JP2003115370A - High frequency heating equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress fall of the power factor of an inverter circuit power supply by lessening distortion of the input current waveform, which originates at the time of change of the power supply voltage, in the high frequency heating equipment. SOLUTION: It has a booster transformer 30, which supplies high-voltage electric power to a magnetron 24, an inverter circuit 22, which rectifies the commercial electric power supply 21, and changes it into alternate current of a predetermined frequency to supply it to the booster transformer 30, and an output setting means 23. The inverter circuit 22 has a modulation part 27, a driving part 28, and a semiconductor switching element 29, and the modulation part 27 generates a modulation signal from a power supply voltage waveform detection means 25, which detects the voltage waveform of the commercial power supply 21, from which the inverter circuit 22 obtains electric power, a power supply voltage level detection means 26 to detect the voltage value of the commercial power supply 21, and the output setting means 23. The driving part 28 is made to have a composition, which determines a pulse signal for driving the semiconductor switching element 29 based on the modulation signal of the modulation part 27.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter power supply for driving a magnetron used in a microwave oven.

[0002]

2. Description of the Related Art FIG. 6 is a block diagram showing a circuit configuration for driving a magnetron. In the figure, 1 is a commercial power supply, 2 is an inverter circuit, and 3 is a magnetron. The inverter circuit 2 includes a full-wave rectification circuit 4 that full-wave rectifies the voltage of the commercial power supply 1, a filter circuit unit 5 that reduces noise, a semiconductor switching element 6, a step-up transformer 7,
A drive unit 8 for driving the semiconductor switching element 6, a power supply voltage detection means 9 for detecting the voltage of the commercial power supply 1,
It is composed of a modulator 10. The modulation section 10 produces a modulation signal to be sent to the drive section 8 based on the signal from the power supply voltage detection means 9 and the signal from the output setting means 11. The drive unit 8 determines the ON time of the pulse for driving the semiconductor switching element 6 based on the modulation signal. This is a circuit configuration in which a step-up transformer 7 steps up a high-frequency voltage obtained by the operation of the semiconductor switching element 6 to generate a high voltage for driving the magnetron 3.

FIG. 7 shows a voltage or current waveform of each part of the inverter circuit 2, and FIGS. 7 (a) to 7 (c) show the time axis together. FIG. 5A shows a voltage waveform of a portion output through the filter circuit unit 5 after full-wave rectification of the commercial power source, and a case where the commercial power source of 60 Hz is used. The solid line in FIG. 7B shows the input current waveform of the inverter circuit 2 at the rated voltage. The control of the inverter circuit 2 is as shown in the circuit block diagram of FIG.
It is instructed by a modulation signal provided to a driving unit 8 which produces a pulse for driving the semiconductor switching element 6. The modulation unit 10 includes a signal from the power supply voltage detection unit 9 and an output setting unit 11
The modulated signal is generated based on the signal of (1) and the modulated signal shown in (c) of FIG. The output voltage waveform of the modulator 10 in FIG. 7C acts so that the ON time of the pulse for driving the semiconductor switching element 6 becomes longer as the voltage becomes higher. As shown in FIG. 6, the drive unit 8 determines the drive pulse by the modulation signal from the modulation unit 10. Since the modulation signal is determined based on the signals of the power supply voltage detection means 9 and the output command means 11, when increasing the output of the magnetron 3, the DC voltage value of the output setting means 11 given by the DC voltage is set. Make it higher By doing so, the voltage value of the output voltage waveform (modulation signal) of the above-described modulator 10 becomes high, the ON time of the pulse signal for driving the semiconductor switching element 6 becomes long, and the output of the magnetron 3 becomes high.

[0004]

However, the conventional method has the following problems.

When the voltage of the commercial power source fluctuates (is low),
Since the output voltage waveform of the modulator is created based on the signal of the power supply voltage detection means and the signal of the output setting means, FIG.
As indicated by the broken line. When the inverter circuit is driven with such a modulation waveform, the input current is changed to that shown in FIG.
There is a problem in that the distortion occurs as indicated by the broken line in FIG. 1 and causes a reduction in the power factor of the inverter circuit.

