JPS6332013B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention provides for, when a forward overvoltage is applied to a pair of thyristors connected in anti-parallel connection, the thyristor on the side to which the voltage is applied forcibly fired to reduce the tolerance level. The present invention relates to a thyristor control device equipped with a protection circuit (hereinafter referred to as "OVP circuit") that eliminates overvoltage exceeding .

[Technical background of the invention]

A thyristor control reactor thyristor device (hereinafter referred to as "TCR thyristor device") used as a reactive power compensator or a system voltage stabilizer is composed of a pair of thyristors connected in antiparallel.

FIG. 1 is a diagram showing a schematic configuration of an arc furnace reactive power compensator using a thyristor device for TCR. The TCR thyristor device 1 is constructed by connecting a pair of thyristors 1a and 1b in antiparallel.
By controlling the phase of these thyristors 1a and 1b, the current flowing through the reactor 2 connected in series with the thyristor is changed, and the capacitor 3, which is a fixed capacitance, is connected in parallel with the reactor 2.
This compensates for the reactive power generated by the load (arc furnace) 4. Since a surge voltage, such as a switching surge voltage, is applied from the outside to the thyristors 1a and 1b, an OVP circuit may be provided for overvoltage protection. This OVP circuit fires the thyristors within the permissible voltage value of the thyristors 1a and 1b when a forward overvoltage is applied to the thyristors 1a and 1b, and prevents the overvoltage exceeding the permissible value from being applied to the thyristors 1a and 1b. This is a protection circuit to prevent this. By providing this OVP circuit, the number of thyristors connected in series can be reduced because the thyristors do not need to coordinate with the applied overvoltage to determine the number of thyristors connected in series, so their use has become popular in recent years. In particular, in the case of antiparallel connected thyristors used in TCR thyristor devices, the thyristor can be activated regardless of the direction of overvoltage by firing one of the thyristors connected in antiparallel according to the order or reverse direction of overvoltage. It is attracting attention as a very effective protection method.

FIG. 2 shows a configuration diagram of an anti-parallel connected thyristor control device provided with an OVP circuit. The overvoltage detection circuit 5 is connected in parallel between the anode and cathode of one phase of thyristors 1a and 1b which are connected in antiparallel. Overvoltage forced ignition signals 6a and 6b, which are output signals of the overvoltage detection circuit 5, are sent to gate circuits 7a and 7b corresponding to forward overvoltage. In the gate circuits 7a and 7b, a regular gate signal 8 is generated by phase control from a control device (not shown).
A, 8b and the overvoltage forced ignition signals 6a, 6b are logically summed by an OR circuit 9, amplified by a pulse amplifier 10, and output to the thyristor 1a or 1b.
It is configured to be applied as an ignition control pulse to the gate of the In addition, overvoltage forced ignition signals 6a, 6
Either one of b is output depending on the polarity of the overvoltage applied to the thyristors 1a and 1b.

Providing the OVP circuit in the TCR thyristor device as described above is very effective in terms of overvoltage protection, but depending on the timing at which the OVP circuit operates, problems may occur in turning off the thyristors 1a and 1b.

[Problems with background technology]

FIG. 3 shows voltage and current waveforms at various parts to explain the operation of the conventional thyristor control device shown in FIG. In the following explanation, the operation for one phase will be explained, but the operation for other phases of the multiphase alternating current is also similar.

A voltage 11 is applied to the thyristor device 1, and an ignition control pulse 1 is applied to each thyristor 1a, 1b.
When 2a and 12b are given, a thyristor current 13 flows, and at this time a voltage waveform 14 is obtained between the anode and cathode of the thyristors 1a and 1b. If the applied voltage 11 increases for some reason at the current time T ₁ , the OVP circuit operates, a forced firing pulse 15 is generated, and the U-phase thyristor fires, the thyristor current 13 continues to flow until time t ₄ . . On the other hand, a regular firing control pulse is sent to the X-phase thyristor at time _t3 , but since the reverse phase (U phase) is energized, the firing control pulse is not sent to the thyristor immediately, and the At _t4 , when a forward voltage is applied to the X phase, the ignition control pulse is output and the X phase thyristor is ignited. Generally, high-voltage thyristor devices are usually provided with a gate circuit for controlling the ignition control pulse given to the gate in accordance with the voltage condition applied to the thyristor.

If we consider the turn-off of the thyristor when the _OVP circuit operates, the forward voltage _drop of the It can be seen that it is turned off as a counter pressure. Therefore, if the time from time t ₄ to t ₅ is too short to ensure the required turn-off time of the thyristor, the U-phase thyristor cannot be turned off, and the forward voltage 16 is applied at time t ₅ . This had the disadvantage of causing voltage breakdown.
Note that a waveform 17 indicated by a dotted line in the waveform diagram of the thyristor current 13 is a normal thyristor current when the OVP circuit does not operate. Similarly, waveform 18 shows the normal anode-cathode voltage.

Generally, when a reverse voltage is not applied to a thyristor,
It has the characteristic that the turn-off time is doubled to five times longer. Therefore, as described above, even when turning off the thyristor by using the forward voltage drop (at most 1V to 2V) of the opposite phase thyristor as a reverse voltage, the turn-off time required by the thyristor is several times longer than the normal time. Therefore, the time that is the negative phase energization period after OVP circuit operation
There is a possibility that it cannot turn off between t ₄ and t ₅ .

In this way, when an OVP circuit is provided in a TCR thyristor device, depending on the timing at which the OVP circuit operates, there is a possibility that the thyristor may be destroyed due to the reverse phase operation status after the OVP operation.

