JP2740383B2 - Electromagnetic cooker - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic cooker.

[0002]

2. Description of the Related Art Generally, in an electromagnetic cooker disclosed in Japanese Patent Publication No. 3-41953, in which a heating coil is driven by an AC power supply, an abnormally high voltage is generated due to generation of an inrush current, and loud noise and noise are generated. It is necessary to supply current from the AC power supply to the heating coil at the time of zero voltage crossing so as not to cause the generation. This is also true for an electromagnetic cooker in which a heating coil is driven by a three-phase AC power supply.

[0003] However, when the heating coil is driven by the three-phase AC power supply, the configuration in which the heating coil is energized from each phase at the time of zero voltage crossing of each phase of the three-phase AC power supply becomes considerably complicated.

[0004]

SUMMARY OF THE INVENTION The present invention provides an electromagnetic cooker which can supply current to the heating coil from each phase at the time of zero voltage crossing of each phase of a three-phase AC power supply and which can achieve this with a simple configuration. It is assumed that.

[0005]

Means for Solving the Problems The present invention includes a R-phase and S-phase
In an electromagnetic cooker in which a heating coil is driven by a three-phase AC power supply composed of a T-phase, a heating coil is provided for each phase of the three-phase AC power supply.
Switches for controlling the power supply to the heating coil for each phase.
Switching element and one correlated power in the three-phase AC power supply.
First specific value detecting means for detecting a specific value of pressure;
One phase of the remaining two correlation voltages in the AC power supply
A second specific value detecting means for detecting a specific value of the intermediate voltage;
The power supply frequency is determined based on the detection interval of the specific value by the first specific value detecting means.
Frequency determining means for determining the number, and the first specific value detecting means.
The second specific value detecting means from the point in time when the specific value is detected in the step
To determine the connection order of each phase based on the time until
Connection state determination unit, the frequency determination unit, and the connection state determination
Based on the determination result of the first specific value detecting means,
From the point when a specific value is detected until the zero voltage of one phase
From this point, and from this point the zero voltage arrival of the other phase
Delivery time and based on this time
And a controller for controlling the energization of the heating coil.

[0006]

According to the determination of the power supply frequency and the connection state to the three-phase AC power supply, power is supplied from each phase to the heating coil at the time of zero voltage crossing of each phase of the three-phase AC power supply.

[0007]

FIG. 1 shows a circuit of an electromagnetic cooker according to an embodiment of the present invention driven by a three-phase AC power supply (200 V). The connection states when the R, S, and T phases of the electromagnetic cooker are connected to a three-phase AC power supply are summarized into two sets in consideration of only the phases of the respective phases. That is, if one is a set whose phases are shifted in the order of the R, S, and T phases, the other is a set whose phases are shifted in the order of the R, T, and S phases. In this case, it is assumed that the R, S, and T phases are connected in a state where the phases are shifted in the order of the R, S, and T phases.

A series circuit of a heating coil 5 and a switching transistor 6 is connected to each of the R, S, and T phases via a three-phase thyristor mixing circuit 1, a discharge resistor 2, a choke coil 3, and a smoothing capacitor 4. A resonance capacitor 7 is connected in parallel with the switching transistor 6. When the switching operation of the switching transistor 6 is performed, a high-frequency current is generated, the high-frequency current flows through the heating coil 5, and the pot 8 made of iron or the like placed on the heating coil 5 is induction-heated. As shown in detail in FIG. 2, the three-phase thyristor mixing circuit 1 has a switch corresponding to each phase .
It has thyristors 9, 10, 11 serving as switching elements and diodes 12, 13, 14.

[0009] First and second power transformers 15 and 16 are connected to the R, S, and T phases in the preceding stage of the three-phase thyristor mixing circuit 1. The first power transformer 15 is between the R and S phases, and the second power transformer 16 is
Straddling between the phases. These first and second power transformers 1
The waveforms of the R / S phase voltage and the S / T phase voltage input to 5, 5 are R, S, T of a, as shown in FIG.
The waveforms shown in FIG. Then, the first output voltage of the second power transformer 15, 16 would correspond to the input voltage, and inputs the first of the next, to the second zero-cross detection circuits 17 and 18. Here,
The low cross detection circuit 17 corresponds to the first specific value detection circuit
The second zero-cross detecting circuit 18 detects the second specific value.
It corresponds to an intelligent circuit. The first and second zero-crossing detection circuits 17 and 18 periodically output a zero-crossing signal at a specific value of the input voltage, that is, at a zero-crossing time of the R / S phase voltage and the S / T phase voltage as shown in c and d. Output.

