JP2007149445A - Power control device for high frequency induction heating, and its control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power control device for high frequency induction heating which is not affected by variations in a kind of magnetron, its characteristics, and power supply voltage fluctuations or the like. <P>SOLUTION: Input current detecting parts 71, 72 to detect an input current of an inverter circuit 10 to convert an alternate current power supply voltage 20 into high frequency electric power by rectifying 31 and high-frequency switching are provided, ON voltage information 92 is output by mixing input current waveform information 90 of the input current detecting part and electric power control information 91 to control by a mixing circuit 81 so that output of the input current detecting part becomes to have a prescribed value, it is compared with a saw-tooth wave from a saw-tooth wave generating circuit 83 by a PWM converter 82 and pulse width modulation, and a driving signal to on/off control a switching transistor 39 of the inverter circuit is output. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

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

  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. 8 is a diagram for explaining a high-frequency heating apparatus that implements this control method. In FIG. 8, 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 in which the output setting signal is compared by the level conversion circuit 720. A waveform shaping circuit 721 that shapes the shaping signal and the output of the rectifier circuit 710 that rectifies 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 is the comparison voltage generation circuit. A comparison reference voltage is output when the output is smaller than the output of the comparator, and a comparison circuit 711 that inverts and amplifies the output when the output is larger. The output of the superimposing means 712, the oscillation circuit 713, and the oscillation circuit 713 is subjected to pulse width modulation by the pulse width control signal, and this modulation output is used. It has a structure comprising 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 712.

  According to this configuration, the waveform shaping circuit 721 that inputs the rectified voltage of the AC power supply 704 and outputs the rectified voltage to the comparison circuit 711 performs shaping according to the output setting. 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. Since the magnetron VAK (anode-cathode voltage) -Ib characteristic is a non-linear load as shown in FIG. 9, the ON width is modulated according to the phase of the commercial power supply and the input current waveform is made closer to a sine wave to improve the power factor. 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. 9 is a graph showing the anode-cathode applied voltage-anode current characteristics of the magnetron, where (a) is different depending on the type of magnetron, (b) is different depending on whether the power supply matching of the magnetron is good or bad, and (c) is depending on the temperature of the magnetron. 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.

  In response to the above problem, there is a control method disclosed in Patent Document 2. FIG. 10 is a configuration diagram illustrating a high-frequency heating device that implements the control method.

  In FIG. 10, 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 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. 11 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-7-136375 JP 2004-30981 A

  However, in the configuration described in Patent Document 2, as shown in FIG. 11, 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.

  Further, since the output voltage waveform of the smoothing circuit 30 immediately before the start of the first on-operation of the transistor 239 becomes a direct current regardless of the phase of the commercial power supply, the use of the auxiliary modulation signal 811 changes the commercial power supply phase at the start of the on-operation. It is necessary to control the auxiliary modulation signal 811 to be the smallest, that is, to control the vicinity of 90 degrees and 270 degrees where the on-time width of the transistor 239 is the smallest, to prevent an excessive voltage from being applied to the magnetron. There was a problem that became complicated.

  Therefore, the present invention simplifies the configuration of the apparatus and enables further downsizing of the apparatus. Even if there are variations in the type and characteristics of the magnetron, the ebm depends on the temperature of the anode of the magnetron and the load in the microwave oven. To provide a power control device for high-frequency dielectric heating and its control method capable of improving operating efficiency without being affected by fluctuations in (anode-cathode voltage) and even power supply voltage fluctuations. It is in.

  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 and modulates the on-time of high-frequency switching of a switching transistor to convert it to high-frequency power, An input current detector that detects an input current from the AC power source to the inverter circuit and outputs the input current waveform information; and the input current waveform information is set so that instantaneous fluctuation of the input current waveform information is suppressed. A conversion unit that converts the drive signal to the switching transistor of the inverter circuit.

  It is connected between the input current detection unit and the conversion unit, and mixes the input current waveform information and power control information for controlling the current or voltage at an arbitrary position of the inverter circuit to be a predetermined value, A mix circuit for generating an on-voltage signal can be further provided. In this case, the conversion unit converts the on-voltage signal into the drive signal so that a portion where the input current is large has a short on-time and a portion where the input current is small has a long on-time. The mix circuit may be configured to mix the input current waveform information and power control information for controlling the output of the input current detection unit to have a predetermined value to generate an on-voltage signal.

  Preferably, the input current waveform information is directly input to the mix circuit, and the mix circuit inverts the input current waveform information input directly and mixes the input current waveform information with the power control information.

