JP2006066194A - Magnetron drive power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetron drive power supply in which the distortion of input current is always suppressed even if the temperatures of a magnetron rise, and which has a high power factor and little harmonics of the input current. <P>SOLUTION: The input current of an inverter circuit 4 is detected by an input current detection part 12 and adjusted by a pulse modulation part 16 so as to become a target waveform of a target waveform generating part 14 and a semiconductor switch element 3 is driven. Thereby, regardless of variations in oscillation starting voltage of the magnetron 7 due to the temperature changes of the magnetron 7 and the difference in oscillation starting voltage due to the types of the magnetron 7, drive power supply in which distortion of the input current is always suppressed and which has a high power factor with less harmonics of input current is obtained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

  Conventionally, as a power source for driving a magnetron, one having the following configuration is known (for example, see Patent Document 1).

That is, a commercial power supply that is alternating current is once converted into a DC voltage, and the inverter circuit generates a high-frequency voltage in the primary winding of the high-voltage transformer by turning on and off the semiconductor switch element, and the high-voltage transformer is converted into the secondary winding. Excites high frequency high voltage. This high frequency high voltage is rectified to a DC high voltage by a high voltage rectifier circuit and applied to the magnetron. The magnetron is driven by this DC high voltage and generates a radio wave of 2.45 GHz.
JP-A-7-176375

  However, in the conventional configuration, when the temperature of the magnetron rises due to continuous operation or the like, the current waveform is distorted. This is due to the fact that the oscillation start voltage of the magnetron has temperature characteristics, and the oscillation start voltage of the magnetron decreases as the temperature of the magnetron rises. As a result, the ON signal of the semiconductor switch element and the input voltage waveform Is lost, and the input current waveform is distorted.

  The present invention solves the above-described conventional problems, and even if the temperature of the magnetron rises due to continuous operation or the like, the distortion of the input current is always suppressed, and the power source for driving the magnetron with high power factor and less harmonics of the input current The purpose is to provide.

  In order to solve the above-described conventional problems, the magnetron driving power source of the present invention detects the input current of the inverter circuit and adjusts it to have a target waveform to drive the semiconductor switch element.

  As a result, regardless of changes in the magnetron oscillation start voltage due to changes in the magnetron temperature and differences in the oscillation start voltage due to the type of magnetron, distortion of the input current is always suppressed and harmonics of the input current are generated at a high power factor. It can be less.

  The magnetron driving power source according to the present invention can always suppress distortion of the input current, and can have a high power factor and less harmonics of the input current.

  The first invention includes an inverter circuit that generates a high-frequency voltage by turning on and off the semiconductor switch element, a high-voltage rectifier circuit that rectifies the high-frequency voltage into a DC high voltage, a magnetron that is driven by the DC high voltage and generates radio waves, A control unit that controls ON / OFF of the semiconductor switch element, the control unit detecting an input current of the inverter circuit, and a target waveform generating unit that forms a target waveform by a signal of the output command unit An error calculation unit that inputs signals from the input current detection unit and the target waveform generation unit and calculates a waveform error between the target waveform and the input current waveform, and a pulse width modulation unit that adjusts the input current waveform to be the target waveform And a magnetron driving power source having a driving unit for driving the semiconductor switch element by the output signal of the pulse width modulation unit. Regardless of changes in the oscillation start voltage of the magnetron due to changes in the temperature of the netron and differences in the oscillation start voltage due to the type of magnetron, distortion of the input current is always suppressed, high power factor and low harmonics of the input current can do.

  In the second invention, in particular, in the first invention, since the input current detection unit is configured by a resistor, the input current can be detected with a small configuration.

  In particular, in the second invention, the negative voltage detected from the resistor is changed to the positive voltage by inverting and amplifying the output voltage of the resistor to obtain a detection signal of the input current detector. Therefore, the power source of the control unit can be configured with a unidirectional power source, and the inverter circuit can be downsized.

  In a fourth aspect of the invention, in particular, in the first aspect of the invention, the input current detection unit is composed of a current transformer and a rectification unit, so that the current transformer can detect a current without limiting the current detection position, and Since the control unit can be composed of a unidirectional power supply, the degree of freedom in designing the inverter circuit is increased, and the inverter circuit can be downsized.

  According to a fifth aspect of the invention, in particular, in the first aspect of the invention, the target waveform generator is configured to obtain the target waveform by full-wave rectifying the voltage of the commercial power supply, so that the target waveform is always input to the magnetron driving power supply. The semiconductor switch element can be driven with a drive pulse that can be synchronized with the source and ensure that the input current waveform is approximately sinusoidal, so that distortion of the input current waveform is suppressed regardless of the magnetron state, and harmonic components Therefore, the magnetron driving power source can be operated with a small input current.

