JP3501136B2 - Power supply for magnetron drive - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetron driving power source having a magnetron such as a microwave oven as a load.

[0002]

2. Description of the Related Art A conventional magnetron driving power source will be described with reference to the drawings. FIG. 20 is a circuit diagram of a conventional magnetron driving power supply. The conventional magnetron driving power supply is a commercial power supply 1 that is an alternating current, and a diode bridge 2
Is converted into a DC voltage by the ON / OFF operation of the semiconductor switching elements 3 and 4, the inverter circuit 5 generates a high frequency voltage in the primary winding of the high voltage transformer 6, and the high voltage transformer 6 generates a high frequency voltage in the secondary winding. Exciting voltage. The high frequency high voltage is rectified by the high voltage rectifier circuit 7 into a DC high voltage and applied to the magnetron 8. The magnetron 8 is driven by this DC high voltage and generates a radio wave of 2.45 GHz.

FIG. 21 is a diagram showing operation waveforms of a conventional magnetron driving power source. AC voltage V1 of commercial power supply 1
Is rectified into a DC voltage by the diode bridge 2. Although the inductor 9 and the capacitor 10 form a smoothing circuit, the capacity of the capacitor 10 is such that a DC voltage can be held for the inverter circuit 5 operating at 20 kHz to 50 kHz in order to reduce the size of the inverter circuit 5. The capacity of the commercial power supply 1 (50H
z or 60 Hz) has no smoothing ability. Therefore, the voltage V10 of the capacitor 10 shows a waveform obtained by simply full-wave rectifying the commercial power supply 1, and shows a pulsating waveform that varies from almost 0 voltage to the maximum voltage of the commercial power supply 1. The inverter circuit 5 uses the pulsating voltage V10 of the capacitor 10.
Since the envelope waveform of the high frequency voltage generated in the primary winding of the high voltage transformer 6 becomes a waveform as shown by V6 (Lp), only a low voltage can be generated in the period when the voltage V10 of the capacitor 10 is low. Absent.

On the other hand, the operating characteristics of the magnetron 8 are shown in FIG.
As shown in (4), a non-linear voltage-current characteristic is shown in which the anode current does not flow unless a predetermined voltage or more is applied between the anode and cathode. Therefore, when the voltage generated in the primary winding of the high voltage transformer 6 is low, the voltage excited in the secondary winding is also lowered at the same time, so that the waveform of the voltage V8 applied to the magnetron 8 is VAK (TH ) Will occur for some time. During this period, since the magnetron 8 stops oscillating, the load magnetron 8
Since the electric power is not consumed in, the current I1 of the commercial power supply 1 stops flowing. As a result, the waveform of the current I1 of the commercial power source 1 is shown in FIG.
As shown in (1), the waveform has a very distorted waveform having a period in which the current is zero, which causes a reduction in the power factor of the magnetron driving power supply and a harmonic current in the input current.

To solve such a problem, there has been proposed a circuit configuration shown in FIG. 23, in which the active filter circuit 13 is provided in the preceding stage of the inverter circuit 5 to improve the power factor of the input current and suppress harmonics. There is. The active filter circuit 13 has a so-called step-up chopper circuit configuration,
The boosted voltage can be controlled by the on-time ratio of the semiconductor switch element 17.

The operation in this case will be described with reference to FIG. The voltage of the commercial power supply 1 shows an AC voltage waveform as indicated by V1. The active filter circuit 13 generates a boosted voltage in the capacitor 15 by controlling the voltage obtained by full-wave rectifying the AC voltage V1 by the diode bridge 2 by turning on and off the semiconductor switch element 14. Although the pulsation rate of the boosted voltage V15 changes depending on the capacity of the capacitor 15, it can be prevented from completely decreasing to 0 like V10 in the configuration of FIG. Therefore, the voltage V6 (Lp) generated in the primary winding of the high voltage transformer 6 can be generated at a predetermined value or more even when the voltage of the commercial power supply 1 is near zero. As a result, the voltage applied to the magnetron 8 can always be kept higher than the oscillating voltage. As a result, the input current I1 can have a substantially sinusoidal waveform with no period of 0 as shown in the figure, and the input power factor can be improved and the harmonic current can be suppressed.

However, in such a configuration, the active filter circuit 13 is added to the inverter circuit 5, and the process of power conversion is rectification → step-up → high frequency generation (inverter circuit) → high-voltage rectification, so the process of power conversion increases. However, there is a problem in that the conversion efficiency is lowered and the circuit scale is increased.

Therefore, a structure in which the constituent parts and circuit functions are further shared is disclosed in Japanese Patent Laid-Open No. 10-271846. FIG. 25 is a circuit diagram showing the circuit configuration of the present invention. With this circuit configuration, boosting function,
The operation of the inverter function is performed at the same time to improve the input power factor and simplify the circuit configuration. 26 and 27 are diagrams for explaining the circuit operation, and FIGS. 26 (a) to 26 (d) are diagrams for explaining the respective energization paths by turning on / off the semiconductor switch elements Q1 and Q2, and FIG. 27 corresponds to them. It is an operation waveform diagram. The circuit operation will be described with reference to FIGS. For convenience of description, the description begins with the semiconductor switch element Q2 turned on in the direction in which the voltage polarity of the commercial power supply 1 is as shown in the figure. When the semiconductor switch element Q2 is on, as shown in FIG. 26A, the capacitor C2 → the commercial power source 1 → the inductive load circuit 19 → the semiconductor switch element Q2.
A current flows through the path of, and the current IQ2 of the semiconductor switch element Q2 monotonically increases as shown in FIG. When the semiconductor switch element Q2 is turned off in a predetermined time, the current path shifts to the state of FIG. 26 (b), and the capacitor C1 is charged through the path of diode D2 → commercial power supply 1 → inductive load circuit 19 → diode D3 → capacitor C1. . When all the energy stored in the inductive load circuit 19 is released, the capacitor C1 is used as a power source, and the capacitor C1 → semiconductor switch element Q1 → inductive load circuit 19 → commercial power source 1 → the path of FIG. An electric current flows in. When the semiconductor switch element Q1 is turned off in a predetermined time, the inductive load circuit 19 tries to flow a current in the same direction, so the path shown in FIG. 26 (d) (commercial power supply 1 → capacitor C2 → diode D4 → inductive load circuit). At 19), a current flows and the energy stored in the inductive load circuit 19 is charged into the capacitor C1. When all the energy stored in the inductive load circuit 19 is released, a current again flows through the path of FIG. 26 (a) and the circuit operation continues. Japanese Patent Laid-Open No. 10-2718
Although not disclosed in 46, in order to realize this operation, the capacitances of the capacitors C1 and C2 need to have a capacitance relationship as shown in Expression 1.

