JPS6039999Y2 - induction heating cooker - Google Patents

Description

[Detailed description of the invention] The present invention relates to a power control method for a power conversion circuit for an induction heating cooker. Conventionally, there was a method of controlling the power by changing the output frequency, but due to limitations due to the performance of power semiconductor elements and Due to restrictions such as the need for ultra-audible frequencies, it is practically possible to use only a narrow frequency range, making it difficult to obtain a sufficient range of output variation.

Therefore, in order to improve the above-mentioned conventional drawbacks, the present invention attempts to obtain a sufficient output variation range by controlling the current flowing directly to the heating coil using a saturable reactor.

An embodiment of the present invention will be described below with reference to the accompanying drawings.

In FIG. 1, 1 is a commercial power source, 2 is a power conversion circuit for converting the commercial power frequency to an ultrasonic frequency, 3 is a heating coil composed of a Litz wire, and 4 is a pot 5.
The top plate is made of a non-metallic, non-magnetic material, such as a ceramic plate, on which the top plate is placed.

By passing the ultrasonic frequency current obtained by the power conversion circuit 2 through the heating coil 3, a high frequency magnetic field indicated by the dotted line is generated, and an eddy current as shown by the arrow flows in the bottom of the pot 5.

After all, the pot is heated by Joule heat.

In FIG. 2, a commercial power source 1 is full-wave rectified by a full-wave rectifier 7, and is added to a series circuit of a current-limiting inductor 6, a high-frequency thyristor B, and a high-speed diode 9 connected in antiparallel.

゛The series resonant circuit of the commutating capacitor 11 and the variable inductance commutating inductor 10' is connected to the high frequency thyristor 8.
are connected in parallel.

Furthermore, a filter capacitor 12 and a saturable accumulator 13 are provided.
The series connection body consisting of the heating coil 3 and the commutation capacitor 1
1 in parallel.

These commutating inductor 10', commutating capacitor 11, filter capacitor 12, saturable reactor 13
, a resonant circuit constituted by the heating coil 3 serves as a commutation circuit for the high-speed thyristor 8.

Further, in order to create a DC power supply for the control circuit using the diode 200 and the capacitor 201, this series connection body is connected in parallel to the DC side of the full-wave rectifier 7.

A stabilized power supply circuit 105 for the control circuit uses the capacitor 201 as a power supply.

The stabilized power supply circuit 105 is generally known, and includes a fixed resistor 202, an NPN transistor 203,
A regulated output voltage is obtained between the emitter of NPN transistor 203 and line 99, consisting of a Zener diode 204.

The zero volt pulse generation circuit 101 includes voltage dividing resistors 205, 2
07 is connected in parallel to the DC side of the full-wave rectifier 7, that is, to the unfiltered full-wave rectified power supply, the base is connected to the midpoint of the voltage dividing resistor, the emitter is connected to the line 99 side, and the collector is connected to the stabilized power supply via the resistor 206. (NPN) transistor connected to it.

Therefore, when the voltage across lines 98-99 approaches zero,
That is, only at zero volts of the power supply voltage, the transistor 208 becomes O.
It becomes FF, and a zero volt pulse appears on its collector.

The delay circuit 102 connects a series circuit of a fixed resistor 209 and a capacitor 210 to a stabilized power supply, and utilizes the delay time until the terminal voltage of the capacitor 210 reaches a predetermined value due to the charging time constant of the capacitor 210 when the power is turned on. are doing.

103 indicates a DFF, and its truth table (truthta)
ble) is as described above.

That is, by inputting the rising pulse from the zero volt generation circuit 101 to the CK terminal, the voltage from tn to tn+□
Therefore, if the D terminal is 0, the Q terminal will remain 0 no matter how many pulses are input to the CK terminal.
When l is input to the D terminal, the Q terminal outputs 1 at the rising edge of the pulse input to the CK terminal.

Therefore, the output of the zero volt pulse generation circuit 101, that is, the output synchronized with the zero volt of the power supply and delayed by the delay circuit 102, is obtained as the output of the DFF 103.

The gate pulse generation circuit 106 consists of a pulse signal generation circuit using an operational amplifier 217 and a pulse signal amplification circuit formed from a transistor 218 and a resistor 219.

The pulse signal generation circuit includes a resistor 215, a variable resistor 211, a capacitor 212, reference value setting resistors 213 and 214, a feedback resistor 216, and an operational amplifier 217, which are pulse interval setting elements.

The above zero volt generation circuit 101, delay circuit 11102 and DF
A control circuit is composed of the F I Q 3 and the gate pulse generation circuit, and controls the firing of the high frequency thyristor, which is a semiconductor switch.

The reference voltage correction circuit 108 corrects the set value of the power setting circuit 111 so that even if the commercial power supply 1 becomes abnormally high due to voltage fluctuation, the input power does not exceed a predetermined input power.

It is composed of voltage dividing resistors 226 and 227 and a Zener diode 228 connected in parallel with one fixed resistor 227, and a correction reference voltage power source appears between the terminals of the Zener diode 228.

Therefore, until the power supply voltage reaches the zener voltage of the zener diode 228, a reference voltage power supply for power setting proportional to the power supply voltage is obtained, but once the power supply voltage reaches a predetermined level or higher, the power remains constant. Serves as reference voltage power supply for setting.

In the power setting circuit 111, a series connection body of a power setting variable resistor 233 and a resistor 234 is connected to a power setting reference voltage power source.

Note that the power setting variable resistor 233 is connected to a user drive means that allows the user to directly adjust the power setting variable resistor 233.

The voltage obtained by this power setting circuit 111 serves as a reference voltage for the power control comparison amplifier 114.

The input current detection means 117 which is the second detection means and the first
The heating coil current detection means 116, which is the detection means of the heating coil current detection means 116, generates a voltage substantially proportional to the input current of the inverter and the heating coil current, respectively.

The diodes 238 and 237 are connected bodies forming a judgment circuit for giving priority to the higher signal, and are connected to the signal input terminals of the respective comparators 112, 113, and 114 via the diodes 238 and 237. It is connected.

Generally speaking, if current is passed through the heating coil 3 under a standard load, the input current will be larger than the heating coil current, but in the case of an abnormal load, the heating coil current will be larger than the input current, so only the input current will be detected. If the heating coil current is controlled by the heating coil 3, there is a risk that a large current will flow through the heating coil 3 at the time of abnormal load.

Therefore, it is necessary to compare the input current and the heating coil current and control the heating coil current according to the larger current value.

The power comparison amplifier 114, which is a comparator, generates an output according to the difference between the reference input terminal and the signal input terminal.The power comparison amplifier 114 generates an output according to the difference between the reference input terminal and the signal input terminal. Since the heating coil current flowing through the controlled winding whose impedance changes according to the current value can be controlled, the heating coil current can be maintained at a desired value determined by the current setting resistor 233 that determines the output of the power comparison amplifier 114. It is something.

The soft start circuit 107 is an input current detector 1 at startup.
17 and the heating coil current detector 116, an excessive control current flows through the control winding of the saturable reactor 13, and this circuit prevents an excessive heating coil current from flowing.

That is, at startup, even if the output of the power comparison amplifier 114 is output,
By selecting the time constants of the resistors 223, 225 and the capacitor 222 to desired values, a shunt type is formed, and no current flows through the control winding of the saturable reactor 13.

After a predetermined period of time, the output of the power comparison amplifier 114 is caused to flow to the control winding, depending on the above-mentioned time constant.

Diode 224 is connected to prevent charging of capacitor 222 when lowering the power setting.

The second level setting circuit 110 is used to prevent small items such as forks and spoons from being heated when placed carelessly on the heating coil, and stops oscillation when the heating coil current is below a first level. It is something.

The second level setting circuit is controlled by voltage dividing resistors 231 and 232, and the reference voltage power source is taken from the power setting reference voltage, and the second level setting reference voltage slides and changes according to the power setting value corrected by the input voltage. The output is connected to the reference input terminal of the first rubel comparator 113.

The signal input terminal of the first level comparator 113 is as described above.
Input current detector 117 and heating coil current detector 116
connected to the output of

The output generated according to the difference between the reference input terminal voltage and the signal input terminal voltage of the No. 1 Lebel comparator 113 is the output of the small delay circuit 1
Added to 15.

The small object delay circuit 115 is composed of a capacitor 236 and a transistor 235, and inhibits the small object detection function for a certain period of time when activated.

Note that it is connected to the gate pulse generator 106 via a diode 221 in order to stop the oscillation operation based on the second level detection signal and a second level detection signal to be described later.

The second level setting circuit 112 is a level setting circuit that attempts to stop oscillation especially when a load that causes excessive current flows is placed, and is a level setting circuit that attempts to stop oscillation.
, 230 are connected.

The output of this second level setting circuit is connected to the reference input terminal of the second level comparator amplifier 112.

The outputs of the heating coil current detector 116 and the input current detector 117 are connected to the signal input terminal of the second level comparison amplifier 112, and the output is determined according to the difference between the reference input terminal voltage and the signal input terminal voltage. , a diode 221 similar to the first rubel output signal to stop the oscillation.
is connected to the gate pulse generator 106 via.

FIG. 3 shows a specific example of means for detecting the input power to the heating coil instead of detecting the heating coil current, and the heating power detecting means 116 attempts to detect the difference between the high frequency thyristor current and the feedback diode current. It is something to do.

It is detected by CT (Current Transformer), and windings 249 and 250 are wound around a ferrite ring core 248 with good high frequency characteristics.

Resistors 240 and 241 are resistors for generating magnetic flux in the opposite direction in the magnetic core material to eliminate saturation of the core.

Rectified by diodes 244 and 245, and capacitor 2
42 and 243, and voltages proportional to the high frequency thyristor current 8 and the current of the feedback diode 9 appear across the resistors 246 and 247, respectively.

