Asymmetrical gating of power converter for superconducting energy storage

Large reactive power comparable to the real power is required in an ac-to-dc converter with large current and relatively low voltage, such as a superconductive magnetic energy storage system. Cascade connection of two three-phase thyristor bridges with asymmetrical gating reduces the primary reactive power. The secondary reactive power of the converter transformer, however, cannot be reduced by this method. Both primary and secondary reactive powers are reduced by the gate control where control angles of upper and lower groups of each bridge are also controlled asymmetrically. Though even harmonics exist in this control, total reactive power is smaller than those of symmetrical and conventional asymmetrical gating. Experimental results of the converter for 1.0 Megajoule, 1000 Ampere and 35 kilojoule, 300 Ampere superconducting coils are discussed.