[0006]

The high frequency heating apparatus of the present invention has been made in order to solve the above-mentioned problems. Regarding the reduction of the power factor due to the distortion of the input current caused by the fluctuation of the power supply voltage, the power supply is The voltage level information is reflected in the modulation signal so that an appropriate modulation signal can be obtained even when the power supply voltage changes.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 is a magnetron for micro-heating an object to be heated such as food, a step-up transformer for supplying high voltage electric power to the magnetron, and a commercial power source for rectifying a predetermined frequency. An inverter circuit for converting into an alternating current and supplying it to the step-up transformer is provided, and an output setting means, the inverter circuit has a modulation section, a drive section, and a semiconductor switching element, and the modulation section has the inverter circuit obtain electric power. A power supply voltage waveform detection means for detecting the voltage waveform of the commercial power supply, a power supply voltage level detection means for detecting the voltage value of the commercial power supply, and a modulation signal are generated from the output setting means, and the drive section drives the semiconductor switching element. With the configuration in which the pulse signal for driving is determined based on the modulation signal of the modulation section, information at the time of fluctuation of the power supply voltage is obtained. By reflecting the obtained modulated signal by Le detecting means, when the variation of the supply voltage, more so proper modulation signal even when the output variable of the magnetron is obtained.

The invention according to claim 2 further comprises a power supply current detecting means for detecting the current of the commercial power supply, an output setting means, and a comparing means for comparing the power supply current detecting means with the output setting means. The comparison unit controls the modulation unit so that the signal from the output setting unit and the signal from the power supply current detection unit are the same, and transmits the modulation signal to the drive unit. The electric power is kept constant, and a proper modulation signal can be obtained when the power supply voltage changes and when the output of the magnetron is changed.

According to a third aspect of the invention, the modulator forms a waveform with signals from a power source voltage waveform detecting means for detecting a voltage waveform of the commercial power source and a power source voltage level detecting means for detecting a voltage value of the commercial power source. And an upper limit setting unit for setting an upper limit of the basic waveform generated by the fundamental wave forming unit, and the upper limit setting unit sets the upper limit value by a signal from the output setting unit. As a result, an appropriate modulation signal can be obtained even when the power supply voltage fluctuates and when the output of the magnetron varies.

According to a fourth aspect of the invention, the modulator forms a waveform with signals from a power source voltage waveform detecting means for detecting a voltage waveform of the commercial power source and a power source voltage level detecting means for detecting a voltage value of the commercial power source. And an upper limit setting unit for setting an upper limit of the basic waveform generated by the fundamental wave forming unit, and the upper limit setting unit compares the signals of the power supply voltage detection unit and the output setting unit. By setting the upper limit value with the signal from, the input power of the inverter circuit can be kept constant, and a proper modulation signal can be obtained when the power supply voltage changes and even when the magnetron output is changed. Become.

[0011]

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

FIG. 1 is a block diagram of a magnetron drive circuit used in a high frequency heating apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 21 is a power source, and a commercial power source is used.
Power is supplied to the second inverter circuit. An output command unit 23 commands the magnitude of the output of the magnetron 24. Two
A magnetron 4 is driven by the inverter circuit 22. The inverter circuit 22 includes signals from the power supply voltage waveform detecting means 25 for detecting the voltage waveform of the power supply 21, the power supply voltage level detecting means 26 for detecting the voltage level of the power supply 21, the signals from the power supply voltage waveform detecting means 25 and the power supply voltage level detecting means 26. A modulator 27 for generating a modulation signal by a modulator, a driver 28 for generating a drive pulse from the signals of the modulator 27 and the output setting means 23, and a semiconductor switching element 2 driven by the pulse of the driver 28.
9. The booster transformer 30 boosts the high frequency voltage obtained by the operation of the semiconductor switching element 29. The power of the power supply is supplied to the semiconductor switching device and the step-up transformer via the full-wave rectifier circuit and the filter circuit, but they are omitted in the figure.

