JP4114625B2 - Induction heating cooker - Google Patents

Description

  The present invention relates to an induction heating cooker that heats a pan or the like with a magnetic flux of a heating coil by an inverter circuit.

  Conventionally, this type of induction heating cooker detects the envelope voltage of the voltage across the switching element and stops the driving operation of the switching element when the detected voltage is equal to or higher than a predetermined value (for example, a patent) Reference 1).

FIG. 7 shows a conventional induction heating cooker described in Patent Document 1. As shown in FIG. Hereinafter, a conventional example will be described with reference to FIG. The diode bridge 102 is a diode bridge for full-wave rectification of the commercial power supply 101, and the smoothing capacitor 103 is used to smooth the commercial power supply 101 rectified by the diode bridge 102 into a DC power supply. The inverter circuit 104 includes a switching element 107 including a heating coil 105, a resonant capacitor 106, and an IGBT. The drive control means 108 drives and controls the switching element 107, passes a high-frequency current through the heating coil 105, and turns the switching element 107 on and off at a high frequency so as to heat a pan or the like (not shown) as an object to be heated. The voltage detection means 109 detects the voltage across the switching element 107, and the envelope detection means 110 detects the envelope voltage of the voltage detected by the voltage detection means 109. The voltage change amount detection means 111 outputs a signal for stopping the driving of the switching element 107 to the drive control means 108 as soon as the absolute voltage of the voltage across the switching element 107 detects a predetermined value or more.
JP-A-9-260046

However, in the conventional configuration, the absolute voltage of the voltage across the switching element 107 is detected and the driving of the switching element 107 is stopped. After the voltage detection means 109 detects the absolute voltage, the drive control means 108 switches the switch. It takes several tens of microseconds to stop the driving of the element 107, and if the voltage across the switching element 107 jumps up by several hundred volts for each ON / OFF switching of the switching element 107, the response is delayed and switched. in some cases by corrupted broken beyond the breakdown voltage of the device 107.

  An object of the present invention is to provide an induction heating cooker that detects a jump due to a sudden change in the voltage across a switching element and prevents destruction of the switching element.

In order to solve the above-described conventional problems, an induction heating cooker according to the present invention includes a voltage detection unit that detects a voltage across a switching element, and an envelope detection that detects an envelope of a high-frequency voltage detected by the voltage detection unit. and means, the voltage change amount detection means for said envelope detecting means detects the inclination of the voltage detection, the drive control unit, the voltage variation detecting means that the gradient has become a predetermined value or more has been detected In this case, the driving of the switching element is stopped for a first predetermined time .

By detecting the slope of the voltage detected by the envelope detection means, the voltage across the switching element is reduced due to a malfunction of the drive control means due to sudden fluctuations in the power supply voltage at the time of lightning surge, instantaneous power failure, and recovery from power failure, or impulse noise. Destruction caused by a sudden jump can be prevented.

  The induction cooking device of the present invention can prevent destruction of the switching element due to lightning, power failure, etc., which is an abnormality in which a sudden jump in the voltage across the switching element occurs.

The first invention includes a heating coil and an inverter circuit including a resonance capacitor and a switching element, a drive control means for driving and controlling the pre-Symbol switching element turned on and off at a high frequency, the voltage detecting means for detecting the voltage across the switching element If, comprising an envelope detection means for detecting an envelope of the high frequency voltage by the voltage detection unit detects a voltage change amount detection means for detecting an inclination of a voltage the envelope detection unit detects the drive control means , if the slope is the voltage variation detecting unit that becomes a predetermined value or more is detected, before SL by a first predetermined time halting the driving of the switching element, lightning surge or momentary power failure and recovery The voltage at both ends of the switching element jumped up suddenly due to malfunction of the drive control means due to sudden fluctuation of power supply voltage or impulse noise Preparative since the driving of the early detection and the switching element is stopped first predetermined time, it is possible to prevent the breakdown of the switching element.

