Induction heating system and method

Abstract

An excitation system for heating food, water, or both in airplanes uses induction heating. The system includes at least one load circuit including an inductor that is excited with a load circuit AC voltage, a load circuit alternating current, or both the load circuit AC voltage and the load circuit alternating current. The load circuit AC voltage, the load circuit alternating current, or both the load circuit AC voltage and the load circuit alternating current are generated from an AC voltage signal that is amplitude-modulated with a frequency of a mains AC voltage from a voltage supply. The frequency of the AC voltage signal can be predetermined.

1. A method for heating food, beverage, or both in an airplane using induction heating, the method comprising:
 exciting at least one load circuit including an inductor with a load circuit AC voltage; 
 generating the load circuit AC voltage from an AC voltage signal having a predetermined frequency by amplitude-modulating the AC voltage signal with a frequency of a mains AC voltage from a voltage supply having multiple phases; and 
 controlling the power supplied to the load circuit by influencing the frequency of the AC voltage signal. 
 
     
     
       2. The method of  claim 1 , wherein a frequency of the AC voltage signal is larger than the frequency of the mains AC voltage. 
     
     
       3. The method of  claim 1 , further comprising rectifying the mains AC voltage, and generating the AC voltage signal in an inverter from the rectified mains voltage. 
     
     
       4. The method of  claim 1 , further comprising controlling the power supplied to the load circuit by omitting individual pulses during generation of the AC voltage signal. 
     
     
       5. The method of  claim 1 , further comprising:
 measuring an actual power supplied to the at least one load circuit; 
 comparing the measured power to a predetermined nominal power; and 
 adjusting the actual power supplied to the at least one load circuit until the actual power supplied to the at least one load circuit matches the predetermined nominal power. 
 
     
     
       6. An excitation system of an induction heater for use on an airplane for heating food, beverage, or both, the system comprising:
 a voltage supply connector adapted for receiving a mains AC voltage from an aircraft voltage supply having multiple phases, and 
 multiple excitation units connected to the voltage supply connector, each of which excitation units provided for a respective phase of the multiple phases, each excitation unit comprising: 
 a rectifier for rectifying a respective portion of the mains AC voltage, 
 a load circuit with an inductor that is excited by a load circuit AC voltage generated in the excitation unit, and 
 an AC voltage generator for generating an amplitude-modulated load circuit AC voltage through amplitude modulation of an AC voltage signal with the frequency of the mains AC voltage, wherein the AC voltage signal has a frequency that is predetermined and is generated from a rectified voltage output from the rectifier. 
 
     
     
       7. The excitation system of  claim 6 , further comprising a control associated with the AC voltage generator, wherein the AC voltage generator is designed as inverter, and wherein the control can be used to adjust switching or striking times of a switching element of the inverter. 
     
     
       8. The excitation system of  claim 6 , further comprising a filter element between the rectifier and the AC voltage generator. 
     
     
       9. The excitation system of  claim 8 , wherein the filter element includes a smoothing capacitor with a capacitance that is smaller than the capacitance of the load circuit. 
     
     
       10. The excitation system of  claim 9 , wherein the smoothing capacitor capacitance is smaller than the load circuit capacitance by a factor of ten. 
     
     
       11. The excitation system of  claim 9 , wherein the smoothing capacitor capacitance is smaller than the load circuit capacitance by a factor of seven. 
     
     
       12. The excitation system of  claim 9 , wherein the smoothing capacitor capacitance is smaller than the load circuit capacitance by a factor of five. 
     
     
       13. The excitation system of  claim 6 , wherein the load circuit is a series oscillating circuit having at least one capacitor and at least one inductor. 
     
     
       14. The excitation system of  claim 6 , wherein the voltage supply connector comprises a connector for each of several phases of the voltage supply, and one excitation unit is connected to one phase and one neutral connection (N), or to two phases. 
     
     
       15. The excitation system of  claim 6 , wherein one or more of the excitation units can be switched on and off. 
     
     
       16. The excitation system of  claim 6 , further comprising a central auxiliary voltage generating unit. 
     
     
       17. The excitation system of  claim 16 , wherein the central auxiliary voltage generating unit is connected to at least one phase of the voltage supply and includes an active PFC member. 
     
     
       18. The excitation system of  claim 16 , wherein the central auxiliary voltage generating unit is connected to each phase of the voltage supply. 
     
