JPS598149B2 - frequency converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a frequency converter, and particularly to a frequency converter that directly converts low frequency alternating current into high frequency alternating current, and a control circuit thereof.

Conventionally, there have been very few examples of direct frequency conversion devices that directly convert low frequency alternating current to high frequency alternating current, and their control circuits have had the disadvantage of being extremely complex.

When applied to induction heating cookers, etc., there is a drawback that the heating output changes depending on the material of the pot, and the load fluctuation is large, so in order to obtain stable oscillation, the heating coil current is detected and constant output current is controlled. However, the control circuit was complicated and the price was high. In consideration of the above drawbacks, the present invention directly changes low frequency alternating current to high frequency alternating current using a simple control circuit and frequency conversion circuit, and is particularly stable against load fluctuations when applied to an induction heating cooker. , it is possible to realize an induction heating cooker with little variation in heating output depending on the material of the pot.

An embodiment of the present invention will be described in detail below with reference to the drawings.

In Figure 1, power switch 2 is connected to low frequency AC power source 1.
An alternating current voltage is applied to the frequency conversion circuit 3 via.

The frequency conversion circuit 3 directly converts low frequency AC into high frequency AC, and its oscillation is controlled by the control circuit 4. The frequency conversion circuit 3 connects a rich yoke coil 32 to one input terminal of an input capacitor 31 connected in parallel with the AC power source 1.
A series circuit of a power semiconductor block capable of bidirectional conduction is connected in series with the input capacitor 31, and is connected in parallel with the input capacitor 31.

In addition, a series RC circuit consisting of a snubber capacitor 34 and a snubber resistor is connected in parallel with the power semiconductor block 33, and
A series resonant circuit including a resonant capacitor 36 and an induction heating coil 37 which also serves as a resonant inductor is connected in parallel. The power semiconductor block 33 includes thyristors 33a, 3
3b are connected in anti-parallel, and when AC power supply 1 is positive, the thyristor with positive anode voltage conducts first, and then the thyristor connected in anti-parallel conducts, so a wide gate current is controlled. It is given from circuit 4. The control circuit 4 includes AC power input terminals 41a and 41b, a voltage detection terminal 42 of the power semiconductor block 33, and a thyristor 33a,
Gate output terminals 43a, 43a' connected to the gate-cathode terminal of 33b, gate output terminals 43b, 43b
′. FIG. 2 shows the current, voltage waveforms and gate current waveforms of the power semiconductor block 33, where Ith is the power semiconductor block current and has a sinusoidal pulse waveform.
is the thyristor node current that conducts first and its pulse width is Ts, and i2 is the regenerative current that is the waveform of the thyristor current that conducts next and its pulse width is TD.

Also, Th is the power semiconductor voltage waveform, and its pulse width is T
Set it to 2. Further, the gate trigger currents of the thyristors 33a and 33b are the same, and their pulse width T is longer than Ts and shorter than T1-TS+TD. The control circuit 4 according to the present invention is for keeping the off period, ie, T2, of the power semiconductor block 33 constant, and one embodiment thereof is shown in FIG.

In FIG. 3, there is a turn-off voltage detection circuit 44 that detects the voltage of the power semiconductor block 33, a timer circuit 45 that operates according to its output current, a comparison circuit 46 that compares the timer circuit output voltage with a set voltage level, and a comparison circuit. The gate trigger circuit 49 includes a trigger signal generating circuit 48 and a gate trigger circuit 49, which operate according to the output of the trigger signal generating circuit 48 and the gate trigger circuit 49.