In the second invention, in particular, when the voltage change amount detecting means detects that the slope of the voltage detected by the envelope detecting means is equal to or greater than a predetermined value , the drive control means controls the driving of the switching element. instead be stopped for a predetermined time, by continuing to reduce the on-time of the switching element to a second predetermined time said first predetermined time, rapid supply voltage during a lightning surge or momentary power failure and recovery It is possible to detect at an early stage that the voltage across the switching element has jumped rapidly due to a malfunction of the drive control means due to fluctuations, impulse noise, etc., and to prevent the switching element from being destroyed. In addition, since the switching element drive is not stopped even when an abnormality is detected, the current flowing in the pan changes abruptly when heating is stopped or when heating is restarted, preventing the occurrence of pan noise caused by the pan vibrating. Heating can be continued at the same time.

  According to the third aspect of the invention, in particular, when the inverter circuit of the first or second aspect is a voltage resonance inverter, a voltage higher than the power supply voltage is normally generated at both ends of the switching element, particularly in the case of the voltage resonance inverter. Therefore, it is easy to become high voltage due to malfunction of the drive control means due to sudden fluctuation of power supply voltage at the time of lightning surge, instantaneous power failure and recovery, impulse noise, etc., but it is early that the voltage at both ends of the switching element jumped suddenly It is possible to prevent the switching element from being broken.

In the fourth aspect of the invention, in particular, since the inclination detection by the voltage change amount detecting means of the first aspect of the invention can be constituted by a differential circuit by using a differential circuit, a simple circuit can be realized without using a digital IC or the like. It can be realized with a configuration.

In particular, the fifth aspect of the invention is that the lower limit of the passband frequency boundary of the differentiation circuit of the fourth invention is the substantially oscillating frequency of the switching element, so that both ends of the switching element respond to a rapid change above the switching element operating frequency. Since the voltage jump is detected, it can be reliably detected.

In the sixth invention, in particular, the voltage change amount detecting means of any one of the first to third inventions detects a voltage difference for each oscillation cycle of the switching element, so that a lightning surge, an instantaneous power failure and When the voltage at both ends of the switching element suddenly jumps up due to a malfunction of the drive control means due to sudden fluctuations in the power supply voltage at the time of return or impulse noise, it can be caught that the switching element has started to jump up abnormally. Abnormalities in the voltage across the terminals can be detected early.

In the seventh aspect of the invention, in particular, since the voltage change amount detecting means of any one of the first to sixth aspects of the invention is provided with a noise filter configuration using an integration circuit, high frequency noise can be cut, so that a simple circuit configuration is provided. It is possible to prevent malfunction due to noise.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a configuration diagram of an induction heating cooker according to the first embodiment of the present invention. This will be described below with reference to FIG.

  The diode bridge 2 performs full-wave rectification of the commercial power source 1, and the smoothing capacitor 3 smoothes the commercial power source 1 rectified by the diode bridge 2 to be a DC power source. The inverter circuit 4 includes a heating coil 5, a resonant capacitor 6, and a switching element 7 made of IGBT or the like. The drive control means 8 drives and controls the switching element 7, passes a high-frequency current through the heating coil 5, and turns the switching element 7 on and off at a high frequency so as to heat a pan or the like (not shown) as an object to be heated. The voltage detection means 9 detects the voltage across the switching element 7. The envelope detector 10 detects an envelope voltage which is the maximum value of one cycle of the high frequency operating frequency of the voltage detected by the voltage detector 9, and is constituted by a peak hold circuit having a transistor emitter follower. The voltage change amount detecting means 11 is configured to detect the inclination by a differentiating circuit 11a comprising a resistor R2, a resistor R3, and a capacitor C2. The capacitance of the capacitor C2 is the emitter of the transistor of the envelope detecting means 10. The value is one digit or more smaller than the capacitance of the peak hold capacitor C1 connected between the terminal and the common potential.

  FIG. 2 is a diagram showing waveforms of main parts of the induction heating cooker configured in FIG. (A) is the voltage Vc across the resonant capacitor 6; (b) is the envelope of the voltage Vce across the switching element 7; (c) is the voltage V1 detected by the envelope detector 10 and the voltage change detection means 11; Is the detected voltage V2. Here, the capacitor C2 can respond to a high frequency change in the potential difference between V1 and V2 by making the capacitance sufficiently smaller than that of the capacitor C1, and when the commercial power source 1 is 60 Hz, the voltage V1 is 120 Hz that is full-wave rectified. A resistor R3 and a capacitor C2 are connected in series with the voltage V2, and the voltage at the connection point is higher than 120 Hz, which is obtained by adding the differentiated value of the voltage V1 to the divided voltage of the resistor R2 and the resistor R3. The waveform is superimposed. The frequency characteristics of the voltage V1 and the voltage V2 are as shown in FIG. The normal drive control means 8 inputs the value of the voltage V1 and controls it so as not to exceed the predetermined voltage, and the voltage change amount detection means 11 compares the voltage V2 with the predetermined voltage Vref1 by the comparator 11b, and the voltage V2 Operates to send a signal to the drive control means 8 when the voltage exceeds the voltage Vref1.

