System and method for providing RF power to a load
First Claim
1. A radio frequency (RF) power supply for providing RF power to a tank circuit coupled to an output of the RF power supply, comprising:
- a direct current (DC) voltage source;
an amplifier, coupled to said DC voltage source, to provide an alternating voltage to the tank circuit;
a frequency controller, coupled to said amplifier, to control a frequency of said alternating voltage provided by said amplifier; and
a sensor, coupled to the tank circuit and to said frequency controller, comprising a current sensor that measures current flowing into the tank circuit and a voltage sensor that measures a voltage across the tank circuit, wherein said sensor provides to said frequency controller a signal representative of the admittance of the tank circuit, and said frequency controller uses said signal representative of the admittance of the tank circuit to modify said frequency of said alternating voltage so that said frequency of said alternating voltage tracks a resonant frequency of the tank circuit.
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Accused Products
Abstract
An RF power supply that is capable of tracking rapid changes in the resonant frequency of a load and capable of quickly responding to varying load conditions so as to deliver the desired amount of power. The present invention also provides an RF power supply capable of delivering a wide range of power over a broad frequency range to a load that is remotely located from the power supply. According to one embodiment, the RF power supply includes a direct current (DC) voltage source that provides a DC voltage within a predetermined voltage range; an amplifier, coupled to the DC voltage source, that provides an alternating voltage to a tank circuit connected to an output of the RF power supply; a frequency controller, coupled to the amplifier, to set the frequency of the alternating voltage produced by the amplifier; and a sensor, coupled to the load, to provide a signal to the frequency controller, where the frequency controller sets the frequency of the alternating voltage based on the signal received from the sensor.
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Citations
22 Claims
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1. A radio frequency (RF) power supply for providing RF power to a tank circuit coupled to an output of the RF power supply, comprising:
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a direct current (DC) voltage source;
an amplifier, coupled to said DC voltage source, to provide an alternating voltage to the tank circuit;
a frequency controller, coupled to said amplifier, to control a frequency of said alternating voltage provided by said amplifier; and
a sensor, coupled to the tank circuit and to said frequency controller, comprising a current sensor that measures current flowing into the tank circuit and a voltage sensor that measures a voltage across the tank circuit, wherein said sensor provides to said frequency controller a signal representative of the admittance of the tank circuit, and said frequency controller uses said signal representative of the admittance of the tank circuit to modify said frequency of said alternating voltage so that said frequency of said alternating voltage tracks a resonant frequency of the tank circuit. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
a first full wave bridge connected to an input of said tank circuit;
a first filter connected to said full wave bridge; and
a first gain stage connected to said filter.
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5. The radio frequency power supply of claim 1, wherein said voltage sensor includes:
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a second full wave bridge connected to said input of said tank circuit;
a second filter connected to said second full wave bridge; and
a second gain stage connected to said second filter.
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6. The RF power supply of claim 1, wherein said frequency controller includes a processor coupled to a signal generator, wherein an output of said signal generator controls said frequency of said alternating voltage.
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7. The RF power supply of claim 6, wherein said signal generator is a frequency synthesizer.
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8. The RF power system of claim 7, wherein said frequency synthesizer is a direct digital synthesizer.
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9. The RF power system of claim 7, wherein said frequency synthesizer is coupled to said amplifier through a delay circuit and a driver circuit.
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10. The RF power supply of claim 1, wherein the frequency of the alternating voltage is between about 1 kHz and 15 MHz.
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11. The RF power supply of claim 1, wherein the frequency of the alternating voltage is between about 50 kHz and 490 kHz.
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12. The RF power supply of claim 1, wherein the frequency of the alternating voltage is between about 515 kHz and 2 MHz.
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13. The RF power supply of claim 1, wherein the amplifier operates at a dc voltage ranging between about 50 VDC and 350 VDC, wherein said DC voltage source generates said dc voltage.
