JP2019040785A - Induction heating apparatus for cooking device - Google Patents

Abstract

To provide a user friendly induction heating apparatus for cooking device without increasing the component tolerance of a switching element, while using a noise prevention capacitor and a noise removable coil of small capacity.SOLUTION: An induction heating apparatus for cooking device includes a rectifier circuit 2 for rectifying an AC power supply into a DC power supply, an inverter 12 for converting the DC power supply into a high frequency current by switching elements, and supplying to a resonance circuit 9 having a heating coil and a resonance capacitor, thus heating a load 8 placed in the vicinity of the heating coil 6, current detection means 14 for detecting the current flowing through the DC power supply, and control means for grasping the output power by processing the current detection means when heating the load, and changing the ON time of the switching elements, where the control means substantially equalizes increment and decrement of the ON time of the switching elements.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an inverter control circuit of an induction heating device for a cooker.

  In recent years, as a method of reducing the electrical noise generated from the inverter of the induction heater, the oscillation frequency of the oscillation means for determining the on / off frequency of the switching element is set to the frequency f0 → f0 + Δf → f0 with the fundamental frequency (f0) as the center. Patent Document 1 discloses an induction heating cooker that reduces a noise component by controlling by changing up and down from −Δf → f0.

JP 2004-55312 A

  In the case of Patent Document 1, the frequency is fluctuated rapidly from f0 + Δf to f0−Δf in the process of changing the frequency up and down from f0 → f0 + Δf → f0−Δf → f0 around the basic frequency (f0). Timing occurs.

  A switching circuit that is turned on and off at high speed based on this frequency is connected to a resonance circuit consisting of a heating coil and a resonance capacitor, and the size, material, and placement of the load (pan) heated by the heating coil. The current that flows depends on the position. Further, the position of the load may always change during cooking, and in that case, the flowing current also changes.

  In such a usage, when the frequency of the switching element that is turned ON / OFF at a high speed overlaps with the movement of the load, the ON / OFF timing of the switching element and the switching Since the loss of the switching element is increased due to a change in the current flowing through the element and the switching element may be damaged, it is expected that the circuit design takes time and the margin of the circuit and parts needs to be increased.

  The present invention has been made to solve the above-described conventional problems, and includes a rectifier circuit that rectifies an AC power source and converts it into a DC power source, a DC coil that converts the DC power source into a high frequency current by a switching element, and a heating coil. An inverter unit for supplying a resonance circuit having a resonance capacitor and heating a load disposed in the vicinity of the heating coil, a current detection means for detecting a current flowing through the DC power supply, and the current when the load is heated Control means for processing the detection means to grasp the output power and changing the ON time of the switching element, and the control means changes the ON time of the switching element substantially the same as the increment and subtraction. It is to make.

  According to the present invention, it is possible to provide an induction heating device for a cooker that is easy to use without specially increasing the component tolerance of a switching element while making a noise prevention capacitor and a noise removal coil small in capacity.

It is a circuit block diagram of the inverter control circuit which shows one example of the prior art and the present invention. It is the figure which showed the current voltage waveform of the switching element 10 in this invention.

  Hereinafter, an embodiment of the present invention will be described in detail using a jar rice cooker as an example with reference to the drawings.

  FIG. 1 is a circuit block diagram of an embodiment of an inverter control circuit of the induction heating apparatus of the present invention.

  In the figure, reference numeral 1 denotes an AC commercial power source. Reference numeral 2 denotes a rectifier circuit, which is composed of a plurality of rectifiers. The input is connected to an AC commercial power source 1, and the AC power supplied from the commercial power source 1 is rectified and converted into a DC power source for output. One end of the choke coil 3 is connected to the plus terminal of the rectifier circuit 2 via the current detection means 14, the other end is connected to one end (high voltage side terminal) of the smoothing capacitor 4, and the other end of the smoothing capacitor 4 is grounded. . A smoothing circuit 5 is formed by the choke coil 3 and the smoothing capacitor 4 and smoothes the DC power output from the rectifier circuit 2.

  A heating coil 6 is connected in parallel to the resonance capacitor 7, and one end thereof is connected to the high-voltage side terminal of the smoothing capacitor 4. Reference numeral 8 denotes an inner pot (load) of the IH jar rice cooker, which is disposed near the heating coil 6 and is induction-heated by the magnetic flux generated by the heating coil 6. A resonance circuit 9 includes a heating coil 6, a resonance capacitor 7, and an inner hook 8.

  Reference numeral 10 denotes a switching element. The collector terminal is connected to one end different from the connection point of the heating coil 6 with the smoothing circuit 5, the emitter terminal is grounded, and high-frequency switching is performed in the resonance circuit 9, that is, the heating coil 6. It is what flows.

  A diode 11 has a cathode terminal and an anode terminal connected to a collector terminal and an emitter terminal of the switching element 10, respectively. Reference numeral 12 denotes an inverter unit, which is formed of a switching element 10 and a diode 11.

  Reference numeral 13 denotes a drive circuit whose output is connected to the base terminal of the switching element 10 and converts the input signal into a driving voltage suitable for driving to drive the switching element 10.

  Reference numeral 18 denotes a microcomputer, and an output terminal OUT1 outputs a pulse signal for setting power and is connected to the drive circuit 13. The input terminal IN1 is connected to the current detection means 14 described later, the input terminal IN2 is connected to the voltage detection means 15 described later, the input terminal IN3 is connected to the power supply frequency detection means 16 described later, and the input terminal IN4 is the output terminal of the trigger circuit 17. Connected to. The microcomputer 18 has a plurality of heating modes.