Therefore, the difference in current can be extracted between the cathode terminals of the diode 244 and the diode 245, and as a result, a voltage proportional to the power consumed by the heating coil can be extracted.

Even if this value is used instead of the control using the heating coil current, the heating power can be kept constant and good performance can be obtained.

FIG. 4 shows a specific example in which a heating coil voltage detection means 118 is used instead of detecting the heating coil current.
The voltage is obtained by dividing the voltage using voltage dividing resistors 251 and 252.

This method has the advantage of being very inexpensive.

5 to 8 show specific configuration examples of the saturable reactor 13.

Since a large high-frequency current flows through the controlled winding, the core constituting the magnetic circuit through which the high-frequency magnetic flux flows is made of a material substantially free from eddy current loss and hysteresis loss, such as a ferrite core.

In FIG. 5, it has a control winding terminal 50, and a core 5.
A control current is passed through the control winding 51 wound around the coil 6.

A controlled current, for example a heating coil current, is applied to a winding having a controlled winding terminal 52 and having controlled windings 53 and 54 wound around both legs of the U core 57 so that the respective magnetic fluxes are in the same direction. be swept away.

(2) The core 56 is configured to form a closed magnetic circuit with the U core 57 and I core 56.

The magnetic flux φC9φB generated by the controlled winding 53.54 is I
completely canceled at core 56 and control winding terminal 50
The structure is such that no voltage is generated due to the controlled winding current.

The degree of saturation of the controlled winding is changed by the magnetic flux φA caused by the control current, thereby varying the controlled winding current.

Note that gaps 58, 59 are provided in the magnetic circuit to prevent excessive saturation due to the controlled current itself.

In order to prevent voltage from being induced in the control winding 51 due to unbalance of the controlled windings 53 and 54, the present invention makes the central I core 56 movable in the direction of the arrow, and eliminates the variation in the conventional controlled coils. This correction was previously performed by adjusting the number of turns of the coil, etc., but now the correction is performed by fixing it at a position where no voltage is induced.

FIG. 6 shows another configuration example for the same purpose as FIG. 5, in which U core 57 and I core 55 in FIG.
The core 57.55 is used, and the operation is exactly the same as described above.

FIG. 7 shows a specific configuration example in which the controlled windings 53, 54 and the control winding 51 are wound around the E core 57, and the {circle around (2)} core 55 is arranged to form a closed magnetic circuit.

The magnetic spacer 60 is inserted to ensure the gap 58, 59, which makes it possible to use an E core with equal leg lengths and good mass production.

FIG. 8 is a further improvement of FIG. 7, with spacer 61
is used as a support plate, and holes are made at the positions of gaps 58 and 59.

Of course, the spacer 61 is cut out from the magnetic plate.

As described above, according to the present invention, since a saturable reactor is provided in the resonant circuit, by changing the impedance of this saturable reactor, the range of change in input power can be changed even when the firing frequency of the semiconductor switch remains constant. It can hold up well.

Further, a second detection means for detecting the input current and a first detection means for detecting the heating coil current or voltage are provided, and a determination circuit is provided for transmitting the higher output of these detection means to the comparator with priority. Because of this configuration, there is no risk of excessive current flowing through the induction heating coil even during abnormal loads, and input power can be accurately controlled during normal loads.

Furthermore, in the embodiment, the second level setting circuit can prevent small items such as forks and spoons from being heated, and the second level setting circuit can reliably stop oscillation when a load through which an excessive current flows is placed.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a pot mounting part of an induction heating device showing an embodiment of the present invention, Fig. 2 is a circuit diagram of an inverter having a control circuit constructed from the main elements of the present invention, and Fig. 3 is a power supply 4 is a circuit diagram of a means for detecting the difference between the semiconductor switching element current and the feedback diode current, FIG. 4 is a circuit diagram of the means for detecting the voltage between terminals of the heating coil, and FIG. 5 is a diagram showing the specific configuration of the saturable reactor. FIG. 6 is a diagram showing a modification of the specific structure of the saturable reactor, FIG. 7 is a diagram showing still another modification, and FIG. 8 is a diagram showing still another modification. 1... Commercial power supply, 2... Power conversion circuit, 3... Heating coil, Thyristor, 10... Commutation inductor, 13...
Saturable reactor.

Claims (1)

[Scope of utility model registration request] A semiconductor switch comprising a rectifier circuit for rectifying a commercial power supply, a resonant circuit having a saturable reactor consisting of an induction heating coil, a control winding, and a controlled winding, and for turning on and off the resonant circuit; A first detection means that includes a control circuit for controlling on and off and detects the current or voltage flowing through the heating coil;
a determination circuit that outputs the larger output signal from the first detection means and the second detection means; and an input of the rectification circuit. An induction heating cooker provided with a comparator that compares the output with a power setting circuit that sets the electric power and controls the current flowing through the control winding of the saturable reactor.