JP5304701B2 - Magnetron drive power supply - Google Patents

Description

  The present invention relates to a power source for driving a magnetron using a magnetron such as a microwave oven as a load.

  A conventional magnetron driving power supply will be described with reference to the drawings. FIG. 5 is a configuration diagram of a conventional magnetron driving power source mounted in a so-called inverter type microwave oven sold mainly in Japan.

  A conventional magnetron driving power source converts an AC commercial power source 51 into a DC voltage once by a diode bridge 52, and this inverter voltage is applied to a primary winding of a high voltage transformer 56 by turning on and off the DC voltage. The high voltage transformer 56 excites a high frequency high voltage in the secondary winding. The high frequency high voltage is rectified to a high DC voltage by the high voltage rectifier circuit 58 and applied to the magnetron 59. The magnetron 59 is driven by this DC high voltage and generates a radio wave of 2.45 GHz.

  An IGBT (insulated gate bipolar transistor) is generally used as the semiconductor switch element 55, and a high-frequency voltage is generated in the high-voltage transformer 56 by switching the element at a high frequency of several tens of kHz.

  The magnetron 59 is a so-called vacuum tube oscillator, and a high voltage is applied between the anode and the cathode. By heating the cathode to about 2100 K or more to emit thermoelectrons, microwaves can be stably extracted.

  However, if the cathode temperature cannot be maintained at a predetermined value, thermionic emission is insufficient, the operation becomes unstable, and modal oscillation occurs.

  In the conventional magnetron driving power supply, the average value of the input current is compared with a predetermined value, and it is determined whether the magnetron 59 is oscillating normally or modally oscillating according to the magnitude relationship.

Japanese Patent Laid-Open No. 7-135076

  However, in the magnetron driving power source of the conventional configuration, when feedback control for controlling the input current of the inverter circuit to a constant value is operated, the input current is always controlled to a predetermined value, so that a modal oscillation is caused. It is very difficult to distinguish from a state of normal oscillation.

  Further, since the modal oscillation is a phenomenon that occurs sporadically rather than a phenomenon that occurs stably over the entire range of the commercial power supply cycle, it is difficult to specify the occurrence even if the average value of the input current is measured.

  The present invention solves the above-mentioned conventional problems, and an input current waveform is compared with a reference value at a specific position in a commercial power supply cycle by a sample and hold circuit to reliably detect an abnormality in the input current due to a magnetron's modal oscillation. In addition, since the inverter circuit can be protected and stopped, it is an object of the present invention to provide a magnetron driving power source that can improve the reliability of the protection operation.

  In order to solve the above-described conventional problems, a magnetron driving power source according to the present invention includes a resonance circuit having a semiconductor switch element, a high-voltage transformer, and a high-voltage rectifier circuit, and supplies power to the magnetron by turning on and off the semiconductor switch element. An inverter circuit and a control unit for controlling on / off of the semiconductor switch element are provided. The control unit detects a driving circuit unit for driving the semiconductor switch element, a switching control unit for controlling on / off timing, and a modal oscillation of the magnetron. A modal oscillation detection unit that detects an input current and an input voltage of the inverter circuit, detects a difference at a predetermined timing via a sample hold circuit, and calculates the difference as a voltage. When this voltage value exceeds a predetermined threshold, the magnetron It is obtained by the determining configuration and has a over loading oscillation.

  This makes it possible to reliably detect magnetron oscillations from abnormal input current waveforms, improve the reliability of inverter circuit and magnetron protection operations, and reliably avoid damage to inverter circuits and magnetrons due to moding oscillations. Can be made.

  The magnetron driving power source according to the present invention can reliably detect abnormal currents due to magnetron's modal oscillation and prevent damage to inverter circuits such as semiconductor switching elements and high voltage circuits, and to prevent damage to the magnetron due to modal oscillation.

Configuration diagram of magnetron driving power source in Embodiment 1 of the present invention Operation waveform diagram of magnetron in steady state in Embodiment 1 of the present invention Operation waveform diagram of magnetron at the time of modal oscillation in Embodiment 1 of the present invention Configuration diagram of power source for driving magnetron in embodiment 2 of the present invention Configuration diagram of conventional magnetron drive power supply

  A first invention includes a resonance circuit having a semiconductor switch element, a high-voltage transformer, and a high-voltage rectifier circuit, an inverter circuit for supplying power to the magnetron by turning on and off the semiconductor switch element, and control for controlling on / off of the semiconductor switch element And the control unit includes a drive circuit unit that drives the semiconductor switch element, a switching control unit that controls the on / off timing, and a modal oscillation detection unit that detects the modal oscillation of the magnetron. The modal oscillation detection unit detects an input current and an input voltage of the inverter circuit, and converts a difference between the input current and the input voltage obtained at a predetermined timing via a sample hold circuit. When the voltage value obtained by It is to determine that the oscillation.

