Microwave power source and method of automatic adjustement of operation frequence

Abstract

Disclosed are a microwave power source and a method of adjusting operation frequency for a microwave oven. The microwave power source comprises: a phase-locked frequency generator configured to generate a plurality of operation frequencies; a standing wave detection circuit configured to detect, for each operation frequency, a standing wave in a chamber of the oven and provide information about the standing wave; and a microcontroller configured to select one of the operation frequencies based on the information, and control the generator to generate the selected operation frequency so that the microwave oven operates at the selected operation frequency. Embodiments of the present disclosure can automatically adjust the operation frequency of the oven according to VSWR in the oven chamber.

1 . A microwave power source for a microwave oven, comprising:
 a phase-locked frequency generator configured to generate a plurality of operation frequencies;   a standing wave detection circuit configured to detect, for each of the plurality of operation frequencies, a standing wave in a chamber of the microwave oven and provide information about the standing wave; and   a microcontroller configured to select one of the plurality of operation frequencies based on the information about the standing wave, and control the phase-locked frequency generator to generate the selected operation frequency on that the microwave oven operates at the selected operation frequency.   
     
     
         2 . The microwave power source of  claim 1 , wherein when the microwave oven is powered on, the standing wave detection circuit performs the detection, and the microcontroller performs the selection and control, to adjust the operation frequency of the microwave oven. 
     
     
         3 . The microwave power source of  claim 1 , wherein the microcontroller is further configured to compute a Voltage to Standing Wave Ratio (VSWR) for each of the operation frequencies based on the information about the standing wave, and to select one of the operation frequencies corresponding to the minimal VSWR among the computed VSWRs. 
     
     
         4 . The microwave power source of  claim 1 , wherein the phase-locked frequency generator is further configured to generate the plurality of operation frequencies within a preset range in a stepwise manner,
 The microcontroller is further configured to compute a VSWR for each of the operation frequencies, and to record each operation frequency and its corresponding VSWR in a frequency-VSWR correspondence table.   
     
     
         5 . The microwave power source of  claim 3 , wherein the microcontroller is further configured to:
 compare the minimal VSWR with a preset safe VSWR,   control to issue a warning indicating a high VSWR, if the minimal VSWR, is larger than the safe VSWR, and   select the operation frequency corresponding to the minimal VSWR, if the minimal VSWR is not larger than the safe VSWR.   
     
     
         6 . The microwave power source of  claim 1 , wherein the phase-locked frequency generator comprises:
 a phase-locked frequency source configured to generate the plurality of operation frequencies under control of the microcontroller, and to output microwave signals at the plurality of operation frequencies; and   a microwave attenuator configured to operate in a low attenuation state or a high attenuation state to attenuate the microwave signals from the phase-locked frequency source under control of the microcontroller.   
     
     
         7 . The microwave power source of  claim 2 , wherein the microwave attenuator is controlled by the microcontroller to operate in a high attenuation state during adjustment of the operation frequency of the microwave oven. 
     
     
         8 . The microwave power source of  claim 1 , wherein the standing wave detection circuit comprises:
 a directional coupler configured to sample forward coupling power and reflected coupling power of the standing wave in the chamber of the microwave oven; and   a microwave detection circuit configured to convert each of the forward coupling power and the reflected coupling power sampled by the directional coupler into DC voltages, and to provide the DC voltages to the microcontroller as the information about the standing wave.   
     
     
         9 . The microwave power source of  claim 8 , further comprising: a microwave amplifier arranged between the phase-locked frequency generator and the standing wave detection circuit and configured to amplify power of the microwave signals from the phase-locked frequency generator for use in heating. 
     
     
         10 . The microwave power source of  claim 9 , further comprising: a coaxial waveguide switch arranged before or after the standing wave detection circuit and configured to switch the microwave signals from a coaxial port to a waveguide port. 
     
     
         11 . The microwave power source of  claim 10 , wherein the microwave amplifier comprises a driving amplifier and a solid state power amplifier successively connected,
 the driving amplifier is connected to the phase-locked frequency generator,   if a microstrip coupler is used as the directional coupler of the standing wave detection circuit, the solid state power amplifier is connected to the directional coupler, and further to the coaxial waveguide switch via the directional coupler,   if a chamber coupler is used as the directional coupler of the standing wave detection circuit, the solid state power amplifier is connected to the coaxial waveguide switch, and further to the standing wave detection circuit via the coaxial waveguide switch.   
     
     
         12 . The microwave power source of  claim 11 , wherein the driving amplifier comprises:
 a first gain control circuit configured to adjust rated output power of the microwave oven,   a second gain control circuit configure to adjust in-use output power of the microwave oven, and   a microwave low power amplifier configured to amplify power of the microwave signals.   
     
     
         13 . The microwave power source of  claim 12 , wherein during fabrication of the microwave oven, the output power of the microwave oven is adjusted to the rated output power by adjusting the gain value of the first gain control circuit while maintaining the gain value of the second gain control circuit at its largest value, and then the adjusted gain value of first gain control circuit is fixed. 
     
     
         14 . The microwave power source of  claim 12 , wherein during use of the microwave oven, a user can adjust the in-use output power of the microwave oven by adjusting the gain value of the second gain control circuit. 
     
     
         15 . The microwave power source of  claim 12 , wherein the solid state power amplifier is connected to a coaxial port via a microstrip, and further to the coaxial waveguide switch via the coaxial port,
 the microstrip has an impedance less than 50 Ohm.   
     
     
         16 . A method for adjusting an operation frequency of a microwave oven, the method comprising:
 upon power-on of the microwave oven, generating a plurality of operation frequencies, and detecting a standing wave in a chamber of the microwave oven for each of the plurality of operation frequencies to obtain information about the standing wave; and   selecting one of the plurality of operation frequencies based on the information about the standing wave, and controlling the microwave oven to operate at the selected frequency.   
     
     
         17 . The method of  claim 16 , wherein selecting one of the plurality of operation frequencies comprises: computing a Voltage to Standing Wave Ratio (VSWR) for each of the operation frequencies based on the information about the standing wave, and selecting one of the operation frequencies corresponding to the minimal VSWR among the computed VSWRs. 
     
     
         18 . The method of  claim 17 , wherein selecting one of the plurality of operation frequencies further comprises: comparing the minimal VSWR with a preset safe VSWR; issuing a warning indicating a high VSWR, if the minimal VSWR is larger than the safe VSWR; and selecting the operation frequency corresponding to the minimal VSWR, if the minimal VSWR is not larger than the safe VSWR. 
     
     
         19 . A method for adjusting rated operating power of a microwave oven, the method comprising:
 during fabrication of the microwave oven, adjusting the output power of the microwave oven to the rated power by adjusting the gain value of a first gain control circuit of the microwave oven while maintaining the gain value of a second gain control circuit of the microwave oven at its largest value, and fixing the adjusted gain value of first gain control circuit; and   during use of the microwave oven, adjusting the in-use output power of the microwave oven by adjusting the gain value of the second gain control circuit.