Apparatus and method for inductive heating

• US 20050000959A1
• Filed: 07/02/2003
• Published: 01/06/2005
• Est. Priority Date: 07/02/2003
• Status: Active Grant

• Current Assignee: ITherm Technologies, L.P.
• Original Assignee: ITherm Technologies, L.P.
• Inventors: Kagan, Val
• Granted Patent: US 7,034,263 B2
• Time in Patent Office: Days
• US Class Current: 219/660
• CPC Class Codes: H05B 2206/024 the resistive heat generated in the induction coil is conducted to the load
• CPC Class Codes: H05B 6/04 Sources of current
• CPC Class Codes: H05B 6/062 for cooking plates or the like
• CPC Class Codes: H05B 6/1209 induction cooking plates or the like and devices to be used in combination with them
• CPC Class Codes: H05B 6/1245 with special coil arrangements
• CPC Class Codes: Y02B 40/00 Technologies aiming at improving the efficiency of home appliances, e.g. induction cooking or efficient technologies for refrigerators, freezers or dish washers

Abstract

A system and method for inductive heating, in which a power source provides current pulses with high-frequency harmonics to a heater coil, the coil generating a magnetic flux for inductive heating of an article. The high-frequency harmonics enhance a relative proportion of inductive heating, compared to resistive heating of the heater coil. Providing these high-frequency harmonics, occurring above the border frequency of the heating system, enables the system to deliver an increased proportion of inductive heating, compared to resistive heating, without requiring an increase in the Root Means Square (RMS) current in the coil. Providing better coupling between the coil and the core, such as by embedding the coil wholly or at least partially in the core, and providing a magnetic yoke to close the loop with the core, can provide a significantly decreased border frequency. This reduction of the border frequency then can be utilized to provide larger amounts of energy in the high-frequency harmonics of the current pulses, and thus provide a greater percentage of inductive heating without increasing the current in the coil. The current pulses preferably have steeply varying portions, such as a steeply varying leading edge and/or trailing edge.

Claims

1. An apparatus comprising:

a power source providing current pulses with high frequency harmonics to a heater coil, the coil generating a magnetic flux for inductive heating of an article.

2. An apparatus according to claim 1,

wherein the high frequency harmonics enhance a relative proportion of inductive heating compared to resistive heating of the heater coil.

3. An apparatus according to claim 1,

wherein the current pulses produce an increased amount of inductive heating compared to a resonance sinusoidal signal.

4. An apparatus according to claim 1,

wherein the current pulses produce an increased amount of inductive heating compared to a sinusoidal current of a same magnitude and same fundamental frequency.

5. An apparatus according to claim 1,

wherein the current pulses have an associated energy component above a border frequency of the heater coil.

6. An apparatus according to claim 1,

wherein the current pulses increase an inductive portion of heating in the article without increasing the Root Mean Square (RMS) current in the heater coil.

7. An apparatus according to claim 1,

wherein the power source includes a low or line frequency current source.

8. An apparatus according to claim 1,

wherein the heater coil includes a resistive conductor for generating resistive heat.

9. An apparatus according to claim 8,

wherein the resistive conductor is in thermal communication with the article.

10. An apparatus according to claim 1,

wherein the heater coil is inductively coupled to a load which includes the article.

11. An apparatus according to claim 10,

wherein the magnetic flux induces eddy currents in the load.

12. An apparatus according to claim 10,

wherein the load includes a closed loop for the magnetic flux.

13. An apparatus according to claim 12,

wherein the load includes a ferromagnetic core and ferromagnetic yoke which form the closed loop.

14. An apparatus according to claim 10,

wherein the load includes a core and the heater coil is at least partially embedded in the core.

15. An apparatus according to claim 10,

wherein the load includes a core and a yoke and the heater coil is disposed between or embedded within at least one of the core and yoke.

16. An apparatus according to claim 15,

wherein the core and yoke form a closed loop for the magnetic flux.

17. An apparatus according to claim 15,

wherein the core and yoke are ferromagnetic.

18. An apparatus according to claim 10,

wherein the load includes a core having a passageway for a flowable material.

19. An apparatus according to claim 18,

wherein the core heats the flowable material.

20. An apparatus according to claim 1,

wherein the heater coil is positioned in the core so that heating is concentrated in the passageway.

21. An apparatus according to claim 1,

wherein the article forms at least part of a closed loop for the magnetic flux, the article having a first portion in which inductive heating is more concentrated compared to a second portion of the article.

22. An apparatus according to claim 21,

wherein the second portion creates discontinuities or restrictions to the flow of eddy currents.

23. An apparatus according to claim 22,

wherein the second portion has slots creating the discontinuities or restrictions.

24. An apparatus comprising:

a variable power source for providing current pulses with an adjustable energy content to a heater coil so as to adjust a ratio between inductive and resistive heating produced by the coil.

25. An apparatus comprising:

a heater coil inductively coupled to an article;

the article having a passageway for a flowable material to be heated;

the coil being positioned in the article to deliver heat generated inductively in the article to the flowable material in the passageway; and

a source of adjustable nonsinusoidal current pulses coupled to the heater coil for adjusting the delivery of inductive heating to the flowable material in the passageway.

26. A method comprising:

providing a heater coil in thermal communication with and inductively coupled to an article; and

providing an adjustable nonsinusoidal current pulse signal to the heater coil for adjusting the ratio between inductive and resistive heating of the article.

27. A method comprising:

providing a heater coil inductively coupled to an article; and

providing a nonsinusoidal current pulse signal to the heater coil with the pulse having a rate of change which produces high frequency harmonics.

28. An apparatus comprising:

an article to be inductively heated;

a heater coil generating a magnetic flux and inductively coupled to the article;

the article forming at least a portion of a closed loop for the magnetic flux;

the heater coil being at least partially embedded in the article; and

a current pulse signal with high frequency harmonics supplied to the heater coil.