JPS59119423A - Gate controlling system of thyristor switch for opening and closing capacitor - Google Patents

Abstract

PURPOSE:To make an ignition device small-sized and low in its loss by intermitting a gate current to a thyristor switch in accordance with a current flowing to a capacitpr for compensating a reactive power. CONSTITUTION:A current transformer 10 for detecting a capacitor current, a comparator 8 for comparing a detected current value with positive and negative set values, an AND element 9 for executing an AND operation of an output of the comparator 8 and an output from a turn-on and turn-off control device 5, and a monostable element 11 are added to this system. In ths state, if an instantaneous value of a capacitor current detected in an on-period of a thyristor switch 3 exceeds a prescribed level, a gate current is cut off, and if said value is below the prescribed level, the gate current is supplied only for a prescribed time when the monostable element 11 is operated. In this way, an ignition device can be made small-sized and low in its loss.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gate control method for a thyristor switch for opening and closing a capacitor.

Generally, when operating a load that draws power from an AC power source with a large lagging power factor, such as an arc furnace or rolling equipment for steel manufacturing, the waveform is distorted by the inductance of the power supply system, causing voltage fluctuations and flickering. Since this may cause inductive disturbances, a capacitor for reactive power compensation is installed in the power supply to prevent this.

FIG. 1 is a block diagram showing a conventional example of a thyristor type capacitor switching device, and FIG. 1A is a waveform diagram of each part for explaining its operation. In FIG. 1, 1 is a transformer, 2tI'!
, a capacitor for power factor improvement or reactive power adjustment, 3 is a thyristor switch (AC switch), 4 is a transformer, and 5 is the input of capacitor 2.

A control device for controlling shutoff, 6 is a pulse amplifier, and 7U pulse transformer.

When a capacitor closing/cutting command C is applied from a monitoring device or the like (not shown) that monitors reactive power in the power supply system, the closing/cutting control device 5 controls the phase that has a small influence on the power supply system, that is, normally the power supply voltage. Point 10 when becomes the peak value
(See FIG. 1A) to output a predetermined signal. This signal is amplified by the pulse amplifier 6 and pulse transformer 7
Since the signal is applied to the gate of the silice through the switch 3, the switch 3 is turned on or off, and the power to the capacitor 2 is turned on or off. In addition, power supply voltage E, capacitor 2
The current of [. The waveforms of the gate current 18 are shown as shown in FIGS. 1A (a), (b), and (c), respectively. By the way, in such a device, the capacitor current l
. The reason for this is that transient imaging current is likely to occur due to the resonance phenomenon when the SIRISK switch is turned on, and that it absorbs harmonic currents generated externally by other loads etc. during the switch-on period.
If the υ current is intermittent due to reasons such as superimposed flow in the thyristor switch or large changes in current due to disturbances in the power supply, ignition failure may occur. To ensure the on state at all times, during the switch on period, please refer to Figure 1A (c).
It was necessary to continuously supply a gate current with a predetermined value as shown in FIG. For this reason, the pulse transformer and control amplifier that supply the current to the SIRISK switch have become larger, and as a result, the ignition device as a whole has become thicker, and the ignition power supply has also had to have a large capacity. There was a drawback that it was necessary.

The present invention has been made to eliminate such drawbacks, and an object of the present invention is to provide a gate control system for a thyrisk switch that allows highly accurate out-of-control control using simple and inexpensive means.

Its feature is turned on by a cyrisk switch.

The current flowing through the capacitor that is controlled to be off and adjust reactive power is monitored, and the gate current is cut off during periods when the capacitor current is large and the switch is considered to be in the on state, and the current is small and unstable. By supplying a gate current during the period when this is considered to be the case, it is possible to reduce the size, loss, and cost of the gate control device without impairing its reliability.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a configuration diagram showing an embodiment of the present invention, and FIG. 2A is a waveform diagram of each part explaining its operation. As is clear from FIG. 2, this embodiment is different from the conventional one shown in FIG. The present invention is characterized in that it is provided with a comparator 8, an AND element 9 which performs an AND operation between the output of the comparator 8 and the output from the ON/OFF control device 5, and a monostable element 11.

Assume now that the capacitor 2 is charged to a value close to the peak value of the power supply voltage, and the twin-ristor switch 3 is off, with no current flowing.

