Induction heater having a power inverter and a variable frequency output inverter

Claim 2

An induction heater comprising: a first inverter having a first inverter output; a variable frequency output inverter having a variable frequency inverter input; a first coupling circuit in electrical communication between said first inverter output and said variable frequency output inverter input, wherein said variable frequency output inverter is cascaded with said inverter; an induction head; and a second coupling circuit in electrical communication between said variable frequency output inverter and said induction head.

Claim 3

The induction heater of claim 1 wherein said first inverter is a phase modulated inverter.

Claim 4

The induction heater of claim 1 wherein said induction heater comprises control means for controlling said first inverter and further wherein said control means includes feedback means for providing control signals to said control means in response to the power output of said induction head.

Claim 5

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

Claim 6

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

Claim 7

The induction heater of claim 1 further including a frequency controller in electrical communication with said variable frequency output inverter.

Claim 8

The induction heater of claim 6 wherein said variable frequency output inverter is operable in the range of from about 10 kHz to about 1 MHz.

Claim 9

The induction heater of claim 1 further including a DC power source coupled to said first inverter.

Claim 10

The induction heater of claim 8 wherein said DC power source includes an AC power source and a rectifier.

Claim 11

The induction heater of claim 8 wherein said power source is coupled to no more than one inverter.

Claim 12

The induction heater of claim 1 wherein said first coupling circuit includes a transformer.

Claim 13

The induction heater of claim 11 wherein said first coupling circuit includes a rectifier.

Claim 14

The induction heater of claim 1 wherein said first inverter provides a first AC signal and said second inverter provides a second AC signal, and said second coupling circuit includes a coaxial transformer which provides a third AC signal.

Claim 15

The induction heater of claim 1 wherein said induction head is a two turn coil.

Claim 16

The induction heater of claim 1 wherein said first inverter is a power inverter.

Claim 17

The induction heater of claim 1 wherein said first inverter is a pulse width modulated inverter.

Claim 18

An induction heater comprising: a phase modulated inverter operable at a first frequency; first coupling means, having an AC input receiving a first output signal from said phase modulated inverter, for providing a DC output signal having a magnitude responsive to the phase modulation of said phase modulated inverter; an adjustable frequency inverter receiving said DC output signal, wherein said adjustable frequency inverter provides a second output signal having a magnitude responsive to the magnitude of said DC output signal; an induction head for coupling energy to a workpiece in response to an applied electrical signal; second coupling means in electrical communication between said adjustable frequency inverter and said induction head; and control means, in electrical communication with said phase modulated inverter, for providing a feedback signal indicative of the power output of said induction head and for controlling the phase modulation of said phase modulated inverter in response to said feedback signal.

Claim 19

An induction heater comprising: a phase modulated inverter operable at a first frequency; first coupling means, having an AC input receiving a first output signal from said phase modulated inverter, for providing a DC output signal having a magnitude responsive to the phase modulation of said phase modulated inverter; an adjustable frequency inverter receiving said DC output signal, wherein said adjustable frequency inverter provides a second output signal having a magnitude responsive to the magnitude of said DC output signal; an induction head for coupling energy to a workpiece in response to an applied electrical signal; second coupling means in electrical communication between said adjustable frequency inverter and said induction head; and control means, in electrical communication with said phase modulated inverter, for providing a feedback signal indicative of the power output of said induction head and for controlling the phase modulation of said phase modulated inverter in response to said feedback signal.

Claim 20

The induction heater of claim 17 wherein said second coupling means includes a transformer having a primary winding in electrical communication with said second inverter and a secondary winding in electrical communication with said induction head.

Claim 21

The induction heater of claim 17 wherein said control means is further in electrical communication with said second inverter, and further includes means for selecting the frequency of operation of said adjustable frequency inverter.

Claim 22

An induction heater comprising: first inverter means for receiving a first DC signal and providing a first modulated AC signal; second inverter means for receiving a second DC signal and providing a second AC signal at an adjustable frequency, said second AC signal having a magnitude responsive to the magnitude of said second DC signal; first coupling means, in electrical communication between said first inverter means and said second inverter means, for receiving said first AC signal and converting said first AC signal to said second DC signal, said second DC signal having a magnitude responsive to the modulation of said first AC signal; an induction head for coupling energy; and second coupling means, in electrical communication between said second inverter means and said induction head, for receiving said second AC signal and providing a third AC signal to said induction head, said third AC signal having a magnitude responsive to a magnitude of said second AC signal.

Claim 23

An induction heater comprising: first inverter means for receiving a first DC signal and providing a first modulated AC signal; second inverter means for receiving a second DC signal and providing a second AC signal at an adjustable frequency, said second AC signal having a magnitude responsive to the magnitude of said second DC signal; first coupling means, in electrical communication between said first inverter means and said second inverter means, for receiving said first AC signal and converting said first AC signal to said second DC signal, said second DC signal having a magnitude responsive to the modulation of said first AC signal; an induction head for coupling energy; and second coupling means, in electrical communication between said second inverter means and said induction head, for receiving said second AC signal and providing a third AC signal to said induction head, said third AC signal having a magnitude responsive to a magnitude of said second AC signal.

Claim 24

The induction heater of claim 20 further including control means, in electrical communication with said first inverter means, for controlling the modulation of said first AC signal.

Claim 25

The induction heater of claim 21 wherein said first inverter means includes a plurality of switches and wherein said control means includes phase modulation means for modulating the phase at which said plurality of switches are turned on and off.

Claim 26

The induction heater of claim 22 wherein said control means further includes feedback means, for providing a feedback signal indicative of the power output of said induction head.

Claim 27

The induction heater of claim 22 wherein said control means further includes feedback means, for providing a feedback signal indicative of the non-coupling losses in said induction head.

Claim 28

The induction heater of claim 21 wherein said first inverter means includes means for providing a frequency modulated AC signal.

Claim 31

The method of claim 26 further including the steps of: providing a feedback signal indicative of the power output of the induction head; and adjusting the pulse width of the first AC signal in response to the feedback signal.

Claim 32

The method of claim 27 wherein the step of inverting the first DC signal includes the step of phase modulation to adjust the pulse width of the first AC signal.

Claim 33

The method of claim 26 wherein the frequency of said second AC signal is the same as the frequency of said third AC signal.

Claim 34

The method of claim 26 wherein the frequency of said second AC signal is selected in response to feedback.

Claim 35

An induction heater comprising: first inverter means for receiving a first DC signal and providing a first modulated AC signal; second inverter means for receiving a second DC signal and providing a second AC signal at an adjustable frequency, said second AC signal having a magnitude responsive to the magnitude of said second DC signal; first coupling means, in electrical communication between said first inverter means and said second inverter means, for receiving said first AC signal and converting said first AC signal to said second DC signal, said second DC signal having a magnitude responsive to the modulation of said first AC signal; and an induction head coupled to the second inverter means.

Claim 36

An induction heater comprising: first inverter means for receiving a first DC signal and providing a first modulated AC signal; second inverter means for receiving a second DC signal and providing a second AC signal at an adjustable frequency, said second AC signal having a magnitude responsive to the magnitude of said second DC signal; first coupling means, in electrical communication between said first inverter means and said second inverter means, for receiving said first AC signal and converting said first AC signal to said second DC signal, said second DC signal having a magnitude responsive to the modulation of said first AC signal; and an induction head coupled to the second inverter means.

Claim 37

The induction heater of claim 31 wherein said induction head includes means for coupling energy to a workpiece, said energy having a magnitude responsive to a magnitude of said second AC signal.