JP5138164B2 - Power control apparatus for high frequency dielectric heating and control method thereof - Google Patents

Abstract

Provided is a power control device for high-frequency dielectric heating not affected by the magnetron type, characteristic irregularities, or power voltage fluctuation. The device includes input current detection units (71, 72) for detecting input current of an inverter circuit (10) for rectifying (31) AC source voltage (20), performing high-frequency switching, and converting it into a high-frequency power. A mixing circuit (81) mixes input current waveform information (90) on the input current detection units and power control information (91) for controlling the output of the input current detection units to be a predetermined value, thereby outputting ON voltage information (92). A PWM comparator (82) compares the ON voltage information to a saw-tooth wave from a saw-tooth wave generation circuit (83). Pulse width modulation is performed and a drive signal is outputted to perform ON/OFF control of a switching transistor (39) of the inverter circuit.

Description

  The present invention relates to high-frequency dielectric heating using a magnetron such as a microwave oven, and more particularly to high-frequency dielectric heating that is not affected by differences in the characteristics and types of magnetron characteristics and the temperature of the anode of the magnetron. .

  Conventional known high-frequency heating devices adjust the power supplied to the magnetron by the output pulse width of the inverter control circuit. When the output voltage of the signal superimposing means is increased, the output pulse width of the inverter control circuit is increased, and the power supplied to the magnetron is increased. With this configuration, it is possible to change the heating output of the magnetron continuously by changing the output voltage of the signal superimposing means.

  In addition, since the heater also served as the cathode of the magnetron, the transformer that supplies power to the magnetron also supplies power to the heater, so the power supplied to the heater also changes as the power supplied to the magnetron changes. Was. For this reason, if the heater temperature is set within an appropriate range, only a slight change in the heating output can be obtained, and the heating output cannot be changed continuously.

  As a high-frequency heating apparatus that solves this, there is a control method disclosed in Patent Document 1. FIG. 12 is a diagram for explaining a high-frequency heating apparatus that implements this control method. In FIG. 12, this heating control system includes a magnetron 701, a transformer 703 that supplies high-voltage power to a high-voltage rectifier circuit 702 that supplies secondary winding power to the magnetron 701, and simultaneously supplies power to the heater 715 of the magnetron 701. Inverter circuit 705 that rectifies AC power supply 704, converts it into alternating current of a predetermined frequency and supplies it to transformer 703, power detection means 706 that detects input power or output power of inverter circuit 705, and a desired heating output setting An output setting unit 707 for outputting the output setting signal, a power adjustment unit 708 for comparing the output of the power detection means 706 with the output setting signal and controlling the DC level of the power adjustment signal so as to obtain a desired heating output, The output of the detecting means 706 is higher than the output level 718 of the reference voltage generating means. Then, an oscillation detection means 719 in which the oscillation detection signal as an output changes from LO to HI, a comparison voltage generation circuit 716 that generates a voltage corresponding to the output setting signal, and a waveform shaping in which the output setting signal is compared by the level conversion circuit 720. A waveform shaping circuit 721 for shaping the signal and the output of the rectifier circuit 710 for rectifying the AC power supply voltage 704 based on the waveform shaping signal and the oscillation detection signal; and the output signal of the waveform shaping circuit 721 for the comparison voltage generation circuit. The comparison circuit 711 outputs a comparison reference voltage when it is smaller than the output, and inverts and amplifies it when larger, and a signal superposition that superimposes the fluctuation signal of the output of the comparison circuit 711 on the power adjustment signal and outputs a pulse width control signal The output of the means 712, the oscillation circuit 713, and the oscillation circuit 713 is subjected to pulse width modulation by the pulse width control signal, and the modulated output is obtained. Ri has a configuration including an inverter control circuit 714 for driving the inverter circuit 5.

The high-frequency heating device adjusts the power supplied to the magnetron 701 based on the output pulse width of the inverter control circuit 714. When the output voltage of the signal superimposing means 712 increases, the output pulse width of the inverter control circuit 714 increases, and the power supplied to the magnetron 701 increases. In this apparatus, it is possible to continuously change the heating output of the magnetron 701 by continuously changing the output voltage of the signal superimposing means 12. According to this configuration, the waveform of the rectified rectified voltage AC power 704 by the rectifier circuit 710 is shaped in accordance with the output setting by the waveform shaping circuit 721, Ru is output to the comparison circuit 711. The output of the waveform shaping circuit 721 is inverted and amplified by a comparison circuit 711 having, as a reference voltage, a comparison voltage generation circuit 716 that generates a reference signal of a level corresponding to the heating output setting signal, and the inverted amplification signal and the power adjustment unit 708. When the heating output setting is low, the level near the maximum amplitude of the AC power supply 704 is lower in the pulse width control signal, which is the output signal of the signal superimposing means 712. Thus, the level of the non-oscillating portion of the magnetron becomes higher, so that the oscillation period per one power supply cycle of the magnetron becomes longer. This increases the power supplied to the heater. Further, when the output is high, the input current waveform of the inverter is convex near the envelope peak and becomes a waveform close to a sine wave rectified waveform, thereby suppressing the harmonic current.

  In this way, the waveform shaping circuit 721 controls the power supply current harmonics to be low by controlling the power supply current harmonics to be small at high output so that the heater current is large at low output when the pulse width control signal is low output. In addition, the change in the heater current can be reduced, and a highly reliable high-frequency heating device can be realized.

  However, in this control, the ON / OFF drive pulse of the switching transistor is subjected to pulse width modulation using a modulation waveform obtained by processing and shaping the commercial power supply waveform, and the “expected control method” is used so that the input current waveform approaches a sine wave. Since waveform shaping is performed, the waveform is not affected by variations or types of magnetron characteristics, ebm (anode-cathode voltage) fluctuations due to magnetron anode temperature or load in the microwave oven, and even power supply voltage fluctuations. It turned out that shaping did not follow.

  Here, the variations and types of the characteristics of the magnetron that have motivated the present invention will be briefly described. Magnetron's VAK (anode-cathode voltage) -Ib characteristic is a non-linear load as shown in FIG. I was letting.

  The nonlinear characteristics of the magnetron vary depending on the type of magnetron, and also vary depending on the magnetron temperature and the object to be heated (load) in the microwave oven.

  FIG. 13 is a graph showing the anode-cathode applied voltage-anode current characteristics of the magnetron, where (a) shows the difference depending on the type of magnetron, (b) shows the difference due to the matching of the power supply of the magnetron, and (c) shows the magnetron temperature. The vertical axis represents the anode-cathode voltage and the horizontal axis represents the anode current in common with (a) to (c).

  Therefore, looking at (a), A, B, and C are characteristic diagrams of three types of magnetrons. In the case of magnetron A, the current flows only as little as IA1 until VAK becomes VAK1 (= ebm). . However, when VAK exceeds VAK1, the current IA starts to increase rapidly. In this region, IA changes greatly with a slight difference in VAK. Next, in the case of magnetron B, VAK2 (= ebm) is lower than VAK1, and in the case of magnetron C, VAK3 (= ebm) is lower than VAK2. As described above, the non-linear characteristics of the magnetron differ depending on the types A, B, and C of the magnetron. Therefore, in the case of a modulation waveform adapted to a magnetron having a low ebm, the input current waveform is distorted when a magnetron having a high ebm is used. . Conventional devices could not cope with these problems. Therefore, it has been a challenge to make a high-frequency dielectric heating circuit that is not affected by these types.

