JPH0237676B2 - TAKOJUDOKANET SUCHORIKI - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multi-port induction heating cooker, and an object of the present invention is to prevent the generation of noise due to distortion of the driving frequency when adjacent heating ports are operated simultaneously.

In the case of an induction heating cooker having two or more heating ports, if the cooking pots placed in each heating port are made of different materials, the driving frequencies will be different, and as a result, noise will occur due to the frequency difference between the two. The disadvantage was that the user felt uncomfortable.

The present invention has been made to eliminate such drawbacks, and maintains the oscillation frequency of the high-frequency inverter constant regardless of the material of the cooking pot serving as the load, thereby eliminating the frequency difference between adjacent heating ports. . Embodiments of the present invention will be described in detail below based on the drawings.

In FIG. 1, AC is an alternating current power supply, SW is a power switch, DB ₁ is a rectifier circuit, and L ₁ and C ₁ are a coil and a capacitor that constitute a filter circuit. _L2 is an induction heating coil, _L3 is a variable inductor connected in series to the induction heating coil _L2 , and a control coil _L3 is provided which is electromagnetically coupled to this, and the inductance is changed by the current. C ₂
is a resonant capacitor connected in series with the induction heating coil _L2 and variable inductor _L3 , S is a switching element connected in parallel to this capacitor _C2 , such as a GTO gate turn-off thyristor, and D is connected in antiparallel to this GTO S. The above-mentioned parts constitute a high frequency inverter INV. U is a cooking pot made of ferrous metal placed on an induction heating coil, _L2 . CT is
A current transformer that detects the current input to the inverter INV, 300 is a current transformer CT
This is a control circuit that inputs the detection signal of the GTO S and the terminal voltages of the capacitors C ₁ and C ₂ respectively, and outputs the drive signal of the GTO S and the inductance adjustment current of the control coil L ₃ '. With the above configuration, one heating port is formed. The other heating ports have the same configuration as those described above and are connected in parallel to the alternating current power source AC, but are not shown.

FIG. 2 shows the control circuit 300 further divided, 10 is an input power setting circuit that inputs the input current detection signal from the current transformer CT and outputs a comparison signal with a predetermined level, and 11 is an input power setting circuit. 12 is an on-pulse generator that detects the oscillation state of the high-frequency inverter INV and issues an on signal after the GTO S is turned off; 13 is a starting pulse generation circuit that outputs an oscillation starting signal for the high-frequency inverter INV; 14 is an output pulse from the frequency control circuit 11 as a GTO on-pulse, and output pulses from the on-pulse generation circuit 12 and the starting pulse generation circuit 13; This is a waveform shaping circuit that inputs GTO as an on-pulse, and is composed of flip-flops. A gate drive circuit 15 is driven by the output of the waveform shaping circuit 14, and applies an on/off signal to the gate of the GTO S. Reference numeral 16 denotes a frequency holding circuit which inputs a voltage level signal set in the frequency control circuit 11 according to the signal output from the input power setting circuit 10 and causes a current corresponding to the signal to flow through the control coil L ₃ '. So, cooking pot U, induction heating coil
Variable inductor L ₃ is adjusted so that the sum of the inductances of L ₂ and variable inductor L ₃ is constant.

The basic operation of high frequency inverter INV will be explained. The waveform shaping circuit 14 is activated by the activation pulse generated from the activation pulse generation circuit 13 when the inverter INV is started, and by the ON pulse generated from the ON pulse generation circuit 12 when the inverter INV oscillation continues, and the gate drive circuit 15 is activated. and turn on GTO S.
The on period of the GTO S is determined by the input power setting circuit 10 and the frequency control circuit 11, and when the set time arrives, an off pulse is output from the frequency control circuit 11, and the off pulse is output via the waveform shaping circuit 14 to the gate drive circuit 15. to operate off. This results in
GTO S will be turned off. When GTO S is turned off,
Resonance occurs between the induction heating coil _L2 , the variable inductor _L3 and the resonant capacitor _C2 , and the resonant capacitor _C2 is charged and then discharged. The terminal voltage of resonant capacitor _C2 increases as it charges and discharges,
When the falling telegraph drops to near OV, the on-pulse generating circuit 12 operates and outputs an on-pulse. Therefore, after the discharge of capacitor _C2 , when the forward current of diode D has finished flowing, GTO S turns on and the next oscillation cycle begins.

FIG. 3 shows a specific circuit example of the main part of the present invention, and the input power setting circuit 10 is a current transformer.
A rectifier circuit that rectifies the detection signal (alternating current) from the CT,
DB ₂ and a rectifier circuit, including a comparator COM ₁ where the DB ₂ output is applied to the ○- input terminal. A reference level voltage obtained by dividing a constant voltage +Vc.c. by resistors R ₁ and R ₂ is input to the ○+ input terminal of the comparator COM ₁ . Therefore, an "H" level signal is obtained at the output terminal of the comparator COM ₁ when the input detection level is lower than the reference level, and an "L" level signal is obtained in the opposite case.

