JPS6057293B2 - DC switching circuit protection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protection system for a DC switching circuit using a self-extinguishing semiconductor element such as a large capacity transistor (GTR) or a gate turn-off thyristor (GTO).

Common examples of DC switching circuits using self-extinguishing semiconductor devices include inverter circuits and chopper circuits, and it is well known that DC short circuits can occur in these circuits due to gate signal malfunctions.

If a self-extinguishing semiconductor element is turned off in the event of such a DC short-circuit accident, the switching time is very fast, so overvoltage is likely to occur due to the influence of circuit inductance, and there is a risk that the element may be destroyed by this overvoltage. . In addition, there is a limit to the anode current that can be cut off in a GTO, and if the anode current exceeds this current value and the anode current is cut off, switching loss increases and the GTO is destroyed. In a DC switching circuit using an element, the reliability of the circuit used is greatly influenced by how the element is protected in the event of a DC short circuit accident. This invention has been made in view of the above problems, and relates to a protection method for a DC switching circuit using a self-extinguishing semiconductor element, and is intended to reliably protect the self-extinguishing semiconductor element in the event of a DC short circuit accident. , aims to provide a highly reliable protection method for DC switching circuits.

An embodiment of the present invention is shown in FIG. 1, and waveforms for explaining the operation are shown in FIG.

In Figure 1, 11 is an AC input terminal, 12 is an input terminal, 13 is a rectifier, 14 is a DC reactor, 15 is a DC filter capacitor, 16 is a reactor, 17 is an inverter circuit, and 18 is an output terminal. , 19 is a load, 20 is a current transformer, 21 is a DC short circuit detector, 22 is a short circuit protection circuit,
23 is a self-extinguishing type semiconductor element protection circuit, 24 is a short circuit, and FIG. 2 shows an embodiment in which the present invention is applied to a constant voltage type inverter circuit. As a DC short circuit protection method for a constant voltage inverter circuit, when a DC short circuit occurs in the inverter circuit 17, the fault current IS is first removed from the DC filter capacitor.
begins to flow, this is detected by the current transformer 20, and via the DC short circuit detector 21 and the short circuit protection circuit 22, a command to disconnect the input/output shields 12 and 13 and ignition of the short circuit 24 is issued. Normally, protection is provided by issuing a command to restrict the phase of the rectifier 13 or to cut off the gate. At this time, a DC short circuit accident occurs at time Illllt in Fig. 2, and when the short circuit 24 is ignited at time 2, most of the fault current is shunted to the short circuit 24, and normally, as shown in Fig. A current corresponding to the shaded portion flows through the inverter circuit 17. Therefore, if the fault current is appropriately divided when a DC short circuit occurs, fuseless protection can be achieved without providing a fast-acting fuse in the DC circuit. But the time marshal,
If the self-arc-extinguishing semiconductor element of the inverter circuit 17 is disconnected as described above during the period from 1 to 3, there is a risk that the element will be destroyed due to overvoltage or insufficient disconnection capability. Therefore, in this invention, the cutting operation is not performed until a time t1 when the DC short circuit fault 1s is flowing toward the positive bus bar, and the current 1s is flowing in the opposite direction to the above-mentioned time T1.
The self-extinguishing semiconductor element protection circuit 23 determines that the current direction of the current transformer 20 has been reversed after the short circuit is detected by the short circuit detector 21 so that the element is activated or disconnected between time 3 and time ζ. protection. If the self-arc-extinguishing semiconductor element is reliably extinguished during this period, no fault current will flow after time z, and the fault current 13 will continue to flow repeatedly, causing the element to be destroyed due to thermal problems. can be prevented.
Furthermore, even if the current is cut off during this period, the current in the element is at zero, so there is no risk of the element being destroyed due to overvoltage generation or insufficient breaking ability. Therefore, according to the present invention, since the self-arc-extinguishing semiconductor element can be reliably protected, the reliability of the circuit used can be greatly improved.
FIG. 3 shows another embodiment of the invention.

Similarly, FIG. 3 shows an embodiment in which the present invention is applied to a constant voltage inverter circuit. In Figure 1, self. The arc-extinguishing semiconductor device protection circuit 23 is a means for determining the period from time T3 to time T4, and the DC short circuit detector 21 detects a short circuit and then reverses the current direction of the current transformer 20. It was explained that it is determined. However, it is a normal inverter circuit or chopper circuit. In a DC switching circuit such as a circuit, if the main circuit constants, main circuit wiring routes, etc. are determined, the period from time T3 to time T3 (similarly, the period from T4 to T4) is necessarily determined. Therefore, the DC short circuit detector 21 can detect a DC short circuit as shown in FIG. Protection can be achieved by providing a self-turn-off type semiconductor device protection circuit 25 which has a delay element and instructs the self-turn-off type semiconductor device to shut off after a predetermined period of time. The effects and actions in this case are also the same as in the case of FIG. In this invention, the period during which the self-arc-extinguishing type semiconductor element is commanded to be cut off is time T3 in FIG.
to T4, and is not limited to the period from t to T4.
The measurement may be performed from the time when the immediately preceding DC short circuit current 1 s has decreased to a predetermined value.

The time for issuing this command can be adjusted by adjusting the delay time of the self-extinguishing semiconductor element protection circuit 25 shown in FIG. Various other modified circuits can be constructed without changing the gist of the invention.

As explained above, the present invention provides the following effects.

(1) After a predetermined period of time from the time when a DC short circuit is detected, it is possible to instruct a self-extinguishing semiconductor element, which is a switching element such as an inverter circuit or a chopper circuit, to turn on and off.

Since the DC short-circuit fault current decreases to a predetermined value within this predetermined period of time, damage due to lack of shearing ability of self-extinguishing semiconductor devices, overvoltage or D
Destruction caused by excessive v/Dt can be prevented.

(2) Since the causes of destruction caused by the characteristics inherent to self-arc-extinguishing semiconductor devices can be eliminated by the effect of item (1) above in the event of a DC short circuit accident, the reliability of DC switching circuits using self-arc-extinguishing semiconductor devices can be improved. It provides a high level of protection.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram when the present invention is implemented in a constant voltage inverter circuit, Fig. 2 is a DC short circuit fault current waveform diagram, and Fig. 3 is a diagram of the DC short circuit fault current waveform.
The figure is a circuit diagram when another embodiment of the present invention is applied to a constant voltage type inverter circuit. 11...AC input terminal, 12...Input switch, 1
3... Rectifier, 14... DC reactor, 15...
・DC filter capacitor, 16...Reactor, 1
7... Inverter circuit, 18... Output circuit breaker, 1
9... Load, 20... Current transformer, 21... DC short circuit detector, 22... Short circuit protection circuit, 23, 25... Self-extinguishing semiconductor element protection circuit, 24... short circuit.

Claims (1)

[Claims] 1. In a DC switching circuit consisting of a self-arc-extinguishing semiconductor element installed between a DC power source equipped with a smoothing capacitor and a smoothing reactor, in the event of a DC short circuit accident in which the DC power source is short-circuited via the DC switching circuit, a DC short circuit accident occurs. A protection method for a DC switching circuit, characterized in that the polarity of the current is detected, and after the polarity is reversed, a burnout command is given to the self-arc-extinguishing semiconductor element to eliminate a DC short circuit accident.