  In the sixth aspect of the invention, in particular, in the fifth aspect of the invention, the target waveform generation unit is configured to vary the amplitude according to the signal of the output command unit, so that any current level corresponds to each input current level. Since the semiconductor switch element is driven by the drive pulse, the inverter circuit can always be operated at a high power factor regardless of the change in the input current level.

  In the seventh aspect of the invention, in particular, in any one of the first to sixth aspects of the invention, since the maximum value limit is provided for the output pulse width of the pulse width modulation unit, the on-time may be increased due to an abnormality in the power supply voltage. Even if the control pulse is set to be long, the on-time of the semiconductor switch element is limited. Therefore, the inverter circuit is prevented from being damaged without causing a long on-time that causes destruction of the semiconductor switch element.

  In an eighth aspect of the invention, in particular, in any one of the first to seventh aspects of the invention, since the minimum value limit is provided for the output pulse width of the pulse width modulation unit, the on-time may be increased due to an abnormality in the power supply voltage. Even if an attempt is made to set the control pulse to be abnormally short, the minimum value of the on-time of the semiconductor switch element is set, so that the input current is not interrupted and control instability can be eliminated.

  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 to 3 show a magnetron driving power source according to an embodiment of the present invention.

  As shown in FIG. 1, in the present embodiment, an AC commercial power source 1, a diode bridge 2 of a rectifying unit that converts this into a DC voltage, and an inverter that generates a high-frequency voltage by turning on and off the semiconductor switch element 3. A circuit 4; a high-voltage rectifier circuit 6 for rectifying the high-frequency voltage into a DC high voltage; a magnetron 7 driven by the DC high voltage to generate a radio wave of 2.45 GHz; and a control for controlling on / off of the semiconductor switch element 3 Part 11.

  In addition to the semiconductor switch element 3, the inverter circuit 4 constitutes a high-voltage transformer 5, an inductor 8 and a capacitor 9 constituting a smoothing circuit, a primary winding of the high-voltage transformer 5 and a resonance circuit, and a high-frequency high in the secondary winding. It has a capacitor 10 for exciting the voltage and operates at 20 kHz to 50 kHz.

  The control unit 11 includes an input current detection unit 12 that detects an input current of the inverter circuit 4, a target waveform generation unit 14 that forms a target waveform based on a signal from the output command unit 13, and an input current detection unit 12. An error calculation unit 15 that inputs a signal from the target waveform generation unit 14 and calculates a waveform error between the target waveform and the input current waveform, a pulse width modulation unit 16 that adjusts the input current waveform to be a target waveform, and a pulse width And a drive unit 17 that drives the semiconductor switch element 3 by an output signal of the modulation unit 16.

  The input current detection unit 12 of the control unit 11 is constituted by a resistor 18, and this output voltage is inverted and amplified by an inverting amplifier 19 and used as a detection signal of the input current detection unit 12. As a result, the input current can be detected with a small configuration, and the negative direction voltage detected from the resistor 18 is inverted and amplified to the positive direction voltage. The inverter circuit 4 can be downsized.

  The target waveform generator 14 is configured to obtain a target waveform by full-wave rectifying the voltage of the commercial power source 1 and to vary the amplitude according to the signal from the output command unit 13. As a result, the target waveform can always be synchronized with the input voltage source of the magnetron drive power supply, and the semiconductor switch element 3 is driven with a drive pulse that ensures that the input current waveform is substantially sinusoidal. Regardless of the state, the distortion of the input current waveform is suppressed, and the semiconductor switch element 3 is driven with a drive pulse corresponding to each input current level at any current level. It becomes possible to always operate the inverter circuit with a high power factor.

  The pulse width modulation unit 16 reduces the pulse width when the error value calculated by the error calculation unit 15 is positive, and conversely increases the pulse width when the error value is negative. Pulse width modulation is applied to the pulse train applied to. As a result, when the input current waveform is lower than the target waveform, the input current can be increased. Conversely, when the input current is larger than the target waveform, the input current can be decreased, and the input current waveform is shaped into the target waveform. Can be controlled. In this operation, the inverter circuit 4 is continuously operated, and even if the magnetron 7 generates heat and the oscillation start voltage of the magnetron 7 changes, the modulation degree of the pulse width modulation of the pulse train driving the semiconductor switch element 3 changes. The inverter circuit 4 can be driven by a pulse train that can be absorbed and always shapes the input current waveform to the target waveform regardless of the change in the oscillation voltage of the magnetron 7.

  Further, the pulse width modulation unit 16 is configured to limit at least one of the maximum value and the minimum value of the output pulse width. For example, the pulse width modulation unit 16 tries to set the control pulse so that the ON time becomes long due to an abnormality of the power supply voltage. However, since the on-time of the semiconductor switch element 3 is limited, it is possible to prevent the inverter circuit 4 from being damaged without having a long on-time that causes the semiconductor switch element 3 to be destroyed. Conversely, even if the control pulse is set so that the on-time becomes abnormally short, the minimum value of the on-time of the semiconductor switch element 3 is set, so that the input current is not interrupted and the control instability is eliminated. ing.

  Next, FIG. 2A shows the input current waveform of the inverter circuit 4, and FIG. 2B shows the waveform obtained by superimposing the detection signal of the input current detection means 12 and the output signal of the target waveform generator 14. ing. Further, (c) shows the waveform error calculated by the error calculation unit 15, and (d) shows the change in the ON time of the pulse train modulated by the error by the error calculation by the error calculation unit 15. . In this way, the pulse width is shortened during the period when the error shows a positive value, and conversely, when the error is a negative value, the pulse width is increased so that the input current waveform is substantially sinusoidal. Can keep. By performing such an operation, a target current waveform is created regardless of changes in the operating characteristics of the magnetron 7, and the drive signal of the semiconductor switch element 3 is pulsed so that the input current waveform matches the target current waveform. Since the width modulation is performed, it is possible to control the input current waveform to be substantially sinusoidal regardless of changes in the operating characteristics of the magnetron 7. This eliminates the need to change the design of the circuit constants of the inverter circuit 4 depending on the type of the magnetron 7 to be mounted, thereby facilitating the design of the inverter circuit 4. Further, by changing the target current waveform according to the value of the input current, the current waveform can always be maintained in a sinusoidal shape, so that the inverter circuit 4 always operates at a high power factor without changing the power factor depending on the value of the input current. be able to. Furthermore, since the peak value of the input current waveform can be reduced by operating at a high power factor, the effective current value can be reduced, the heat generation of the elements constituting the inverter circuit 4 can be reduced, and the element cooling design can be facilitated. The effect that it is possible can be demonstrated.

  FIG. 3 shows another example of the present embodiment, and the input current detection unit 12 is configured by a current transformer 20 and a rectification unit 21. With this configuration, the position where the input current detecting means 12 is inserted can be set to an arbitrary position before and after the rectification of the diode bridge 2, so that the degree of freedom in mounting the inverter circuit 4 can be improved. It is possible to reduce the size of the circuit 4.

  As described above, the magnetron driving power source according to the present invention can always suppress distortion of the input current and can reduce the harmonics of the input current with a high power factor, so that a magnetron such as a microwave oven can be used as a load. Applicable to what to do.

Block diagram of magnetron driving power supply in the embodiment of the present invention (A) Input current waveform diagram of the inverter circuit in the magnetron driving power source (b) Voltage waveform diagram of the input current detecting means and the target waveform generating unit (c) Diagram showing the waveform error calculated by the error calculating unit (d) The figure which shows the change of the pulse width which the pulse width modulation part outputs Block diagram showing another example of power source for driving the magnetron

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Commercial power supply 2 Diode bridge 3 Semiconductor switch element 4 Inverter circuit 5 High voltage transformer 6 High voltage rectifier circuit 7 Magnetron 10 Capacitor 11 Control part 12 Input current detection part 13 Output command part 14 Target waveform generation part 15 Error calculation part 16 Pulse width modulation part 17 Drive unit 18 Resistor 19 Inverting amplifier 20 Current transformer 21 Rectifier

Claims (8)

An inverter circuit that generates a high-frequency voltage by turning on and off the semiconductor switch element, a high-voltage rectifier circuit that rectifies the high-frequency voltage to a DC high voltage, a magnetron that is driven by the DC high voltage to generate radio waves, and the semiconductor switch element is turned on and off A control unit that controls the input circuit, an input current detection unit that detects an input current of the inverter circuit, a target waveform generation unit that forms a target waveform by a signal from the output command unit, and an input current detection unit An error calculation unit that inputs signals from the target waveform generation unit and calculates a waveform error between the target waveform and the input current waveform, a pulse width modulation unit that adjusts the input current waveform to be a target waveform, and a pulse width modulation unit A magnetron driving power source having a driving unit for driving the semiconductor switch element by the output signal of The magnetron driving power source according to claim 1, wherein the input current detection unit is configured by a resistor. The magnetron driving power source according to claim 2, wherein the output voltage of the resistor is inverted and amplified to be a detection signal of the input current detection unit. The magnetron driving power source according to claim 1, wherein the input current detection unit includes a current transformer and a rectification unit. The magnetron driving power source according to claim 1, wherein the target waveform generator is configured to obtain a target waveform by full-wave rectifying the voltage of the commercial power source. 6. The magnetron driving power source according to claim 5, wherein the target waveform generator is configured to vary the amplitude according to a signal from the output command unit. The power supply for driving a magnetron according to any one of claims 1 to 6, wherein a maximum value limit is provided for an output pulse width of the pulse width modulation section. The power supply for driving a magnetron according to any one of claims 1 to 7, wherein a minimum value restriction is provided on an output pulse width of the pulse width modulation section.

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