  Reference numeral 15 denotes voltage detection means for detecting the voltage of the commercial power source 1. In addition, it is possible to detect an arbitrary voltage within a one-cycle waveform obtained by rectifying the commercial power supply. Reference numeral 16 denotes a power supply frequency detection means which can detect a power supply waveform 0V and detect the frequency of the commercial power supply. Reference numeral 14 denotes current detection means. The detection unit is connected between the power source 1 and the rectifier circuit 2, the output unit is connected to the input terminal IN1 of the microcomputer 18, and the microcomputer 18 detects the current flowing through the heating coil 6. The microcomputer 18 grasps the output power of the inverter unit 12 and detects the inner hook 8 from this current value.

  Next, the operation for heating the inner pot 8 will be described. First, the state of the circuit and the operation of the microcomputer 18 before the start of heating will be described. An AC power source is supplied from the commercial power source 1 to the rectifier circuit 2, rectified by the rectifier circuit 2, smoothed by the smoothing circuit 5, and converted into a DC power source.

  This DC power source is in a ready state to supply current to the resonance circuit 9 and the switching element 10 in the inverter unit 12 connected to the inner pot 8 selected by the microcomputer 18 when the resonance circuit 9 is driven. . The microcomputer 18 is energized and stands by without outputting an active signal from the output terminal OUT1 until a heating start signal from a user (not shown) is input.

  When the user's heating start signal is input to the microcomputer 18, the microcomputer 18 understands that fact and starts the heating operation as follows. In response to the heating start signal, the microcomputer 18 outputs a power setting pulse signal suitable for the inner pot 8 from the output terminal OUT1, and this signal is transmitted to the base of the switching element 10 in the inverter unit 12 via the drive circuit 13. Then, the switching element 10 is driven. When the switching element 10 is driven, a current is supplied from the DC power source to the resonance circuit 9 and a current starts to flow through the heating coil 6 and the switching element 10.

  A current flows through the switching element 10 only during the ON time of a predetermined pulse signal output from the output terminal OUT1 of the microcomputer 18, and the pulse signal is generated between the collector terminal and the emitter terminal of the switching element 10 after being turned OFF. The trigger circuit 17 that detects the voltage, that is, the resonance voltage of 0 V, starts operating, and its output is transmitted to the input terminal IN 4 of the microcomputer 18.

  When the signal of the trigger circuit 17 is transmitted to the microcomputer 18, the microcomputer 18 outputs a pulse signal from the output terminal OUT1 at a frequency synchronized with the signal. Thereafter, the signal is transmitted in a loop from the output terminal OUT1 of the microcomputer 18, the drive circuit 13, the switching element 10, the trigger circuit 17, the input terminal IN4 of the microcomputer 18, and so on. Thereby, since the switching element 10 is periodically driven at the ON timing by the microcomputer 18, the high-frequency current continuously flows through the heating coil 6, and the inner pot 8 is heated.

  The current detection means 14 detects the current flowing through the DC power supply in response to the high-frequency current and inputs it to the input terminal IN1 of the microcomputer 18. The microcomputer 18 appropriately processes the input primary current to output power. To understand.

  FIG. 2 shows a voltage / current waveform of the switching element 10 when the resonance circuit 9 is driven at a high frequency. The ON time t of the switching element 10 is determined by the ON time of a predetermined pulse signal output from the output terminal OUT1 of the microcomputer 18. Assuming that a half-wave waveform obtained by rectifying the commercial power supply 1 by the rectifier circuit 2 is one cycle, the ON time t of the switching element 10 is a fixed value within the above-described one cycle. In this case, since the fundamental wave has one fixed frequency, the noise generated from the device has a large value.

  Therefore, as shown in FIG. 2, when the ON time of the switching element 10 is changed, the increment and decrement are made substantially the same, so that a large change in the ON time is not caused by one increase or decrease of the ON time. By repeating t, t + x1, t + x2, t + x1, t, t-x1, t-x2, t-x1, t,..., The frequency of the fundamental wave is changed and plural noises are emitted from the device. It becomes possible to disperse for each frequency, and the maximum value of noise can be suppressed, and a noise prevention capacitor and a noise removal coil can be made small and inexpensive. In addition, when applied to an induction heating cooker, the frequency change timing of the switching element 10 that is turned on and off is reduced by reducing the change in the frequency and thereby reducing the change in the current flowing through the switching element 10. When the movement of the load (pan) during cooking overlaps, the margin for loss of the switching element 10 is maintained.

  Although the above description was performed by the IH type jar rice cooker, the induction cooking device which heats the inner pot 8 as a general pot may be used. The microcomputer 18 may be a control means 18 that performs an equivalent operation.

  DESCRIPTION OF SYMBOLS 1 ... Commercial power supply, 2 ... Rectifier circuit, 3 ... Choke coil, 4 ... Smoothing capacitor, 5 ... Smoothing circuit, 6 ... Heating coil, 7 ... Resonance capacitor, 8 ... Inner hook, 9 ... Resonant circuit, 10 ... Switching element, 11 ... Diode, 12 ... Inverter part, 13 ... Drive circuit, 14 ... Current detection means, 15 ..Voltage detection means, 16 ... power supply frequency detection means, 17 ... trigger circuit, 18 ... microcomputer

Claims (1)

A rectifier circuit that rectifies an AC power supply and converts it to a DC power supply;
The DC power supply is converted into a high-frequency current by a switching element and supplied to a resonance circuit having a heating coil and a resonance capacitor,
An inverter unit for heating a load disposed in the vicinity of the heating coil;
Current detection means for detecting a current flowing through the DC power supply;
A control means for processing the current detection means to grasp output power when heating the load, and changing an ON time of the switching element;
The induction heating device for a cooking appliance, wherein the control means changes the ON time of the switching element so that an increment and a subtraction are substantially the same.

Images