  Similarly, regarding (b), the characteristic diagrams of the three types of magnetrons show good and bad impedance matching of the heating chamber as seen from the magnetron. When the impedance matching is good, VAK1 (= ebm) is the maximum and becomes smaller as it gets worse. As described above, since the nonlinear characteristics of the magnetron greatly differ depending on whether the impedance matching is good or bad, it is a problem to produce a high-frequency dielectric heating circuit that is not affected by these types.

  Similarly, looking at (c), the characteristics of the three types of magnetrons show the temperature of the magnetron. When the temperature is low, VAK1 (= ebm) is maximum, and ebm gradually decreases as the temperature gradually increases. Therefore, when the temperature of the magnetron is adjusted to the lower side, the input voltage waveform may be distorted when the temperature of the magnetron is increased.

  As described above, the non-linear characteristics of the magnetron are greatly different depending on the temperature difference of the magnetron. Therefore, it is an object to produce a high-frequency dielectric heating circuit which is not affected by the kind of the magnetron. The conventional circuit and the above circuit have not compensated for these fluctuations.

  In response to the above-described problem, a control method disclosed in Patent Document 2 has been disclosed. FIG. 14 is a configuration diagram illustrating a high-frequency heating device that implements the control method.

  In FIG. 14, the AC voltage of the AC power supply 220 is rectified by a diode bridge type rectifier circuit 231 including four diodes 232, and converted to a DC voltage via a smoothing circuit 230 including an inductor 234 and a capacitor 235. After that, the resonance circuit 236 composed of the capacitor 237 and the primary winding 238 of the transformer 241 and the inverter circuit composed of the switching transistor 239 are converted into high frequency alternating current, and the high frequency high voltage is applied to the secondary winding 243 via the transformer 241. Induced.

  The high frequency and high voltage induced in the secondary winding 243 is applied between the anode 252 and the cathode 251 of the magnetron 250 through the voltage doubler rectifier circuit 244 including the capacitor 245, the diode 246, the capacitor 247, and the diode 248. The The transformer 241 has a tertiary winding 242, which heats the heater (cathode) 251 of the magnetron 250. The above is the inverter main circuit 210.

  Next, the control circuit 270 that controls the switching transistor 239 of the inverter will be described. First, the current detection means 271 such as CT detects the input current of the inverter circuit, the current signal from the current detection means 271 is rectified by the rectification circuit 272, smoothed by the smoothing circuit 273, and the other heating output. The comparison circuit 274 compares the signal from the output setting unit 275 that outputs the output setting signal corresponding to the setting. Since the comparison circuit 274 performs comparison for controlling the magnitude of power, the anode current signal of the magnetron 250 or the collector current signal of the switching transistor 239 or the like is an input signal instead of the input signal. Is also effective.

  On the other hand, the AC power source 220 is rectified by the diode 261 and the waveform is shaped by the shaping circuit 262. Thereafter, the signal from the shaping circuit 262 is inverted by the inversion / waveform processing circuit 263 to perform waveform processing. The output signal from the shaping circuit 262 is changed by a gain variable amplifier circuit 291 to be described later, and a reference waveform signal is output. The input current waveform signal from the rectifier circuit 272 and the reference waveform signal from the gain variable amplifier circuit 291 are output. The difference is output as a waveform error signal by the waveform error detection circuit 292. The waveform error signal from the waveform error detection circuit 292 and the current error signal from the comparison circuit 274 are mixed and filtered by a mix and filter circuit 281 (hereinafter referred to as “mix circuit”) to output an ON voltage signal, and a sawtooth wave The sawtooth wave from the generation circuit 283 is compared with the PWM comparator 282, and the pulse width modulation is performed to control the switching transistor 239 of the inverter circuit on / off.

  FIG. 15 shows an example of the mix circuit 281. The mix circuit 281 has three input terminals. An auxiliary modulation signal is added to the terminal 811, a waveform error signal is added to the terminal 812, and a current error signal is added to the terminal 813, and they are mixed by an internal circuit as shown in the figure. A high frequency cut filter 810 has a function of removing a high frequency component of a current error signal that does not require a high frequency component. This is because if there is a high-frequency component, fluctuations in the waveform error signal will not appear cleanly when mixed with the waveform error signal.

  As described above, the waveform reference following the magnitude of the input current is automatically created by the variable gain amplifier circuit 291, and the waveform reference and the input current waveform obtained from the current detection means 271 are used as the waveform error detection circuit. In 292, the waveform error information is obtained by comparison, and the obtained waveform error information is mixed with the output of the input current control and converted into an on / off drive signal for the switching transistor 239 of the inverter circuit. is there.

In this way, the control loop operates so that the input current waveform matches the waveform reference following the magnitude of the input current, so that even if there are variations in the type and characteristics of the magnetron, Even if there is ebm (anode-cathode voltage) fluctuation due to temperature or load in the microwave oven, and even power supply voltage fluctuation, the input current waveform can be shaped without being affected by them.
JP-A-7-176375 JP 2004-30981 A

  However, in the configuration described in Patent Document 2, as shown in FIG. 14, waveform shaping is performed using the auxiliary modulation signal 811 from the inversion / waveform processing circuit 263. This is based on the reason that the waveform shaping can be performed well by using the auxiliary modulation signal 811 in addition to the waveform error signal 812 reflecting the actually flowing current. However, since the inversion / waveform processing circuit 263 and the rectifier circuit 272 are required, there is a problem that the structure is complicated and large-scale.

  In addition, with the adoption of the auxiliary modulation signal 811, eventually the adjustment of the auxiliary modulation signal 811 is required according to the type and characteristics of the magnetron, and eventually individual design for each circuit corresponding to the target magnetron is required. There was a problem of becoming.

  As is well known, since a magnetron is a kind of vacuum tube, there is a delay time (hereinafter abbreviated as start-up time) from when an electric current is supplied to the heater until the electromagnetic wave is oscillated and output. Although the start-up time is shortened by increasing the heater current, since the impedance between the magnetron anode and cathode is infinite within the start-up time, the voltage applied to the both ends is increased, so it does not become excessive. There was a problem that such measures were necessary.

  Therefore, the present invention simplifies the configuration of the apparatus, reduces the size of the apparatus, and even if there are variations in the type and characteristics of the magnetron, the temperature of the anode of the magnetron and the ebm (anode) depending on the load in the microwave oven The object of the present invention is to provide a high-frequency dielectric heating power control apparatus and its control method that are not affected by fluctuations in the voltage between the cathodes and the power supply voltage.

  It is another object of the present invention to provide a high-frequency dielectric heating method and apparatus in which the applied voltage of the magnetron does not become excessive with respect to the withstand voltage of each part and the start-up time is shortened. Further, when the power control is performed at a small value, the influence of the non-linear load of the magnetron becomes large, but it is an object to provide a power control device for high frequency dielectric heating and a control method thereof that can suppress a power factor decrease at that time. Yes.

The present invention provides a high-frequency dielectric heating power control device that controls an inverter circuit that rectifies the voltage of an AC power supply, modulates the on-time of high-frequency switching of a switching transistor, and converts it into high-frequency power, detecting an input current to the inverter circuit, an input current detecting unit for outputting the input current waveform information, detects the input voltage to the inverter circuit from the AC power source, the input current at the maximum output setting the amplitude An input voltage detection unit that outputs input voltage waveform information set to 50% to 20% of the waveform information, a selection unit that selects a larger one of the input current waveform information and the input voltage waveform information, and a selected input When the selected waveform information is large with respect to either the current waveform information or the input voltage waveform information, the polarity is selected so as to shorten the on-time. When the waveform information is small in polarity to increase the on-time, and a converter for converting an on-off drive signal of the switching transistor of the inverter circuit.