[0010] The microcomputer 19 controls the electromagnetic cooker. This microcomputer 19
The first power supply transformer 15
As soon as the microcomputer 19 is connected to the three-phase AC power supply of the electromagnetic cooker, the microcomputer 19 immediately inputs a drive voltage from the first power transformer 15 and starts controlling the electromagnetic cooker. The second power transformer 16 is also used as a drive voltage supply source, and is supplied to any circuit component except the microcomputer 19.

The microcomputer 19 performs a control which starts after the input of the driving voltage.
The frequency of the three-phase AC power supply is 50 Hz or 60 Hz based on the zero cross signal from the first zero cross detection circuit 17 fetched through the first external interrupt input port 21.
Hz. That is, the frequency determination unit 20 performs the frequency determination based on the time interval t1 (FIG. 3) of generating the zero-cross signal from the first zero-cross detection circuit 17, which corresponds to the time interval of the zero-cross of the R-S phase voltage. . If the time interval t1 is about 8.33 ms, it is determined to be 60 Hz, and if it is 10 ms, it is determined to be 50 Hz.

Next, the microcomputer 19
Are connected to the first and second external interrupt input ports 21 and 23 by the connection state determination unit 22.
The connection state to the three-phase AC power supply is determined based on the zero cross signals from the zero cross detection circuits 17 and 18.
That is, the connection state determination unit 22 is based on a time interval t2 (FIG. 3) of generating a zero-cross signal from the first and second zero-cross detection circuits 17 and 18, which corresponds to a generation interval of a zero-cross between two phase voltages. To determine the connection state. If the time interval t2 is about 5.56 ms or about 6.67 ms, it is determined that the R, S, and T phases are connected in a state where the phases are shifted in the order of R, S, and T phases, while about 2. If the time is 78 ms or about 3.33 ms, it is determined that the connection is made such that the phases are shifted in the order of the R, T, and S phases. In this case, R,
It is determined that the phases are shifted in the order of the S and T phases. Note that the former value at each determination corresponds to a frequency of 60 Hz, and the latter value corresponds to a frequency of 50 Hz.

The microcomputer 19 stores the judgment results of the frequency judging section 20 and the connection state judging section 22 in the internal memory 24, and the control section 25 controls the respective phases of the three-phase AC power supply based on these judgment results. At the time of zero crossing of the voltage. That is, the time Ta from when the zero-cross signal is output from the first zero-cross detection circuit 17 to when the R-phase voltage crosses zero, the time Tb after which the voltage of the next phase crosses zero, and the time until the voltage of the next phase crosses zero Is recognized. In the determination of the connection state that the phases are shifted in the order of the R, S, and T phases as described above, the times Ta and Tb are 1.388 ms and 5.556 ms at a frequency of 60 Hz, respectively.
At a frequency of 50 Hz, 1.667 ms and 6.6 ms, respectively.
67 ms.

When the start key is operated by the external key input unit 26, the control unit 25 of the microcomputer 19 firstly causes the first external interrupt port of the zero cross signal from the first zero cross detection circuit 17 to be output. Based on the input to 21, an activation port 27 is activated as shown in FIG. Then, the pulse oscillation control circuit 28 generates a frequency signal of 23 KHz to drive the transistor drive circuit 29, and the switching transistor 6 starts the switching operation.

In this state, the first external interrupt port
When the zero-cross signal is input to the port 21, the control unit 25 causes the timer 30 to count the time Ta, and waits for the timer 30 to count this time. When the counting of the time Ta by the timer 30 is completed, the control unit 25
The first thyristor starting port 31 is activated as shown in FIG.
The thyristor 9 corresponding to the R phase is turned on via the thyristor trigger circuit 32. Thus, the R-phase power is supplied to the heating coil 5 near the voltage of zero.

Then, the control unit 25 sets the time Tb
Is counted by the timer 30, and it waits for the timer 30 to count this time. Similarly, when the counting of the time Tb is completed, the control unit 25 activates the second thyristor starting port 33 as shown in FIG. 3G according to the connection state determination result, and through the second thyristor trigger circuit 34, the thyristor 10 corresponding to the S phase. Turn on. Further, according to the end of the counting of the next time Tb, as shown in FIG.
Then, the thyristor 11 corresponding to the T phase is turned on via the third thyristor trigger circuit 36. As a result, the heating coil 5 near the zero voltage of the S and T phase power supplies
It is thrown into.

In this manner, the heating coil 5 is energized from each phase of the three-phase AC power supply at the time of zero voltage crossing, and no inrush current is generated, abnormally high voltage is generated and loud noise and noise are generated. Nothing to do.

Next, an electromagnetic cooker is connected to a three-phase AC power supply by R,
Assuming that the phases are shifted in the order of the T and S phases, the waveforms input to the first and second power transformers 15 and 16 are, as shown in FIG. The waveforms shown in FIG. The determination by the frequency determination unit 20 is as described above. In the connection state determination unit 22, the time interval t2 is about 2.78.
ms or about 3.33 ms, and R, S, T phases are R, T,
It is determined that the phases are shifted in the order of the S phase. Thereafter, the control unit 25 of the microcomputer 19 determines the time Ta related to the zero cross of the voltage of each phase,
Tb is recognized, but in the determination of the connection state that the phases are shifted in the order of the R, T, and S phases as described above, the time T
a and Tb are 6.94 each at a frequency of 60 Hz.
4 ms and 5.556 ms, and 8.333 ms and 6.667 ms respectively at a frequency of 50 Hz.

Based on these times Ta and Tb and the connection state determination result, the control unit 25 controls the first, third and second thyristor starting ports 31 and 3 as shown in FIGS. 4f, g and h.
Thyristors 9 and T corresponding to the R phase
The thyristor 11 corresponding to the phase and the thyristor 10 corresponding to the S phase are sequentially turned on. Thus, at this time, the heating coil 5 is also energized from each phase of the three-phase AC power supply at the time of the voltage zero crossing. Similarly, no inrush current is generated, abnormally high voltage is generated, and loud noise or noise is generated. Never do.

The above-mentioned times Ta and Tb for the above-mentioned frequency judgment result and connection state judgment result are summarized as shown in FIG. 5 and FIG.

[0021]

According to the electromagnetic cooker of the present invention, the heating coil is not affected by the power supply frequency and the connection state to the three-phase AC power supply, and the heating coil is started from each phase at the time of zero voltage crossing of each phase of the three-phase AC power supply. And the occurrence of an abnormal high voltage due to the generation of an inrush current and generation of loud noise and noise can be remarkably suppressed.

Further, the detection of the voltage zero crossing point of each phase is performed based on the detection of a specific value of two inter-phase voltages, and it is not necessary to provide three detection circuits for each phase, and the circuit is complicated. Can be suppressed.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an electromagnetic cooker according to an embodiment of the present invention.

FIG. 2 is a detailed circuit diagram of a three-phase thyristor mixing circuit of the cooking device.

3 is a waveform diagram of each part of the circuit in FIG. 1 in a connection state in which the phases are shifted in the order of R, S, and T phases.

4 is a waveform diagram of each part of the circuit of FIG. 1 in a connection state in which the phases are shifted in the order of R, T, and S phases.

FIG. 5 shows a frequency determination result, a connection state determination result, and time T.
It is a figure which shows the relationship with a.

FIG. 6 is a diagram illustrating a relationship between a frequency determination result and a time Tb.

[Explanation of symbols]

 5 Heating coil 17 First zero-cross detecting circuit (specific value detecting means) 18 Second zero-cross detecting circuit (specific value detecting means) 20 Frequency determining section 22 Connection state determining section 25 Control section

Continuation of front page (56) References JP-A-3-30284 (JP, A) JP-A-3-285287 (JP, A) JP-A-2-119084 (JP, A) JP-A-1-95488 (JP) JP-A-3-34287 (JP, A) JP-A-4-54871 (JP, A) JP-A-1-3155891 (JP, A) JP-A-60-21190 (JP, U) 3-41953 (JP, B2)

Claims (1)

(57) [Claims] 1. A electromagnetic cooker for driving the heating coil at 3-phase AC power source consisting of a R-phase and S-phase and T-phase, the
The heating coil is provided for each phase of the three-phase AC power supply and for each phase.
Switching element for controlling the power supply to the
Detecting a specific value of one correlation voltage in a power supply
Specific value detection means and the remaining two in the three-phase AC power supply
Detecting a specific value of one of the correlation voltages
The second specific value detecting means and the first specific value detecting means;
Frequency judgment method for judging the power supply frequency from the fixed value detection interval
Stage and the time when the first specific value detecting means detects the specific value
From the time when the second specific value detecting means detects the time
A connection state determination unit that determines the connection order of each phase in
Based on the determination results of the number determination unit and the connection state determination unit
Whether the first specific value detecting means detects the specific value.
Specify the time until the voltage of one phase becomes zero,
From this point, the time to reach the zero voltage of other phases is specified.
And a control unit for controlling energization of the heating coil based on the specified time .