  According to the present invention, since the difference between the input current and the input voltage can be compared at a predetermined time by the sample and hold circuit, it is possible to reliably identify whether the magnetron is oscillating normally or modally. It is.

  In the second invention, particularly in the first invention, the sample and hold circuit takes a timing by the ZVP circuit that detects the timing when the commercial power input to the inverter circuit becomes substantially zero, and determines the sample and hold timing. Is.

  According to the present invention, the difference between the input current and the input voltage can be matched by a ZVP circuit that detects the timing when the input voltage becomes substantially zero, and compared at a predetermined time by the sample and hold circuit. Since the modal oscillation of the magnetron can be determined at a specific phase, it is possible to reliably identify whether the magnetron is oscillating normally or modal.

  In the third invention, particularly in the second invention, the sample hold circuit takes a timing by the ZVP circuit and samples and holds at a plurality of time points in the cycle of the commercial power supply. It is determined whether or not the magnetron is oscillating.

  According to the present invention, the difference between the input current and the input voltage can be matched with a ZVP circuit that detects the timing when the input voltage becomes substantially zero, and compared at a predetermined time by the sample and hold circuit. Since the comparison time is performed at a plurality of points, it is possible to more reliably identify whether the magnetron is oscillating normally or modal.

  According to a fourth aspect of the present invention, in particular, in the first to third aspects of the present invention, the operation unit is provided in the magnetron driving power source, and the magnitude of the power converted by the inverter circuit is determined by the control signal of the operation unit, and the modal oscillation The threshold value of the detection unit is determined by the control signal of the operation unit.

  According to the present invention, even if the conversion power of the inverter circuit fluctuates due to the operation unit, the reference voltage power supply is set according to the fluctuation. Therefore, whether the magnetron is oscillating modal regardless of the conversion power of the inverter circuit. And the reliability of the protective operation of the inverter circuit can be improved.

  According to a fifth aspect of the invention, in particular, in the first to fourth aspects of the invention, when the modal oscillation of the magnetron is detected by the modal oscillation detector, the operation of the oscillation circuit is stopped so as to stop the switching operation of the inverter circuit. Is.

  According to the present invention, it is possible to prevent an excessive voltage and current from being generated in the inverter circuit due to the modal oscillation of the magnetron, and an excessive current voltage duty is imposed on the component parts such as the semiconductor switch element constituting the inverter circuit. It is possible to realize a magnetron driving power source with high reliability without this.

  According to a sixth aspect of the present invention, in particular, in the first to fourth aspects of the present invention, a counter means is provided in the modal oscillation detection unit, and when the number of times the magnetron has been modified exceeds a predetermined number, it is determined that the magnetron is oscillating modally. Then, the switching operation of the inverter circuit is stopped.

  According to the present invention, even if the modal oscillation detection unit erroneously senses the magnetron modal due to a single noise, the inverter circuit does not stop immediately, thereby detecting the magnetron modal with high accuracy. can do.

  According to a seventh aspect of the invention, in particular, in the sixth aspect of the invention, a timer means is provided in the modal oscillation detection unit to measure the time during which the magnetron is oscillating normally, and a predetermined time after the last modal oscillation is detected. When no modal oscillation is detected, the count of the number of modals is cleared.

  According to the present invention, it is possible to ignore the accidental magnetron moding and continue the operation. Therefore, it is possible to distinguish the moding generated by the magnetron degradation from the accidental moding. it can. Therefore, the magnetron mod oscillation at the end of the life can be detected with high accuracy, and it can be protected from the destruction of the inverter circuit due to the application of the excessive current voltage duty caused by the mod oscillation.

  According to an eighth aspect of the present invention, in particular, in the sixth aspect of the invention, the ZVP count circuit is provided in the modal oscillation detector, and the modal oscillation is not detected after the last modal oscillation is detected. When counting the number of times, the count of the number of times of morning is cleared.

