JPS6222333B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an emergency firing detection circuit for series-connected thyristors that detects an emergency firing that occurs in each of a plurality of thyristors connected in series, and particularly relates to an emergency firing detection circuit that detects an emergency firing that occurs in each of a plurality of thyristors that are connected to a series connection point. can be detected using a single light emitting diode. Conventionally, an overvoltage protection circuit having a single breakover diode is connected between the respective gates of two thyristors connected in antiparallel to each other.
An overvoltage protection circuit is known in which the single overvoltage protection circuit causes each of the two thyristors to perform emergency ignition when overvoltage is applied to provide common protection. In order to protect the thyristor from destruction due to loss of forward blocking ability during emergency ignition for overvoltage protection, the breakover diode BOD is activated when the forward voltage of the thyristor exceeds a certain value.
The overvoltage protection function is performed by supplying a gate current to the corresponding thyristor and making the thyristor conductive to protect it from the applied overvoltage. For example, in this type of overvoltage protection circuit having the configuration shown in FIG. 1, a diode D7',
Rectifier bridge circuit D connected via D8'
A breakover diode BOD and a current limiting resistor R3 are connected in series between the DC terminals 1 to D4, and when the forward voltage of one thyristor TH2 exceeds a certain value, the breakover diode BOD
becomes conductive, and [D5→D1→R3→BOA→
The gate current flows through the path D4 → TH2 gate, and thyristor TH2 fires. On the other hand, when designing a thyristor AC/DC converter with such a configuration, the breakover diode BOD is set not to operate during normal operation, so if the breakover diode BOD operates, it means that some abnormal condition has occurred. Show that. Therefore, it is common for the device to detect whether or not the breakover diode BOD has operated and then take some kind of action. Therefore, the operation of the breakover diode BOD can be performed by placing it in series with diodes D7' and D8' respectively, or by placing the breakover diode BOD in series with diodes D7' and D8' respectively.
A light emitting element is connected in series with the BOD itself, and detection can be performed based on the light emission output signal of the light emitting element. Generally, the optical output signal resulting from detection of the breakover diode operation by such a light emitting element is guided to a monitoring device via a light guide and subjected to appropriate arithmetic processing, but since the light guide is relatively expensive, the light guide is It is desirable to reduce the number of light-emitting elements used, and therefore the number of light-emitting elements used, as much as possible. However, for a high-voltage, large-capacity thyristor AC/DC converter in which multiple sets of antiparallel-connected thyristors are connected in series and equipped with the above-mentioned overvoltage protection circuit, the above-mentioned light-emitting element and light for detecting abnormal conditions are required. Conventionally, when providing a guide,
A light emitting element and a light guide were provided for each breakover diode for overvoltage protection provided in each set of thyristors. The disadvantages are that the number of circuits used increases, the manufacturing cost of this type of emergency ignition detection circuit increases, and the structure becomes complicated. An object of the present invention is to eliminate the above-mentioned conventional drawbacks, and to increase the number of light emitting elements and light guides used when provided in conjunction with a high-voltage, large-capacity thyristor AC/DC converter in which a plurality of thyristors are connected in series and parallel. An object of the present invention is to provide an emergency ignition detection circuit for series-connected thyristors that significantly reduces the ignition of thyristors. That is, the emergency ignition detection circuit of the present invention consists of a plurality of pairs of thyristors connected in series in anti-parallel relation to each other, and the AC terminals of a rectifier bridge circuit connected to each gate with a breakover diode between the DC terminals. and connecting a light emitting diode between the DC terminals of other rectifier bridge circuits, each of which has an AC terminal connected to the AC terminal of the rectifier bridge circuit in each set of these thyristors and the series connection point of the thyristors. The present invention is characterized in that emergency firing occurring in each of a plurality of thyristors connected to a series connection point can be commonly detected. The present invention will be described in detail below with reference to the drawings. First, a configuration example of the emergency ignition detection circuit of the present invention will be explained in the second section.
As shown in the figure. The illustrated configuration has an overvoltage protection circuit including a breakover diode, which is similar to that shown in Figure 1, in which two sets of anti-parallel connected diodes are connected in series, and the upper set of overvoltage protection circuit has a ground potential side and a lower set of overvoltage protection circuits. The high-potential side of the overvoltage protection circuit of the side set is commonly connected to one of the AC terminals of the rectifier bridge circuit D7 to D10, in which a light emitting diode PD is connected between the DC terminals, and the other AC terminal is connected to the inside of the series-connected thyristor. It is connected to the sex point. In the series-connected thyristor AC/DC converter having such a configuration, the P side shown in the figure is positive and the thyristor
When an excessive forward voltage is applied to thyristor TH21 due to unbalanced voltage sharing between TH21 and TH22, [D15→D11→R13→BOD1 conductive due to overvoltage→D14→R12→D7→PD
→ D10 → TH21 cathode],
A gate current is supplied to the gate of thyristor TH21 via diode D14, and the thyristor TH
21 becomes conductive, and the light emitting diode
Emergency firing of the thyristor TH21 is detected by the light emission of the PD. On the other hand, if the illustrated P side is positive as described above and an excessive forward voltage is applied to the thyristor TH22, [D9→PD→D8→D25→D21
→D23→BOD2→D24→R22], gate current is supplied to the gate of thyristor TH22 via diode D24, thyristor TH22 becomes conductive, and light emission from light emitting diode PD causes thyristor TH
22 emergency firings are detected. Contrary to the above, even if the illustrated N side is positive and an excessive forward voltage is applied to the thyristor TH11, [D9→PD→D8→D
16→D13→R13→BOD1→D12→R1
1 → cathode of TH11], the gate current flows through the thyristor through the diode D12.
