Control Device for a Thyristor Switch
Abstract Generated abstract
This paper describes a control device for a five-channel thyristor switch intended for commutation of single-phase or multiphase AC circuits using inverse-parallel thyristor power elements. The device classifies the input alternating voltage into five preset levels through relay elements with different thresholds, stores the resulting code in flip-flops, and uses synchronized logic gates to trigger the corresponding thyristor element near the zero crossing of each half-cycle. Implemented with standard T-102 series potential-pulse industrial automation elements, the circuit provides phase-shifted control for positive and negative half-cycles and resets its memory at the beginning of each positive half-cycle. Experimental testing is reported to have shown stable control of the power thyristor elements.
Full Text
Control Device for a Thyristor Switch
L. A. Volynskaya, V. M. Razin
Two thyristors connected in inverse parallel form a power element which is, in essence, a fast-acting contactless switch, by means of which single-phase and multiphase AC circuits can be commutated.
The block diagram of a five-channel controlled thyristor switch is shown in Fig. 1, where 1 is the block of power thyristor elements, 2 is the synchronization circuit, and 3 is the control device. The operating principle of the switch is as follows: at the beginning of each period of the alternating voltage, by means of one of the five power thyristor elements, commutation is performed of that circuit whose number corresponds to the level of the alternating voltage applied to the input of the control device in the preceding cycle. The structural diagram of the switch control device is shown in Fig. 2, where 1—4 are relay elements; 5—8 are inverters; 9—12 are pulse shapers; 13—16 are power amplifiers; 17—20 are memory; 21—24 are inverters; 25—28 are power amplifiers; 29—38 are “AND” circuits; 39 is the synchronization circuit; 40—41 are amplifiers; 42 is a delay for the appearance; 43—44 are inverters; 45—46 are amplifiers.
Fig. 1. Block diagram of a thyristor switch
The control device under consideration is implemented using standard potential-pulse elements of industrial automation of the unified T-102 series, which have high reliability, broad functional capabilities, and sufficient speed. The output alternating voltage is applied to relay elements 1—4 of type T-202, which have different operating thresholds. Discrete signals from the outputs of elements 1—4, shaped, inverted, and amplified, are fed to the inputs of “memory” elements 17—20, for which T-102 flip-flops are used. The states of flip-flops 17—20 are determined by the operating thresholds of elements 1—4 and by the level of the input voltage. The outputs of the flip-flops control two groups of “AND” circuits 29—33 and 34—38. Synchronization circuit 39 generates clock pulses when the sinusoidal voltage passes through zero, which ensures switching on the thyristors practically at the moment when the si—
Fig. 2. Structural diagram of the control device
Visible labels in the diagram: Input, Outputs, Sync. circuit.
sinusoid. If the input voltage is equal to or exceeds the maximum preset level, then all the relay elements operate, and signals corresponding to unit levels appear at the outputs of flip-flops 17–20. In this case, clock pulses from the synchronization circuit are passed through those “AND” circuits that control the thyristor element switching the circuit with the number corresponding to the maximum level of the input signal.
If, however, the input voltage is below the minimum level, then the relay elements do not operate, and the flip-flops retain their initial zero levels; the clock pulses are passed by the “AND” circuits to the control electrodes of the thyristor element switching the circuit with the number corresponding to the minimum level of the input voltage.
At intermediate values of the input voltage, only some of the relay elements operate; therefore the clock pulse is applied to one of the three remaining thyristor elements.
Since each of the five input-voltage levels corresponds to two “AND” circuits with identical control codes, and the synchronization circuit generates clock pulses shifted in phase by 180°, the control device provides circuit switching in both the positive and the negative half-cycles of the sinusoidal voltage.
Resetting flip-flops 17–20 is carried out by a clock pulse delayed by 70 μsec at the beginning of each positive half-cycle of the input voltage.
Experimental testing of the control device showed that it provides stable control of power thyristor elements.
REFERENCES
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V. V. Girshberg [et al.]. Standard Units Based on Semiconductor Logic and Functional Elements of the ET Series. Moscow, Energiya, 1966.
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V. V. Girshberg [et al.]. Unified Series of Semiconductor Logic and Functional Elements for Industrial Automation, ET. Moscow, Energiya, 1966.