  According to the present invention, it is possible to ignore the accidental magnetron moding and continue the operation. Therefore, it is possible to distinguish the moding generated by the magnetron degradation from the accidental moding. it can. Therefore, the magnetron mod oscillation at the end of the life can be detected with high accuracy, and it can be protected from the destruction of the inverter circuit due to the application of the excessive current voltage duty caused by the mod oscillation.

  According to a ninth aspect of the invention, in particular, in the fifth to eighth aspects of the invention, the controller is provided with magnetron activation determining means, and the determination by the modal oscillation detector is invalidated while the magnetron is controlled in the activated state. is there.

  According to the present invention, since the modal oscillation generated during the transition from the startup state to the steady oscillation state is not sensed, the magnetron can be surely brought into the oscillation state, and the magnetron driving can be performed without excessively operating the protection operation. Power supply can be operated.

  According to a tenth aspect of the present invention, in particular, in the fifth to eighth aspects of the present invention, the controller is provided with a magnetron activation determining means, and the period during which the magnetron is controlled in the activated state and the predetermined time after the activation determination of the magnetron The determination by the detection unit is invalidated.

  According to the present invention, since the modal oscillation generated during the transition from the startup state to the steady oscillation state is not sensed, the magnetron can be surely brought into the oscillation state, and the magnetron driving can be performed without excessively operating the protection operation. Power supply can be operated.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a configuration diagram of a magnetron driving power supply according to the first embodiment of the present invention. In FIG. 1, an inverter circuit 1 once rectifies an AC voltage obtained from a commercial power source 2 into a unidirectional voltage by a diode bridge 3 and smoothes it by a smoothing circuit including a choke coil 4 and a smoothing capacitor 5.

  This smoothing circuit does not have the ability to maintain and smooth the voltage with respect to the commercial power supply frequency of 60 Hz or 50 Hz, and the circuit is small enough to have a smoothing ability that can maintain a DC voltage with respect to the switching frequency of the inverter circuit 1. Is playing. Further, a high frequency high voltage is induced on the secondary side of the high voltage transformer 7 by exciting a resonance circuit composed of the resonance capacitor 6 and the high voltage transformer 7 by turning on and off the semiconductor switch element 8.

  The high voltage rectifier circuit 9 rectifies the high frequency high voltage and supplies a DC high voltage to the magnetron 10, and the magnetron 10 is configured to generate a 2450 MHz microwave by the DC high voltage. The control unit 11 includes a switching control unit 12 that controls the on / off timing of the semiconductor switch element 8, a drive circuit unit 13 that drives the semiconductor switch element 8, and a magnetron moding detection unit 14. The unit 13 turns on and off the semiconductor switch element 8 based on the pulse train output from the switching control unit 12.

  The magnetron moding detector 14 samples and holds the detection signal of the current detector 16 that detects the current of the commercial power supply 2 and detects the voltage rectified by the diode bridge 3 and samples and holds it. A sample and hold circuit 142, a difference circuit 143 that calculates a difference between detection signals of the two sample and hold circuits 141 and 142, a comparison circuit 145 that compares a reference voltage power supply 144 and an output signal of the difference circuit 143, and The counting circuit 146 counts the output of the comparison circuit 145, and the timer circuit 147 counts the time using the output of the comparison means 145 as a trigger.

  The count circuit 146 counts the number of times that the output signal of the comparison circuit 145 is inverted, and counts this count number as the number of times that the magnetron 10 has undergone modal oscillation. The magnetron moding detection unit 14 is configured to transmit a signal to the switching control unit 12 and prevent transmission of the switching signal to the semiconductor switch element 8 when the count number reaches a predetermined number.

  The detailed operation and action of the magnetron driving power source configured as described above will be described below.

  FIG. 2 is a diagram showing the applied voltage Vak and passing current Ia of the magnetron 10 and the voltage V2 and current waveform I2 of the commercial power supply 2 when the inverter circuit 1 is in a normal state.

  As described above, the smoothing circuit provided at the input of the inverter circuit does not have the ability to smooth the voltage of the commercial power source 2. For this reason, the input voltage of the inverter circuit 1 fluctuates in synchronization with the voltage of the commercial power supply 2.

  The resonant circuit excited by the semiconductor switch element 8 fluctuates due to this fluctuating voltage, and as a result, the output voltage of the high-voltage transformer 7 fluctuates naturally, and the voltage applied to the magnetron 10 is boosted during the period when the voltage of the commercial power supply 2 is low. Insufficient, the oscillation of the magnetron 10 is stopped.