The turn-off voltage detection circuit 44 is connected to the power semiconductor block 3.
3 is turned off, the applied voltage is detected, and one input of diodes 442a, 442b, 442c, and 442d constitutes a diode bridge, which is a series circuit of constant voltage diodes 440a, 440b and resistor 441 connected in reverse series. The output of the diode bridge that is connected to the terminal and has a positive output is connected to the base of the transistor 443, and the output of the diode bridge that is a negative output is connected to the emitter of the transistor 443, and a base-emitter resistor 444 is connected between the base and emitter. . When the input terminal 42 of the turn-off voltage detection circuit 44 is positive or negative, the transistor 443 is conductive, and when the voltage of the power semiconductor block 33 is very low or when it is turned on, the transistor 443 is in the off state and the collector resistor 450 is connected to the base. The transistor 451 turned on and off similarly turns on and off, and its collector voltage Vz becomes L level when the power semiconductor block 33 is on, and H level when it is off, as shown in FIG. Apply voltage to 455. Inverter 45
6 turns the transistor 458 on and off via the output resistor 457 when the signal Vz becomes L level, and rapidly discharges the timer capacitor 455. Comparison circuit 46 is PUT
The anode voltage VA of 46O is compared with the gate voltage VG, that is, the voltage divided by the variable resistor 461 and the resistor 462.The control voltage V is used to change the gate voltage VG.
Control c. Control voltage Vc is transistor 4
Diode 46 whose lowest voltage operates at 0R by voltage dividing resistors 465, 466 and variable resistor 467 that determine the base potential of 64
3a, when the anode voltage of the diode 463b increases, the T2 period changes (FIG. 3 VAO).
As the filtered output voltage of the AC power supply voltage detection circuit 47 becomes higher, Vc becomes higher and T2 becomes longer.
In other words, the power semiconductor block current is prevented from increasing due to an increase in the power supply voltage. The cathode current of PUT 46O turns on transistor 480, and its collector voltage Vr has a pulse waveform as shown in FIG. 4r. Timer capacitors 482a, 482b, inverters 483a, 483b and timer resistors 484a, 4
The output signal VO of the monostable multivibrator 84b is applied to the gate trigger circuit 49. Gate trigger circuit is Darlington transistor 493,494
The two secondary windings of a pulse transformer 497 connected to the collector of the thyristors 33a and 33b simultaneously trigger the thyristors 33a and 33b and simultaneously apply a reverse bias voltage. It is a voltage waveform, and Ith indicates a current waveform of the power semiconductor block 33. In particular, this gate trigger circuit 49 uses the rebound voltage of the pulse transformer 497 as a reverse bias voltage. Note that since oscillation can be inhibited by setting the terminal e drawn from the collector of the transistor 458 to zero, it is designated as the prohibited terminal e. As described above, the present invention controls the turn-off period T2 of a frequency conversion circuit including at least two anti-parallel connected thyristors to a constant value. The commutation energy is constantly charged to the resonant capacitor and then the turn-on signal is sent, making the oscillation very stable.

Induction heating cookers also have the advantage of reducing variations in output depending on the material of the pot. Furthermore, it is stable against fluctuations in the input AC power supply, and has the feature that the voltage applied to the power semiconductor remains almost constant even in a no-load state.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a frequency conversion device showing an embodiment of the present invention, Fig. 2 is a waveform diagram of each essential part of the same, Fig. 3 is a specific circuit diagram of a control circuit according to the present invention, and Fig. 4 is its diagram. It is a waveform diagram of each part. 1... Input AC power supply, 2... Power switch, 3... Frequency conversion circuit, 4...
Control circuit, 31... Input capacitor, 32...
...Chiyo coil, 33...Semiconductor block, 33a, 33b...Semiconductor block.

Claims (1)

[Claims] 1. Consists of a frequency conversion circuit that directly exchanges low-frequency AC into high-frequency AC and its control circuit, and the frequency conversion circuit includes at least one power semiconductor block capable of bidirectional conduction, a resonant capacitor, and a resonant capacitor. The control circuit includes a turn-off voltage detection circuit that detects a terminal voltage of the power semiconductor block when it is turned off, a timer circuit that operates according to an output signal of the turn-off voltage detection circuit, and a timer circuit that operates according to an output signal of the turn-off voltage detection circuit. A frequency conversion device comprising: a comparison circuit that compares the output of a timer circuit with a set voltage level; and a trigger signal generation circuit that supplies a trigger signal to the semiconductor block according to the output signal of the comparison circuit. 2. The frequency conversion device according to claim 1, wherein the turn-off voltage detection circuit stops the operation of the timer circuit in the vicinity of zero voltage of the power semiconductor block voltage. 3. The frequency conversion device according to claim 1, wherein the timer circuit is charged and discharged according to the output signal of the turn-off voltage detection circuit. 4. The frequency conversion device according to claim 1, wherein the trigger signal generation circuit includes a monostable multivibrator. 5. The frequency conversion device according to claim 1, wherein the control circuit simultaneously provides a trigger signal to the thyristors connected in antiparallel that constitute the power semiconductor block.