  Here, when the instantaneous power failure start t1 and voltage recovery occur in the commercial power source 1 as in the third cycle of FIG. 2, the voltage Vce jumps rapidly at time t2 with respect to the change in the voltage Vc, and as a result, the voltage V1 When the slope changes and the differentiated value of the voltage V 1 increases, an abnormal jump of the voltage Vce across the switching element 7 is detected, and a signal is sent to the drive control means 8. The drive control means 8 receives the signal from the voltage change amount detection means 11 and stops driving or shortens the ON time of the switching element 7 to a second predetermined time (for example, the ON time is 10 μs), and the first predetermined time (for example, 2 s) In the meantime, the switching element 7 can be prevented from being destroyed by returning to the original on-time. Here, when the drive control unit 8 stops the switching element 7, the electric charge charged in the capacitor C <b> 2 of the voltage change amount detection unit 11 is changed by continuing the stop for a first predetermined time (for example, for 2 s). It can be discharged, and when the switching element 7 is driven again, the voltage and voltage change can be detected accurately. Further, it is considered that the power supply environment or the like that is caused during the first predetermined time stop or during the short on-time is restored. Further, when the ON time of the switching element 7 is shortened, since the heating is continued, the influence on cooking and the like can be reduced, and it is also possible to prevent the occurrence of a pan sound due to sudden heating stop. The detection by the voltage change detection means 11 does not simply detect the absolute voltage of the voltage across the switching element 7, so that an abnormality can be detected earlier. Further, the voltage detecting means 11 can be easily and inexpensively realized by detecting the inclination and using an RC differentiating circuit. Note that the tilt detecting means can use a digital IC, a microcomputer, or the like, or can detect the difference by providing a delay time. Further, the switching element 7 is driven at a frequency of 20 kHz or higher so that the driving frequency is higher than the audible range. As shown in FIG. 3, the lower limit of the pass band frequency boundary of the differentiating circuit, that is, the frequency boundary where a high gain can be obtained. When the oscillation frequency f1 is set, the jump of the voltage across the switching element 7 can be reliably captured.

  In the present embodiment, the jump of the voltage across the switching element 7 at the time of an instantaneous power failure is shown. However, the difference between the voltage across the switching element 7 jumping up similarly when the power supply voltage jumps due to a lightning surge or the like. The same effect can be obtained. The same effect can also be obtained when the voltage across the switching element 7 changes suddenly, such as when the drive control means 8 malfunctions due to impulse noise.

  In this embodiment, the inverter circuit is a monolithic voltage resonance inverter. However, even in a full-bridge or half-bridge inverter, the voltage across the switching element depends on the power supply voltage. The effect is obtained.

  Further, by adding an integration circuit 12 to the input stage of the comparator 11b as shown in FIG. 4 and setting the cut-off frequency to a frequency that is one digit higher than the oscillation frequency of the switching element 7, a simple and inexpensive circuit configuration can be obtained. High frequency noise like impulse noise can be cut to prevent malfunction due to erroneous detection.

(Embodiment 2)
FIG. 5 is a configuration diagram of an induction heating cooker according to the second embodiment of the present invention. In addition, the same number is provided about the structure shown in Embodiment 1, and only a different structure is demonstrated.