  FIG. 3 is a diagram showing the applied voltage Vak and the passing current Ia of the magnetron 10 when the modal oscillation is generated in the magnetron 10 during the operation of the inverter circuit 1. It is assumed that the magnetron 10 has undergone modal oscillation during the period from time T1 to time T2. When the magnetron 10 causes modal oscillation, the magnetron 10 oscillates at a higher voltage (about 6 kV) than the normal oscillation state.

  As a result, the anode current of the magnetron 10 rapidly decreases. In addition, the input current I2 also decreases rapidly from the normal oscillation state.

  The current detection means 16 is constituted by a current transformer or the like and detects this input current, so that this current change is detected as it is. The sample hold circuit 141 takes a timing with the ZVP circuit 140 that detects the timing when the voltage of the commercial power supply becomes substantially zero, and receives the signal from the ZVP circuit 140 and detects the input current after a predetermined time. At the same time, the voltage after rectification is detected by the sample and hold circuit 142 at the same timing.

  The difference circuit 143 calculates the difference between the two sample hold circuits 141 and 142. The output of the difference circuit outputs a constant value in the state of normal oscillation, but the waveform changes as shown in FIG. 3 in the state where the magnetron 10 causes modal oscillation, so the output of the difference circuit 143 is normal. It becomes a larger value than the state.

  The comparison circuit 145 compares the change with the reference voltage power supply 144 to generate a pulse when the magnetron 10 causes the modal oscillation, and can detect that the magnetron 10 causes the modal oscillation.

  The counter circuit 146 can measure the number of times that the magnetron 10 has caused modal oscillation by counting the number of pulses output from the comparison circuit 145. When this number of measurements reaches a predetermined number, it is determined that the magnetron 10 is abnormal, it is determined that the magnetron 10 is oscillating, and the magnetron oscillating detector 14 issues a stop command to the switching controller 12. The voltage is applied and the operation of the inverter circuit 1 is stopped.

  For this reason, it becomes possible to realize a highly reliable magnetron driving power source in which the magnetron 10 does not continuously generate modal oscillation, and an excessive voltage / current duty of the inverter circuit is not applied. .

  Further, even if the comparison circuit 145 generates a detection pulse by mistake due to the occurrence of a moderation or noise caused by the counting of the number of modal oscillations of the magnetron 10 by the counter circuit 146, the operation of the inverter circuit 1 is caused by a malfunction. It is possible to detect stable modal oscillation without stopping the operation.

  Furthermore, the timer circuit 147 counts the time since the comparison circuit 145 last issued the detection pulse, and when this time exceeds a predetermined time, the counter circuit 146 clears the number of times the modal oscillation is detected. Even when the comparison circuit 145 erroneously generates a detection pulse due to the occurrence of moding or noise, the operation of the inverter circuit 1 can be detected more reliably without erroneously stopping the operation of the inverter circuit 1. Is possible.

  The operation unit 15 transmits a control signal for determining the conversion power of the inverter circuit 1, and based on this signal, the inverter circuit 1 controls the switching operation of the semiconductor switching element 8 to perform predetermined power conversion. Do.

  At the same time, by increasing or decreasing the abnormality determination reference voltage power supply 144 of the magnetron moding oscillation detection unit 14 by this control signal, the moding oscillation of the magnetron 10 is always performed regardless of the conversion power setting. Therefore, a more reliable magnetron driving power source can be realized.

(Embodiment 2)
FIG. 4 is a configuration diagram of a magnetron driving power source according to the second embodiment of the present invention. Components having the same reference numerals as those in the first embodiment described above perform the same operations and actions, and detailed description thereof is omitted here. This embodiment is different from the above-described embodiment in that an activation control unit 17 is added to the control unit 11.

  The activation control unit 17 controls the activation state from when the inverter circuit 1 starts the switching operation until the magnetron 10 becomes ready to oscillate microwaves. The magnetron 10 cannot oscillate microwaves until the cathode temperature reaches a predetermined temperature (generally 2000K to 2100K).

  In particular, in a home microwave oven or the like, it is general that the cathode of the magnetron 10 is heated from the auxiliary heater winding of the step-up transformer 6 for the purpose of downsizing the magnetron driving power source.