The selection unit is connected between the input current detection unit and the conversion unit, and includes any one of the input current waveform information and the input voltage waveform information, an input current signal of the inverter circuit, an anode current signal of a magnetron, a switching the collector current signal of the transistor, or any of the collector voltage signal of the switching transistor is mix and power control information, the controlling to a predetermined value, is composed of the mixing circuit for generating an on voltage signal.

  A comparison circuit that compares the output of the input current detection unit with an output setting signal and outputs the power control information may be further provided.

  The input current detection unit may include a current transformer that detects the input current and a rectifier circuit that rectifies and outputs the detected input current.

  The input current detector may be configured to detect and output a unidirectional current after rectifying the input current of the inverter circuit.

  Further, the input current detection unit includes a shunt resistor that detects a unidirectional current after rectifying the input current of the inverter circuit, and an amplifier circuit that amplifies a voltage generated at both ends of the shunt resistor, and the amplification A comparison circuit is further provided for inputting the output obtained by the circuit directly to the mix circuit as the input current waveform information and comparing the output obtained by the amplifier circuit with the output setting signal to output the power control information. be able to.

The mix circuit can be configured to cut a high frequency component of the power control information .

Here, the mix circuit includes a filter circuit, and the time constant of the filter circuit is set to be large when the input current is increased , and the time constant of the filter circuit is set to be small when the input current is decreased. Can be. Furthermore, the mix circuit can be configured such that collector voltage control information for controlling the collector voltage of the switching transistor to a predetermined value is input, and the circuit configuration is switched according to the magnitude of the collector voltage. Further, the mix circuit includes a filter circuit, and when the collector voltage is low , the time constant of the filter circuit is set large, and when the collector voltage is high , the time constant of the filter circuit is set small. Can be configured.

  The input current detection unit may be provided with a filter circuit that attenuates high-frequency portions such as a high-order frequency portion and a high-frequency switching frequency of a commercial power supply. Here, the input current detection unit may be configured by adding phase lead compensation to the filter circuit.

  The input voltage detection unit may include a pair of diodes that detect an input voltage from the AC power supply to the inverter circuit, and a shaping circuit that shapes the input voltage detected by the diode and outputs the waveform. . Here, the shaping circuit can be configured to attenuate the higher-order frequency portion of the input voltage. The shaping circuit may further be provided with phase lead compensation.

  In addition, the conversion unit may be configured by a pulse width modulation circuit that generates a driving signal for the switching transistor by superimposing the ON voltage signal and a predetermined carrier wave.

Further, an oscillation detection circuit for detecting the oscillation of the magnetron is further provided, and the input voltage waveform information from the input voltage detection unit after the oscillation starts according to the oscillation and non-oscillation of the magnetron detected by the oscillation detection circuit. It is also possible to configure so that the magnitude of is attenuated compared to before the oscillation starts .

Further, the present invention provides a high-frequency dielectric heating power control method for controlling an inverter circuit that rectifies the voltage of an AC power source and modulates the on-time of high-frequency switching of the switching transistor to convert it to high-frequency power. Detecting an input current from the AC power source to the inverter circuit, acquiring input current waveform information corresponding to the input current, and detecting an input voltage from the AC power source to the inverter circuit. A step of acquiring input voltage waveform information corresponding to the input voltage and having an amplitude set to 50% to 20% of the input current waveform information when the maximum output is set; and the input current waveform information and the input A step of selecting a larger one of the voltage waveform information, the selected input current waveform information and the input voltage waveform information. On the other hand, when the selected waveform information is large, the polarity of the on-time is shortened, and when the selected waveform information is small, the polarity of the on-time is lengthened. Converting the off drive signal.

  According to the present invention, the input current waveform information of the inverter circuit that rectifies the AC power supply voltage and converts it into alternating current of a predetermined high frequency is used after being converted to the on / off drive current of the switching transistor of the inverter circuit. A control loop that corrects the input current is formed so that the large part is small and the small part is large. Even if the type and characteristics of the magnetron vary, the ebm depends on the temperature of the magnetron anode and the load in the microwave oven. Even if there is a fluctuation in (anode-cathode voltage) or a fluctuation in the power supply voltage, the input current waveform shaping that is not further affected can be performed with a very simple configuration.

  In addition, since the input voltage waveform information is also input to the correction loop, the magnetron start-up time is shortened, and the power factor at a low input current is improved.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

(Embodiment 1)
FIG. 1 is a block diagram illustrating a high frequency heating apparatus according to Embodiment 1 of the present invention. In FIG. 1, the high-frequency heating device includes an inverter circuit 10, a control circuit 70 that controls a switching transistor 39 of the inverter, and a magnetron 50. Inverter circuit 10 includes an AC power supply 20, a diode bridge rectifier circuit 31, a smoothing circuit 30, a resonance circuit 36, a switching transistor 39, and a voltage doubler rectifier circuit 44.

  The AC voltage of the AC power supply 20 is rectified by a diode bridge type rectifier circuit 31 including four diodes 32, and is converted into a DC voltage through a smoothing circuit 30 including an inductor 34 and a capacitor 35. After that, it is converted to high frequency alternating current by an inverter circuit including a resonance circuit 36 composed of a capacitor 37 and a primary winding 38 of a transformer 41 and a switching transistor 39, and high frequency high voltage is induced in the secondary winding 43 via the transformer 41. Is done.

  The high-frequency and high-voltage induced in the secondary winding 43 is applied with a high voltage between the anode 52 and the cathode 51 of the magnetron 50 through the voltage doubler rectifier circuit 44 including the capacitor 45, the diode 46, the capacitor 47, and the diode 48. Is done. Further, the transformer 41 has a tertiary winding 42 to heat the heater (cathode) 51 of the magnetron 50. The above is the inverter circuit 10.

  Next, the control circuit 70 that controls the switching transistor 39 of the inverter will be described. First, a current detection unit including a CT (Current Transformer) 71 provided between the AC power supply 20 and the diode bridge type rectifier circuit 31 is connected to the rectifier circuit 72, and the CT 71 and the rectifier circuit. 72 constitutes an input current detector for detecting the input current to the inverter circuit. The input current to the inverter circuit is insulated and detected by CT 71, and its output is rectified by rectifier circuit 72, and input current waveform information 90 is generated.

  The current signal obtained by the rectifier circuit 72 is smoothed by the smoothing circuit 73, and the signal from the output setting unit 75 that outputs the output setting signal corresponding to the other heating output setting is compared by the comparison circuit 74. . Note that the comparison circuit 74 compares the input current signal smoothed by the smoothing circuit 73 with the setting signal from the output setting unit 75 in order to control the magnitude of power. Therefore, instead of the input current signal smoothed by the smoothing circuit 73, an anode current signal of the magnetron 50, a collector current signal of the switching transistor 39, a collector voltage signal of the switching transistor 39, or the like can be used as an input signal. That is, the comparison circuit 74 outputs the power control information 91 for controlling the output of the input current detection unit to be a predetermined value, but the comparison circuit 74 and the power control information 91 are not essential for the present invention as will be described later. .

