Induction heater having feedback control responsive to heat output

• US 5,504,309 A
• Filed: 06/07/1994
• Issued: 04/02/1996
• Est. Priority Date: 08/23/1991
• Status: Expired due to Term

• Current Assignee: Illinois Tool Works Inc.
• Original Assignee: Miller Electric Mfg Company (Illinois Tool Works Inc.)
• Inventors: Geissler, Steven J.
• Primary Examiner(s): Leung, Philip H.
• Application Number:
  US08/254,935
• Time in Patent Office: 665 Days
• Field of Search: 219/665, 219/666, 219/667, 219/663
• US Class Current: 219/663
• CPC Class Codes: H02M 7/4807 having a high frequency intermediate AC stage
• CPC Class Codes: H05B 6/04 Sources of current
• CPC Class Codes: H05B 6/06 Control, e.g. of temperature, of power

Abstract

An induction heater comprises a coupled pair of inverters and an induction head for generating heat, coupled to the second inverter. The output signal of the first inverter which operates at a fixed frequency, is controlled by feedback indicative of the heat output of the induction head. A control circuit processes the feedback information to compensate for power losses in the induction head. The output of the first inverter is electrically coupled to the input of the second inverter, which operates at an adjustable frequency which is selected by the user to optimize heating. The power delivered to the induction head is dependent on the output voltage of the second inverter, which is dependent on the output signal of the first inverter.

Claims

1. An induction heater comprising:

a first inverter with a first output capable of providing a first output power signal having a magnitude, wherein the first inverter has a control input and the magnitude of the output power is responsive to the control input;

a second inverter, coupled to the output of the first inverter, with a second output capable of providing a second output power signal;

an induction head;

a coupling circuit in electrical communication between the second output of the second inverter and the induction head; and

a control circuit including a feedback circuit and a control output coupled to the first inverter control input, wherein the control output is responsive to the heat output of the induction head whereby the power loss in the induction head is compensated for.

2. The induction heater of claim 1 wherein the feedback circuit includes means to provide a signal indicative of the magnitude of the current provided to the coupling circuit.

3. The induction heater of claim 2 wherein the feedback circuit includes means to provide a signal indicative of the magnitude of the power provided to the coupling circuit.

4. The induction heater of claim 3 wherein the feedback circuit includes means to provide a signal indicative of the magnitude of the resistive losses in the coupling circuit.

5. The induction heater of claim 4 wherein the control output is responsive to the magnitude of the resistive losses in the coupling circuit and the power provided to the coupling circuit.

6. The induction heater of claim 1 wherein the feedback circuit includes means to provide a signal indicative of the magnitude of the current provided to the induction head.

7. The induction heater of claim 6 wherein the feedback circuit includes means to provide a signal indicative of the magnitude of the power provided to the induction head.

8. The induction heater of claim 7 wherein the feedback circuit includes means to provide a signal indicative of the magnitude of the resistive losses in the induction head.

9. The induction heater of claim 8 wherein the control output is responsive to the magnitude of the resistive losses in the induction head and the power provided to the induction head.

10. A method of induction heating comprising:

disposing an induction head near an object to be heated;

providing power to the induction head;

monitoring a magnitude of resistive losses in the induction head;

controlling the magnitude of the power provided in response to the resistive losses in, and the power provided to, the induction head, whereby the power loss in the induction head is compensated for.

11. The method of claim 10 including the step of monitoring the magnitude of the current provided to the induction head and wherein the magnitude of the power is controlled in response to the magnitude of the current provided to the induction head,

12. The method of claim 11 including the step of monitoring the magnitude of the power provided to the induction head and wherein the magnitude of the power is controlled in response to the magnitude of the power provided to the induction head.

13. An induction heater comprising:

an induction head capable of being disposed near an object to be heated;

power means for providing power to the induction head, wherein the power means is in electrical communication with the induction head;

monitoring a magnitude of resistive losses in the induction head; and

feedback means for controlling a magnitude of the power in response to the magnitude of resistive losses in the induction head, whereby the power loss in the induction head is compensated for.

14. The apparatus of claim 13 including means for monitoring the magnitude of the current provided to the induction head and controlling in the magnitude of the power signal in response to the magnitude of the current provided to the induction head.

15. The apparatus of claim 14 including means for monitoring the magnitude of the power provided to the induction head and for controlling the magnitude of the power signal in response to the magnitude of the power provided to the induction head.

16. An induction heater comprising:

a power circuit capable of providing an output power signal having a magnitude, wherein the power circuit has a control input and the magnitude of the output power is responsive to the control input;

an induction head;

a coupling circuit in electrical communication between the power circuit and the induction head; and

a control circuit including a feedback circuit and a control output coupled to the power circuit control input, wherein the feedback circuit includes means to provide a signal indicative of a magnitude of resistive losses in the coupling circuit and the induction head, and further wherein the control output is responsive to the magnitude of the resistive losses in the coupling circuit and the induction head, whereby the power loss in the coupling circuit and the induction head is compensated for.

17. The induction heater of claim 16 wherein the feedback circuit includes means to provide a signal indicative of the magnitude of the current provided to the coupling circuit.

18. The induction heater of claim 17 wherein the feedback circuit includes means to provide a signal indicative of the magnitude of the power provided to the coupling circuit.