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14. The RF power supply of claim 1, wherein the amplifier operates at a dc voltage ranging between about 100 VDC and 350 VDC, wherein said DC voltage source generates said dc voltage.
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15. The RF power supply of claim 1, wherein the amplifier operates at a dc voltage ranging between about 200 VDC and 350 VDC, wherein said DC voltage source generates said dc voltage.
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16. A method for inductively heating a workpiece placed in proximity to an inductor coil of a tank circuit, wherein the tank circuit has a resonant frequency within a known frequency range, comprising the steps of:
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(1) applying an alternating voltage to the tank circuit, said alternating voltage having a frequency within the known frequency range, and said alternating voltage having a first voltage level;
(2) determining a coarse estimate of the resonant frequency;
(3) based on said coarse estimate, determining a fine estimate of the resonant frequency;
(4) setting said frequency of said alternating voltage to said fine estimate of said resonant frequency;
(5) after performing step (4), rapidly increasing said voltage level of said alternating voltage from said first voltage level to a second voltage level; and
(6) while said voltage level is being increased and until a heat off indication is generated, continuously tracking the resonant frequency.
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17. A method for inductively heating a workpiece placed in proximity to an inductor coil of a tank circuit, wherein the tank circuit has a resonant frequency within a known frequency range, comprising the steps of:
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applying an alternating voltage to the tank circuit, said alternating voltage having a frequency within the known frequency range, and said alternating voltage having a first voltage level;
determining a coarse estimate of the resonant frequency;
based on said coarse estimate, determining a fine estimate of the resonant frequency;
rapidly increasing said voltage level of said alternating voltage from said first voltage level to a second voltage level; and
while said voltage level is being increased and until a heat off indication is generated, continuously tracking the resonant frequency, wherein said step of determining a coarse estimate of the resonant frequency comprises the steps of;
determining a first admittance value of the tank circuit;
storing said first admittance value in a first memory location and storing a first frequency value representing said frequency of said alternating voltage in a second memory location;
changing said frequency of said alternating voltage by an offset amount;
determining a second admittance value of the tank circuit;
comparing said second admittance value to said admittance value stored in said first memory location;
if the tank circuit is a series resonant tank circuit and said second admittance value is greater than said admittance value stored in said first memory location, storing said second admittance value in said first memory location and storing a second frequency value representing said frequency of said alternating voltage in said second memory location; and
if the tank circuit is a parallel resonant tank circuit and said second admittance value is less than said admittance value stored in said first memory location, storing said second admittance value in said first memory location and storing a third frequency value representing the frequency of said alternating voltage in said second memory location.
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18. A method for inductively heating a workpiece placed in proximity to an inductor coil of a tank circuit, wherein the tank circuit has a resonant frequency within a known frequency range, comprising the steps of:
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applying an alternating voltage to the tank circuit, said alternating voltage having a frequency within the known frequency range, and said alternating voltage having a first voltage level;
determining a coarse estimate of the resonant frequency;
based on said coarse estimate, determining a fine estimate of the resonant frequency;
rapidly increasing said voltage level of said alternating voltage from said first voltage level to a second voltage level; and
while said voltage level is being increased and until a heat off indication is generated, continuously tracking the resonant frequency, wherein the step of tracking the resonant frequency comprises the steps of;
(1) setting said frequency of said alternating voltage to a predetermined frequency;
(2) determining an admittance of the tank circuit at said predetermined frequency;
(3) setting said frequency of said alternating voltage to F+, where F+ equals said predetermined frequency plus a first offset amount;
(4) determining said admittance of the tank circuit at said F+ frequency;
(5) setting said frequency of said alternating voltage to F−
, where F−
equals said predetermined frequency minus a second offset amount;
(6) determining said admittance of the tank circuit; and
(7) changing said frequency of said alternating voltage based on said admittance determined in step (1), said admittance determined in step (3), and said admittance determined in step (5).