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

  The apparatus may further include a comparison circuit that outputs the power control information in comparison with the input current and the output setting signal.

  Further, the input current detection unit can be configured to detect and output a unidirectional current after rectifying the input current of the inverter circuit. Here, the input current detection unit is provided with a shunt resistor for detecting a unidirectional current after rectifying the input current of the inverter circuit, and an amplifier circuit for amplifying 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 comparison circuit that outputs the power control information by comparing the output obtained by the amplifier circuit with an output setting signal can be further provided.

  Furthermore, the said mix circuit can be equipped with the structure which cuts the high frequency component of the said power control information.

  Further, the mix circuit is controlled between when the input current is controlled to increase (hereinafter referred to as “increase control”) and when it is controlled to decrease (hereinafter referred to as “decrease control”). In this way, the circuit configuration can be switched. In this case, the time constant of the mix circuit increases during the increase control of the input current, and the time constant decreases during the decrease control of the input current.

  In addition, collector voltage control information for controlling the collector voltage of the switching transistor to a predetermined value is input to the mix circuit, and the circuit configuration can be switched according to the magnitude of the collector voltage. In this case, the time constant of the mix circuit increases when the collector voltage is low, and decreases when the collector voltage is high.

  Further, the input current detection unit can be provided with a filter circuit for attenuating high-frequency portions such as a high-order frequency portion and a high-frequency switching frequency of a commercial power supply. Phase lead compensation may be added to the filter circuit.

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

  Furthermore, 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 the input current from the AC power source to the inverter circuit, obtaining the input current waveform information corresponding to the input current, and so as to suppress instantaneous fluctuations of the input current waveform information. Converting input current waveform information into a drive signal for the switching transistor of the inverter circuit.

  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 frequency is converted into the drive signal of the switching transistor of the inverter circuit so that the instantaneous fluctuation is suppressed. . For example, input current waveform information is converted into an on / off drive signal for a switching transistor of an inverter circuit using an on-time modulation method. Therefore, a control loop for correcting the input current by inverting so that the portion where the input current is large is small and the small portion is large is configured. Therefore, even if there are variations in the type of magnetron and its characteristics, ebm (anode-cathode voltage) fluctuations due to magnetron anode temperature and load in the microwave oven, and even power supply voltage fluctuations, these effects The input current waveform shaping that is not subject to this can be obtained with a simpler configuration, and the stable output of the magnetron can be achieved with a simple configuration.

  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. The 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, the resonance circuit 36 including the capacitor 37 and the primary winding 38 of the transformer 41 and the switching transistor 39 convert the high frequency alternating current, and a high frequency high voltage is induced in the secondary winding 43 through the transformer 41.

  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.

  In the present embodiment, the input current waveform information 90 and the power control information 91 from the comparison circuit 74 are mixed by the mix circuit 81 and filtered to output the ON voltage signal 92, and the sawtooth wave generation circuit 83 receives the sawtooth signal. The input current waveform information detection system is simplified by comparing the wave with the PWM comparator 82, performing pulse width modulation, and controlling on / off of the switching transistor 39 of the inverter circuit. 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 it when the input current is small. Therefore, in order to obtain such a waveform, the input current waveform information is 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 two input terminals. The power control information 91 is added to one of them, and the input current waveform information 90 is added to the other, and they are mixed by an internal circuit as shown in the figure. The input current waveform information 90 is input to the mix circuit 81 and inverted by the inverting circuit to become a correction signal.

  Further, as shown in FIG. 4B, a high-frequency cut filter is configured between the power control information 91 and the output as shown in the AC equivalent circuit in the mix circuit 81. As a result, the high-frequency component included in the power control that has interfered with the input current waveform information 90 for shaping the input current waveform is cut by this filter.

  Further, as shown in FIG. 4C, a low frequency cut filter is configured between the input current waveform information 90 and the output as shown by an AC equivalent circuit in the mix circuit 81. 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 is converted into an AC component.

  In the first embodiment, as described above, the input current waveform information is converted into an on / off drive signal for the switching transistor 39 of the inverter circuit and used. In general, inverters used in microwave ovens are well known. 50 to 60 cycles of commercial AC power is rectified and converted to DC, and the converted DC power is converted to high frequency of, for example, about 20 to 50 KHz by the inverter. The converted high frequency is boosted by a step-up transformer, and a high voltage rectified by a voltage doubler rectifier circuit is applied to the magnetron.

  As an inverter circuit system, for example, two switching transistors connected in series such that a commercial power supply is often used in a 230V region or the like are alternately turned on, and the output is changed by controlling the switching frequency (half). Switching is performed using a bridge circuit system and one switching transistor 39 as shown in FIG. 1 of the present invention, FIG. 1 of Patent Document 2, etc., 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 one-stone 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.

  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. 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.

  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. (B) in FIG. 5A is ON voltage information 92 which is a correction output of the mix circuit 81. The ON voltage information 92 changes in magnitude following the input current waveform information 90 and the power control information 91. Further, in order to complement and correct the distortion of the input current, it is output as the inverted waveform of (a).

  (C) in FIG. 5A 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 (2). 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 a correction waveform with respect to the input current waveform information (b), in the portion where the input of the input current waveform information (b) is large (near 90 degrees and 270 degrees), In the part where the ON time is shortened as in the pulse train signal of (D) and the input of the input current waveform information (A) is small (near the zero cross of 0 degrees and 180 degrees), the on time is lengthened and increased ( (B) is the reverse of the inverted output. As a result, an effect of correcting the input waveform can be obtained, but this effect is particularly great in the vicinity of the zero cross.

  The lower waveform (G) shows the ON width of the switching transistor 39, and the input current waveform information of 50 Hz (or 60 Hz) shown in (A) shows the ON voltage information (C) of the corrected waveform obtained by inverting the input current waveform information. By comparing with the high-frequency sawtooth wave of (d), the inverter is converted to a high frequency of 20 KHz to 50 KHz, etc., and the on / off signal of (e) is generated. 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, 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 detection unit, and the subsequent input current waveform information is based on this input current waveform information. Control is made. 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 (power control) by the other means. 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 an ebm (anode-cathode voltage) fluctuation due to the load and a power supply voltage fluctuation, the input current waveform can be shaped 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.

  The subject of the present invention is to convert input current waveform information having this information into a drive signal for a switching transistor of an inverter circuit so that distortion and instantaneous fluctuation of the input current waveform are suppressed. 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. Therefore, the use of the mix circuit 81 and the PWM comparator 82 is merely an example of the embodiment, and what corresponds to the conversion unit that performs the above-described conversion only needs to exist 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 with FIG. 5A when the input current is small. FIG. 5B is the input current waveform information when the input is small. ) Corresponds to (i), (ri) is ON voltage information, (nu) 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.

(Embodiment 2)
Next, a second embodiment of the present invention will be described. The second embodiment of the present invention relates to the configuration of the control circuit. As shown in FIG. 1, the inversion circuit is incorporated in the mix circuit 81 as compared with the conventional example of FIG. Since the rectifier diode 261, the shaping filter 262, the gain variable amplifier 291, the inversion / waveform processing circuit 263, and the waveform error detection circuit 292 in FIG. 10 are omitted, the waveform error detection line is greatly simplified. In addition, practical downsizing of the device configuration is facilitated, the control procedure is simplified, and the processing time can be shortened, leading to improvement in device reliability.

  Here, the input current waveform information 90 and the power control information 91 from the comparison circuit 74 are mixed, filtered, and converted into an on / off drive signal for the switching transistor 39 of the inverter circuit. With this configuration, 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 the control circuit itself is controlled by the mix circuit 81. In particular, the conversion efficiency is maintained as a configuration that does not interfere.

(Embodiment 3)
The third embodiment relates to an input current detection unit. As shown in FIG. 1, the input current detection unit detects an input current of an inverter circuit with a CT 71 or the like, and rectifies and outputs it from a rectification circuit 72. It is comprised as follows. 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.

  Further, the amplifier circuit 85 of the input current detection unit shown in FIG. 2 is configured to attenuate high-frequency portions such as high-order frequency portions of commercial power supplies and high-frequency switching frequencies, thereby preventing unnecessary resonance. Specifically, as shown in the detailed diagram of the input current detection unit in FIG. 3, the amplification circuit 85 uses a high-frequency cut capacitor as shown in FIG. In addition, high-frequency portions such as a 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. The rectifier circuit 72 of FIG. 1 can also use a configuration that attenuates the high-frequency portion or a configuration that adds phase lead compensation to prevent a transient time delay.

(Embodiment 4)
The fourth embodiment relates to the mix circuit 81 shown in FIGS. 1 and 2. As shown in the configuration diagram of the mix circuit shown in FIG. 4A, the mix circuit 81 includes input waveform information 90 and power control. Information 91 is input to each of the two terminals. The input current waveform information 90 is inverted by an inverting circuit for correction output. Both signals 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 output 91 as shown in the equivalent circuit diagram of FIG. With this configuration, the high frequency 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, a low-frequency cut filter is configured for the input current waveform information 90 to perform waveform maintenance.

