Apparatus for delivering harmonic inductive power

Abstract

Method and apparatus for providing harmonic inductive power, and more particularly for delivering current pulses providing a desired amount of pulse energy in high frequency harmonics to a load circuit for inductive heating of an article. By controlling the shape and/or frequency of such current pulses, the apparatus and method can be used to enhance the rate, intensity and/or power of inductive heating delivered by the heater coil and/or to enhance the lifetime or reduce the cost and complexity of an inductive heating power supply. Of particular significance, the apparatus and method may be used to significantly increase the power inductively delivered to a ferromagnetic or other inductively heated load, without requiring an increase of current in the heater coil. This enables new heating applications, and in some known applications, decreases the energy consumption or cooling requirements and/or increase the lifetime of the heater coil.

1 - 10 . (canceled) 
   
   
       14 - 46 . (canceled) 
   
   
       44 . A method for generating current pulses providing a desired amount of pulse energy in high frequency harmonics in a load circuit for inductive heating of an article, the method comprising:
 generating current pulses with high frequency harmonics, each pulse comprising at least one steeply varying portion for delivering at least 50% of the pulse energy in the load circuit in high frequency harmonics;   controlling the on/off timing of the current pulses to generate a plurality of such pulses as a desired current signal for inductive heating.   
   
   
       45 . The method of  claim 44 , wherein the on/off timing is controlled to produce two or three oscillations in each current pulse. 
   
   
       46 . The method of  claim 44 , wherein the on/off timing is controlled so that each current pulse ends after its amplitude falls by at least 50% from an amplitude of a maximum peak in the current pulse. 
   
   
       47 . The method of  claim 46 , wherein the on/off timing is controlled so that each current pulse ends after its amplitude falls by at least 75% from an amplitude of a maximum peak in the current pulse. 
   
   
       48 . The method of  claim 47 , wherein the on/off timing is controlled so that each current pulse ends after its amplitude falls by at least 90% from an amplitude of a maximum peak in the current pulse. 
   
   
       49 . The method of  48 , wherein the on/off timing is controlled so that each current pulse ends after its amplitude falls by at least 95% from an amplitude of a maximum peak in the current pulse. 
   
   
       50 . The method of  claim 44 , wherein the on/off timing is controlled such that each current pulse includes at least one steeply varying portion having a maximum rate of change at least 5 times greater than a maximum rate of change of a sinusoidal signal of the same fundamental frequency and RMS current amplitude. 
   
   
       51 . The method of  claim 50 , wherein maximum rate of change is at least 10 times greater. 
   
   
       52 . The method of  claim 51 , wherein the maximum rate of change is at least 20 times greater. 
   
   
       53 . The method of  claim 50 , wherein an upper limit of the maximum rate of change is determined based on a voltage limit of the load circuit. 
   
   
       54 . The method of  claim 44 , wherein the on/off timing is controlled such that each current pulse contains at least two complete oscillation cycles before damping to a level below 10% of an amplitude of a maximum peak in the current pulse.