Adaptive preheating and filament current control for magnetron power supply

1. A system for adaptive preheating of a magnetron, comprising:

one or more temperature sensors in communication with a magnetron and configured to sense a temperature of the magnetron, the magnetron associated with a microwave oven and having an internal filament and a plurality of cooling fins;

and

a power supply controller coupled to a power supply of the microwave oven and to the temperature sensors, the power supply controller including at least one processor and configured to:

receive a requested power setting associated with a cooking cycle;

determine a preheat time based on the sensed temperature;

start a preheat timer corresponding to the preheat time;

and

direct the power supply to apply a preheat current to the internal filament during the preheat time.

2. The system of claim 1 , wherein the sensed temperature includes at least one of:

a core temperature associated with a core of the magnetron;

and

a frame temperature associated with at least one of an outer frame of the magnetron and the cooling fins.

3. The system of claim 2 , wherein the power supply controller is configured to determine the preheat time based on the lower of the core temperature and the frame temperature.

4. The system of claim 1 , wherein the preheat time is no less than a predetermined minimum preheat time and no more than a predetermined maximum preheat time.

5. The system of claim 1 , wherein the microwave oven is in a standby state.

6. The system of claim 1 , wherein the requested power setting is below a duty cycle threshold, and the power supply controller is configured to:

set the requested power setting to the duty cycle threshold;

calculate a duty cycle ratio of on-time to off-time;

and, during each duty cycle of the cooking cycle,

1) direct the power supply to provide a high voltage (HV) direct current to the magnetron during the on-time; and

2) direct the power supply to provide the preheat current during a short-preheat time within the off-time.

7. The system of claim 6 , wherein the duty cycle ratio is between a predetermined minimum ratio and a predetermined maximum ratio.

8. The system of claim 6 , wherein the duty cycle ratio is based on a ratio of the requested power setting to the duty cycle threshold.

9. The system of claim 1 , wherein the power supply controller is configured to sense a rate of increase of the sensed temperature over time.

10. The system of claim 9 , wherein the power supply controller is configured to generate an empty cavity alert based on the rate of increase exceeding a first threshold.

11. The system of claim 9 , wherein the power supply controller is configured to generate an empty cavity alert based on an average of the rate of increase exceeding a second threshold over a sequence of consecutive time periods.

12. The system of claim 1 , wherein the power supply controller is configured to regulate the preheat current at a predetermined interval during the preheat time.

13. A system for filament current control of a magnetron, comprising:

one or more temperature sensors in communication with a magnetron and configured to sense a temperature of the magnetron, the magnetron associated with a microwave oven and having an internal filament, a plurality of resonant cavities, and a plurality of cooling fins;

a power supply electronically coupled to the magnetron and configured to:

generate an electromagnetic (EM) field between the internal filament and the resonant cavities by providing a high voltage (HV) direct current to the magnetron;

and

provide a filament current to the internal filament by superimposing an alternating current on the HV direct current; and

a power supply controller coupled to the power supply and to the temperature sensors, the power supply controller including at least one processor and configured to:

receive a requested power setting associated with a cooking cycle;

determine a filament current setpoint based on the requested power setting;

and

direct the power supply to apply the filament current corresponding to the filament current setpoint during the cooking cycle.

14. The system of claim 13 , wherein the power supply controller is configured to, at a regular interval during the cooking cycle:

1) receive a sensed temperature from the temperature sensors;

2) calculate a current offset based on the received sensed temperature; and

3) correct the filament current based on the calculated current offset.

15. The system of claim 13 , further comprising:

a memory coupled to the power supply controller, the memory configured to store a plurality of predetermined current settings, each predetermined current setting corresponding to a predetermined power setting.

16. The system of claim 15 , wherein the power supply controller is configured to set the filament current setpoint to a first current setting when the requested power setting is equal to a first power setting corresponding to the first current setting.

17. The system of claim 15 , wherein the power supply controller is configured to interpolate the filament current setpoint between a first current setting and a second current setting when the requested power setting is between a first predetermined power setting corresponding to the first current setting and a second predetermined power setting corresponding to the second current setting.