System and method for providing RF power to a load

A method for inductively heating a workpiece, comprising the steps of:

• generating an alternating voltage having a first frequency;
• providing said alternating voltage to a tank circuit;
• generating a first admittance signal that represents the admittance of the tank circuit at said first frequency;
• setting said frequency of said alternating voltage to a second frequency;
• generating a second admittance signal that represents the admittance of the tank circuit at said second frequency;
• comparing the magnitude of said first admittance signal to said second admittance signal;
• and
• modifying said frequency of said alternating voltage as a function of a result of said comparison so that said frequency of said alternating voltage tracks a resonant frequency of the tank circuit.

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, comprising the steps of:

• applying an alternating voltage to the tank circuit, said alternating voltage having a frequency, and said alternating voltage having a first voltage level;
• determining a coarse estimate of the resonant frequency of the tank circuit;
• based on said coarse estimate, determining a fine estimate of the resonant frequency of the tank circuit;
• setting said frequency of said alternating voltage to said fine estimate of said resonant frequency;
• increasing said voltage level of said alternating voltage from said first voltage level to a second voltage level after setting said frequency of said alternating voltage to said fine estimate of said resonant frequency;
• and
• while said voltage level is being increased and until a heat off indication is generated, modifying said frequency of said alternating voltage so that said frequency of said alternating voltage tracks the resonant frequency of the tank circuit.

A method for inductively heating a workpiece placed in proximity to an inductor coil of a tank circuit, comprising the steps of:

• (1) applying an alternating voltage to the tank circuit, said alternating voltage having a frequency;
• (2) determining an admittance of the tank circuit;
• (3) increasing 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 said admittance determined in step (2), then increasing said frequency of said alternating voltage, otherwise decreasing said frequency of said alternating voltage.

A method for inductively heating a workpiece placed in proximity to an inductor coil of a tank circuit, comprising the steps of:

• (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 (2), said admittance determined in step (4), and said admittance determined in step (6).

A method for inductively heating a workpiece, comprising the steps of:

• applying an alternating voltage to a tank circuit, the alternating voltage having a frequency and a first voltage level, the tank circuit having an initial resonant frequency;
• determining a coarse estimate of the initial resonant frequency of the tank circuit;
• based on the coarse estimate, determining a fine estimate of the initial resonant frequency of the tank circuit;
• setting the frequency of the alternating voltage to the fine estimate of the resonant frequency;
• increasing the voltage level of the alternating voltage from the first voltage level to a second voltage level after determining the fine estimate of the resonant frequency;
• and
• while the voltage level is being increased and until a heat off indication is received, modifying the frequency of the alternating voltage so that the frequency of the alternating voltage tracks the resonant frequency of the tank circuit.