  Similarly, as shown in FIG. 2, the input current detection unit is composed of a current detection unit composed of a shunt resistor 86 provided between the diode bridge type rectifier circuit 31 and the smoothing circuit 30, and an amplifier circuit 85 that amplifies the voltage at both ends thereof. The output may be the input current waveform information 90. The shunt resistor 86 detects the input current after being rectified in a single direction by the diode bridge type rectifier circuit 31.

  On the other hand, in the present embodiment, the control circuit 70 detects a voltage of the AC power supply 20 and a pair of diodes 61 that rectifies, and a shaping circuit 62 that shapes the rectified voltage and generates input voltage waveform information 94. The input voltage detection part which consists of these is also provided.

  In the present embodiment, the larger one of the input current waveform information 90 and the input voltage waveform information 94 is selected in the mix circuit 81, and the selected information and the power control information 91 from the comparison circuit 74 are selected by the mix circuit 81. ON voltage information 92 is output after mixing and filtering, the sawtooth wave from the sawtooth wave generating circuit 83 is compared with the PWM comparator 82, pulse width modulation is performed, and the switching transistor 39 of the inverter circuit is controlled to be turned on / off. In addition, the input current waveform information detection system is simplified. In particular, the present embodiment employs a simplified configuration in which the input current waveform information 90 is directly input to the mix circuit 81.

  The PWM comparator 82 is a pulse width modulation circuit that generates a drive signal for the switching transistor 39 by superimposing the ON voltage information 92 and a sawtooth wave that is a predetermined carrier wave. However, in this portion, the ON voltage information 92 is used as a drive signal for the switching transistor of the inverter circuit so that the ON time is short when the input current from the AC power supply 20 is large and the ON time is long when the input current is small. What is necessary is just to be comprised as a conversion part to convert, and it is not limited to this structure.

  The on / off control of the switching transistor 39 with respect to the input current waveform information is converted with a polarity that shortens the on-time when the input current is large, and conversely increases when the input current is small. Similarly, the input voltage waveform information is also converted with a polarity that shortens the on-time when the input voltage is large and vice versa when the input voltage is small. Therefore, in order to obtain such a waveform, the input current waveform information and the input voltage waveform information are used after being inverted in the mix circuit 81 described later.

  FIG. 4A shows an example of the mix circuit 81. The mix circuit 81 has three input terminals, to which power control information 91, input current waveform information 90, and input voltage waveform information 94 are added, and are mixed by an internal circuit as shown in the figure.

  Further, as shown in FIG. 4B, a high frequency cut filter is configured between the power control information 91 and the output of the mix circuit 81 as shown by an AC equivalent circuit. As a result, the high-frequency component included in the power control that has interfered with the input current waveform information for shaping the input current waveform is cut by this filter.

  On the other hand, as shown in FIG. 4C, a low frequency cut filter is configured between the input current waveform information 90 and the input voltage waveform information 94 and the output of the mix circuit 81 as shown by an AC equivalent circuit. Therefore, the power control information 91 is converted into a DC component of the output of the mix circuit 81, and the input current waveform information 90 and the input voltage waveform information 94 are converted into an AC component.

  Therefore, the power control information 91 is converted into a DC component of the output of the mix circuit 81, and the input current waveform information and the input voltage waveform information are converted into an AC component.

In the first embodiment, as described above, the larger one of the input current waveform information 90 and the input voltage waveform information 94 is selected, converted into an on / off drive signal for the switching transistor 39 of the inverter circuit, and used. It is. In general PWM inverter for use in microwave ovens and the like are collective wisdom, converted into DC by rectifying the commercial power supply of 50 to 60 cycles, by an inverter to convert direct current, for example, converted into about 20 to 50 k Hz frequency The boosted high frequency is boosted by a boosting transformer, and a high voltage rectified by a voltage doubler rectifier circuit is applied to the magnetron.

  As an inverter circuit method, for example, a commercial power supply is often used in a 230V region or the like, and two switching transistors connected in series are alternately turned on, and the switching frequency is controlled to change the output (half) bridge. As shown in FIG. 1 of the present invention, FIG. 1 of Patent Document 2, etc., switching is performed by using one switching transistor 39, and the output is changed by changing the ON time of the switching pulse. There are two types of on-time modulation methods using a voltage resonant circuit. The monolithic voltage resonance type circuit system requires only one switching transistor 39. The output can be reduced if the on-time is shortened, and the output can be increased if the on-time is lengthened. It is a simple method.

  FIG. 5 is a diagram for explaining a waveform obtained by the first embodiment of the present invention. This example is a situation in which the magnetron normally oscillates, that is, during normal operation, and the input current waveform information and the input voltage waveform information are converted into an on / off drive signal for the switching transistor 39 and used. .

  5A and 5B are diagrams for explaining waveforms obtained by the first embodiment of the present invention. FIG. 5A shows a case where the input current is large, and FIG. 5B shows a case where the input current is small. In order to obtain 39 on / off drive signals, the current waveform is selected in the case of FIG. 5A, and the voltage waveform (dotted line) is selected in the case of FIG. 5B. As will be described later, the solid line represents the signal shape after correction by the power control apparatus of the present invention, which is mainly used in the following description, and the broken line represents the signal shape of the instantaneously changing output from the AC power supply 20 before correction. Represent. The dotted line indicates input voltage waveform information.

  5A, the waveform of the input current waveform information from (a) from the top is the input current waveform information 90 which is the output of the rectifier circuit 72 in FIG. 1 and the output of the amplifier 85 in FIG. Shows the waveform before correction resulting from the non-linear load characteristics of the magnetron. Also, the waveform of the input voltage waveform information (A) is the input voltage waveform information 94 that is an output from the shaping circuit 62. The waveform (b) in FIG. 5A is ON voltage information 92 that is a correction output of the mix circuit 81. This ON voltage information 92 is input current waveform information 90, input voltage waveform information 94, and power control information 91. Then, the magnitude of the waveform changes, and in order to complement and correct the distortion of the input current, it is output as an inverted waveform of (a).

  (C) in FIG. 5 (a) shows the equivalent of the ON voltage information 92 shown in (b), and this ON voltage information and the sawtooth from the modulation sawtooth wave generation circuit 83 shown in (d). The waves are compared by the PWM comparator 82, and a PWM signal that is an on / off signal of the switching transistor 39 is generated. That is, as shown in the figure, the PWM comparator 82 is input with the (c) ON voltage information 92 and the (D) sawtooth wave as a PWM command signal for comparison, and the period in which the sawtooth wave and the ON voltage information 92 cross each other is On-time modulation of a pulse having an on-time pulse width is performed. In the portion where the amplitude value of the command signal (ON voltage information) 92 is large (0 °, near 180 °, the portion where the input current is small), since the crossing period with the sawtooth wave is also large, the on time is long and the pulse width is widened. The polarity is corrected to increase the input current. In addition, the portion where the amplitude value of the ON voltage information 92 is small (near 90 °, 270 °, the portion where the input current is large) has a short crossing period with a sawtooth wave, so the on time is short and the pulse width is narrowed. A pulse train having an on / off period such as (e) for correcting the polarity to decrease the current is output as a PWM signal. That is, since the ON voltage information (b) is inverted as the correction waveform with respect to the input current waveform information and the input voltage waveform information (b), the input of the input current waveform information and the input voltage waveform information (b) is large ( In the vicinity of 90 degrees and 270 degrees, the ON time is shortened and the input current waveform information and input voltage waveform information (A) are small (near zero crossings of 0 degrees and 180 degrees) as in the pulse train signal (d). In () part, the ON time is lengthened and increased, which is converted into an inverted output opposite to (A). As a result, an effect of correcting the input waveform can be obtained, and this effect is particularly great in the vicinity of the zero cross.

