초록 ▼

A system and method for limiting the temperature of a burner for a cooking appliance without the use of a temperature sensor. The method includes the step of sensing the conduction state of a thermal switch and feeding back the sensed signal to control the duty-cycle (and thus “on” tim

A system and method for limiting the temperature of a burner for a cooking appliance without the use of a temperature sensor. The method includes the step of sensing the conduction state of a thermal switch and feeding back the sensed signal to control the duty-cycle (and thus “on” time) of bang-bang thermal limiting control. The power to the burner is reduced until the sensed duty-cycle (near 100%) cycling is reduced (lower frequency and amplitude) resulting in smoother power and temperature control. Preferably, the control system and method is implemented for controlling power applied to a burner for a glass-ceramic cooktop.

대표청구항 ▼

1. A thermal limiter control system for a heating element provided in a cooking appliance, said appliance implementing bang-bang thermal limiting control whereby a conduction state of a thermal switch device is engaged to either interrupt or enable application of power to said heating element accord

1. A thermal limiter control system for a heating element provided in a cooking appliance, said appliance implementing bang-bang thermal limiting control whereby a conduction state of a thermal switch device is engaged to either interrupt or enable application of power to said heating element according to a temperature of said heating element, the thermal limiter control system comprising:a means for sensing said conduction state of said thermal switch device when engaged during a thermal limiting cycle; anda feedback control means utilizing said sensed conduction state to control a duty cycle of said bang-bang thermal limiting control during said thermal limiting cycle, said feedback control means further actuating power amount applied to said heating element during said thermal limiting cycle. 2. The thermal limiter control system according to claim 1, wherein said feedback control means comprises:a thermal limit controller device for directly receiving a signal representing said sensed conduction state of said thermal switch when implementing bang-bang thermal limiting control and, a signal representing a desired duty cycle for bang-bang thermal limiting control, and generating a thermal limiting power command signal based on a difference between said sensed conduction state and said desired duty cycle signals. 3. The thermal limiter control system according to claim 2, wherein said thermal limit controller device includes a proportional plus integral controller circuit for generating said thermal limiting power command signal based on said difference between said sensed conduction state and said desired duty cycle signals. 4. The thermal limiter control system according to claim 3, further comprising:a power control device responsive to said thermal limiting power command signal for applying power to said heating element for maintaining a temperature of said heating element at about a thermal limit by enabling thermal switch conduction state switching at said desired duty cycle having an increased an on-time. 5. The thermal limiter control system according to claim 3, wherein said thermal limit controller device further comprises:means for estimating a duty cycle of said sensed conduction state and generating a signal representing said duty cycle estimate, said thermal limit controller device generating said thermal limiting power command signal based on a difference between said duty cycle estimate and said desired duty cycle signals. 6. The thermal limiter control system according to claim 5, wherein said means for estimating a duty cycle of bang-bang thermal limiting control comprises:a device for forming an instantaneous duty cycle estimate representing a ratio of a cumulative “on” time to a cumulative total time since an immediately prior bang-bang thermal limiting cycle; and,a latching device for latching said instantaneous duty cycle estimate at an end of a thermal limiting cycle;wherein said current instantaneous duty cycle estimate is a maximum of a previously latched estimate held constant from said immediately prior thermal limiting cycle:and said current instantaneous duty cycle estimate. 7. The thermal limiter control system according to claim 5, wherein said duty cycle estimate control device comprises a low pass filter device for receiving said sensed conduction state, said low pass filter device having a time constant greater than said on-time of said thermal switch conduction state. 8. The thermal limiter control system according to claim 5, further comprisinga device for enabling input of a desired user temperature setting for said heating element, and generating a user power command signal representative of said desired user temperature setting; and,a minimum selector device for selecting a minimum of either said user power command signal or, said thermal limiting power command signal for controlling application of power to said heating element. 9. The thermal limiter control system accord ing to claim 8, further comprising:an anti-wind up controller connected to said thermal limiter controller for tracking a thermal limit power level represented by said thermal limiting power command signal to a user power level represented by said user power command signal and, applying a difference between said thermal limit power level and user power level to said proportional plus integral controller circuit, said proportional plus integral controller circuit preventing wind up of an integrator in said proportional plus integral controller circuit. 10. The thermal limiter control system according to claim 8, further comprising a change detector device for detecting a change of said input user power command signal and resetting an integrator in said proportional plus integral controller circuit in response to a detected change. 11. The thermal limiter control system according to claim 1, wherein said feedback control means comprises:a means for estimating a duty cycle of said sensed conduction state and generating a signal representing said duty cycle estimate; and,a means responsive to said duty cycle estimate signal and a currently generated thermal limiting power command signal for predicting a power level needed to maintain temperature of said heating element at about said thermal limit and generating a predicted power level signal; and,a periodic reset logic circuit for periodically calculating and applying said predicted power level signal needed to maintain temperature at the thermal limit. 12. The thermal limiter control system according to claim 11, wherein said predicting means includes:an averaging circuit for generating an average of how much power is being applied to the heating element based on said thermal limiting power command signal; and,a multiplier device for multiplying said average power with said estimated duty cycle signal to provide said predicted power level. 