C1 >> C2 (Equation 1) In order to satisfy such a relationship, it is necessary to use a capacitor such as an electrolytic capacitor that can handle a large capacity as the capacitor C1.

By such an operation, the current from the commercial power source 1 can be made to flow over almost the entire power source cycle, and the power factor of the input current is improved, harmonics are suppressed, and the circuit is simplified.

[0011]

However, the above-mentioned conventional structure has the following problems.

That is, when feedback controlling the inverter circuit, the input current can be easily feedback controlled by providing a current detector such as a current transformer. However, when the voltage of the commercial power supply fluctuates, only the input current is used. When feedback control is performed, the converted power of the inverter circuit fluctuates according to the voltage fluctuation of the commercial power supply. Therefore, in the inverter having the configuration as described in the first conventional example, the voltage obtained by rectifying the commercial power supply is detected, and the value of the input current for feedback control is changed by using the detected voltage to change the voltage of the commercial power supply. Can also stabilize the conversion power of the inverter circuit. However, in the configuration of the third conventional example having the configuration most similar to the present invention, the voltage obtained by boosting the voltage of the commercial power source becomes the voltage generated by the inverter circuit, and the voltage of the commercial power source cannot be easily detected. . For this reason, it is necessary to correct the converted power with respect to the voltage fluctuation of the commercial power supply.

The present invention has been made in view of the above problems, and it is possible to stabilize the conversion power of the inverter circuit and reduce the thermal stress of the inverter circuit even if the voltage of the commercial power supply fluctuates. Has an aim.

[0014]

In order to solve the above-mentioned conventional problems, a magnetron driving power source of the present invention comprises a first and a second series-connectable semiconductor switch element connected in series, and a first and a second serial connection element. A series connection body of two diodes is connected in parallel, first and second capacitors are respectively connected in parallel to the first and second diodes, and the first and second semiconductor switch elements capable of reverse conduction The connection point and the first
A commercial power supply and a series circuit of a primary winding of the high-voltage transformer are connected between the connection points of the second diode and the second diode, and the output of the secondary winding of the high-voltage transformer energizes the magnetron through the high-voltage rectifier circuit. A drive circuit for driving the first and second semiconductor switch elements, and an input current feedback control unit for detecting an input current input from the commercial power source and controlling the input current to a predetermined value. The first and second semiconductor switching elements are complementarily driven, and the drive signals are exchanged depending on whether the commercial power source is a positive electrode or a negative electrode, and the input current feedback control unit controls the first and second capacitors. Depending on the output voltage of the series connection ,
The voltage generated in the first and second capacitors
In this configuration, the value of the input current for feedback control is increased / decreased.

This makes it possible to stabilize the converted power of the inverter circuit even when the voltage of the commercial power supply fluctuates, and reduce the thermal stress of the inverter circuit.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claims 1 and 2 is directed to a series connection body of first and second semiconductor switch elements capable of reverse conduction, and a series connection body of first and second diodes. Are connected in parallel, first and second capacitors are connected in parallel to the first and second diodes, respectively, and a connection point of the first and second reverse conducting semiconductor switch elements and the first A commercial power supply and a series circuit of a primary winding of the high-voltage transformer are connected between the connection points of the second diode and the second diode, and the output of the secondary winding of the high-voltage transformer energizes the magnetron through the high-voltage rectifier circuit. A drive circuit for driving the first and second semiconductor switch elements, and an input current feedback control unit for detecting an input current input from the commercial power source and controlling the input current to a predetermined value. The first and second The conductor switching elements are driven complementarily, and the drive signals are switched depending on whether the commercial power source is a positive electrode or a negative electrode, and the input current feedback control unit outputs the output voltage of the series connection body of the first and second capacitors. Depending on
Outputs to the first and second capacitors regardless of the voltage of the commercial power supply.
Equalize the ratio of the generated voltage or the detection signal of the voltage detection means.
By adjusting the input current value for feedback control to increase or decrease,
Since the feedback control value of the input current is increased or decreased according to the output voltage of the series connection body of the second capacitors, the converted power of the magnetron driving power supply can be kept constant even if the voltage of the commercial power supply fluctuates.