  The voltage change amount detection means 11 includes a delay means 11c and a comparator 11d. The voltage change amount detecting means 11 detects the both-end voltage for each oscillation frequency of the switching element 7, holds the both-end voltage before one switching by the delay means 11d, and the current both-end voltage and one-before-switching by the comparator 11d. Voltages at both ends are compared, and a signal is transmitted to the drive control means 8 when the difference is equal to or greater than a predetermined voltage difference. During normal oscillation, the voltage at both ends of the switching element 7 only changes by several tens of V for each switching. However, when the power supply voltage is abnormal such as a lightning surge or instantaneous power failure, it changes every several hundreds V. A signal is sent to the drive control means 8 as an abnormality when the voltage change exceeds the threshold value as the threshold value. The drive control means 8 can prevent the switching element 7 from being destroyed by stopping the driving or shortening the ON time of the switching element 7 in response to the signal from the voltage change detection means 11. Here, when the drive control unit 8 stops the switching element 7, the electric charge charged in the capacitor (not shown) of the detection circuit of the voltage change amount detection unit 11 is discharged by continuing the stop for a predetermined time thereafter. When the switching element 7 is driven again, the voltage and the voltage change can be accurately detected. Further, when the ON time of the switching element 7 is shortened, since heating is continued, the influence on cooking and the like can be reduced, and it is also possible to prevent the occurrence of a pan sound due to sudden stop of heating or restart of heating. The detection by the voltage change detection means 11 does not simply detect the absolute voltage of the voltage across the switching element 7, so that an abnormality can be detected earlier.

  In this embodiment, the inverter circuit is a monolithic voltage resonance inverter. However, even in a full-bridge or half-bridge inverter, the voltage across the switching element depends on the power supply voltage. The effect is obtained.

  Further, as shown in FIG. 6, the integration circuit 12 is added, and the cut-off frequency is set to a frequency larger by one digit or more than the oscillation frequency of the switching element 7, so that a high-frequency noise like an impulse noise with a simple and inexpensive circuit configuration. It is possible to prevent malfunctions due to erroneous detection by cutting.

  As described above, the induction heating cooker according to the present invention can detect a change in the voltage at both ends of the switching element constituting the inverter relatively quickly, and can detect an abnormal jump in the voltage at both ends to prevent destruction. It is possible and can be applied to the induction heating field other than the cooking device.

The block diagram of the induction heating cooking appliance in Embodiment 1 of this invention Same as above, waveform diagram of main part of induction heating cooker Same as above, Frequency characteristics of voltage change detection means Same noise filter configuration diagram The block diagram of the induction heating cooking appliance in Embodiment 2 of this invention Same noise filter configuration diagram Configuration diagram of a conventional induction heating cooker

Explanation of symbols

DESCRIPTION OF SYMBOLS 4 Inverter circuit 5 Heating coil 6 Resonance capacitor 7 Switching element 8 Drive control means 9 Voltage detection means 10 Envelope detection means 11 Voltage change amount detection means 11a Differentiation circuit 12 Integration circuit

Claims (7)

A heating coil and an inverter circuit including a resonance capacitor and a switching element, a drive control means for driving and controlling the pre-Symbol switching element turned on and off at a high frequency, a voltage detecting means for detecting the voltage across the switching element, said voltage detecting means an envelope detection means but of detecting the envelope of the detected high-frequency voltage, and a voltage change amount detection means for detecting an inclination of a voltage the envelope detection unit detects the drive control means, wherein the slope is predetermined when the voltage variation detecting unit that a value or detects, the induction heating cooker of the drive before Symbol switching element that stops the first predetermined time. When driving dynamic control means for voltage variation detecting unit that inclination of the voltage envelope detection unit detects is equal to or larger than a predetermined value is detected, instead causing the driving of the switching element is stopped first predetermined time The induction heating cooker according to claim 1 , wherein the on-time of the switching element is shortened to a second predetermined time and continued for the first predetermined time. The induction heating cooker according to claim 1 or 2, wherein the inverter circuit is a voltage resonance inverter. The induction heating cooker according to claim 1 , wherein voltage gradient detection by the voltage change amount detection means is configured by a differentiation circuit. The induction heating cooker according to claim 4 , wherein the lower limit of the passband frequency boundary of the differentiating circuit is set to the approximate oscillation frequency of the switching element. The induction heating cooker according to any one of claims 1 to 3, wherein the voltage change amount detection means detects a voltage difference for each oscillation cycle of the switching element. The induction heating cooker according to any one of claims 1 to 6 , wherein the voltage change amount detection means has a noise filter configuration by an integration circuit.

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