Supplied to the gate of TH11, light emitting diode PD
emits light. On the other hand, if the illustrated N side is positive as described above and an excessive forward voltage is applied to the thyristor TH12, the [D
26 → D23 → R23 → BOD2 → R21 → D7
→ PD → D10 → cathode of TH12], the gate current is supplied to the gate of the thyristor TH12 via the diode D22, and the light emitting diode PD is generated. As described above, in the configuration example shown in the second diagram,
The emergency ignition generated in each of the four thyristors TH11 to TH22 is transmitted to one light emitting diode PD.
It can be detected by Therefore, in the thyristor AC/DC converter having the configuration shown in the second figure, for example, if the P side shown in the figure is positive, and the thyristors TH21 and TH2
An excessive forward voltage is simultaneously applied to breakover diodes BOD1 and BOD1, respectively.
If BOD2 becomes conductive almost simultaneously and emergency firing occurs in thyristors TH21 and TH22 at the same time, the rectifier bridges D7 to D10 will be balanced and no current will flow through the light emitting diode PD. The occurrence of an emergency ignition may not be detected. In other words, in the emergency firing operation of the thyristor in the configuration shown in Fig. 2, the forward voltage in one of the thyristors becomes excessive, one of the breakover diodes BOD1 and BOD2 is connected, and after several microseconds, they are turned off. The process is completed when the thyristor becomes conductive. After the thyristor is turned on, the voltage across PN shown in the figure becomes zero, so no current flows through the light emitting diode PD. Therefore, for the detection of emergency firing of the thyristor, the breakover diode BOD
It is necessary to perform emergency ignition detection by causing the light emitting diode PD to emit light during a period when only either BOD 1 or BOD 2 is conductive. Here, the P side shown is positive and the thyristor
Analyzing the above using the case where TH21 and TH22 are simultaneously activated in an emergency, both breakover diodes BOD1 and BOD2 become conductive due to the simultaneous firing of thyristors TH21 and TH22, and furthermore, thyristors TB21 and TH22 become conductive. TH22
is not yet conductive, and the equivalent circuit when it is in a non-conductive state is as shown on the right side of FIG. Note that the following assumptions are made between this equivalent circuit and the actual circuit shown on the left side of FIG. R ₂ = R12 = R22 R ₃ = R13 = R23 R _PD : Equivalent resistance of PD R _B = R _B1 = R _B2 E _B : Terminal voltage of C _B1 and C _B2 (does not change during the analysis period) E _g : Thyristor For the equivalent circuit shown in Figure 3, the following determinant holds true. Solving the above equation, we get From the above formula, E/E _g =2(1+R ₃ /R ₂
), then i ₄ =0, that is, the current flowing through the light emitting diode PD becomes zero, and emergency ignition detection becomes impossible. Therefore, in order for the current of the light emitting diode PD to not become zero even when the breakover diodes BOD1 and BOD2 are conductive at the same time, and for emergency ignition detection to be possible, the resistor R2 must be adjusted so that the above conditions do not hold. It is only necessary to appropriately set the value of R3. Alternatively, regardless of the circuit constants of the equivalent circuit described above, the breakover diodes BOD1, BOD
In order to enable emergency ignition detection of the thyristor even when the thyristors are simultaneously conductive, a branch circuit is added to the rectifier bridge circuit for emergency ignition detection in the configuration shown in Figure 2, as shown in Figure 4. Breakover diodes BOD1 and BOD2 for diode PD
It can also be configured so that the sum of the currents flows. As is clear from the above description, according to the present invention, as shown in the configuration examples of FIGS. 2 and 4, the current flowing through the breakover diode for detecting the overvoltage applied to the thyristor is detected. By connecting a light emitting diode for detecting emergency firing of the thyristors between the DC terminals of the rectifier bridge circuit, for example, an emergency firing phenomenon occurring in four thyristors can be detected by one light emitting diode. This makes it possible to significantly reduce the number of light emitting elements and light guides required for detecting emergency ignition compared to the conventional method.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing the configuration of a conventional anti-parallel connected thyristor AC/DC converter circuit with an overvoltage protection circuit, Figure 2 is a circuit diagram showing an example of the configuration of an emergency firing detection circuit for series connected thyristors of the present invention, and Figure 3. is an equivalent circuit diagram thereof, and FIG. 4 is a circuit diagram similarly showing another example of the configuration. TH _i ...thyristor, BOD _i ...breakover diode, D _i ...diode (rectifier), C _i
... Capacitor, R _i ... Resistor, PD ... Light emitting diode, E _i ... Voltage source, i _i ... Current.

Claims (1)

[Claims] 1 A plurality of pairs of thyristors are connected in series in which the AC terminals of a rectifier bridge circuit are connected in antiparallel to each other and a breakover diode is connected between the DC terminals of each gate, and the A plurality of thyristors connected to the series connection point by connecting a light emitting diode between the DC terminals of other rectifier bridge circuits each having an AC terminal connected to the AC terminal of the rectifier bridge circuit and the series connection point of the thyristors. 1. An emergency firing detection circuit for series-connected thyristors, characterized in that emergency firings occurring in each of the series can be commonly detected.