The invention according to claim 3 is the first and second aspects.
And a series connection body of semiconductor switch elements capable of reverse conduction and a series connection body of first and second diodes are connected in parallel,
First and second capacitors are connected in parallel to the first and second diodes, respectively, and a connection point of the first and second semiconductor switch elements capable of reverse conduction, and the first and second diodes. Connect a commercial power source and a series circuit of the primary winding of the high-voltage transformer between the connection points of
The output of the secondary winding energizes the magnetron via a high-voltage rectifier circuit, detects the input current input from the drive circuit that drives the first and second semiconductor switch elements, and the commercial power source, and detects the input current. An input current feedback control unit for controlling to a predetermined value is provided, the drive circuit complementarily drives the first and second semiconductor switch elements, and a drive signal is supplied when the commercial power source is positive and negative. The input current feedback control unit measures the output voltage of the series connection body of the first and second capacitors immediately before the magnetron driving power supply is started, and the commercial power supply voltage is changed according to the measured voltage.
The voltage generated in the first and second capacitors regardless of the pressure
By configuring the input current value for feedback control to be equal, it is possible to detect only the voltage fluctuation of the commercial power supply, regardless of the converted power of the magnetron drive power supply, so the voltage of the commercial power supply fluctuates accurately. Even so, the converted power of the power supply for driving the magnetron can be kept constant.

According to a fourth aspect of the present invention, in addition to the magnetron driving power source according to the third aspect, a switchgear is provided between the commercial power source and the magnetron driving power source, and the input current feedback control sections are the first and second. The voltage of the first and second capacitors is measured with a delay time after the switchgear is closed until the output voltage of the series connection body of the capacitors becomes stable, and the magnetron driving power supply is started. With this configuration, the transient output voltage of the series connection body of the first and second capacitors, which occurs when the switchgear is changed from the open state to the closed state, is not erroneously detected, so that the commercial power source can be accurately used. Even if the voltage fluctuates, the converted power of the magnetron driving power supply can be kept constant.

The invention according to claim 5 is the same as claim 1 or
The input current feedback control unit of the magnetron driving power supply described in 2 constantly measures the output voltage of the series connection body of the first and second capacitors, and sets the voltage of the series connection body to the withstand voltage of the semiconductor switch element or less. By limiting the voltage to the specified value, the overvoltage application tendency of the semiconductor switching element that occurs when the voltage of the commercial power supply becomes lower than the rated voltage is suppressed, the breakdown voltage of the semiconductor switching element is prevented, and at the same time the magnetron drive Since it works to suppress the converted power of the power source, it is possible to prevent an increase in thermal stress of the magnetron driving power source due to the reduction of the cooling capacity of the cooling fan due to the voltage drop of the commercial power source.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) A first embodiment of the present invention will be described with reference to FIGS. 1 to 5. FIG. 1 shows a first magnetron driving power source of the present invention.
3 is a circuit diagram showing an embodiment of FIG. A series connection body of the first and second semiconductor switching elements 20 and 21 and a series connection body of the first and second diodes 22 and 23 are connected in parallel, and the first and second
The first and second capacitors 24 and 25 are connected in parallel to the diodes 22 and 23, respectively, and the commercial power source 1 and the high voltage transformer 26 are connected between the connection points of the semiconductor switch elements 20 and 21 and the diodes 22 and 23. It is configured to connect a series circuit. The secondary winding output of the high voltage transformer 26 is connected to the high voltage rectifier circuit 7 and applies a high DC voltage to the magnetron 8. The magnetron 8 is energized by this high DC voltage and generates a radio wave of 2.45 GHz. In this embodiment, the first and second semiconductor switching devices are IGBTs (insulated gate bipolar transistors) that conduct in the forward direction.
However, it is needless to say that the present invention is also applicable to the case where an element such as a MOSFET having a diode inside is used. The drive circuit 27 gives a drive signal to the respective semiconductor switching elements so as to complementarily drive the first semiconductor switching element 20 and the second semiconductor switching element 21 with a predetermined dead time. The input current feedback control unit 28 is configured to detect the voltage of the current transformer 29 for detecting the input current of the magnetron driving power source and the voltages of the first and second capacitors, and the input current feedback control unit 28 detects these detection signals. Based on this, the ON signal width of the first and second semiconductor switching elements output from the drive circuit 27 is determined.

FIG. 2 is a diagram showing a path through which a current flows in each period of the inverter circuit, and FIG. 3 is an operation waveform diagram corresponding thereto. The description starts from the state in which the semiconductor switch element 21 is turned on with the polarity of the commercial power supply 1 being shown. In this state, as shown in FIG.
Primary winding of high-voltage transformer 26-> semiconductor switch element 21
→ A current flows through the path of the diode 23, and the current indicated by I21 in the period of FIG. 3A flows through the semiconductor switch element 21 and the primary winding of the high voltage transformer 26, so that the primary winding of the high voltage transformer 26. Store energy in. When the semiconductor switch element 21 is turned off for a predetermined time, the primary winding current of the high voltage transformer 26 tries to continue flowing in the same direction, and this time, as shown in FIG. 2B, the commercial power source 1 → the primary of the high voltage transformer 26. The energy stored in the primary winding of the high-voltage transformer 26 is charged in the capacitor 24 along the path of winding → parallel diode of the semiconductor switching element 20 → capacitor 24. By this operation, the voltage obtained by boosting the voltage of the commercial power supply 1 is stored in the capacitor 24. When all the energy stored in the primary winding of the high-voltage transformer 26 is released, the path shown in FIG.
The energy charged in No. 4 is taken out through the path of capacitor 24 → semiconductor switch element 20 → primary winding of high-voltage transformer 26 → commercial power supply 1. Then, when the semiconductor switching device 20 is turned off for a predetermined time, the primary winding of the high voltage transformer 26 tries to keep the current flowing in the same direction. Therefore, as shown in FIG. A current flows through the parallel diode path of the power supply 1 → capacitor 25 → semiconductor switch element 21. When the voltage polarity of the commercial power supply 1 is opposite to that shown in the figure, the semiconductor switch elements 20, 21, the diodes 22, 23, and the capacitors 24, 25 are replaced with each other to perform the same operation.

