JPH0732586B2 - Thyristor protector - Google Patents

Description

TECHNICAL FIELD The present invention relates to a protective device for preventing a turn-off failure of a thyristor.

[Prior Art] FIG. 3 shows a conventional example of this type of protection device. FIG. 3 shows one thyristor element, but in an actual thyristor device, many elements are often connected to a power source in series. In this case, there is a variation in the timing of the turn-off operation of each element, and depending on the degree of this variation, the power supply voltage after the off-operation may be directly applied to a specific thyristor. Further, there is a voltage increase due to commutation in the other phase after the reverse voltage is applied.

If the forward withstand voltage is not sufficiently recovered after the thyristor is turned off, the thyristor breaks down due to the overvoltage. FIG. 3 protects the thyristor from this state. In the figure, 1 is an optical thyristor,
A, G and K are the anodes of this optical thyristor,
The gate and cathode are shown. Reference numerals 2 and 3 are a capacitor and a resistor that form a snubber, which are connected in series and inserted between the anode and cathode of the optical thyristor 1.
A voltage detector 21 is inserted between the anode and cathode of the optical thyristor 1, and sends the detected anode-cathode voltage VD to the light emitting element 22. The optical signal sent from the light emitting element 22 is passed through the light guide 23 and the reverse voltage time detector 24
Sent to. The output of the reverse voltage time detector 24 is sent to the reverse voltage time shortage determiner 25, and the output of the reverse voltage time shortage determiner 25 drives the gate signal generator 26. The gate signal generator 26 generates a gate signal IGO, and the gate signal IGO is converted into an optical gate signal by the light emitting element 27 to be a light guide.
It is supplied to the gate of the optical thyristor 1 through 28.

Like the normal thyristor, the optical thyristor 1 recovers the forward withstand voltage by applying a reverse voltage after passing a current. Now, at the time t ₄ shown in FIG. ₄ , after the off operation,
It is assumed that the reverse voltage starts to be applied between the anode and the cathode of the optical thyristor 1 and this reverse voltage application time continues until time t ₅ . The reverse voltage time T is detected by the reverse voltage time detector 24 and compared with the specified time T ₀ by the reverse voltage time shortage determiner 25. When the detected reverse voltage time T is shorter than the specified period T ₀ , the reverse voltage time shortage determiner 25 outputs a detection signal. The gate signal generator 26 is driven by this detection signal, and an optical gate signal is output from the light emitting element 27 (time
t ₆ ). The time from time t ₅ to t _{6 is} the time required to determine the shortage of the reverse voltage time and output the optical gate signal.

The optical gate signal is a pulse on a predetermined time axis T _W , and the optical thyristor 1 receives this optical gate signal and fires at time t ₇ . It is sufficient that the anode-cathode voltage VD of the optical thyristor 1 at the time of this ignition is within the allowable value.

[Problems to be Solved by the Invention] Since the conventional protection device is configured to detect the reverse voltage time and compare it with a preset specified period, the thyristor having a shortage of the reverse voltage time is protected. , zero point of the output time reverse voltage of the gate signal (fourth diagram of the time t ₅ corresponds) becomes slower, when the voltage rate of rise of the forward voltage after a reverse voltage is applied also joined applying such a surge voltage is greater Has a problem that it is difficult to provide sufficient protection and lacks reliability.

The present invention has been made to solve the above problems,
An object of the present invention is to obtain a highly reliable thyristor protection device capable of preventing turn-off failure and protecting the thyristor reliably.

[Means for Solving the Problem] In order to solve the above problems, the present invention comprises a series body of a capacitor and a resistor connected between the anode and the cathode of a thyristor, and a voltage between the anode and the cathode across the resistor. (V) A differentiating circuit that outputs a voltage corresponding to the time differential value (dv / dt), and when the output value from this differentiating circuit exceeds a predetermined value determined by the allowable voltage increase rate of the thyristor, A gate signal generating circuit for supplying a gate signal is provided.

[Operation] According to the present invention, when a steep voltage is applied between the anode and the cathode after the thyristor is turned off, the differentiation circuit immediately detects this and does not wait for the zero point of the reverse voltage, but the gate signal generation circuit. Since the gate signal is supplied from the thyristor to the thyristor, the thyristor can be reliably protected even when the forward voltage applied to the thyristor has a surge property that cannot be protected by the conventional protection device.

[Embodiment] FIG. 1 shows an embodiment of the present invention. In the figure, 4 and 5 are capacitors and resistors that form a differentiating circuit, which are inserted in series between the anode and cathode of the optical thyristor 1. 6 and 7 are the first
And a second non-linear resistance element, which are connected in series with each other and in parallel with the resistor 5. Reference numeral 8 denotes a light emitting element, which is connected in parallel to the non-linear resistance element 7 and is connected to the light emitting element 8 in parallel with a protection diode 9. Optical signal sent by the light emitting element 8 and the conventional light emitting element described in FIG.
The optical signals sent by 27 are light guides 10 and 28, respectively.
It is supplied to the gate G of the optical thyristor 1 as an optical gate signal through the optical combiner 11.

Since the present application focuses exclusively on the protection device, the description of the configuration of the gate signal system related to the original phase control of the thyristor is omitted, including the drawing.