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19. A method for inductively heating a workpiece placed in proximity to an inductor coil of a tank circuit, wherein the tank circuit has a resonant frequency within a known frequency range, comprising the steps of:
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applying an alternating voltage to the tank circuit, said alternating voltage having a frequency within the known frequency range, and said alternating voltage having a first voltage level;
determining a coarse estimate of the resonant frequency;
based on said coarse estimate, determining a fine estimate of the resonant frequency;
rapidly increasing said voltage level of said alternating voltage from said first voltage level to a second voltage level; and
while said voltage level is being increased and until a heat off indication is generated, continuously tracking the resonant frequency, wherein the step of tracking the resonant frequency comprises the steps of;
(1) determining an admittance of the tank circuit and storing said admittance in a first memory location;
(2) decreasing said frequency of said alternating voltage;
(3) determining said admittance of the tank circuit;
(4) comparing said admittance stored in said first memory location with said admittance determined in step (3);
(5) if said admittance determined in step (3) is less than or equal to said admittance stored in said first memory location, storing said admittance determined in step (3) in said first memory location, and returning to step (2), otherwise continuing to step (6);
(6) increasing said frequency of said alternating voltage;
(7) determining said admittance of the tank circuit and storing said admittance in said first memory location;
(8) increasing said frequency of said alternating voltage;
(9) determining said admittance of the tank circuit;
(10) if said admittance determined in step (9) is less than or equal to said admittance stored in said first memory location, storing said admittance determined in step (9) in said first memory location, and returning to step (8), otherwise continuing to step (11); and
(11) decreasing said frequency of said alternating voltage and returning to step (1).
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20. A method of for estimating the resonant frequency of a tank circuit, comprising the steps of:
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applying an alternating voltage to the tank circuit, said alternating voltage having a frequency;
determining a first admittance value of the tank circuit;
storing said first admittance value in a first memory location and storing a first frequency value representing said frequency of said alternating voltage in a second memory location;
changing said frequency of said alternating voltage by an offset amount;
determining a second admittance value of the tank circuit;
comparing said second admittance value to said admittance value stored in said first memory location;
if the tank circuit is a series resonant tank circuit and said second admittance value is greater than said admittance value stored in said first memory location, storing said second admittance value in said first memory location and storing a second frequency value representing said frequency of said alternating voltage in said second memory location; and
if the tank circuit is a parallel resonant tank circuit and said second admittance value is less than said admittance value stored in said first memory location, storing said second admittance value in said first memory location and storing a third frequency value representing the frequency of said alternating voltage in said second memory location.
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21. A method for inductively heating a workpiece placed in proximity to an inductor coil of a tank circuit, comprising the steps of:
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(1) applying an alternating voltage to the tank circuit, said alternating voltage having a frequency;
(2) determining an admittance of the tank circuit at said frequency;
(3) setting said frequency of said alternating voltage to F+, where F+ equals said frequency plus a first offset amount;
(4) determining said admittance of the tank circuit at said F+frequency;
(5) setting said frequency of said alternating voltage to F−
, where F−
equals said frequency minus a second offset amount;
(6) determining said admittance of the tank circuit; and
(7) changing said frequency of said alternating voltage based on said admittance determined in step (1), said admittance determined in step (3), and said admittance determined in step (5).
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22. A method for inductively heating a workpiece placed in proximity to an inductor coil of a tank circuit, comprising the steps of:
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(1) applying an alternating voltage to the tank circuit, said alternating voltage having a frequency;
(2) determining an admittance of the tank circuit;
(3) decreasing said frequency of said alternating voltage;
(4) determining said admittance of the tank circuit;
(5) comparing said admittance determined in step (2) with said admittance determined in step (4);
(6) if said admittance determined in step (4) is less than or equal to said admittance determined in step (2), then decreasing said frequency of said alternating voltage, otherwise increasing said frequency of said alternating voltage.
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Specification