On the current balance of phase-controlled thyristor converter having interphase reactors.

A parallel connected thyristor converter with an interphase reactor has been used widely as a low voltage high current DC power supply because of high efficiency, compared with a series one. It seems to be the most suitable for superconducting magnetic energy storage systems in particular. If the parallel converter consisting of two thyristor converters is operated under different firing angles in the two due to imperfect adjustment in the control circuit or something like that, unbalance may occur in the output DC current of each converter.The purpose of this paper is to discuss the current unbalance of a parallel thyristor converter in detail. The main points are summarized as follows:(1) It is clarified theoretically that the unbalance of DC output current may occur even when the difference of firing angles is less than 1°.(2) It is verified experimentally that the proposed simple current feedback makes it possible to balance the DC output current of the parallel thyristor converter.(3) An interphase reactor without gap is able to take the place of a conventional interphase reactor with gap which is used widely. Compared with the conventional one, the volume of the interphase reactor without gap is much small.