1. Field of the Invention
The invention relates to a master-slave method and device for controlling a thyristor bridge in case of a multiphase current.
2. Description of the Prior Art
As disclosed in particular in the book of H. Lilen "Thyristor et triac" published by the Editions Radio, it is known in the art to use a circuit for controlling the time duration of the conduction of a thyristor during an halfwave of the feed voltage in order to control the power passing through a load. Such a circuit has been developed by the Applicant under the name of "Circuit L1" and exhibits in particular the advantage to permit a linear control of the feed power through a load.
In the prior art, an application of such circuits in a multiphase network and in particular in a three-phase network is disclosed in chapter 13 of the above cited book of H. Lilen, in particular in FIGS. 13-24 of this book which is shown in attachment (FIG. 1). Referring to FIG. 1, three circuits "L1" are used for controlling the three thyristors present on the phases U, V and W. Said three circuits "L1" are respectively connected for being fed and timed to the phases VU, UW, WV, said connections being made through three coupling transformers (not shown in FIG. 1). Said thyristor control circuit of the prior art presents several drawbacks. The first drawback stands in the necessity to provide for three circuits "L1" or analogous or three coupling transformers to permit the control of the power in the three-phase circuit, which increases the costs, the complexity and the bulk of the control device. The second drawback stands in the necessity to suitably connect each circuit "L1" to different determined phases of the three-phase feed circuit, whereby the error risk is not negligible. A third drawback stands in the fact that the circuits "L1" are circuits which have to be adjusted while inserted in a network; accordingly, three independent adjustments are necessary for balancing the circuit.