In the above operation, the capacitors 24 and 25
Can perform both an inverter operation for generating a high frequency current in the primary winding of the high voltage transformer 26 by turning on / off the semiconductor switching elements 20 and 21, and an operation for generating a voltage boosted with respect to the voltage of the commercial power source 1 in the capacitors 24 and 25. The capacitors 24 and 25 are designed to have the same capacitance, and the capacitors 24 and 25 have the same capacitance. As a result, when the voltage polarity of the commercial power supply 1 is shown, the voltage obtained by boosting the voltage of the commercial power supply 1 is stored in the capacitor 24. On the contrary, when the voltage polarity of the commercial power supply 1 is opposite to that shown in the figure, the commercial power supply is stored in the capacitor 25. It operates to store the voltage obtained by boosting the voltage of 1. Therefore, regardless of the voltage polarity of the commercial power source 1, the capacitors 24, 25
Since the voltages generated at 1 and 2 can be made equal, the current of the commercial power source 1 can have a positive and negative symmetrical waveform. Then, by continuing such an operation, the voltage waveforms of the capacitors 24 and 25 with respect to the cycle of the commercial power source 1 generate a boosted voltage according to the voltage polarity of the commercial power source 1 as shown in FIG. Therefore, the envelope waveform of the current flowing through the primary winding of the high voltage transformer 26 has a waveform as shown by V26 (Lp). Since this voltage is boosted by the high voltage transformer 26 and applied to the magnetron 8, the voltage applied to the magnetron 8 shows a waveform like V8, and the oscillation voltage VAK (TH) is always present.
It is possible to maintain the above voltage. As a result, the input current I1 can flow in any period of the commercial power supply 1, and the power factor can be improved and harmonics can be suppressed.

Further, in FIG. 3, periods (a) to (b)
The operation is such that the diode 23 is cut off at the time of shifting to, but since the semiconductor switching element 21 is connected in series as a current path, the current is cut off.
Therefore, the switching speed of the diode 23 is not required. Further, since the voltage applied to the diode 23 at the time of turning off is zero, no switching loss occurs at the time of turning off. Therefore, the diode 22,
As the design of 23, it is possible to design so as to focus on the loss during conduction by designing with emphasis on the forward ON voltage VF, and the diodes 22 and 23 are cooled at the same time as the diodes 22 and 23 are downsized. It is easy to simplify the configuration. In particular, a magnetron driving power source used in a microwave oven handles a high power of 1000 W or more, so the current of the inverter circuit becomes a very large current level of about 40 A to 50 A, and the forward ON voltage VF is important in designing the diodes 22 and 23. It is useful to improve the efficiency of the inverter circuit by reducing the conduction loss. Therefore, the total power loss of the inverter circuit can be suppressed to a very low level, and a highly efficient magnetron driving power source can be realized.

As described above, in the magnetron driving power supply of this embodiment, the diodes 22 and 23 can be designed with the emphasis on the forward ON voltage VF by the circuit operation which is completely different from the circuit shown in the conventional example. The loss of the diodes 22 and 23 is minimized to improve the power conversion efficiency of the magnetron driving power source as a whole. The effect is that the capacitors 24 and 25 are operated by the inverter and the capacitors 24 and 25.
5 is a unique effect in the present invention exhibited by also performing the operation of applying the voltage obtained by boosting the voltage of the commercial power supply 1 to 5, and is disclosed in the conventional example.
It is realized by a circuit function and a circuit operation of a capacitor different from the configuration of.

FIG. 5 shows the input power of the magnetron driving power source when the input current feedback control unit 28 makes the input current IIN of the magnetron driving power source detected by the current transformer 29 constant regardless of the voltage fluctuation of the commercial power source 1. It is a figure showing change of output voltage VC of a series connection body of VA and the 1st and 2nd capacitors 24 and 25. ● in the figure
Respective changes in □ indicate changes in VC and VA when the input current IIN is feedback controlled to different values. In this case, the input power VA of the magnetron driving power supply fluctuates as the voltage of the commercial power supply 1 fluctuates. Therefore, the electric power of the radio wave output by the magnetron 8 also fluctuates, and when the magnetron driving power source is mounted in a microwave oven, the finish of cooking greatly varies depending on the voltage of the commercial power source 1. Therefore, in the configuration of this embodiment, the converted power VA of the magnetron driving power supply is the commercial power supply 1
The ratio of the output voltage VC of the first and second capacitors 24 and 25 to the input current IIN detected by the current transformer 28 is feedback-controlled to be a constant value so as to have a constant value regardless of the voltage fluctuation. Therefore, the input currents IIN and VC change A to E and F to J in FIG. On the other hand, since the input power VA of the magnetron driving power source changes from K to O, it does not fluctuate with respect to the voltage fluctuation of the commercial power source 1 and the cooking finish is stable when used as a microwave oven. become.

FIG. 6 shows the voltage of the commercial power source and the first and second capacitors 2 before the power source for driving the magnetron is started.
It is the figure which showed the time change of the output voltage VC of 4 and 25.
In the state before the magnetron driving power source is started, the first and second capacitors 24 and 25 and the first and second capacitors are provided.
Since the semiconductor switching devices 20 and 21 are connected in antiparallel to each other to perform full-wave voltage doubler rectification, a voltage of 2VP that is exactly twice the maximum value VP of the input voltage is applied to the first and second capacitors 24, 24. 25 output voltage. As a matter of course, when the commercial power supply 1 changes in voltage, the VP changes in the same manner as the commercial power supply 1, and therefore exhibits a variation characteristic with respect to the voltage of the commercial power supply as shown in FIG.

