JP3702131B2 - Induction heating device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an induction heating device, and more particularly to a domestic induction heating device.
[0002]
[Prior art]
The induction heating device supplies a high-frequency current to a heating coil in an inverter, generates a high-frequency alternating magnetic field with the heating coil, and induction-heats an object to be heated that is disposed in proximity to the heating coil.
[0003]
Such an induction heating device includes, for example, a full-wave rectification circuit for full-wave rectification of an AC power supply voltage, an induction heating coil connected to the full-wave rectification circuit, and the like as shown in Japanese Patent Publication No. 6-48636. inverter comprising switching elements for supplying an oscillating current to the induction heating coil - in the induction heating device having a capacitor circuit, and is arranged close to a more induction heating coil to the AC input current inputted to the full-wave rectifier circuit Load discriminating means for discriminating whether or not the load is appropriate.
[0004]
[Problems to be solved by the invention]
However, in such an apparatus, when a metal structure is provided in the vicinity of the heating coil, a load that can be heated (18.8 t1.5, 18.8 t2.0, etc.) and a load that cannot be heated (small items 7 cm, small items 8 cm, etc.) ) Are substantially overlapped (see FIG. 4) and cannot be determined. In addition, if an attempt is made to accurately determine, there is a problem that the input level at the time of detection is limited to the overlapping portion or less.
[0005]
[Means for solving the problems and effects thereof]
According to the first aspect of the present invention, there is provided an inverter comprising a full-wave rectification circuit for full-wave rectification of an AC power supply voltage, an induction heating coil connected to the full-wave rectification circuit, and a switching element for causing an oscillating current to flow through the induction heating coil. An induction heating device comprising:
Input current detection means for detecting the alternating current input to the full-wave rectifier circuit as a voltage value, coil current detection means for detecting the current flowing through the induction heating coil as a voltage value, and an operation for setting the input power Based on a command voltage value to the inverter circuit for adjusting the ON period length of the switching element so that the input power set by the operating means and the voltage value detected by the input current detecting means are equal. Te, and ON or OFF the switching element, a drive circuit for continuing the oscillation of the inverter circuit, a multiplier circuit for multiplying the voltage value detected by the command voltage value and the coil current detecting means, on entry force current detecting means output value and the upper Symbol output value and application of a load disposed in the immediate vicinity of the induction heating coil by comparing the multiplication circuit, to determine unsuitable And load determining means, the is provided.
[0006]
With the above configuration, the determination boundary between the load that can be heated and the load that cannot be heated does not overlap, and the input level can be accurately determined without limitation.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the induction heating apparatus of the present invention will be described below with reference to the drawings.
[0008]
FIG. 1 is a circuit block diagram of an embodiment of the induction heating apparatus according to the present invention. -It is a coil.
[0009]
3 is a filter capacitor connected to the choke coil 2, 4 is an induction heating coil connected to the choke coil 2, 5 is a resonance capacitor that forms a resonance circuit with the induction heating coil 4, and 6 is this resonance capacitor 5. , A switching transistor 7 connected in parallel, and a damper diode 7 connected in reverse parallel to the switching transistor 6. An inverter circuit 8 is formed by these filter capacitors 3 to 7. Yes.
[0010]
Reference numeral 9 denotes a driving circuit that controls the ON / OFF of the switching transistor 6 and supplies a base voltage to the switching transistor 6.
[0011]
Reference numeral 10 denotes an ON pulse generation circuit that compares the voltage across the heating coil 4 to detect the ON timing of the switching transistor 6 and applies an ON pulse to the flip-flop circuit 11. A signal is given to the drive circuit 9 so that the switching transistor 6 is turned on.
[0012]
12 input power detection circuit as an input current detecting means for outputting an input power level corresponding to a first of the input current receiving a signal from the current transformer 13 for detecting an AC input current, 14 operation setting input power The operation means 16 is connected to a second current transformer 17 for detecting the resonance current in the inverter circuit 8 and serves as a coil (vibration) current detection means for outputting a level signal corresponding to the magnitude of the resonance current. resonance current detection circuit, 18 is a level adjusting means for adjusting the magnitude of the level signal from the resonance current detection circuit 16, these operating means 14, the input power detection circuit 12, level from the resonance current detection circuit 16 signal are each a digital de-in a / D converter circuit 19 - data Pref, Power, is converted to iPr.
[0013]
20 is a subtractor that calculates Pref-Power (t) in accordance with the t-th A / D conversion timing in the A / D conversion circuit 19, and 21 is a pre-ON period one time before the Pref-Power (t). An adder which is used as new ON period data Pcon (t) in addition to the data Pcon (t−1) is shown. The ON period data Pcon (t) is stored in the adder 21 via the delay circuit 22. Is given to the input side.