By detecting the level (value) of the power supply voltage by the power supply voltage level detection means 26, level information when the power supply voltage changes can be obtained, and this signal is transmitted to the power supply voltage waveform detection means 25. After being corrected by fluctuations in the power supply voltage, this signal is transmitted to the modulator 27. The modulator 27 performs processing on the basis of this signal and the signal from the output setting means 23, so that an appropriate modulated signal can be obtained even when the power supply voltage changes and when the output of the magnetron 24 changes.

FIG. 2 is a block diagram of a magnetron drive circuit used in a high frequency heating apparatus according to another embodiment of the present invention, in which constituent elements equivalent to those in FIG.
The description of the function is omitted.

The comparison means 31 compares the signals of the power supply current detection means 32 for detecting the current of the power supply 21 and the output setting means 23 and outputs a signal corresponding to the difference between the two. Comparison means 3
The signal of No. 1 is transmitted to the modulator 27, outputs the modulated signal, and the driver 28 responds to this signal by the semiconductor switching element 2
Determine the pulse that drives 9. As a result, the power source 21
The input current of is controlled to have a constant magnitude set by the output setting means 23. That is, the input power to the inverter circuit 22 can be determined by the output setting means 23. Further, since the signal of the comparison means 31 is transmitted to the modulation section 27, the modulation section 27 produces a modulation signal from this signal, the signal of the power supply voltage waveform detection means 25, and the signal of the power supply voltage level detection means 26. As a result, the modulator 27 can keep the input power of the inverter circuit 22 constant, and can obtain an appropriate modulation signal when the power supply voltage changes and when the output of the magnetron 24 changes.

FIG. 3 is a block diagram of a magnetron drive circuit used in a high frequency heating apparatus according to another embodiment of the present invention. Components equivalent to those in FIGS. 1 and 2 are designated by the same reference numerals and their functions are described. The description is omitted.

The modulation section 27 is a fundamental wave forming means for forming a waveform by signals from a power supply voltage waveform detecting means 25 for detecting the voltage waveform of the commercial power supply 21 and a power supply voltage level detecting means 26 for detecting the voltage value of the commercial power supply. 33, and an upper limit setting means 34 for setting the upper limit of the basic waveform created therein. The upper limit setting means 34 sets the upper limit value by a signal from the output setting means 23. With such a configuration, an appropriate modulation signal can be obtained even when the power supply voltage changes and when the output of the magnetron 24 changes.

FIG. 4 is a block diagram of a magnetron drive circuit used in a high frequency heating apparatus according to another embodiment of the present invention, in which components equivalent to those in FIGS. 1, 2 and 3 are denoted by the same reference numerals. The description of the function is omitted.

The modulation section 27 is a fundamental wave forming means for forming a waveform with signals from a power supply voltage waveform detecting means 25 for detecting the voltage waveform of the commercial power supply 21 and a power supply voltage level detecting means 26 for detecting the voltage value of the commercial power supply. 33, and an upper limit setting means 34 for setting the upper limit of the basic waveform created therein. The upper limit setting means 34 sets the upper limit value by a signal from a comparing means for comparing the signals of the power supply voltage waveform detecting means 25 and the output setting means 23. With such a configuration, the input power of the inverter circuit 22 is kept constant, and an appropriate modulation signal can be obtained when the power supply voltage changes and when the output of the magnetron 24 changes.

Next, in order to clarify the operation of each component, description will be made with reference to the waveforms of the components in FIG. The waveforms of (a) to (h) in the figure are shown together with time. Further, the waveforms with the symbols of waveforms (1) to (7) shown in the same figure indicate the waveforms of the portions where the symbols of waveforms (1) to (7) shown in FIG. 3 are described. There is. That is, the waveform (1) is the output waveform of the power supply voltage waveform detecting means 25, the waveform (2) is the output waveform of the power supply voltage level detecting means 26, the waveform (3) is the input waveform of the fundamental wave forming means 33, and the waveform (4) is The output waveform of the fundamental wave forming means 33, the waveform (5) is the output waveform of the output setting means 23, the waveform (6) is the input waveform of the inverting means 35, and the waveform (7) is the output waveform of the inverting means 35.