Therefore, by setting the input current value IIN for feedback control by the input current feedback control unit 28 as shown in Equation 2, the converted power of the magnetron driving power supply is stabilized against the voltage fluctuation of the commercial power supply 1. You can Therefore, similarly to the above-mentioned method, the input power VA of the magnetron driving power source does not fluctuate with respect to the voltage fluctuation of the commercial power source 1, and the finished cooking becomes stable when used as a microwave oven.

IIN_REF = IIN_REF (Rating) × VC / α (Equation 2) IIN_REF; Input current value for feedback control IIN_REF (Rating); Input current value α for controlling period at rated voltage; First and first at rated voltage 2 output voltage VC of the series connection body of the capacitors 24 and 25; output voltage VC of the series connection body of the first and second capacitors 24 and 25 FIG. 8 shows the output voltage VC of the series connection body of the first and second capacitors 24 and 25. Series connection of input power VA of magnetron driving power supply, input current IIN and first and second capacitors 24, 25 with respect to voltage fluctuation of commercial power supply when maximum value of output voltage does not exceed a predetermined value 5 is a diagram showing a change in the output voltage VC of FIG. When the voltage of the commercial power source 1 becomes lower than the rated voltage, the first and second capacitors 24, 2
The output voltage of the serial connection body of 5 becomes high, and the first and second
Since the voltage applied to the semiconductor switching elements 20 and 21 has a tendency of overvoltage, when the voltage of the commercial power source 1 decreases to a certain degree with respect to the rating, the maximum value of VC is set to the maximum value of the semiconductor switching element 20 in order to mitigate the tendency of overvoltage. It is limited to a predetermined value equal to or lower than the withstand voltage of 21. As a result, the converted power VA of the magnetron driving power supply is kept constant until the voltage of the commercial power supply 1 reaches a certain level, but when the voltage of the commercial power supply drops further, the input of the magnetron driving power supply is limited in order to limit VC. Power VA and input current IIN
Will fall. Microwave oven guaranteed operating range is ± 10%
Therefore, in this range, the voltage to start limiting the maximum value of VC is set so that the input power of the magnetron driving power supply does not change. On the other hand, a fan motor of a cooling fan used for cooling a microwave oven is generally a shading motor. Since the rotation speed of this fan motor changes according to the applied voltage, the rotation speed decreases with a decrease in the voltage, and as a result, the cooling capacity decreases.

Therefore, by limiting the output voltage of the series connection of the first and second capacitors 24 and 25 when the voltage of the commercial power source 1 drops below a predetermined value as in the configuration of this embodiment. Input power VA of magnetron drive power supply
The input power VA can be reduced in accordance with the decrease in the cooling capacity due to the decrease in the voltage of the commercial power source 1 by reducing the voltage of the commercial power source 1. Therefore, the thermal power of the magnetron driving power source when the voltage of the commercial power source 1 decreases It is possible to relieve stress and realize a more reliable microwave oven.

(Second Embodiment) FIG. 9 is a circuit diagram showing a magnetron driving power source according to a second embodiment of the present invention. The components designated by the same reference numerals as those in the above-mentioned embodiment operate in the same manner. In this embodiment, an opening / closing device 30 is installed between the commercial power source 1 and the magnetron driving power source. The opening / closing device 30 forms a closed state before the magnetron driving power source is started, and supplies a voltage to the magnetron driving power source to bring it into an operable state. Further, when the operation of the magnetron driving power source is completed, the magnetron driving power source is opened, and the commercial power source 1 is disconnected from the magnetron driving power source.

FIG. 10 is a diagram showing a change with time of the output voltage VC of the series connection body of the first and second capacitors 24 and 25 depending on the on / off state of the switchgear 30. The switchgear 30 is operated during the period when the voltage of the commercial power source 1 is positive or negative.
When is closed, the voltage changes as shown in FIG. On the other hand, when the voltage of the commercial power source 1 is close to zero, the voltage changes as shown in FIG. This is due to the transient response of the LC smoothing filter circuit 31 provided in the magnetron driving power supply. Therefore, when the input current feedback control unit 28 determines the feedback amount of the input current with reference to the voltage in this transient state, it is determined that the input voltage is high even when the voltage is low, and the input power V of the magnetron driving power supply is determined.
There is a possibility that A is not stable. However, in the configuration of this embodiment, a delay time is provided until the output voltage of the series connection body of the first and second capacitors 24 and 25 stabilizes, and the series connection body of the first and second capacitors 24 and 25 is provided. Since the output voltage is measured, the voltage of the commercial power supply 1 is not erroneously determined, and the input power VA of the magnetron driving power supply is
Is stable.

As a result, the input power VA of the magnetron driving power source does not fluctuate with respect to the voltage fluctuation of the commercial power source 1, and the cooking finish becomes stable when used as a microwave oven.

(Embodiment 3) FIG. 11 is a circuit diagram showing a magnetron driving power source according to a third embodiment of the present invention. The constituent elements denoted by the same reference numerals as those in the above-described first and second embodiments are the same. In this embodiment, the input current feedback controller 28 uses the current transformer 29 to input the input current II of the magnetron driving power source.
In addition to detecting N, the voltage of the second capacitor 25, the voltage at the connection point between the commercial power supply 1 and the step-up transformer 26, and the output voltage of the series connection body of the first and second capacitors 24 and 25 are measured. There is.