13. The thermal limiter control system according to claim 12, wherein said periodic reset logic circuit includes:a means for comparing said estimated duty cycle against a predetermined threshold and generating a thermal limiting power command signal comprising one of:a full power level for initiating bang-bang thermal control or, said predicted power level at said thermal limit, wherein said bang-bang thermal control is periodically initiated. 14. The thermal limiter control system according to claim 1, wherein said heating element is provided in a burner of a glass-ceramic cooktop appliance. 15. A method for controlling an amount of power being applied to a heating element provided in a cooking appliance, said appliance implementing bang-bang thermal limiting control whereby a conduction state of a thermal switch device is engaged to either interrupt or enable application of power to said heating element according to a temperature of said heating element during a thermal limiting cycle, the thermal limiter control method comprising the steps of:a) sensing said conduction state of said thermal switch device when engaged during a thermal limiting cycle; andb) utilizing said sensed conduction state to control a duty cycle of said bang-bang thermal limiting control during said thermal limiting cycle, and, actuate power to said heating element during said thermal limiting cycle. 16. The method according to claim 15, further including the steps of:directly receiving a signal representing said sensed conduction state of said thermal switch when implementing bang-bang thermal limiting control;receiving a signal representing a desired duty cycle for bang-bang thermal limiting control; and,generating a thermal limiting power command signal based on a difference between said sensed conduction state and said desired duty cycle signals. 17. The method according to claim 16, further comprising the step of:providing proportional plus integral control circuit for generating said thermal limiting power command signal based on said difference between said sense d conduction state and said desired duty cycle signals. 18. The method according to claim 17, further comprising the steps of:applying power to said heating element in response to said thermal limiting power command signal, said power for maintaining a temperature of said heating element at about a thermal limit by enabling thermal switch conduction state switching at said desired duty cycle having an increased on-time. 19. The method according to claim 17, wherein said sensing step a) comprises the steps of:c) estimating a duty cycle of said sensed conduction state and generating a signal representing said duty cycle estimate, wherein said utilizing step b) comprises:generating said thermal limiting power command signal based on a difference between said duty cycle estimate and said desired duty cycle signals. 20. The method according to claim 19, wherein said step c) of estimating a duty cycle of bang-bang thermal limiting control comprises the steps of:forming an instantaneous duty cycle estimate representing a ratio of a cumulative “on” time to a cumulative total time since an immediately prior bang-bang thermal limiting cycle; and,latching said instantaneous duty cycle estimate at an end of a thermal limiting cycle,wherein said current instantaneous duty cycle estimate is a maximum of a previously latched estimate held constant from said immediately prior thermal limiting cycle and said current instantaneous duty cycle estimate. 21. The method according to claim 19, wherein said step of estimating a duty cycle of bang-bang thermal limiting control comprises the step of providing a low pass filter for receiving said sensed conduction state, said low pass filter having a time constant greater than said on-time of said thermal switch conduction state. 22. The method according to claim 19, further comprising the steps of:enabling input of a desired user temperature setting for said heating element, and generating a user power command signal representative of said desired user temperature setting; and,selecting a minimum of either said user power command signal or, said thermal limiting power command signal for controlling application of power to said heating element. 23. The method according to claim 22, further comprising the step of preventing wind up of an integrator in said proportional plus integral control circuit by:tracking a thermal limit power level represented by said thermal limiting power command signal to a user power level represented by said user power command signal; and,applying a difference between said thermal limit power level and user power level to said proportional plus integral control circuit. 24. The method according to claim 22, further comprising the step of:detecting a change of said input user power command signal; and resetting an integrator in said proportional plus integral control circuit in response to a detected change. 25. The method according to claim 15, wherein said sensing step a) comprises the step of:c) estimating a duty cycle of said sensed conduction state and generating a signal representing said duty cycle estimate; said utilizing step b) comprising:d) predicting a power level needed for maintaining temperature of said heating element at about said thermal limit and generating a predicted power level signal; and,e) periodically calculating and applying said predicted power level signal needed to maintain temperature at the thermal limit. 26. The method according to claim 25, wherein said predicting step includes:generating an average of how much power is being applied to the heating element based on said thermal limiting power command signal; and,multiplying said average power with said estimated duty cycle to provide said predicted power level. 27. The method according to claim 26, wherein said periodically calculating and applying step comprises the step of:comparing said estimated duty cycle against a predetermined threshold and,generating a thermal limiting pow er command signal comprising one of: a full power level for initiating bang-bang thermal control or, said predicted power level at said thermal limit, wherein said bang-bang thermal control is periodically initiated. 28. A thermal limiter control system for a heating element provided in a heating appliance, said appliance implementing bang-bang thermal limiting control whereby a conduction state of said thermal switch device is engaged to either interrupt or enable application of power to said heating element according to a temperature of said heating element during a thermal limiting cycle, the thermal limiter control system comprising:means for sensing said thermal switch conduction state and estimating a duty cycle of said conduction state during said thermal limiting cycle;thermal limiter control device for receiving said duty cycle estimate and a reference duty cycle representing a thermal limit for said heating device, and generating a thermal limiting power level based on a difference between said duty cycle estimate and a reference duty cycle; and,means responsive to said thermal limiting power level for reducing power applied to the heating element during said thermal limiting cycle while increasing a duty cycle of said thermal switch conduction state according to reference duty cycle, wherein a temperature of said heating element is at or about said thermal limit during said thermal limiting cycle.