The lower waveform (G) indicates the ON width of the switching transistor 39. The ON voltage information of the correction waveform obtained by inverting the input current waveform information and input voltage waveform information of 50 Hz (or 60 Hz) shown in (A). by comparing (c) high-frequency sawtooth wave (d), 20 k Hz~50 the frequency of k Hz etc. are inverters converted, is generated on-off signals (e). In response to the on / off signal (e), the switching transistor 39 is driven to input high frequency power to the primary side of the step-up transformer and generate a high voltage boosted to the secondary side of the step-up transformer. (G) plots each on-time information on the Y-axis to visualize how the on-time of each pulse of this on / off signal (e) changes within the cycle of the commercial power supply. , It connects the points.

  The above description shows the same signal as that when the input current from the AC power supply 20 is obtained in an ideal state (for example, a sine wave). However, generally, the input current from the AC power supply 20 deviates from an ideal sine wave and fluctuates when viewed instantaneously. A broken line signal indicates such a realistic state. As indicated by the broken line, even in an instantaneous period of a half cycle (0 to 180 degrees) of the commercial power supply, the actual signal generally deviates from the ideal signal state, and instantaneous fluctuations are generally generated. Such a signal shape is generated by a transformer, a boosting action by a voltage doubler circuit, a smoothing characteristic of the voltage doubler circuit, and a magnetron characteristic in which an anode current flows only when the voltage is only ebm or higher. That is, it can be said that it is an unavoidable variation in an inverter circuit for a magnetron.

  In the power control apparatus of the present invention, when the input current waveform information (see (A)) indicated by the broken line reflecting the fluctuation state of the input current is obtained from the input current detector and the input current waveform information is selected ( FIG. 5A), the subsequent control is performed based on the input current waveform information (the change in the input current is irrelevant to the input voltage waveform information, so the description of the input voltage waveform information is omitted here). To do). This control is performed so that the instantaneous fluctuation of the input current waveform information that appears in a period such as a half cycle is suppressed so as to approach an ideal signal as indicated by an arrow. This suppression is achieved by adjusting the drive signal of the switching transistor 39. Specifically, when the input current waveform information is smaller than the ideal signal, the above-described on-time is longer and the pulse width is wider. When the input current waveform information is larger than the ideal signal, the above-described ON time is shorter and the pulse width is narrower. Even in the case of instantaneous fluctuations for a shorter period, the changed waveform is reflected in the on-time information, and the same correction as described above is performed.

  Due to the instantaneous fluctuation suppressing action of the switching transistor 39 to which the drive signal is given, the input current waveform information is corrected as indicated by an arrow, and an input close to the ideal wave is always given to the magnetron. The corrected (c) and (e) are not shown. Here, the ideal signal described above is a virtual signal, but this signal is a sine wave.

That is, in a short period such as a half cycle of the commercial power supply, the instantaneous error or the sum of the correction amount of the ideal signal waveform and the input current waveform information is controlled by other means (the power control). So it is almost zero. In addition, since the portion where the input current does not flow due to the non-linear load is corrected in the flowing direction, the portion where the input current is large is decreased to establish the above substantially zero. This is to correct even the nonlinear load so that the current waveform can be regarded as a linear load.Since the commercial power supply voltage waveform is a sine wave, the ideal waveform is a sine wave. become.

  In this way, the input current is corrected with the reverse polarity of the waveform so as to cancel the change in the input current waveform and the excess or deficiency with respect to the ideal waveform. Therefore, a sudden current change in the commercial power supply cycle caused by the non-linear load of the magnetron, that is, distortion is canceled out by this control loop, and the input current waveform shaping is performed.

  Furthermore, since the control loop operates with the input current waveform information that follows the instantaneous value of the input current in this way, even if there are variations in the type and characteristics of the magnetron, the temperature of the anode of the magnetron and the microwave oven Even if there is ebm (anode-cathode voltage) fluctuation due to load and further power supply voltage fluctuation, it is possible to perform input current waveform shaping without being affected by them.

  In particular, in the present invention, the switching transistor is controlled based on instantaneously varying input current waveform information. Instantaneous fluctuations in input current are directly input to the mix circuit 81 in the form of input current waveform information and reflected in the ON voltage information. Therefore, suppression of input current waveform distortion and switching with excellent follow-up to instantaneous fluctuations are possible. A driving signal for the transistor can be obtained.

  In the present invention, input current waveform information or input voltage waveform information having information that suppresses distortion and instantaneous fluctuation of the input current waveform is converted into a drive signal for the switching transistor of the inverter circuit. The power control information 91 is not essential for achieving the purpose. The power control information 91 is information for controlling power fluctuations in a long period, that is, a period longer than the commercial power supply period, and corrects instantaneous fluctuations for a short period such as a half cycle of AC targeted by the present invention. It is not information. Accordingly, the use of the mix circuit 81 and the PWM comparator 82 is merely an example of the embodiment. The mix circuit 81 selects at least the larger one of the input current waveform information and the input voltage waveform information, and the PWM comparator 82 uses these. What corresponds to a conversion unit that converts information into a drive signal for the switching transistor may be present between the input current detection unit and the switching transistor.

  Even when the power control information is used, it is not essential to input the power control information 91 for controlling the output of the input current detection unit to a predetermined value as in the above-described embodiment. That is, in the above-described embodiment, the power control information 91 originates from the current detector 71 and the rectifier circuit 72 (FIG. 1) or the shunt resistor 86 and the amplifier circuit 85 (FIG. 2) that detect the input current. Information for controlling the current or voltage at an arbitrary position of the inverter circuit 10 to be a predetermined value can be input to the mix circuit 81 as power control information. For example, information from the collector of the switching transistor 39 is input as it is or smoothed through the smoothing circuit 73 and input to the comparison circuit 74, and the information after comparison with the output setting signal in the comparison circuit 74 is used as power control information. be able to.

  Next, FIG. 5B shows a comparison of the waveforms when the input current is small with respect to FIG. 5A, and FIG. 5B shows the input current waveform information when the input is small. (A) corresponds to (A), (L) is ON voltage information, (N) is the ON width of the switching transistor, and corresponds to (B) and (G) in FIG. . Although not shown, the sawtooth wave comparison process shown in (c), (d), (e), and (f) in FIG. Of course.

  When the input current is relatively small and the value of the input current waveform information is small as shown in FIG. 5B, the waveform shaping ability of the input current is lowered. Therefore, in the present invention, as shown in FIG. 5B, when the input voltage waveform information (dotted line) is larger than the input current waveform information, the input voltage waveform information is used for waveform shaping. In the present embodiment, the input voltage is attenuated to obtain input voltage waveform information, and the input current is converted to voltage to obtain input current waveform information, whereby the magnitudes of the two can be directly compared.

  As described above, when the input current is controlled to be small, the input current waveform information becomes small and the input current waveform shaping ability is lowered. However, since the input voltage waveform information larger than the current waveform is selected and the input current waveform shaping is performed, the deterioration of the input current waveform shaping capability is suppressed. Therefore, even when the input current is small, it is possible to prevent the power factor from greatly decreasing. The amplitude of the input voltage waveform information (threshold for determining whether or not the input current is small) is a commercial power supply voltage waveform such that the amplitude of the input current waveform information is about 50% to 20% of the maximum input current, for example. This can be realized by setting the damping rate (voltage division ratio) from

  The above description based on FIG. 5 is an explanation regarding the normal operation of the magnetron. Next, the operation when the magnetron is activated will be described. The time of start-up refers to a state in a preparatory stage before the oscillation is started although a voltage is applied to the magnetron but no oscillation occurs (corresponding to the time of non-oscillation). At this time, the impedance between the anode and the cathode of the magnetron becomes equal to infinity, unlike during steady operation.