Next, the operation of the inverter circuit will be described with reference to FIGS. FIG. 12 is a diagram showing a path through which a current flows in each period of the inverter circuit, and FIG. 13 is an operation waveform diagram corresponding thereto. The description starts from the state in which the semiconductor switch element 21 is turned on with the polarity of the commercial power supply 1 being shown. In this state, as shown in FIG. 12A, a current flows through the path of the commercial power source 1 → the primary winding of the high-voltage transformer 26 → the semiconductor switch element 21 → the diode 23, which is indicated by I21 in the period of FIG. 13A. Energy flows in the primary winding of the high-voltage transformer 26 as the current flows through the semiconductor switching device 21 and the primary winding of the high-voltage transformer 26. When the semiconductor switch element 21 is turned off for a predetermined time, the primary winding current of the high voltage transformer 26 tries to continue flowing in the same direction, so that FIG.
As shown in (b), commercial power source 1 → high voltage transformer 1
The energy stored in the primary winding of the high voltage transformer 26 is charged in the capacitor 24 along the path of the secondary winding → parallel diode of the semiconductor switching element 20 → capacitor 24. By this operation, the voltage obtained by boosting the voltage of the commercial power supply 1 is stored in the capacitor 24. When all the energy stored in the primary winding of the high-voltage transformer 26 is released, the path of FIG. 12C is formed, and this time, the energy charged in the capacitor 24 is transferred to the capacitor 24 → semiconductor switch element 20 → the primary winding of the high-voltage transformer 26. Take the line → commercial power supply 1 route. When the semiconductor switch element 20 is turned off for a predetermined time, the primary winding of the high voltage transformer 26 tries to keep the current flowing in the same direction, so that the high voltage transformer 2 as shown in FIG.
A current flows in the path of the parallel winding of the primary winding of 6, the commercial power source 1, the capacitor 25, and the semiconductor switching element 21. When the voltage polarity of the commercial power supply 1 is opposite to that shown in the figure, the semiconductor switch elements 20, 21, the diodes 22, 23, and the capacitors 24, 25 are replaced with each other to perform the same operation.

Next, a method for the input current feedback control unit to read the voltage fluctuation of the commercial power source will be described with reference to FIG.
FIG. 14A shows the voltage of the commercial power supply, FIG. 14B shows the voltage of the second capacitor, and FIG. 14C shows the voltage of the connection point of the commercial power supply and the step-up transformer, with their time axes being common. Regarding the voltage polarity of the commercial power source, the voltage polarity shown in FIG. 11 is taken in the positive direction. Here, the voltage waveform of the second capacitor produces a voltage when the voltage of the commercial power source has a negative polarity due to the above-described operation. Further, when the voltage polarity of the commercial power source is in the positive direction, the operation is such that almost no voltage is generated.

As a result, the commercial power source 1 and the step-up transformer 26
As shown in FIG. 14C, when the voltage polarity of the commercial power source 1 is positive, the voltage measured from the connection point is almost equal to the voltage of the commercial power source 1. On the other hand, the voltage polarity of the commercial power source 1 is In the case of negative polarity, a voltage waveform corresponding to the operation of the inverter circuit is measured. Therefore, in the present embodiment, the voltage of the commercial power supply 1 is measured by measuring the voltage during the period when the voltage of the second capacitor 25 is not generated, and the input power VA of the magnetron driving power supply is constant using this measured voltage. The feedback control amount of the input current IIN detected by the current transformer 29 is changed so that Further, the input current feedback control unit 28 measures the output voltage of the series connection body of the first and second capacitors 24 and 25, and acts so as to limit the maximum value so that this voltage does not exceed a predetermined voltage. Therefore, the input current IIN and the input power VA of the magnetron driving power supply change with respect to the voltage fluctuation of the commercial power supply 1 as shown in FIG.

As a result, the input power of the magnetron driving power supply does not fluctuate with respect to the voltage fluctuation of the commercial power supply 1, and the cooking finish becomes stable when used as a microwave oven. Further, when the commercial power supply 1 drops below a predetermined value, the first and second capacitors 2
The input power VA of the magnetron driving power source is reduced by limiting the output voltage of the series connection body of Nos. 4 and 25, so that the input power is reduced in accordance with the reduction of the cooling capacity accompanying the voltage reduction of the commercial power source 1. Therefore, the thermal stress of the magnetron driving power source when the voltage of the commercial power source 1 drops can be relieved, and a more reliable microwave oven can be realized.

FIG. 16 shows an example of a circuit configuration in which the commercial power source 1 is provided with a power polarity determining means 32 for determining the voltage polarity of the commercial power source 1 and the measurement of the voltage of the second capacitor 25 is abolished. . It goes without saying that this configuration can also exhibit the same effects as the above.

(Fourth Embodiment) FIG. 17 is a circuit diagram showing a fourth embodiment of the magnetron driving power source of the present invention. The components designated by the same reference numerals as those in the above-described first, second and third embodiments are the same, and detailed description thereof will be omitted here.