(Embodiment 5)
In the fifth embodiment of the present invention, as shown in the configuration diagram of the mix circuit according to the fifth embodiment in FIG. 6, the input current waveform information of the input current detector and the output of the input current detector are set to a predetermined value. The characteristic of the mix circuit that synthesizes the power control information to be controlled is controlled with a difference between the input current increase control and the decrease control.

  In the configuration diagram of FIG. 6A, SW1 is turned on / off by the power control information 91, and the ON voltage information 92 is lowered / increased. At the time of input current increase control, 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.

  At the time of input current reduction control, the SW1 is turned on and the ON voltage information is rapidly reduced with the time constant of C * {R1 * R2 / (R1 + R2)} as shown in the equivalent circuit of FIG. Control is performed so that the ON width of the switching transistor is narrowed. 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, as shown in the configuration diagram of the mix circuit according to the sixth embodiment in FIG. 7, the collector voltage control information for controlling the collector voltage of the switching transistor 39 to a predetermined value is stored in the mix circuit. 81.

  As shown in FIG. 7, 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.

  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 power control for high-frequency dielectric heating of the present invention, a control loop is configured that corrects the input current by inverting so that the portion where the input current is large is small and the small portion is large. Therefore, even if there are variations due to magnetron types and characteristics, anode-cathode voltage fluctuations, power supply voltage fluctuations, etc., input current waveform shaping that is not affected by these effects can be obtained with a simpler configuration. Can be achieved with a simple configuration.

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 high frequency dielectric heating power control apparatus which comprised the input current detection part which concerns on Embodiment 3 of this invention with amplifier. FIG. 3 is a circuit diagram showing details of the amplifier circuit shown in FIG. 2. The circuit diagram of the mix circuit which concerns on Embodiment 4 of this invention. The wave form diagram of each part of the power control apparatus for high frequency dielectric heating 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 block diagram of the conventional high frequency heating apparatus. The anode-cathode applied voltage-anode current characteristic view of the high-frequency heating device shown in FIG. The block diagram of the conventional electric power control apparatus for high frequency dielectric heating. FIG. 11 is a configuration diagram of a mix circuit shown in FIG. 10.

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 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 amplification circuit 86 shunt resistor 90 input current Waveform information 91 Power control information 92 ON voltage information 93 Collector voltage control information

Claims (17)

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;
A converter that converts the input current waveform information into a drive signal of a switching transistor of the inverter circuit so that instantaneous fluctuation of the input current waveform information is suppressed;
A power control apparatus for high frequency dielectric heating comprising: A power control apparatus for high frequency dielectric heating according to claim 1,
It is connected between the input current detection unit and the conversion unit, and mixes the input current waveform information and power control information for controlling the current or voltage at an arbitrary position of the inverter circuit to be a predetermined value, A mix circuit for generating an on-voltage signal;
The converter is a high-frequency dielectric heating power control device that converts the on-voltage signal into the drive signal so that a portion with a large input current has a short on-time and a portion with a small input current has a long on-time. . A power control apparatus for high frequency dielectric heating according to claim 2,
The high-frequency dielectric heating power control device, wherein the mix circuit mixes the input current waveform information and power control information for controlling the output of the input current detection unit to have a predetermined value to generate an on-voltage signal. A power control apparatus for high frequency dielectric heating according to claim 2,
The input current waveform information is directly input to the mix circuit, and the mix circuit inverts the input current waveform information input directly and mixes it with 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,
A power control apparatus for high frequency induction heating, further comprising a comparison circuit that outputs the power control information in comparison with the input current and an output setting signal. 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. The power control device for high frequency dielectric heating according to claim 7,
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 mixing circuit is a high-frequency dielectric heating power control device in which a circuit configuration is switched between when the input current is increased and when the input current is decreased. A power control apparatus for high frequency dielectric heating according to claim 10,
The power control apparatus for high frequency dielectric heating, wherein the mix circuit has a time constant that increases when the input current is increased and decreases when the input current is decreased. 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. The power control device for high frequency dielectric heating according to claim 12,
The mix circuit is a high frequency dielectric heating power control apparatus in which a time constant increases when the collector voltage is low and a time constant decreases when the collector voltage is high. 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. The power control device for high frequency dielectric heating according to claim 14,
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 2,
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 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;
Converting the input current waveform information into a drive signal for the switching transistor of the inverter circuit so that instantaneous fluctuation of the input current waveform information is suppressed;
A power control method for high-frequency dielectric heating comprising:

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