JPS6137746B2 - - 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 a difference in drive frequency when adjacent heating ports are operated simultaneously.

For induction heating cookers that have two or more heating ports, if the cooking pots placed in each heating port are made of different materials, each drive frequency will be different, and noise will be generated due to the frequency difference, which may cause problems for the user. The disadvantage was that it made people feel uncomfortable.

The present invention has been made to solve these problems, and will be described below with reference to embodiments.

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 filter coil and a filter capacitor. L ₂ is an induction heating coil, C ₂ is a resonant capacitor connected in series to this induction heating coil L ₂ , 1 is a DTO (gate turn-off thyristor) connected in parallel to this capacitor C ₂ , and D ₁ is connected to this GTO 1. The high frequency inverter 2 is composed of the above-mentioned parts. 3 is a cooking pot made of ferrous metal placed on the induction heating coil _L1 . CT ₁ is a current transformer that detects the input current, CT ₂ is a current transformer that detects the peak current of the high frequency inverter 2, and 200 is the detection signal of each of the current transformers CT ₁ and CT ₂ and the capacitors C ₁ and C _2. This is a control circuit that controls oscillation of the high frequency inverter 2 by inputting terminal voltages respectively.

FIG. 2 shows this control circuit 200 further divided into smaller parts, and 10 is an input power setting circuit that inputs the input current detection signal from the current transformer CT ₁ , compares it with a predetermined input, and adjusts it; 11 is an Ip compensation circuit that determines the peak value Ip of the current flowing through the high-frequency inverter 2; 12 is an Ip compensation circuit after GTO1 is turned off;
An on-pulse generation circuit detects the oscillation state of the inverter 2 and issues an on-signal; 13 is a starting pulse generation circuit that outputs an oscillation start signal for the inverter 2; 14 is a waveform inputting the signals output from each of the above circuits; A shaping circuit 15 is a waveform shaping circuit 14
A gate drive circuit driven by the output of
Turn on and off the gate of GTO1. One heating port is formed with the above-described configuration. The other heating ports have the same configuration as above and are connected in parallel to the alternating current power source AC. Note that only one heating port is shown in the figure.

The operation of such a configuration will be explained. The waveform shaping circuit 14, specifically the flip-flop, is activated by the activation pulse when the inverter is started, and by the on-pulse when the inverter continues to oscillate, operating the gate drive circuit 15 and turning on the GTO1.
The on period of the GTO 1 is determined by the input power setting circuit 10, and when the set time arrives, an off pulse is output from the input power setting circuit 10 and applied to the gate drive circuit 15 via the waveform shaping circuit 14. This turns GTO1 off. G.T.O.
1 is turned off, resonance occurs between the induction heating coil L ₂ and the resonant capacitor C ₂ , and the capacitor C ₂ is charged and then discharged. The voltage at the _two terminals of capacitor C rises and falls with the above charging and discharging. When this falling potential drops to around OV, the on-pulse generating circuit 12 operates and outputs an on-pulse.
Therefore, once the forward current has finished flowing through the diode _D1 after discharging the capacitor _C2 , the GTO1 is turned on and the next oscillation cycle begins.

The present invention is a cooking appliance having such an oscillation function, in which the inverter oscillation frequency defined by the input power setting circuit 10 is kept approximately constant, in fact within a range of about 2 KHz. That is, in this example, the maximum frequency value is 25.6KHz, and the minimum frequency value is 25.6KHz.
It is set to 23.2KHz. The frequency difference is about 2KHz,
To heat pots made of different materials and obtain a constant input, the frequency must be varied. Generally speaking, if you want to accurately obtain an input of 1300W, for example, you have to change the frequency in the range of about 20KHz to 27KHz, but if one heating port is 20KHz and the other is 27KHz, there is a difference. 7KHz causes quite a lot of noise. Therefore, in this example, we have decided to allow an input difference of about 10% around a range that is acceptable as a practically constant input, for example 1300W, and have set a frequency from 23.2KHz to 25.6KHz that corresponds to this range. It is something.

Even if the p-compensation circuit 11 is oscillating within the above frequency range, there is a risk that the peak current p flowing to the inverter may exceed the rated current of the GTO 1 in a special pot where the input is easy to enter. Therefore, it was designed to prevent this,
When such a situation occurs, the oscillation frequency is increased and the peak current p is reduced. The frequency upper limit set by this p compensation circuit 11 is 25.6KHz, which is set by the above-mentioned input power setting circuit 10.
matches.

FIG. 3 shows a specific circuit example of the input power setting circuit 10 and the p-compensation circuit 11. In the input power setting circuit 10, DB ₂ is a rectifier circuit, COM ₁ is a comparison circuit that inputs the output of the rectifier circuit DB ₂ to the input terminal,
A reference level voltage obtained by dividing the constant voltage Vcc is input to the input terminal. 16 is an integrating circuit consisting of resistors R ₁ and R ₂ and a capacitor C ₃ , and is connected to the output terminal of the comparator COM ₁ via the resistor R ₃ . _R4 , _R5
is a dividing resistor, 17 is an integrating circuit consisting of a resistor R ₆ and a capacitor C ₄ , Q is a transistor connected in parallel to the capacitor C ₄ , and COM ₂ is an integrating circuit 11
The output of the integrating circuit 16 is input to the input terminal through the dividing resistors R ₄ and R ₅ , and the output is input to the waveform shaping circuit 14 consisting of a flip-flop in the next stage. It will be done.