Here, when a capacitor input command is given from a device (not shown), the control device 5 operates near the peak value of the power supply voltage E as shown in FIG. 2A (a) (time 1 (see ) sends out a sirisk switch-on command to the AND element 9. At this time, the switch 3I''i
Since it is in the off state, the current 10 of the capacitor 2 as shown in FIG. 2A (b) is approximately zero, and therefore the capacitor current i from the comparator 8. A signal indicating that is below a predetermined level is applied to AND element 9. As a result, the AND element 9 is established and a gate current supply command is generated at its output. A gate current is applied to the switch 3, the switch 3 is turned on, and current begins to flow. Then the capacitor current i. When the compaction exceeds the predetermined set level of the rake 8, the output of the comparator 8 is inverted, the AND element 9 no longer holds true, and the input to the monostable element 11 is cut off, so that the pulse amplifier 6 and the pulse transformer 7 The gate current supplied through the thyristor switch 30 is cut off after a predetermined time period determined by the characteristics of the monostable element 11, even during the on-command period of the thyristor switch 30. Thereafter, each time the capacitor current iC falls below a predetermined threshold, the output of the comparator 8 is inverted, a gate current supply command is generated via the AND element 9, and gate current supply is started; i. continues until it reaches a predetermined level. According to this embodiment, the capacitor current changes drastically due to disturbances in the power supply, etc.
Even if the output width of the AND element 9 is narrow, the monostable element 11
Since the minimum gate current width can be limited to a predetermined time width T1, frequent gate current supply,
Shutdown and narrow gate current supply are prevented, ensuring stable operation. Note that such a function can also be realized by providing the comparator 8 with a large hysteresis.

FIG. 3 is a configuration diagram showing another embodiment of the present invention, and FIG. 3A is a waveform diagram of each part for explaining its operation.

In this embodiment, an OR element 1 which takes the logical sum of the output of a monostable element 11 similar to that shown in FIG.
2 are provided, and gate control is performed based on the output of the longer one, and the other points are the same as that shown in FIG. 2. That is, the ON time of the thyrisk switch 3 is the set time T1 of the monostable element 11 or 11'.
This is determined by whichever is longer than T2. The set time T2 of the monostable element 11 is set to 5 to sufficiently attenuate the resonance phenomenon when the thyristor switch is turned on, and generally the set time T1 of the monostable element 11 is also selected to be sufficiently long. , the gate current applied to the thyrisk switch 3 is sufficiently long, for example, as shown in FIG. 3A (c). It goes without saying that this length is chosen to be shorter than that shown in FIG. This makes it possible to ensure reliable ignition even if a severe transient phenomenon occurs when the capacitor is turned on.

As described above, according to the present invention, a simple comparison and logic circuit is added to the conventional control circuit, and if the instantaneous value of the capacitor current detected during the ON period of the thyristor switch is equal to or higher than a predetermined level, the gate It is possible to reduce the size and loss of the ignition device by cutting off the current and supplying the gate current if it is below a predetermined level. This has the effect of providing a capacitor switching device.

Note that the ignition method according to the present invention can be applied not only to the above-mentioned si-risk switch but also to separately excited converters.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is a configuration diagram showing a conventional example of the thyrisk switch control system, Fig. 1A is a waveform diagram of each part to explain its operation, and Fig. 2 shows an embodiment of the present invention. Fig. 2A is a diagram showing the waveform of each part to explain the operation; Fig. 3 is a diagram showing the configuration of another embodiment of the present invention; Fig. 3A is a waveform diagram of each part to explain the operation. be. Code explanation 1...--Transformer, 2...Reactive power adjustment (
power factor improvement) capacitor, 3-...Sirisk switch (AC switch), 4...Voltage detector, 5-...
...Capacitor input, cutoff control device, 6...
...Pulse amplifier, 7...Pulse transformer, 8
...Comparator for current detection, 9...
AND element, 10...- Current detector, 11.11
'...Monostable element, 12...Orgate agent Akio Namiki, patent attorney Patent attorney Kiyoro Matsuzaki゜T network Show 59-119423 (4) Figure 2 Figure 2A t, It

Claims (1)

[Claims] A capacitor that is connected to an AC power source and compensates for reactive power generated by a load; a thyrisk switch that is made up of an anti-parallel thyristor connected in series with the capacitor and that turns the capacitor on and off from the power source; and a capacitor. In a gate control method for a capacitor opening/closing thyrisk switch, the current detecting means detects a current flowing through the capacitor, the gate control method comprising: switch control means for controlling the supply of gate current to the gate of the thyrisk based on an on/off command. and monostable circuit means that operates for a predetermined time based on the logical product output of the detection output and the output from the control means, so that the absolute value of the capacitor current is smaller than the predetermined value. A gate control method for a thyristor switch for opening and closing a capacitor, characterized in that a gate current is supplied to the thyristor for a predetermined time period during which the monostable circuit means operates.