JPH0145273Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a control device for a current source inverter having an LC resonant circuit in the load.

LC for loads such as current source inverters for induction heating
A current source inverter having a resonant circuit (tank circuit) has a main circuit configuration shown in FIG. 1, for example.
The DC power converted by the forward converter 1 is made into a constant current through the DC reactor 2, and is converted into a constant current by the inverter body 3 having a thyristor bridge configuration.
It is converted into an alternating current that matches the resonant frequency of the LC resonant circuit and is supplied to the load 4.

Thyristors TH1 to TH4 of inverter main body 3
Since the commutation is performed by applying a reverse bias by the induced voltage of the load, the thyristors TH1 to TH4 are fired at an advanced phase angle. FIG. 2 shows the voltage Vout, current Iout, and gate signal timing during commutation. In the figure, the firing angle β of the thyristor is determined by the overlap time μ from the gate signal application time t ₁ until the application of the reverse voltage to the thyristor that has been in the on state until then starts, and the commutation margin time τ during the reverse voltage application period. The gate of the thyristor is controlled to ensure commutation margin time τ for the thyristor.

The conventional control device has the configuration shown in FIG. 3 to ensure commutation margin time τ. The waveforms of each part in the figure are shown in FIG. 4. Inverter output voltage Vout
Only the fundamental wave component (signal a in FIG. 4) is extracted through the filter circuit 11, and the zero point timing signal (c in FIG. 4) is extracted from this signal (b in FIG. 4) by the zero cross detector 12. is detected and used as a reset signal for the flip-flop 13. on the other hand,
The inverter output current Iout (f in FIG. 4) is detected by the zero cross detector 14 at its zero point timing signal (g in FIG. 4), and the inverter output current Iout (f in FIG.
5 reset signal. flipflop 1
3 and 15, the output of a voltage-frequency converter 20 (described later) is given to the set signal, and this output (fourth
l) in the figure is the setting period of the flip-flop 13 (d in Figure 4) when the firing angle β of the inverter body is reached.
corresponds to the firing angle β, and the setting period of the flip-flop 15 (h in FIG. 4) corresponds to half (μ/2) of the overlap time μ.

The output of the flip-flop 13 is integrated by an integrator circuit 16 with a gain of 1 and converted into an averaged DC voltage signal (e in FIG. 4), and the output of the flip-flop 17 is integrated by an integrator circuit 17 with a gain of -2 and converted into an averaged DC voltage signal (e in FIG. 4). It is converted into a voltage signal (i in FIG. 4) and a voltage signal corresponding to the overlap angle μ is extracted. These signals are set in the τ setting device 18 (thyristors TH1 to TH
The DC voltage (j in Fig. 4) corresponding to the commutation margin angle τ (determined by 4) is added and compared, and the deviation of these three signals is amplified by the deviation amplifier 19 ( k), voltage-frequency converter 20
voltage input. The output of this converter 20 is used not only as a set signal for flip-flops 13 and 15, but also as a gate phase signal for a gate circuit 21.
The thyristor is controlled by the gate output of the gate circuit 21.
Ignition control of TH1 to TH4 is performed. That is,
The output pulse phase of the voltage-frequency converter 20 is controlled so that the difference between the firing angle β, the overlap angle μ, and the commutation margin angle τ becomes zero, thereby ensuring the commutation margin angle τ.

Here, the deviation amplifier 19 is provided with a τ limiter circuit 22 that limits its output. The τ limiter circuit 22 sets the gate signal phase at τ when the voltage Vout and current Iout signals are not fed back.
The limiter value is 1/2 (single phase) of the limiter output frequency of the voltage-frequency converter 20.
The frequency is determined so that the frequency of the load 4 matches the tank circuit frequency of the load 4. For this matching, converter 2
Even if the 1/2 frequency of the 0 limiter output deviates by about -40%, stable starting is possible, but if the frequency deviates beyond this, starting becomes unstable. On the other hand, the half period T of the tank circuit frequency is the limiter output period T ₀ of the converter 22.
If it becomes shorter than , constant τ control becomes impossible,
The commutation margin time of the thyristor is T ₀ − than the set value.
It becomes shorter by the time T.

Therefore, it is necessary to change the rated output frequency of the inverter device according to the tank circuit frequency of the load 4, and also change the limiter value of the τ limiter circuit 22, and the output frequency range of the inverter device is also limited, which reduces the utilization efficiency of the device. becomes worse.

The present invention was developed in view of the above-mentioned circumstances, and by providing a means for switching the limiter value of the τ limiter circuit according to the load tank circuit frequency, constant τ control can be reliably and easily performed over a wide output frequency range. An object of the present invention is to provide an inverter control device that increases the versatility of the device and facilitates handling.

FIG. 5 shows an embodiment of the present invention, in which the output frequency is switched in two stages. The difference between this figure and FIG. 3 is that two circuits 22A and 22B having mutually different limiter values are prepared in the τ limiter circuit provided in the deviation amplifier 19, and the τ limiter circuit 2
The point is that one of 2A and 22B is switched by a changeover switch 23 to function as an output limiting circuit for the deviation amplifier 19. The changeover switch 23 is switched by an on/off changeover signal FC.

In such a configuration, either one of the τ limiter circuits 22A and 22B controls the limiter value of the deviation amplifier 19 by controlling the signal FC,
Enables constant τ control according to output frequency switching of the inverter device.

Therefore, according to the present invention, by changing the load,
Differences in LC resonant circuit frequency can be detected by switching the τ limiter circuit to one suitable for the frequency, and only controlling and operating the switching signal FC can secure the commutation margin angle required for the thyristor in the inverter main body 3. The inverter device can be applied to various loads.

[Brief explanation of the drawing]

Fig. 1 is a main circuit configuration diagram of a current source inverter, Fig. 2 is a waveform diagram for explaining the commutation margin time in Fig. 1, Fig. 3 is a conventional control device circuit diagram, and Fig. 4 is a diagram of a conventional control device.
The figure is a waveform diagram of each part of FIG. 3, and FIG. 5 is a circuit diagram of a control device showing an embodiment of the present invention. 3... Inverter main body, 4... Load, 11...
Filter circuit, 12, 14... zero cross detector,
13,15...flipflop, 16,17...
...Integrator circuit, 18...τ setting circuit, 19... Deviation amplifier, 20... Voltage-frequency converter, 21...
Gate circuit, 22, 22A, 22B...τ limiter circuit, 23... Changeover switch.

Claims (1)

[Scope of utility model registration request] In a current source thyristor inverter with an LC resonant circuit in the load, the firing angle (β) of the inverter main circuit thyristor is determined from the time difference between the zero cross timing signal of the inverter output voltage and output current waveforms and the timing signal of the inverter output frequency control signal. Detect the DC signal corresponding to the overlap time (μ), and obtain the deviation between this detection signal and the DC signal corresponding to the commutation margin time (τ) of the thyristor.The output of the deviation amplifier is set to the frequency of the inverter output frequency control signal. A current characterized in that the control signal is provided with a switching means for switching the output limiter value of the deviation amplifier to a value that controls the commutation margin time (τ) to a constant value according to the resonant frequency of the LC resonant circuit of the load. Control device for type inverter.