  In the present invention, the voltage from the commercial AC power supply 20 is multiplied by the ON voltage information, that is, the commercial power supply voltage is amplitude-modulated by the ON voltage information and applied to the primary side of the transformer 41. The peak value of the applied voltage on the primary side is related to the applied voltage to the magnetron 50, and the area defined from the applied voltage and elapsed time is related to the power supplied to the heater.

  In the present invention, the input voltage waveform information 94 is input to the mix circuit 81 even when the input current waveform information 90 is small. In other words, a format is adopted in which the input voltage compensates for the shortage of input current as a reference signal especially at the time of startup.

  FIG. 6 is a diagram for explaining the operation when the input voltage waveform information is added and when the input voltage waveform information is not added. FIG. 6A shows the case where the input voltage waveform information is not added in order from the top (during steady operation). ) ON voltage information, applied voltage on the transformer primary side, magnetron applied voltage, and heater input power.

  FIG. 6B illustrates the operation when the input voltage waveform information is added (at startup). 6 (a) and 6 (b) both show a case where the peak value of the applied voltage on the transformer primary side is limited by the configuration of the sixth embodiment described later. Further, FIG. 6 (b) shows the trapezoidal shape of the waveform of the transformer primary application voltage and the magnetron application voltage suppressed by the action of the added input voltage waveform information. 6B also shows the waveforms of the ON voltage information, the transformer primary side applied voltage, the magnetron applied voltage, and the heater input power from the top in the same manner as FIG. 6A.

  As shown in FIG. 5, since the ON width of the switching transistor is large in the vicinity of the phase of 0 degree and 180 degrees, the transformer primary side applied voltage and the magnetron applied voltage have a relatively large amplification width. On the other hand, in the vicinity of the phase of 90 degrees and 270 degrees, since the ON width of the switching transistor is small, the amplification width is relatively suppressed. From the relative relationship with the amplification width at the phase of 0 degree and 180 degrees, the entire waveform is shown. It has a trapezoidal shape with peaks suppressed.

  Comparing the magnetron applied voltages of FIG. 6A and FIG. 6B, the heater input power when the magnetron applied voltage is the same is the heater input power of FIG. 6B. Since it increases and the waveform area increases, the heater can be heated in a short time and the startup time can be shortened.

  FIG. 7 shows a comparison inversion circuit (comparison selection circuit; large / small comparison / switching inversion circuit) that is used in the first embodiment of the present invention to select and invert the larger one of the input current waveform information and the input voltage waveform information. It is a figure which shows an example. This comparison and inverting circuit is provided in the mix circuit 81 as shown in FIGS.

  The input current waveform information 90 and the input voltage waveform information 94 are each input to a buffer transistor, and the output is input to two transistors having a common emitter resistance and collector resistance. The buffer transistor is provided to prevent interference between the input current waveform information 90 and the input voltage waveform information 94. At the common connection point of the common emitter resistance of the two transistors, the one with a larger input signal than the diode characteristic of the transistor is selected and output, and the transistor to which the selected signal is input is conducted. The emitter current and collector current of the conducting transistor reflect the magnitude of the input signal. The magnitude of the collector current is reflected in the potential at the common connection point of the common collector resistor.

  Here, as the emitter voltage increases, the collector current increases and the common collector resistance voltage drop increases, that is, the collector voltage decreases, so that the polarity of the collector voltage is inverted with respect to the input signal. Also, the signal conversion coefficient varies depending on the resistance value ratio between the collector resistance and the emitter resistance. In terms of interference with the power control signal, it is more effective to convert the impedance of the signal at the common collector connection point through a buffer and connect it to the subsequent capacitor. Thus, in this circuit, the magnitude determination and selection of the two signals are automatically performed, and the selected signals are inverted and output.

(Embodiment 2)
Next, a second embodiment of the present invention will be described with reference to the drawings. In the second embodiment of the present invention, the signal having the larger input current waveform information and input voltage waveform information is selected, the selected signal and the power control information from the comparison circuit 74 are mixed, filtered, and the inverter circuit This relates to the configuration of the control circuit that is used after being converted into an on / off drive signal for the switching transistor 39.

  In the second embodiment, as shown in FIG. 1, the variable gain amplifier 291, the inversion / waveform processing circuit 263, the waveform error detection circuit 292, etc., as shown in FIG. Simplification and miniaturization can be achieved. Further, since the start-up time is shortened with a simple configuration and a safety measure for preventing the application of an excessive voltage to the magnetron anode 52 is added, the reliability of the product is improved.

  Further, by configuring as described above, the control loop using the input current waveform information 90 is specialized for waveform shaping of the input current, the control loop using the power control information 91 is specialized for power control, and mutual control does not interfere with each other. As a configuration, conversion efficiency is maintained.

(Embodiment 3)
The third embodiment of the present invention relates to an input current detection unit, and is configured to detect an input current of an inverter circuit with a CT 71 or the like and to rectify and output from a rectifier circuit 72 as shown in FIG. In this configuration, since the input current is detected using CT or the like, a large signal can be extracted while maintaining insulation, so that the effect of shaping the input current waveform is great and the quality of the input current is improved.

  In the example illustrated in FIG. 2, the input current detection unit detects the unidirectional current rectified by the rectifier circuit 31 of the inverter circuit via the shunt resistor 86 disposed between the rectifier circuit 31 and the smoothing circuit 30. The voltage generated at both ends is amplified by an amplifier circuit (amplifier) 85 and output. This configuration has an advantage that the input current detection unit can be configured at low cost because the detection unit does not need to be insulated from the electronic circuit and does not need to be rectified.

  As shown in FIG. 2, the amplifier circuit 85 of the input current detection unit is configured to attenuate high-frequency parts such as high-frequency parts of commercial power supplies and high-frequency switching frequencies to prevent unnecessary resonance. . Specifically, as shown in the detailed diagram of the input current detection unit in FIG. 3, the amplifier circuit 85 uses a high-frequency cut capacitor as shown in FIG. High frequency parts such as high frequency switching frequency are attenuated.

  Further, by inserting a high-frequency cut capacitor of the amplifier circuit 85, a phase delay compensation is added by inserting a resistor in series with the capacitor to generate a phase delay as shown in the phase characteristic diagram of FIG. This prevents transient time delays and ensures the stability of the control loop. Further, as shown in FIG. 8, the rectifier circuit 72 of FIG. 1 also has a transient time delay by adding a configuration that attenuates the high frequency portion (parallel insertion of a capacitor) and phase lead compensation (serial insertion of a capacitor). The structure which prevents can be used.