In the frequency control circuit 11, 17 is a resistor
An integrating circuit consisting of R ₃ , R ₄ and capacitor C ₃ ,
Connected to the output terminal of the comparator COM ₁ through the resistor R ₅ . R ₁₂ and R ₆ are dividing resistors, 18 is an integrating circuit consisting of resistor R ₇ and capacitor C ₄ , and Q ₁ is a capacitor C _4.
The on/off control is performed by the output of the waveform shaping circuit 14, which is a transistor connected in parallel to the waveform shaping circuit 14. COM ₁
is a comparator to which the output of the integrator circuit 18 is applied to the - input terminal, and the output of the integrator circuit 17 is applied via resistors R ₅ and R ₆ , and its output is applied to the waveform shaping circuit 1 in the next stage.
Added to 4.

The frequency holding circuit 16 includes an operational amplifier OP and
A transistor whose current amount is controlled by its output
Including _Q2 . The output voltage of the integrating circuit 17 is applied to the ○+ input terminal of the operational amplifier OP via the resistor _R8 , and the constant voltage +Vc.c. is applied to the ○− input terminal through the resistor.
It is divided into R ₉ , R ₁₀ , and R ₁₁ and applied. A constant voltage +VB is connected to the collector of the transistor _Q2 , and a control coil _L3 ' is connected between the emitter and base.

Next, the operation of the above configuration will be explained. When the on-pulse generation circuit 12 generates an on-pulse, the on-pulse is generated via the waveform shaping circuit 14 and the gate drive circuit 15.
A gate-on signal is applied to GTO S to make it conductive. At this time, the waveform shaping circuit 14 issues a signal to turn off the transistor _Q1 in the frequency control circuit 11, and charging of the capacitor _C4 is started. When this charging voltage becomes equal to or higher than the reference level of the ○+ input terminal, the output of the comparator COM ₁ changes from the "H" level to the "L" level and an off pulse is output.
That is, the ON period of GTO S is determined by the time constant of the integrating circuit 18 and the + side reference level of the comparator _COM1 . In this example, the ○+ side reference level is controlled; if this reference level is high, the on period becomes longer, the inverter oscillation frequency decreases, and therefore the input increases, and conversely, if the reference level is low, the on period becomes shorter. As a result, the oscillation frequency increases and the input decreases. comparator
The ○+ side reference level of COM ₁ is input power setting circuit 1.
It changes depending on the output of 0. That is, if the detection signal level of the current transformer CT is higher than the ○+ side reference level of the comparator COM ₁ , the "H" level period of the output of the comparator COM ₁ becomes longer, and the voltage level of the integrating circuit 17 decreases. On the other hand, if it is lower than the detection signal level, the "H" level period of the comparator COM ₁ output becomes longer and the voltage level of the integrating circuit 17 increases. In this way, the comparator COM ₁ of the frequency control circuit 11
○As the + side reference level rises or falls, the inverter oscillation frequency increases or decreases, and the input changes.

The output voltage of the integrating circuit 17 is applied to the ○+ input terminal of the operational amplifier OP, and is compared with the ○- side reference level, and the difference voltage is amplified. Therefore, when the ○+ side signal level is high, the operational amplifier OP output becomes large, and the transistor _Q2 becomes conductive.
Therefore, a relatively large current flows through the control coil L ₃ ', the inductance of the variable inductor L ₃ becomes small, the total inductance of the induction heating coil L ₂ and the cooking pot U decreases, and the oscillation frequency decreases accordingly. input power decreases. A decrease in input power appears as a decrease in input current, which lowers the output level of the integrating circuit 17. In this way, the oscillation frequency reaches and maintains a constant value. When the output level of the integrating circuit 17 is low, on the contrary, the oscillation frequency is lowered and approaches a constant value.

Figure 4 shows the current i flowing through the control coil L ₃ ′,
The relationship between the inductance l of the variable inductor _L3 is shown.

Normally, the output voltage of the integrating circuit 17 varies depending on the material of the cooking pot, and in the case of an enameled pot, the integrated voltage is high;
It will be lower for a three-layer laminated pot made of stainless steel and iron. This is because the inductance of each type of pot is different, and in this example, we will use a variable inductor to compensate for this difference.
Adjusted at L ₃ , this is set to a constant value regardless of the pot material. In this example, the value of the set frequency is selected to be about 22 KHz, but this value can be set to any value above the audible frequency of 20 KHz.

As explained above, the multi-hole induction heating cooker of the present invention can keep the oscillation frequency constant, and therefore the input constant, regardless of the material of the cooking pot, so that adjacent heating ports can be used at the same time. Even if it is operated, noise due to the difference in both heating frequencies will not be generated.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of an embodiment of the present invention, Fig. 2 is a block diagram showing the control circuit portion, Fig. 3 is a main circuit diagram, and Fig. 4 shows the relationship between the control coil current and the inductance of the variable inductor. FIG. L ₃ ... variable inductor, L ₃ ′ ... control coil,
INV...High frequency inverter, 200...Control circuit, 10...Input power setting circuit, 11...Frequency control circuit, 12...On-pulse generation circuit, 13...
...Starting pulse generation circuit, 14...Waveform shaping circuit,
15... Gate drive circuit, 16... Frequency holding circuit.

Claims (1)

[Claims] 1. A multi-port induction heating cooker equipped with at least two high-frequency inverters each including an induction heating coil, including a variable inductor connected in series to each of the induction heating coils, a control coil for changing the inductance of the variable inductor, and each of the above-mentioned high-frequency inverters. Input current detection means for detecting the input current to the inverter, and frequency holding means for controlling the current flowing through the control coil according to the output of the detection means and keeping the oscillation frequency of each of the high frequency inverters constant. A multi-mouth induction heating cooker featuring: