JPH04264384A - Inverter device for induction heating device - Google Patents

Abstract

PURPOSE:To simplify a control system, and always maintain a power factor of the alternating current power source side at a high power factor by short- circuiting a power inverter at each cycle corresponding to a set power to stop the power supply to a load without controlling voltage. CONSTITUTION:A diode rectifier 10 generates, the pulse train signal by a cycle, which corresponds to a difference between an upper limit value of a set output voltage and a set value of an output power setting unit 12. When a command unit 15 receives this pulse train, the command unit 15 converts it to the short- circuit command, which is synchronized with the pulse of a wave rectifier 11 and having a pulse width by one cycle, and sent it to a gate circuit 16. When the gate circuit 16 receives the short-circuit command, the gate circuit 16 outputs the predetermined gate pulse to thyristors 3-6 to short-circuit a power inverter INV. Consequently, during this short-circuit command period, current is not flowed from an induction heating coil 7 and a capacitor 8. Since the power to be supplied to a load is controlled by only the control of the power inverter, a control system is simplified.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device for an induction heating device.

0002

[Prior Art] Figure 3 shows "Journal of the Institute of Electrical Engineers of Japan," Vol. 107, No. 7 (
FIG. 2 is a configuration diagram of a high-frequency inverter device for an induction heating device described in the publication (published in 1988). In the figure, 1A is a thyristor rectifier, 2 is a smoothing reactor, 3 to 6 are semiconductor switching elements (thyristors) constituting the inverter INV, 7 is an induction heating coil, and 8 is a power factor improvement capacitor. 24 is a voltage detector that detects the output voltage V of the inverter INV, 12A is an output voltage setter that sets the output voltage of the inverter INV, and 25 is a comparator. Comparator 2
5 is the set voltage Vk of the output voltage setter 12A and the output voltage V
gate circuit 2 of thyristor rectifier 1A by detecting the difference between
Give to 6. 21 is a reverse voltage time setter, 22 is a reverse voltage time detector, 23 is a comparator, and 16 is a gate circuit of the inverter INV.

The operation of this inverter device will be explained with reference to the waveform diagram of FIG. The output voltage V of the inverter INV oscillates sinusoidally at a period corresponding to the resonance frequency of the induction heating coil 7 and the power factor correction capacitor 8. Electric power is supplied to the induction heating coil 7 by sending out a gate pulse from the gate circuit 16 in synchronization with this output voltage and turning the thyristors 3 and 6 and 4 and 5 on and off alternately. The comparator 23 compares the reverse voltage time TOFF of the thyristor detected by the reverse voltage time detector 22 with the set time TK of the reverse voltage time setter 21, and determines the firing timing of the thyristor when the two match.

On the other hand, the output voltage V is
It is controlled by controlling the firing phase of the thyristor that constitutes the thyristor.

[0005]

[Problem to be solved by the invention] In this way, conventionally,
The output voltage V is controlled by controlling the thyristor rectifier 1A, and voltage control (phase control of the thyristor rectifier 1A) and reverse voltage time control (control of the inverter INV) are performed independently. In addition to the problem that a control circuit is required and the control system becomes complicated, there is also the problem that the smaller the output voltage V of the inverter INV, the lower the power factor on the AC power source side.

[0006] The present invention was made to solve this problem, and only the inverter is controlled, which makes the control system simpler than before, and also increases the power factor on the AC power supply side. It is an object of the present invention to provide an inverter device for an induction heating device that can maintain the power factor.

[0007]

[Means for Solving the Problems] In order to achieve the above objects, the present invention provides a rectifier for converting commercial alternating current into direct current, a smoothing reactor for smoothing the output of this rectifier, and an inverter for converting the smoothed direct current into alternating current. In an inverter device that supplies power to a parallel circuit of an induction heating coil and a power factor correction capacitor, the rectifier is a diode rectifier, and the output power set by the set output voltage upper limit value and the output power setting device A pulse train signal for a period corresponding to the difference between the values is generated, and this pulse train signal is synchronized with the AC output voltage of the inverter to generate a short circuit command.
The configuration was such that the inverse converter was short-circuited.

[0008] According to a second aspect of the present invention, an A/D converter converts the output of the output power setting device into a digital value, and an A/D converter that inputs the digital value and converts the output voltage with a period corresponding to the difference between the digital value and a set output voltage upper limit digital value. The waveform shaper converts the AC output voltage of the inverter into a pulse waveform by synchronizing the pulse train signal of this memory with the pulses of a waveform shaper. It was configured to convert to .

[0009]

[Operation] In the present invention, when the output voltage is set to the upper limit value, the inverter INV turns ON/OFF in synchronization with the output voltage.
Repeating F, if the setting is lower than the upper limit value, the inverter INV will be short-circuited at a certain period and the power supply to the load will be suspended, and this suspension period will become longer as the set value of the output voltage is lower.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is a diode rectifier. 11 is a waveform shaper, which is shown in FIG. 2 of the inverter INV (
(B) in Fig. 2 synchronized with the positive half-wave of the output voltage V shown in A).
) generates the pulse waveform shown below. 12 is an output power setting device, and 13 is a digital value N of the setting value of the output power setting device 12.
14 is a memory, and 15 is a command device. The other configurations are the same as those shown in FIG. 3 above.

Next, the operation of this device will be explained with reference to the time chart of FIG. For convenience of explanation, the output power setter 12 can set the output power upper limit value in the range of 0 to 1.0, and the range of the digital value output by the A/D converter 13 is 0 to 1000. The digital value 1000 is a period corresponding to the set output power upper limit value. The digital value N of the set power value set by the output voltage setter 12 is 1000.
, the memory 14 has 1000-1000=
Since it is 0, no output is made, and the command unit 15 does not send out a short circuit command. For example, if the digital value N is 800,
Since 1000-800=200, a pulse train corresponding to a period of 200 cycles is generated. As a result, this occurs once every five cycles, and when the command unit 15 receives this pulse train, the waveform shaper 11
It synchronizes with the pulse of , converts it into a pulse with a pulse width of one cycle (which serves as a short circuit command), and sends it to the gate circuit 16. When the gate circuit 16 receives this short circuit command, it outputs the gate pulse shown in (D-2) in FIG. 2 to the thyristors 3 and 6, and the gate pulse shown in (E-2) in FIG. 2 to the thyristors 4 and 5. , short-circuiting the inverter INV. Therefore, during this short circuit command period, no current flows through the load circuit consisting of the induction heating coil 7 and capacitor 8 as shown in (F-2) in FIG.
The power supplied to the load circuit is the upper limit value of 0.8. During this short-circuit command period, the output voltage is slightly attenuated, but since the load circuit is a resonant circuit, the output voltage continues to oscillate.

In this way, when the set power is N/1000, the period of the pulse train output by the memory 14 is (1000-N) out of 1000 periods, but the period of the pulse train output by the memory 14 is (1000-N) out of 1000 periods. The percentage of period during which no supply is provided is (
1000-N)/1000, and the ratio of the period during which power is supplied to the load is N/1000 of the power upper limit value, and the output power setter 12 can set any output power.

When the above-mentioned short circuit command does not occur (when the output of the command unit 15 is (C-1) in FIG. 4), the inverse converter I
NV operates in the same way as before. The gate pulses to thyristors 3 and 6 and the gate pulses to thyristors 4 and 5 at this time are shown in (D-1) and (E-1) of FIG. 4, respectively. In this case, power supply to the load continues as shown in (D-1) in FIG.

The pulse train of a constant period outputted by the memory 14 is such that when N=1000, the pulse train to be sent out is 0, N
When N=800, once every 5 cycles, when N=500, twice
The data is stored in the memory 14 in a 1:1 ratio with respect to the digital value N from the A/D converter 13, once every cycle. In the case of an odd value such as N=784, the pulse train for (1000-784) periods is divided into 100
The data are stored in the memory 14 so as to be scattered as evenly as possible during the 0 cycle. This is because when the period of the pulse train of the memory 14, that is, the short-circuit period of the inverter INV, extends over a continuous period, the waveform of the output voltage is attenuated and it becomes impossible to obtain the voltage necessary for firing or extinguishing the thyristor. .

[0015] When the set output voltage level becomes a small value such as 0.1 times the upper limit value, the above-mentioned short-circuit period becomes longer, but in general, it is often used at 0.3 times or more.
A limit may be placed so that it does not fall below 0.3 times.

[0016] In this way, in this embodiment, a period during which the power supply is suspended is provided, and this suspension cycle is changed according to the set power, so that the load supply power can be controlled without performing voltage control as in the conventional case. be able to.

Since the above-mentioned period is obtained by short-circuiting the inverter INV, the power factor on the AC power source side can always be maintained at approximately 1.

Although the above embodiment uses an output power setting device, this may also be an output power setting device. In that case, the output power is generally proportional to the square of the output voltage, so the square calculation is performed. You will need a device.

[0019]

[Effects of the Invention] As explained above, the present invention has a structure in which the inverter is short-circuited every certain period corresponding to the set power without performing voltage control, and the power supply to the load is stopped. Since the power supplied to the load can be controlled only by controlling the inverter, the control system can be simplified compared to conventional voltage control, and the power factor on the AC power supply side can always be maintained at a high power factor. It can be maintained to cough.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a waveform time chart showing waveforms of various parts in the above embodiment.

FIG. 3 is a circuit diagram of a conventional inverter device for an induction heating device.

FIG. 4 is a waveform time chart showing waveforms of various parts in the conventional example.

[Explanation of symbols]

1 Diode rectifier 3-6 Thyristor 7 Induction heating coil 8 Capacitor 11 Waveform shaper 12 Output power setting device 13 D/A converter 14 Memory 15 Command unit 16 Gate pulse generator 21 Reverse voltage time setting device 22 Reverse voltage time detector 23 Comparator

Claims (2)

[Claims] Claim 1: A rectifier that converts commercial alternating current to direct current, a smoothing reactor that smoothes the output of this rectifier, and an inverter that converts the smoothed direct current to alternating current, and an induction heating coil and a power factor improvement capacitor connected in parallel. In an inverter device that supplies power to a circuit, the rectifier is a diode rectifier, and generates a pulse train signal for a period corresponding to the difference between the set output voltage upper limit value and the output power set by the output power setting device. An inverter device for an induction heating device, characterized in that the pulse train signal is synchronized with the AC output voltage of the inverter to generate a short-circuit command, and when the short-circuit command is issued, the inverter is short-circuited. 2. An A/D converter that converts the output of the output power setting device into a digital value, which inputs the digital value and generates a pulse train for a period corresponding to the difference between the digital value and a set output voltage upper limit digital value. It has a memory that generates a signal, and a circuit that synchronizes the pulse train signal of this memory with the pulse of a waveform shaper to generate a short circuit command. The inverter device for an induction heating device according to claim 1, wherein the inverter device converts a wave into a pulse waveform.