[0014]
The ON period data Pcon (t) is a command voltage value to the inverter circuit .
23 at oscillation initial, on behalf of the Pcon (t-1) from the delay circuit, low-level software Star to the adder 21 - with Dinner - give data Soft Soft Star - shows the door circuit, when the oscillation start The output from the subtracter 20 is cut off, and this Soft is output from the adder 21 as ON period data.
[0015]
Reference numeral 24 denotes a current value setter that generates a set resonance current value Iref that increases in response to the increase in Pref, that is, a setting input in the operation means 14, and 25 denotes a t-th A / D conversion in the A / D conversion circuit 19 A subtractor that sequentially calculates Iref-IpR (t) in accordance with the timing, and 26 is an adder that generates limiting data Ipcon ( t) for limiting the resonance current. once before the restriction de delivered - in data Ipcon (t-1) by adding Ir e f-Ip R (t ) from the subtractor 25 calculates a new Ipcon (t).
[0016]
28 is an ON period counter that starts counting by a signal from the flip-flop circuit 11, 29 is a comparator that compares the count value of the ON period counter 28 and Pcon (t), and 30 is a counter of the ON period counter 28. A comparator that compares the count value with Ipcon (t), and when either of the comparators 29 and 30 is matched, the flip-flop circuit 11 is cleared via the OR gate 31; There is no signal output to the drive circuit 9 and the ON period counter 28.
[0017]
32 is a multiplication circuit that multiplies the data IpR (t) corresponding to the resonance current and the ON period data Pcon (t) and then linearly converts them to calculate the improper load detection level PLS (t). A circuit 33 is a load discriminator serving as a load discriminating means for comparing the PLS (t) with the data Power (t) corresponding to the input power. When Power <PLS, the OR gate 31 is set. Through the flip-flop circuit 11.
[0018]
An overcurrent protection circuit 34 detects whether or not the resonance current detected by the second current transformer 17 exceeds a predetermined value. When an overcurrent is detected, a flip-flop is provided via the OR gate 31. A clear is applied to the circuit 11.
[0019]
In such an induction heating device, when oscillation starts in a state where the cooking pot, which is an object to be heated, is placed close to the induction heating coil 4, a signal is first supplied from the ON pulse generation circuit 10 to the flip-flop circuit 11.
[0020]
The flip-flop circuit 11 gives a signal to the drive circuit 9 and the ON period counter 28, the switching transistor 6 is turned ON, and the counting operation of the ON period counter 28 is started.
[0021]
This count value is compared with Pcon and Ipcon by comparison circuits 29 and 30.
[0022]
In oscillation the initial state, the soft static as described above - DOO circuit low de-level via the adder 21 from 23 - because data Soft are gills given as a Pcon (0) to the comparison circuit 29, ON period When the count value of the counter 28 becomes Soft, the flip-flop circuit 11 is cleared from the comparator 29 via the OR gate, the switching transistor 6 is turned off by the drive circuit 9, and the ON period counter 28 is also turned on. Stop counting and clear its contents.
[0023]
Thereafter, due to resonance in the inverter circuit 8, the collector voltage of the switching transistor 6 rises once and then decreases again.
[0024]
The fall of the collector voltage is detected by the ON pulse generation circuit 10 by reversing the voltage across the heating coil 4, and a signal is given to the flip-flop circuit 11.
[0025]
As a result, a signal is generated again from the flip-flop circuit 11, the switching transistor 6 is turned ON, and the ON period counter 28 starts counting.
[0026]
Such an operation is continued and oscillation of the inverter circuit 8 is continued.
[0027]
Simultaneously with the start of the oscillation, the operation of the A / D conversion circuit 19 is started, and the set input power value in the operation means 14, the level signal from the input power detection circuit 12, and the level signal from the resonance current detection circuit 16 are digital. A / D conversion is performed on the data Pref (t), Power (t), and OPR (t) in a time-sharing manner.
[0028]
Further, such A / D conversion is performed in units of one cycle for each half wave of commercial alternating current.
[0029]
The subtractor 20 calculates Pref-Power (t) from the A / D converted data and sends it to the adder 21. The adder 21 supplies the ON period data immediately before given through the delay circuit 22. Pcon the (t-1) to the Pr e f-Power (t) is added and the new oN time data Pcon (t).
[0030]
That is, the ON period length is adjusted so that the power becomes equal to Pref by sequentially correcting the ON period data.
[0031]
Therefore, after the oscillation starts, this function increases the ON period length of the switching transistor 6 so that Power becomes equal to Pref.