  In order to make the magnetron 10 transition to a state where oscillation is possible, it is necessary to heat the cathode. However, if this warm-up state is long, the effective heating time is shortened. It is desirable to shorten the up-time, so that a voltage of about 7 kV is applied to the magnetron 10 during the warm-up so that the magnetron is warmed up with more current supplied to the cathode than in the steady state.

  For this reason, when the transition from the warm-up to the steady oscillation state is made, the state of the modal oscillation always transits instantaneously.

  In the present embodiment, the activation control unit 17 is detected during this transition in order to prohibit the operation of the comparison circuit 145 of the magnetron moding detection unit 14 during the warm-up or for a certain period of time from the end of the warm-up operation. Moding oscillations are not counted, and normal operation can be performed without counting abnormal modal oscillations that occur every time the magnetron drive power supply is operated, thus realizing a more reliable magnetron drive power supply. It becomes possible.

  As described above, the magnetron driving power source according to the present invention is represented by a microwave oven because it can detect an abnormal current due to the magnetron's modal oscillation and can prevent the inverter circuit and the magnetron from being damaged. The present invention can also be applied to applications such as a heating device using dielectric heating, a garbage disposal machine, or a microwave power source of a plasma power source that is a semiconductor manufacturing device.

DESCRIPTION OF SYMBOLS 1 Inverter circuit 7 High voltage transformer 8 Semiconductor switch element 9 High voltage rectifier circuit 10 Magnetron 11 Control part 12 Switching control part 13 Drive circuit part 14 Magnetron moding detection part 141, 142 Sample hold circuit 143 Difference circuit 146 Count circuit 147 Timer circuit

Claims (10)

A resonance circuit having a semiconductor switch element and a high-voltage transformer, and a high-voltage rectifier circuit, comprising: an inverter circuit for supplying power to the magnetron by turning on and off the semiconductor switch element; and a controller for controlling on / off of the semiconductor switch element, The control unit includes a drive circuit unit that drives the semiconductor switch element, a switching control unit that controls on / off timing, and a modal oscillation detection unit that detects the modal oscillation of the magnetron, and the modal oscillation detection Voltage value obtained by detecting the input current and input voltage of the inverter circuit, and converting the difference between the input current and the input voltage obtained at a predetermined timing via the sample hold circuit. When the value exceeds the predetermined threshold, the magnetron Determining a magnetron drive power supply with. The power source for driving a magnetron according to claim 1, wherein the sample and hold circuit takes a timing by a ZVP circuit that detects a timing when the commercial power source input to the inverter circuit becomes substantially zero, and determines a timing for sample and hold. The sample hold circuit takes a timing by the ZVP circuit, samples and holds at a plurality of time points in the cycle of the commercial power supply, and the modal oscillation detection unit determines whether the magnetron is oscillating modal for each sample hold. The magnetron drive power supply according to claim 2. The operation unit is provided, and the magnitude of the power to be converted by the inverter circuit is determined by the control signal of the operation unit, and the threshold value of the modal oscillation detection unit is determined by the control signal of the operation unit. The magnetron driving power source according to item 1. 5. The magnetron driving device according to claim 1, wherein when the modal oscillation of the magnetron is detected by the modal oscillation detection unit, the operation of the oscillation circuit is stopped so as to stop the switching operation of the inverter circuit. 6. Power supply. 5. A counter means is provided in the modal oscillation detection unit, and when the number of times the magnetron has been modified exceeds a predetermined number, it is determined that the magnetron is oscillating and the switching operation of the inverter circuit is stopped. The magnetron driving power source according to any one of the above. A timer means is provided in the modal oscillation detection unit to measure the time during which the magnetron is oscillating normally. If no modal oscillation is detected for a predetermined time since the last modal oscillation was detected, the modal oscillation is detected. The magnetron drive power supply according to claim 6, wherein the count of the number of times is cleared. A ZVP count circuit is provided in the modal oscillation detection unit. When the modal oscillation is detected and the ZVP count circuit counts the predetermined number of times since the last modal oscillation was detected, the modal count is counted. The power supply for driving a magnetron according to claim 6, which is cleared. The magnetron drive power supply according to any one of claims 5 to 8, wherein magnetron activation determination means is provided, and determination by the modal oscillation detection unit is invalidated while the magnetron is controlled in the activated state. The magnetron activation determination means is provided, and the determination by the modal oscillation detection unit is invalidated for a period during which the magnetron is controlled in the activated state and a predetermined time after the activation determination of the magnetron. Magnetron drive power supply.

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