A low-pass filter 33 (hereinafter abbreviated as LPF) is inserted in the path for measuring the voltage at the connection point between the commercial power supply 1 and the step-up transformer 26 input to the input current feedback control unit 28. The frequency characteristic of the LPF 33 is as shown in FIG. 18, which is the frequency of the commercial power source 1 of 50.
The characteristics are such that the signal component is not attenuated for Hz and 60 Hz, and the signal component can be sufficiently attenuated for the operating frequency of the inverter of 20 kHz to 50 kHz. Therefore, even if this voltage is detected during the operation of the inverter circuit, the fluctuation of the signal caused by the operation of the inverter can be sufficiently attenuated and the voltage of the commercial power supply 1 can be accurately measured. Then, based on this detection signal, the input current feedback control unit 28 corrects the input power VA of the magnetron driving power supply so as not to fluctuate with respect to the voltage fluctuation of the commercial power supply 1. Further, the input current feedback control unit 28 measures the output voltage of the series connection body of the first and second capacitors 24 and 25, and the measured voltage is the voltage of the commercial power source 1 and the input current I at that time.
When it falls below a predetermined value determined by IN, it acts to reduce the input current IIN for feedback control. This function is added to prevent destruction of the magnetron 8 due to thermal runaway. The operating characteristics of the magnetron 8 exhibit the nonlinear characteristics as described in the conventional example, and the voltage applied between the anode and the cathode of the magnetron 8 is VAK (T
When H) is exceeded, the impedance sharply decreases and the anode current flows. This threshold voltage VAK (TH)
Causes the magnetic force of the permanent magnets forming the magnetron 8 to decrease with increasing temperature. Therefore, the temperature characteristic of VAK (TH) becomes a characteristic as shown in FIG. 19, and when the temperature further rises and rises to a temperature exceeding the Curie point of the permanent magnet, the magnetic force is rapidly lost and the magnetron 8 runs thermal runaway. On the other hand, the influence of this change in VAK (TH) on the operation of the inverter circuit is that when the input current IIN of the circuit is controlled to a certain constant value, the series connection of the first and second capacitors 24 and 25 The output voltage has a characteristic of decreasing with the decrease of VAK (TH). Therefore, in this embodiment, when this voltage drops to a predetermined value, the input current IIN of the power source for driving the magnetron is reduced at a predetermined rate to reduce the thermal stress of the magnetron 8 and prevent the magnetron 8 from being destroyed.

As a result, in the magnetron driving power source of this embodiment, the input power V of the magnetron driving power source is
A does not fluctuate with respect to the voltage fluctuation of the commercial power supply 1, and the cooking finish becomes stable when used as a microwave oven. Further, when the commercial power supply 1 drops below a predetermined value, the first and second capacitors 2
By limiting the output voltage of the series connection body of 4 and 25 to reduce the input power VA of the magnetron driving power supply, the input power VA is adjusted in accordance with the decrease of the cooling capacity accompanying the voltage decrease of the commercial power supply 1. Since it can be reduced, it becomes possible to reduce the thermal stress of the magnetron driving power source when the voltage of the commercial power source 1 drops,
A more reliable microwave oven can be realized.
Further, since it is determined that the magnetron 8 is in the overheated state and the input power VA of the power source for driving the magnetron is reduced, the thermal stress of the magnetron can be reduced and the destruction of the magnetron 8 can be prevented.

[0043]

As described above, according to the first to fifth aspects of the present invention, the input current can flow through almost the entire area of the commercial power source even if the load has a nonlinear characteristic such as a magnetron. In addition, it is possible to suppress the loss generated in the inverter circuit even in a device such as a microwave oven that handles high conversion power, and realize a highly efficient power supply for driving the magnetron, and even if the voltage of the commercial power supply fluctuates. Since the input power of the driving power source can be stabilized, the cooking finish can be made stable regardless of the voltage of the commercial power source when used in a microwave oven.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a magnetron driving power source according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a path through which a current flows in each period of the inverter circuit of the magnetron driving power supply.

FIG. 3 is an operation waveform diagram of an inverter circuit of the power supply for driving the magnetron.

FIG. 4 is a diagram showing an envelope waveform of the power supply for driving the magnetron.

FIG. 5: Input power V of the magnetron drive power supply when the input current is constant in the magnetron drive power supply
The figure which showed the change of the output voltage VC of the serial connection body of A and the 1st, 2nd capacitors 24 and 25.

FIG. 6 is a diagram showing the voltage of the commercial power source and the first and second capacitors 24 and 25 before the power source for driving the magnetron is started.
Diagram showing the time variation of the output voltage VC of the

FIG. 7 is a first and second power supply for driving the magnetron.
Of fluctuation characteristics of output voltage of the capacitors 24 and 25 of FIG.

FIG. 8 shows first and second power supplies for driving the magnetron.
The input power VA, the input current IIN of the power supply for driving the magnetron with respect to the voltage fluctuation of the commercial power supply when the maximum value of the output voltage of the series connection body of the capacitors 24 and 25 is set not to exceed the predetermined value, and the first and the first 2 capacitors 24,
Showing changes in output voltage VC of 25 serially connected bodies

FIG. 9 is a circuit diagram showing a magnetron driving power source according to a second embodiment of the present invention.

FIG. 10 is a diagram showing a power supply for driving the magnetron, wherein first and second capacitors 24 are turned on / off by opening / closing a switchgear 30;
Of the time series change of the output voltage VC of 25 series-connected bodies

FIG. 11 is a circuit diagram showing a magnetron driving power source according to a third embodiment of the present invention.

FIG. 12 is a diagram showing a path through which a current flows in each period of the inverter circuit of the magnetron driving power supply.

FIG. 13 is an operation waveform diagram of an inverter circuit of the power supply for driving the magnetron.

FIG. 14 is a diagram showing a voltage waveform of a commercial power source 1 of the magnetron driving power source, a voltage of a second capacitor, and a voltage waveform of a connection point between the commercial power source and a step-up transformer.

FIG. 15 is an input current IIN of the power supply for driving the magnetron.
And a diagram showing the relationship between the input power VA

FIG. 16 is a diagram showing another circuit configuration example of the magnetron driving power supply.

FIG. 17 is a circuit diagram showing a magnetron driving power source according to a fourth embodiment of the present invention.

FIG. 18 is a diagram showing frequency characteristics of a low-pass filter 33 of the magnetron driving power supply.

FIG. 19 is an oscillation threshold voltage VAK (T
Diagram showing temperature dependence of H)

FIG. 20 is a circuit diagram showing a conventional magnetron driving power supply.