[0032]
Thereafter, the ON period length is maintained.
[0033]
On the other hand, data Iref−IpR (t) obtained by subtracting IpR (t) from Iref generated according to Pref by the subtractor 25 is made in accordance with the operation of the A / D conversion circuit 19 and is given to the adder 26. .
[0034]
The adder 26 forms a new restriction data Ip c on (t) by adding the Iref-IpR (t) to the restriction data Ipcon before once applied through a delay circuit 27 (t-1) .
[0035]
That is, here, the limit data Ipcon is sequentially corrected to adjust the ON period length so that Iref becomes equal to IpR (t).
[0036]
However, when a cooking pot made of a strong magnetic material such as iron or enamel is used, the resonance current in the inverter circuit 8 is smaller than that of the AC input, and the normal ON period data Pcon is used for the switching transistor 6. The ON period length is determined.
[0037]
However, when a stainless steel pot with a weak magnetic material is used, the resonance current in the inverter circuit 8 is relatively larger than that in the above case compared to the AC input power, and the ON period of the switching transistor 6 is determined by the limit data Ipcon. The length is regulated, and the output is substantially controlled by comparing Iref and IpR.
[0038]
The overcurrent protection circuit 34 also detects the overcurrent that flows through the switching transistor 6 when the resonance current in the inverter circuit 8 suddenly increases during such control, or when a coincidence output is not output due to a failure of the comparison circuits 29 and 30. Detecting and clearing the flip-flop circuit 1 turns off the switching transistor 6 to protect it.
[0039]
Further, along with such an oscillation operation, the load discriminator 33 compares the load discriminating levels PLS and Power generated by the arithmetic circuit 32 in proportion to IpR, and discriminates that the load is improper when PLS <Power. Clear circuit 11. In this case, as shown in FIG. 2, accurate discrimination is possible without overlapping the discrimination boundary between a load that can be heated (18.8t1.5, 18.8t2.0, etc.) and a load that cannot be heated (7cm, 8cm, etc.). Can be done.
[0040]
FIG. 3 shows a flowchart of the determination.
[0041]
Step S1 for obtaining a voltage value output I p R (t) (coil current) by the resonance current detecting means 16, step S2 for obtaining a voltage value output Power (t) (input current) by the input power detecting means 12, and Step S3 for obtaining the command voltage value Pcon (t), a step of multiplying the voltage value output I p R (t) of the resonance current detecting means 16 and the command voltage value Pcon (t) (VCO (frequency)). S4 and step S5 in which the result PLS (t) obtained by multiplication and the output voltage value Power (t) of the input power detecting means 12 are compared by the load discriminator 33 based on the comparison table data. application of the load by (step S7), and you determine unsuitable (step S6).
Therefore, when a small load such as a knife or fork is placed close to the induction heating coil or a non-magnetic cooking pan is used and PLS> Power is satisfied, the inverter oscillation is stopped.
[0042]
Furthermore, since the ratio of PLS and Power is substantially constant if the load is the same, the output adjustment in the soft start period overlaps as described above, and the load whose power change with respect to Pref is not linear is appropriate or inappropriate. Even when making a determination, the determination can be made reliably.
[Brief description of the drawings]
FIG. 1 is a circuit block diagram of an induction heating device of the present invention.
FIG. 2 is an input current characteristic diagram.
FIG. 3 is a flowchart of load determination.
FIG. 4 is a conventional input current characteristic diagram.
[Explanation of symbols]
1 Full-wave rectifier circuit
4 Induction heating coil
8 Inverter circuit
12 Input current detection means
16 Coil current detection means
32 Multiplier circuit
33 Load discrimination means

Claims (1)

A full-wave rectifier circuit for full-wave rectification of an AC power supply voltage; and an inverter circuit comprising an induction heating coil connected to the full-wave rectification circuit and a switching element for causing an oscillating current to flow through the induction heating coil. In induction heating equipment,
Input current detection means for detecting the alternating current input to the full-wave rectifier circuit as a voltage value, coil current detection means for detecting the current flowing through the induction heating coil as a voltage value, and an operation for setting the input power Based on a command voltage value to the inverter circuit for adjusting the ON period length of the switching element so that the input power set by the operating means and the voltage value detected by the input current detecting means are equal. Te, and ON or OFF the switching element, a drive circuit for continuing the oscillation of the inverter circuit, a multiplier circuit for multiplying the voltage value detected by the command voltage value and the coil current detecting means, on entry force current detecting means output value and the upper Symbol output value and application of a load disposed in the immediate vicinity of the induction heating coil by comparing the multiplication circuit, to determine unsuitable Induction heating apparatus characterized by comprising a load determination means.

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