(Embodiment 4)
The fourth embodiment of the present invention relates to a mix circuit 81. As shown in FIG. 4A, the mix circuit includes input current waveform information 90, input voltage waveform information 94, and power control. Three terminals for inputting information 91 are provided. The input current waveform information 90 and the input voltage waveform information 94 are input to a comparison / inversion circuit as shown in FIG. 7, and a comparison / inversion process is performed. The processed signal and the power control information 91 are input to a filter circuit composed of C, R1, and R2, respectively, and after filtering, are output to the PWM comparator 82 as ON voltage information 92. The filter circuit is configured to cut the high frequency component of the power control information 91 as shown in the equivalent circuit diagram of FIG. With this configuration, the component that hinders the shaping of the input current waveform is cut, so that the quality of the input current waveform is improved. On the other hand, as shown in the equivalent circuit diagram of FIG. 4C, the low-frequency cut filter is configured for the input current waveform information 90 and the input voltage waveform information 94 to perform waveform maintenance.

(Embodiment 5)
In the fifth embodiment of the present invention, power control is performed so that the input current waveform information 90 of the input current detection unit, the input voltage waveform information 94 of the input voltage detection unit, and the output of the input current detection unit become predetermined values. The characteristic of the mix circuit 81 that synthesizes the information 91 is controlled by providing a difference between the input current increase control and the decrease control. FIG. 9 is a configuration diagram of a mix circuit according to the fifth embodiment.

  In the configuration diagram of FIG. 9A, the SW1 is turned on / off by the power control information 91, and the ON voltage information 92 is lowered / increased. During the increase control of the input current, SW1 is turned off, and the ON voltage information is gradually increased with the time constant of C * R2, as shown in the equivalent circuit of FIG. Is controlling.

  During input current reduction control, SW1 is turned on and the ON voltage information is rapidly reduced with a time constant of C * {R1 * R2 / (R1 + R2)} as shown in the equivalent circuit diagram of FIG. Thus, the ON width of the switching transistor is controlled to be narrow. That is, the circuit configuration of the mix circuit 81 is switched between the input current increase control and the input current decrease control. In particular, the time constant is set large during input current increase control, and the time constant is set small during input current decrease control.

  By providing a difference in this way, a control characteristic that normally responds gently and a control characteristic that reduces the input current with a quick response when the input current rises transiently for some reason to prevent component destruction, etc. it can. In addition, the stability of the control characteristics against the non-linear load of the magnetron can be ensured.

(Embodiment 6)
In the sixth embodiment of the present invention, the collector voltage control information for controlling the collector voltage of the switching transistor 39 to a predetermined value as shown in the block diagram of the mix circuit according to the sixth embodiment in FIG. To enter.

  As shown in FIG. 10, the SW2 is on / off controlled by the collector voltage control information 93 that compares the collector voltage with the reference value. When the collector voltage is low, the SW2 is turned off and the ON voltage information is gradually increased with the time constant of C * R2 so that the ON width of the switching transistor is increased. When the collector voltage is high, the SW2 is turned on and the ON voltage information is rapidly lowered with the time constant of C * {R2 * R3 / (R2 + R3)} so that the ON width of the switching transistor is narrowed. That is, the circuit configuration of the mix circuit 81 is switched according to the magnitude of the collector voltage of the switching transistor 39. In particular, the time constant increases when the collector voltage is low, and decreases when the collector voltage is high.

  This control is effective in preventing application of an excessive voltage to the magnetron when the magnetron is not oscillating, that is, when the power control is not functioning. Further, after the start of oscillation of the magnetron, it is preferable to set a larger reference value compared with the collector voltage than before the start of the magnetron oscillation in order to disable this control and not affect the power control.

(Embodiment 7)
In Embodiment 7 of the present invention shown in FIG. 11, a configuration is adopted in which the amount of input voltage waveform information added to input current waveform information is switched between before and after magnetron oscillation. In the seventh embodiment, a changeover switch SW3 is provided between the shaping circuit 62 and the mix circuit 81 in FIG. 1, and an oscillation detection circuit 63 for detecting the start of magnetron oscillation from the output of the rectifier circuit 72 is provided. . The connection point between the changeover switch SW3 and the shaping circuit 62 is switched between A and B by the output of the oscillation detection circuit 63. The shaping circuit 62 is provided with three voltage-dividing resistors connected in series between the diode 61 and the ground, and divides and outputs power supply voltage information from the commercial power supply voltage. The power supply voltage information at the connection point A closer to the commercial power supply 20 is larger because the amount of attenuation from the commercial power supply voltage is smaller than that at the connection point B closer to the ground. Further, the capacitor provided in the shaping circuit 62 suppresses intrusion of noise from the commercial power supply to the power supply voltage information.

  When the magnetron is started (corresponding to non-oscillation), the impedance between the anode and the cathode becomes equal to infinity, unlike during steady operation. Since the difference between the steady operation and the start-up affects the state of the input current via the transformer 41, the oscillation detection circuit 63 starts the magnetron from the current value obtained from the rectifier circuit 72. It can be determined whether or not it is sometimes.

  When it is detected from the output of the oscillation detection circuit 63 that the magnetron is being activated, SW3 is switched to the connection point A side. In this case, as described above, a larger signal (input voltage waveform information) is input to the mix circuit 81 than the switching to the connection point B side, and the startup time is shortened.

  When the oscillation start is detected by the oscillation detection circuit 63, the switch SW3 is switched to the connection point B side and attenuates the signal. Therefore, the input current waveform shaping when the input current is large is not hindered and the input current is small. When the power factor is improved. Thus, by providing the power supply voltage information amplitude switching means before and after the start of magnetron oscillation, the case where the amplitude switching means is not provided and the case where the amplitude of the power supply voltage information after the start of oscillation is set to be the same. However, since the amplitude before the start of oscillation can be set larger, the effect of shortening the startup time described above becomes larger.

  This oscillation detection circuit uses, for example, the characteristic that the input current increases when the magnetron starts oscillating, and the output of the input current detection unit is compared with the oscillation detection threshold level by a comparator or the like, and the output is latched. .

  Although various embodiments of the present invention have been described above, the present invention is not limited to the matters shown in the above-described embodiments, and those skilled in the art can make modifications and applications based on the description and well-known techniques. This is also the scope of the present invention, and is included in the scope for which protection is sought.

  According to the present invention, the input current waveform information of the inverter circuit that rectifies the AC power supply voltage and converts it into alternating current of a predetermined high frequency is used after being converted to the on / off drive current of the switching transistor of the inverter circuit. A control loop that corrects the input current is formed so that the large part is small and the small part is large. Even if the type and characteristics of the magnetron vary, the ebm depends on the temperature of the magnetron anode and the load in the microwave oven. Even if there is a fluctuation in (anode-cathode voltage) or a fluctuation in the power supply voltage, the input current waveform shaping that is not further affected can be performed with a very simple configuration. In addition, since the input voltage waveform information is also input to the correction loop, the magnetron start-up time is shortened, and the power factor at a low input current is improved.

