A technology based on thyristors will be used to manufacture the super-conducting coil AC/DC converters because of the low ratio of cost over installed power compared to a design based on GTO or similar technology. But phase-controlled converter suffers from fundamental disadvantage. They inject current harmonics into the input ac mains due to their nonlinear characteristics, thereby distort the supply voltage waveform, and demand reactive power from the associated ac power system at retarded angles. To overcome this disadvantage, in the case of two series converters at the DC side, connected to the same step-down transformer, apply for the sequence control. It is the most simple and efficient way to reduce the reactive power consumption at low cost. Analytical sequence control algorithm is suggested, the validity of the proposed scheme has been verified by experimental results with the small-scaled International Thermonuclear Experimental Reactor (ITER) Power Supply to minimize reactive power consumption.

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