The waveform (1) of FIG. 5 (a) is in the form of full-wave rectification of a sine wave because the voltage of the power source 21 using a commercial power source is detected. The waveform (2) in FIG.
The voltage is smoothed and divided, and has the opposite polarity to the fluctuation characteristics of the power supply voltage. That is, it has a characteristic that it decreases as the power supply voltage increases, and increases as the power supply voltage decreases. The waveform (3) in FIG. 7C is a combination of the waveforms (1) and (2), and even when the power supply voltage fluctuates, the same signal as the waveform (1) can be obtained. It is like this. The waveform (4) in FIG. 6D is the lower limit of the waveform (1) set, and this waveform becomes the fundamental wave of the modulation signal. The waveform (5) is the waveform of the output setting means 23.
The waveform (6) is the input waveform of the inverting means 35, and the upper limit of the waveform (4) is set by the value obtained in the waveform (5). The upper limit of the waveform (4) is set by the voltage value of the waveform (5). Although the value is set, since the waveform (4) and the waveform (5) are combined via the resistor, the waveform (4) is not cut by the voltage value of the waveform (5), but the waveform (5) is not cut. The upper limit is gently limited from the voltage value of), and it is configured to have a smooth waveform such as the waveform (6) indicated by the broken line. The waveform (7) in FIG. 7E is a waveform obtained by inverting the waveform (6) by the inverting means 35. The signal of waveform (7) is given to the drive unit 28, and the drive pulse of the semiconductor switching element 29 is determined. That is, as the voltage of the waveform of waveform (7) becomes higher, the semiconductor switching element 2
The ON time of the pulse for driving 9 is set to be long. The output of the inverter circuit increases as the ON time of the pulse increases.

Here, a case where the power supply voltage fluctuates will be described. It is assumed that the signal of the output setting means 23 is fixed when the power supply voltage decreases. In that case, FIG.
As shown in (f), the waveform of the power supply voltage waveform detecting means 25 changes from the waveform (1) to the waveform (8). The waveform of the power supply voltage level detecting means 26 shown in FIG.
Changes to a waveform (9). By adding this signal, the waveform (8) and the waveform (9), the waveform (h) and the waveform (10) in FIG.
This can be input to the fundamental wave forming means 33. On the contrary, even when the power supply voltage rises, the opposite phenomenon described above occurs, and a substantially constant waveform can be input to the fundamental wave forming means 33.

As described above, according to the present invention, even when the power supply voltage fluctuates, a substantially constant waveform can be output to the fundamental wave forming means 33, so that the inverter circuit 22 has a substantially constant modulation waveform. By being driven, distortion of the input current and further reduction of the power factor of the inverter circuit can be suppressed. Further, when the output of the magnetron 24 is variable, that is, in accordance with the signal of the output setting means 23, a proper modulation signal can be generated, and distortion of the input current and further reduction of the power factor of the inverter circuit can be suppressed.

[0024]

As described above, according to the present invention, it is possible to obtain a proper modulation signal even when the power supply voltage fluctuates, reduce the distortion of the input current, and reduce the power factor of the inverter circuit power supply. Can be suppressed. Further, when the output of the magnetron is variable, that is, in accordance with the signal of the output setting means, a proper modulation signal can be produced, distortion of the input current can be reduced, and a reduction in the power factor of the inverter circuit can be suppressed.

[Brief description of drawings]

FIG. 1 is a block diagram of a magnetron drive circuit of a high frequency heating apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a magnetron drive circuit of another high-frequency heating device according to the first embodiment of the present invention.

FIG. 3 is a block diagram of a magnetron drive circuit of another high-frequency heating device according to the first embodiment of the present invention.