1 is a configuration diagram of a high-frequency dielectric heating power control apparatus according to Embodiment 1 of the present invention. FIG. The block diagram of the power control apparatus for high frequency dielectric heating which has the input current detection part which detects the unidirectional current which concerns on Embodiment 3 of this invention. FIG. 3 is a detailed view of an input current detection unit shown in FIG. 2. The circuit diagram of the mix circuit which concerns on Embodiment 4 of this invention. The figure which shows the basic waveform of each part of the power control apparatus for high frequency dielectric heating shown in FIG. The wave form diagram for demonstrating operation | movement of the power control apparatus for high frequency dielectric heating shown in FIG. FIG. 5 is a circuit diagram showing an example of the comparison / selection circuit shown in FIG. 4. FIG. 2 is a detailed circuit diagram of the shaping circuit shown in FIG. The block diagram of the mix circuit which concerns on Embodiment 5 of this invention. The block diagram of the mix circuit which concerns on Embodiment 6 of this invention. The figure which shows the switching circuit of the input voltage waveform information which concerns on Embodiment 7 of this invention. The block diagram of the conventional high frequency heating apparatus. The anode-cathode applied voltage-anode current characteristic view of the magnetron shown in FIG. The block diagram of the conventional electric power control apparatus for high frequency dielectric heating. The circuit diagram of the mix circuit shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Inverter circuit 20 AC power supply 30 Smoothing circuit 31 Diode bridge type rectifier circuit 32 Diode 34 Inductor 35 Capacitor 36 Resonant circuit 37 Capacitor 38 Primary winding 39 Switching transistor 41 Transformer 42 Tertiary winding 43 Secondary winding 45 Capacitor 46 Diode 47 Capacitor 48 Diode 50 Magnetron 51 Cathode 52 Anode 61 Diode 62 Shaping Circuit 63 Oscillation Detection Circuit 70 Control Circuit 71 Current Detection Unit 72 Rectifier Circuit 73 Smoothing Circuit 74 Comparison Circuit 75 Output Setting Unit 81 Mix Circuit 82 PWM Comparator 83 Sawtooth Wave Generation Circuit 85 Amplifier circuit 86 Shunt resistor 90 Input current waveform information 91 Power control information 92 ON voltage information 93 Collector voltage control information 94 Input voltage waveform information News

Claims (18)

A power control device for high-frequency dielectric heating that controls an inverter circuit that rectifies the voltage of an AC power supply, modulates the on-time of high-frequency switching of a switching transistor, and converts it into high-frequency power,
An input current detection unit that detects an input current from the AC power source to the inverter circuit and outputs input current waveform information ;
An input voltage detector that detects an input voltage from the AC power supply to the inverter circuit and outputs input voltage waveform information in which the amplitude is set to 50% to 20% of the input current waveform information when the maximum output is set ;
A selection unit that selects a larger one of the input current waveform information and the input voltage waveform information;
When either of the selected input current waveform information and the input voltage waveform information, the selected waveform information is large, the polarity is set to shorten the on time. When the selected waveform information is small, the on time is set. A conversion unit that converts the on / off drive signal of the switching transistor of the inverter circuit into a longer polarity;
A power control apparatus for high frequency dielectric heating comprising: A power control apparatus for high frequency dielectric heating according to claim 1,
The selection unit is connected between the input current detection unit and the conversion unit, and includes any one of the input current waveform information and the input voltage waveform information, an input current signal of the inverter circuit, an anode current signal of a magnetron, a switching the collector current signal of the transistor, or any of the collector voltage signal of the switching transistor is mix and power control information, the controlling to a predetermined value, high-frequency dielectric heating are constituted by the mixing circuit for generating an on voltage signal Power control device. A power control apparatus for high frequency dielectric heating according to claim 2,
A power control device for high frequency dielectric heating comprising a comparison circuit that compares the output of the input current detection unit with an output setting signal and outputs the power control information. A power control apparatus for high frequency dielectric heating according to claim 1,
The power control device for high frequency dielectric heating, wherein the input current detection unit includes a current transformer that detects the input current, and a rectifier circuit that rectifies and outputs the detected input current. A power control apparatus for high frequency dielectric heating according to claim 3,
The high-frequency dielectric heating power control device configured to detect and output a unidirectional current after rectifying the input current of the inverter circuit. A power control apparatus for high frequency dielectric heating according to claim 5,
The input current detection unit includes a shunt resistor that detects a unidirectional current after rectifying the input current of the inverter circuit, and an amplifier circuit that amplifies a voltage generated at both ends of the shunt resistor.
The output obtained by the amplifier circuit is directly input to the mix circuit as the input current waveform information,
A power control apparatus for high frequency induction heating, further comprising a comparison circuit that outputs the power control information by comparing an output obtained by the amplifier circuit with an output setting signal. A power control apparatus for high frequency dielectric heating according to claim 2,
The high-frequency dielectric heating power control apparatus has a configuration in which the mix circuit cuts a high frequency component of the power control information. A power control apparatus for high frequency dielectric heating according to claim 2,
The mix circuit includes a filter circuit, and sets the time constant of the filter circuit to be large when the input current is increased, and sets the time constant of the filter circuit to be small when the input current is decreased. apparatus. A power control apparatus for high frequency dielectric heating according to claim 2,
A power control apparatus for high-frequency dielectric heating in which collector voltage control information for controlling a collector voltage of the switching transistor to a predetermined value is input to the mix circuit, and a circuit configuration is switched according to the magnitude of the collector voltage. A power control apparatus for high frequency dielectric heating according to claim 9,
The mix circuit includes a filter circuit. When the collector voltage is low, the time constant of the filter circuit is set large. When the collector voltage is high, the time constant of the filter circuit is set small. Power control device. A power control apparatus for high frequency dielectric heating according to claim 1,
The input current detection unit is a high-frequency dielectric heating power control apparatus having a filter circuit that attenuates high-frequency parts such as a high-order frequency part and a high-frequency switching frequency of a commercial power supply. A power control apparatus for high frequency dielectric heating according to claim 11,
The input current detection unit is a high frequency dielectric heating power control apparatus in which phase lead compensation is added to the filter circuit. A power control apparatus for high frequency dielectric heating according to claim 1,
The input voltage detector is
A set of diodes for detecting an input voltage from the AC power supply to the inverter circuit;
A power control apparatus for high-frequency dielectric heating, comprising: a shaping circuit that shapes the waveform of an input voltage detected by the diode and outputs the waveform. The power control device for high frequency dielectric heating according to claim 13,
A power control apparatus for high-frequency dielectric heating, wherein the shaping circuit has a configuration for attenuating a higher-order frequency portion of the input voltage. The power control device for high frequency dielectric heating according to claim 14,
A power controller for high frequency dielectric heating, wherein the shaping circuit further comprises phase lead compensation. A power control apparatus for high frequency dielectric heating according to claim 1,
A power control apparatus for high frequency dielectric heating, wherein the conversion unit includes a pulse width modulation circuit that superimposes the ON voltage signal and a predetermined carrier wave to generate a drive signal for the switching transistor. A power control apparatus for high frequency dielectric heating according to claim 1,
An oscillation detection circuit for detecting the oscillation of the magnetron; in response to the oscillation and non-oscillation of the magnetron detected by the oscillation detection circuit, the input voltage waveform information from the input voltage detection unit after the start of oscillation; A power control device for high frequency dielectric heating that attenuates the size compared to before the start of oscillation. A power control method for high-frequency dielectric heating that controls an inverter circuit that rectifies the voltage of an AC power supply, modulates the on-time of high-frequency switching of a switching transistor, and converts it into high-frequency power,
Detecting an input current from the AC power source to the inverter circuit;
Obtaining input current waveform information corresponding to the input current ;
Detecting an input voltage from the AC power source to the inverter circuit;
Obtaining input voltage waveform information corresponding to the input voltage and setting the amplitude from 50% to 20% of the input current waveform information at the time of setting the maximum output ;
Selecting the larger of the input current waveform information and the input voltage waveform information;
When either of the selected input current waveform information and the input voltage waveform information is selected, the polarity is such that the on-time is shortened when the selected waveform information is large, and the on-time when the selected waveform information is small. Converting the on / off drive signal of the switching transistor of the inverter circuit to a polarity that lengthens
A power control method for high-frequency dielectric heating comprising:

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