Next, the operation of this device will be described with reference to the waveform chart of FIG. In FIG. 2, V _AK is a voltage applied to the optical thyristor 1, IGO is an optical gate signal output from the light emitting element 8, VDI is a forward voltage at a level that does not damage even when the optical thyristor 1 is ignited, and VD2 is an optical thyristor 1. Is a level of forward voltage that will be damaged when ignited. The broken line shows the self-ignition state of the optical thyristor 1 when there is no optical gate signal to the optical thyristor 1. Further, t ₁ is the reverse voltage start time, t ₂ is the surge application start time, and t ₃ is the ignition time of the optical thyristor 1.

When a voltage with a high voltage rising rate is applied to the optical thyristor 1 due to a voltage increase due to other-phase commutation after the reverse voltage is applied to the optical thyristor 1 or a surge application during application of the reverse voltage, the capacitance of the capacitor 4 is changed to C , R is the resistance value of the resistor 5 and v is the applied voltage, v = i · R + C ∫ idt (1) However, when the initial condition t = 0, ∫ idt = 0 Here, if the time constant CR is made sufficiently small, the voltage V5 across the resistor 5 becomes V5 = CRK = CR (dv / dt) (3), and the voltage rise rate dv of the applied voltage to the optical thyristor 1 becomes dv / dt
Proportional to.

Now, when the operation start voltage of the non-linear resistance elements 6 and 7, that is, the voltage at which the resistance value thereof rapidly decreases is set to a predetermined voltage value obtained from the allowable voltage increase rate (dv / dt) of the optical thyristor 1,
When the voltage V5 reaches this predetermined voltage value, a current flows through the nonlinear resistance elements 6 and 7. This current shunts into the light emitting element 8 and causes the light emitting element 8 to emit light. The optical output of the light emitting element 8 is supplied to the gate of the optical thyristor 1 as an optical gate signal IGO through the light guide 10 and the optical combiner 11, and the optical thyristor 1 is ignited.

To explain again along the time axis of FIG. ₂ , the light emitting element 8 emits light immediately after the reverse voltage application starts at time t ₁ of the off operation and then at time t _{2 the} voltage increase rate dv / dt rapidly increases. Then, the optical gate signal is output to the optical thyristor 1. That is, the optical gate signal is output without waiting for the zero point of the reverse voltage. As a result, since the optical thyristor 1 is turned on at time t ₃ , the voltage V _AK of the optical thyristor 1 at that time is the allowable level V
It stays at D1 and prevents the destruction of the optical thyristor 1. Due to the firing of the optical thyristor 1 at time t ₃ , the voltage v of the resistor 5, and thus dv / dt, also becomes zero, and the optical gate signal also disappears. Here, the time of (t ₃ −t ₂ ) is the optical thyristor 1
The time delay until the optical gate signal is input to the optical thyristor 1 is actually turned on, which corresponds to (t ₇ −t ₆ ) in FIG. 4 of the related art.

When the voltage V5 is equal to or lower than the predetermined voltage value, no current flows in the non-linear resistance elements 6 and 7, so that the light emitting element 8 does not emit light.

Therefore, according to the present embodiment, even when a forward voltage having a high rate of voltage rise that cannot be achieved by the conventional protection method is applied when the reverse voltage time is insufficient, the thyristor is ignited at a voltage level below which the thyristor is not damaged. be able to.

The diode 9 is provided so as to cut off the negative dv / dt and protect the light emitting element 8 from a reverse voltage.

In the above embodiment, the optical signal from the light emitting element 8 according to the present invention and the optical signal from the light emitting element 27 according to the conventional protection system are ORed by the optical combiner 11 and supplied to the gate of the optical thyristor 1. However, it goes without saying that the output of the light emitting element 8 may be directly supplied to the gate of the optical thyristor 1 without adopting the conventional method.

[Advantages of the Invention] As described above, according to the present invention, a predetermined differentiating circuit and a predetermined non-linear resistance for outputting a voltage corresponding to the time differential value (dv / dt) of the voltage applied between the anode and the cathode of the optical thyristor. A gate signal generating circuit which is composed of an element and a light emitting element and operates by the output of the differentiating circuit to supply an optical gate signal to the optical thyristor, and forcibly ignites the thyristor to protect it. Therefore, the gate signal can be supplied promptly and reliably, and the thyristor can be reliably protected even if a voltage having a high voltage winning rate is applied.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram for explaining the operation of the above embodiment, FIG. 3 is a circuit diagram showing a conventional protection device, and FIG. FIG. 6 is a waveform diagram for explaining an example operation. In the figure, 1 ... Optical thyristor, 4 ... Capacitor,
5 ... Resistance, 6, 7 ... Non-linear resistance element, 8 ... Light emitting element, 11 ... Photocombiner. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A thyristor, which is ignited by the input of an optical gate signal, comprises a series body of a capacitor and a resistor connected between the anode and the cathode of the thyristor.
A differential circuit that outputs a voltage corresponding to the time differential value (dv / dt) of the cathode-to-cathode voltage (v), and a series body of first and second non-linear resistance elements connected across the resistance of the differential circuit And an issue element connected to both ends of the second non-linear resistance element, and when the voltage of the resistance becomes equal to or higher than a predetermined value determined by the allowable voltage increase rate of the thyristor, the resistance value of the non-linear resistance element Rapidly decreases to flow a current, and this current is shunted into the issuing element to provide a gate signal generating circuit for supplying an optical gate signal from the issuing element to the thyristor, and is applied to the thyristor after the thyristor is turned off. A protection device for a thyristor, characterized in that the above thyristor is protected by forcibly turning on the thyristor.