     
       19. The excitation system of  claim 6 , further comprising a central control. 
     
     
       20. The excitation system of  claim 19 , wherein the central control comprises a digital programmable logic module. 
     
     
       21. The excitation system of  claim 19 , wherein the central control receives a voltage or a current measured at an intermediate circuit within the excitation system. 
     
     
       22. The excitation system of  claim 21 , further comprising a measuring device that measures the voltage or the current at the intermediate circuit and transmits the measured voltage or current to the central control. 
     
     
       23. The excitation system of  claim 22 , further comprising a galvanic separation provided between the measuring device and the central control. 
     
     
       24. The excitation system of  claim 22 , wherein the measuring device comprises operational amplifiers having differential inputs. 
     
     
       25. The excitation system of  claim 19 , wherein current values of the load circuit are transmitted to the central control. 
     
     
       26. The excitation system of  claim 25 , further comprising a measuring device that measures the voltage or the current of the load circuit and transmits the measured voltage or current to the central control. 
     
     
       27. The excitation system of  claim 25 , further comprising a galvanic separation provided between the measuring device and the central control. 
     
     
       28. The excitation system of  claim 25 , wherein the measuring device comprises operational amplifiers having differential inputs. 
     
     
       29. An induction heater for use on an airplane, the induction heater comprising:
 a voltage supply connector adapted for receiving an aircraft voltage supply having at least two phases and supplying a mains AC voltage; and 
 at least one excitation unit provided for each phase of the aircraft voltage supply and connected to the voltage supply connector, each excitation unit comprising:
 a rectifier for rectifying a respective portion of the mains AC voltage, 
 
 a load circuit with an inductor that is excited by a load circuit AC voltage generated in the excitation unit,
 an AC voltage generator for generating an amplitude-modulated load circuit AC voltage through amplitude modulation of an AC voltage signal with the frequency of the mains AC voltage, and 
 a filter element for attenuating harmonics generated within the excitation unit to mitigate deleterious effects on the aircraft voltage supply, 
 
 wherein the AC voltage signal has a frequency that is predetermined and is generated from a rectified voltage output from the rectifier. 
 
     
     
       30. The induction heater of  claim 29 , wherein one or more of the at least one excitation units comprise a first load circuit configured for heating food. 
     
     
       31. The induction heater of  claim 30 , wherein one or more of the at least one excitation units comprise a second load circuit configured for heating beverage. 
     
     
       32. The induction heater of  claim 31 , wherein the same number of first and second load circuits is connected to each phase of the voltage supply. 
     
     
       33. A method for heating food, beverage, or both in airplanes using induction heating, the method comprising:
 exciting at least one load circuit including an inductor with a load circuit AC voltage; 
 generating the load circuit AC voltage from an AC voltage signal having a predetermined frequency by amplitude-modulating the AC voltage signal with a frequency of a mains AC voltage from a voltage supply having multiple phases; and 
 controlling the power supplied to the load circuit by omitting individual pulses during generation of the AC voltage signal. 
 
     
     
       34. The method of  claim 33 , wherein a frequency of the AC voltage signal is larger than the frequency of the mains AC voltage. 
     
     
       35. The method of  claim 33 , further comprising rectifying the mains AC voltage, and generating the AC voltage signal in an inverter from the rectified mains AC voltage. 
     
     
       36. A method for heating food, beverage, or both in an airplane using induction heating, the method comprising:
 exciting at least one load circuit including an inductor with a load circuit AC voltage; 
 generating the load circuit AC voltage from an AC voltage signal having a predetermined frequency higher than a frequency of an airplane mains AC voltage by amplitude-modulating the AC voltage signal with the frequency of the airplane mains AC voltage; and 
 attenuating harmonics of the load circuit AC voltage from reaching an airplane mains AC voltage supply by filtering the harmonics with a filter element. 
 
     
     
       37. The method of  claim 36  wherein the filter element further comprises a smoothing capacitor having a capacitance that is smaller than a capacitance of the at least one load circuit. 
     
     
       38. The method of  claim 37  wherein the smoothing capacitor is at least five times smaller than the capacitance of the at least one load circuit. 
     
     
       39. The method of  claim 36  further comprising controlling the power supplied to the load circuit by influencing the frequency of the AC voltage signal. 
     
     
       40. The method of  claim 36 , further comprising rectifying the airplane mains AC voltage, and generating the AC voltage signal in an inverter from the rectified airplane mains voltage. 
     
     
       41. The method of  claim 36 , further comprising controlling the power supplied to the load circuit by omitting individual pulses during generation of the AC voltage signal.