JPS5854751B2 - Thyristor inverter drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drive circuit for a thyrisk inverter that drives an inductive load in induction heating or the like.

High-frequency impark using Cyrisk has been increasingly used as a high-frequency power source in recent years.

Conventionally, in order to start the high frequency inverter in such a drive circuit for a high frequency inverter, a starting circuit is prepared and a starting pulse is applied to both ends of the load.

Therefore, the device configuration of the entire drive circuit becomes complicated.

Furthermore, such a circuit has the disadvantage that if the timing of supplying the starting pulse is inappropriate, the starting will not be performed.

The present invention has been made to solve the drawbacks of the conventional drive circuit for a silice inverter, and one embodiment of the present invention will be described in detail below with reference to the drawings.

In the drawing, 1 is a forward conversion circuit that is composed of, for example, a three-phase bridge-connected thyristor and converts low-frequency AC power such as a commercial frequency into DC power, 2 is a DC reactor, and 3 is, for example, thyristors 4 to 7. An inverter 8 is configured in a bridge shape to convert DC power into high-frequency AC power, 8 is a load 11 including a glue accumulator 9 such as induction heating, and a resistor 10, and a capacitor 12 for compensating the power factor of the load 11. This is the load circuit that is used.

The load circuit 8 is an oscillating circuit having a natural frequency due to the reactance 9 and the capacitor 12.

13 is a control circuit, and the control circuit is connected to the thyristor 6.
voltage dividing resistor 14 for detecting the voltage between the terminals of
It includes a voltage conversion circuit 16.

The turn-off time/voltage conversion circuit 16 outputs a voltage corresponding to the turn-off time of the voltage signal from the midpoint of the voltage dividing resistors 14 and 15 according to the conversion characteristic diagram shown in FIG.

However, in FIG. 2, the horizontal axis is the turn-off time, and the vertical axis is the output voltage.

The output signal of the conversion circuit 16 is supplied to the other input terminal of a differential amplifier 17, one input terminal of which is grounded.

Further, the terminal 18 is biased with a negative voltage.

The output terminal of the differential amplifier 17 is connected to the base terminal of the transistor 19.

One end of the transistor is grounded via a capacitor 20, and the other end is applied with a positive bias voltage.

The midpoint between the transistor and the capacitor is connected to the base of the unijunction transistor 21.

The unijunction transistor is transistor 19
A pulse with a frequency corresponding to the time constant of an RC circuit including a capacitor 20 and a capacitor 20 is generated.

Therefore, the oscillation frequency is changed by changing the base voltage of the transistor 19.

22 is a current control resistor, and 23 is a load resistor.

The output terminal of the unijunction transistor is connected to an output circuit 24.

The output circuit 24 is a unijunction transistor 21
The output pulses of G0 and G0 are shaped to create two types of pulses, each having a phase difference of 900 degrees, and these output pulses are sent to the output terminals G0. G2, G3, and G4 respectively connect the gate terminals Gl' of the thyristors 4.5, 6, and 7.
p G2' p G3'yG4'.

Note that the terminal 18 connected to the input terminal of the differential amplifier 17
The negative bias voltage value applied to is such that when only the bias becomes the input signal of the differential amplifier 17, the frequency of the output pulse from the output circuit 24 becomes a frequency that is much larger than the resonant frequency fo of the load 11. It is set to a value such that

In the above-described configuration, in the initial state in which the forward conversion circuit 1 is not operated, the output signal of the turn-off time/voltage conversion circuit 16 is 0, so the input signal of the differential amplifier 17 is applied from the terminal 18. It is based only on a negative bias voltage signal, so that the differential amplifier 17 supplies a constant positive voltage to the base terminal of the transistor 19.

As a result, when fi is the frequency of the output pulse output from the output circuit 24 in the initial state, fi is the third
As shown in the figure, the frequency is much higher than the resonant frequency fo of the load 11.