[Purpose of the invention]

An object of the present invention is to provide a thyristor control device for a TCR thyristor device equipped with an OVP circuit that does not cause destruction of the thyristor during operation of the OVP circuit.

[Summary of the invention]

In order to achieve the above-mentioned object, the present invention provides protection that, when a forward overvoltage is applied to a pair of thyristors connected in antiparallel, the thyristor on the side to which it is applied is forcibly fired to remove the overvoltage exceeding the allowable value. In the thyristor control device comprising a circuit, a thyristor that operates in response to a forced firing signal from the protection circuit and to which a forward overvoltage is applied is provided in a path for transmitting firing control pulses to the pair of thyristors. The present invention is characterized in that a pulse lock circuit is provided for blocking the ignition control pulse transmitted to the thyristor in the opposite phase for at least one cycle.

[Embodiments of the invention]

FIG. 4 is a circuit diagram showing an embodiment of the present invention. Note that the same parts as shown in FIG. 2 are given the same reference numerals and their explanations will be omitted.

The present invention is characterized in that a pulse lock circuit 19 is provided within the gate circuits 7a and 7b. Ignition control pulses 8a, 8 from a control device (not shown)
The signal b is sent to gate circuits 7a and 7b, and sent to a pulse amplifier 10 through a pulse lock circuit 19 and an OR circuit 9, which will be described later, and its output signal is sent as an ignition control pulse to the gates of thyristors 1a and 1b. When an overvoltage is applied to the thyristors 1a and 1b, this is detected by the overvoltage detection circuit 5, the polarity is determined, and an overvoltage forced ignition signal 6 is generated.
Gate circuits 7a corresponding to a and 6b, respectively.
Or sent to 7b. When the gate circuits 7a and 7b receive the overvoltage forced ignition signals 6a and 6b,
At the same time as outputting the overvoltage forced ignition pulse through the OR circuit 9, the normal ignition control pulse 8a or 8b on the negative phase side is locked in the pulse lock circuit 19 on the negative phase side for a certain period of at least one cycle, Stops operation using ignition control pulses. Thereafter, the pulse lock circuit 19 releases the lock and the regular ignition control pulse 8a or 8 is activated by phase control.
Return to operation in b.

FIG. 5 is a waveform diagram for explaining the operation of the circuit shown in FIG.
The waveforms of the voltage between the anode and cathode of the U-phase thyristor are shown.

Assume that there is a sudden and large reactive power fluctuation after the pulse 20 on the U-phase side is output, and in order to compensate for this, the control circuit sharply reduces the phase and outputs the pulse 21 on the X-phase side. As a result, the thyristor current 13 flows until time _tx . Therefore, the U phase side
The operable range of the OVP circuit is the period from time t _x to t ₂ which is the normal ignition pulse time of the U phase. Assuming that the OVP circuit operates at time t _x and the overvoltage forced ignition pulse 15 is output, the thyristor current 13 flows until the special time t ₄ .

Here, since the U-phase OVP circuit operates as described above, the X-phase regular pulse is locked for at least one cycle by the X-phase pulse lock circuit 19, so that the pulse 22 has an open phase. Therefore, since the negative phase voltage 23 is applied to the W-phase thyristor during the period from time t ₄ to t ₆ , the thyristor can be turned off reliably. The X-phase pulse lock circuit 19 is 1
Since the lock is released after locking the pulse for more than one cycle, the operation returns to normal ignition control pulse 24 in the next cycle.

Although the example shown in FIG. 5 shows the case where the X-phase pulse lock is only one cycle, the lock time is not limited to one cycle and may be one or more cycles. Normally, when an OVP circuit operates, the applied voltage is extremely distorted, which is not favorable for thyristor operation, so it may be preferable to continue locking for several cycles as long as it does not cause problems in control performance.

〔Effect of the invention〕

As explained above in detail based on the examples,
In this invention, since a pulse lock circuit is provided to cut off the regular ignition control pulse for at least one cycle when the OVP circuit is operating, the thyristor can be turned off reliably without causing any damage, and furthermore, the operation can be stopped. This has the advantage that it is possible to provide a highly reliable thyristor control device without any problems.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of an arc furnace reactive power compensator using a TCR thyristor device, Figure 2 is a circuit diagram showing the configuration of a conventional thyristor control device, and Figure 3 explains the operation of Figure 2. Various waveform diagrams, 4th
The figure is a circuit diagram of a thyristor control device showing one embodiment of the present invention, and FIG. 5 is various waveform diagrams for explaining the circuit operation of FIG. 4. 1a, 1b...Thyristor, 5...Overvoltage detection circuit, 6a, 6b...Overvoltage forced ignition signal (forced ignition signal), 7a, 7b...Gate circuit, 8a,
8b...Ignition control signal, 11...Applied voltage, 13
...Thyristor current, 15...Overvoltage forced ignition pulse.

Claims (1)

[Claims] 1. In a thyristor control device equipped with a protection circuit that, when a forward overvoltage is applied to a pair of thyristors connected in antiparallel, forcibly fires the thyristor on the side to which it is applied to remove the overvoltage exceeding the allowable value,
The ignition control pulse is operated in response to a forced ignition signal from the protection circuit within a path for transmitting the ignition control pulse to the pair of thyristors, and is transmitted to the thyristor in opposite phase to the thyristor to which the forward overvoltage is applied. A thyristor control device comprising a pulse lock circuit that blocks the ignition control pulse for at least one cycle.