FIG. 4 is a block diagram of a magnetron drive circuit of another high-frequency heating device according to the first embodiment of the present invention.

FIG. 5 (a) is an output voltage waveform diagram of the power supply voltage detecting means of the high-frequency heating apparatus, and (b) is an output voltage waveform diagram of the power supply voltage level detecting means of the high-frequency heating apparatus. Input voltage waveform diagram of the means (d) Basic wave forming means of the high frequency heating device, output voltage waveform diagram of the output setting means, input voltage waveform diagram of the inverting means (e) Output voltage waveform diagram of the inverting means of the high frequency heating device (F) Output voltage waveform diagram of the power supply voltage waveform detection means when the power supply voltage is reduced in the same high-frequency heating apparatus (g) Output voltage waveform chart of the power supply voltage level detection means when the power supply voltage is reduced in the same high-frequency heating apparatus (H) Input voltage waveform diagram of the fundamental wave forming means when the power supply voltage is reduced in the same high-frequency heating device

FIG. 6 is a block diagram of a magnetron drive circuit used in a conventional high-frequency heating device.

FIG. 7 (a) is an output voltage waveform diagram of a filter section of a conventional high-frequency heating apparatus. (B) is an input current waveform chart of a conventional high-frequency heating apparatus. (C) is an output voltage waveform chart of a modulation section of the conventional high-frequency heating apparatus.

[Explanation of symbols]

21 power supply 22 Inverter circuit 23 Output setting means 24 magnetron 25 Power supply voltage waveform detection means 26 Power supply voltage level detection means 27 Modulator 28 Drive 29 Semiconductor switching elements 30 step-up transformer 31 Comparison means 32 power supply current detection means 33 fundamental wave forming means 34 Upper limit setting means

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takeshi Kitazumi             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Haruo Suenaga             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F term (reference) 3K086 AA08 BA08 CA20 CD11 DB11                       DB15 DB16                 5H007 AA02 BB04 CB02 CC03 CC32                       DA04 DC02 DC04 DC05

Claims (4)

[Claims] 1. A magnetron, a step-up transformer that supplies high-voltage power to the magnetron, an inverter circuit that rectifies a commercial power source, converts the commercial power source into an alternating current of a predetermined frequency, and supplies the alternating current to the step-up transformer, and an output setting unit. The inverter circuit includes a modulator, a driver, and a semiconductor switching element, and the modulator includes a power supply voltage waveform detection unit that detects a voltage waveform of a commercial power supply from which the inverter circuit obtains power, and a voltage value of the commercial power supply. A power supply voltage level detection means for detecting the output voltage and a modulation signal from the output setting means, and the drive section determines a pulse signal for driving the semiconductor switching element based on the modulation signal of the modulation section. High frequency heating device. 2. A power source current detecting means for detecting a current of a commercial power source, an output setting means, and a comparing means for comparing the power source current detecting means with the output setting means, wherein the comparing means has the output setting. A high-frequency heating device configured to control the modulator so that the signal from the means and the signal from the power supply current detector are the same and transmit the modulated signal to the driver. 3. The modulating section includes a power supply voltage waveform detecting means for detecting a voltage waveform of a commercial power supply, and a fundamental wave forming means for forming a waveform by a signal from the power supply voltage level detecting means for detecting a voltage value of the commercial power supply. The high frequency wave according to claim 1, further comprising an upper limit setting unit that sets an upper limit of the basic waveform created by the fundamental wave forming unit, and the upper limit setting unit sets the upper limit value by a signal from the output setting unit. Heating device. 4. The power source voltage waveform detecting means for detecting the voltage waveform of the commercial power source, the modulating section, and the fundamental wave forming means for forming a waveform by the signal from the power source voltage level detecting means for detecting the voltage value of the commercial power source. It has an upper limit setting means for setting an upper limit of the basic waveform created by the fundamental wave forming means, and the upper limit setting means sets an upper limit value with a signal from a comparing means for comparing the signals of the power supply current detecting means and the output setting means. The high-frequency heating device according to claim 2, which is configured to be set.