resonating current in a resonant tank.

21. The method of claim 19 wherein the step of switching includes the step of detecting a zero crossings and providing a signal indicative of frequency.

22. The method of claim 21 wherein the step of producing a signal includes providing a voltage ramp resetting the ramp at zero crossing.

23. The method of claim 22 wherein the step of switching includes detecting a peak voltage.

24. The method of claim 23 wherein the step of switching includes detecting a n output voltage.

25. The method of claim 24 wherein the step of switching includes predicting the zero voltage using peak voltage, output voltage and the signal indicative of frequency.

26. The method of claim 19 wherein the step of switching includes detecting peak voltage.

27. The method of claim 26 wherein the step of switching includes providing a current feedback signal and producing an error output in response thereto, and includes the step of soft switching.

19. A method of induction heating comprising the step of:

providing power, by switching a power supply, wherein the power across a switch crosses zero;

sensing at least one output parameter;

predicting the zero crossing in response to the at least one output parameter; and

beginning the switching process before the switch zero crossing.

28. A resonant power supply comprising:

an output tank;

at least two bus bars connected to the output tank, wherein the bus bars are disposed with a gap therebetween;

a coil disposed between the bus bars; and

a feedback circuit connected to the coil.

30. The apparatus of claim 30 wherein the bus bars are substantially parallel.

29. The apparatus of claim 30 wherein the feedback circuit includes a filter.

31. An induction heating power supply comprising:

an output circuit having first and second inputs;

a first bus bar connected to the first input; and

a second bus bar connected to the second input;

wherein the first and second bus bars are comprised of a plurality of plates.