FIG. 21 is an operation waveform diagram of the power supply for driving the magnetron.

FIG. 22: Operating characteristic diagram of conventional magnetron

FIG. 23 is a circuit diagram of a conventional magnetron driving power supply to which an active filter circuit is added.

FIG. 24 is an operation waveform diagram of the power supply for driving the magnetron.

FIG. 25 is a circuit diagram of a power supply device disclosed in Japanese Unexamined Patent Publication No. 10-271846.

FIG. 26 is a circuit diagram showing a current path in each operation mode of the power supply device.

FIG. 27 is an operation waveform diagram of the power supply device.

[Explanation of symbols]

1 Commercial power supply 7 High voltage rectifier circuit 8 magnetron 20 First semiconductor switch element 21 Second semiconductor switch element 22 First diode 23 Second diode 24 First capacitor 25 Second capacitor 26 high voltage transformer 27 Drive circuit 28 Input current feedback controller 30 switchgear 32 Power supply polarity determination means

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Haruo Suenaga 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Emiko Ishizaki 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. (72) Inventor Hideaki Moriya 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference JP-A-8-280173 (JP, A) JP-A-55-130093 (JP, A) JP-A-3-257789 (JP, A) JP-A-2002-110337 (JP, A) JP-A-2002-110338 (JP, A) JP-A-2002-270361 (JP, A) JP-A-2002-272100 (JP, A) ) JP 2002-272118 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H05B 6/68 H02M 3/28 H02M 7/12 H05B 6/12

Claims (5)

(57) [Claims] 1. A series connection body of first and second semiconductor switch elements capable of reverse conduction and a series connection body of first and second diodes are connected in parallel, and are respectively connected to the first and second diodes. A first and a second capacitors are connected in parallel, and a commercial power source and a high voltage transformer are connected between a connection point of the first and second semiconductor switch elements capable of reverse conduction and a connection point of the first and second diodes. Drive circuit for connecting the series circuit of the primary windings of the above, and the output of the secondary winding of the high-voltage transformer for energizing the magnetron through the high-voltage rectifying circuit to drive the first and second semiconductor switching elements. And an input current feedback control unit that detects an input current input from the commercial power supply and controls the input current to a predetermined value, and the drive circuit complementarily drives the first and second semiconductor switch elements. Do with before Note that the drive signals are switched depending on whether the commercial power source is a positive electrode or a negative electrode, and the input current feedback control unit responds to the output voltage of the series connection body of the first and second capacitors regardless of the voltage of the commercial power source. 1st and 2nd conden
A power supply for driving a magnetron configured to increase / decrease the value of the input current for feedback control so that the voltage generated in the antenna is equalized . 2. A first and a second reverse conducting semiconductor strip.
A series connection of switch elements and first and second diodes
Connected in parallel, and connecting the first and second
Connect the first and second capacitors in parallel to the ion
And the first and second semiconductor switches capable of reverse conduction
The connection point of the element and the connection of the first and second diodes
Series circuit of commercial power supply and primary winding of high-voltage transformer between connection points
The output of the secondary winding of the high-voltage transformer.
Energizing the magnetron via a flow circuit, said first and
A drive circuit for driving a second semiconductor switch element and the quotient
Detects the input current input from the power supply for power supply and determines the input current
The input current feedback control unit for controlling the value of
A path complements the first and second semiconductor switching elements.
When the commercial power source is positive and negative
In some cases, the drive signals are replaced, and the input current feedback control unit
The output voltage of the series connection body of the first and second capacitors
According to the configuration, the value of the input current for feedback control is increased or decreased,
The input current feedback control unit input current the detecting means first
And the second of said input current detecting means and said voltage configuration and the Ma Gunetoron driving power source for constant feedback controlling the ratio of the detection signal of the detection means which has a voltage detecting means for detecting an output voltage of the series connection of a capacitor . 3. A series connection body of first and second semiconductor switch elements capable of reverse conduction and a series connection body of first and second diodes are connected in parallel, and each is connected to the first and second diodes. A first and a second capacitors are connected in parallel, and a commercial power source and a high voltage transformer are connected between a connection point of the first and second semiconductor switch elements capable of reverse conduction and a connection point of the first and second diodes. Drive circuit for connecting the series circuit of the primary windings of the above, and the output of the secondary winding of the high-voltage transformer for energizing the magnetron through the high-voltage rectifying circuit to drive the first and second semiconductor switching elements. And an input current feedback control unit that detects an input current input from the commercial power supply and controls the input current to a predetermined value, and the drive circuit complementarily connects the first and second semiconductor switch elements. Drive The drive signals are switched depending on whether the commercial power source is a positive electrode or a negative electrode, and the input current feedback control unit measures the output voltage of the series connection body of the first and second capacitors immediately before the magnetron driving power source is started. However, depending on the measured voltage, the first,
A power supply for driving a magnetron configured to determine the value of an input current for feedback control so that the voltage generated in the second capacitor becomes equal . 4. A switchgear is provided between a commercial power supply and a magnetron drive power supply, and the input current feedback control unit is the switchgear until the output voltage of the series connection body of the first and second capacitors reaches a stable voltage. 4. The magnetron drive power supply according to claim 3, wherein the magnetron drive power supply is started by measuring the voltage of the first and second capacitors with a delay time after the switch is closed. 5. The input current feedback controller constantly measures the output voltage of the series connection body of the first and second capacitors, and sets the voltage of the series connection body to a predetermined value equal to or lower than the withstand voltage of the semiconductor switch element. Claim 1 or the structure which is restricted
The power supply for driving the magnetron according to 2 .