However, in FIG. 3, the vertical axis represents the Q value of resonance, and the resonance characteristics are shown by a solid line.

Now, in order to start up the high frequency inverter, forward conversion circuit 1
When operating, the resonant frequency f.

A higher frequency fi minocate signal is applied to each thyristor 4,
5, 6, and 7, the inverter 3 starts oscillating.

The first oscillation frequency f1 is the resonance frequency f.

Because of the more striped pattern, the voltage across the terminals of the thyristor 6 detected from the midpoint of the resistor 14.15 has a phase lag with respect to the waveform at the resonance frequency, which is shown by the dotted line in Figure 4, and is shown by the solid line in Figure 4. This results in a large turn-off time T.

Has FF. Therefore, the turn-off time/voltage conversion circuit 16 generates an output voltage corresponding to this turn-off time, which is fed back to the differential amplifier 17.

As a result, the output signal of the differential amplifier 17 decreases, and therefore the output frequency of the output circuit 24 and the oscillation frequency of the inverter 3 are controlled to decrease, and finally the inverter 3 becomes a differential amplifier as shown in FIG. Balanced oscillation is performed at a specific frequency ff corresponding to the value when the output signal of the amplifier is O.

Generally, there is a relationship between the turn-off time and the oscillation frequency as shown in FIG. 5, so that for some reason the oscillation frequency of the inverter 3 becomes f.

If it decreases further, the turn-off time or the current turn-off time becomes smaller than the current turn-off time Tf, so the output signal of the turn-off time/voltage conversion circuit 16 decreases, which tends to increase the oscillation frequency of the output circuit 24. controlled.

Conversely, when the oscillation frequency of the inverter 3 increases, the turn-off time also increases, so the output signal of the turn-off time/voltage conversion circuit 16 increases, and therefore the oscillation frequency of the output circuit 24 is controlled to decrease. .

As described above, in the drive circuit for the thyrisk inverter according to the present invention, a gate signal with a frequency higher than the resonant frequency of the load is applied to the thyrisk to easily cause commutation to start the inverter, and after starting the inverter, Since the oscillation frequency gradually shifts to the operating frequency, a special starting circuit is not required and starting can be performed reliably.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing an embodiment of the present invention, Figure 2 is a diagram showing the conversion characteristics of the turn-off time/voltage conversion circuit, and Figure 3 is the relationship between the oscillation frequency at startup and the resonant frequency of the load. FIG. 4 is a diagram showing an example of electromagnetic waveforms at both ends of the thyristor 6, and FIG. 5 is a diagram showing the relationship between the turn-off time and the oscillation frequency of the inverter. 1: Forward conversion circuit, 2: DC reactor, 3: Inverter, 4, 5, 6, 7: Cyrisk, 8: Load circuit, 9: Reactance, 10: Resistance, 11: Load, 12, 20:
Capacitor, 13: Control circuit, 14, 15, 22, 23
:Resistance, 16: Turn-off time/voltage conversion circuit, 17:
Differential amplifier, 18: Terminal, 19: Transistor, 21 Unijunction transistor, 24: Output circuit.

Claims (1)

[Claims] 1 Convert the DC output from the forward conversion circuit to high frequency output,
In a circuit for driving a Cyrisk inverter that supplies the output to a load having a unique resonant frequency, an output circuit for supplying a gate signal to a gate terminal of the Cyrisk;
A circuit that detects the turn-off time of the commutated thyrisk based on the gate signal from the output circuit and generates a signal corresponding to the turn-off time, and a differential amplifier to which the signal from the circuit is supplied to one input terminal. The oscillation frequency is changed according to the output signal of the differential amplifier, and the frequency of the gate signal supplied to the oscillator whose output signal is supplied to the output circuit and the Cyrisk inverter is changed when the Cyrisk inverter is activated. A drive circuit for a thyrisk inverter comprising a bias source connected to one input terminal of the differential amplifier in order to make the resonant frequency higher than the resonant frequency of the load.