In the p compensation circuit 11, R ₇ is a resistor that converts the detected current into a voltage signal, and C ₅ and R ₈ are C
The capacitor and resistor forming the coupling circuit function to match the phase of the voltage signal with the AC power supply voltage phase. D ₂ is a backflow prevention diode, R ₉ , R ₁₀
is a dividing resistor, COM ₃ is a comparator, and the pulsating voltage obtained at the terminal 110a is divided by the resistors R ₁₁ and R ₁₂ and applied to the input terminal.The input terminal receives the detection signal of the current transformer CT _2. is input, and its output is input to the waveform shaping circuit 14.

Next, the operation will be explained. Input power setting circuit 10
generates an off pulse for GTO1, and when GTO1 is turned on by the on pulse, transistor Q is turned off by the output of the waveform shaping circuit 14, and charging of capacitor _C4 is started. When this charging voltage reaches or exceeds the input terminal level, the comparator COM ₂ output changes from “H” level to “L” level.
level, and an off pulse is output. Therefore, the ON period of GTO1 is determined by the time constant of the integrating circuit 17 and the side reference level of the comparator _COM2 . In this example, the side reference level is controlled, and if this reference level is high, the on period will be longer and the inverter oscillation frequency will be lowered, so the input will increase, and conversely, if the reference level is low, the on period will be shorter and the inverter will oscillate. The frequency increases and therefore the input decreases. The reference level is changed by changing the time constant of the integrating circuit 16. That is, when the input current detected by the current transformer CT ₁ is higher than a certain level, the output of the comparator COM ₁ is "L", and therefore the resistor R ₃ is added to the capacitor C ₃ forming the integrating circuit 16. As a result, the reference level falls and the frequency rises. On the other hand, when the detected current is lower than a certain level, the comparator COM ₁ output is “H”
Therefore, the time constant of the integrating circuit 16 does not change. In this way, the maximum frequency
25.6KHz and minimum frequency 23.2KHz are set.
During this frequency range, the comparator COM ₁ output is “H”
and the reference level changes according to the “L” period ratio,
Input power is set.

Cooking pots with a three-layer structure of 18-8 stainless steel-iron-18-8 stainless steel or aluminum-iron-aluminum allow input to easily enter, resulting in a large input current, and therefore the "L" of the comparator COM ₁ output. ``The period will be longer. From this point on, the frequency increases and the input decreases. At this time, the frequency is 25.6KHz and the input power is approximately 1430W. On the other hand, a casting pot is a pot that is difficult to input, but in this case the oscillation frequency is approximately
232KHz, input power is approximately 1170W.

In this way, when heating a pan whose input absorption amount varies depending on the material, it is possible to secure a substantially constant input power around 1300W, and the frequency difference that occurs at this time can also be reduced.
It's only 2.4KHz. Normally, when two adjacent heating ports are operated at the same time, the interference sound caused by the difference in their oscillation frequencies increases as the frequency difference becomes wider, so it is better to keep the difference as small as possible. As mentioned above, it is practically difficult to make the frequency difference 0, so it is desirable to be able to obtain a constant input that does not cause any practical problems even with a frequency difference as close to 0 as possible.
2KHz satisfies this requirement. Actual 2KHz
Experiments have confirmed that the noise is weak when the frequency difference is moderate. In such a cooking device with a substantially constant frequency, output adjustment is performed using a duty control method.

As explained above, the multi-port induction heating cooker of the present invention controls the oscillation frequency so that the input current is constant within a range where the frequency difference between each inverter is small, so noise generation is suppressed. Therefore, a predetermined input current can always be obtained regardless of the load material.

[Brief explanation of the drawing]

FIG. 1 shows an overall circuit diagram of an embodiment of the present invention, FIG. 2 shows a circuit block diagram, and FIG. 3 shows a specific circuit diagram of main parts. 2...High frequency inverter, 10...Input power setting circuit, 11...P compensation circuit, 12...On pulse generation circuit, 13...Starting pulse generation circuit, 14...Waveform shaping circuit, 15...Gate drive circuit.

Claims (1)

[Claims] 1. In a multi-port induction heating cooker comprising a plurality of heating ports in close proximity to each other, each heating port is equipped with an inverter circuit, an input current detection means for detecting the input current to the inverter circuit, and an input current detection means for detecting the input current to the inverter circuit. an input power setting circuit that controls the oscillation frequency of the inverter circuit so that the detection level becomes a predetermined value;
Frequency adjustment means for adjusting the oscillation frequency of the inverter circuit so that the noise generated due to the oscillation frequency difference with other inverters falls within a predetermined range commonly determined for each inverter so that the noise is below a predetermined value. A multi-mouth induction heating cooker featuring the following features: